Stationary shoulder friction stir welding of Al–Cu dissimilar materials and its mechanism for improving the microstructures and mechanical properties of joint

Abstract

The fundamental reasons for the poor mechanical properties of the Al–Cu conventional friction stir welding (CFSW) joints are serious material mixing and excessively thick intermetallic compounds (IMCs). In this study, stationary shoulder friction stir welding (SSFSW) was innovatively applied to join the Al–Cu dissimilar materials. The results indicated that the material mixing and the IMCs growth were successfully suppressed. Compared with the CFSW, the grains in the SZ of the SSFSW joint were refined and the plastic deformation in the SZ was enhanced. This was attributed to the frictional driving force of SSFSW was higher than that of CFSW. The mutual diffusion reaction of Al and Cu elements was inhibited owing to the lower heat input of the SSFSW. The mechanical properties of the joints were significantly improved by the SSFSW. The tensile strength of the optimal SSFSW joint was found to be 211.4 MPa which is 15.1% higher than that of the optimal CFSW joint. Moreover, the fracture occurred in the Al matrix. Reducing the stress concentration in the SZ caused by materials mixing was shown to be the main mechanism for SSFSW to improve the tensile performance of the joint.