Optimizing underwater friction-stir welding parameters for AA356/SiC composites using CoCoSo and MEREC: enhancing joint performance and quality

ABSTRACT This study investigates the underwater friction stir welding (UFSW) of stir-cast A356 reinforced with 2,4 and 6wt% silicon carbide (SiC) to enhance weld joint performance. A hybrid optimization approach integrating CoCoSO (Combined Compromise Solution) and MEREC (Method based on the Removal Effect of Criteria) was employed to determine the optimal welding parameters. The study optimized welding speed (A), rotational speed (B), axial force (C), and SiC content (D) to maximize tensile strength (TS), elongation (E), and microhardness (HV). The L16 orthogonal array with four factors at four levels was implemented, followed by ANOVA. Optimization results significantly improved welding quality, with CoCoSO identifying ideal parameter combinations, MEREC determining influential parameter weights and RSM optimizing the relationship between process parameters and output responses. The optimal process parameters—welding speed (0.57 mm/s), rotational speed (1300 rpm), axial force (6000 N), and SiC content(8wt%)—enhanced joint efficiency from 63.81% to 97.90%. As a result, tensile strength increased from 191.7 MPa to 222.3 MPa, elongation improved from 2.4% to 7.9%, and yield strength from 117.7 MPa to 261.84 MPa. Microstructural analysis revealed that tensile strength decreased with increasing strain on the advancing side(AS) due to tool deviation ranging from −1.6 to 1.6 mm. These findings validate the effectiveness of optimization in UFSW, demonstrating their potential for achieving superior mechanical properties and defect-free welds in SiC-reinforced aluminum alloys.