Influence of tool rotational speed, welding speed, and tool pin diameter on mechanical properties of friction stir-welded AZ31B magnesium alloy

Magnesium alloys are increasingly used in the automotive and aerospace sectors because of their excellent strength-to-weight ratio and other favourable properties. Among manufacturing operations, welding and machining remain key factors influencing the production of components for the automotive and aviation industries. In this study, the friction stir welding of a 6 mm thick Mg-AZ31B alloy plate was systematically investigated to examine the effects of tool rotational speed, welding speed, and tool pin diameter on weld quality using an H13 steel tool. Experiments were designed using Taguchi L9 orthogonal array, followed by ANOVA and TOPSIS for single-response and multi-response optimization. The optimal combination of parameters determined by TOPSIS was tool rotational speed-1000 rpm, welding speed-60 mm/min, and tool pin diameter-6.0 mm, which resulted in tensile strength of 190.5 MPa, 9.28% elongation, and 46.6 HV microhardness. The ANOVA results show that tool rotational speed has the most significant contribution to the mechanical performance of the friction stir-welded AZ31B joint, followed by welding speed and tool pin diameter. These findings emphasize that proper selection of FSW parameters could substantially enhance the weld quality and mechanical properties of the AZ31B Mg alloy joint.