Characterisation of Tool Geometries for Friction Stir
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How to cite this thesis
Surname, Initial(s). (2012) Title of the thesis or dissertation. PhD. (Chemistry)/ M.Sc. (Physics)/ M.A. (Philosophy)/M.Com. (Finance) etc. [Unpublished]: University of Johannesburg. Retrieved from: https://ujcontent.uj.ac.za/vital/access/manager/Index?site_name=Research%20Output (Accessed: Date). CHARACTERISATION OF TOOL GEOMETRIES FOR FRICTION STIR
LAP WELDS OF ALUMINIUM AND COPPER
TITLE PAGE
By
EWUOLA, OLUWATOYIN OLABISI
A dissertation submitted to the
FACULTY OF ENGINEERING AND THE BUILT ENVIRONMENT
in fulfilment of the requirements for the degree of
MASTERS OF PHILOSOPHY
In MECHANICAL ENGINEERING
At the UNIVERSITY OF JOHANNESBURG
SUPERVISOR: PROF E. T. AKINLABI CO-SUPERVISOR: MR D. M. MADYIRA
NOVEMBER 2015
DECLARATION
I understand what plagiarism means. Where I have used the works of others, I have adequately referenced. I have not submitted this work for academic credit at any other institution. This research work is fully mine.
______
EWUOLA Oluwatoyin Olabisi
201338860
______
Prof AKINLABI Esther T. Mr MADYIRA Daniel M.
Supervisor Co-supervisor
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ABSTRACT
The patenting of the Friction Stir Welding (FSW) process in 1991 opened up a process that was known within a relatively small circle of researchers to the entire research community. As a ground-breaking process in the field of joining, FSW offered a chance for the types of joining that had been fraught with lots of difficulties using the prevalent traditional means of joining.
Dissimilar metal joining had been plagued with more challenges compared to similar metal joining due to issues related to differences in thermal expansion and conductivity, wettability, melting properties, microstructural properties and other material properties. Fusion welding of some dissimilar materials such as Aluminium and titanium; Aluminium and Steel had been nearly impossible; the few welds that were successful resulted in defects (like wormhole, lack of penetration, porosity, cracks) and welding imperfections. Hence, the advent of FSW, a solid state welding technique, provided a way out of the many difficulties that arise in the joining of dissimilar metals.
Aluminium and copper are also two of such dissimilar metals whose material properties make them useful for a wide range of applications. However, due to the wide differences in their material properties, both metals had been difficult to join using the fusion welding technology. Recently, lots of successes have been achieved in the joining of both dissimilar metals using FSW and a lot of these are recorded in the open literature. Nonetheless, most of the successes recorded in the
FSW of aluminium and copper have been in the butt weld configuration. Literatures abound on the FSW of aluminium and copper in butt configuration, while there are
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limited literatures in the open space on the FSW of both dissimilar metals in lap configuration. This suggests that the joining of both dissimilar metals in the lap configuration has either not been sufficiently researched or is faced with lots of difficulties and little successes.
As a result, it is necessary to produce successful welds of both dissimilar aluminium and copper in the lap configuration and study the effects of the welding parameters on the quality of the produced welds. This research study presents the results of the
FSW of aluminium and copper using the lap configuration and the characterisation of the produced welds.
Welding was conducted by varying the input processing parameters in order to evaluate the relationship between the input processing parameters and the qualities of the welds produced. Welding was initially proposed to be done by three different tools (triflute, conical and concave). However, results from preliminary welds limited the final weld matrix to 15 welds produced by varying the rotational speed between
600 and 1200 rpm, traverse speed between 50 and 250 mm/min, plunge depth between 4.5 and 4.8 mm and only two tool profiles (conical and concave) were employed.
The produced welds were characterized using microstructural and mechanical properties determination, electrical resistivity measurements and residual stress analysis. The relationships between the input welding parameters and the results of the characterisations were established where trends were observed based on the results from other studies.
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Visual inspection of the surfaces of the produced welds revealed welds with good physical appearances and no surface defects observed in most of the produced welds. Weld defects were however observed in all the produced welds with voids being the most notable defect observed. The sizes of the voids were compared to the input processing parameters and it was observed that the sizes of the voids decreased with an increase in the plunge depth. Microstructural evaluation revealed an increase in the grain sizes with an increase in the distance from the weld center.
All the four (4) microstructural zones (Heat Affected Zone, Thermomechanically
Affected Zone, Stir Zone and unaffected Base Metal) were observed in all the produced welds. Grain deformation was observed in the grains of the copper even though they still maintained the equiaxed grain structure. However, only slight modification was observed in the grains of the aluminium.
Tensile lap shear tests showed a dependence on the plunge depth and the traverse speed. Microhardness profiling revealed that the hardness values of the welds were similar to the hardness values of both parent materials suggesting that there were no intermetallic compounds in the produced welds (or present in very little concentrations). This was confirmed by both the XRD and the EDS analysis on the
SEM. The electrical resistivity results were observed at the joint interface and found to increase with an increase in the heat input. Compressive stresses were observed for both the traverse and the longitudinal stresses.
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DEDICATION
To God Almighty
The creator of Heaven and Earth, my source, my inspiration, my father and my future
To my Dad, Professor S. O. Ewuola
Who always sees the best in me and desires me to actualize my potentials
To the memory of my late mum, Mama Eunice Ibidunni Ewuola
Who loves me more than any other woman could ever love me
I love you all
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ACKNOWLEDGEMENTS
Too numerous to mention, how does one appreciate those along the road of success?
He alone deserves all the glory, honour and praise. He is the El-Shaddai, the
Almighty God. I give you all the thanksgiving for the success of this phase and how you brought me this far Lord.
They have helped me in one way or the other. I cannot even mention all of them since they are too many. I know I am a product of their influence no matter what. I therefore thank all who have assisted me along the way to get to this point. Whilst they are too numerous to mention, I will make a feeble attempt.
Without the following, settling down in South Africa wouldn’t have been easy, conducting research would have been harder: Dr Mutiu, Dr Enoch, Tshepo Ntsoane,
The entire MAMS Research Group, Postgraduate Association of UJ, The FEBE
Tutor Center team of 2014, 2015 and 2016. Thank you all.
Ms Tersia Davids, the Residence Assistant, Dr Bryan Doyle, for giving me the chance to be a super tutor and earn my living while here, Dr Zach Simpson, for trusting me to lead the bunch.
For spiritual growth, Pastor Gee, Pastor Titi, Minister Kode, the Board of Ministers and the entire members of The Pacesetters Church, Johannesburg, The drama, follow-up and Technical teams of TPC, Pacesetters assembly of the Gospel Faith
Mission International (Nigeria), Magodo assembly of the Gospel Faith Mission
International (Nigeria), Pastor Oluwanimotele, Pastor Awodimila deserve mentioning.
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Friends who encourage you along the way, Kiro, Flaky and the tall man beside her,
Barrister Ologbonyo, Bro Femi Akinnubi, Seun Akande, Ope (who ensured I settled down nicely in a strange land), Victor, Otunba, Ife Adekoya, Yaya Barira, Bro
Bukunmi (a brother indeed).
Though we started out as friends, now we are family: Sis Bola, Queen, King,
Angelina and the great man I only met after his departure, Bro Shina. For the calls and gifts even while in a strange land, Mum Komolafe, Mum Aina.
For your support on every side, for your valuable insight and academic advise, for pushing our relationship beyond the barriers of academics, Prof Esther Akinlabi, I salute you. Uncle Stephen, Akin and Steph, thank you for being by my side. Oluwole
(my brother from another mother) and his beautiful spouse Samira, you rock.
My accomplishments are not without the influence of family. Victorola, Ifeoluwa,
Senzyflash, Aristotle, Delegation, Rose baby, Nicebaby, Kirk, Sola, Sefunmi, mum
AB, Gift, I’m glad we’re in that boat called family. Let’s do greater things together.
Mum Goodness, I love you.
Never stopped to encouraged me, never stopped believing in me, never stopped praying for me, never stopped checking my welfare, Dad, thank you. I am grateful. I pray I surpass your lofty expectations.
My number one fan, number one critic, number one comfort, number one support,
Iyawo mi, oto l’aye e.
I pray we all continue to do better on every side. God bless you all.
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TABLE OF CONTENTS
TITLE PAGE ...... i
DECLARATION ...... ii
ABSTRACT ...... iii
DEDICATION ...... vi
ACKNOWLEDGEMENTS ...... vii
TABLE OF CONTENTS ...... ix
LIST OF FIGURES...... xiv
LIST OF TABLES ...... xvii
ABBREVIATIONS...... xviii
NOMENCLATURE ...... xx
CHAPTER ONE ...... 1
INTRODUCTION ...... 1
1.1 Background ...... 1
1.2 Problem Statement ...... 5
1.3 Aim ...... 5
1.4 Objectives ...... 6
1.5 Hypothesis Statement ...... 6
1.6 Research Methods ...... 7
1.7 Delimitation of Research ...... 8
1.8 Assumptions ...... 8
1.9 Significance of Research ...... 9
1.10 Project Layout ...... 9
1.11 Structure of the Dissertation ...... 10
CHAPTER TWO...... 12 ix | P a g e
FRICTION STIR WELDING: FACTORS, PROCESSES AND DISSIMILAR METAL
JOINING ...... 12
2.1 Introduction ...... 12
2.2 Welding...... 12
2.2.1 Fusion welding ...... 13
2.2.2 Solid state welding ...... 15
2.3 Friction Stir Welding ...... 18
2.4 Applications of Friction Stir Welding ...... 22
2.4.1 Marine industry ...... 22
2.4.2 Aerospace industry ...... 23
2.4.3 Rail ...... 24
2.4.4 Automotive industry ...... 25
2.5 Microstructures of FS Welds ...... 26
2.6 Factors Affecting FSW ...... 29
2.6.1 FSW Tool ...... 29
2.6.2 Rotational speed ...... 35
2.6.3 Transverse speed ...... 36
2.6.4 Joint types ...... 37
2.6.5 Tool tilt angle and plunge depth ...... 39
2.6.6 Forces acting during FSW ...... 41
2.6.7 Heat generation in FSW ...... 42
2.7 Properties of FS Welds ...... 43
2.7.1 Mechanical and material properties of FS Welds ...... 43
2.7.2 Electrical properties of FSW ...... 48
2.8 Aluminium and its Alloys ...... 50 x | P a g e
2.9 Copper and its Alloys ...... 51
2.10 Weldability of Aluminium and Copper Alloys ...... 52
2.11 FSW of aluminium and copper alloys ...... 53
2.12 Summary ...... 64
CHAPTER THREE ...... 66
EXPERIMENTAL SET UP ...... 66
3.1 Introduction ...... 66
3.2 The Friction Stir Welding (FSW) Machine ...... 66
3.3 Fixtures ...... 67
3.4 Control System of the FSW Platform ...... 70
3.5 Workpiece Preparation ...... 72
3.6 Tool Design and Selection for the FSLW of Al/Cu ...... 72
3.7 Preliminary Welds ...... 75
3.8 Position of the Workpieces during the FSLW Process ...... 76
3.9 Process Parameters for FSLW of Al/Cu ...... 76
3.10 Parent Materials ...... 79
3.11 Sample Layout for Characterisations ...... 79
3.12 Characterisation of the Produced Weld ...... 81
3.12.1 Microstructural Evaluation ...... 81
3.12.2 Residual Stress Analysis and Phase Identification ...... 83
3.12.3 Microhardness Testing ...... 84
3.12.4 Tensile Strength Measurements ...... 85
3.12.5 Electrical Resistivity Measurements ...... 86
3.13 Summary ...... 88
CHAPTER FOUR ...... 89 xi | P a g e
RESULTS AND DISCUSSION ...... 89
4.1 Introduction ...... 89
4.2 Interplay of Input and Output Friction Stir Welding (FSW) Process
Parameters ...... 89
4.3 Visual Inspection and Macro Appearances of the Produced Welds ...... 93
4.3.1 Visual inspection of the produced welds ...... 93
4.3.2 Effect of input process parameters on the resulting macrostructure . 97
4.4 Microstructural Analysis ...... 105
4.4.1 FSW Microstructural Zones ...... 105
4.4.2 Scanning Electron Microscopy ...... 112
4.5 Mechanical Properties ...... 116
4.5.1 Tensile Test Results ...... 116
4.5.2 Microhardness Analysis ...... 120
4.6 Electrical Resistivity measurements ...... 123
4.7 X-Ray Diffraction Analysis for Residual Stress Determination ...... 126
4.8 Summary ...... 129
CHAPTER FIVE ...... 131
CONCLUSIONS AND RECOMMENDATIONS ...... 131
5.1 Introduction ...... 131
5.2 Conclusions ...... 131
5.3 Future Work ...... 134
REFERENCES ...... 136
APPENDIX A ...... 164
APPENDIX B ...... 170
APPENDIX C ...... 171 xii | P a g e
APPENDIX D ...... 180
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LIST OF FIGURES
Figure 1.1: The FSW setup ...... 2
Figure 1.2: Project Layout ...... 9
Figure 2.1: Microstructural zones of a typical fusion weld ...... 14
Figure 2.2: Solid state welding processes chart showing energy and thermal
sources, mechanical loadings and shielding method ...... 17
Figure 2.3: Important operating features of FSW ...... 19
Figure 2.4: The Super Liner Ogasawara ...... 23
Figure 2.5: Panel and Wing of an aircraft manufactured by Gatwick Technologies . 24
Figure 2.6: The British Rail Class 395 manufactured by Hitachi Ltd ...... 25
Figure 2.7: The front subframe of the 2013 Honda Accord ...... 26
Figure 2.8: Microstructural zones of a typical fusion weld ...... 27
Figure 2.9: A selection of some FSW tools ...... 30
Figure 2.10: Different types of joint design ...... 37
Figure 2.11: Common defects observed in FSW: (a) Lack of penetration (b) Joint
mismatch (c) Wormhole (d) Large mass of flash (e) Kissing bond
and hook defects ...... 45
Figure 3.1: The I-STIR PDS FSW Machine ...... 67
Figure 3.2: The fixture system with the backing plate...... 69
Figure 3.3: Schematics of the I-STIR PDS showing moving axes ...... 70
Figure 3.4: Front views of initially proposed tools ...... 74
Figure 3.5: Preliminary welds produced using the triflute pin at different
combinations of rotational and traverse speeds...... 75
Figure 3.6: Parent materials set-up ...... 79
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Figure 3.7: Layout of the samples used for characterisations ...... 80
Figure 3.8: Olympus BX51M optical microscope ...... 83
Figure 3.9: Loaded tensile-shear specimen ...... 86
Figure 3.10a: Circuit diagram of the electrical resistance determination ...... 87
Figure 3.10b: Experimental set-up of the electrical resistance determination
using the s-302-4 ...... 87
Figure 4.1 (a): Fx, Fy and Fz forces during welding at 1200 rpm, 50mm/min and
4.5 mm plunge depth ...... 90
Figure 4.1 (b): Torque values during welding at 1200 rpm, 50mm/min and 4.5
mm plunge depth ...... 91
Figure 4.2: Surfaces of welded samples produced at: (a) 600 rpm and 150
mm/min; (b) 600 rpm and 250 mm/min; (c) 900 rpm and 50 mm/min;
(d) 900 rpm and 250 mm/min; (e) 1200 rpm and 50 mm/min; (f) 1200
rpm and 150 mm/min ...... 94
Figure 4.3: Weld produced at 900 rpm, 250 mm/min and 4.8 mm plunge depth
showing the voids, the hooking and the kissing bond defects ...... 96
Figure 4.4: Weld produced at 900 rpm, 50 mm/min and 4.8 mm plunge depth
showing the flow of aluminium and copper ...... 98
Figure 4.5: Determination of the total void area for sample produced at 900 rpm,
50 mm/min and 4.8 mm plunge depth ...... 100
Figure 4.6 (a): Area of void vs traverse speed for all welds produced at 4.5 mm
plunge depth ...... 101
Figure 4.6 (b): Area of void vs vertical force, Fz, for all welds produced at 4.8 mm
plunge depth ...... 102
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Figure 4.7: Different levels of flow of copper at (a) 50 mm/min (b) 150 mm/min
and (c) 250 mm/min ...... 102
Figure 4.8: Chart showing the average void sizes for the two plunge depths ...... 104
Figure 4.9: Microstructural images of the various weld zones ...... 107
Figure 4.10: The presence of microcracks in the aluminium ...... 110
Figure 4.11: (a) Schematic of the material flow due to the influence of the tool ..... 111
Figure 4.11: (b) Microstructural image of the weld produced at 900 rpm, 150
mm/min and 4.8 mm plunge depth ...... 111
Figure 4.12: Flow regions of samples E, G, 1CC1 and 3C1 produced at a) 900
rpm, 150 mm/min and 4.5 mm b) 1200 rpm, 50 mm/min and 4.5 mm
c) 900 rpm, 50 mm/min 4.8 mm and conical tool and d) 900 rpm, 50
mm/min, 4.8 mm and a concave tool respectively ...... 113
Figure 4.13: EDS results of sample made at 900 rpm, 50 mm/min and 4.8 mm
plunge depth ...... 115
Figure 4.14 (a): Shear load versus extension of the sample welded with the
conical tool at 900 rpm, 50 mm/min and plunge depth of 4.8 mm ...... 117
Figure 4.14 (b): Average tensile shear loads of all the samples ...... 118
Figure 4.15: Sample locations of microhardness profiling ...... 121
Figure 4.16 (a): Vickers microhardness values of the welds made at 1200 rpm
and plunge depth of 4.8 mm ...... 121
Figure 4.16 (b): Vickers microhardness results for sample produced at 600 rpm,
50 mm/min and plunge depth of 4.5 mm ...... 122
Figure 4.17: Electrical resistivity versus Heat Index of the produced welds ...... 125
Figure 4.18 (a): Traverse stress of the produced welds ...... 128
Figure 4.18 (b): Longitudinal stress of the produced welds ...... 128 xvi | P a g e
LIST OF TABLES
Table 3.1: Features and dimensions of FSW Tools ...... 76
Table 3.2: FSW Process Parameters ...... 77
Table 3.3: Final Weld Matrix ...... 78
Table 4.1: Input process parameters and output data ...... 92
Table 4.2: Weld defects observed during visual inspection of the produced welds .. 94
Table 4.3: Atomic percentage of Aluminium and Copper in the SZ of samples E,
G, 1CC1 and 3C1 ...... 114
Table 4.4: Maximum load borne by the produced welds before failure ...... 116
Table 4.5: Electrical resistivities of the produced welds ...... 124
Table 4.6: The traverse and longitudinal stresses on the copper side of the weld
interface ...... 127
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ABBREVIATIONS
AA - Aluminium Alloy
AISI - The American Iron and Steel Institute
Al - Aluminium
AS - Advancing side
ASTM - American Society for Testing and Materials
BM - Base Metal
Cu - Copper
DOE - Design of Experiments
EDS - Energy Dispersive Spectroscopy
FS - Friction Stir
FSLW - Friction Stir Lap Welding
FSW - Friction Stir Welding
FSWed - Friction Stir Welded
FSWeld - Friction stir weld
HAZ - Heat Affected Zone
HI - Heat Index
HV - Vickers hardness
IMC - Intermetallic Compounds
MPa - Mega Pascal mm - Millimetres mm/min - Millimetres per minute
NaOH - Sodium Hydroxide
NZ - Nugget Zone
OM - Optical Microscope rpm - Revolutions per minute
RS - Retreating Side
SEM - Scanning Electron Microscope
SiC - Silicon Carbide
SZ - Stir Zone
TMAZ - Thermo-Mechanically Affected Zone
TWI - The Welding Institute
XRD - X-Ray Diffraction
UK - The United Kingdom
UV - Ultraviolet
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NOMENCLATURE
A - cross-sectional area (mm2)
푑퐴 - infinitesimal area element (mm2)
HI - heat index
L - length (mm)
2 MT - the sticking component of the torque (Nm )
2 ML - the sliding component of the torque (Nm )
O(f) - the objective function
PN - axial pressure (Pa)
ρ - electrical resistivity (Ωm)
R - resistance of the material (Ω)
Tm - melting temperature (K) v - traverse speed (mm/min)
훿 - spatially variable fractional slip
푟퐴 - distance of any infinitesimal area element from the tool axis (m)
휏 - shear yield strength (MPa)
휇푓 - coefficient of friction
σ - electrical conductivity (S/m)
- tool rotational speed (rpm)
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CHAPTER ONE
INTRODUCTION
1.1 Background
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. It can be classified into two broad categories: fusion and solid state welding. A joining that is often done by melting the work pieces and adding a filler material to form a pool of molten material (the weld pool) is known as fusion welding. In fusion welding, the molten material cools to become a strong joint, sometimes in the presence of pressure, to produce the weld.
In solid state welding, joining takes place without fusion; there is no liquid (molten) phase in the joint [1]. Hence, the welds are made in the solid phase of the materials.
Some of the basic categories of solid state welding include; cold, ultrasonic, friction
[1].
Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser ray, an electron beam, friction, and ultrasound. Despite the different uses and applications of conventional fusion welding, dissimilar metals are difficult to join using this type of welding due to their different chemical and physical characteristics [2], [3], [4]. Solid state joining methods have received much attention
[5] because of their relative successes in joining dissimilar materials [6], [7].
Friction Stir Welding (FSW), one of such solid state joining methods, is a revolutionary joining process patented by The Welding Institute (TWI) of the United
Kingdom [8]. According to Mishra and Ma [9], the process has been shown to be an
Chapter One Introduction effective way of joining materials with poor fusion weldability such as high-strength aluminium and its alloys and magnesium alloys.
A non-consumable rotating tool, usually harder than the base material, is plunged into the abutting edges of the sheets to be joined under sufficient axial force and advanced along the line of the joint as shown in Figure 1.1. The tool consists of two parts namely; the shoulder and the pin. The material around the tool pin is softened by the frictional heat generated by the tool rotation while the advancement of the tool pushes the plastically deformed material from the front to the back of the tool to complete the joining process [9].
Figure 1.1: The FSW setup [10]
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Chapter One Introduction
Since FSW is a solid state process, a solidification structure is absent in the weld.
Therefore, all the defects related to the presence of brittle inter dendritic and eutectic phases in fusion welds are eliminated [11]. Previous researches have shown that the major FSW process parameters which influence the joint strength and microstructure are the tool rotational speed, the traverse speed, the axial force and the tool tilt angle
[12]. The dimensions and the geometry of the tool play a crucial role in obtaining sound joints [12], [13]. The tool design, welding parameters, joint configuration, tool displacement, and heat input during the FSW process have a complex interplay and significantly alter the material flow and the consolidation of the plasticized material during the welding process [14], [15], [16].
There are different types of joint designs which include butt joint, corner joint, T - joint, lap joint and edge joint. While the butt joint involves welding the abutting edges of the materials to be joined, lap joint involves an overlap of the surfaces to be joined before welding is done. Lap joints have the advantage of being used in the joining of materials of dissimilar thicknesses over the butt joints and do not require two perfectly flat surfaces. The only important surfaces in lap joints are the overlapping surfaces. However, lap joints may require expensive fixtures to ensure stability during the welding process and may also be limited in use due to aesthetic and mechanical reasons.
Aluminium is the third most abundant element in the crust of the Earth, man has been able to exploit this metal and, as a result of the excellent properties it has, use it in different applications. Some of the specific properties of aluminium alloys that enhance their diverse use and makes them unique include the light weight, low density, good structural strength, relative ease of production, good resistance to
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Chapter One Introduction corrosion, good electrical properties, ease of machining / reshaping, alloyability, recyclability, among others.
The metal has a relatively low yield strength in the pure form (7 – 11 MPa) that increases up to 8500% when alloyed (200 – 600 MPa). Generally, the mechanical properties of aluminium are high strength, low density and low weight, making it the metal of choice for a wide range of applications.
Copper is a soft, ductile and highly malleable metal with very high thermal conductivity and very low electrical resistance. Some of the properties of copper include high ductility, high electrical and thermal conductivities, high thermal diffusivity, recyclability, alloyability, malleability, high strength, good corrosion resistance, and so on.
As a result of the peculiar properties of the metal, copper is used in a wide range of industries and applications including electricity, heat, building, household, art, among others. As such, the metal is used in making electrical wires, industrial machinery, plumbing and roofing materials, parts used in the transportation industry, among others. Copper is the material of choice for electrical and heat applications and it is also accepted for use in many industrial areas. Joining copper is necessary, depending on the specific application for which it will be used.
Weld heat input required for copper is much higher when compared to that of aluminium and its alloys due to the greater dissipation of heat through the work piece
[12]. While literatures abound on the dissimilar welding of aluminium and copper using the butt configuration, the reports available on the lap configuration are very limited [17], [18], [19], [20], [21], [22], [23], [24]. Considering the advantages of the
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Chapter One Introduction lap weld configuration and the limited number of studies done in this regard, it is necessary to research the effect of tool geometry and process parameters on friction stir welds of aluminium and copper in the lap weld configuration.
1.2 Problem Statement
Joints of aluminium and copper in the electrical industries are mostly achieved through the use of mechanical fasteners resulting in lack of good contact and loss of energy. Against this background, FS lap welds of aluminium and copper were produced by employing two (2) different tool geometries and process parameters to characterise the effect of the parameters on the quality of the produced welds. Given that FSW is a fairly new technological development, there exists a deficiency of information regarding the characterisation of joint interfaces of FSW of aluminium and copper for different tool geometries and process parameters especially, using the lap welding configuration.
1.3 Aim
The aim of this research work is to achieve Friction Stir lap welds of aluminium and copper using two different tool geometries at rotational speeds of 600, 900 and 1200 rpm, traverse speeds of 50, 150 and 250 mm/min and plunge depths of 4.5 and 4.8 mm. Based on the most common tools used in the industry, two (2) tool geometries
(conical and concave) were chosen to achieve the Friction Stir lap welds.
The joint integrities were then investigated to determine the effect of the processing parameters on the qualities of the produced welds. They were characterised with respect to the evolving microstructure, microhardness, electrical properties and tensile strengths of the weld. The results were compared to each other and the
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Chapter One Introduction parent material to determine which tool geometry and processing parameters result in the most robust weld.
1.4 Objectives
The objectives of this research study are listed as follows:
To research and write a literature review on FSW process parameters
(including tool geometry, rotational speed, transverse speed and plunge depth),
FSW defects and other aspects of FSW.
To produce FS Lap Welds of aluminium and copper using rotational speeds of
600, 900 and 1200 rpm, traverse speeds of 50, 150 and 250 mm/min, plunge
depths of 4.5 and 4.8 mm and welding tools with conical and concave pin
profiles.
To analyse the properties of the FSWed cross-sectional areas macroscopically
and microscopically.
To determine the mechanical properties of the produced specimens including
the tensile and the hardness properties.
To determine the electrical conductivity of the produced specimens.
To evaluate the effect of the FSW process on the residual stress of the
specimens
To correlate the processing parameters to the evolving properties, deduce
conclusions and make recommendations.
1.5 Hypothesis Statement
Though the effect of FSW process parameters has been widely researched for butt welds of aluminium and copper, the effect of processing parameters and different
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Chapter One Introduction tool geometries have not been widely researched for Friction Stir lap welds of aluminium and copper. The effect of the tool plunge depth on the mechanical properties and the microstructures of 3 mm thick FSWed aluminium and copper sheets was investigated. Friction Stir Welds of aluminium and copper were produced and characterised through the microstructure, microhardness, tensile and electrical properties. It is expected that the joint integrity of the weld is dependent on the FSW process parameters.
1.6 Research Methods
An extensive literature study was sourced to ensure a good understanding of the research topic. The literature review included the Friction Stir Welding process and the parameters, the material properties of aluminium and copper and the effects recorded for previous dissimilar works on aluminium and copper as well as similar works on other materials.
Friction Stir Welding of 3 mm aluminium and copper sheets were carried out at various process parameters (different tool geometries, traverse, rotational speeds and plunge depths). As a result, different Friction Stir Welds were produced for analysis and characterisation.
The analyses and the characterisations of the welded samples were done by conducting macro and micro evaluations to determine the material mixing, electrical conductivity, and the tensile behaviour. The various testing methods employed and the objective of the testing are as highlighted:
Tensile testing - to determine the effects of the process parameters and the different tool geometries on the strength and ductility of the joint.
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Chapter One Introduction
Electrical conductivity - to determine, and attempt to establish a relationship between, the effects of the process parameters and different tool geometries on the material flow and the electrical conductivity.
Microhardness – to determine the effects of the process parameters and the different tool geometries on the hardness of the joint materials.
Microstructure - to determine the effects of the process parameters and the different tool geometries on the grain structure across the cross-sectional area of the welds.
1.7 Delimitation of Research
The following were the limitations in this research work:
The project was limited to joining 3 mm sheets of commercially available pure
aluminium and pure copper.
Only the lap weld configuration was produced.
The project was focused on the characterisation of the effects of the process
parameters
1.8 Assumptions
The following assumptions were made during the course of this research work:
Efforts were made to remove the oxide layers on the surfaces of the
workpieces before welding. It is therefore assumed that oxidation during the
welding process had negligible effect on the weld quality.
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Chapter One Introduction
1.9 Significance of Research
Within the University of Johannesburg: Expanding the research field of Friction
Stir Welding.
General: Documentation of the FSW processing parameters that achieve the highest quality Friction Stir Lap Weld of aluminium and copper will improve the knowledge that is at the moment not very clear and expand the industrial use of
FSW in the manufacturing industry.
1.10 Project Layout
The project activities as carried out are presented in Figure 1.2.
Tool design & Preliminary welds
Final Matrix & tool design
FSLW Al & Cu
Electrical Visual Microstructural Mechanical XRD resistivity inspection testing analysis evaluation measurement
Macrographs & Micrographs
Figure 1.2: Project Layout
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Chapter One Introduction
The tools were first designed before preliminary welds were produced.
Subsequently, a final weld matrix was decided on based on results from the preliminary welds. FSLW of the Aluminium and Copper were then done using the welding parameters from the weld matrix and resulting welds were characterised.
1.11 Structure of the Dissertation
The organisation of the dissertation is as follows:
Chapter one briefly introduces the concept of FSW, the aims and objectives, the hypothesis statement, the methods, delimitations and the significance of this research study.
Chapter two presents a review of existing literatures with a focus on the FSW process, the processing parameters that affect the FSW output, weldability of aluminium and copper alloys and a critical review of the existing literatures on similar and dissimilar FSW of aluminium and copper in both butt and lap configurations.
Chapter three introduces the equipment used in this research work and presents the scientific procedures employed in the production of the welds and the characterisation of the samples, the layout of the samples used for the various characterisations, the parent materials and the preliminary welds produced.
Chapter Four presents the final weld matrix, the interplay of the input and the output parameters employed for the production of the welds, the material characterisations of the welds using visual inspection, mechanical testing, electrical resistivity measurements, microstructural analysis and residual stress measurements.
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Chapter One Introduction
Chapter Five concludes this research report and gives recommendations for future studies.
The appendix section consists of results and other materials that may be consulted for a better understanding of this research report.
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CHAPTER TWO
FRICTION STIR WELDING: FACTORS, PROCESSES AND
DISSIMILAR METAL JOINING
2.1 Introduction
This chapter introduces the concept of welding and then goes further to place emphasis on Friction Stir Welding (FSW), the factors affecting FSW; including the welding tool, the rotational and traverse speeds, type of joints, tool tilt angle, plunge depth, welding forces and the heat generated during FSW; and the properties of a typical FS weld. Furthermore, Aluminium and Copper, the materials that were used for this study, and their weldability are also presented in this chapter. Finally, a review of some of the existing literatures on FSW of dissimilar materials are presented before a critical review of the existing literatures on the dissimilar FSW of
Aluminium and Copper are presented.
The following section introduces the concept of welding and the types of welding available today.
2.2 Welding
Welding is the process of joining two or more metals or materials together in the presence of heat, it is an age old practise that enables bonding, accompanied by appreciable interatomic penetration. Depending on the method, welding can be achieved under pressure, or otherwise, and may or may not require a filler material to be used during the process. The heat that is generated or added to the process may or may not result in the melting of the materials to be joined. However, even in
Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining the absence of melting, this heat is usually responsible for, or involved in, the joining process.
2.2.1 Fusion welding
Fusion welding encompasses welding procedures that ultimately result in the fusion of the materials after they have passed through the process of melting and the subsequent solidification phase. Chemical bonding occurs at the molten phase of the process with or without the use of a filler material. The major types of fusion welding processes are: arc, oxy-fuel, electric resistance, laser beam, electron beam and thermite welding. The source of energy for the technique is either electrical – as in
Gas Tungsten Arc Welding (GTAW), Shielded Metal Arc Welding (SMAW), Flash
Welding (FW), Percussion Welding (PEW), Induction Welding (IW) etc.) – or chemical – as in Oxyacetylene Welding (OAW), Oxyhydrogen Welding (OHW), Air
Acetylene Welding (AAW) and Thermite Welding (TW). However, the joining of dissimilar metals through the conventional welding techniques have been associated with a large Heat Affected Zone (HAZ) and a host of different types of welding defects due to the difference in their melting temperatures and other factors [20],
[25], [26].
During the fusion welding process, melting and solidification is done at a very high temperature gradient within a relatively small zone with the peak temperature located at the centre of the fusion zone. According to [27], the metallurgical structure of a fusion welded joint varies from the base metal to the fusion zone with notable variations in the mechanical properties. Basically, a fusion weld could be divided into four separate zones namely: the fusion zone (FZ), the weld interface, the heat affected zone (HAZ) and the unaffected base metal zone as shown in Figure 2.1. In
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining fusion welding, the HAZ is the weakest section of the weldment based on change in the microstructural and mechanical properties of the section [27].
Figure 2.1: Microstructural zones of a typical fusion weld [28]
The fusion zone is the weld itself, consisting of a mixture of the melted filler metal and the base material. The mixing in this zone is driven majorly by convection in the molten pool [27]. The properties of the FZ depend on the compatibility between the filler metal and the base material. The weld interface, also called the mushy zone, is a thin zone composed of base material that was partially melted but did not have the opportunity to be involved in the mixing process. In a lot of literature, the weld interface is usually not taken into consideration as a distinct zone due to the fact that it is a relatively thin zone. It is located in-between the FZ and the HAZ.
Though it remains unmelted during the welding process, the HAZ is largely affected at the microstructural level resulting in a change of its microstructural and metallurgical properties. The portion of the base materials that has been altered by heat is known as the HAZ. The change experienced in the HAZ is largely due to the heat from the welding process and the cooling that happens subsequently. Fusion welding usually produces welds with a large HAZ. The formation of the HAZ could include physiological changes on the surface of the base metal like heat-tint.
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Depending on the application, this may be undesirable for the resulting weld, even though such changes in colour are largely cosmetic. The heat-tint may give an indication of the width of the HAZ. However, this may not necessarily be accurate because both the heat-tint and HAZ are sometimes affected by different factors.
While the heat-tint is superficial, the HAZ is not a surface phenomenon, rather, it lies deep within the metal. Factors that influence the HAZ include; the amount of heat input, the peak temperature reached, the time at the elevated temperature, the thermal diffusivity of the base metal, the weld filler metal and the cooling rate [27],
[29]. The HAZ usually exhibits a heat-treated structure that involves grain growth, carbide precipitation, intermetallic phase transformation and recrystallization.
The unaffected base metal zone presents itself after the HAZ and it is sometimes easy to detect using visual inspection. The base metal retains the initial properties of the rolled structure with a little grain growth. Though the zone directly surrounding the HAZ is found to be in a state of high residual stress [27], it is however not significantly altered in any way during the welding process.
2.2.2 Solid state welding
The group of welding processes that produce coalescence at temperatures lower than the melting points of the base materials, usually in the absence of a filler material, are referred to as solid state welding [30]. As the name suggests, coalescence is achieved in all the processes while the metal is not melted.
Coalescence is due to pressure, time, vibration and temperature acting individually or in combination with other factors [30]. The source of energy for the technique is either electrical, (as in Hot Pressure Welding {HPW}, Forge Welding {FOW},
Induction Welding {IW}, Upset Welding {UW}, Resistance Spot Welding {RSW} etc.),
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining mechanical (as in Friction Welding {FRW}, Friction Stir Welding {FSW}, Ultrasonic
Welding {USW}, Cold Welding {CW}), or chemical (as in Pressure Gas Welding
{PGW}, Diffusion Welding {DFW}, Explosion Welding {EXW} etc.). Figure 2.2 shows a list of the solid state welding processes, including their energy and thermal sources, type of mechanical loading necessary and the shielding method needed.
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
Figure 2.2: Solid state welding processes chart showing energy and thermal sources, mechanical loadings and shielding method. [31]
Where;
CEW - Coextrusion welding IW - Induction welding
CW - Cold welding PGW - Pressure gas welding
DFW - Diffusion welding RSEW - Resistance seam welding
EXW - Explosion welding RSW - Resistance spot welding
FOW - Forge welding ROW - Roll welding
FRW - Friction welding USW - Ultrasonic welding
FSW - Friction stir welding UW - Upset welding
HPW - Hot pressure welding
As shown in Figure 2.2, the major sources of heat in solid state welding processes are: radiation, induction, resistance, flame contact, explosion and friction. Solid state welding includes some of the very oldest of the welding processes (FOW welding) and some of the very newest like FSW [30]. Even though pressure, time, vibration and temperature are involved, the time element is very short in some of the processes, ranging from microseconds up to a few seconds. However, the time element is extended to several hours in other processes. To achieve strong bonds, both surfaces must be devoid of oxide films, residues, metalworking fluids, absorbed layers of gas or any other contaminants [32].
With solid state welding, thermal expansion and conductivity do not pose significant risks as they do in arc welding processes when dissimilar metals are being joined
[33], [34], [35]. Also, the mechanical properties of the welds may be similar to that of 17 | P a g e
Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining the parent materials [36]. However, the initial cost of the equipment to be used for the solid state processes are usually more expensive than their fusion welding counterparts.
Forge welding, one of the solid state welding processes, was employed in the production of the 1600-year old ‘Iron pillar of Delhi’ [37] and the steel katana swords used by samurais in ancient Japan [38]. Over the years, the use of other solid state welding processes has grown significantly. The use of these welding processes are seen in the replacement of existing bolts, nuts and rivets in the aerospace industry
[39], the near net shape forming in the aerospace industry [39], the welding of steel and aluminium in the hulls of ship or compound plates [40], the joining of metal parts having opposed planar and parallel surfaces [41] and the dissimilar welding of metals that have proven difficult to weld using fusion welding techniques [42].
While the weldability of aluminium and copper via traditional fusion welding techniques has been seen to be difficult and replete with different defects, FSW, a type of solid state welding, offers a way for producing quality welds of both metals.
2.3 Friction Stir Welding
Revolutionizing new welding processes are not created very often and, upon its invention and patenting in 1991 by The Welding Institute (TWI) [8] in 1991, FSW was one of such occurrences [9]. FSW, as a solid state welding process, is a fairly recent process that produces welding by a strong shearing of the material using a rotating tool to mix the materials to be assembled without melting them [43]. Figure 2.3 shows the important operating features of FSW.
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
Figure 2.3: Important operating features of FSW [11]
As shown in Figure 2.3, FS welding is done by the rotating tool plunging into the materials to be welded, which results in the stirring of the grains of both materials and culminates in the welding of both materials. The basic operating principles of a typical FSW process is as described viz: The tool is made to rotate, usually at a constant acceleration, until it reaches a constant rotational speed to be used for the specific welding operation before it is plunged into the surface of two abutting or lapping sheets. This phase is referred to as the plunging phase. Once the constantly rotated tool reaches the desired welding depth, it continues to rotate in this position for a specified period (referred to as the dwell stage) to allow a thorough initial mixing of the materials before it is fed traversely along the clamped pieces of abutting or lapping materials. The speed with which the rotating tool traverses the materials may be constant or varied, depending on the desired processing parameters. The tool is then removed from the materials once the tool has traversed the materials and welding has been completed. During welding, the side of the weld for which the
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining rotating tool is moving in the same direction as the welding direction is commonly known as the 'advancing side' while the other side, where the tool rotation is opposite to the welding direction, is known as the 'retreating side'.
As a result of FSW being a solid state welding process, it has several advantages over fusion welding processes that occur due to problems resulting from cooling down from the liquid state. As a result, all the defects that occur as a result of brittle inter dendritic and eutectic phases being present are usually eradicated [11].
Porosity, solidification and liquation cracking are all not present in FSW. Along with the foregoing, some other advantages of the FSW process are:
Ability to weld aluminium alloys [44] and a wide range of other materials.
Lack of porosities.
Reduction in surface preparation [43].
Lack of the need for a filler metal, shielding gas or consumables.
Lack of fumes, metal spatter or ultraviolet (UV) emission.
Reduction in deformation when compared to arc welding [43].
Ability to produce welds with superior weld strengths and mechanical properties
[45].
No need for post weld heat treatment on produced welds [45].
No need for much expensive machining after welding because the appearance
and thickness of the welds are generally acceptable.
Low environmental impact [45].
It is energy efficient, environmental friendly, and versatile [9].
Ability to operate in all dimensions (X, Y and Z).
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
Little cost and training is required for the conversion/automation of a simple
milling machine to produce FS welds [45].
However, FSW is not without its own demerits and is associated with a number of unique defects. Some of the disadvantages generally associated with FSW are:
Defects such as “kissing bonds”, tunnel-like defects along the weld as well as
lack-of-penetration defects may all be present in FSW if the welding is not done
at optimum welding parameters.
At the end of the weld, an exit hole is left where the tool is withdrawn from the
welded materials
An effective clamping system, producing larger downward forces than needed
for fusion welding, is required to hold the materials to be welded together.
Unless used regularly, FSW machines require some warm-up time before
welding can commence.
The probe (pin), protruding from the base of the tool (shoulder) is an important feature of the tool, and it is only marginally shorter in length than the combined thickness of the sheets. The high normal pressure and the shearing effect of the welding tool and the metals being welded are responsible for the frictional heat that is generated during the welding operation. This frictional heat, along with the heat that is generated by the mechanical mixing process and the adiabatic heat within the material, results in a much softened region of the material to form everywhere around the tool without resulting in the melting of the material.
This softened region of material cannot escape as it is constrained by the tool shoulder and the clamping force. Hence, as the tool traverses, the materials along 21 | P a g e
Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining the joint line, some of the softened materials are swept around the tool probe between the retreating side and the undeformed material. This results in a mechanical inter-mixing of the softened materials resulting in the dynamic recrystallization of the base metals. The softened, intermixed metal is then joined by the mechanical pressure exerted on it by the FSW tool.
Hence, FSW is both a deformation and a thermal process, despite the lack of bulk fusion [46], [47]. Some reports have suggested that the temperature of the material in contact with the pin may be as high as the solidus temperature [48]. However, validating this experimentally is difficult due to the intense deformation at the interface and the complexities of the process [49], [50]. Different theories and models have been developed over the years in order to try and explain the heat generation and the transfer during the FSW process [51], [52].
2.4 Applications of Friction Stir Welding
With the development and greater understanding of the process, FSW has been used in a lot of industries. Among others, FSW finds its application in the following industries:
2.4.1 Marine industry
Since the metallurgical properties of heat affected zone, distortion and residual stresses in steel are not expected to largely change due to the low heat input during
FSW [53], FSW finds its application in shipbuilding. The process is already in use for the welding of the aluminium alloy used in the Amphibious Assault Vehicle (AAAV) of the US marine [9], steel and aluminium for use in the hull of ships among others. A
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining typical example is the Super Liner Ogasawara, the largest FSWed ship so far in the world shown in Figure 2.4.
Figure 2.4: The Super Liner Ogasawara [54]
2.4.2 Aerospace industry
Being one of the most conservative industries, the aerospace industry is one that does not easily change its manufacturing process due to a long process demand for certification. However, the FSW process offers a way of reducing the weight of aircraft by eliminating the need for thousands of riveting pins in wings and other parts of the aircraft. Since the fuselage, wings, fins and other parts of the aircraft are usually composed of aluminium alloys which are difficult to join using fusion welding methods, FSW could be used for joining these aluminium alloys. This represents a significant reduction in system cost, assembly cost, design cost, maintenance cost and parts count [39] hence, Boeing [55], Eclipse aviation [45] and GKN aerospace
[39] are already adopters of the FSW technology in the aerospace industry.
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
Figure 2.5: Panel and Wing of an aircraft manufactured by Gatwick
Technologies [56]
2.4.3 Rail
The body of the carriages for some of the trains on the Chinese High Speed Rail
Network was manufactured using the Powerstir FSW machines by Precision
Technologies Group [57] while Hydro Marine Aluminium used a bespoke 25 m long
FSW machine to manufacture the curved side and roof panels for the Victoria line trains of the London Underground [58]. Some parts of the British Rail Class 395 shown in Figure 2.6, the Pendolino trains, Japanese commuter and express A-trains,
Stadler KISS double decker rail cars and Wuppertal suspension railway are all made using the FSW technology [45].
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
Figure 2.6: The British Rail Class 395 manufactured by Hitachi Ltd.
[59]
2.4.4 Automotive industry
FSW is being used in the automotive industry for the manufacture of doors, roofs, bonnets, trunks and so on. So far, it has been used in the front subframe of the 2013
Honda Accord [60], rear hatch of the 2010 Toyota Prius, parts of the space frame of the 2007 Audi R8 as shown in Figure 2.7, trunk and hood of the 2006 Mazda MX-5
Miata, rear doors and hood of the 2004 Mazda RX-8 [61] etc.
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
Figure 2.7: The front subframe of the 2013 Honda Accord [62]
2.4.5 Other applications – in electronics, Apple seamlessly joined the front and back sections of their 2012 iMac and endorsed the technology during its product launch [63]. Apple has since adopted FSW in the design and manufacture of subsequent models of the iMac. FSW has also found application in the fabrication of façade panels and cathode sheets, Bizerba meat slicers, Siemens x-ray vacuum vessels, vacuum valves and vessels, encapsulation of nuclear waste, hunting knives, production of heat exchangers and in robotics [45].
Despite the various uses of FSW, the process has enormous potentials and may be further applied in many other industries and applications. To achieve this, a better understanding of the process than is presently known is needed. The following section looks at the microstructural zones that are present in a typical FS weld.
2.5 Microstructures of FS Welds
FSWed metals have distinct microstructures as a result of the solid state nature of the process and the effect of the dynamic interplay of the tool components and the base materials. As a result, the following zones are present in a typical friction stir weld: the base metal (BM), the heat-affected zone (HAZ), the thermo-mechanically affected zone (TMAZ), and the nugget zone (NZ) as shown in Figure 2.8. In this section, these metallurgical zones will be examined in greater detail.
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
Figure 2.8: Microstructural zones of a typical fusion weld [64]
Base metal (BM) - as in fusion welding, the base metal is the section of the metal whose microstructure is unaffected by the effect of the rotating tool on the metals being joined. The colour remains the same and the structure of the grains are left unchanged.
Heat-affected zone (HAZ) - present in most welding processes, the HAZ is the region of the material that experiences sufficient heat to only slightly alter the microstructure. The type of material and the choice of the tool parameters usually determine to what extent the microstructure of the HAZ is altered. However, there is no dynamic recrystallization of the grains at this microstructural zone. The HAZ is located next to the BM on both sides. Aydın et al. [65] observed different behaviours at the microstructural level of different samples within the HAZ as a result of the presence or absence of hardening precipitates. This difference in the behaviour is also observed by other studies [66], [67], [68].
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Thermo-mechanically affected zone (TMAZ) – located next to the HAZ on both sides is the thermo-mechanically affected zone. There is an absence of dynamic recrystallization in this zone. The TMAZ is characterized by slight deformation and rotation of the grains even though the grains are still recognizable as belonging to the parent materials. A combination of high temperature and deformation due to internal stresses results in thermo-mechanical alterations in the grains. Even though this zone is not directly subjected to the action of the tool pin and the shoulder, the mechanical properties of this zone are usually lower than that of the nugget zone due to the strengthening precipitates becoming more coarse as a result of the effect of the mixing and heat input in the nugget zone [65]. The TMAZ is peculiar only to the FSW process [69].
Nugget zone (NZ) - also known as the stir zone, the NZ corresponds to the fusion zone in fusion welding and it is characterized by a region of highly deformed materials. This is the zone that experienced the direct impact of the action of the rotating tool pin and the shoulder. The grains in this zone are usually equiaxed but smaller than those of the parent materials. Dynamic recrystallization occurs in this zone and may result in the formation of intermetallic compounds particularly in dissimilar joints [65], [70]. Depending on the processing parameters, the NZ possesses mechanical properties that are higher or lower than the TMAZ or HAZ, an important feature depending on the application for which the welded material is to be used.
For the production of successful welds and effective application of the technology, the factors that combine together in FSW must be well evaluated and understood.
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The following section presents some of the factors that affect the quality of a FS weld.
2.6 Factors Affecting FSW
Considering its vast applications and possibilities, certain factors affect the results of a FSW process. These factors/parameters interplay in the success or otherwise of a
FSW process. Depending on the parameters chosen, a FS weld may or may not prove to be useful for the particular application for which it was intended to be used.
The major factors that affect FSW include the FSW tool, the rotational speed, the traverse speed, plunge depth, direction of travel, joint type, forces during the FSW process and the heat input. Some of these will be further considered and presented in greater details in this section.
2.6.1 FSW Tool
Since FSW is produced by the action of a non-consumable rotating tool on the metals to be joined, the tool is an important element in a FSW process. Research has established specific factors of the tool that play a crucial role in obtaining sound joints to include the pin geometry [71], [72], the pin design [12], sheet / plate dimensions [23] and the profile of the shoulder [73] of the FSW tool.
2.6.1.1 Tool geometry
Tool geometry describes the interplay of the shape and the size of both the pin and the shoulder. The geometry of the tool affects the power required, heat generation, uniformity of the welded joints and flow of the plasticised material. Both the pin and the shoulder have a part to play in the quality of a produced weld hence, a good understanding of how both affect the weld quality is necessary.
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Depending on the thickness of the materials being welded, both the pin and the shoulder of the tool may be involved in heat generation for the welding operation. For thinner materials, the pin is usually responsible for the heat supplied while both the pin and the shoulder are responsible for the heat supplied for the welding of thicker metals.
Different tool pin profiles have been designed over the years which include: straight square, straight hexagon, straight octagon, tapered square, tapered octagon, straight cylindrical, threaded cylindrical, tapered cylindrical, square, triangle, concave, conical among others. [71], [74], [75]. Figure 2.9 shows a selection of some of these tool profiles that have been designed.
Figure 2.9: A selection of some FSW tools [76]
With the developments in tool geometry comes the need for researchers to validate the viability or otherwise of the different designs. A lot of work has gone into researching the effects of the different tool geometries on a wide range of materials with different thicknesses and weld configurations.
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In 2013, Venkateswarlu et al. [77] investigated the effects of tool geometries on
AA7039 welds and concluded that the pin diameter and the shoulder diameter have a great influence on the mechanical integrity of the produced welds. Blignault et al.
[78] used different tool geometries to predict the ultimate tensile strength of produced
FS welds using Response Surface Methodology (RSM). They concluded that a wide range of tool geometries can produce welds with acceptable mechanical properties within a range of input process parameters.
Rajakumar et al. [79] also investigated threaded tool geometries for the optimization of the FSW process for maximizing the tensile strength of 7075-T6 aluminium alloy and developed an empirical Equation for predicting the tensile strength of the joints depending on the tool geometries and other process parameters. Palanivel et al. [75] examined the influences of tool pin profiles on mechanical and metallurgical properties of dissimilar aluminium alloy welds using the straight cylindrical, square, threaded cylindrical, tapered octagon and tapered square tool pin geometries. The square straight tool produced the welds with the best result of all the tools used in the study.
Srirangarajalu et al. [67] used four different tool pin profiles, Straight Threaded (ST),
Straight Cylindrical (SC), Tapered Cylindrical (TC) and Tapered Threaded Cylindrical
(TTC) and Cylindrical to determine the microstructure and the mechanical behaviour of friction stir welded copper. All other design considerations were kept the same. Of the four different tools employed, only the TTC produced welds that were free of defects. The other tools produced welds with wormhole defects and lack of penetration defects.
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2.6.1.2 Tool design
If the tool would produce successful welds, it must enhance weld quality and allow for a maximum possible speed. Tool design includes the selection of material as well as the geometry to employ. It is one of the crucial factors that significantly alters material flow, consolidation of plasticized material, the uniformity of microstructure, mechanical properties and the process load during welding [13], [80], [81].
In designing the tool, a suitable material must be strong, tough and hard wearing at the welding temperature [45], withstand the welding process, provide the necessary friction between the to-be-welded materials as well as ensure adequate heat generation [82]. To select the right material, the material characteristics for each friction stir application must be known. Characteristics such as wear resistance, machinability, reactivity as well as other physical properties of a material will influence the type of material to be used as a FSW tool [83]. Materials that are commonly used for FSW tools include tungsten alloys, Polycrystalline Cubic Boron
Nitride (PCBN), nickel alloys and hot-worked tool steel, such as AISI H13 [84].
Fujii et al. [85] examined the effect of tool shape on the mechanical properties and microstructures of 5 mm thick welded aluminium sheets using pins of column without threads, column with threads and the triangular prism shape probes. They discovered that the response to tool shape varies for different aluminium sheets.
Palanivel et al. [71] varied tools of different designs by focusing on tools with different pin geometries while maintaining other design parameters. They did not observe any defect in the welds made using the straight tool profiles while tapered tool profiles produced welds with tunnel defects at the bottom of the joints. They also
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining observed that the variations in the observed tensile strengths resulted from material flow behaviour, dissolution and over aging, loss of cold work in the HAZ and the formation of macroscopic defects in the weld zone.
2.6.1.3 Tool pin
Partly responsible for the stirring of the plasticised materials [86], the tool pin is another important factor of the FSW tool. The shape of the FSW tool pin has been shown to directly affect the material flow around the pin. The length of the pin is an equally important factor of the tool pin. The pin length is usually designed to be shorter than the width of the materials to be welded and yet long enough to ensure a thorough stirring of the materials.
A short pin will result in incomplete stirring and hence defect formation in the produced weld. With a shorter pin length, also comes the possibility of plunging the shoulder into the materials to be welded, resulting in the production of more flashes than necessary, and hence, a reduction in the thickness of the cross section of the produced weld. The pin diameter also plays an important role in the weld quality as a big or small pin diameter may result in defects in the produced welds. The pin diameter is one of the factors that determines the flow of the plasticized material around the tool.
Samer and Qasim [87] used five (5) different pin profiles to investigate the effect of tool geometry on the mechanical and microstructural properties of aluminium. They concluded that the shape of the pin has an effect on the mechanical properties of the joints. While increasing the tool pin diameter and keeping other parameters constant led to an increase in the mechanical properties of the produced welds.
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2.6.1.4 Tool shoulder
Elangovan and Balasubramanian [88] investigated the influences of tool pin profile and the tool shoulder diameter on the formation of friction stir processing zone in aluminium using five (5) different tool pin profiles and three different shoulder diameters. They observed that all the welds produced by the square tool pin profile were defect free, notwithstanding the shoulder diameters, and also that all the welds produced by tools with the 18 mm shoulder diameter were defect free, notwithstanding the tool pin profile.
Leal et al. [89] examined the effect of shoulder geometry on the material flow in the heterogeneous friction stir welding of thin aluminium sheets using a scrolled shoulder and a shoulder with a conical cavity. They discovered that the welds produced by the tool with the conical cavity shoulder had the onion ring structure while the scrolled shoulder produced welds without the onion ring structure despite the extensive mixing of the base materials around the rotating pin. They concluded that the pin- driven flow and the shoulder-driven flow are major determinants in the measurements of the amount of the plasticised materials moved from the advancing side to the retreating side of the tool.
Arora et al. [90] studied the optimum FSW tool shoulder diameter for welding aluminium alloys. Using a three-dimensional heat transfer and visco-plastic flow computer model, they proposed a criterion for identifying the optimum shoulder diameter. They proposed that the maximum value of the objective function O(f) corresponds to the optimum diameter and is given by Equation 2.1:
푀 푀 푂(푓) = ( 푇 × 퐿 ) ...... 2.1 푀푇 + 푀퐿 푀푇 + 푀퐿
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Where MT, the sticking component of the torque is given by Equation 2.2:
푀푇 = ∮ 푟퐴 × (1 − 훿)휏 × 푑퐴 ...... 2.2
And ML, the sliding component of the torque is given by Equation 2.3:
푀푇 = ∮ 푟퐴 × 훿휇푓푃푁 × 푑퐴 ...... 2.3
In Equations 2.2 and 2.3, 푟퐴 is the distance of any infinitesimal area element 푑퐴, from the tool axis, 훿 is the spatially variable fractional slip, 휏 is the shear yield strength, 휇푓 is the coefficient of friction and 푃푁 is the axial pressure.
Mehta et al. [91] used computational method to determine the optimum shoulder diameter for a FS weld and validated the results with experimental data. They investigated the influence of shoulder diameter on power requirements, peak temperatures, torque and the thermal cycles during an FSW operation and observed that an increase in shoulder diameter, corresponded to a higher spindle power, peak temperature and torque requirement. Their results validated the model proposed by
Arora et al. [90] as shown in Equations 2.1 – 2.3.
2.6.2 Rotational speed
One of the major welding parameters affecting the quality of the FS weld is how fast the tool rotates, either clockwise or anti clockwise, during the welding operation [92].
This is referred to as the rotational speed. The tool rotational speed is responsible for the stirring and the mixing of the plasticized materials, influences the heat input and the shoulder force variations [67], [93]. Nandan et al. suggested that the rotational
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining speed influenced the heat generation rate while the traverse speed does not influence the heat generation rate [12].
Due to the tool rotation, three types of flow affecting the overall transport of plasticized materials during FSW can be observed. The rotation of the tool and the resulting friction between the tool and the work-piece results in a slug of plasticized material rotating around the tool. The rotational motion of the pin then tends to push the plasticized material downward close to the pin, resulting in an equivalent amount of the material being driven further away. The simultaneous interactions of these three flows determine the overall motion of the plasticized material and results in the formation of the joint [12].
2.6.3 Transverse speed
Sometimes called the feed rate or the welding speed, the traverse speed is a measure of how quickly, or slowly, the tool pin moves along the weld interface. The traverse speed is another important welding parameter as it influences the heat input into the FSW process. While the rotational speed is responsible for the stirring and the mixing of the plasticized materials, the translational motion of the rotating tool results in the transportation of the plasticised material from the front of the tool to the back before coalescence [94], [95], [96].
There is a complex interplay between the traverse speed, the rotational speed and the heat input during FSW. While increasing the rotational speed results in a hotter weld, only a reduction in the traverse speed will achieve the same effect. For a colder weld, the reverse holds true as a reduction in the rotational speed, or an increase in the traverse speed, will result in a colder weld [67], [97], [98].
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Balasubramanian [99] extensively studied the relationship between the base metal properties of different aluminium alloys and the traverse speed. They discovered that while the traverse speed is inversely proportional to the yield strength and the hardness of the aluminium alloys, it is directly proportional to the ductility of the aluminium alloys.
For a good weld, the material surrounding the tool needs to be hot enough to enable the required plastic flow while minimising the forces acting on the tool. An excessive heat input could result in defects due to a liquidation of low-melting-point phases or, at least, a reduction in the properties of the weld. Without the necessary heat however, voids and other forms of defects may develop in the stir zone [45]. These different behaviours in the presence of an excessive or reduced heat input means that for a successful weld, a "processing window" is necessary. This is the range of processing parameters for both tool rotational speed and traverse speed that will produce enough heat input that results in enough material plasticity and the mixing that are necessary for the production of a successful weld.
2.6.4 Joint types
The way the materials to be joined are laid out depends on the application for which the welds are being made and different configurations exist for such. These include, but are not limited to: butt, corner, lap, edge and T joints (Figure 2.10) [1].
Figure 2.10: Different types of joint designs [1] 37 | P a g e
Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
A lap joint is formed by overlapping two plates and welding them either in the joint where they meet, as it is done in gas tungsten arc welding (GTAW) and plasma arc welding (PAW), or through the top plate and into the bottom plate [100]. Lap joints are especially useful because they can be used to weld pieces of dissimilar thicknesses and materials. Lap joint does not require that the cut faces be perfectly flat and parallel, a major requirement of the butt weld. Rather, in a lap joint, the only critical surfaces are the faces of the parts where they overlap, and the tolerances on this overlap are fairly high [100].
The advantages of lap joints over many other types of joints include:
the technique reduces the number of critical weld parameters (which makes the
joint easer to prepare and increases the likelihood of a successful weld);
materials of different thicknesses can be easily welded together (care should
however be taken to weld the thinner piece on top);
thin materials, such as foils and diaphragms, can be welded together by using
this technique [100].
overlaps are sometimes desirable for aesthetic, mechanical or structural
reasons.
Notwithstanding its advantages, the lap joint also has its demerits which include:
the welds tend to have much lower tensile strengths than butt joints as the total
effective area of the weld is lower [100];
the welds tend to be much less stiff than their counterparts, as the thin weld
tends to act as a pivot point [100];
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the joints do not provide self-alignment (and therefore may require the use of
expensive welding fixture to ensure alignment).
2.6.5 Tool tilt angle and plunge depth
The plunge depth is the measure of how deep the tool (pin and shoulder) penetrates below the surface of the welded plate. It is an important welding parameter that also affects the quality of the welds alongside the rotational and the traverse speeds.
Ensuring that the shoulder is plunged below the surface of the plates results in an increase in the pressure below the tool. This enhances an adequate forging of the materials at the rear of the tool.
Careful consideration should be made in the choice of plunge depth to ensure adequate downward pressure and full penetration of the weld by the tool. Choosing a high plunge depth may result in excessive flash during the welding operation or the tool pin rubbing the backing plate surface. The plunge depth of the tool into the workpiece is directly proportional to the axial force and the frictional heat generated during the welding operation [101], [102], [103].
Literature has suggested that to enhance the forging process, the tool must be tilted at the correct angle to ensure that the rear end of the tool is lower than the front of the tool [104]. Tool tilt angle is, therefore, the angle between the axis of the welding tool and the normal to the surface of the welded sheets. The tool is tilted to ensure that as the plasticized materials flow from the RS to the AS, they plug into the holes created by the traversing pin and are then forged by the action of the pressure created by the tilted tool pin. Having the tool tilt angle at an optimum value is important as a high or low value may result in defects [104], [105].
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Sundaram and Murugan [101] observed that the tool axial force is directly proportional to the plunge depth of the tool. They recorded that an increase in the tool plunge depth results in an increase in the tensile strength until a maximum value is reached where further increase in the plunge depth resulted in a decrease of the tensile strength.
Seighalani et al. [104] investigated the effects of the tool material, geometry, and the tilt angle on FSW of pure titanium and obtained sound, defect free welds at a tool tilt angle of 1 degree. However, the presence of weld surface defects were observed at a tilt angle of 3 degrees as a result of voids that resulted from the discontinuity that occurs as more plasticized materials escaped from the bottom of the tool shoulder when the tilt angle was increased. This results in more materials gathering at the AS of the weld while there are less materials observed in the RS.
Kimapong and Takehiko [105] studied the effect of welding process parameters on the mechanical properties of FSW lap joint between aluminium alloy and steel by varying the tool tilt angle between 0 and 4. At tool tilt angles of 0 degree and 4 degrees, it was also observed that the produced welds had defects while the best weld quality was produced with a tool tilt angle of 1 degree. The shear test confirmed the weld quality with an average shear strength of about 112 MPa, the highest value of the four configurations. An increase in the tool tilt angle resulted in a decrease in the shear strength of the joint, a relationship directly linked to the formation of FeAl and Fe2Al5 intermetallic compounds. Seighalani et al. [104] observed that even though pure titanium samples were successfully welded, a tool tilt angle of 3 degrees produced welds with defects and low shear strengths. The welds produced at the tool tilt angle of 1 degree were however observed to be defect free.
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2.6.6 Forces acting during FSW
A number of forces are usually experienced by the tool during welding. It is necessary to maintain a balance between the force acting on the tool and the optimum welding parameters necessary for ensuring good quality welds in order to minimise the wear and tear on the tool and to prevent tool fracture. These forces include:
a vertical force, that acts downwards towards the materials being welded,
necessary to maintain the plunge depth of the tool. It is usually positive in the
downward direction and may vary during the welding operation. Even though
a lot of FSW machines have force controls, a lot of the welding operations are
usually carried out using the position control, leading to variations of the force
as the welding operation continues.
a horizontal force that acts in the direction of motion of the tool and is usually
positive in the traverse direction. Most welds are usually carried out with a
preset traverse speed and since the material heats up and softens during the
welding operation, this force is expected to decrease as the welding operation
continues as a result of the heat input into the material.
a lateral force that acts perpendicular to the traverse direction of the tool and
is usually considered positive towards the advancing side.
a torque needed to ensure the rotation of the tool in either the clockwise or the
anticlockwise direction. It is usually considered positive in the direction of the
rotation of the tool. The value of the torque varies, depending on the
coefficient of sliding friction, the downward force and the flow strength of the
surrounding material.
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Gemme et al. [68] measured and optimized the vertical force during the successful welding of aluminium sheets by iterating the initially measured values. They also recorded the longitudinal force and the torque applied by the rotating tool during the welding operation and observed a sharp increase in both forces during the plunge and dwell phases and a slow decrease in the forces until steady state is reached where the forces were stable. They suggested that the welding conditions were stable in the central parts once steady state was reached.
2.6.7 Heat generation in FSW
The heat generated during FSW is of particular interest as the quality of the produced welds depends on it. While there is no definite value of heat input that can be stipulated for all different welds, understanding the relationship between the welding parameters, the parent materials and the corresponding heat that will be generated given those parameters is important. As such, this has been a source of constant study in the FSW community [12], [45], [106], [107].
Quantifying the heat that is transferred into the materials being welded is more complex as some of the heat generated will be dissipated into the tool, the backing plate and the atmosphere. It is also noted that the heat generated at the top of the plate will not be the same as that at the bottom of the sheets due to variations in the heat conductivities of the materials.
Hence, different models have been proposed to evaluate the heat generated and/or transferred to the materials during welding. In most of all the models proposed, two major factors always play significant roles in the quantification of the heat generated
– the tool rotational speed and the traverse speed. Both of these are known to affect
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining the amount of the heat generated during the welding operation. Hence, Arbegast
[108] developed a simple expression to evaluate the peak temperature, T, during welding using the heat index, HI, as shown in Equations 2.4 and 2.5.
푇 = 푘(퐻퐼)훼 ...... 퐸푞푢푎푡𝑖표푛 2.4 푇푚
휔2 퐻퐼 = ...... 퐸푞푢푎푡𝑖표푛 2.5 푣 × 104
Where Tm is the melting temperature of the base alloy, k is a constant that range between 0.65 and 0.75, is a constant that range from 0.04 to 0.06, is the tool rotational speed and v is the traverse speed. Equations 2.4 and 2.5 give an idea of the working temperature during a typical FSW.
2.7 Properties of FS Welds
The properties of the resulting welds in FSW depend on the choice of processing parameters and tool. As such, an understanding of the properties of welds produced using FSW will help in determining the quality and the suitability of the produced weld for their particular applications. In this section, the mechanical and the electrical properties of welds produced using FSW will be examined.
2.7.1 Mechanical and material properties of FS Welds
The properties of a material that involve a reaction to an applied load are known as the mechanical properties of that material. They determine the range of the possibilities for practical use of a material and give an indication of the service life of the material during operation. Defects, grain sizes, microhardness, tensile and shear properties are some of the properties that will be examined in this section.
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2.7.1.1 Defects
Defects in FSW occur as a result of several factors such as poor choice of FSW tool, the processing parameters or contacts between the welded materials [16], [102].
These may result from insufficient or excessive heat input, poor flow of the plasticized materials, insufficient forging, softening of the HAZ among others [68],
[88], [102]. Defects in welds result in lower tensile strength [16], [102], [109] and a reduction in the weld quality. Some of the defects associated with FSW are shown in
Figure 2.11 and they include:
lack of penetration defect
joint mismatch
wormhole or tunnel defect
Large mass of flash
kissing bond
hook defect
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
a b
c d
e
Figure 2.11: Common defects observed in FSW: (a) Lack of
penetration (b) Joint mismatch (c) Wormhole (d) Large mass of flash
(e) Kissing bond and hook defects [110], [111]
The lack of penetration (LOP) defect, also known as root flaw or incomplete root penetration, occurs as a result of a shallow stirred zone in the welded material and may be avoided by the right selection of the tool pin and the plunge depth to ensure adequate stirring of the materials close to the bottom of the welded materials [68].
Joint mismatch is a defect that results from the vertical or the horizontal displacement of the edges of the welded material under the action of the stirring tool and are usually corrected by ensuring proper clamping positions and pressure before the onset of the welding operation [82].
Wormhole defects, also known as tunnels, voids, or cavities run along the weld and may be found on the surface or subsurface. They may or may not be continuous
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining along the length of the weld. Subsurface wormholes cannot be easily detected by non-destructive testing methods and are sometimes caused due to insufficient forging pressure, poor clamping [112], incorrect tool design or insufficient welding temperatures [68].
Large mass of flash, or excessive weld flash or top sheet thinning, results when the heat input is too high, the shoulder diameter is too small or the plunge depth is too high [82]. They may not be easily avoidable in a force controlled welding due to changes in the vertical position of the tool as the force varies during the welding operation.
Kissing bond, resulting from low temperatures, kissing bonds occur as a result of discontinuity of bond between the materials from each side of the weld. Insufficient cleaning of the workpieces before welding, large shoulder diameters or incorrect tool offset could lead to kissing bond defect. They are also called 'zig-zag line', 'Lazy-Ss',
'swirl zones (SWZ)', 'joint line remnants' or 'entrapped oxide defects' [113], [114].
Hook defects, occurring as a result of the upward movement of the lower material in a lap weld, the hook defects may sometimes further result in wormhole defects.
However, this upward movement may also result in a thorough mixing of both materials and hence, may not be classified as defects in such cases. Both kissing bonds and hook defects are typical of welds made in the lap welding configuration.
2.7.1.2 Microhardness
The measure of the resistance of a material to plastic deformation is known as hardness. Indentation hardness has been shown to be directly proportional to tensile strength [115]. Microhardness measurements are usually determined using
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining indentation hardness tests. Different researches have shown the microhardness values to be linked to grain sizes, the average size of the crystals forming the material [116]
During FSW, dynamic recrystallization occurs, resulting in a decrease in the grain sizes from the parent material to the nugget zone. This dynamic recrystallization results in the formation of fine-equiaxed grains in the nugget zone [109], [116], [117].
Dynamic recrystallization may result due to different processing parameters including traverse speed [118], heat input, rotation rate and traverse speed [116], [119].
2.7.1.3 Tensile and shear properties
Tensile properties, the measure of how a material behaves under a tension load, is a fundamental mechanical property that describes the quality of the welded sample.
The tensile and shear strengths of the welded materials are often compared to that of the base material to give an indication of the joint efficiency. A lot of research has gone into the tensile properties of FS welded joints as a percentage of that of the base material [120], [121] including the relationship of the process parameters and the resultant tensile properties [71], [122]. For lap welds, tensile shear strength, the maximum shear stress a material can withstand under a tensile load, is often used to characterise such joints [17], [19], [22].
Kundu et al. [122] studied the microstructure and the tensile strength of friction stir welded joints between interstitial free steel and commercially pure aluminium. They reported a maximum tensile strength of about 123 MPa, about 86% of that of the aluminium base metal, using a rotational speed of 600 rpm. Xue et al. [23] reported a tensile shear load as high as 2.68 kN in a FS lap weld of aluminium and copper
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining when the aluminium was placed in the advancing side while Cerderqvist and
Reynolds [97] observed a value of 9.6 kN as the average shear load of FS lap welded aluminium sheets.
Kimapong and Watanabe [105] studied the effect of welding process parameters on the mechanical property of FSW lap joint between aluminium and steel and compared the values of the shear strength with that of the parent material. They reported a shear strength value of about 77% that of the aluminium parent material, a value acceptable for many applications where lap welds are desirable.
2.7.2 Electrical properties of FSW
Different materials exhibit different responses when they are in an electric field.
Electrical properties are the properties of a material that explain how that material will behave in the presence of an electric field. Examples include electrical resistivity, electrical conductivity, dielectric constant, dielectric strength, piezoelectric constant among others. Focus was placed on electrical resistivity in this study.
Electrical resistivity, also known as resistivity or volume resistivity, gives a measure of the resistance of a material to the flow of electric current. It is an intrinsic property of such a material. A material with low resistivity will allow more current to flow through it than a material with a higher resistivity. Unlike resistance, the electrical resistivity, ρ, of a material does not greatly vary with the shape or size of the material and it is calculated from Equation 2.6:
퐴 𝜌 = 푅 ...... 2.6 푙
Where: R - resistance of the material
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A - cross-sectional area of the material
l - length of the material
Conversely, a material that allows current to flow more readily through it is said to have a high electrical conductivity value. Electrical conductivity, σ, is defined as the measure of the ability of a substance to conduct electric current and is given as
Equation 2.7:
1 𝜎 = ...... 2.7 𝜌
The electrical resistivity of a material varies with temperature. The expression in
Equation 2.8 [123]
𝜌(푇) = 𝜌0[1 + 훼(푇 − 푇0)] ...... 2.8 is used to estimate the linear approximation of the electrical resistivity of a material given a little variation in temperature. ρ(T) and ρo are the resistivities at temperature
T and a fixed reference temperature To respectively and α is the temperature coefficient of resistivity. The calculation of electrical resistivity of metals at high temperatures becomes hugely complex due to the electron–phonon interactions.
Akinlabi and Akinlabi [94] compared the electrical resistivities of FSWed aluminium and copper at different heat inputs and observed a maximum percentage increase of
9.8%, compared to the average resistivity value. Akinlabi et al. [124] also monitored the effect of heat input on the electrical resistivity of dissimilar friction stir welded joints of aluminium and copper and reported an increase in the electrical resistivity of the welded metals. They also observed a maximum increase of 9.8% compared to the average resistivity of the parent materials.
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2.8 Aluminium and its Alloys
Aluminium, an element with an atomic number of 13, belongs to lightweight group of metals including lead and tin. The metal has been in use for a long time, though it was not until the 1800s that advances in research made it possible to produce pure aluminium [125].
The uses of aluminium are varied and diverse. Today, it is used in commerce, transportation and other industries. Some of its applications are well known, while others are not so obvious. Its weight is a third of that of copper or steel. Also, its durability and recyclability, translates into savings for companies that use them.
Many specific properties of aluminium and its alloys, including light weight and good structural strength, enable them to be applied for structural parts. Heinz et al. [126] stated that the demand of aircraft and the automotive industries for lightweight materials is met by aluminium and its alloys. Aside from the aircraft and automotive industries, aluminium is also used extensively in household equipment, construction, packaging, electric tools and materials among others.
There are lots of different alloys of aluminium and the choice of the alloy to use depends on the application for which it is desired. The increasing demand for lightweight materials in the aircraft and automotive industries has been met by aluminium alloys over the years [75]. The 5000 and 6000 aluminium alloy series have been used extensively in fabricating aircraft structures, rocketry, structures of all other forms of transportation and also in other structural applications [126].
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2.9 Copper and its Alloys
Copper is one of the most important metals in the world [127] and it is a tough, malleable and highly conductive metal. Apart from the fact that it is essential to all living things, copper continues to play an important role in modern technology even though it has served humanity for over 7,000 years [127], [128].
Since it was first used in 8000 B.C., people have discovered different uses of copper.
Tools made of this element helped advance civilization during the Stone Age and since that time, it has become an integral part of many industries. Its resistance to corrosion, thermal conductivity and malleability ensures that it will continue to be used for a long time. It is the third most widely used metal in the industries next to aluminium and iron.
No other metal, alone or in alloy form, so effectively offers the amount and breadth of useful properties as copper. Over the coming decades, technological progress will largely depend on advanced materials such as metals, alloys, composites and other structures, many of which can potentially contain copper [129]. The high ductility of the metal makes it a practical tool for industrial use. It is commonly used in shipbuilding. Copper has the best electrical conductivity compared to other metals, except silver [130]. Also, since its heat dissipation capacity is superior to that of aluminium [127], copper is the metal of choice in the electrical circuitry, microprocessors, heat sinks and exchangers.
The most important feature of copper is alloying. Manufacturers can combine it with different metals, depending on the practical application and the intended use.
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Copper combined with tin makes bronze. Alloyed with zinc, the result is brass. When combined with nickel, cupronickel is the metal formed.
2.10 Weldability of Aluminium and Copper Alloys
Before the advent of welding, mankind had found different ways of joining metals for her use. However, the method of choice for joining metals since the discovery of welding was the conventional fusion welding method due to the many advantages of the method over earlier modes of joining. However, fusion welding had disadvantages of its own, primarily the numerous welding defects that develop during the process including hot cracking, precipitate dissolution, voids formation, loss of work hardening, LOP defects and distortion [131]. Also, the high thermal diffusivity of both aluminium and copper make welding them using traditional fusion welding difficult.
However, FSW offers a way of overcoming the problems encountered during welding using fusion welding techniques. A lot of research has been done on joining aluminium alloys together with considerable success. Also, considerable efforts have also gone into researching FSW of copper and its alloys with lots of successes recorded. Different alloys of aluminium and copper with different thicknesses have been successfully welded over the years. Fisher [32] reported that aluminium plates of up to 75 mm have been successfully welded by the FSW process. Also, quite a few studies have been conducted on the FSW of different thicknesses of copper sheets [132], [133].
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2.11 FSW of aluminium and copper alloys
Certain applications require different properties from the different parts making up such assemblies. Examples of these are found in applications that require weight reduction (Al to Mg or Steel), electrical connections (Al to Cu), transportation industries (where fuel economy, weight reduction and improved safety are desired) among others. Thus, it is sometimes necessary for dissimilar metals to be joined together for use in such situations. Bolts and nuts, brazing, forging, riveting, welding and other means of joining have been used for joining dissimilar metals.
Since FSW offers a way of providing better weld qualities than fusion welding, it is the method of choice for applications that require sound joints with acceptable mechanical, physical and chemical properties. Recently, Honda Motor Corporation implemented FSW in joining the steel subframe of the Honda Accord to some die cast suspension components. They claimed that this reduced the total body weight of the vehicle by 25% and reduced the electricity consumption by 50% [60].
Aluminium and copper are the most common metals that are in used in the electric power industry where the Al–Cu joints are widely used for transmitting the electricity.
However, there are difficulties in making electrically stable joints between both dissimilar metals using traditional bolts and other joining technologies [132]. This has resulted in lots of effort being placed on the welding of aluminium and copper in the last decades. Due to the high possibilities of forming brittle intermetallic compounds
(IMCs) and the differences in the mechanical, chemical and physical properties of aluminium and copper, their dissimilar joining using fusion welding comes with a great deal of difficulty.
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Since solid-state welding methods eliminate some of the problems posed by these differences and increases the chances of producing successful welds between dissimilar metals, lots of studies have been conducted on the dissimilar joining of aluminium and copper with different scopes for each study. This section presents a critical review of some of the existing literatures on the FSW of aluminium and copper.
Thomas and Nicholas [134] explored the potentials for the FSW process in the transportation industry including the application of FSW in airframes, fuel tanks and skins in aerospace, sheet bodywork and engine support frames in the automotive, railway wagon, coachwork and bulk carrier tanks in the transportation and hull, decks and the internal structures for high speed ferries and LPG storage vessels for the shipbuilding industry. They saw the opportunity for FSW to open up new markets and opportunities as the technology receives wider recognition as the way forward in welding.
Thomas et al. [80] further reviewed the developments made in the design of FSW tools both for the butt and lap joint configurations. They showed that even though a tool might produce very good results for one welding configuration, it may not be a good tool to use for another configuration. While results from the Whorl™ and MX-
Triflute™ tools produced welds of acceptable qualities for the butt weld configuration, the A-Skew™ and Flared-Triflute™ were two tools that were showing promising results for the lap weld configuration due to the need for a wider weld width. They however concluded that additional work needs to be done to further minimise the severity and occurrence of defects in the lap weld configuration of FSW.
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Ouyang et al. [135] researched the microstructural evolution in the friction stir welded
6061 aluminium alloy (T6-tempered condition) to copper, concentrating on the microstructural evolution and temperature distribution of the produced welds. They observed the presence of different intermetallic compounds formed during the solidification process or as a result of the attainment of complete phase equilibrium in the liquid state. However, their work was limited to the butt weld configuration and therefore, not totally applicable to the lap weld configuration.
Liu et al. [25] studied the microstructure and XRD analysis of FSW joints for copper and aluminium 5A06 dissimilar materials. They concluded that a rotational speed of
950 rpm and a travel speed of 150 mm/min produced the weld with the highest quality based on the results obtained from metallographic, tensile and XRD tests.
They reported that there was no presence of new Cu-Al intermetallic compounds in the weld nugget zone.
Shukla and Shah [136] reported considerable difficulties while investigating the joint properties of FSW of aluminium 6061 alloy to copper. Of the four welds produced, only two of them produced sound welds with the copper on the advancing side and a tool offset of 1 mm towards the copper sheets. They concluded that it was necessary to conduct more research on the process conditions that would produce sound welds of high quality by plasticizing the faying areas.
Galvão et al. [72] studied the flow of materials in heterogeneous FSW of thin sheets of aluminium and copper and observed that both the tool geometry and the relative positions of the sheets in the advancing and the retreating sides of the tool had a huge influence on the morphology and the distribution of the aluminium and copper
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining as well as the formation of intermetallic compounds. However, the work was limited to welds of only four different welding parameters with three of the welds produced with the same tool while the other tool was used to produce only one weld.
Galvão et al. [137] further studied the influence of FSW process parameters on the formation and the distribution of brittle intermetallic structures in FSW of aluminium and copper. They varied the rotational-transverse speed ratio to control the relative heat input and discovered that increasing the heat input resulted in an increase in the dimensions of the intermetallic layer while no apparent pattern was found for the intermetallics formed at reduced heat inputs.
Xue et al. [121] researched the enhanced mechanical properties of FS welded aluminium and copper joints, focusing on characterising the formed intermetallic compounds and the tensile properties of the produced welds. However, their work was limited to the single welding configuration of 600 rpm rotational speed and 100 mm/min traverse speed.
Xue et al. [138] improved on their initial research by examining the effect of FSW parameters on the interface microstructure, surface morphology and the mechanical properties of aluminium and copper joints. The FS welds were produced at a constant traverse speed of 100 mm/min while the range of the rotational speed was expanded to between 400 and 1000 rpm. They observed that the position of the copper plate, as well as the offset position are important in the production of defect free welds. As they increased the rotation rate, better joints qualities were observed while defects were formed at the lowest rotational speed.
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
Li et al. [120] also examined the microstructure and the mechanical properties of dissimilar pure copper and 1350 aluminium alloy FSW butt joints using the pin-off technique for offsetting most of the tool pin into the aluminium alloy. They produced good welds at a rotational speed of 1000 rpm and traverse speed of 80 mm/min.
From XRD analysis, they observed a lamella structure and vortex-like pattern without the presence of any intermetallic compound. However, their work was limited to only the 1000 rpm rotational speed and 80 mm/min.
Rajakumar et al. [26] examined the influence of FSW and tool parameters on the strength properties of AA 7075-T6 aluminium alloy joints. They evaluated the tensile strengths of the welds and correlated them to the microstructure and the microhardness of the weld nuggets. They were able to show that the tool rotational speed, welding speed, axial force, tool shoulder diameter, pin diameter and tool hardness all have effects on the eventual tensile strengths of the FSWed samples.
However, the work focused on the tensile strength properties of the welded samples.
Microstructural and microhardness evaluations were carried out mainly to explain the yield strength properties observed.
Agarwal et al. [139] produced butt joints of AA 6063 aluminium alloy and commercially pure copper using a milling machine operating at 1000-1400 rpm, traverse speed between 40 and 80 mm/min and pin offsets between 0 and 1 mm.
They investigated the effects of the varied welding parameters on the interface microstructure, surface morphology and mechanical properties of the produced welds. Like Xue et al. [138], they also observed that placing copper in the advancing side resulted in relatively better joints and concluded that the tool offset should be
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining low and restricted to being placed in the softer material. Their study was however also limited to the butt weld configuration.
Akinlabi and Akinlabi [140] examined the tensile fracture location characterisations of
FSWed aluminium and copper. The study varied the tool shoulder diameters, rotational speeds and the feed rates. It was discovered that most of the welds fractured in the advancing side of the welds, resulting from the presence of intermetallic compounds at the joint interfaces. They concluded that the evaluation of the tensile fracture locations of the dissimilar FS welds of aluminium and copper revealed that the fracture locations are dependent on the internal structures of the weld regions, either due to the presence of weld defects or intermetallic compounds in the joints. The study was however focused only on the fracture location characterisation without considerations to other parts of the materials.
Akinlabi et al., [124] examined the effect of heat input on the electrical resistivity of dissimilar FSWed joints of aluminium and copper. They discovered that metallurgical bonding was achieved at the joint interfaces of the produced weld. They also discovered that the electrical resistivity of the produced joints increased as the heat input into the welds increased. This work was however limited to the electrical resistivity and the heat input during the welding process.
Akinlabi et al. [141] continued their earlier research on the FSWed copper and aluminium using the SEM for microstructural characterisations and established that welds produced at lower feed rates exhibited better metallurgical bonding and good mixing. They also observed that more defects were produced in welds at the higher feed rate of 300 mm/min than those produced at lower feed rates.
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
Akinlabi et al. [142] reconfigured a milling machine to achieve friction stir welds of aluminium and copper. They designed the FSW tools from steel and inserted it into the chuck of the milling machine. They also designed a backing plate and varied the traverse and the rotational speeds using the control system on the milling machine.
Even though an optimum joint speed of 74% was achieved, there is a need for further work in incorporating temperature measurements and measurements of forces acting during the process.
Furthermore, Akinlabi and Akinlabi [73] studied the effect of heat input on the properties of dissimilar friction stir welds of aluminium and copper. They varied the shoulder diameters (using 15, 18 and 25 mm), rotational speeds (using 600 and
1200 rpm) and traverse speeds (between 50 and 300 mm/min) to ensure varied heat inputs into the welds. They observed good mixing between both materials, resulting in a reduction of grain sizes at the stir zones and higher Vickers microhardness values. They also reported an increase of 9.8% in the average electrical resistivity compared to the parent material. However, their microstructural evaluation was limited to the optical microscopy analysis.
Akinlabi [143] researched the effect of shoulder size on the weld properties of dissimilar aluminium and copper FSWelds using three tools of 15, 18 and 25 mm shoulder diameters, 600, 950 and 1200 rpm rotational speeds and traverse speeds between 50 and 300 mm/min. Characterisations were done through microstructural evaluation, tensile testing, microhardness measurements, x-ray diffraction analysis and electrical resistivity. The author concluded that the welds produced at 950 rpm and either intermediate or hot welding conditions were the best in each group.
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
Akinlabi et al. [144] reported on the non-destructive testing conducted on dissimilar
FSW between 5754 aluminium alloy and C11000 copper. The welding was done with rotational speed ranging from 600 to 1200 rpm and feed rates between 50 and 300 mm/min. Using the x-ray radiographic testing and visual inspection, they observed the presence of wormhole defects and discontinuities in some of the welds. They concluded that visual inspection is not a good measure of testing the weld integrity as all the welds passed the visual inspection tests whereas, the x-ray radiographic testing revealed the presence of the defects. The results indicated that the welds produced using the 950 rpm rotational speed had the best qualities among the configurations considered.
Akinlabi and Akinlabi [145] further varied the rotational speeds and feed rates of
FSWed aluminium and copper and, after carrying out the statistical analysis of the weld data, concluded that the configuration with rotational speed of 950 rpm and traverse speed of 150 mm/min produced the weld with the optimum result. They also found out that the downward vertical force has a significant effect on the Ultimate
Tensile Strength of the weld. However, this study was also limited to the butt weld configuration.
Mubiayi and Akinlabi [146] examined the present state of FSW of dissimilar materials, focusing on aluminium and other materials. It was revealed that significant progress has been made. However, the work also demonstrated the need for a full understanding of the dissimilar FSW process in order to enhance the industrial applications of the technology. The study also advocated for more work to be done in order to understand the qualities and properties of the current welds produced using the FSW process.
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
Akinlabi and Akinlabi [94] also used 600, 950 and 1200 rpm rotational speeds and
50, 150 and 300 mm/min feed rates to produce FSWed aluminium and copper while monitoring the temperature generated by the welding process. The welding temperature was found to be below the melting point of both the aluminium and copper, confirming FSW as a solid state process. They also reported that the average electrical resistivity of the weld produced increased slightly when compared to the electrical resistivity of the parent material. They recommended that the process parameters may be easily used for FSW of aluminium and copper.
However, it remains to be seen whether the result will be applicable for the lap weld configuration since the work focused only on the butt weld configuration.
With lots of studies having been conducted on the butt weld configuration of aluminium and copper using FSW, much fewer literatures exist on the lap weld configuration. The few literatures available are examined and presented below.
Akbari et al. [18] examined the effect of the position of materials on friction stir lap welding of aluminium to copper by investigating the heat generation, microstructural and mechanical properties using shear and hardness tests. They found out that the position of the material had an effect on the strength of the weld and also affects the heat input during the FSW process. Conversely, they also observed that the heat input affects the quality of the weld and concluded that a better weld was produced when the aluminium was on top of the copper plate.
Abdollah-Zadeh et al. [17] first reported successful FS lap welds between 1060 aluminium alloy and commercially pure copper in 2008. The welds were done using a threaded geometry tool pin, welding speed between 30 and 375 mm/min while
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining rotational speed was varied between 750 and 1500 rpm. They examined the microstructural and mechanical properties of the FS welded aluminium/copper lap joints and reported the effect of the formation of Al4Cu9, AlCu and Al2Cu intermetallic compounds on the shear strengths of the joints.
They observed a decrease in the shear load that joints could bear when there was an increase in the rotational speed up to 1500 rpm. The same effect was observed when decreasing the welding speed down to 30 mm/min. They however observed imperfect joints at low rotational speed (750 rpm) and high welding speed (95 mm/min).
Saeid et al. [22] reported successful FS lap welds of aluminium and copper using welding speeds ranging from 30 - 375 mm/min and a constant rotational speed of
1180 rpm. They investigated the effect of the welding speed on joint strength, microstructure and interface morphology of the produced welds. They detected the formation of Al4Cu9 and Al2Cu intermetallic compounds as well as the presence of microcracks. Increasing the welding speed resulted in a decrease of the frequency of the microcracks. However, cavity defects were observed inside the joints at higher welding speeds of 118 and 190 mm/min. They reported few microcracks, no cavity defects and the maximum tensile shear strength at welding speed of 95 mm/min.
Recently, Bisadi et al. [19] successfully joined AA5083 aluminium alloy and commercially pure copper sheets using FSLW and studied the influences of welding and rotational speeds on the mechanical properties and microstructures of the produced welds. They performed the experiments using rotational speeds between
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining
600 and 1550 rpm, and welding speeds of 15 and 32 mm/min. The best weld was achieved at 32 mm/min welding speed and 825 rpm rotational speed.
They reported the highest ultimate tensile stress values as about 74% of the aluminium sheets and 78% of the copper sheets parent materials. They also reported the presence of many joint defects like channels, hooking defects and cavities at very low or high welding temperatures. It was also observed that increasing the process temperature resulted in a decrease in the ultimate tensile stresses and higher amounts of intermetallic compositions, higher diffusion of copper particles to the aluminium sheet and higher numbers of micro cracks.
Elrefaey et al. [20] introduced an intermediary layer of zinc in between the copper and aluminium sheets as they lap welded both metals and observed a significant improvement in the joint performances. The significant improvements included the limitation of the black and grey structure present in the control experiment, a better microstructural image, much higher fracture load and fracture in a ductile/brittle manner as opposed to the brittle manner in which the control experiments broke.
However, the study was limited to a single tool whose shape is unknown. Also, the work was limited to copper and aluminium sheets of dissimilar thicknesses. It remains to be seen if the results will be replicated with both metals having the same thicknesses.
Xue et al. [23] further successfully FSWed 3 mm thick aluminium and copper sheets at a rotation speed of 600 rpm using a pin of 8 mm diameter. They achieved a high property friction stir welded aluminium/copper lap joint at low heat input with a high failure load of 2860 N occurring in the aluminium side of the weld. They observed
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining the formation of pure Cu and other intermetallic compound layers at the lower part of the nugget zone. The formation of the intermetallic layers was seen as the reason for the increased hardness observed.
From the literatures presently available, it is obvious that while very few studies have been conducted on the effects of the rotational and traverse speeds on the weld quality of FSLW of aluminium and copper, the effect of the plunge depth and tool pin profile are not readily available in the open literature. Hence, while this study is not exhaustive in dealing with these issues, the effects of each of these processing parameters viz: rotational speed, traverse speed and plunge depth on the friction stir lap welds of aluminium and copper will be examined in this study.
2.12 Summary
This chapter provided basic information on the FSW process with particular interest in the FSW of dissimilar materials. The attention that dissimilar welding has attracted recently is due to exciting prospects that the process offers for different applications and industries. As a result, lots of efforts have gone into studies on the joining of copper, titanium, steel and aluminium alloys via FSW.
The aluminium alloy used in this study belong to the “commercially pure” wrought family of aluminium. Formed by extrusion or rolling, the 1060 aluminium alloy is widely used in the electrical and the chemical industries. This is because it has high workability and corrosion resistance, low electrical resistivity and low mechanical strength compared to other more significantly alloyed metals. The copper alloy used in the study is the commercially available pure copper C11000 extensively used in
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Chapter Two Friction Stir Welding: Factors, Processes and Dissimilar Metal Joining the electrical applications due to the low electrical resistivity and high thermal conductivity.
In the characterisation of aluminium and copper alloys chosen for this study, the tool geometry, plunge depth, traverse speed and rotational speed were varied in order to evaluate the effect of each of these processing parameters. Other parameters, including the tool tilt angle, backing plate, sheet thickness, pin length, pin and shoulder diameters, were kept constant. The choice of processing parameters were made from careful study of the literature and other previous studies.
A review of the presently existing literature on FSW and other related aspects of this research project has been presented in this chapter. The experimental set-up, testing procedures, sample sizes and locations as well as standards employed in testing will be presented in the following chapter.
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CHAPTER THREE
EXPERIMENTAL SET UP
3.1 Introduction
In this chapter, the experimental set-up and techniques employed leading to and during the characterisation of the produced FS welds are reported. Experimental procedures, limits of equipment used as well as factors considered in the choice of different modes employed are discussed. Finally, the final weld matrix as well as the characterisation of the parent materials used in this research work are presented.
3.2 The Friction Stir Welding (FSW) Machine
The Intelligent Stir Welding for Industry and Research (I-STIR) Process
Development System (PDS) FSW Machine made by MTS Systems Corporation and located at the Friction Stir Processing Research Institute of the Nelson Mandela
Metropolitan University (NNMU) in Port Elizabeth was employed in the production of the welds in this research work. The I-STIR PDS is a total FSW system that employs motion and force control with advanced mechanical, software, cooling and electrical systems in the production of FS welds.
The machine has a maximum load capacity of 88.9kN (Z-axis), maximum speed of
10000 mm/min (Y-axiz), maximum range of 2000 mm (Y-Axiz), maximum spindle speed of 2000 rpm and pitch range between -15 degrees to +15 degrees. Figure 3.1 shows the I-STIR PDS platform while the major sub-systems and system specifications [147] are shown in Appendices A1 and A2 respectively.
Chapter Three Experimental Set-up
Figure 3.1: The I-STIR PDS FSW Machine
3.3 Fixtures
Ensuring the rigidity of the materials to be welded is often a critical and complicated phase of the welding process as any form of movement of the materials will usually result in defects in the produced welds. Clamping is done in such a way that the upward, forward and side forces are resisted as the welding process ensues. At the plunging phase of the welding process, these forces are relatively high. Since the forces have a tendency to both shear and lift the workpiece, adequate fixtures must overcome these forces and prevent any form of vibrations. Literature suggests that for materials with thickness not more than 13 mm, a root opening of less than 10% of the thickness of the material is tolerable [148]. To reduce the clamping load, the fixtures holding the material in place are placed as close to the joint as the tool pin/shoulder will allow.
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Chapter Three Experimental Set-up
A backing plate is used to resist the normal forces between the FSW tool and the workpiece. During welding, there is a tendency for the materials being welded to be joined to the material below the joint materials, usually the platform of the FSW machine. Hence, a backing plate is also useful in ensuring that the bed of the FSW platform remains flat by preventing the materials being welded from being joined to the FSW platform. The backing plate also helps in absorbing some of the heat generated during the welding operation at the weld root, hence ensuring smaller grain sizes [9]. Mishra et al. [149] suggest that the backing plate may be unnecessary for materials with high thicknesses in the lap weld configuration.
Figure 3.2 shows the FSW platform with the fixturing system and backing plate used in this study.
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Chapter Three Experimental Set-up
Figure 3.2: The fixture system with the backing plate
Literature has shown different types of steels (mild, carbon and stainless steel) as good choices for use as backing plates [122], [123], [124], [125]. In this work, a 500 x
400 x 12 mm mild steel, electroplated with zinc, backing plate was used. To ensure adequate fixturing, the backing plate was securely fastened to the bed of the FSW platform using appropriate bolts.
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Chapter Three Experimental Set-up
3.4 Control System of the FSW Platform
To produce a FS weld, the FSW machine has to be commanded to carry out the welding operation. This is achieved by means of a compiled computer programme that details the operation of the machine. The parameters that are defined in the programme include the initial positions of the tool pin (X, Y and Z), the forge position, the rotational speed, the welding distance, the plunge depth and the transverse forces as well as the X control mode. Figure 3.3 shows the schematics of the I-STIR
PDS machine with the possible directions of motion.
Figure 3.3: Schematics of the I-STIR PDS showing moving axes [150]
The I-STIR PDS is capable of operating both in the position control and the force control modes. In the position control, the initial position, traverse direction, final position as well as other processing parameters (dwell time, traverse speed, rotational speed, and tool tilt angle) are stated in the program. To achieve these parameters, the vertical force (Fz) will vary, depending on the stage of welding and the welding conditions. However, in force control, the vertical force (Fz) is
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Chapter Three Experimental Set-up predetermined and stated in the program. The machine will vary the processing parameters (the tool position) to ensure that the Fz is kept constant. Other parameters are also stated in the program in force control. The machine is sensitive to changes in force. This makes it possible for the machine to determine when it is nearly touching the materials.
As in all procedural programming, the FSW machine picks the instructions to be executed in a sequential basis from the welding programme. At the expiration of the last command, the welding operation is supposed to end. Hence, the last command usually instructs the gantry to move away from the material into open space. A copy of the programme employed in the welding of the materials is presented in Appendix
A3.
For the production of the FS welds in this work, the following procedure was followed:
i. The tool pin is moved to the weld start position on top of the materials.
ii. Rotation of the spindle starts and rapidly accelerates to the desired speed.
iii. The tool pin is plunged into the materials until the plunge depth is attained.
iv. Rotation at the initial position is maintained until the dwell time is reached,
ensuring the plasticity of the workpieces.
v. The tool begins to traverse the workpieces along the weld direction at the
traverse speed indicated until it reaches the end position. This is the stage at
which the welding of the workpieces is taking place.
vi. The tool is lifted up from the workpieces and taken to the position specified in
the program, ending the welding process.
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Chapter Three Experimental Set-up
The FSW machine has a remote control pendant that aids the control of the welding process. The pendant also includes the emergency stop button for stopping the operation of the machine whenever necessary even though the welding program may not have reached the end of the current process. Also, on the pendant are the start / stop and position control buttons.
3.5 Workpiece Preparation
Prior to welding, some operations were carried out on the workpieces to ensure good weld qualities and reproducibility of the produced welds. The materials to be welded were first scrubbed with Silicon Carbide (SiC) paper to get rid of physical impurities.
The sheets were then cleaned with acetone to get rid of impurities present.
Furthermore, to ensure reproducibility, some other factors were put into consideration viz:
Care was taken to ensure that the sides of the sheets that were placed on top
for both copper and aluminium was the same for all the welded samples.
To ensure that the tool pin profile and dimensions are maintained, the tool
was cleaned after each weld to ensure that the deposited materials on the tool
pin and shoulder were removed. Cleaning was initially done by leaving the
tool in Sodium Hydroxide (NaOH) solution (25g of NaOH and 120 ml of water)
for 4 hours. Since this was time consuming, subsequent cleaning was done
by remachining the tool.
3.6 Tool Design and Selection for the FSLW of Al/Cu
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Chapter Three Experimental Set-up
Three tool shoulder configurations were considered for this research work: the flat, the conical and the concave shoulders. For dissimilar welding of aluminium and copper, researchers have observed fairly good results using concave tool shoulders
[120]. [145]. The cavity in the concave shoulder aids thorough mixing and it is needed in the formation of compressed annular ring around the tool pin [71], [151].
The cavity also aids in the prevention of plasticized materials from escaping from beneath the tool. While Li [120] and Scialpi [151] used tools with 16 mm and 15 mm shoulder diameters respectively, Akinlabi and Akinlabi [145] used tools with 15, 18 and 25 mm shoulder diameters to achieve sound welds of aluminium and copper.
Wei [74] used a tool with 25 mm shoulder diameter for the dissimilar joining of aluminium and titanium using the lap weld configuration and obtained good results.
Rodrigues et al. [152] used two different tools of conical and scrolled shoulders to achieve FS welds of aluminium and copper. The conical shoulder cavity was inclined at an angle of 80 and had a diameter of 10 mm while the scrolled shoulder had a diameter of 14 mm. They observed that the welds with the scrolled shoulder had smaller nugget grain sizes with a lot of coarsened precipitates. Leal et al. [89] also used two different tools of conical and scrolled shoulders with 10 mm and 14 mm diameters respectively to achieve sound welds of aluminium sheets that exhibited the onion ring structure.
Three pin profiles were also considered for this research work: the cylindrical, conical and triflute pins. While frustum shaped pins, like the conical pin, tend to displace less materials compared to a cylindrical pin with the same root diameter, the triflute pin reduces the volume of the displaced material even further [9]. Nandan et al. [12] indicated that the triflute tool with expanded flute will produce successful lap welds
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Chapter Three Experimental Set-up due to an expanded stir region and wider welds resulting from a large swept volume in contrast to the pin volume. The flute helps to increase the total surface area of the interacting surfaces between the tool and the base materials. This helps to increase the rate of heat generation, make the materials softer and enhance material flow
[12].
As a result of previous research works that have been done, this research work proposed to use tools with concave, conical and flat shoulders with 18 mm diameter and cylindrical, conical and flat pin profiles of 5 mm tool tip diameter. Front views of the proposed tools are presented in Figure 3.4 while the dimensions and profiles of the tools are presented in Appendix A4
Figure 3.4: Front views of initially proposed tools
Figure 3.4 (a) is a tool with concave shoulder and cylindrical pin, (b) is a tool with conical shoulder and conical pin while (c) is a tool with flat shoulder with triflute pin.
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Chapter Three Experimental Set-up
In this report, Figure 3.4 (a) will be referred to as the concave tool, (b) as the conical tool and (c) as the triflute tool. The tools were made from H13 tool steel (W302) and heat-treated to 52 HRC as shown from previous studies [78].
3.7 Preliminary Welds
Preliminary experiments were initially conducted, using all the initially proposed tools, after which physical inspections were done. Physical inspection of the preliminary welds produced with the triflute tool revealed surface defects that run deep from the aluminium into the copper sheets as shown in Figure 3.5. Varying the rotational speed and feed rate did not seem to have any much improved effect on the surface defects observed in the welds. However, the welds produced with the concave and conical tools produced welds that passed the physical inspection test.
Figure 3.5: Preliminary welds produced using the triflute pin at different
combinations of rotational and traverse speeds.
As a result of the failure of the physical inspection test of the welds produced with the triflute tool, this research work focuses on producing the FS welds using the
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Chapter Three Experimental Set-up concave and the conical tools. The produced welds were then further tested to determine the quality of the produced welds using scientific testing methods. Table
3.1 lists the features and dimensions of each of the two tools used.
Table 3.1: Features and dimensions of FSW Tools
Concave Tool Conical Tool Pin Tip ɸ 5 mm 5 mm Pin Length 4.8 mm 4.5 and 4.8 mm Pin Profile Cylindrical Conical Shoulder ɸ 18 mm 18 mm Shoulder type Concave Conical
3.8 Position of the Workpieces during the FSLW Process
Previous studies have shown that the positions of the workpieces relative to the rotation of the tool is an important parameter in FSW. Knowledge of material transport in FSW has seen previous studies placing the material with the lower melting point in the advancing side [82], [122], [153]. However, Xue et al. [23] had previously shown that the relative horizontal position of materials have no effect on the mechanical properties of welds produced using the lap weld configuration.
Hence, in this research work, the aluminium plate was placed on top while the copper was placed below the aluminium plate.
3.9 Process Parameters for FSLW of Al/Cu
As stated earlier, the FSW process parameters play important roles in the quality of the produced welds. Three different rotational speeds (600, 900 and 1200 rpm) were
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Chapter Three Experimental Set-up chosen to represent the high, medium and low speed ranges. Traverse speeds of
50, 150 and 250 mm/min were also chosen to represent the high, medium and low speed ranges while two plunge depths (4.5 and 4.8 mm) were selected for the study.
Dwell time was set at 3 seconds while tool tilt angle of 20 was used. Due to the size requirements of the tests to be carried out, it was necessary to ensure that the length of the welds made was sufficient to accommodate the sizes of all the samples for the different tests. Hence, welds of 120 mm each were produced for each process parameter combination. Table 3.2 summarizes the process parameters chosen in this research work while Table 3.3 shows the final weld matrix and designation of each of the produced welds.
After the welds were produced using the tool with the conical pin profile and cut across the cross section perpendicularly to the FSW direction, physical inspection of the weld cross sections of all the welds revealed wormhole defects in all the cut samples. The sizes of the voids were inspected and it was observed that the weld produced at 900 rpm and 250 mm/min had the smallest void size. Other welds produced at 900 rpm also had voids that were smaller than those seen in the welds produced by the other rotating speeds. It was then hypothesized that using a different tool (conical pin profile) and the same tool, repeating the welds at a higher value of plunge depth may produce better results. As such, the final weld matrix was expanded to include welds produced using the tool with the concave pin profile. The weld matrix is determined in line with the Taguchi Design of Experiment (DOE) method.
Table 3.2: FSW Process Parameters
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Chapter Three Experimental Set-up
Parameter Used Values Material on top Aluminium Material below Copper Tool rotational speed 600, 900, 1200 (rpm) Traverse speed 50, 150, 250 (mm/min) Dwell time (s) 3 Tool tilt angle (o) 1 Plunge depth (mm) 4.5, 4.8 Length of weld (mm) 120
Table 3.3: Final Weld Matrix
Rotational Traverse Speed Plunge Weld Tool Pin Speed (rpm) (mm/min) Depth (mm) Designation Profile 600 50 4.5 A1 Conical 600 150 4.5 A2 Conical 600 250 4.5 A3 Conical 900 50 4.5 B1 Conical 900 150 4.5 B2 Conical 900 250 4.5 B3 Conical 1200 50 4.5 C1 Conical 1200 150 4.5 C2 Conical 1200 250 4.5 C3 Conical 900 50 4.8 1CC1 Conical 900 150 4.8 1CC2 Conical 900 250 4.8 1CC3 Conical 900 50 4.8 1C1 Concave 900 150 4.8 1C2 Concave 900 250 4.8 1C3 Concave
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Chapter Three Experimental Set-up
3.10 Parent Materials
The parent materials consist of 3 mm thick aluminium and copper sheets cut to rectangular sheets of 600 x 100 mm each as shown in Figure 3.6. The aluminium was the 1060 alloy (AA) while the copper was the C11000 commercially available pure copper. The parent materials were characterised along with the produced welds in order to evaluate their chemical composition, microstructure, residual stress values, tensile strength, microhardness values as well as their electrical resistivities.
The results for the characterisations will be presented in Chapter 4 for easier comparison with the produced welds.
Figure 3.6: Parent materials set-up
3.11 Sample Layout for Characterisations
The samples for the characterisations were selected from specific locations to ensure that the quality of the weld in the tested areas are consistent with the other
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Chapter Three Experimental Set-up welds produced. Care was taken not to take any sample close to any of the edges in order to eliminate the use of samples where proper mixing had not taken place. As such, an offset of 11 mm from the weld center is left on both sides of the weld.
Samples for characterisations were taken from between these offsets. The layout of the sample is as shown in Figure 3.7.
Figure 3.7: Layout of the samples used for characterisations
T1, T2 and T3 – Tensile Shear samples
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Chapter Three Experimental Set-up
M – Microstructure, microhardness and XRD sample
E – Electrical Resistivity sample
To maintain the integrity of the weld, a Dynamic Waterjet XD machine by FLOW
International Corporation with a 2 mm nozzle was used to cut the samples. A typical drawing of the program fed into the water-jet machine is shown in Appendix B. A 2 mm tack was left in specific locations of the sample to ensure that the:
i. samples did not fall into the bed of the water jet cutting machine while the
cutting operation was ongoing.
ii. cut parts of the metals did not fly up and damage the nozzle of the water jet
machine.
The samples were then labelled accordingly with a permanent marker before the tack was finally removed in the laboratory using a small hack saw. Once the samples were removed, the sample characterisations were done as described in the following section.
3.12 Characterisation of the Produced Weld
To ascertain the quality of the produced weld, the sample characterisation was done using microstructural, XRD, mechanical and electrical resistivity evaluations. The methods used are described in this section.
3.12.1 Microstructural Evaluation
Microstructural evaluation was carried out on the sample designated M using an
Olympus BX51M optical microscope (OM) for observation of the microstructure and
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Chapter Three Experimental Set-up grain size measurements, and a VEGA3 XMU Scanning Electron Microscope (SEM) by TESCAN ORSAY Holding Company for the chemical analysis of the phases at the weld interface and further observation of the microstructure at higher levels of magnifications. Sample size for the microstructural evaluation was 20 x 5 x 6 mm3.
The sample was first mounted in a polyfast thermoplastic hot mounted resin with the copper on the right using a CitoPress-1 mounting press by Struers Incorporated. The samples were then prepared using standard metallographic procedures. The etching of the aluminium was done using flick’s reagent for 10 seconds while the copper was etched using a freshly prepared solution of Ammonia (70 ml), distilled water (70 ml) and Hydrogen Peroxide 3% (20ml) for 5 seconds. Initially, the microstructure of the welds was not clearly visible. Hence, to ensure a good visibility of the microstructure, the time of etching was increased to 25 seconds for the Al while the volume of the
Hydrogen Peroxide (H2O2) was reduced to 14 ml.
On the OM, a white balance of the microscope was first done before the samples were placed for observation. The images were captured using the Stream Essentials software. Grain size determination was done in line with the standard testing method for determining average grain size according to ASTM E112 – 96 [154]. SEM analysis was done using the Vega SEM Software while the INCA software was used for the Energy Dispersive Spectroscopy. A picture of the OM is presented in Figure
3.8, while images of the SEM, mounting press and grinding and polishing machine, the standard metallographic procedures and composition of reagents used are presented in Appendices C1-C4.
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Chapter Three Experimental Set-up
Figure 3.8: Olympus BX51M optical microscope
3.12.2 Residual Stress Analysis and Phase Identification
X-Ray Diffraction (XRD) analysis was carried out on the sample designated M using a D8 Discover x-ray diffractometer by Bruker Corporation for residual stress analysis.
A copper x-ray tube, monochrometer, 0.8 mm collimeter, video and laser system for positioning and alignment are all present on the primary site. On the secondary site, a 2-D ventec 500 detector was used. The x-ray generator was operated at 40 kV and
40 mA. The sample was mounted on a xyz sample stage, allowing for adjustments along all the 3D axes. The General Area Detector Diffraction System (GADDS)
V4.1.42 software was used for the analysis. As a result of the very high Bragg peaks, the detector was mounted on the negative scale to be able to accommodate the peaks. A detector position at 0.5 mm from the weld interface was chosen to ensure consistency across all samples.
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Chapter Three Experimental Set-up
Measurements were done for 6 different phi, φ, rotations (0o, 180o, 90o, 270o, 45o and 225o). For each of the phi rotations, 8 different psi, ψ, (tilt) angles with a step size of 100 was used while measurements were taken for 240 seconds per frame.
Analysis of the peaks were done after the peak measurements had been taken. The peaks to measure were selected and the Poisson’s ratio and the Young’s modulus analysis option were selected on the GADDS software for the analysis.
Phase identification was initially done using the D8 Advance x-ray diffractometer by
Bruker Corporation in order to observe and identify the presence of intermetallic compounds. However, there were no notable peaks of any form of intermetallic compounds observed. This is further explained in the following chapter under results and discussion. Pictures of the D8 Discover and D8 Advance and the GADDS software during analysis are shown in Appendix C5-C7.
3.12.3 Microhardness Testing
The sample designated M was used for the microhardness tests using an automatic
DuraScan microhardness tester by EMCO-TEST Prüfmaschinen GmbH. The surface of the mounted sample was first prepared using standard metallographic procedures as stated in section 3.12.1 to ensure that the lines of indentations are easily distinguished from scratches on the surface of the sample. Etching of the sample was not done as it was not necessary to view the microstructural grains. The preferred microhardness test employed in this research work is the Vickers microhardness test conducted according to ASTM E-384 [155]. Though ASTM E-384 states 1 kgf to 120 kgf as the recommended load for Vickers hardness tests of metallic materials, a load of 200 gf was applied on the sample for 15 seconds dwell
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Chapter Three Experimental Set-up time based on literature [82] since the test was for the microhardness properties of the metals. The DuraScan internally computes the Vickers microhardness value according to Equation 3.1:
1860 퐹 × 2 푆𝑖푛 ( ) 퐻푉 = 2 ...... 3.1 푑2
Where HV – Vickers hardness
F – applied force in kgf
d – average length of the indentation diagonal in mm
Microhardness measurements were taken at the weld interface and 4 other points on either side of the weld interface, at a distance of 0.5 mm separating each points. The indentation positions were manually chosen to ensure that indentations were not made on weld defects. The diagonals were also manually confirmed to ensure that the edge of the diagonals were accurately selected to avoid errors in the Vickers microhardness calculations. An image of the DuraScan microhardness tester is shown in Appendix C8.
3.12.4 Tensile Strength Measurements
Samples designated T1, T2 and T3 with dimensions 127 x 23 x 6 mm were used to evaluate the tensile strengths of the welds. Since the metals were welded using the lap weld configuration, the tensile shear strength was evaluated using a modified version of the standard test method for apparent shear strength of single-lap-joint adhesively bonded metal specimens by tension loading (metal-to-metal) – ASTM
D1002 [156]. A modified version of the standard, as seen in the literature, was
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Chapter Three Experimental Set-up adopted as there is no specific standard for the tensile shear test of welded metals.
Tensile shear test was done on an Instron 1195 tensile testing machine on an
Instron 5500R Universal Test Frame at an extension rate of 1 mm/min. The tensile- shear specimen with dimensions are shown in Figure 3.9 while the tensile testing machine with loaded sample is shown in Appendix C9.
Figure 3.9: Loaded tensile-shear specimen
To ensure that the applied load is parallel to the welded sheets, supports of 23 mm each were provided at each end of the Cu and Al sheets at the point of clamping.
3.12.5 Electrical Resistivity Measurements
The sample designated E was used for the electrical resistivity determination as shown in Section 2.7.2. Sample size for the sample is 20 x 5 x 6 mm3, cut across the lapping interface of the two metals. A signatone (s-302-4) Four-Point probe meter was used in the determination of the electrical resistance of the sample. The collinear probe spacing of the s-302-4 was 1.6 mm. Circuit diagram and the experimental set-up are presented in Figure 3.10a and Figure 3.10b.
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Chapter Three Experimental Set-up
Figure 3.10a: Circuit diagram of the electrical resistance determination
Figure 3.10b: Experimental set-up of the electrical resistance
determination using the s-302-4
Current was passed into the sample through probe 1, by increasing the voltage, and passed outside of the sample through probe 4. The current flowing into the sample was measured before entering probe 1 using an ammeter. The voltage across the sample was then measured using a voltmeter connected to probes 2 and 3. The electrical resistance of the sample was then determined according to the ASTM
B193-02 [157]. 87 | P a g e
Chapter Three Experimental Set-up
3.13 Summary
The preliminary welds and the information available from the literature provided insights into the choice and the dimensions of the tools used; and the process parameters employed in this research work. The aluminium was placed on top while the copper was placed underneath. Tool rotational speed was varied at 600, 900 and
1200 rpm while the traverse speeds of 50, 150 and 250 mm/min were used. Dwell time was set at 2 seconds, tool tilt angle at 2o, plunge depth was varied between 4.5 and 4.8 mm while welds of 120 mm length were produced.
The machine and sample setup, the process parameters used in this research work as well as the procedures used for characterising the welds have been presented and discussed. In the next chapter, the results of the characterisations of the welds produced and the parent materials will be presented and discussed.
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CHAPTER FOUR
RESULTS AND DISCUSSION
4.1 Introduction
In this chapter, the results of the welds produced and the experiments carried out are presented and discussed. The welds, produced using position control with the processing parameters presented in the matrix as shown in Chapter 3, were visually inspected before being analysed for microstructural evaluation, microhardness profiling, tensile testing, residual stress analysis and electrical resistance determination. Relationships between the obtained results and the processing parameters are identified and subsequently used in arriving at conclusions.
4.2 Interplay of Input and Output Friction Stir Welding (FSW)
Process Parameters
For the two tools considered, the tool rotational speed and the traverse speed play important roles in the qualities of the produced welds [82], [158]. As stated in chapter
3, these, along with the plunge depth, are the only process parameters that were varied in this study. Table 4.1 details the weld designations, tool rotational speed, traverse speed, plunge depth, pitch as well as the heat input for each of the unique input process parameters. Pitch, in FSW, is the ratio of the traverse speed to the rotational speed and, like both input speeds, it is constant for each of the welds. It is also known as the weld pitch or the revolutionary pitch. A maximum pitch of 0.417 mm/rev and a minimum pitch of 0.042 were used in this study. Values for the heat input were calculated based on Equations 2.4 and 2.5 as shown in section 2.6.7.
Chapter Four Results and Discussion
As described in section 2.6.6, four (4) major forces act during a normal FSW operation. These forces are also detailed in Table 4.1 as output parameters during each welding operation. The force and the torque values presented are averages taken from the recorded FSW machine data. Care was taken to only use the values recorded when the welding operation was stable (20 mm to 100 mm) as described by Gemme et al. [68]. Figure 4.1a presents the weld data showing the Fx, Fy and Fz plotted against the weld distance for the sample produced at 1200 rpm, 50 mm/min and 4.5 mm plunge depth using the conical tool while Figure 4.1b presents the feedback torque value for the same sample.
8
6
4
2
0 -20 0 20 40 60 80 100 120 140 Signal Value Signal -2
-4
-6 Distance (mm) X Force Feedback, kN Y Force Feedback, kN Z Force Feedback, kN
Figure 4.1 (a): Fx, Fy and Fz forces during welding at 1200 rpm,
50mm/min and 4.5 mm plunge depth
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Chapter Four Results and Discussion
15
10
5
0 -20 0 20 40 60 80 100 120 140
-5
Spindle Torque (Nm) Torque Spindle -10
-15
-20 Distance (mm)
Figure 4.1 (b): Torque values during welding at 1200 rpm, 50mm/min
and 4.5 mm plunge depth
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Chapter Four Results and Discussion
Table 4.1: Input process parameters and output data
Weld Rotational Traverse Weld Heat Plunge Tool Pin Fx (kN) Fy (kN) Fz (kN) Torque, Designation Speed Speed Pitch Index Depth Profile T (kNm) (rpm) (mm/min) (mm/rev) (mm) A 600 50 0.083 0.72 4.5 Conical 1.52 1.02 3.73 0.18 B 600 150 0.25 0.24 4.5 Conical 2.05 1.28 4.76 9.28 C 600 250 0.417 0.144 4.5 Conical 2.39 1.54 4.85 10.07 D 900 50 0.056 1.62 4.5 Conical 1.12 0.86 3.52 -0.89 E 900 150 0.167 0.54 4.5 Conical 1.42 0.91 4.26 4.08 F 900 250 0.278 0.324 4.5 Conical 2.14 1.18 4.82 5.51 G 1200 50 0.042 2.88 4.5 Conical 1.19 0.46 3.33 -3.18 H 1200 150 0.125 0.96 4.5 Conical 1.47 0.52 3.84 -0.69 I 1200 250 0.208 0.576 4.5 Conical 2.03 0.58 4.45 5.00 1C1 900 50 0.056 1.62 4.8 Concave 2.4 0.45 4.14 19.53 2C1 900 150 0.167 0.54 4.8 Concave 2.78 1.98 4.87 23.67 3C1 900 250 0.278 0.324 4.8 Concave 3.13 2.47 6.79 27.63 1CC1 900 50 0.056 1.62 4.8 Conical 1 0.67 2.94 4.90 2CC1 900 150 0.167 0.54 4.8 Conical 3.11 1.24 3.97 26.86 3CC1 900 250 0.278 0.324 4.8 Conical 3.28 1.25 5.93 32.65
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Chapter Four Results and Discussion
From the weld data, it is seen that as the vertical force (Fz), that is required to maintain the vertical position of the pin in the workpieces, increases, both the horizontal force (Fx), that is required to traverse the workpieces at the same depth, and the torque (T), that is necessary to maintain the same rotational speed, both increase. This is in agreement with Vilaça et al. [159] where it was observed that the total mechanical power that the tool delivered into the workpieces was increasing as the vertical force was increased.
It is also observed that the total mechanical power delivered (based on the vertical force, horizontal force and the torque) by the tool increased with an increase in the tool traverse speed. This is in tandem with the data recorded by Akinlabi [82] where the machine data for 3 different shoulder diameters, tool rotational speed and traverse speed confirmed that an increase in the traverse speed exhibited a corresponding increase in the horizontal force, Fx, vertical force, Fz, and torque, T.
4.3 Visual Inspection and Macro Appearances of the Produced
Welds
4.3.1 Visual inspection of the produced welds
On the surface, most of the produced welds had good physical appearances and showed no surface defect. Figure 4.2 shows a collage of some of the surface appearance of some of the welded samples. All other surface appearances and a typical cut weld are presented in Appendix D0.
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Chapter Four Results and Discussion
Figure 4.2: Surfaces of welded samples produced at: (a) 600 rpm and
150 mm/min; (b) 600 rpm and 250 mm/min; (c) 900 rpm and 50
mm/min; (d) 900 rpm and 250 mm/min; (e) 1200 rpm and 50 mm/min;
(f) 1200 rpm and 150 mm/min
After cutting the produced samples across the cross section of the welds, each of the samples for characterisations were physically observed by visual inspection. It was discovered that all of the produced welds had voids, otherwise known as wormhole defects, which ran across the entire length of the welds. It was also observed that the sizes of the defects were different for each of the samples. The relationship between the process parameters and the defect sizes will be evaluated in sections
4.3.2.2 and 4.3.2.3. After mounting the samples and with observations under the
Optical Microscope, the samples were also further checked for other microscopic defects. Table 4.2 details the types of defects observed for each of the produced welds.
Table 4.2: Weld defects observed during visual inspection of the produced welds
Weld Defects Designation
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A Voids
B Voids, Hook
C Voids, Hook
D Voids
E Voids, Hook
F Voids, Hook
G Voids, Hook
H Voids
I Voids, Hook, Microcracks
1C1 Voids
2C1 Voids, Hook
3C1 Voids
1CC1 Voids, Hook
2CC1 Voids, Hook
3CC1 Voids, Hook As shown in Table 4.2, all of the welds had voids running through them. Hooking defect was also seen in all of the welds. The hooks were found at the advancing side while the retreating side showed signs of kissing bonds. This is in tandem with the observations of Yazdanian and Chen [160] who observed that hooking was a common defect found on the advancing sides of FS Lap welds in their observation of
FSLW of two aluminium sheets. The same trend was observed by Wang et al. [161] in their investigation of the effect of pin length on the hook size and joint properties in
FSLW of aluminium. The typical schematic diagram of this macrostructural defect and weld 3CC1, produced at 900 rpm, 250 mm/min and plunge depth of 4.8 mm,
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Chapter Four Results and Discussion showing the defects found in the produced welds are shown in Figure 4.3. The typical kissing bond and hook defect has earlier been shown in Figure 2.11e.
Figure 4.3: Weld produced at 900 rpm, 250 mm/min and 4.8 mm
plunge depth showing the voids, the hooking and the kissing bond
defects
As shown in Figure 4.3, the faying surface on the advancing side is seen to fold upwards along the boundaries of the WZ while the faying surface on the retreating side initially lifts up before penetrating into the WZ. All the produced welds exhibited this hooking and the kissing bond behaviour at different stages as shown in Figure
4.3. It has been suggested that the level of kissing bond and the hooking will depend on the amount of heat transferred into the base metals as the welding operation is being carried out [160]. Even though there was no definite trend observed in this study relating the heat input with the kissing bond and the hooking behaviour, this study observes that the level of hooking and the kissing bond was different for each of the different samples observed.
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Chapter Four Results and Discussion
Aside from the general defects observed, the weld produced at 1200 rpm and 250 mm/min at the plunge depth of 4.5 mm (sample I) also showed cracks when observed under the microscope. It should be noted that this sample is of interest as it was very fragile when held and showed signs of very little bonding.
4.3.2 Effect of input process parameters on the resulting macrostructure
4.3.2.1 Relationship between the material flow and defects
The flow of materials in FSW is a fairly complex process that depends on the tool pin profile, the welding parameters, the materials to be welded as well as the welding configuration. While material flow in FS butt welding has received lots of attention and propositions, the FSW community is yet to agree on the material flow due to the complexities involved. Even more interesting is FS lap welding configuration.
Research has however shown that in lap welds, the material below is transported upwards at the retreating side while the material on top is pushed downwards at the advancing side [9]. This typical flow behaviour was seen in all the welds produced as shown in Figure 4.4.
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Figure 4.4: Weld produced at 900 rpm, 50 mm/min and 4.8 mm plunge
depth showing the flow of aluminium and copper
As shown in Figure 4.4, a large part of the copper is seen to rise from the bottom of the weld and flow upwards while the aluminium is also seen to have been pushed downwards into the groove left by the displaced copper. This behaviour was observed by Guerra et al. [162] where they concluded that the vertical upward movement occurred in the rotational zone as a result of the action of the tool pin.
They suggested that the vertical transport of materials followed a helical trajectory which was due to the rotation of the pin, vertical flow, as well as, the translational motion of the pin.
However, unlike the FSW of dissimilar materials in the butt configuration and the
FSLW of similar metals where there are visible mixing of the grains of both base metals, only minor visible mixing of the grains of the aluminium and the copper was observed. Despite the upward, vertical flow of the copper, the grains of the copper and aluminium are visibly distinct from each other. This may be as a result of the
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Chapter Four Results and Discussion wettability of both base metals at the plasticizing temperatures. While the material underneath, copper, has a melting temperature of 1085oC, the aluminium, on top, has a much lower melting temperature of 660oC. Hence, before the copper heats up sufficiently to plasticize, the aluminium would be close to the melting temperature even though it is yet to reach such a temperature when the welding takes place as suggested by the FSW process. As such, wettability, the ability of a liquid to adhere to the surface of a solid, of the plasticized aluminium with copper is expected to play a big role in the intermixing of the grains of both metals.
As seen from Figure 4.4, it was observed that the grains of both the aluminium and copper showed a great affinity for the grains of their individual parent materials. This same trend was observed even in the welding zone where the aluminium and the copper particles are not seen to mix. All through the produced welds, there was always a distinct interfacial boundary between the aluminium and the copper particles. The result of these are the voids that appear in the spaces left by the copper as there is no sufficient flow of the aluminium to fill these voids. Bisadi et al.
[19] also observed the production of voids in their observation of some of the FS lap welds of aluminium and copper they produced in their study. These reported that the voids resulted from the shrinkage of the aluminium, due to quenching, after mixing with the copper particles effectively during the welding operation. However, in this present study, this was not the case as there was no effective mixing of the copper and the aluminium particles.
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4.3.2.2 Relationship between the defect size and mechanical force
To optimize processing parameters in the future, it is necessary to understand the relationship between the defects that occur in the produced welds and the processing parameters. This section looks at the areas of the voids in the produced welds and correlates them with their processing parameters. The total surface area of the voids were determined from the cross section of the mounted samples using the closed polygon measuring tool of the Stream Essentials software of the OM. The areas of all the individual voids in each of the welds were measured as shown in
Figure 4.5. These were then exported and summed to determine the total area of the voids in each of the produced welds.
Figure 4.5: Determination of the total void area for sample produced at
900 rpm, 50 mm/min and 4.8 mm plunge depth
The mechanical force required for a weld produced at 4.5 mm plunge depth (while keeping all other parameters constant) will be lower than that required at 4.8 mm plunge depth. It has also been established in this study, that the total mechanical
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Chapter Four Results and Discussion force is dependent on the vertical force, Fz, of the tool. As such, Figure 4.6 (a) shows a graph of the welds produced at the plunge depth of 4.5 mm with the areas of the voids produced versus the traverse speed, Figure 4.6 (b) shows a graph of the welds produced at plunge depth of 4.8 mm showing the defect area versus the vertical force (Fz) of the tool while Figure 4.7 shows a collage of the flow of copper for welds produced at 4.5 mm plunge depth and 900 rpm. A Table showing the areas of the voids is shown in Appendix D1.
2.5
2.0
1.5 600 rpm 1.0 900 rpm
Area of(mm²) Void 1200 rpm 0.5
0.0 50 150 250 Traverse speed (mm/min)
Figure 4.6 (a): Area of void vs traverse speed for all welds produced at
4.5 mm plunge depth
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Chapter Four Results and Discussion
0.8
0.7
0.6
0.5
0.4 Concave tool 0.3 Conical tool
Area of Void (mm²) 0.2
0.1
0.0 0 2 4 6 8 Vertical Force, Fz (kN)
Figure 4.6 (b): Area of void vs vertical force, Fz, for all welds produced
at 4.8 mm plunge depth
Figure 4.7: Different levels of flow of copper at (a) 50 mm/min (b) 150
mm/min and (c) 250 mm/min
From Figure 4.6a, it can be seen that the voids produced at a traverse speed of 50 mm/min increased in size at 150 mm/min before again reducing at 250 mm/min. With observation of the macrostructures of the welds, it is observed that the aluminium does not flow into the copper at 50 mm/min and 150 mm/min for all the welds produced at 4.5 mm plunge depth. Also, the flow of the copper is seen to increase
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Chapter Four Results and Discussion with an increase in the traverse speed as shown in Figure 4.7. This is attributed to the insufficient stirring of the interface and the thermal softening of copper that is lower than that of the aluminium sheet as observed by Bisadi et al. [19].
It is observed from Figure 4.6 (b) that for the welds produced at 4.8 mm plunge depth, a vertical force of about 4 kN seemed to produce the welds with the least amount of defects for all the welds produced. While one weld was produced with a conical tool at 900 rpm and 150 mm/min, the other was produced at 900 rpm and 50 mm/min using the concave tool. Hence, the mechanical force exerted on the metals by the tool depends on the profile of the tool pin.
4.3.2.3 Relationship between the defect size and plunge depth
The relationship between the weld quality and the plunge depth has not been the subject of intense research in FSW. A lot of the previous studies focused on the use of a single plunge depth in their studies. Hence, not much is known about the relationship between the plunge depth and the weld quality is little known. In this research, the plunge depth was varied and the effect it has on the quality of the weld is presented in this section. Figure 4.8 shows a chart of the average void sizes for the two plunge depths considered in this study.
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Chapter Four Results and Discussion
2.0 ) ² 1.5
1.0
0.5
0.0 4.5 4.8 Average Average Area of Voids (mm Plunge Depth (mm)
Figure 4.8: Chart showing the average void sizes for the two plunge
depths
For the two plunge depths used in this study, the welds produced at 4.8 mm showed voids that are much smaller in sizes to the ones seen in welds produced at 4.5 mm.
As shown in Figure 4.8, the average void area of the welds made at the plunge depth of 4.5 mm is 1.58 mm2, 1 mm2 more than the average void areas of the welds produced at 4.8 mm plunge depth (0.58 mm2). The greater plunge depth corresponds to a higher mechanical force as the average vertical force, Fz, horizontal force, Fx, and torque, T, show significantly higher values than the equivalent forces at 4.5 mm.
Close observation of the macrographs for each set of welds showed that the material flow of both copper and aluminium fared a lot better in the welds produced at 4.8 mm than for those produced at 4.5 mm. It was observed that despite the tool pin plunging more into the copper at 4.8 mm, particles of the aluminium are seen to flow into the voids created by the tool pin in an attempt to cover them up and form quality welds.
Hence, a higher plunge depth, which resulted in a higher mechanical force and a higher torque (according to the machine data) resulted in better material flow for both 104 | P a g e
Chapter Four Results and Discussion metals being welded. This trend will not always hold true as this pattern is envisaged to peak at some point. This should be a source for much further study in the future leading to the optimization of other processing parameters with the 4.8 mm plunge depth.
4.4 Microstructural Analysis
Microstructural observations of the produced welds were carried out in order to gain a better understanding into the grain structures and the properties of the welds at the microstructural level. These were done using the Optical Microscope and the
Scanning Electron Microscope as explained in section 3.12.1. The observations made are presented in the following sections.
4.4.1 FSW Microstructural Zones
Previous studies have shown that there are four (4) distinct microstructural zones in a typical FSW weld viz: the Weld Zone, WZ (otherwise known as the Nugget Zone), the Thermomechanically Affected Zone, TMAZ, the Heat Affected Zone, HAZ, and the Base Metal, BM [9]. With microstructural observation of the samples, all the four zones were found to be present in the produced welds. Figures 4.9 a-i shows some of the microstructural images used for the microstructural analysis of the produced welds.
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Chapter Four Results and Discussion
a b
(a) Cu PM (b) Al PM
c d
(c) TMAZ and HAZ section on a weld (d) the HAZ
f g
(e) TMAZ (g) WZ showing flow of Cu
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Chapter Four Results and Discussion
h
(h) Flow of Al
i
(i) WZ of both Al and Cu
Figure 4.9: Microstructural images of the various weld zones
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Chapter Four Results and Discussion
The Cu PM showed the equiaxed grain structure with distinct grain boundaries as seen in Figure 4.9a. The FSW process did not distinctly alter this grain structure as microstructural evaluations reveal equiaxed grain structures for the copper in the other microstructural zones. However, the FSW process caused a reduction in the grain sizes observed in the different zones.
In the HAZ, adjacent to the BM, alterations of the grains were observed with grain thinning and elongation. The grains maintained an equiaxed structure despite the grain coarsening that occurred at this zone. This is due to the effect of the heat input into the weld that ensures the plasticization of the base metal to enhance stirring and the subsequent bonding. Observations of the HAZ for the different welds revealed different widths of the zone for the different welds at the copper side. It was observed that an increase in the traverse speed led to a decrease in the width of the HAZ zone with some welds showing very little widths of the HAZ. This is due to the reduction in the heat input as the traverse speed is increased and consistent with the earlier calculations of the heat index as shown in Table 4.1.
Another observation made at the HAZ was a decrease in the grain size at this zone compared to the average grain size of the parent copper. While Miličić et al. [163] stated that the copper grains in the HAZ were larger in their study of FSW of copper alloys, this study observed a reduction in the average grain sizes of the copper in
HAZ. However, the grains in this zone were still observed to be the largest sizes when compared to the grains of the TMAZ and WZ.
It was observed that even though all the microstructural zones were present in the
AS and the RS, the zones in the AS showed a very sharp gradient due to the
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Chapter Four Results and Discussion hooking phenomenon. Hence, the widths of all the microstructural zones were not as big as those at the RS of the welds. This makes easy distinction of the different zones at the AS difficult, compared to the RS.
Both the TMAZ and the WZ showed much refined grains than the HAZ even though the grain structures still remained equiaxed. The grain sizes here were observed to be a lot smaller than the average grain sizes of the copper at both the HAZ and BM.
This is due to the dynamic recrystallization of the grains that occurs at the TMAZ and
WZ during the plasticization and the mixing due to the tool rotation. However, it was observed that the grains in the WZ were smaller than those found in the TMAZ.
The grains of the TMAZ were observed to gradually increase in size further away from the WZ with an increase in the distance from the WZ resulting in less plastic deformation further from the WZ. Proximity to the WZ results in better plasticization, higher grain refinement and recrystallization, hence, the increase in grain sizes further from the WZ. The grains in the WZ are the most refined in all the grains observed for the different microstructural zones.
The aluminium grains showed signs of little or no deformation in all the microstructural zones of the produced welds. This is due to the nature of the aluminium alloy used. The aluminium alloy used is expected to show little deformation due to the age hardening and manufacturing procedures. Hence, the heat input during the welding operation has very little effect on the grains of the aluminium as explained by Mishra et al. [149].
Furthermore, there is a distinct interfacial region between the copper and the aluminium observed which has been explained to be due to the wettability of the
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Chapter Four Results and Discussion aluminium and copper alloys. The interfacial layer is also due to the difference in the thermal conductivity and diffusivity of both alloys, as well as the melting points of both materials, preventing proper mixing of the grains of both materials.
However, the grains of each alloys were observed to go through thorough mixing with themselves as shown in Figures 4.9 g and h. There is a good material flow within the grains of the aluminium and copper alloys. Even though the grains do not show the typical onion ring structure of FSW [16], the lines of material flow are still visible and conspicuous in both the copper and the aluminium.
The presence of microcracks were also observed to be present in the aluminium alloy in some of the welds as shown in Figure 4.10. The cracks were observed to begin at the point where the hook of the copper ends. These were particularly found in the samples where the hook was only seen to begin and end abruptly without adequate flow. The cracks then propagated along the line of flow of the aluminium particles in the RS of the welds. Microstructural images showed that the lines of microcrack usually followed the direction of flow of the aluminium particles and acts as the boundary between the aluminium particles that were involved in the material flow and those that were not involved in the material flow.
Figure 4.10: The presence of microcracks in the aluminium 110 | P a g e
Chapter Four Results and Discussion
The flow of materials in FSW is a complex phenomenon and a source of constant research [16], [164]. Certain observations can be made from the microstructural images from the produced welds. Figures 4.11 a-b show a schematic of the material flow of the aluminium and the copper particles and a microstructural image of one of the produced welds.
FSW Tool Welding Direction Downward force from the tool shoulder FS Front Normal reaction due to the tool shoulder FN
Figure 4.11: (a) Schematic of the material flow due to the influence of
the tool
Figure 4.11: (b) Microstructural image of the weld produced at 900
rpm, 150 mm/min and 4.8 mm plunge depth
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Chapter Four Results and Discussion
As seen in Figure 4.11a, the tool shoulder exerts a force, FS, on the plasticized materials during rotation. This causes a downward, spiral motion of the aluminium particles at the back of the weld. However, the downward motion is limited to the aluminium particles directly under the influence of the tool shoulder. The aluminium particles that have been traversed does not experience this downward motion.
Hence, there is a relative displacement of the aluminium particles resulting in the crack between the aluminium particles that are not under the influence of the tool and those that are influenced by the tool shoulder and pin. The influence of this is also felt by the copper particles as there is a backward, upward flow of the copper particles resulting from the shear effect of the aluminium particles that are being pushed downwards into the copper and a normal reaction, FN, to FS. This results in the hooking motion normally expected in FSLW [161] as seen in Figure 4.11b.
On the front however, the effect of the tool shoulder is not felt in terms of material flow of the aluminium particles as much as at the back due to the tool tilt. Flow of the materials were observed to be more as a result of the effect of the tool pin, resulting in an upward, spiral flow of the copper particles. This upward motion of the copper results in the thinning motion expected in a typical FSLW [161] as observed in this study.
4.4.2 Scanning Electron Microscopy
The Energy Dispersive Spectroscopy function (EDS) of the Scanning Electron
Microscope (SEM) was used to analyse different regions of the welded samples in order to evaluate the chemical compositions of the analysed regions. The chemical composition of the welded regions will suggest the presence, or otherwise, of
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Chapter Four Results and Discussion intermetallic compounds (IMCs) within the produced welds. Each sample was analysed and the results are presented in Appendix D2. Figure 4.12 a – d shows the micrographs of the SZ at the joint interfaces of some of the samples analysed.
Figure 4.12: Flow regions of samples E, G, 1CC1 and 3C1 produced at
a) 900 rpm, 150 mm/min and 4.5 mm b) 1200 rpm, 50 mm/min and 4.5
mm c) 900 rpm, 50 mm/min 4.8 mm and conical tool and d) 900 rpm,
50 mm/min, 4.8 mm and a concave tool respectively
The limited material flow, as observed in Figures 4.12 a – c, resulted in no discernible presence of intermetallics detected in the regions analysed. Depending on the region, the EDS results showed a very high percentage of either copper or of
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Chapter Four Results and Discussion aluminium, leaving only a trace percentage of the other material as shown in Table
4.3.
Table 4.3: Atomic percentage of Aluminium and Copper in the SZ of samples E, G,
1CC1 and 3C1
Sample Al, Cu, Designation weight% weight%
E 6.09 93.91
G 7.72 92.28
1CC1 2.17 97.83
3C1 0.44 99.56
Table 4.3 and Figure 4.12 indicate that if there any intermetallic compounds were present, they were only present in very small concentrations. This explains the results observed from the Vickers hardness tests where the maximum Vickers hardness value obtained was HV 176, a much lower value to that obtained in other studies where the presence of intermetallic compounds were observed in the FSW of
Aluminium and Copper [82].
The weld produced at 900 rpm, plunge depth of 4.8 mm, traverse speed of 50 mm/min and the conical tool pin demonstrated the highest possibility of the presence of intermetallic compounds as shown in Figure 4.13.
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Chapter Four Results and Discussion
Figure 4.13: EDS results of sample made at 900 rpm, 50 mm/min and
4.8 mm plunge depth
The presence of intermetallic compound was suggested in the weld made at 900 rpm, 50 mm/min and 4.8 mm plunge depth due to a 41.46 % Aluminium and 58.54 %
Copper in the EDS results. As shown in Appendix D3, these atomic percentages correspond to the Al2Cu intermetallic compound. Xue et al. [23], Abdollah-Zadeh
[17], Saeid et al. [22], Zhang et al. [24] and Galvao et al. [165] all observed the presence of Al2Cu as one of the intermetallic compounds found in their FSLW of
Aluminium and Copper.
Phase analysis using the X-Ray diffraction did not however confirm the presence of this phase. This is attributed to the low peaks and minimal presence of the 115 | P a g e
Chapter Four Results and Discussion intermetallic compounds. This also explains why other intermetallic compounds observed in other studies were not observed in this study. The formation of intermetallic compounds are known to be thermally activated [17], hence the heat inputs in the produced welds are not high enough to ensure their formation in high quantities in this study.
4.5 Mechanical Properties
4.5.1 Tensile Test Results
Table 4.4 reports the shear loads for all the samples tested. The tensile lap shear test was conducted on each of the samples as shown in section 3.12.4. The average shear load is computed and also included in Table 4.4. The load versus extension graph of a typical sample produced with the conical tool at 900 rpm, 50 mm/min and
4.8 mm plunge is presented in Figure 4.14a. The remaining graphs are presented in
Appendix D4. Only one sample was tested for the weld produced at 1200 rpm and
250 mm/min (weld designation I) as the other two (2) samples fell inside the waterjet cutting machine while cutting.
Table 4.4: Maximum load borne by the produced welds before failure
Shear Load (N) Average Shear Weld Load (N) T1 T2 T3
A 714.00 453.98 2 032.59 1 066.86
B 316.10 1 004.91 1 539.97 953.66
C 1 571.69 1 602.41 1 540.76 1 571.62
D 806.18 1 788.34 2 125.87 1 573.46
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Chapter Four Results and Discussion
E 528.78 481.29 1 099.96 703.34
F 656.07 717.11 631.58 668.25
G 2 041.72 3 036.42 2 529.97 2 536.04
H 1 205.45 1 421.32 1 223.77 1 283.51
I 862.90 862.90
1C1 3 948.64 4 068.02 4 208.45 4 075.04
2C1 3 742.94 3 877.75 3 810.73 3 810.47
3C1 2 016.53 2 107.39 2 148.44 2 090.79
1CC1 4 249.59 3 700.46 3 407.16 3 785.74
2CC1 2 715.39 4 563.06 4 146.42 3 808.29
3CC1 3 289.83 3 310.72 4 421.42 3 673.99
4500 4000 3500 3000 2500 2000
Shear Load (N) Shear Load 1500 1000 500 0 0 0.5 1 1.5 2 2.5 3 Extension (mm)
Figure 4.14 (a): Shear load versus extension of the sample welded
with the conical tool at 900 rpm, 50 mm/min and plunge depth of 4.8
mm 117 | P a g e
Chapter Four Results and Discussion
Observations of the tensile test results showed the samples produced at plunge depth of 4.8 mm to have better tensile resilience than the samples welded at 4.5 mm plunge depth. While the highest tensile shear load borne at 4.5 mm plunge depth was 2.5 kN, the samples produced at 4.8 mm plunge depth sheared at an average tensile shear load of 3.5 kN. Figure 4.14b shows the average shear loads of all the samples tested.
4 500
4 000
3 500
3 000 600, 4.5 mm 2 500 900, 4.5 mm 2 000 1200, 4.5 mm
Shear Load(N) 1 500 900 C, 4.8mm
1 000 900 CC, 4.8mm
500
- 50 150 250 Traverse Speed (mm/min)
Figure 4.14 (b): Average tensile shear loads of all the samples
It is observed from Figure 4.14b that all the samples welded at 4.5 mm had low tensile shear loads compared to the welds that were made at 4.8 mm plunge depth.
This is attributed to the material flow of the samples made at 4.8 mm plunge depth.
The better flow of the aluminium in the spaces left by and around the hooks that the copper makes provides a greater grip for the produced weld and prevents the aluminium and copper from shearing off each other. This ensures that a higher load is applied before the samples are sheared.
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Chapter Four Results and Discussion
It was initially hypothesized that the sample F would require a high tensile shear load. However, the actual testing showed this sample to shear under a very small load. Hence, it is proposed that the tensile shear ability of the produced welds is not a function of the void area or metallurgical bonding at the two faying surfaces.
Rather, it depends on the length of the hook from the material that is placed underneath and the bonding between this and the material on top.
Figure 4.14b also revealed a general trend for the tensile shear load. It is observed that the tensile shear load reduced with increases in the traverse speeds. This same trend was observed by Akinlabi [82] where it was reported that the Ultimate Tensile
Strength of the FSW of Aluminium and Copper decreased with increases in the feed rates. Even though this trend is more pronounced at some rotating speeds than others, a change in the plunge depth did not change the observed trend as both plunge depths showed the tensile shear load to reduce with an increase in the traverse speed.
It is also observed from Figure 4.14a that all the results from the tensile shear test showed ductile behaviours for the produced welds. However, while Xue et al. [23] observed that the lap welds of aluminium and copper they produced fractured with the aluminium at the HAZ, the results observed in this study produced welds that did not fracture at either the aluminium or the copper sides. Rather, the aluminium and copper both sheared off each other. Therefore, it is expected that the behaviour of the tensile shear test will exhibit ductile behaviour.
It is also interesting that while previous studies reported fracture loads that were less than 2.700 kN [17], [22], [23], this present study observed a maximum shear load of
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Chapter Four Results and Discussion
4.563 kN for the weld produced at 900 rpm, 50 mm/min and plunge depth of 4.8 mm.
It is also observed that while the welds produced at 4.5 mm plunge depth agree with the tensile results of previous studies, the average shear load of the samples produced at 4.8 mm in this study was 3.541 kN. This is attributed to the effect of the depth of the hooks produced at 4.8 mm that prevents both materials from easily shearing off each other at low shear loads, hence ensuring proper bonding until sufficient shear load was applied.
4.5.2 Microhardness Analysis
The microhardness values of the produced weld was taken across the line of welding at 0.5 mm intervals as shown in Figure 4.15. Vickers microhardness (HV) profiles were taken above and below the line of welding. The average Vickers microhardness of the parent materials were also taken at different locations on the parent materials.
While copper had an average value of HV 91.8, the aluminium had an average value of HV 37.7. Some of the results of the Vickers microhardness tests are presented in
Figures 4.16 (a) and (b). The entire microhardness profiles obtained are presented in
Appendix D5.
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Chapter Four Results and Discussion
Figure 4.15: Sample locations of microhardness profiling
140
120
100
80 G 60 H 40 I
Viickers microhardness (HV) 20
0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 Distance from weld center (mm)
Figure 4.16 (a): Vickers microhardness values of the welds made at
1200 rpm and plunge depth of 4.8 mm
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200 180 160 140 120 100 80 60 40 Vickers microhardness(HV) 20 0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 Distance from weld center (mm)
Figure 4.16 (b): Vickers microhardness results for sample produced at
600 rpm, 50 mm/min and plunge depth of 4.5 mm
The results from the Vickers microhardness profiling showed a common trend for most of the produced welds as shown in Figure 4.16a. Close to the edge of the
Copper parent material, the Vickers microhardness values was close to that of the original parent material. This indicated that the effect of the heat input into the welded metals did not have any significant effect on the parent material side of the weld. No specific trend was however observed for the other parts of the weld on the
Copper side as the results varied for the different processing parameters.
At the weld centre, it is also observed that there was a variety in the results, with some producing a Vickers microhardness value higher than that of the original copper. This is attributed to the grain refinement that occurs at the WZ according to the Hall-Petch relation. HV values of about HV 57 at the weld centre for sample 3C1 suggest a thorough mixing of the aluminium and copper at the centre, hence the reduction in the HV value of the copper and higher HV value than the aluminium.
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Chapter Four Results and Discussion
The high HV value observed in the sample 1C1 at the HAZ of the aluminium is attributed to copper particles that flowed into the aluminium.
At the aluminium section of the weld, it was observed that there is no significant increase or decrease in the obtained HV values. This is attributed to the fact that the aluminium alloy used in this study (1060) cannot be strengthened by heat treatment and therefore, not likely to undergo any further grain refinement due to the heat input during the welding process. This was well explained by Nandan et al. [12] in their literature investigation of the recent advances in FSW.
Figure 4.16 (b) shows the sample welded at 4.5 mm plunge depth, 600 rpm and 50 mm/min with a slightly high microhardness value of HV 176. This is thought to be as a result of the presence of intermetallic particles and will be further examined using the EDS analysis. While the HV at HAZ close to both parent materials have values that are similar to those of the parent materials, the values at the TMAZ and WZ are higher than those of the parent materials. This is due to the grain refinement of the aluminium and the copper resulting in grain boundary strengthening in line with the
Hall-Petch relation as observed by Morris [166]. The tensile profiling data suggests that there was no sufficient heat input to favour the formation of intermetallic compounds except for the sample shown in Figure 4.16b where a higher HV value suggests the presence of intermetallics. This will be further investigated in section
4.6.
4.6 Electrical Resistivity measurements
To ensure good (low) electrical resistivity values, the areas in contact play crucial roles as more current carrying electrons will be able to flow freely across the welded 123 | P a g e
Chapter Four Results and Discussion surfaces in a bigger contact area than a smaller one. The electrical resistivity measurements of the welded samples were taken as described in sections 2.6.2 and
3.12.5 while the results are presented in Table 4.5. Figure 4.17 compares the electrical resistivities and heat indices of the produced welds.
Table 4.5: Electrical resistivities of the produced welds
Percentage change in ρ Weld Resistivity, ρ compared to the average for Designation (nΩm) parent materials
Cu 14.37
Al 11.17
Average ρ 12.77
A 48.88 383
B 44.12 345
C 29.08 228
D 45.72 358
E 45.26 354
F* 18.67 146
G* 43.15 338
H* 49.85 390
I 40.76 319
1C1* 19.02 149
2C1* 22.55 177
3C1* 39.95 313
1CC1* 31.78 249
2CC1* 21.78 171
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Chapter Four Results and Discussion
3CC1* 22.21 174
60
50 (nΩm)
ρ 40 600, 4.5 mm 30 900, 4.5 mm 1200, 4.5 mm 20 900 C, 4.8 mm 10 900 CC, 4.8 mm Electrical Resistivity, Electrical Resistivity,
0 0 1 2 3 Heat Index, HI
Figure 4.17: Electrical resistivity versus Heat Index of the produced
welds
While the presence of intermetallics is one of the reasons for an increase in electrical resistivity [167], the massive percentage increase in the electrical resistivities of the welded samples is easily attributable to the voids formed since there is no significant presence of intermetallics observed in the produced welds. It is observed that the resistivity increased as the total surface areas of the voids increased. This is due to the reduction in the total surface area through which the current carrying electrons are able to flow through. Since the voids have reduced this surface area, there will be less current carrying electrons from one point to the other. This reduces the ability of the formed weld to conduct electricity.
The general trend observed was an increase in the electrical resistivities of the produced welds as more heat was generated during the welding process as seen in 125 | P a g e
Chapter Four Results and Discussion
Figure 4.17. It is suggested that the electrical resistivity increases with an increase in the heat generated during welding. However, this remains to be confirmed in welds that do not contain voids and have a close total contact surface area. The only exceptions were the welds produced at 900 rpm, and plunge depth of 4.8 mm which saw a decrease in the resistivities as the heat input increased.
Since electrical resistivity, ρ, of a material is inversely proportional to the electrical conductivity, σ, of the same material, (as shown in Equation 2.7), the welded samples are expected to have poor values of electrical conductivity.
Hence, the results suggest that the produced welds are not readily applicable for electrical applications. However, considering that the electrical resistivity data suggests that a greater plunge depth corresponds to better electrical resistivity values resulting from the contact surfaces of both metals, further studies are suggested in order to determine the effects of higher plunge depths on the electrical resistivities of both metals.
4.7 X-Ray Diffraction Analysis for Residual Stress Determination
To evaluate how the welding process affected the residual stress distribution of the original materials after welding, the X-Ray diffractometer was employed for the residual stress analysis as explained in section 3.12.2 using the sin2ψ method.
Studies have shown that transverse stresses (normal to the welding direction) are not directly affected by the rotational speed [168]. In this study, since they produced the welds with the minimal voids, only the samples produced at 4.8 mm were analysed for residual stress.
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Chapter Four Results and Discussion
The residual stresses were measured at two points: (i) on the unaffected base copper after the HAZ and (ii) on the copper side of the weld just after the weld interface. The results are presented in Table 4.6 and Figures 4.18a and b. The results of the residual stresses are shown in Appendix D6.
Table 4.6: The traverse and longitudinal stresses on the copper side of the weld
interface
Traverse Stress, Longitudinal
σ1 Stress, σ2
Average Cu -87.2 -107
1C1 -59.9 -85.5
2C1 -56.6 -83.1
3C1 -121.6 -98
1CC1 -60.8 -73.6
2CC1 -58.4 -91.2
3CC1 -38.6 -45.2
Avg 1C1 2C1 3C1 1CC1 2CC1 3CC1 0
-20
-40
-60 Stress -80
-100
-120
-140
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Chapter Four Results and Discussion
Figure 4.18 (a): Traverse stress of the produced welds
Avg 1C1 2C1 3C1 1CC1 2CC1 3CC1 0
-20
-40
-60 Stress -80
-100
-120
Figure 4.18 (b): Longitudinal stress of the produced welds
The following are observed from the residual stress results:
First, while previous studies have observed the traverse stresses to be compressive and longitudinal stresses (parallel to the welding direction) to be tensile [169], this present study consistently observed both traverse and longitudinal stresses to be compressive. Second, the longitudinal stresses are generally higher than the traverse stresses. This is in agreement with the study of Donne et al. [170] who observed the longitudinal stresses to be higher than their traverse counterparts notwithstanding the pin diameter, traverse speed nor tool rotational speed. Third, while the traverse stress seem to decrease with an increase in the traverse speed, the behaviour of the longitudinal stress cannot be immediately ascertained. This is at variance with the study of Peel et al. [168] who observed an increase in the traverse stress with an increase in the traverse speed. Fourth, it is generally observed that the residual stresses were lower than the average residual stress of the parent 128 | P a g e
Chapter Four Results and Discussion material, a trend observed by different previous studies [171], [172]. This is attributed to the compressive stresses originally present in the original base metal. The clamping effect and the stirring action of the FSW tool induced tensile stresses into the base metals, hence relieving some of the compressive stresses [172].
4.8 Summary
Friction Stir Lap Welds of Aluminium and Copper have been successfully made using different welding configurations, visually examined and characterised for microstructure, microhardness, tensile, and electrical properties of the produced welds. The plunge depth is seen to have a significant effect on the quality of the produced welds. Tensile shear test results showed a ductile behaviour with the weld bearing a relatively high tensile shear load before shearing. Microhardness profiling suggested the presence of little or no intermetallic structure. The electrical resistivity tests showed a dependence of the defect area on the resistivity of the produced weld suggesting that a defect free weld will have a very good electrical conductivity properties. Microstructural evaluation revealed refined grains for the copper while showing a better material flow for the welds made at a higher plunge depth. X Ray
Diffraction analysis revealed a reduction in the residual stress in the produced welds while confirming the absence of the formation of intermetallic compounds in the produced welds.
The process window evaluated in this research work will require further research in order to produce better quality welds and hence cannot be recommended as it is.
Also, the two different tool geometries used in this study cannot be recommended yet and require further studies in order to study their effects in greater details. Other
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Chapter Four Results and Discussion processing parameters will need to be put into consideration in order to optimize the processing parameters suitable for the lap welding of aluminium and copper using
Friction Stir Welding. General conclusions will be made in the next chapter as well as suggestions for future work based on this present research work.
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CHAPTER FIVE
CONCLUSIONS AND RECOMMENDATIONS
5.1 Introduction
The objective of this study was to produce Friction Stir Lap welds of 1060 aluminium alloy (AA) and C11000 Copper (Cu) and characterise the produced welds using microstructural evaluation, X-Ray Diffraction analysis, mechanical properties testing and electrical resistivity measurements in order to evaluate the effects of the processing parameters on the qualities of the produced welds. This chapter presents the conclusions drawn from the study and recommendations made.
5.2 Conclusions
Visual inspection of the surfaces of the produced welds suggested that the welds were successfully joined due to the physical appearances and lack of surface defects. However, slicing through the welds for further visual inspection and characterisations revealed defects in all the produced welds. The defects observed included voids, hook defects and microcracks.
All the produced welds showed the typical hook and kissing bond movement for the copper with varying degree of movement observed for the different parameters. It is concluded that an increase in the traverse speed resulted in an increase in the flow of copper.
Observation of the relationship between the input parameters and the output data revealed that both the torque, T, and the advancing force, Fx, increased with increases in the downward force, Fz, while the heat input decreased with an
Chapter Five Conclusions and Future Work increase in the downward force. As a result, the highest heat inputs were observed at 50 mm/min while 250 mm/min presented the welds with the lowest heat inputs for each set of processing parameters. Generally, the sizes of the voids were seen to be dependent on the plunge depth. A higher plunge depth produced welds with smaller void areas.
The tensile strength was found to be dependent on both the plunge depth and the traverse speed as an increase in the plunge depth resulted in an increase in the tensile strength of the welds while an increase in the traverse speed resulted in a decrease in the tensile strength. The welds produced at 4.8 mm plunge depth showed greater tensile strengths at all times than those produced at 4.5 mm.
The data from the microhardness profiling suggested the absence, or presence in very little concentrations, of intermetallic compounds in most of the produced welds.
While this was desirable, poor mixing of the aluminium and copper particles was seen to result in this. It remains to be seen if future studies will produce welds with better weld qualities and minimal intermetallic compounds.
Generally, it is concluded that the heat input affected the electrical resistivity results as an increase in the heat generated during welding resulted in an increase in the electrical resistivity of the produced welds. While this does not hold true for both plunge depths, the electrical resistivity was seen to be totally dependent on the area of the voids as the electrical resistivity increased with an increase in the void areas.
While all the four microstructural zones (the SZ, TMAZ, HAZ and BM) were present in all the produced welds, it is concluded that an increase in the traverse speed resulted in a decrease in the width of each of the microstructural zones, resulting
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Chapter Five Conclusions and Future Work from the reduction in heat input into the welds. Grain sizes were also seen to reduce across the different microstructural zones with a dependence on the heat input into the welds. The changes in the grain size correlated to the microhardness profiling as the hardness values were seen to be dependent on the sizes of the grains in each microstructural zone. It was also observed that the zones at the advancing side of the welds were smaller than those at the retreating side of the welds.
Even though the aluminium grains showed very little signs of grain deformation, the copper particles were generally deformed during the welding operation. However, the grain deformation was limited to changes in the grain sizes and not the grain structure as the copper grains maintained an equiaxed structure in all the different microstructural zones.
EDS analysis suggested the absence of intermetallic compounds in most of the welds, confirming the observed tensile test results. However, no definite trend was concluded from the results of the EDS analysis. Much like the EDS analysis, the
XRD analysis only confirmed the absence, or presence in very minor peaks, of intermetallic compounds in the produced welds as suggested by the tensile test results.
The longitudinal residual stresses were observed to be higher than the traverse residual stresses for all points observed while the residual stresses in the welded samples were found to be lower than the residual stress of the copper parent material. Finally, it is concluded that both the traverse and the longitudinal stresses present in the welds were compressive.
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Chapter Five Conclusions and Future Work
The proposed aim and the objectives of this research work were successfully achieved. Friction Stir lap welds of dissimilar 1060 aluminium alloy and C11000
Copper were successfully produced using different processing parameters and characterised.
While all the produced welds had defects, this research work has been able to establish that the quality of the produced welds depends a lot on the plunge depth where the Friction Stir Welding of aluminium and copper is concerned using the lap welding configuration.
This research work is important as it has been able to provide some vital information on the dissimilar Friction Stir lap welding of aluminium and copper and offers deeper insights into the interplay of the processing parameters. This should be a good tool for the research community especially as the research into the Friction Stir Welding of aluminium and copper using the lap welding configuration is concerned because it will provide information into what has not worked well so far in the FSLW of both metals. The author has also been able to master the characterisation techniques conducted in the course of this research study.
5.3 Future Work
A lot still remains to be done in order to fully understand the FSLW of aluminium and copper and despite what has been done in this study, further investigations are still required before the optimization of the processing parameters can be achieved. The following recommendations are in order:
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Chapter Five Conclusions and Future Work
i. A wider range of input processing parameters should be researched in order
to identify a suitable processing window for the FSW of both dissimilar
aluminium and copper metals in the lap configuration.
ii. The quality of the produced weld has been seen to depend on the plunge
depth. This is expected to peak and then decline at a certain point. Further
investigation is required to determine the relationship between the plunge
depth and the weld quality in order to optimize the plunge depth for better
weld quality.
iii. Since both aluminium and copper are used in the electrical industries, the
effect of galvanic corrosion on the produced welds should be studied in order
to be able to determine the suitability of the process for the electrical industry
in design of bus bars and other applications requiring aluminium-copper joints.
iv. No clear standard was found to be presently available in the open literature
for the determination of the tensile shear strength of welded metals. This
should be a source of research in order to ensure duplicity of tensile results
for lap welds within the research community.
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Appendix A1
APPENDIX A
A1. THE MAJOR SUB-SYSTEMS OF THE I-STIR PDS FSW PLATFORM
The key sub-systems of the I-STIR PDS FSW platform are described briefly below:
Pin/adapter tooling: a tool holder with three (3) welding modes viz: the fixed, adjustable and self-retracting pin is provided. The fixed pin tool, shown in Figure A1, was used in this study.
Figure A1: FSW Tool holder [173]
Machine base: acting as the foundation for the I-STIR PDS system, the machine base provides stability for the entire setup.
Weld head assembly: attaches the tool to the rotational drive system of the I-STIR PDS.
Z axis manipulator and self-reacting load table: equipped with a system to manipulate the z-axis and a self-reacting load table, the z axis manipulation system enables the movement of the weld head for workpiece set up while the load reaction table restricts the amount of forces that can be induced on the machine base to the weight of the I-STIR PDS.
X axis manipulator: with a hydraulically controlled pitch, this system is responsible for driving the head assembly in the welding direction.
Y axis manipulator: this system is responsible for driving the weld table within a 164 | P a g e
Appendix A1
±305 mm range.
Pitch axis and pitch adjustment: the pitch axis is a gimbal axis that allows the weld head to move in the X-Z plane while the forge beam assembly allows the weld head to be adjusted within a ±150 range (pitch).
Measurement and control sensors: there are different sensors to both measure and control the major process parameters of the I-STIR PDS including the tool rotation, torque, tool cooling flow, temperature, forces and displacements.
Specimen welding table: this is used as a high generic clamping surface and has the dimensions 1651 x 1016 x 92.25 mm.
Hydraulic distribution system: consists of the hose distribution, the Hydraulic Service Manifold (HSM) and the Hydraulic Power Unit (HPU). The hose distribution ensures the distribution of necessary fluids to the appropriate systems in the machine. The HSM regulates the pressure of the fluids in the hose distribution. The HPU provides the hydraulic cooling fluids for the spindle and spindle hydraulic motor us consists of three (3) pump modules.
MTS SchemaTM VME Digital control system: this system enables the operator to easily modify, control, select, and record the processing parameters. The main operator interface is a PC.
Remote station control pendant: this is used to control each of the axes of the machine. It also includes the emergency stop button of the machine.
165 | P a g e
Appendix A2
A2. THE I-STIR PDS FSW SYSTEM SPECIFICATIONS
Table A2-1 presents the specifications of the system axis of the I-STIR PDS.
Table A2-1: System specifications [150]
Axis Travel Max Speed Max Speed Load Range (Loaded) (Unloaded) Capacity
X 1000 mm 6000 mm/min 6000 mm/min 31.1 kN
Y 2000 mm 10000 mm/min 10000 31.1 kN mm/min
Z 680 mm 1400 mm/min 1750 mm/min 88.9 kN
Pitch ±15 degrees 300 deg/min 300 deg/min 31.1 kN
Roll ±15 degrees 300 deg/min 300 deg/min 31.1 kN
Spindle (60 Hz) NA 2000 rpm 2000 rpm 430 N-m3
Forge Actuator 30 mm 300 mm/min 300 mm/min 88.9 kN
Pin 30 mm 1000 mm/min 1000 mm/min 88.9 kN
166 | P a g e
Appendix A3
A3. PROGRAM EMPLOYED IN THE WELDING
#HOME CO_ORDINATE POSITION FROM EDGE BED: 337 MM
#NO RUN ON TAB
COORDS/PART
BREAK/"PRESS RESUME WHEN READY"
#1
FEEDRATE/RATE,400,RAMP,2000
FORGEMOVE/POSITION,5.0,RATE,500,RAMP,500
GOTO/150,0,0,0
DELAY/SEC,1.0
#PROBE SURFACE
FORGEMOVE/TOUCH,0,RATE,25,OVERTRAVEL,15,FORCE,2
BREAK/"CONFIRM ON SURFACE"
FORGEMOVE/POSITION,1,RATE,100,RAMP,200,RELATIVE
# Plunge
SPINDLE/RPM,900,RAMP,500
DELAY/SEC,3.0
FORGEMOVE/POSITION,-1,RATE,10,RAMP,200,RELATIVE
FORGEMOVE/POSITION,-3.8,RATE,10,RAMP,240,RELATIVE
DELAY/SEC,5
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Appendix A3
# 120 mm FSP, Ramp up over 20 mm then proceed in position control
FEEDRATE/RATE,150,ACCEL,9.375,DECEL,700
GOTO/270,0,0
# RETRACT TOOL
FORGEMOVE/POSITION,5,RATE,500,RAMP,200
SPINDLE/RPM,0,RAMP,600
FEEDRATE/RATE,800,RAMP,2000
GOTO/270,0,30,0
DELAY/SEC,1
GOTO/120,0,30,0
COORDS/PART
BREAK/"PRESS RESUME WHEN READY"
168 | P a g e
Appendix A4
A4. TOOL DIMENSIONS AND PROFILES
Tool Concave Conical Triflute Designation
Tool shoulder Concave Conical Flat profile
Tool pin profile Cylindrical Conical Triflute
Tool base 25 25 25 diameter
Tool shoulder 18 18 18 diameter
Tool pin base 5 9 5 diameter
Tool pin tip 5 5 5 diameter
Tool pin height 4.8 4.5 and 4.8 4.5
169 | P a g e
Appendix B
APPENDIX B
THE DRAWING OF THE CAD PROGRAM USED BY THE WATERJET CUTTING MACHINE
Figure B: Diagramatical representation of the CAD drawing fed into the waterjet cutting machine
170 | P a g e
Appendix C1
APPENDIX C
C1. SCANNING ELECTRON MICROSCOPE
Figure C1-1: Scanning Electron Microscope (VEGA3 XMU)
171 | P a g e
Appendix C2
C2. MOUNTING PRESS
Figure C2-1: Mounting Press (CitoPress-1)
172 | P a g e
Appendix C3
C3. GRINDING AND POLISHING MACHINE
Figure C3-1: Grinding and polishing machine (LaboPol-25)
173 | P a g e
Appendix C4
C4. Metallographic sample preparation
The surface of the samples were prepared for the metallographic study as presented in Tables C4-1 and C4-2.
Table C4-1: Procedure for metallographic sample preparation (Grinding)
Step Plane grinding Final grinding Surface SiC-Paper 320# MD-Allegro Grit/Suspension 320 DiaPro Largo Lubricant Water Rpm 150 150 Force (N) 180 180 Time Until plane 4 minutes
Table C4-2: Procedure for metallographic sample preparation (Polishing)
Step Diamond Polishing Final Polishing Surface MD-Mol OP-Chem Suspension DiaPro Mol OP-S Rpm 200 200 Force (N) 150 90 Time 2 minutes 2 minute
The samples were washed under running water with liquid soap and dried with acetone in the presence of pressurised air.
The etchants used are:
i. A solution of 70ml NH3, 70ml H2O and 14ml H2O2 and ii. Modified Flick’s reagent, consisting of:
15ml HF and 100ml H2O
174 | P a g e
Appendix C5
C5. Residual Stress Analysis
Figure C5-1: Residual Stress Analysis (D8 Discover)
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Appendix C6
C6. Residual Stress Analysis
Figure C6-1: GADDS software during analysis
176 | P a g e
Appendix C7
C7. Phase Identification
Figure C7-1: Phase Identification (D8 Advance)
177 | P a g e
Appendix C8
C8. Microhardness Profiling
Figure C8-1: Microhardness Profiling (DuraScan)
178 | P a g e
Appendix C9
C9. Tensile-Shear Testing
Figure C9-1: Tensile-Shear Testing (Instron 1195)
179 | P a g e
Appendix D0
APPENDIX D
D0. Surface of Produced Welds and Sample Layout
Figure D0-1: Surfaces of welds produced with conical tool at 600 rpm, 4.5 mm and (a) 50 mm/min; (b) 150 mm/min; (c) 250 mm/min
Figure D0-2: Surfaces of welds produced with conical tool at 900 rpm, 4.5 mm and (a) 50 mm/min; (b) 150 mm/min; (c) 250 mm/min
Figure D0-3: Surfaces of welds produced with conical tool at 1200 rpm, 4.5 mm and (a) 50 mm/min; (b) 150 mm/min; (c) 250 mm/min
Figure D0-4: Surfaces of welds produced with concave tool at 900 rpm, 4.8 mm and (a) 50 mm/min; (b) 150 mm/min; (c) 250 mm/min
Figure D0-5: Surfaces of welds produced with conical tool at 900 rpm, 4.8 mm and (a) 50 mm/min; (b) 150 mm/min; (c) 250 mm/min
180 | P a g e
Appendix D0
Figure D0-6: A typical weld after being cut by the waterjet cut off machine
181 | P a g e
Appendix D1
D1. Determination of the Total Area of Voids
The sum of all the area of the voids in each sample is presented in Table D1
Table D1-1: Total area of voids
Weld Rotational Traverse Speed Plunge Total Area of Designation Speed (rpm) (mm/min) Depth (mm) Void (mm²) A 600 50 4.5 1.72 B 600 150 4.5 2.09 C 600 250 4.5 1.86 D 900 50 4.5 1.82 E 900 150 4.5 1.83 F 900 250 4.5 0.23 G 1200 50 4.5 1.44 H 1200 150 4.5 1.69 I 1200 250 4.5 1.54 1C1 900 50 4.8 0.42 2C1 900 150 4.8 0.60 3C1 900 250 4.8 0.73 1CC1 900 50 4.8 0.70 2CC1 900 150 4.8 0.39 3CC1 900 250 4.8 0.66
182 | P a g e
Appendix D2
D2. EDS Analysis
Some of the results from the EDS analysis are presented below and summarized in Table D2-1.
Cu_PM a EDS
Spectrum processing : Peaks possibly omitted : 0.267, 0.517, 1.865, 9.870, 16.075, 16.931 keV
Processing option : All elements analyzed (Normalised) Number of iterations = 1
Standard : Cu Cu 1-Jun-1999 12:00 AM
Element Weight% Atomic% Cu K 100.00 100.00 Totals 100.00
Comment:
Al_PM a EDS
Spectrum processing : Peaks possibly omitted : 0.270, 0.520, 0.690, 2.980, 4.480, 6.400 keV
Processing option : All elements analyzed (Normalised) Number of iterations = 1
Standard : Al Al2O3 1-Jun-1999 12:00 AM
Element Weight% Atomic% Al K 100.00 100.00 Totals 100.00
Comment:
183 | P a g e
Appendix D2
A SZ a EDS
Spectrum processing : Peaks possibly omitted : 0.270, 0.521, 2.980, 4.480, 6.408 keV
Processing option : All elements analyzed (Normalised) Number of iterations = 4
Standard : Al Al2O3 1-Jun-1999 12:00 AM Cu Cu 1-Jun-1999 12:00 AM
Element Weight% Atomic% Al K 94.73 97.69 Cu K 5.27 2.31 Totals 100.00
Comment:
E SZ a EDS
Spectrum processing : Peaks possibly omitted : 0.268, 0.520, 1.862, 16.089, 16.971 keV
Processing option : All elements analyzed (Normalised) Number of iterations = 3
Standard : Al Al2O3 1-Jun-1999 12:00 AM Cu Cu 1-Jun-1999 12:00 AM
Element Weight% Atomic% Al K 2.68 6.09 Cu K 97.32 93.91 Totals 100.00
Comment:
I SZ a EDS 184 | P a g e
Appendix D2
Spectrum processing : Peaks possibly omitted : 0.267, 0.511, 1.865, 16.064, 16.916 keV
Processing option : All elements analyzed (Normalised) Number of iterations = 2
Standard : Al Al2O3 1-Jun-1999 12:00 AM Cu Cu 1-Jun-1999 12:00 AM
Element Weight% Atomic% Al K 0.42 0.99 Cu K 99.58 99.01 Totals 100.00
Comment:
1C1 a EDS
Spectrum processing : Peaks possibly omitted : 0.268, 0.519, 1.862, 16.080, 16.922 keV
Processing option : All elements analyzed (Normalised) Number of iterations = 2
Standard : Al Al2O3 1-Jun-1999 12:00 AM Cu Cu 1-Jun-1999 12:00 AM
Element Weight% Atomic% Al K 0.20 0.47 Cu K 99.80 99.53 Totals 100.00
Comment:
2CC1 a EDS
185 | P a g e
Appendix D2
Spectrum processing : Peaks possibly omitted : 0.271, 0.522, 1.876, 2.980, 16.080, 16.930 keV
Processing option : All elements analyzed (Normalised) Number of iterations = 3
Standard : Al Al2O3 1-Jun-1999 12:00 AM Cu Cu 1-Jun-1999 12:00 AM
Element Weight% Atomic% Al K 23.12 41.46 Cu K 76.88 58.54 Totals 100.00
Comment:
Table D2-1: Weight and Atomic percentages of Aluminium and Copper in the EDS analysed samples
Aluminium Copper Weight % Atomic % Weight % Atomic % Cu_PM 100 100 Al_PM 100 100 A 94.73 97.69 5.27 2.31 B 1.19 2.76 98.81 97.24 C 99.79 99.91 0.21 0.09 D 99.17 99.65 0.83 0.35 E 2.68 6.09 97.32 93.91 F 99.3 99.7 0.7 0.3 G 3.43 7.72 96.57 92.28 H 99.46 99.77 0.54 0.23 I 0.42 0.99 99.58 99.01 1C1 0.2 0.47 99.8 99.53 2C1 98.45 99.34 1.55 0.66 3C1 0.19 0.44 99.81 99.56 1CC1 99.31 99.71 0.69 0.29 2CC1 23.12 41.46 76.88 58.54 3CC1 0.2 0.46 99.8 99.54
186 | P a g e
Appendix D3
D3. Calculation of the Intermetallic Compounds from Weight Percentages of
Aluminium and Copper
For determining the intermetallic compounds present, the calculation used is:
퐴푡표푚𝑖푐 푤푒𝑖푔ℎ푡 표푓 푒푙푒푚푒푛푡 × 푁푢푚푏푒푟 표푓 푎푡표푚푠 𝑖푛 푡ℎ푒 푐표푚푝표푢푛푑 % 퐸푙푒푚푒푛푡 = 푇표푡푎푙 푤푒𝑖푔ℎ푡 표푓 푐표푚푝표푢푛푑
Where atomic weight of Aluminium is 26.98 and the atomic weight of copper is 63.55
For AlCu,
63.55 × 1 % 퐶표푝푝푒푟 = × 100 (26.98 + 63.55)
% Al = 30% and % Cu = 70%
For Al2Cu,
63.55 × 1 % 퐶표푝푝푒푟 = × 100 (26.98 × 2) + 63.55
% Al = 46% and % Cu = 54%
For Al3Cu,
63.55 × 1 % 퐶표푝푝푒푟 = × 100 (26.98 × 3) + 63.55
% Al = 56% and % Cu = 44%
For AlCu2,
63.55 × 2 % 퐶표푝푝푒푟 = × 100 26.98 + (63.55 × 2)
% Al = 18% and % Cu = 82%
For AlCu3,
63.55 × 3 % 퐶표푝푝푒푟 = × 100 26.98 + (63.55 × 3)
% Al = 12% and % Cu = 88%
187 | P a g e
Appendix D4
D4. Tensile Lap Shear Results
The results from the tensile Lap shear tests are presented in Figures D4-1 to D4-15
2500
2000
1500 A1 1000 A2 Shear Load(N) 500 A3
0 0 1 2 3 4 5 6 Extension (mm)
Figure D4-1: Weld A (600 rpm, 50 mm/min, 4.5 mm, Conical)
2000
1500
1000 B1 500 B2 0
Shear Load(N) B3 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 -500
-1000 Extension (mm)
Figure D4-2: Weld B (600 rpm, 150 mm/min, 4.5 mm, Conical)
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Appendix D4
2000
1500
1000 C1 C2
Shear Load(N) 500 C3
0 0 1 2 3 4 5 6 Extension (mm)
Figure D4-3: Weld C (600 rpm, 250 mm/min, 4.5 mm, Conical)
2500
2000
1500 D1 1000 D2 Shear Load(N) 500 D3
0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Extension (mm)
Figure D4-4: Weld D (900 rpm, 50 mm/min, 4.5 mm, Conical)
1200 1000 800 600 E1 400 E2 Shear Load(N) 200 E3 0 0 0.5 1 1.5 2 2.5 3 Extension (mm)
Figure D4-5: Weld E (900 rpm, 150 mm/min, 4.5 mm, Conical)
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Appendix D4
1000
800
600 F1 400 F2 200
Shear Load(N) F3 0 0 1 2 3 4 5 6 -200 Extension (mm)
Figure D4-6: Weld F (900 rpm, 250 mm/min, 4.5 mm, Conical)
3500 3000 2500 2000 G1 1500 G2 1000 Shear Load(N) 500 G3 0 0 0.5 1 1.5 2 2.5 Extension (mm)
Figure D4-7: Weld G (1200 rpm, 50 mm/min, 4.5 mm, Conical)
1600 1400 1200 1000 800 H1 600 H2
Shear Load(N) 400 H3 200 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 Extension (mm)
Figure D4-8: Weld H (1200 rpm, 150 mm/min, 4.5 mm, Conical)
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Appendix D4
1000
800
600
400 I3 Shear Load(N) 200
0 0 0.5 1 1.5 2 2.5 3 3.5 4 Extension (mm)
Figure D4-9: Weld I (1200 rpm, 250 mm/min, 4.5 mm, Conical)
5000 4000 3000 2000 1C1a 1000 1C1b
Shear Load(N) 0 1C1c 0 1 2 3 4 5 6 7 8 -1000 -2000 Extension (mm)
Figure D4-10: Weld 1C1 (900 rpm, 50 mm/min, 4.8 mm, Concave)
5000
4000
3000 2C1a 2000 2C1b 1000
Shear Load(N) 2C1c 0 0 2 4 6 8 10 12 14 -1000 Extension (mm)
Figure D4-11: Weld 2C1 (900 rpm, 150 mm/min, 4.8 mm, Concave)
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Appendix D4
2500
2000
1500 3C1a 1000 3C1b Shear Load(N) 500 3C1c
0 0 2 4 6 8 10 Extension (mm)
Figure D4-12: Weld 3C1 (900 rpm, 250 mm/min, 4.8 mm, Concave)
5000
4000
3000 1CC1a 2000 1CC1b Shear Load(N) 1000 1CC1c
0 0 2 4 6 8 10 12 Extension (mm)
Figure D4-13: Weld 1CC1 (900 rpm, 50 mm/min, 4.8 mm, Conical)
5000
4000
3000 2CC1a 2000 2CC1b Shear Load(N) 1000 2CC1c
0 0 1 2 3 4 5 6 7 Extension (mm)
Figure D4-14: Weld 2CC1 (900 rpm, 150 mm/min, 4.8 mm, Conical)
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Appendix D4
5000
4000
3000 3CC1a 2000 3CC1b Shear Load(N) 1000 3CC1c
0 0 2 4 6 8 10 12 14 16 18 Extension (mm)
Figure D4-15: Weld 3CC1 (900 rpm, 250 mm/min, 4.8 mm, Conical)
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Appendix D5
D5. Microhardness Profiles
The microhardness profiles of the welds as well the parent materials are presented in Figures D5-1 to D5-14
96 94 92 90
(HV) Cu Long 88 86
Vickers microhardness -5 -4 -3 -2 -1 0 1 2 3 4 5 Distance from weld center
Fig D5-1: Copper Parent Material
40 39 38 37 Al (HV) (HV) 36 35 -5 -4 -3 -2 -1 0 1 2 3 4 5 Vickers microhardness Distance from weld center
Fig D5-2: Aluminium Parent Material
120 100 80 60 40
(HV) (HV) 1C1 20 0
Vickers microhardness -5 -4 -3 -2 -1 0 1 2 3 4 5 Distance from weld center
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Appendix D5
Fig D5-3: Weld 1C1 (900 rpm, 50 mm/min, 4.8 mm, concave)
150
100
50 2C1 (HV) (HV) 0 -5 -4 -3 -2 -1 0 1 2 3 4 5
Vickers microhardness Distance from weld center
Fig D5-4: Weld 2C1 (900 rpm, 150 mm/min, 4.8 mm, concave)
100 80 60 40 3C1 20 (HV) (HV) 0 -5 -4 -3 -2 -1 0 1 2 3 4 5
Vickers microhardness Distance from weld center
Fig D5-5: Weld 3C1 (900 rpm, 250 mm/min, 4.8 mm, concave)
120 100 80 60 40 1CC1
(HV) (HV) 20 0 -5 -4 -3 -2 -1 0 1 2 3 4 5 Vickers microhardness Distance from weld center
Fig D5-6: Weld 1CC1 (900 rpm, 50 mm/min, 4.8 mm, conical)
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Appendix D5
100 80 60 40 2CC1 20 (HV) (HV) 0 -5 -4 -3 -2 -1 0 1 2 3 4 5
Vickers microhardness Distance from weld center
Fig D5-7: Weld 2CC1 (900 rpm, 150 mm/min, 4.8 mm, conical)
120 100 80 60 40
(HV) (HV) 3CC1 20 0
Vickers microhardness -5 -4 -3 -2 -1 0 1 2 3 4 5 Distance from weld center
Fig D5-8: Weld 3CC1 (900 rpm, 250 mm/min, 4.8 mm, conical)
200
150
100
50 A (HV) (HV) 0 -5 -4 -3 -2 -1 0 1 2 3 4 5 Vickers microhardness Distance from weld center
Fig D5-9: Weld A (600 rpm, 50 mm/min, 4.5 mm)
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Appendix D5
100 80 60 40 B 20 (HV) (HV) 0 -5 -4 -3 -2 -1 0 1 2 3 4 5
Vickers microhardness Distance from weld center
Fig D5-10: Weld B (600 rpm, 150 mm/min, 4.5 mm)
100 80 60 40 C
(HV) (HV) 20 0 -5 -4 -3 -2 -1 0 1 2 3 4 5 Vickers microhardness Distance from weld center
Fig D5-11: Weld C (600 rpm, 250 mm/min, 4.5 mm)
100 80 60 40 G (HV) (HV) 20 0 -5 -4 -3 -2 -1 0 1 2 3 4 5 Vickers microhardness Distance from weld center
Fig D5-12: Weld H (1200 rpm, 50 mm/min, 4.5 mm)
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Appendix D5
100 80 60 40 H 20 (HV) (HV) 0 -5 -4 -3 -2 -1 0 1 2 3 4 5
Vickers microhardness Distance from weld center
Fig D5-13: Weld H (1200 rpm, 150 mm/min, 4.5 mm)
150
100
50 I (HV) (HV) 0 -5 -4 -3 -2 -1 0 1 2 3 4 5 Vickers microhardness Distance from weld center
Fig D5-14: Weld I (1200 rpm, 250 mm/min, 4.5 mm)
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Appendix D6
D6. Residual Stress Results
12/17/2014 13:42 Project: Stress_2D Operator: Bruker Instrument Administrator Site: NECSA Measured: 11/20/14 14:56:28 Sample Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -106.5 ± 3.3 Shear : 0.5 ± 1.3 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 107.9 ± 5.2 Stress Tensor : -86.4 ± 3.7 6.7 ± 3.4 9.2 ± 1.4 6.7 ± 3.4 -106.5 ± 3.4 0.5 ± 1.3 9.2 ± 1.4 0.5 ± 1.3 0.0 ± 0.0
11/18/2014 13:46 Project: Stress_2D Operator: Bruker Instrument Administrator Site: NECSA Measured: 11/12/14 12:24:07 Sample Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -110.5 ± 3.7 Shear : -0.8 ± 1.4 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 114.6 ± 5.8 Stress Tensor : -89.2 ± 4.2 -10.9 ± 3.9 8.8 ± 1.6 -10.9 ± 3.9 -110.5 ± 3.9 -0.8 ± 1.4 8.8 ± 1.6 -0.8 ± 1.4 0.0 ± 0.0
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Appendix D6
Site: NECSA Measured: 11/13/14 09:09:53 Sample Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -85.5 ± 4.4 Shear : -1.1 ± 1.7 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 146.9 ± 7.0 Stress Tensor : -59.9 ± 5.0 -7.5 ± 4.6 12.4 ± 1.9 -7.5 ± 4.6 -85.5 ± 4.6 -1.1 ± 1.7 12.4 ± 1.9 -1.1 ± 1.7 0.0 ± 0.0
12/17/2014 12:15 Project: Stress_2D Operator: Bruker Instrument Administrator Site: NECSA Measured: 11/18/14 12:36:05 Sample Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -118.8 ± 3.0 Shear : 3.4 ± 1.2 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 120.3 ± 4.8 Stress Tensor : -83.4 ± 3.5 -5.5 ± 3.2 7.9 ± 1.3 -5.5 ± 3.2 -118.8 ± 3.2 3.4 ± 1.2 7.9 ± 1.3 3.4 ± 1.2 0.0 ± 0.0
12/17/2014 12:33 Project: Stress_2D Operator: Bruker Instrument Administrator Site: NECSA Measured: 11/19/14 09:28:42 Sample Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 200 | P a g e
Appendix D6
Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -83.1 ± 4.8 Shear : -5.0 ± 1.9 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 135.4 ± 7.5 Stress Tensor : -56.6 ± 5.4 -6.5 ± 5.0 16.4 ± 2.0 -6.5 ± 5.0 -83.1 ± 5.0 -5.0 ± 1.9 16.4 ± 2.0 -5.0 ± 1.9 0.0 ± 0.0
11/18/2014 12:30 Project: Stress_2D Operator: Bruker Instrument Administrator Site: NECSA Measured: 11/11/14 09:24:44 Sample Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -82.3 ± 4.9 Shear : 18.3 ± 1.9 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 208.1 ± 7.8 Stress Tensor : -88.5 ± 5.6 -8.3 ± 5.2 0.9 ± 2.1 -8.3 ± 5.2 -82.3 ± 5.2 18.3 ± 1.9 0.9 ± 2.1 18.3 ± 1.9 0.0 ± 0.0
11/18/2014 14:43 Project: Stress_2D Operator: Bruker Instrument Administrator Site: NECSA Measured: 11/11/14 17:11:09 Sample Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -98.0 ± 7.0 Shear : 28.6 ± 2.7 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 307.0 ± 11.0 201 | P a g e
Appendix D6
Stress Tensor : -121.6 ± 7.9 0.0 ± 7.3 9.4 ± 3.0 0.0 ± 7.3 -98.0 ± 7.3 28.6 ± 2.7 9.4 ± 3.0 28.6 ± 2.7 0.0 ± 0.0
12/17/2014 12:22 Project: Stress_2D Operator: Bruker Instrument Administrator Site: NECSA Measured: 11/19/14 15:13:51 Sample Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -92.7 ± 3.6 Shear : -11.9 ± 1.4 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 96.0 ± 5.7 Stress Tensor : -59.1 ± 4.1 -8.0 ± 3.8 4.8 ± 1.5 -8.0 ± 3.8 -92.7 ± 3.8 -11.9 ± 1.4 4.8 ± 1.5 -11.9 ± 1.4 0.0 ± 0.0
12/17/2014 13:13 Project: Stress_2D Operator: Bruker Instrument Administrator Site: NECSA Measured: 11/20/14 09:12:09 Sample Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -73.6 ± 15.2 Shear : -11.0 ± 5.9 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 144.4 ± 24.0 Stress Tensor : -60.8 ± 17.2 2.3 ± 15.9 11.6 ± 6.5 2.3 ± 15.9 -73.6 ± 15.9 -11.0 ± 5.9 11.6 ± 6.5 -11.0 ± 5.9 0.0 ± 0.0
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Appendix D6
Project: Stress_2D Operator: Bruker Instrument Administrator Site: NECSA Measured: 11/14/14 09:42:28 Sample Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -112.3 ± 3.4 Shear : -3.0 ± 1.3 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 151.7 ± 5.4 Stress Tensor : -89.8 ± 3.8 -2.0 ± 3.6 9.9 ± 1.4 -2.0 ± 3.6 -112.3 ± 3.6 -3.0 ± 1.3 9.9 ± 1.4 -3.0 ± 1.3 0.0 ± 0.0
11/18/2014 15:03 Project: Stress_2D Operator: Bruker Instrument Administrator Site: NECSA Measured: 11/13/14 17:32:28 Sample Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -91.2 ± 4.9 Shear : -7.2 ± 1.9 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 103.0 ± 7.7 Stress Tensor : -58.4 ± 5.5 12.9 ± 5.1 16.7 ± 2.1 12.9 ± 5.1 -91.2 ± 5.1 -7.2 ± 1.9 16.7 ± 2.1 -7.2 ± 1.9 0.0 ± 0.0
11/18/2014 11:57 Project: Stress_2D Operator: Bruker Instrument Administrator Site: NECSA Measured: 11/07/14 12:25:18 Sample 203 | P a g e
Appendix D6
Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -111.6 ± 3.2 Shear : -3.5 ± 1.3 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 107.6 ± 5.1 Stress Tensor : -86.0 ± 3.7 3.0 ± 3.4 4.8 ± 1.4 3.0 ± 3.4 -111.6 ± 3.4 -3.5 ± 1.3 4.8 ± 1.4 -3.5 ± 1.3 0.0 ± 0.0
11/18/2014 15:09 Project: Stress_2D Operator: Bruker Instrument Administrator Site: NECSA Measured : 11/10/14 14:13:51 Sample Material HKL Wavelength 2theta Poisson Young s1 1/2s2 Arx Cu (4 2 0) 0.154055 ( Cu_)Ka1 144.72 0.36 116144.00 -3.100E-6 1.171E-5 1.00 Corrections : Absorption , Background ( 5 ) , Polarisation , Smooth , K alpha 2 ( 0.50 ) Peak Evaluation Method : Pearson VII Stresss Model : Biaxial + Shear Normal : -45.2 ± 6.5 Shear : -4.2 ± 2.5 ( Phi : 90 Psi : 90 ) Pseudo-Hydro : 99.0 ± 10.2 Stress Tensor : -38.6 ± 7.3 7.5 ± 6.8 17.0 ± 2.8 7.5 ± 6.8 -45.2 ± 6.8 -4.2 ± 2.5 17.0 ± 2.8 -4.2 ± 2.5 0.0 ± 0.0
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