摘要：This paper studies the friction stir spot welding of AA2024-T3/AA7075-T6 Al alloys in the ambient and underwater environments by clarifying the nugget features, microstructure, fracture and mechanical properties of the joints. The results show that the water-cooling medium exhibits a significant heat absorption capacity in the AA2024-T3/AA7075-T6 welded joint. Nugget features such as stir zone width, circular imprints, average grain sizes, and angular inter-material hooking are reduced by the water-cooling effect in the joints. Narrower whitish (intercalated structures) bands are formed in the underwater joints while Mg2Si and Al2CuMg precipitates are formed in the ambient and the underwater welded joints respectively. An increase in tool rotational speed (600–1400 rpm) and plunge depth (0.1–0.5 mm) increases the tensile-shear force of the welded AA2024-T3/AA7075-T6 joints in both the ambient and underwater environments. The maximum tensile-shear forces of 5900 N and 6700 N were obtained in the ambient and the underwater welds respectively.
