DEAR-Taguchi analysis of buckling load and shear force in AA6061-T6 friction stir spot welds

Friction Stir Spot Welding (FSSW) is a highly suitable method for joining weldable and non-weldable aluminum alloys. This study aims to determine the optimal welding conditions for FSSW based on two key mechanical outputs: ultimate shear load and buckling load of the weldments. Three variables that significantly influence the welding process are investigated: tool shape, plunge time, and rotational speed. These parameters are studied in the context of welding 6061-T6 aluminum alloy. Each parameter has three levels: pin shape (cylindrical, square, and hexagonal), plunge time (40, 70, and 100 s), and rotational speed (900, 1400, and 1800 rpm). A hybrid approach consisting of Data Envelopment Analysis Ranking (DEAR) and Taguchi experimental design is employed to optimize the welding conditions for the two response variables. The best welding condition obtained is a combination of a hexagonal pin shape, 900 rpm rotational speed, and 70 s plunge time, resulting in a maximum shear force of 4710 N and a maximum buckling load of 4200 N. Additionally, the microhardness of the lower and upper surfaces of the welding zone is measured to provide a comprehensive understanding of the weld quality. These optimized parameters can be applied in the production of high-strength, lightweight structures for the automotive and aerospace sectors, where friction stir spot welding of aluminum alloys is increasingly being adopted.