Optimizing Friction Stir Spot Welding Parameters for Enhanced Mechanical, Thermal, and Microstructural Properties of PA6

The objective of this study is to systematically investigate the effects of friction stir spot welding (FSSW) parameters—rotational speed, dwell time, and pin diameter—on the mechanical, thermal, and microstructural properties of PA6. PA6 plates (5 mm thick, 30 mm wide, 150 mm long) were welded using an Optimum BF20L milling machine, examining key parameters: rotational speed (762, 1146, 1560 rpm), pin diameter (M10, M12), and dwell time (15 s, 60 s). A full factorial design was employed to analyze their effects. Rotational speed emerged as the most significant factor influencing tensile strength, with an optimal speed of 1146 rpm yielding 72.4 MPa. Dwell time also played a major role, improving flexural strength by 56.5% as it increased from 15 to 60 s (40.6 MPa to 63.6 MPa). Although pin diameter had limited influence on tensile performance, larger pins (M12) promoted higher crystallinity (up to 33.37%) and better thermal distribution. The degree of crystallinity and crystalline lamella thickness (λ) varied, indicating that thermal and structural properties can be tailored through parameter optimization. These findings highlight the potential of FSSW to enhance PA6’s performance characteristics, making it a viable joining method for high-performance applications in the automotive, aerospace, and electronics industries. Further research is encouraged to deepen the understanding of the relationship between welding parameters and microstructural evolution, particularly in relation to crystallization behavior.