Integrated MCDM based optimization and sensitivity analysis of process signals in friction stir spot welding of dissimilar al 6061 to polycarbonate

The present work addresses the feasibility of friction stir spot welding (FSSW) of metallic aluminum alloy ( Al6061) to thermoplastic polycarbonate ( PC ) sheets using a tapered pin tool incorporating real-time process monitoring with thrust-torque signals. Sensitivity analysis identified axial tool thrust during dwelling as the most superior indicator for joint integrity (≥ 40.1%) due to its role in enhancing interfacial mixing and bonding. The tool revolving speed primarily governs the process stability (≥ 30.9%) and thus predominantly enhances the weld strength (36.5 MPa) through controlled materials stirring. In contrast, dwell time governs the joint ductility (35.5%) by promoting adequate consolidation, while plunge depth dictates the weld hardness (43%) through prolonged deformation along dissimilar interface. An integrated multi-criteria decision-making (MCDM) analysis using ARAS, TOPSIS, and GRA provided consistent optimization trends with a strong rank correlation coefficient (> 0.9), confirming methodological reliability. The findings establish a quantitative framework for optimizing FSSW of dissimilar Al-PC , offering a validated approach for achieving improved mechanical behaviour through balanced process stability.