Abstract

Achieving high-integrity AA6061-T6 welded joints requires precise control over microstructural evolution and residual stresses. This study introduces a simulation-driven control method using the Coupled Eulerian-Lagrangian (CEL) framework to optimize Underwater Stationary Shoulder Friction Stir Welding (USSFSW) parameters for target properties. Results show that conventional UFSW produces asymmetric stress distributions, high temperatures, and welding flash due to shoulder-induced extrusion. In contrast, USSFSW generates symmetric stress fields, lower peak temperatures, and eliminates flash via localized pin-driven heat input. Residual stress analysis reveals lower longitudinal/transverse stresses with compressive regions, enhancing mechanical performance. Mechanical testing confirms USSFSW improves yield strength, ultimate tensile strength and joint efficiency by 27%, 18% and 14% respectively, albeit with reduced elongation. Strong agreement between simulated thermal fields, defect predictions, and experiments validates the CEL model. These findings establish USSFSW as superior for thermal-sensitive applications requiring high strength, low distortion, and defect-free welds..

Keywords:Thermo-mechanical simulation; Coupled eulerian-lagrangian; Friction stir welding; Stationary shoulder; Underwater welding, Residual stress distribution