Study of friction stir welding parameters in conventional milling machine for 6082-T6 aluminium alloy *

129 Study of friction stir welding parameters in conventional milling machine for 6082-T6 aluminium alloy * S Gopi and K Manonmani Department of Production Engineering, Government College of Technology, Coimbatore, Tamilnadu, India ABSTRACT: A conventional milling (CM) machine is capable of inducing the same axial force parameter as that of a friction stir welding (FSW) machine. In a CM machine, tool shoulder penetration, an alternate parameter instead of axial force of FSW machines, was used to carry out FSW joints. The process parameters such as spindle speed, welding speed, shoulder penetration, pin profile and shoulder profile at five levels were studied. With Taguchi orthogonal array, the process parameters were optimised to maximise the tensile strength of the FSW joint. From the investigation, it was found that the 1100 rpm spindle speed, hexagonal pin profile and 0.15 mm shoulder penetration reveals good results. Metallographic studies were carried out with a scanning electron microscope and energy dispersive x-ray spectrometer. KEYWORDS: Friction stir welding; milling machine; shoulder penetration; aluminium alloy 6082-T6; Taguchi method. REFERENCE: Gopi, S. & Manonmani, K. 2012, Study of friction stir welding parameters in conventional milling machine for 6082-T6 aluminium alloy, Australian Journal of Mechanical Engineering, Vol. 10, No. 2, pp. 129-140, http://dx.doi.org/10.7158/m12-016.2012.10.2. 1 INTRODUCTION Friction stir welding (FSW) is a solid state welding process invented by Thomas et al (1991) at TWI, UK. In this process, the external tool has a probe and shoulder that stirs the material to be joined and forges the surface. FSW combines forging and extrusion processes. The probe and shoulder extrudes the material by stirring and the shoulder alone forges the material surface to be joined. Aluminium material was profitably developed and the welding plates from 1 to 75 mm thickness can be welded in a single pass by the FSW process. Most of the research works considered the parameters of the FSW machine and tool geometry (Peel et al, 2003; Leal & Loureiro, 2006; Rajakumar et al, 2010; Merzoug et al, 2010; Elangovan & Balasubramanian, 2009). The parameters of the FSW machine are tool rotation speed, welding speed and axial force. Some of the parameters of the FSW * Paper M12-016 submitted 14/02/12; accepted for publication after review and revision 22/06/12. Corresponding author S Gopi can be contacted at gooobi@gmail.com. tool geometry are probe or pin diameter, shoulder diameter to probe diameter ratio, probe length, and probe profile (Padmanaban & Balasubramanian, 2009). However, the conventional milling (CM) machine offers tool rotational speed and welding speed through its spindle speed and table feed; only the axial force is difficult to attain in a CM machine (Milton & Mynors, 2006). In a CM machine, tool shoulder penetration executes the force parameter. When the tool shoulder penetration increases, the axial force also increases. Even in a FSW machine axial force is difficult to retain throughout the welding. But the shoulder penetration/plunge depth is maintained (Zimmer et al, 2010). In tool geometry, shoulder profile is considered as a parameter. The inclination angles given for shoulder are 5 inward and 5 outward, 10 inward and 10 outward along with the flat shoulder. The inward slope extrudes the material at nugget area of the joint, which might increase the tensile strength at the joint. Outward slope closely forges the material at nugget area of the joint, which might also increase the tensile strength. Five parameters along with shoulder penetration Institution of Engineers Australia, 2012 Australian Journal of Mechanical Engineering, Vol 10 No 2

130 Study of friction stir welding parameters in conventional milling... Gopi & Manonmani and shoulder profile were considered and the experiments were conducted as per Taguchi s L 25 orthogonal array (Gopi & Manonmani, 2012). The main objective of the work is to perform tensile test on friction stir welded 6082-T6 aluminium alloy (Moreira & Santos, 2009; Fratini et al, 2009; Scialpi et al, 2007). An attempt has been made to optimise the parameters to maximise the tensile strength of the FSW joint. Also, this paper presents the interaction effects of shoulder penetration with other parameters on tensile strength. 2 EXPERIMENTAL WORK 2.1 Milling machine and parameters The experiments were carried out on a conventional HMT FN2V vertical milling machine with the capacity of 7.5 HP and 1800 rpm. Process parameters of spindle speed, welding speed, shoulder penetration, probe profile and shoulder profile were considered. Trial runs were conducted to find the range of process parameters by varying one of the parameters and keeping the rest of them at constant values. Feasible limits of the parameters were chosen in such a way that the joint should be free from visible defects. The obtained range of process parameters are shown in table 1. Shoulder penetration was increased gradually by five steps of 0.05 mm from 0 to 0.20 mm. 2.2 Friction stir welding tool design and manufacturing High carbon high chromium steel (HCHCr) has been favoured among high speed steel and carbides, to weld aluminium alloy materials due to the aluminium alloy s comparatively low melting point and low hardness. Also HCHCr tools cost comparatively less, are easy to process, easily available, and offer high strength and high hot hardness. These are some of the reasons to prefer HCHCr (Vijay & Murugan, 2010). Double end usage of tools minimises material and cost. The collar or step has been provided in midportion to constrain the axial movement of the tool, and it also offers excess area for transfer of torque, which multiplies the force (Shigley & Mitchell, 1984). Twenty-five various FSW tools were established by the combinations of five different pin profiles of Table 1: Process parameter with their range and values at five levels. Process parameters Range Level 1 ( 2) Level 2 ( 1) Level 3 (0) Level 4 (1) Level 5 (2) Spindle speed or tool rotational speed (SS) 700 to 1500 rpm 700 900 1100 1300 1500 Table feed or welding speed (WS) 0.8 to 4.0 mm/s 0.8 1.6 2.4 3.2 4.0 Shoulder penetration (PE) 0.0 to 0.20 mm 0.00 0.05 0.1 0.15 0.20 Probe profile (PP) Probe profile Square SQ Pentagon PN Hexagon HX Heptagon HP Octagon OC Shoulder profile (SP) 10 to 10 10 5 0 5 10 Figure 1: Various tool profiles.

Study of friction stir welding parameters in conventional milling... Gopi & Manonmani 131 square, pentagon, hexagon, heptagon and octagon; and five different shoulder profiles of 10 inward, 5 inward, flat, 5 outward and 10 outward. Few of them are shown in figure 1. Pin diameter, shoulder diameter to pin diameter (D/d) ratio, and the pin length were taken as 6, 3 and 5.7 mm (Elangovan & Balasubramanian, 2008a), respectively. The pin profiles were cut by spark erosion with WEDM machine, and others, including inward and outward tapers of the shoulders, were obtained in CNC turning centre. The tools were oil hardened to obtain a hardness of 60-62 HRC. 2.3 Friction stir welding of 6082-T6 aluminium alloy The 6082-T6 extruded medium to high strength Al-Mg-Si alloys contain manganese to increase ductility and toughness. The T6 condition is obtained through artificial ageing at a temperature approximately 180 C (Ericsson & Sandstorm, 2003). The alloy 6082 is very common in Europe (Alcoa, 2007), and is intended for structural applications including rod, bar, tube and profiles. Composition of 6082-T6 material has been given in table 2. The tensile specimen was prepared as per ASTM E8M-04 standard (ASTM, 2006) and the base metal has been tested in the universal testing machine. Hardness test also conducted and the Rockwell hardness of the 6082-T6 base material was measured. The results are shown in table 3. 2.4 Taguchi experimental design technique Taguchi experimental design technique (Rose, 2005; Belavendran, 1995; Montgomery, 2001; Box et al, 1978) assesses the influence of factors on response, the means and the signal-to-noise (S/N) ratios for all control factors that are to be calculated. Signals are indicators of the effect on average response, and noise is the measure of deviation from the experiment output. Appropriate S/N ratio must be chosen using previous knowledge, expertise and understanding of the process. In this study, S/N ratio has been chosen according to correction, larger-the-better in order to maximise the response. In Taguchi method, S/N ratio (η j ) in the j th experiment can be expressed as: 10log n j Y 1 2 ijk where n is the number of tests and Y ijk is experimental value of the i th quality characteristics in the j th experiment of the k th test. In present study, tensile strength data is analysed to determine the effect of the FSW process parameters. Experimental results are transformed into means and S/N ratio. 2.5 Metallographic study of the welded specimen Welded plates were cut at mid welded portion and specimens of size 30 10 6 mm was obtained for metallographic study. The samples were prepared as per standard metallographic procedure from the welded plates and macro etched using Keller s solution (Beraha & Shpigler, 1977). The images of the macrograph of the etched specimen were captured using an optical scanner. The metallographic study was carried along various zones of parent metal, heat affected zone (HAZ), thermomechanically affected zone (TMAZ) and weld nugget across the cross-sections of friction stir welded specimens using a scanning electron microscope (SEM) and energy dispersive x-ray spectrometer (EDS) (Liu et al, 1997; Rhodes et al, 1997; Flores et al, 1998; Su et al, 2003; Sutton et al, 2002). 3 RESULTS AND DISCUSSION Aluminium 6082-T6 alloy was cut from the extruded strip to dimension 200 76 6 mm. Square butt joint configuration has been prepared to fabricate FSW joints with the designed non-consumable double ended HCHCr tool. The fixture has been specially designed to arrest the material in longitudinal and traverse direction. The FSW was performed in CM machine as per the L 25 orthogonal array shown in table 4. The material has been welded according to specification of welding parameters and the corresponding tensile strength has then been calculated. The results of the tensile tests were tabulated and were used as input for optimisation of the welding parameters (MINITAB, n.d.). The tensile strength in terms of means and S/N ratios are shown in the table 4. For each welded plate, three specimens Table 2: Chemical composition of the 6082 alloy (wt%). Reference Si Fe Cu Mn Mg Cr Ni Zn Ti Typical 0.7-1.3 0.50 0.10 0.4-1.0 0.6-1.2 0.25 0.20 0.10 Actual batch 1.0 0.20 <0.02 0.48 0.65 <0.01 <0.01 0.01 0.02 Table 3: Mechanical properties of the 6082 alloy. Yield strength (MPa) Ultimate strength (MPa) Elongation (%) Hardness (HRB) Density (g/cm 3 ) Melting point ( C) 143.11 300.44 11 117 2.70 555

132 Table 4: Study of friction stir welding parameters in conventional milling... Gopi & Manonmani Design table and experimental value of tensile strength (mean and S/N ratio). Test SS (rpm) WS (mm/s) PE (mm) PP (shape) SP ( ) Tensile strength (MPa) S/N ratio (db) Joint efficiency (%) 1 700 0.8 0.00 SQ 10 110.918 40.900 77.5 2 700 1.6 0.05 PN 5 112.658 41.035 78.7 3 700 2.4 0.10 HX 0 118.374 41.465 82.7 4 700 3.2 0.15 HP 5 119.003 41.511 83.2 5 700 4.0 0.20 OC 10 113.694 41.115 79.4 6 900 0.8 0.05 HX 5 118.897 41.503 83.1 7 900 1.6 0.10 HP 10 120.074 41.589 83.9 8 900 2.4 0.15 OC 10 117.838 41.426 82.3 9 900 3.2 0.20 SQ 5 119.133 41.521 83.2 10 900 4.0 0.00 PN 0 118.501 41.474 82.8 11 1100 0.8 0.10 OC 5 115.377 41.242 80.6 12 1100 1.6 0.15 SQ 0 118.874 41.502 83.1 13 1100 2.4 0.20 PN 5 122.690 41.776 85.7 14 1100 3.2 0.00 HX 10 126.031 42.010 88.1 15 1100 4.0 0.05 HP 10 118.505 41.475 82.8 16 1300 0.8 0.15 PN 10 122.167 41.739 85.4 17 1300 1.6 0.20 HX 10 117.449 41.397 82.1 18 1300 2.4 0.00 HP 5 117.576 41.406 82.2 19 1300 3.2 0.05 OC 0 118.105 41.445 82.5 20 1300 4.0 0.10 SQ 5 120.467 41.617 84.2 21 1500 0.8 0.20 HP 0 112.399 41.015 78.5 22 1500 1.6 0.00 OC 5 113.534 41.103 79.3 23 1500 2.4 0.05 SQ 10 118.097 41.445 82.5 24 1500 3.2 0.10 PN -10 123.257 41.816 86.1 25 1500 4.0 0.15 HX -5 122.596 41.770 85.7 (a) (b) Fracture at HAZ Figure 2: Specimen (a) before and (b) after tensile test. were prepared and tested. Figure 2 shows the tensile specimen before and after fracture. The fracture has occurred mostly in the HAZ on the retreating side of the weldment. Analysis of the mean for each of the experiments gives better combination of parameter levels. The mean response refers to average value of performance characteristics for each parameter at

Study of friction stir welding parameters in conventional milling... Gopi & Manonmani 133 different levels. Mean for one level is calculated as average of all responses that are obtained within that level. Mean response of raw data and S/N ratio of tensile strength for each parameter at levels 1, 2, 3, 4 and 5 were calculated and are presented in table 5. When analysing means and S/N ratio of various process parameters, it was observed that the larger S/N ratio corresponds to better quality characteristics. Therefore, optimal level of process parameter is at the level of highest S/N ratio. Figure 3 shows that the mean effect and S/N ratio calculated by statistical software, which indicate that the tensile strength was maximum while using the parameter level of 1100 rpm spindle speed, hexagonal pin profile, 3.2 mm/s weld speed, 0.15 mm shoulder penetration and 10 outward shoulder taper. Also the response table ranking, given in table 5, interprets the degree of parameter which influences on response. The first dominant parameter was spindle speed, which was followed by welding speed, pin profile, shoulder penetration and shoulder profile. Tensile strength TS OA = SS 3 + WS 4 + PP 3 + PE 4 + SP 5 4T where SS 3 = 1100 rpm spindle speed, WS 4 = 3.2 mm/s weld speed, PP 3 = hexagonal pin profile, PE 4 = 0.15 mm shoulder penetration, SP 5 = 10 shoulder profile, and T = overall mean of the experimental values. The established linear equation that predicts the maximum value of tensile strength at optimum process parameter levels is: TS OA = SS 3 + WS 4 + PP 3 + PE 4 + SP 5 4T = 120.3 + 121.1 + 120.1 + 120.7 + 120.0 (4 118.249) = 129.204 MPa Analysis of variance (ANOVA) for means has been performed to identify statistically significant process parameters that affect tensile strength of FSW joints as shown in table 6. Results of ANOVA indicate that the selected process parameters were highly Figure 3: Parameter effect charts for (a) S/N ratio and (b) means. (a) (b) Table 5: Response table for S/N ratio and means. Level Spindle speed Welding speed Shoulder penetration Pin profile Shoulder profile S/N ratio (db) 1 41.21 41.28 41.38 41.40 41.40 2 41.50 41.33 41.38 41.57 41.39 3 41.60 41.50 41.55 41.63 41.38 4 41.52 41.66 41.59 41.40 41.50 5 41.43 41.49 41.36 41.27 41.58 Delta 0.40 0.38 0.22 0.36 0.20 Rank 1 2 4 3 5 Means (MPa) 1 114.9 116.0 117.3 117.5 117.6 2 118.9 116.5 117.3 119.9 117.5 3 120.3 118.9 119.5 120.7 117.3 4 119.2 121.1 120.1 117.5 118.9 5 118.0 118.8 117.1 115.7 120.0 Delta 5.4 5.2 3.0 5.0 2.8 Rank 1 2 4 3 5

134 Table 6: Study of friction stir welding parameters in conventional milling... Gopi & Manonmani ANOVA for tensile strength (means). Source Degrees of freedom Sum of squares Mean sum of squares F ratio P value SS 4 82.535 20.634 18.30 0.008 WS 4 85.654 21.414 18.99 0.007 PP 4 41.268 10.317 9.15 0.027 PE 4 79.971 19.993 17.73 0.008 SP 4 27.977 6.994 6.20 0.052 Error 4 4.510 1.128 Total 24 321.915 ANOVA for tensile strength (means) considering the interaction terms SS 4 82.535 WS 4 85.654 PP 4 41.268 PE 4 79.971 SP 4 27.977 SS X WS 16 4.510 SS X PP 16 0.0000 SS X PE 16 0.0000 SS X SP 16 0.0000 WS X PP 16 0.0000 WS X PE 16 0.0000 WS X SP 16 0.0000 PP X PE 16 0.0000 PP X SP 16 0.0000 PE X SP 16 0.0000 Error 156 0.0000 Total 24 321.9154 R 2 = 98.60% R 2 = 91.59% adjusted significant factors affecting tensile strength of FSW joints. The effects of interaction between process parameters were not significant. The determination coefficient R 2 indicates goodness of fit for the model. In this case, R 2 = 98.60% indicated that only less than 1% of total variations were not explained by the model. The value of adjusted determination coefficient R 2 = 91.59% was also high, which adjusted indicated a high significance of the model. Predicted R 2 also made a good agreement with the adjusted R 2. Confirmation experiments were carried out at obtained optimum level setting of process parameters. SS 3, WS 4, PP 3, PE 4 and SP 5 were set and tensile testing was carried out. The tensile strength of FSW aluminium alloy 6082-T6 was found to be 123.17 MPa. This occurred within the confidence interval of predicted optimal tensile strength. 3.1 Effects of spindle speed Figure 3 shows the effect of the tensile strength for various spindle speeds. Tensile strength increases with the increase in the spindle speed. Tensile strength reaches the maximum value at the spindle speed of 1100 rpm. It is nearly constant up to 1100 rpm. On further increase of the spindle speed, the tensile strength decreases due to re-precipitation leading to coarse grain structures in the weld zone (Elangovan & Balasubramanian, 2009). At low spindle speeds, frictional heat generation is less which results in the poor plastic flow of materials. Therefore lower tensile strength is observed. At higher spindle speeds, frictional heat generation is high which enhances the plastic flow of materials. Therefore spindle speed at a range of 900-1300 rpm

Study of friction stir welding parameters in conventional milling... Gopi & Manonmani 135 gives better results. Figure 4 shows the effect of the spindle speed and shoulder penetration on the tensile strength of the joint. Tensile strength in the region 0.05 to 0.15 mm penetration with 900-1300 rpm spindle speeds, gives better results due to the combination of higher penetration with lower speeds and lower penetrations with higher speeds. In higher speeds, frictional heat is high and therefore lower penetrations are sufficient to provide better results of tensile strength. In lower speeds, frictional heat is low therefore higher penetrations offer the secondary heat thereby increasing the plastic flow of materials. 3.2 Effects of welding speed Figure 3 shows the effect of the tensile strength for various welding speed. Tensile strength increases with the increase in the welding speed. Tensile strength reaches the maximum value at 3.2 mm/s welding speed. Further increase in the welding speed decreases the tensile strength. At the highest welding speed of 4.0 mm/s and lowest welding speed of 0.8 mm/s, the lower tensile strengths are observed. This is due to the increased frictional heat and insufficient frictional heat respectively (Lee, 2004). The optimum welding speed is 3.2 mm/s, which has the maximum tensile strength. Figure 5 shows the effect of the welding speed and shoulder penetration on the tensile strength of the joint. Tensile strength in the region 0.10 to 0.15 mm penetration with welding speed around 3.2 mm/s gives better results. In higher welding speeds, frictional heat is low; and therefore higher penetrations will increase the plastic flow of materials thereby providing better results of tensile strength. In lower welding speeds, frictional heat is high therefore lower penetrations are sufficient for better results of tensile strength. Figure 4: Contour plot for the effects of shoulder penetration and spindle speed on tensile strength. Figure 5: Contour plot for the effects of shoulder penetration and welding speed on tensile strength. 3.3 Effects of tool pin profile Figure 3 shows the effect of pin profile on the tensile strength. Hexagonal pin profile provides the higher tensile strength comparing to the other profiles. The tool pin profile with flat faces produces pulsating effect and better plastic flow of materials (Elangovan & Balasubramanian, 2008b). Therefore the tool profiles like square, pentagon also produce the joint with increasing order of tensile strength. Tool profiles like heptagon, octagon have the higher number of face edges which is almost the same as the profile of cylinder. Hence there is no pulsating effect which leads to the poor tensile properties. Figure 6 shows the effect of the various pin profiles and shoulder penetration on the tensile strength of the joint. Tensile strength in the region 0.10 to 0.15 mm penetration with square, pentagon and hexagon gives better results. The cross sectional area of probe in stirring zone for the profiles of square, pentagon and hexagon are in the increasing Figure 6: Contour plot for the effects of shoulder penetration and pin profile on tensile strength. order. Square profile has the lesser cross sectional area and therefore lower penetration is sufficient to overcome the frictional resistance for better stirring. In hexagonal profile, cross sectional area of frictional surface is high therefore higher penetration is required. Pentagon profile has the cross sectional area in between square and hexagonal profiles hence intermediate penetrations are sufficient for better results of tensile strength.

136 3.4 Study of friction stir welding parameters in conventional milling... Gopi & Manonmani Effects of shoulder penetration Figure 3 shows the increase in the shoulder penetration, which leads to the increase in the tensile strength up to the maximum value. Further increase in the shoulder penetration decreases the tensile strength. At the highest shoulder penetration and lowest shoulder penetration, lower tensile strengths are observed. This is due to the increase in plunge depth of tool and lowest frictional heat respectively (Ouyang & Kovacevic, 2002). Higher penetration leads to increase the plunge depth/ plunge force. This offers excess heat generation and more plasticised zone around the probe and region under the shoulder. Lower penetration lowers the area of contact of frictional surfaces. This reduces the plunge force and frictional heat generation. The optimum shoulder penetration is 0.15 mm, which has the maximum tensile strength. 3.5 Contour plot for the effects of shoulder penetration and shoulder profile on tensile strength. Figure 8: Macroscopic view of FSW specimen. Effects of tool shoulder profile Figure 3 shows the effect of the tensile strength for the various shoulder profiles. The inward and the outward shoulder profiles provide better results of tensile strength comparing with the flat profile (Badarinarayan et al, 2009). The outer shoulder profile provides increasing order of tensile strength while comparing to the inward profile. This is due to the close forging of the material at the nugget area. The optimum shoulder profile for maximum tensile strength is 10º outward taper. Figure 7 shows the effect of the shoulder profile and shoulder penetration on the tensile strength of the joint. Tensile strength in the region 0.05 to 0.15 mm penetration 10 shoulder profile gives better results. Shoulder profile of 10 outward will have the better results of tensile strength for the wide range of penetration from 0.05 to 0.15 mm. Maximum tensile strength is concentrated at 10 shoulder profile with 0.15 mm shoulder penetration. This shows the interaction effect of shoulder profile and penetration dominates the other parameters interactions on tensile strength. As shown in figure 8, macroscopic view of the FSW specimen gave a clear view of various zones of weld nugget, TMAZ, HAZ and base metal. Weld nugget was finely stirred and narrower in penetration. HAZ was not much wider and did not show any differences among weld nugget and base metal. It was clear from the macroscopic view that FSW specimen was not much affected by heat, which in turn produces narrow penetration and defect free welded joint. From the micro-structural observation by SEM as shown in figure 9 and spectroscopy by EDS results as shown in figure 10, it was clear that the weld nugget zone has harmonised microstructure comparing to other zones. The weld nugget zone had the least magnesium content and magnesium silicide (Mg2Si) particles. Magnesium markedly increases the strength of aluminium without unduly decreasing the ductility. The HAZ had greater silicon Australian Journal of Mechanical Engineering M12-016 Gopi.indd 136 Figure 7: (a) (b) Mg2Si Si (c) Figure 9: Microstructures (SEM images in 100 and 3000 magnifications) of (a) weld nugget, (b) HAZ and (c) parent metal. content, which intensified grey layer dispersion (Mrowka-Nowotnik et al, 2007). The grey layer intensity was lesser in weld nugget because of fewer atomic percentage of silicon in it among the three zones. Silicon, after iron, is the highest impurity Vol 10 No 2 12/11/12 2:53 PM

Study of friction stir welding parameters in conventional milling... Gopi & Manonmani 137 (a) (b) The following observations were made from the studies: Taguchi s orthogonal array has been successfully used to find the optimum level setting of process parameters and response table ranking interprets the degree of parameter influencing on response. As a result the most influencing parameter is spindle speed and the least influencing parameter is shoulder profile. Optimum process parameter levels which are found to achieve greater tensile strength are such as hexagonal pin profile, 3.2 mm/s weld speed, 0.15 mm shoulder penetration, 1100 rpm spindle speed and 10 outward shoulder taper. Weld nugget is finely stirred, narrower and has evenly distributed magnesium silicide (Mg 2 Si) particles. ACKNOWLEDGEMENT (c) The authors are grateful to the Departments of Production Engineering, Mechanical Engineering and Civil Engineering of Government College of Technology, Coimbatore, India, for extending the facilities to carry out the investigation. REFERENCES Alcoa, 2007, Understanding extruded aluminium alloys alloy 6082, 10 December, Cressona, PA, USA, www.alcoa.com/adip/catalog/pdf/extrudedalloy-6082.pdf. Figure 10: Spectrometer (EDS) plot of (a) weld nugget, (b) HAZ and (c) parent metal. level in commercial aluminium. Silicon is used with magnesium at levels up to 1.5% to produce Mg 2 Si. Mg 2 Si has a high melting temperature, low density, high hardness, low thermal expansion coefficient and reasonably high elastic modulus. 4 CONCLUSION Experiments were conducted for various combinations of spindle speed, welding speed, pin profile, shoulder penetration and shoulder profile at five levels in Taguchi s orthogonal array. The strength of the joint was analysed by tensile test and the metallographic study was carried out. ASTM, 2006, ASTM-E08-04 Standard test method for tension testing of metallic materials, Annual book of ASTM standards, Section 3, Vol. 03.01 Metals test methods and analytical procedure, p. 90. Badarinarayan, H., Shi, Y., Li, X. & Okamoto, K. 2009, Effect of tool geometry on hook formation and static strength of friction stir spot welded aluminum 5754-O sheets, International Journal of Machine Tools & Manufacture, Vol. 49, pp. 814-823. Belavendran, N. 1995, Quality by Design, Taguchi techniques for industrial experimentation, Prentice Hall. Beraha, E. & Shpigler, B. 1977, Color Metallography, American Society for Metals. Box, G. E. P., Hunter, W. H. & Hunter, J. S. 1978, Statistics for experiment, John Wiley Publications, New York. Elangovan, K. & Balasubramanian, V. 2008a, Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy, Journals of Materials Processing Technology, Vol. 200, pp. 163-175.

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Study of friction stir welding parameters in conventional milling... Gopi & Manonmani 139 Thomas, W. M., Nicholas, E. D., Needham, J. C., Murch, M. G., Templesmith, P. & Dawes, C. J. 1991, Friction stir butt welding, International patent Application No. PCT/GB92/02203. Vijay, S. J. & Murugan, N. 2010, Influnce of tool pin profile on the metallurgical and mechanical properties of friction stir welded Al-10 Wt% TiB2 metal matrix composite, Materials and Design, Vol. 31, pp. 3585-3589. Zimmer, S., Langlois, L. & Laye, J. 2010, Experimental investigation of the influence of the FSW plunge processing parameters on the maximum generated force and torque, Int. Journal of Advanced Manufacturing Technology, Vol. 47, pp. 201-215.

140 Study of friction stir welding parameters in conventional milling... Gopi & Manonmani S GOPI S. Gopi received his BE degree in Production Engineering from Madras University, Chennai, India, in 2001, and ME degree in Engineering Design from Anna University, Chennai, India, in 2007. He is currently an Assistant Professor at the Department of Production Engineering, Government College of Technology, Coimbatore, India. He is a budding research scholar in the area of welding, especially friction stir welding. He has published few papers in different journals and conferences at national and international levels. His current work covers welding techniques, element design and analysis, operation research, optimisation techniques, and industrial automation. K MANONMANI K. Manonmani received her BE degree in Mechanical Engineering, ME degree in Engineering Design and PhD from Bharathiar University, India, in 1989, 1998 and 2007, respectively. She is currently an Associate Professor at the Department of Mechanical Engineering, Government College of Technology, Coimbatore, India. She has over 20 publications in different journals and conferences. Her current research includes welding techniques, especially high energy welding processes, and well as modelling of welding processes, vibration engineering, non-traditional optimisation, and finite element analysis.

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