Sunpreet Kaur1, Lakhwinder Singh1, Hemant Singh1, Kanwar JS Gill2

International Journal For Emerging Trends in Engineering and Management Research (IJETEMR) –Volume II Issue 1- 21st January 2016

“ To study the effect of tool tilt angle, tool rotational speed and tool welding speed on the mechanical and metallurgical properties of friction stir welded aluminium al6063 alloy”

Sunpreet Kaur1, Lakhwinder Singh1, Hemant Singh1, Kanwar JS Gill2, Sarbjeet Singh3, Gurmeet Kaur Gill4

1. Assistant Professor, Department of Mechanical Engineering, Gulzar Group of Institutes, Ludhiana, Punjab 2. Head, Department of Mechanical Engineering, Gulzar Group of Institutes, Ludhiana, Punjab 3. Student, Department of Mechanical Engineering, GNDEC, Ludhiana, Punjab 4. Assistant Professor, Department of Mechanical Engineering, GNDEC, Ludhiana, Punjab

ABSTRACT

Friction stir welding is a thermo-mechanical solid state process. The material joint can takes place without the influence of melting point of the base alloy. The welding joint between two materials can be formed with the influence of third body material in the form of tool. In this process filler or shielding gas is not used to cast the joint. Aluminium alloys are widely used in industry because of better corrosion resistance and high thermal and electrical conductivity. In the present work, the effect of tool tilt angle, rotational speed and welding speed on the mechanical and metallurgical properties of friction stir welded Al 6063 alloy has been studied using Taguchi’s method. The experimental results showed that tool tilt angle of 3° exhibits influence in eliminating the tunnel formation. The maximum breaking load and hardness has been achieved at moderate tool rotational speed of 1000 rpm while percentage of elongation increases with increase in tool rotational speed i.e. at 1200 rpm tool rotational speed maximum elongation has been obtained. It has been observed that the welding speed has no significant impact on the mechanical properties of the welded joint. The research work showed that tool tilt angle is most influential factor for optimizing the mechanical properties followed by tool rotational speed and welding speed.

Keywords: Friction stir welding, Aluminium alloys, tool, optimizing,welding speed.

1. INTRODUCTION

1.1 Welding: Welding is a technique that fabricates the joining of two materials permanently with a suitable combination of metallurgical, pressure and temperature conditions. The fabrication process joint takes place usually with the application or without the application of heat and pressure and in which filler material may or may not be used. Under different environmental conditions like space, open air, water etc. welding may be performed.

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1.2 Friction Stir Welding At TWI (The welding institute) Wayne Thomas discovered the process called Friction Stir Welding (FSW) in the UK in December 1991. This process has gained lot of importance in industry due to the plentiful use in the joining of aluminium alloys.

FSW is a thermo-mechanical solid state process. The material joint can takes place without the influence of melting point of the base alloy. The welding joint between two materials can be formed with the influence of third body material in the form of tool. In this process filler or shielding gas is not used to cast the joint. FSW is originating as a relevant alternative technique with high efficiency due to high-processing speeds. This method is acceptable for welding numbers of materials those are intricate to weld by conventional fusion welding technique. FSW uses a rotating tool to produce the required heat for the joining process as compared to conventional friction welding. Initially, this process is suitably limited for aluminium alloys but now it can be elongated to other materials also. The weld achieved is of better microstructure and superior in characteristics to that base material. This process finds its application in ship buildings, aerospace, automotive, railway, construction and electrical industries. FSW process has ability to weld dissimilar materials and this technology is cost effective, green one technology, non toxic and fumes are not produced during welding due to the absence of shielding gases and other filler material.

1.3 Welding Parameter: The Lists of primary controllable parameters for friction stir welding are: Tool Rotational Speed 1. Tool transverse Speed 2. Axial Load 3. Tool geometry 4. Probe length 5. Tool shoulder diameter 6. Pin diameter 7. Tool tilt angle 8. D/d ratio of the tool

1.3.1 Effect of tool rotational speed: The rotational speed of the tool exhibits intense mixing and stirring of material from one side to the other side around the rotating pin. It is measured in rpm. At higher tool rotational speed there is rise in temperature due to increase in the frictional heat and results in material mixing. The quality of the weld is affected by the tool rotational speed.

1.3.2 Effect of tool welding speed The stirred material moved from front to back of the pin by the action of transverse speed of the tool. It affects the material flow around the tool pin. With increase in welding speed the heat loss through the tool material can be reduced and similar increase in tool rotational speed produces sound welds.

1.3.3 Effect of axial force The effect of axial force or pressure on the tool is important to produce the weld quality. A pressure or force necessary to push the tool into work surface is easily controlled. If excessive

Www.ijetemr.org/www.ijetemr.in International Journal For Emerging Trends in Engineering and Management Research (IJETEMR) –Volume II Issue 1- 21st January 2016 force is applied to the pushed the tool into the surface of the work piece then metal gets heated up and becomes soft enough so that it can expel the material from the surface.

1.3.4 Effect of tool tilt angle The tool tilt angle greatly influences the quality of the weld. The proper tool tilting assures that shoulder influences the plasticize material and stir it from front to back of the pin and cavity fills. To generate the sound welds, the target depth of the pin is important. The rotating tool cannot stir the mixed material from leading edge to the trailing edge and shoulder of the tool does not touch the work piece, if target depth of the tool is too shallow. The excessive flash will be created if target depth is too deep. The tunneling defect is produced generally in aluminium alloys during friction stir welding and it can be eliminated by increasing the tool tilt angle to some extent.

Fig.1 Schematic view of the tool tilt angle process (Seighalani et al.(2009))

1.4 Microstructure According to Thread gill, the four regions of microstructure are: • Unaffected material or base metal (BM): The mechanical properties and microstructure of the parent metal has not influenced by the heat input. In this zone, material deformation has not been occurred even if it can practice a thermal cycle from the weld.

• Heat-affected zone (HAZ): This region is neighbor to the weld joint. The material has practiced a thermal cycle that has altered the microstructure and the mechanical properties. Anyhow, the plastic deformation has not observed in this zone.

• Thermo mechanically affected zone (TMAZ): This zone circumscribes the nugget of the weld. The plastic deformation has occurred in this zone. The heat input exhibits great impact on the mechanical properties and on microstructure of the material. It may have experienced a limited deformation and lower temperatures.

• Weld nugget (WZ): The zone which is already employed by the tool pin is the stir zone. The weld nugget zone is forged by the excessive plastic deformation caused generally by the pin of

Www.ijetemr.org/www.ijetemr.in International Journal For Emerging Trends in Engineering and Management Research (IJETEMR) –Volume II Issue 1- 21st January 2016 the tool and has fine recrystallized grains. Accordingly this region is also indicated as ‘dynamically recrystallized zone’.

Fig.1.2 Microstructural analysis of FSW, BM(A), HAZ (B), TMAZ (C), WZ(D) (Mishra & Mahoney, 2007)

1.5 Tool Material The friction stir welding is a thermo mechanical deformation process where the tool material temperature reaches the work piece melting temperature. The proper selection of the tool material will depend upon the work piece material to produce high quality welds. The tool material must be strong enough to resists the compressive loads when the tool touches work piece and have acceptable compressive and shear strength at elevated temperature to avoid the fracture of tool during friction stir welding process. The tool materials must not be reactive to environment or work material which gradually changes the mechanical and metallurgical properties of the tool.

1.6 Tool geometry The tool consists of two parts one is tool shoulder and other is tool pin. During the tool forge, the rotating FSW tool is compelled into the work piece. The pin contacts with the work piece generates frictional and deformational heating and softens the work piece material, and shoulder contact to the work piece increases the heating of the work piece and enlarged the zone of softened material. Mostly, the rotational motions of the tool from one place to further increases the volume of deformed material. Transverse load is a load required for the forward motion of the tool similar to the travel direction and the load needed for the shoulder of the tool to remain in touch with the work piece is the normal load.

Welding Defects:

Tunnel formation: The formation of this defect has found particularly in aluminium alloys. It is formed on the retreating side of the joint microstructure. The tunneling defect and pores increases as the welding speed increases and it moves vertical into the weld zone of aluminium. It is caused because the tool has less time to plasticize and shift the materials over the pin and the material flow increases as the ultimate temperature of joint decreases, and forms inappropriate deformation of material. The tunneling defect can be removed by increasing the heat content, by changing the material flow and using proper pin length.

Fig.1.3 Tunnel formation (singh et al.(2015))

2. Problem Formulation Literature review reveals that aluminum alloys are being used effectively for many applications such as automotive, aerospace, shipbuilding etc. because of their high mechanical strength to weight ratio.

Most of the current welding procedure for welding aluminum alloys are to be operated under inert conditions and are costly and require use of filler material, which further creates problem of mismatch in mechanical properties of the weld and base metal. Whereas frictions stir welding provides a solid state approach for joining the materials without the use of any filler material. This approach is useful for welding aluminum alloys and other materials and their alloys which are difficult to weld by any other method.

Literature review reveals that many researchers have done work on the effect of tool shoulder diameter, D/T ratio, axial force and various other process parameters on the mechanical and metallurgical properties of the friction stir welded materials but very less work has been done in investigating the effect of tool tilt angle in case of Al6063 aluminium alloy.

In the present thesis work properly finished aluminium Al6063 plates has been welded using vertical milling CNC machine. Important input parameters that controlled the quality of weld that are tool rotational speed(rpm), tool tilt angle(°) and welding speed(mm/min) are optimized to obtain the sound weld and minimize the tunneling defect which is a major problem in FSW process.

Subsequently, the efforts were made to study the effect of input parameters on the mechanical properties like breaking load, hardness, and percentage elongation and metallurgical properties like micro structural analysis.

3. Objectives 1. To study the effect of tool tilt angle on the mechanical properties of friction stir welded Al6063 alloy.

2. To evaluate the percentage of contribution of the individual input joining parameters, and to determine the optimum sequence of the joining parameters for better probable strength.

4. Methodology

5. EXPERIMENTATION AND OBSERVATIONS 5.1 Work piece Material The work piece material used for conducting the experimentation was Aluminum 6063 alloy plates. Using CNC cutting machine the plates were prepared with the dimensions of 150×100×6 mm for experiment. Table 5.1 Chemical Composition of the work piece

Material Si Cu Fe Mn Mg Cr Zn Ti Al Al 6063 0.2– 0.6 0.1 0.35 0.1 0.45-0.9 0.1 0.1 0.1 Balance

5.2 Tool Material The tool performance depends on the following factors that are design of tool, tool material selection and conditions of heat treatment. The material selected for performing the welding process was H13 tool steel. It resists hot cracking and has excellent mechanical properties. Table 5.2 H13 tool Steel composition

Elements C Cr Mo V Si S P Mn Fe Weight in % 0.40 4.90 1.40 1.00 1.05 0.30 0.30 0.37 Balance

5.3 Tool design The optimum tool design will produce the desired joint quality as well as enable higher welding speed and longer tool life. The tool profile has two main parts that is tool shoulder design and tool pin. Material flow over the tool pin has been affected by the shouldered profile and pin profile produces necessary heating in the work piece. The shape of tool selected for performing operation was threaded truncated cone pin with 12 threads per inch. Threads are used to transport the material from shoulder down to the pin for proper mixing of the material. The tool profiles were prepared on the CNC lathe machine at R & D centre, Ludhiana according to table 5.3 as follows:-

Table 5.3 Tool Specifications

Shoulder diameter 20mm Inner pin diameter 6mm Outer pin diameter 4mm Pin length 5.7mm Tool tilt angle 0° , 1.5° , 3°

Fig. 5.1 Tool Profile for FSW

5.4 Fixture Design: A fixture is supporting or work holding device. The main function of fixture is used to support or holds the plates rigidly during friction stir welding under extreme conditions to overcome the problems regarding high temperature. It should be strong enough to withstand the forces and temperature rising in the welding process without any change in the shape of the work piece. The purpose for having suitable clamping is that the work pieces do not move apart. The material used for fixture was mild steel having high strength and toughness.

Fig. 5.2 Fixture used for FSW

5.5 Equipment used for performing the experimentation

The experimentation was conducted on the CNC vertical milling machine at CTR Ludhiana. The following was the specifications used for welding the work pieces.

5.6 Final Experimentation After a feasibility study or experimental trial run, it has been concluded that welding input process parameters like tool rotational speed, tool transverse speed and tool tilt angle exhibits impact on the mechanical and metallurgical properties. Taguchi technique is the simplest and most accurate approach of designing an experiment that helps to find out the most influence process parameters among the parameters combinations, by using the analysis of variance (ANOVA) and signal-to-noise ratio (S/N).The Taguchi L9 orthogonal array method was used to indentifying all the possible combinations for a given set of factors. This array trail can reduce the number of trail cases while maximizing the test analysis. Table 5.5 Working range of input process parameters

Factors Level 1 Level 2 Level 3

A, Rotational speed(rpm) 800 1000 1200 B, Tool tilt angle (°) 0 1.5 3 C,Transverse speed(mm/min) 20 30 40

5.3 Experimental set up for FSW

5.7 Observations The numerous tests conducted on the welded specimens to optimize the impact of welding parameters on the mechanical and metallurgical properties of Al6063 alloys joints produced by friction stir welding were as follows:

1. Hardness test 2. Percentage elongation

5.7.1 Hardness test The HMV-2 tester testing is based on the penetration method. On the surface of the metal, an indenter is pushed under a distinct load for a specific time interval, and an indentation depth is measured. As the indentation depth or size produced is very small, so to measure the indentation depth or size robust microscope is needed. The hardness of the specimens is measured from the load required to create plastic deformation. Metallographic finish is needed for testing the surface of the specimens. Vickers hardness can be measured by using HMV-2 tester. The Vickers diamond pyramid indenter is in the form of square pyramid and angles between the opposing faces is of 136°. The formula used for calculating the Vickers hardness is when in the test specimen indentation is formed to the indentation area.

HV = 0.1891×F/d2 F: Load (N) D: average length of the two diagonals (mm) HV: Vickers hardness During Vickers hardness testing of the welded specimens the load used was 0.50 N for a time interval of 25 sec.

Fig. 5.4 (a) Vickers Hardness tester, (b) Diamond pin Indenter

Table 5.6 Microhardness values after testing

Experimental No. Microhardness (HV) A1 48.6 B1 50.3 C1 50.6 A2 52.9 B2 52.8 C2 70.0 A3 73.7 B3 44.0 C3 47.8

5.7.2 Percentage of Elongation

Percentage of elongation is determined by the ratio between the difference of final length and initial length to the initial gauge length and multiplying by 100. Initial gauge length used for calculating percent elongation was the distance between the grips of the specimens. The final length of the specimens was calculated by using vernier caliper after tensile testing.

Percentage elongation =

Table 5.7 Percentage Elongation values after tensile testing

Specimen No. Percentage Elongation A1 4

B1 8 C1 12 A2 6 B2 12 C2 16 A3 12 B3 16 C3 20

8. RESULTS AND DISCUSSIONS 8.1 Analysis of breaking load: The Tensile tests were conducted to determine the breaking load in friction stir welded specimens. It is the maximum stress that a material can withstand while being stretched or pulled before necking. Table 8.1S/N RATIO for Breaking Load

Specimen No. Breaking load(N) S/N Ratio Mean A1 1700 64.6090 1700 B1 2000 66.0206 2000 C1 2100 66.4444 2100 A2 2100 66.4444 2100 B2 2500 67.9588 2500 C2 2600 68.2995 2600 A3 2000 66.0206 2000 B3 2400 67.6042 2400 C3 2700 68.6273 2700 Table 8.2 Response table for S/N Ratio

Level Tool rotational Tool tilt angle (deg.) Travel feed rate

speed(rpm) (mm/min) 1 65.69 67.59 66.84 2 67.57 67.19 67.08 3 67.42 67.70 66.81 DELTA 1.88 2.10 0.22 RANK 2 1 3

Main Effects Plot for SN ratios Data Means

rotational speed tool tilt angle feed 68.0

67.5 s o i t a r

67.0 N S

e 66.5 M

800 1000 1200 0.0 1.5 3.0 20 30 40

Signal-to-noise: Larger is better

Fig. 8.1 S/N ratio graph for breaking load

Table 8.3 Response table for mean

Level Tool rotational Tool tilt angle (deg.) Travel feed rate

speed(rpm) (mm/min) 1 1933 1933 2233 2 2400 2300 2267 3 2367 2367 2200 DELTA 467 533 67 RANK 2 1 3

Main Effects Plot for Means Data Means Rotational Speed (rpm) Tool Tilt angle (Deg) Feed (mm/min) 2500

2400 s

n 2300 a e M

2200 n a e

M 2100

1900 800 1000 1200 0.0 1.5 3.0 20 30 40

Fig. 8.2 Mean graph for breaking load

The signal to noise and mean are the two consequences which control the factors response. The controlling level of each preferred joining parameter can be analyzed. The breaking load of joining parameters is taken as the output characteristic. The S/N ratio response table shows that the tool tilt angle ranks first in the contribution to generate the good quality weld and better joint strength followed by tool rotational speed and travel feed rate take second and third rank respectively. From the response table for mean the similar orientation has been observed as shown in the Tables 5.2 and 5.3 respectively. The S/N ratio and Mean graphs are shown in Fig.5.1 and 5.2 respectively.

The breaking load was observed at lower tool rotational speed of 800 rpm. The breaking load increases with increase in tool rotational speed and maximum breaking load was achieved at 1000 rpm after that it starts decreasing with increase in tool rotational speed. As there was no significant effect of travel feed rate. Therefore, the optimum breaking load obtained from the plots is evaluated to be the maximum at tool rotational speed of 1000 rpm, tool tilt angle of 3° and travel feed rate of 30mm/min

The material is forged and moved along the transverse line by the tool inclination but without the tool inclination only the normal mixing of material occurs. With the help of tool tilt angle material can be plastically deformed at the weld region, intense stirring of material and better material flow can be achieved. Each parameter shows a different characteristic behavior when the process parameters are observed individually as per the contribution. The heat input rate increases as the tool rotational speed increases. Then, the optimized value should be higher speed, but here it has resulted in a moderate speed, which indicates that sufficient heat alone is required for plasticized material flow. The tool tilt angle plays

Www.ijetemr.org/www.ijetemr.in International Journal For Emerging Trends in Engineering and Management Research (IJETEMR) –Volume II Issue 1- 21st January 2016 important role in the material movement towards the travel direction and also the stirring of the plasticized material flow in the weld region. (A. Pradeep, S. Muthukumaran, 2013).

Table 8.4 ANOVA for Breaking load (95% confidence level)

SOURCE DOF Adj SS Adj MS F value P value %age

contribution A 2 406667 203333 20.33 0.047 46.22 B 2 446667 223333 22.33 0.043 50.75 C 2 6667 3333 0.33 0.750 0.76 ERROR 2 20000 10000 2.27 TOTAL 8 88000 DOF- degrees of freedom, Adj SS- adjusted sum of squares, Adj MS- adjusted mean square or variance. P<0.05(1-0.95)

Analysis of ANOVA

By using MINITAB software ANOVA has been analyzed. The main purpose of the analysis is to estimate the percentage contribution of the individual joining parameter on the breaking load of the weld joint, and also optimum combination of joining parameters has been obtained. The relative importance of the joining parameters is shown in Table 5.4. The analysis of variance shows that the tool tilt angle is the most dominant parameter with a percentage of 50.75 followed by the tool rotational speed of 46.22% and there was no influence of travel feed rate as its percentage contribution is of 0.76.

By plotting the contour graph, the similar trend has been observed

Contour Plot of Breaking load vs Feed & Rotational Speed Contour Plot of Breaking load vs Rotational Speed & Tool Tilt angle

40 1200 Breaking load Breaking load (N) (N) < 1800 < 1800 1800 – 2000 1800 – 2000

35 2000 – 2200 ) 1100 2000 – 2200

2200 – 2400 m 2200 – 2400 p

) 2400 – 2600 r 2400 – 2600 ( n

i > 2600 > 2600 d m e / e p m

30 S 1000

m l ( a

n d e o i e t F a t o

25 R 900

20 800 800 900 1000 1100 1200 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Rotational Speed (rpm) Tool Tilt angle (Deg)

Fig. 8.3 Contour plots for breaking load

9. CONCLUSION

The tool tilt angle is most dominant factor followed by tool rotational speed and tool travel rate.The optimum breaking load obtained from the S/N ratio and mean plots is evaluated to be the maximum at

Www.ijetemr.org/www.ijetemr.in International Journal For Emerging Trends in Engineering and Management Research (IJETEMR) –Volume II Issue 1- 21st January 2016 tool rotational speed of 1000 rpm, tool tilt angle of 3° and travel feed rate of 30 mm/min.The hardness of the parent metal has been found to be higher than the average hardness of weld nugget zone.

From the main effects plot for S/N ratio it has observed that at moderate tool rotational speed i.e. at 1000 rpm and higher travel feed rate of 40mm/min, the maximum hardness was obtained. The percentage of elongation is greatly influenced by heat input rate. The specimens welded with tool rotational speed of 1200 rpm, tool tilt angle of 3° and travel feed rate of 40mm/min showed maximum elongation while specimens welded with tool rotational speed of 800 rpm, tool tilt angle of 0° and travel feed rate of 30mm/min showed minimum elongation.

10. REFERENCES

American Welding Society (2011) “Vision for Welding Industry”. Baghel Kumar Pushp , Siddiquee Noor Arshad Noor (2012) “Design and development of Fixture for Friction Stir Welding” ISSN 2222-1727 (Paper) ISSN 2222-2871 (Online) Vol 3, No.12. Bisadi H., Tavakoli A., Sangsaraki Tour M., K. Tour Sangsaraki Tour K.(2013) “The influences of rotational and welding speeds on microstructures and mechanical properties of friction stir welded Al5083 and commercially pure copper sheets lap joints” Materials and Design Vol. 43, pp 80–88.

Cavaliere P, Nobile R , Panella W.F., Squillace A.(2015) “Mechanical and Microstructural properties of Al 6056 friction stir welded joints”. Cavaliere , P. Squillance, A. and Panella, F.(2006), “Effect of welding parameters on mechanical and micro structural properties of AA6056 joints produced by friction stir welding”, Journal Materials Process Technology Vol.180 pp 364-372. Dehghani M., Amadeh A., Mousavi S.A.A.Akbari (2014) “Investigation on the effects of FSW parameters on intermetallic and defect formation in joining aluminium alloy to mild steel” Material and Science Vol. 49 ,pp. 433-441.

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