Parametric Optimization and Characterization of AA6061-T6 and AA7075-T6 Tungsten Inert Gas Welding Joints Subjected to Friction Stir Processing

The current study explored the combined influence of tool rotation speed (TRS), traverse speed (TS), and tool tilt angle (TA) on the response variables, namely ultimate tensile strength (UTS), impact toughness (IT), microhardness (MH), and residual stress (RS). A TIG + FSP welding technique was utilized to fabricate the distinct aluminum alloys AA6061-T6 and AA7075-T6 butt welds as per the face-cantered central composite design. The response surface methodology-based desirability function technique was employed to obtain optimum conditions. A validation test was also performed at optimum conditions, and it was observed that the predicted and measured values were in good agreement. Analysis of variance results displayed that the TRS exerts the greatest influence on the response variables, while the TS and TA exert relatively less influence. Increased TRS values improved joint UTS, IT, and MH while decreasing weld RS magnitude. The TIG + FSP welded joint exhibited an optimized UTS of 277.62 MPa, an IT of 15.82 J, an MH of 124.52 HV, and an RS of 26.89 MPa at a TRS of 1400 rpm, a TS of 50.64 mm/min, and a TA of 1.77 degrees. Electron backscatter diffraction (EBSD) demonstrated that the FZ of TIG joints featured coarse dendritic grain structures, whereas the SZ of TIG + FSP joints possessed ultrafine equiaxed morphology. Pole figures (PFs) exhibited that the fusion region of the TIG joint had notable recrystallization A(1)(*) / A(2)(*) and A/ A textures, while the stir region of the TIG + FSP joint had significant shear deformation B/ B and C textures.