Investigation on the influence of FSP parameters on TIG welded dissimilar aluminum joints using RSM and desirability function approach

The present study aimed to explore the cumulative influence of friction stir processing (FSP) parameters, viz., tool spindle speed, traverse speed, and tool tilt angle, on the ultimate tensile strength (TS), ultimate flexural strength (FS), microhardness (MH), and wear rate (WR) of tungsten inert gas (TIG) welded dissimilar AA6061-T6 and AA7075-T6 alloy joints. A face-cantered central composite design (FCCCD) of response surface methodology (RSM) was adopted to design the experiments. Analysis of variance (ANOVA) was employed to identify the significant factors and interaction effects. Multi-response optimization was performed using the desirability function approach to identify parameters that maximize TS, FS, and MH and minimize WR. A confirmation study under optimal conditions were also carried out. FSP significantly improved the TIG joint properties by producing more homogeneous and refined grains (average grain size of 7.75 mu m) without any weld defects. The TS, FS, and MH of TIG welds have increased by 66.87%, 61.95%, and 69.01%, respectively, while the WR decreased by 37.87% after FSP. The fractography revealed that TIG welds lead to a brittle failure mode, and the FSP + TIG welds showed a ductile failure mode. The tool spindle speed was the most influential factor affecting joint properties. With increased spindle speed, the TS, FS, and MH of the joint increased, while the WR decreased. At a spindle speed of 1300 rpm, a traverse speed of 50.75 mm/min, and a tilt angle of 1.76 degrees, the optimum TS of 271.89 MPa, the FS of 298.03 MPa, the MH of 122.23 HV, and the WR of 77.48 mu m were observed.