Optimization of process parameters and material characterization in underwater friction stir welding of dissimilar aluminum alloys using GRA-TOPSIS

This study aims to optimize process parameters for underwater friction stir welding of dissimilar aluminum alloys AA6061-T6 and AA5083-H12 to improve tensile strength and elongation of the weld joints. A multi-criteria decision-making approach is employed, utilizing gray relational analysis and the technique for order preference by similarity to ideal solution. These methods are compared to identify optimal welding parameters, emphasizing their simplicity, ease of use, and computational efficiency. The optimal parameters determined are a tool rotation speed of 1120 rpm and a welding speed of 63 mm/min, which yielded the highest tensile strength and elongation. The findings reveal that welding speed significantly impacts the tensile strength and elongation of the weld joints. The study also includes an analysis of material flow behavior, microstructure, and fracture characteristics. The average grain size obtained at the thermo-mechanically affected zone on the retreating side, stir zone, and thermo-mechanically affected Zone on the advancing side are 8.08 µm, 5.9 µm, and 6.81 µm, respectively. The findings are especially valuable for offshore and marine applications, where high-strength aluminum alloy welding is critical.