Achievement of high-strength Al/Cu dissimilar joint during submerged friction stir welding and its regulation mechanism of intermetallic compounds layer

The control of intermetallic compounds (IMCs) is the key to achieve high-performance Al/Cu dissimilar joints. In the present study, the dissimilar metals of 6061-T6 Al and T2 pure Cu were joined by submerged friction stir welding (SFSW) technology. The results indicated that the peak temperature and dwelling time at high temperature were obviously reduced by applying additional water cooling in SFSW. In comparison to the joint fabricated by normal friction stir welding (FSW), the thickness of IMCs layer at the interface for the SFSW joint was much thinner and its distribution was more uniform, the formation of IMCs was effectively inhibited during the SFSW process. The Al2Cu phase was first formed at the Al/Cu interface, and then Al4Cu9 phase precipitated between Al2Cu phase and Cu. The tensile properties of the Al/Cu joints were significantly improved by the SFSW process. The maximum tensile strength of 255 MPa was obtained in the SFSW joint, which was 41.7% higher than that of the FSW joint. A higher joint efficiency of 91.1% was reached, which was due to the reduced stress concentration at the interface in SFSW caused by the thinner IMCs layer and lower welding heat input. The fracture occurs within Al2Cu phase or along the interface between Al and Al2Cu layer for the FSW joint. In contrast, the SFSW joint fractures at the HAZ on Cu side, showing favorable ductility.