Microstructural characterizations and mechanical properties in friction stir welding technique of dissimilar (Al-Cu) sheets

Abstract

In this study, dissimilar sheets of commercially available pure aluminium and copper, were butt joined by friction stir welding (FSW) with a thickness of 3mm to explore the effect of tool rotational speeds on microstructures and mechanical properties experimentally. Three rotational speeds of 1000, 1750 and 2000 rpm were applied. The transverse speed and the axial force were kept constant at 30 mm/min and 7.5 KN, respectively. The cylindrical shoulder and conical pin tool was used to produce the joints. Macrostructures, microstructures, X-ray diffraction (XRD), Vickers microhardness and tensile strength were investigated at these different rotational speeds. The joint welded at 1750 rpm was compared with their counterparts and observed significantly better. The formation of relatively hard brittle intermetallic compounds (Al2Cu and Al4Cu9) were observed with the joint fabricated at rotational speed of 2000 rpm. The results of microhardness (HV) at the nugget zone (NZ) were superior to those of thermomechanically affected zone (TMAZ), heat affected zones (HAZ) and the base metal (BM). At the rotational speed of 1750 rpm, the tensile strength was higher than other joints. The examination of fractural surface showed that when the dissimilar joints were affected with increasing rotational speeds or heat input; the fracture mode had a tendency to change from ductile to brittle mode.