Friction stir welded butt/lap joints produced from different aluminum 6061-T651 and 7075-T651 alloys will be examined to investigate the effect of various process parameters on mechanical properties. The present work investigated the potential application of the multilayer-multipass friction stir welding (MM-FSW) process to restructure the fabrication of thick-section components using dissimilar aluminum alloy materials, offering a new avenue for industries that require durable and reliable welds. In this study, aluminum 6061-T651 alloy is considered as the base plate with a thickness of 10 mm. The assembly involved stacking two layers and five passes of 3 mm-thick aluminum 7075-T651 alloy plates onto pre-machined stepped grooves in the AA6061-T651 base plate, followed by friction stir welding to create a 10 mm-thick plate. This study investigates the influence of multiple process variables, including rotation speed, traverse speed, and tool pin geometry, on the mechanical properties of the associated butt/lap joint configuration in MM-FS welded dissimilar AA6061-T651 and AA7075-T651 alloys employing Taguchi methods. The optimum tensile strength of 202.65 MPa was obtained at rotational, travel, and tool pin profiles of 1100 rpm, 20 mm/min, and a threadless taper tool pin geometry, respectively, according to the signal-to-noise (S/N) ratio analysis. Additionally, the ANOVA analysis discovered that the rotational speed, tool pin shape, and traverse speed contribute 50.57%, 13.98%, and 35.01%, respectively.
