Analysis of process parameters effect on friction stir welding of aluminium 5083 and 6082

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1 Analysis of process parameters effect on friction stir welding of aluminium 5083 and 6082 Jagtar singh a, Lakshmi shankar b ab Department of mechanical engineering,university college of engineering,punjabi university patiala Abstract-In this study,5083-h111 and 6082-T651 aluminum alloy plates in 6mm thickness that are used, particularly for shipbuilding industry were welded using Friction Stir Welding (FSW) method joined by butt joint with the parameters of 1250rpm and 1050rpm tool rotation,65 mm/min and 55mm/min welding speed and 2* tool tilt angle and with the round and rectangular tool tip shape and tool shoulder size 20mm and 22mm.Tensile tests results showed sufficient joint efficiencies and surprisingly high yield stress values and hardness no. by Vickers hardness test showed hardness at welded surface is more than base metal surface. Tensile strength and hardness of welded area is compared within the different tool shapes (rectangular and round), their diameter (20mm and 22mm) and rotational speed (1050rpm and 1250rpm),welding speed(55mm/min and 65mm/min)with base metal. Keywords-friction stir welding,tensile testing,microhardness, elongation, diameter, rotational speed, welding speed. 1 INTRODUCTION Growing concerns on energy saving and environmental preservations increase the demand for lightweight vehicles. Considerable volumes of aluminium have been applied into automotive parts in order to reach the objective of both weight reduction and crashworthiness enhancement.however, further weight reduction of 30% or more is hardly achievable with exclusive dependence on the use of thinner aluminum sheets.multimaterial vehicle structures is an efficient countermeasure against this problem, which necessitates the development of reliable and cost-effective material joining technique. One of the desired pairs is aluminum alloy. Friction stir welding (FSW), which was first developed by The Welding Institute (TWI) in 1991, has a solid-state nature and therefore exhibits certain advantages over traditional fusion welding methods. First, it can significantly avoid solidification related problems, such as oxidization, shrinkage, porosity, and hydrogen solubility. Second, the associated low heat input can effectively inhibit intermetallic compound (IMC) layer formation, which makes it a promising solution for similar material joining. Several studies have been carried out on FSW of aluminum alloy. Aluminum and aluminum alloys have become increasingly used in production of automobiles and trucks, packaging of food and beverages, construction of buildings, transmission of electricity, development of transportation infrastructures, production of defense and aerospace equipment, manufacture of machinery and tools and marine structures with its unique properties such as corrosion resistance, thermal conductivity, electrical conductivity, high strength with low density, fracture toughness and energy absorption capacity, cryogenic toughness,workability,ease of joining [welding (both solid state and fusion),brazing, soldering, riveting, bolting] and recyclability.5083 aluminum magnesium alloys are strain hardenable and have excellent corrosion resistance, toughness,weldability and moderate strength aluminum magnesium silicon alloys are heat treatable and have high corrosion resistance, excellent extrudibility and moderate strength. Especially with their high corrosion resistance and moderate strength, these alloys are widely used in shipbuilding industry both separately and together. Single or multiplefull high speed ferries employ several aluminum alloys, and there is an increasing need to design lightweight structures such as those in aircraft panels and vehicle body shells. Advanced joining technology is an integral part of the manufacturing processes of lightweight structures. Considerable effort has been expended to develop various joining processes and assess their suitability for use in lightweight structures.5454 as sheet and plate (along with 6082 extruded shapes) with all-welded construction.aluminum welding was once considered limited due to the problems associated with welding processes such as oxide removal and reduced strength in the weld and heat affected zone (HAZ).New aluminum welding techniques have been developed and commercialized in significantly over the past

2 years that solves these welding problems. Although Metal Inert Gas (MIG) and Tungsten Inert Gas (TIG) welding processes were developed in 1940s and used in many industries, there were still some joint problems that reduced joint efficiency under % 50.Welding processes without reaching melting temperature or change of phases in the base material.fsw also made all aluminum alloys weldable that were once considered unweldable or limitedly weldable. Further, the reduced welding temperature made joints with lower distortions and residual stresses, enabling improved fatigue performance, new construction techniques, and making possible the welding of very thin and very thick materials. Even though FSW produced joints that were metallurgically, environmentally and economically better than other welding processes, owing to the typically high forces in the process, FSW was usually practiced as a fully mechanized process, increasing the cost of the equipment compared to arc welding techniques, while reducing the degree of operator skill required. Inspite of all of its benefits and studies that has showed better performance than fusion weldings, FSW has not been still widely commercialized around world, owing to lack of industry standards and specifications, design guidelines and design allowable, informed workforce and high cost of capital equipment and licensing.fsw produces welds by using a rotating, nonconsumable welding tool to locally soften a work piece, through heat produced by friction and plastic work, thereby allowing the tool to stir the joint surfaces. The tool serves three primary functions, that is, heating of the work piece, movement of material to produce the joint, and containment of the hot metal beneath the tool shoulder. As of its invention, FSW process has been found very interesting and widely studied. Many studies have been carried out to understand and analyze the effect of process parameters and tool geometries on microstructural and mechanical properties and formability of joints. Taban and Kaluc et al.(2007) successfully welded 6.45 mm thick 5086-H32 aluminum alloy with TIG, MIG and FSW processes, and their results has demonstrated that the tensile properties of FSW joints were more satisfactory than fusion welded joints[1]. Adamowski and Szkodo et al. (2007) investigated effect of process parameters on the properties and microstructural changes in Friction Stir Welds in the aluminum alloy T6 with 22 different parameters and found that FSW welds is directly proportional to the tool rotation and welding speeds [2]. Cavaliere et al.(2008)studied effect of varying welding speeds on mechanical and microstructural properties of FSWed AA6082-T6 aluminum alloy. He welded 4 mm thick plates with 1600 rpm tool rotation and welding speed varying mm/min. He found that welding speed had a threshold points for grain structure, yield stress and ductility that reversed these properties behavior to the opposite side[3]. Palanivel R et al.(2012)studied effect of tool rotational speed and pin profile on microstructure and tensile strength of dissimilar friction stir welded AA5083-H111 and AA6351- T6 aluminum alloys. He used pin profiles of Straight Square, straight hexagon, straight octagon, tapered square and tapered octagon and three different tool rotational speeds and found that straight square pin profile with 950 rpm tool rotational speed yielded highest strength[4]. Moreira et al.(2009) studied to characterize mechanical and metallurgical properties of friction stir welded butt joints of aluminum alloy 6061-T6 with 6082-T6.For comparison, similar and dissimilar material joints made from each one of the two alloys were micro structurally examined, and micro hardness, tensile and bending tests were carried out. He found that AA 6082-T6 aluminum alloy revealed lower yield and ultimate stress as well as lowest hardness value[5].raja Kumar et al.(2011) used 5 different values for each of tool rotational speed, welding speed, axial force, shoulder diameter, pin diameter and tool hardness parameters of FSW to understand influence of FSW process and tool parameters on strength properties of AA7075-T6 aluminum alloy joints. He found that optimum parameters for providing maximum strength properties of 315 MPa yield strength, 373 MPa of tensile strength, 397 MPa of notch tensile strength, 203 HV of hardness and 77% of joint efficiency were 1400 rpm (tool rotational speed), 60 mm/min (welding speed),8 kn (axial force),with the tool parameters of 15 mm (shoulder diameter), 5 mm (pindiameter),45hrc(tool-hardness)[6]. Kulekci_MK et al.(2008) studied effects of tool rotation and pin diameter on fatigue properties of friction stir welded lap joints of AA5754 aluminum alloy. Test results showed that increasing one value while fixing other resulted worse fatigue strengths[7].kulekci_et al.(2008)found that optimization of tool rotation and pin diameter were required to have better fatigue performance. Sarsılmaz et al.(2012)found that best fatigue performance was provided with application of treated cylindrical pin profile,1120 rpm tool rotational speed and 250 mm/min[8].ericsson and Sandstrom et al.(2003)studied influence of welding speed on the fatigue of friction stir welds, and comparison with MIG and TIG welded joints. According to the results, welding speed in the tested range, 216

3 representing low and high commercial welding speed, had no major influence on the mechanical and fatigue properties of the FS welds while FS welds showed better fatigue performance then MIG and TIG[9].Lombard H et al.(2008)used 11 different values of combination of tool rotational speed, feed and pitch values for optimizing FSW process parameters to minimize defects and maximize fatigue life in 5083-H321 aluminum alloy. Their study has demonstrated that rotational speed governs defect occurrence in this 5083-H321 aluminum alloy and that there was a strong correlation between frictional power input, tensile strength and low cycle fatigue life. Although there were many achievements in FSW of aluminum alloys and both 5083-H111 and 6082-T651 aluminum alloys were studied widely as similar alloy FSWed joints, there were not enough studies about these aluminum alloys as dissimilar alloy joints. In contradiction to their wide usage in industry, especially in shipbuilding industry, there was not enough knowledge about these alloys as dissimilar welds. We aimed to contribute to knowledge of friction stir welding of 5083-H111 and 6082-T651 as similar alloy joints and fulfill the deficiency of knowledge about these alloys as dissimilar FSWed joints. Also, we used different parameters from previous studies to vary knowledge about both similar and dissimilar alloy joints of FSWed 5083-H111 and 6082-T651especially in low welding speed. (FSW) is a solid-state joining technique which was invented at The Welding Institute (TWI), UK, in 1991.The FSW has been found to be effective for joining hard-to-weld metals and for joining plates with different thickness or different materials. In the FSW process a nonconsumable rotating tool with a specially designed pin and shoulder is inserted into the abutting edges of work pieces to be joined and traversed along the line of the joint, as shown in Fig.1.As the tool travels, heat is created by the contact friction between the shoulder and the workpiece, and by the plastic deformation of the materials in the stir zone. The high strain and heat energies experienced by the base metal during stirring causes dynamic recrystallization, which is the formation of new grains in the weld zone. 2 Materials and experimental procedure In this study, 5083 and 6082 aluminum alloys were used as base metals. Chemical composition and mechanical properties obtained by tensile test are given in Table 1. Aluminum alloy plates were cut into coupons according to TS EN ISO for butt welding. Mild steel tool with chemical composition of % C, % Mn, % Fe, % < 0.04 P, % 1250 rpm and 1050rpm rotational speed (counter clockwise), 65 mm/min and 55mm/min welding speed. Tensile test specimens were prepared according to TS EN ISO 4136:2012.In order to determine microstructure properties of these joints, the specimens were cross-sectioned perpendicular to the weld interface using a fatigue test specimens were analyzed with <0.05 S, hardness of HRC71 and the dimensions was used as FSW tool. Welding parameters were scanning electron microscopy (SEM). Table 1: Chemical composition and mechanical properties of base metals. Aluminium alloys Chemical composition (in wt. %) :- Element Si Fe Cu Mn Mg Zn Cr Pb Ti Ga V Al Table 2: Mechanical properties of aluminium alloys:- Element Rp0.2 (MPa) Rm (MPa) Elongation

4 Figure. 1- Schematic drawing of FSW process. Figure.2- Plates of an aluminium-5083 & 6082 Figure.3- Tools = 1, 2 Rectangular shape (20,22mm diameter) 3, 4 Circular shape (20, 22 mm Dia) Friction Stir Welding was operated on CNC machine at R&D centre for bicycle & sewing machine Focal point Ludhiana.Welding tools were four types rectangular and circular with the diameter of 20mm and 22mm and tool tip (pin dia) is 6mm of mild steel. Plates of aluminium 5083 & 6082 cut into 16 pieces of each having length-160mm and bredth-80mm and thickness of platess is 6mm.Tool are of four types having circular and rectangular with 20mm and 22mm shoulder diameter and tool tip (pin diameter) length is 6mm.There are two rotation speed 1050mm and 1250rpm (counter clockwise), and welding speed 55mm/min and 65mm/min. One sided welding is done by butt joint as shown fig-4 218

5 Figure. 4- A schematic illustration of FSW butt-joint, the two sheets has been represented transparent to show the pin. 3. Result and discussion 3.1 Tensile testing Tensile testing (tension testing) is a fundamental material science test in which a sample is subjected to a controlled tension until failure. The results from the test are commonly used to select a material for an application, for quality control, and to predict how a material will react under other types of forces. Properties that are directly measured via a tensile testing are ULTIMATE TENSILE STRENGTH, maximum ELONGATION and reduction in area. From these measurements the following properties can also be measured-young s MODULUS, POISSION S RATIO, YIELD STRENGTH and STRAIN-HARDENING characteristics. In tensile testing, dumbbells are cut in the dimensions as shown in fig-5.tensile testing is done on tensile testing machine at INDIANA TEST, CALIBRATION AND CERTIFICATION SERVICES Mohali. For tensile testing, a dumbble shape specimen is prepared which have following dimensions (fig- 10) Overall length(l)-160mm,distance between shoulders-100mm, gauge length(g)- 62mm,diameter or width(w)-18mm,reduced section(a)-80mm,grip section-30mm and width of grip section- 30mm,Thickness of plate (t) - 6mm. Figure.5- Prepared sample of dumbble for tensile testing The most common testing machine used in tensile testing is the UNIVERSAL TESTING MACHINE. This type of machine has two crossheads; one is adjusted for the length of the specimen and the other is driven to apply tension to the test specimen. There are two types: HYDRAULIC POWERED and ELECTROMAGNETICALLY POWERED MACHINES. The machine must have the proper capabilities for the test specimen being tested. There are four main parameters force, capacity, speed, precision and accuracy. Force capacity refers to the fact that the machine must be able to generate enough force to facture the specimen. The machine must be able to apply the force quickly or slowly enough to properly mimic the actually application. Finally machine must be able to accurately and precisely measure the guage length and forces applied; for instance, a large machine that is designed to mesure long elongations may not work with a brittle material that experiences short elongations prior to fracturing. Alignment of the test specimen in the testing machine is critical, because if the 219

6 specimen is misaligned either at an angle or offset to one side, the machine will exert a bending force on the specimen. This is especially bad for brittle materials, because it will dramatically skew the results. This situation can be minimized by using spherical seats or U- joints between the grips and the test machine. From Table-3, tensile strength of welded area of each sample is less than the tensile strength of base metals aluminium 5083 (300MPa) and 6082 (295MPa). Tensile testing (table-3) Sample Rotation speed Welding speed Tool diameter Tensile strength Elongation (%) no. (mm) (MPa) Round Rectangular Rectangular Round Tensile Strength Rotational Speed 20 round 22 rectangular 20 rectangulr 22 round Figure. 6-Tensile strength-rotational speed/welding speed bar chart 220

7 tensile strength rotational speed/welding speed 22mm Round Figure. 7- Tensile strength rotational speed/welding speed of 22mm diameter round shape tool bar chart 3.2 Micro-hardness test Microhardness (indentation hardness) tests are used in mechanical engineering to determine the hardness of a material to deformation. Several such tests exist, wherein the examined material is intended until an impression is formed; these tests can be performed on a microscopic scale. VICKERS HARDNESS TEST This test was developed in 1921 by Robert L.Smith and George E. Sandland at Vickers Ltd as an alternative to the Brinell method to measure the hardness of materials. The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the indenter, and indenter can be used for all materials irrespective of hardness, is to observe the questioned materials ability to resist plastic deformations from a standard source. The Vickers Hardness test (Table - 4) Sample Rotation Welding Tool diameter no. speed speed (mm) Vickers test can be used for all metals. The unit of hardness Vickers pyramid number (HV) Or Diamond pyramid hardness (DPH).The hardness number can be converted into unit of pascals, but should not be confused with a pressure, which also has units of pascals.the hardness number is determined by the load over the surface area of the indentation and nit the area normal to the force, and is therefore not a pressure. From the table, overall or average hardness no. of base metal is 85-95HV02 and overall or average hardness no. of welded area of 5083 and 6082 aluminium is From obtained data or table, we conclude that welded area is harder than base metal surface. So, welding has more strength and more weldability Hardness no. [base metal HV02] Hardness no. [welded metal HV02] Round Rectangular Rectangular Round

8 hardness Round rotation speed Figure 8- Hardness no. rotational speed/welding speed of 22mm Diameter bar chart round shape tool 3. Conclusion In this study, 6mm thick 5083 and 6082 aluminum alloys that used widely in ship building industry were welded successfully with low rotational and welding speed and following conclusions were drawn: In this study, 6 mm thick 5083 H111 and AW 6082 T6 aluminum alloys that used widely in ship building industry were welded successfully with friction stir welding in butt joint with 1050rpm and 1250rpm rotational speed and also welding speed 55mm/min and 65mm/min. In this one sided welding tool have four types round(20mm),round(22mm), rectangular(20mm) and rectangular (22mm).After friction stir butt joint welding, tensile testing and Vickers hardness tests were performed. From the experimental data, best tensile strength and hardness of welded area is of samples which are welded with round shape tool with 22mm diameter and rotational speed 1250rpm and 65mm/min welding speed. So, these welding samples have better welding quality than other samples and welding of base ACKNOWLEDGMENT metals. F Friction stir welding with butt-joint of 6mm thick of aluminium-5083 and 6082 have good welding quality. After welding of two plates for observing tensile strength, tensile strength testing was done. By calculating the data of tensile strength and elongation bar chart and line chart are drawn. From these bar and line charts we investigate that average tensile strength of samples welded with the round tool shape of 22mm diameter, rotational speed 1250rpm and welding speed 65mm/min have more tensile strength than rectangular shape tool welding, and low rotational and welding speed welding and also elongation of these samples is minimum. So, we can say that tensile strength is more at high rotational and speed welding and elongation is minimum and use of round shape tools will be preferred. By Vickers hardness test, average hardness no. of base metal is between and average hardness of welded area is between But hardness no. of samples which are welded with tool of round shape (22mm),rotational speed 1250rpm and welding speed 65mm/min is more than lower rotational and welding speed or rectangular shape of tool. Surface finish of welded area is also good with these parameters and tool. So, we conclude from the bar chart and line chart (hardness no./tool shape or tool diameter and hardness no./rotational speed or welding speed) that high rotational speed and welding speed welding welded with round shape(more diameter) has more hardness other than welding with lower rotational and welding speed and tool with rectangular shape and also from the hardness of base metals. I would like to express my deep and sincere gratitude to my supervisors, Mr.Lakshmi Shankar Assistant Professors in Department of Mechanical Engineering, University College of Engineering, Punjabi University Patiala (Punjab). I offer special regards to Research & Development centre for Bicycle & sewing Machine, focal point Ludhiana especially to Mr. Paramjit Singh (production manager), Mr. Y.A. Khan (workshop head), Mr. Kulwant Singh (Lathe machine operator), Mr. Harbhajan Singh and Mr. Om Prakash (cylindrical grinding machine operators) and Jaswinder kamboj (tensile testing machine operator) for their immense support in performing the practical work 222

9 REFERENCES [1]E.Taban, Comparison between microstructure characteristics and joint performance of 5086-H32 aluminium alloy welded by MIG, TIG and friction stir welding processes, Kovove. Mater, vol. 45, pp , [2] J. Adamowski, Friction stir welds (FSW) of aluminium alloy AW6082-T6 J. Achievements Mater. Manuf Eng, vol. 20(1-2), pp , [3]P. Cavaliere, Effect of welding parameters on mechanical and microstructural properties of AA6082 joints produced by friction stir welding, J. Mater. Process Techno, vol. 200, pp , [4] R. Palanivel, Effect of tool rotational speed and pin profile on microstructure and tensile strength of dissimilar friction stir welded AA5083-H111 and AA6351-T6 aluminum alloys, Mater Des, vol. 40, pp 7 16, [5]PMGP. Moreira, Mechanical and metallurgical characterization of friction stir welding joints of AA6061-T6 with AA6082-T6, Mater Des, vol 30, pp , [6] S. Rajkumar, Influence of friction stir welding process and tool parameters on strength properties of AA7075-TS aluminium alloy joints, Mater Des, vol. 32, pp , [7] M.K. Kulekci, Effects of tool rotation and pin diameter on fatigue properties of friction stir welded lap joints, J. Adv Manuf Technol,vol. 36, pp , [8] F. Sarsilmaz, Evaluation of microstructure and fatigue properties of dissimilar7075/6061 joints produced by friction stir welding, Kovove Mater, vol. 50, pp , [9] M. Ericsson, Influence of welding speed on the fatigue of friction stir welds, and comparison with MIG and TIG, Int.J.Fatigue, vol. 25, pp