Analysis on the Fracture of Al-Cu Dissimilar Materials Friction Stir Welding Lap Joint

Friction stir welding (FWS) is regarded as a more plausible alternative to other welding methods for Al-Cu dissimilar joining. However, the structure of an FSW joint is different from others. In this study, lap joints of 6061 aluminum alloy and commercially pure copper were produced by FSW, and the effects of rotation rate on macromorphology, microstructure and mechanical properties were investigated. In addition, a fracture J integral model was used to analyze the effect of microstructure on the mechanical properties. The results revealed that the macrodefect-free joints were obtained at a feed rate of 150 mm/min and 1100 rpm and that the failure load of the joint reached as high as 4.57 kN and only reached 2.91 kN for the 900 rpm, where tunnel defects were identified. Particle-rich zones composed of Cu particles dispersed in an Al matrix, and "Flow tracks" were observed by the EDS. The J integral results showed that the microdefects on the advancing side cause serious stress concentration compared with the microdefects located on the Al-Cu interface, resulting in the fracture of the joints.