Friction Stir Process of Magnesium Alloys M

Research Article Volume 9 Issue No. 5 Friction Stir Process of Magnesium Alloys M. Sivamanikandan1, K. Panneerselvam2, R. Rajeswaran3 Prist University,Thanjavur, Tamil Nadu, India

Abstract: The mechanical and micro structural properties of of magnesium alloy resulting from the friction stir processing(FSP)were analysed in the present study the tensile properties were evaluated at room temperature in the longitudinal direction respect to the processing one and also performed at higher temperatures and different strain rates in the nests on parallel to the processing direction in order to analyse the super plastic properties of the recrystallized material and to observe the differences with the parent material as the function of the strong grain refinement due to the friction stir process the dynamic recrystallized structure of the material was observed by employing optical and electron microscopy. The high temperatures behaviour of the material was studied in the parallel direction by means of tensile test in the temperature and strain rate ranges of 150 - 300°C and 10 -2 to 10 -4 s - 1 respectively. the deformation behaviour in the high-temperature regime (275 to 300°C) is related to the grain boundary sliding (GBS)acting in the material parallel to the tensile direction, differing strongly from the lower temperature one in which the deformation is strongly link to grain triple junction fracture.

Keywords: Friction stir processing, Friction stir processing machine, magnesium alloys, AE42 alloy, Berkovich indenter.

I. INTRODUCTION The following unique features of friction stirring is utilised to develop new processes: Friction stir processing is an emerging processing technique  Low amount of heat generated, based on the principles of friction stir welding. Friction stir  Extensive plastic flow of material, welding is a relatively new joining process developed initially  Very fine grain size in the stirred region, for aluminium alloys, by The welding institute(TWI)of UK  Random mis orientation of grain boundaries in stirred (Thomaset al., 1991). Friction stir processing is a method of region, changing properties of a metal through intense localised  Mechanical mixing of the surface layer, plastic deformation. this information is produced by forcibly  Large forging pressure inserting a non consumable to into the work piece and revolving the tool in stirring motion as it is pushed laterally Magnesium alloys are mixtures of magnesium and the other through the work piece. it is a solid state joining technique that metals( called an alloy),often aluminium, zinc, manganese, is energy efficient environment-friendly and versatile. It is silicon, copper, RAR exe and zirconium. Magnesium is the being touted as the most significant development in metal lightest structural metal. Magnesium alloys have a hexagonal joining in a decade. The basic concept of friction stir lattice structure which affect the fundamental properties of the processing is remarkably simple. A rotating tool with pin and alloys. Plastic deformation of the hexagonal lattice is more shoulder is inserted in the material to be joined and traversed complicated than in cubic latticed metals like aluminium, along the line of interest. The heating is localised and copper and steel. Therefore magnesium alloys are typically generated by friction between the two land the workpiece,with used as castalloys, but research of wrought alloys has been additional adiabatic heating from metal deformation. A more extensive since 2003.cast magnesium alloys are used for processed zone is produced by the movement of material from many components of modern cars and magnesium block the front of thepin to the back of the pin. As mentioned later engines have been used in some high performance vehicles; between and shoulder of the two can be modified in a number Cast magnesium alloys are used for many components of to ways to influence material flow and micro structural modern cars, and magnesium block engines have been used in evolution. Figure 1 shows the friction stir processing. some high-performance vehicles; diecast magnesium is also used for camera bodies and components in lenses.

Properties Magnesium is a ductile silver-white, chemically active metal with hexagonal close packed crystalline structure. It is malleable when heated. It was very slowly with cold water. It is not affected by driver but tarnishes in moist air. A Magnesium fire cannot be extinguished by water, since water reacts with hot magnesium and releases hydrogen. Magnesium reacts with halogens and with almost all acids. It is a powerful reducing agent and is used to free other metals from their anhydrous halides.

Uses of magnesium Burning magnesium produces white light this makes it ideal Figure.1. Friction Stir Processing for firework sparklers, flares and flash photography. It is also

International Journal of Engineering Science and Computing, May 2019 22429 http://ijesc.org/ functions as an agent to produce uranium out of salt. the representation of fixture used for FSP is shown in figure elements ions are necessary for every living organism. That is 2.Fixture was connected to to an external chiller unit through why magnesium salt is included in fertilizers and food. In inlet and outlet pipes. It has a rectangular cavity for flow of many cases, magnesium bromide is utilised as a sedative. the cooling fluid (methanol at 20°C) underneath the surface. Thus the fixture was used for clamping the FSP specimen as II. EXPERIMENTATION well as for cooling it. Details about the coding mechanism are There are many promising developments in new design. In given in an earlier publication. Rectangular specimens having addition several recent studies have focused on improving dimensions of 80 mm,40 mm, 3 mm were prepared from the conventional alloys by various thermo-mechanical processing alloy ingot. The FSP tool was cylindrical in shape with year 12 methods. Friction stir processing (FSP) is one such method, mm shoulder diameter 4 mm in diameter and 2.7 pin length. where the microstructure of can be refined by severe plastic The FSP parameters used comprises toolrpm of 900, linear deformation. Number of studies has demonstrated the speed of 60 mm min-1, and plunge depth of 0.3mm. FSP was utilisation of FSP for grain refinement in magnesium based under single pass hustle as double pass condition. During the alloys. Composite materials are increasingly being utilised in double pass, fsp tool was traversed two times over the same automotive parts. Because of their strength stiffness to weight park in the same direction fsp was done under the following ratio, typical composite bars are about 30 to 40% lighter than conditions: Single pass FSP with under-surface cooling at Steel components. FSP was carried out on computer numerical 20°C (SPUSC) Double pass FSP with under-surface cooling at control (CNC) vertical milling machine. A Schematic 20°C (DPUSC). Cooling was done after second pass only.

Figure.2. Schematic representation of the fixture used for friction stir processing

Friction stir processed (FSP) specimens were sectioned in The test parameters comprises a peak load of 1000mN with 10mm - 3mm size along the cross section. The samples were loading and unloading rates of 100mNs-1. ground downby 4000 grit followed by diamond polishing. The ground and polished samples were further polished using III. RESULTS AND DISCUSSION colloidal silica and ethanol. Further polishing was carried out on an ion-beam polishing machine (precision etching Strain Hardening system).Optical microscope and electron back scatter In order to get quantitative information about strain hardening diffraction (EBSD, FEI Quanta 3D FEG (Field emission the strain hardening exponent was calculated from the results gun))were used for the determination of grain structure. For of Nano intonation the load displacement curve for each of the SPUSC specimen, EBSD scans were taken at three different investigator case was used to determine the maximum locations: 0.5, 1.5 and 2.5mmdelivery of surface aunty centre penetration depth(hmax) as well as a residual depth(hr).The of the processed zone. However for DPUSC, EBSD scan at value of strain hardening exponent was calculated within the 0.5mm location could not be indexed due to severe nugget zone at 2.5 mm location. very fine grained friction stir deformation near the shoulder region during the second FSP processing specimens show a higher tendency for work pass. Therefore, EBSD results for DPUSC have been reported hardening compared to the coarse grained as cast AE42 alloy. for two locations only:1.5and 2.5mmbelow the top surface. Contrary to the observation in the current study, some of the The scan area for FSPed specimens was 50mm with a step previous investigations have reported that the strain hardening size of 0.1mm.The data was analysed using TSL OIM capability diminishes with the grain size reduction. These 6.1.3software in which the obtained kikuchi patterns were authors have reported that the friction stir processing indexed for the determination of grain size distribution and specimen demonstrated reduced train availability compared to (0001) pole figures. Transmission electron microscopy (TEM) the base material. The plot showing the grain disorientation was done using nano indentation (Make: Hysitron,Inc., distribution for(a) SPUSC (b) DPUSC specimen. Figure 3 Minneapolis USA;Model: TI-900). Test was done using Load displacement curves for the as-cast AE42 alloy, SPUSC standard three sided Berkovich indenter with a diamond tip. and DPUSC specimen at (a) 1.5mm location (b) 2.5mm location across the specimen cross section.

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Figure.3. Load displacement curves for the as-cast AE42 alloy, SPUSC, and DPUSC specimens at (a) 1.5mm location (b)

2.5mm location across the specimen cross-section nearly 20 and 2.9mmrespectively.Thus the grain structure got The optical images of the cast AE42 as well as SPUSC considerably refined after FSP.EBSD maps as well as grain specimen are shown in figure 4. a and respectively. The size distribution for SPUSC at 0.5, 1.5and 2.5mmlocations. average grain size for as cast alloy and SPUSC d found to be

Figure.4. Shows Optical images of (a) as-cast AE42 (b) the nugget region of Mg alloy AE42 subjected to friction stir processing

Tensile properties: Figure 5 shows the appearance of the BM exhibit airplay under this condition. With increasing the and fsp specimens after tensile test at a strain rate of 5 x 10-4 s tensile temperature, the deformation of the specimen becomes -1. As shown in figure the Elongation to fracture of the FSP more and more uniform. The Elongation to fracture is 489% at specimen is 150% at 573k and necking can be seen clearly on 674K and the Elongation increases to 1050% at 723 K, which the test specimen, indicating that the FSP material does not is the maximum in this study.

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Figure.5. Elongation of FSP specimen at different temperatures& strain rates

IV. CONCLUSION [4]. Mishra,Rajiv," Friction Stir Casting Modification", Friction Stir Processing website (Rolls,MO,U.S.A.: University Tensile test were are also performed at higher temperatures of Missouri-Rolla), retrieved May 16, 2010,"FSP provides an and different strain rates in the nuggets zone parallel to the unique opportunity to embed 'wrought 'microstructure in 'cast' processing direction in order to analyse the super plastic component by localized modification." properties of the recrystallized material and to observe the differences with the parent metal as a function of the strong grain refinement due to the friction stir process. Mechanical properties and microstructure and properties of magnesium alloy resulting from the friction stir processing (fsp)were analysed and were evaluated at room temperature in the longitudinal direction respect to the processing one.The dynamic recrystallization structure of the material was observed by employing optical and electron microscopy. The high temperature behaviour of the material was studied in the parallel direction by means of tensile test.

V. REFERENCES

[1]. Lindemann,J.Schmidt,M.Todte,T.Zeuner (2002). Thermal analytical investigations of the magnesium alloys AM60and AZ91 including the melting range". Thermochim.Acta 382: 269-275 doi:10.1016/S0040-6031(01)00752-3.

[2]. Kiyotaka Masaki,Yasuo Ochi,Toshifumi Kakiuchi (2008)."High cycle Fatigue Property of Extruded Non Combustible Mg Alloy AMCa602". Materials Transaction 49 (5): 1148-1156.doi:10.2320/matertrans. MC2007108., Colin J. (August 2004),"Effects of Friction StirProcessing on the Microstructure and mechanical properties of Fusion Welded 304L Stainless Steel" (PDF), Thesis (Msc) (Provo,UT,US.A.: Brigham Young University, Department of Mechanical engineering), retrieved May 16,2010.

[3]. Friction Stir Processing of Advanced Materials "(PDF),National Transportation Research Centre website, Transportation for the 21st Century (Oak Ridge, TN, U.S.A.:Oak Ridge National Laboratory, U.S. Department of Energy), November 2002, archived from the original on september 29, 2006, retrieved May 16, 2010."

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