Comparative experimental and statistical study of conventional and bobbin tool friction stir welding of AA6061-T6 aluminum alloy

Abstract This study provides a comprehensive comparative analysis of Conventional Friction Stir Welding (CFSW) and Bobbin Tool Friction Stir Welding (BTFSW) for AA6061-T6 aluminum alloy plates. A factorial experimental design was employed to systematically investigate the effects of rotational speed, feed rate, tilt angle or pinching gap, plunge depth, and tool pin profile on joint performance. Regression models for ultimate tensile strength (UTS) and Vickers micro-hardness (HV) were developed and validated through analysis of variance (ANOVA), with all models exhibiting excellent fit ( R 2 > 0.99) and strong predictive capability. The results demonstrate that both CFSW and BTFSW can achieve high-quality, defect-free welds, with CFSW yielding a maximum UTS of 241.52 MPa and BTFSW achieving comparable strength and superior hardness (up to 101.26 HV with a threaded pin). ANOVA revealed rotational speed and tool profile as the most significant factors for UTS, while feed rate and pin geometry predominantly governed hardness. Response surface analysis identified pronounced interaction and quadratic effects, highlighting the importance of simultaneous optimization of multiple process parameters. BTFSW outperformed CFSW in terms of process flexibility, hardness, and defect mitigation, attributed to its symmetrical heat input and elimination of the backing plate. The study delivers validated predictive equations and detailed process maps to guide industrial practitioners in optimizing Friction Stir Welding (FSW) parameters for AA6061-T6, ultimately enabling the tailored achievement of superior mechanical properties and weld integrity.