Investigation of Mechanical Properties on Underwater Friction Stir Welded AA7075 With Pure Copper Dissimilar Joints

Underwater friction stir welding (UFSW) is an emerging technique gaining tremendous significance due to its strong ability to provide superior mechanical properties. This study investigates dissimilar UFSW between pure copper and AA7075 aluminium alloy using three tool pin profiles cylindrical, taper and square, three rotational speeds 1500 rpm, 1600 rpm and 1700 rpm and three welding speeds 10 mm/min, 15 mm/min and 20 mm/min. The weld properties evaluated by tensile, bend, impact, hardness tests, additionally macrostructure, scanning electron microscopy, and optical microscopy were also conducted. Cylindrical pin tool gave good surface finish. The taper pin tool, at 1600 rpm and 20 mm/min, achieved the highest ultimate tensile strength of 90 MPa. It was observed that Vickers microhardness in the weld nugget zone exceeded that of pure copper, ranging from 152 to 162 HV. The maximum absorbed energy of impact test was 17 Joules achieved by square pin tool, 1500 rpm and 20 mm/min. The effective mixing of copper-aluminium with fine grain size in the weld nugget was revealed by scanning electron microscope image. Formation of intermetallic compounds led to brittle fracture at the interface.