Welding speed effects in underwater and conventional friction stir welding of dissimilar aluminum alloy 6061-T6 and 5083-H12 joints

This study investigates the influence of welding speed on the mechanical and microstructural properties of dissimilar aluminum alloy joints (AA6061-T6 and AA5083-H12) joined using Underwater Friction Stir Welding (UFSW) and Conventional Friction Stir Welding (CFSW). The experiments were conducted at a constant tool rotation speed of 1120 rpm and varying welding speeds (20 to 80 mm/min). Results showed that UFSW achieved peak temperatures 13% lower than CFSW. Moreover, the generated peak welding temperature was inversely proportional to welding speed in UFSW and CFSW. Optimal performance was observed at 63 mm/min, where UFSW produced an 89% reduction in intermetallic compound (IMC) thickness and a 21% finer grain size compared to CFSW. Additionally, UFSW joints exhibited a 10.20% increase in tensile strength and a 7% increase in hardness over CFSW. The enhanced cooling effect in UFSW contributed to these improvements, yielding more uniform material flow, refined microstructure, and reduced IMC formation. These findings suggest UFSW as a superior technique for achieving high-quality dissimilar aluminum alloy joints, with significant enhancements in mechanical properties and microstructural refinement.