Multi-response optimization and characterization of friction stir welded dissimilar AA2014/AA6061 aluminium alloys using an innovative lap joint design

The friction stir welding (FSW) of dissimilar aluminium alloys, AA2014 and AA6061, in a butt edge lap joint design is examined in this study. Using the Taguchi L9 orthogonal array and grey relational analysis (GRA), process parameters, i.e., tool rotational speed, traverse speed, and lap length, were optimised in order to examine their impact on mechanical properties such as microhardness, elongation, and ultimate tensile strength (UTS). FSW tool, made of H13 tool steel and heat-treated to a hardness of 61 HRC, consisted of a 5 mm diameter pin and an 18 mm diameter shoulder. Experimental findings indicated that the lap length exerted a significant influence on the UTS, while the tool rotational speed had a notable effect on the elongation and hardness of the specimens. The optimum parameter setting (710 rpm, 25 mm/min, 2 mm lap length) produced improved joint performance. Microstructural studies supported the occurrence of clear weld zones with fine equiaxed grains within the nugget zone due to dynamic recrystallization. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis revealed homogeneous material mixing and elemental diffusion in the stir zone, and also local concentration variations of copper, magnesium, and silicon. The research concludes that the optimized FSW parameters allow for the production of sound welds with favourable mechanical and metallurgical properties.