Optimization of process parameters of RA-GMAW welded joints of dissimilar aluminium alloys by response surface methodology

This study presents an optimization of process parameters and output responses of Rotational Arc Gas Metal Arc Welding (RA-GMAW) welded joints of dissimilar aluminium alloys AA6061 and AA7075 using ER4043 filler. Twenty welds were fabricated using a central composite design (CCD) via response surface methodology. The novelty of this study lies in an integrated experimental–statistical framework that employs a CCD and multi-response optimization to quantify how input parameters govern the output responses of the welded joints. The primary input parameters were welding current ranges of 60 to 90 A, arc rotational speed (ARS) ranges of 800 to 1000 rpm, and gas flow rate (GFR) ranges of 14 to 16 l/min, while the responses included ultimate tensile strength, % strain, Vickers microhardness, and compressive residual stress. The experimental results revealed a tensile strength range of 184.63–269.85 MPa, strain values of 7.24%-11.19%, hardness of 85.63–102.41 HV, and compressive residual stress of 2.3–69.7 MPa. Increasing the ARS and adding more heat to the work yielded maximum tensile strengths of about 270 MPa and hardness above 100 HV, while higher currents coarsened grains. The statistical significance of the quadratic regression models was verified by ANOVA, which yielded coefficients of determination (R2) of 0.9835, 0.9465, 0.9653, and 0.9646 for tensile strength, % strain, hardness, and residual stress, respectively. The optimized values of current, ARS, and GFR were 74.1 A, 809 rpm, and 4.49 l/min, and the optimized values of compressive residual stress, hardness, % strain, and tensile strength were 25.31 MPa, 95.10 HV, 10.01%, and 224.04 MPa, respectively. The maximum joint efficiency compared to AA7075 was 56.66%, and compared to AA6061 was 91.26%, demonstrating effective load transfer while highlighting greater strength degradation in the AA7075.