Research on laser rivet welding to achieve hybrid joining of CFRP and high-strength steel

In this paper, a novel laser rivet welding method is explored for joining CFRP to high-strength steel. The steel plate is locked between steel rivet and CFRP plate by plug riveting, while the connection between steel plate and rivet are obtained by laser welding based on the coupling of the rotation of displacement machine and linear oscillation of laser heat source. The mechanical properties of hybrid joints are assessed by the maximum drawing load, and microstructure, laser energy and temperature field distribution of joints are also investigated. The results show that the hybrid joints are categorized into steel plate/steel rivet welding area (SRA), CFRP plate/steel plate mechanical contact area (SCA) and CFRP plate/steel rivet riveting area (RCA). When laser heat source oscillates in a straight line, the peak value of laser energy reduces, while the transverse area of laser energy increases, which is beneficial to reducing the thermal damage of CFRP plate. At the optimal parameter, the melting depth in SRA is reasonably controlled, the interface temperature in SCA is lower than that of CFRP resin decomposition, and there is no gap in SCA, the fracture mode of joints presents the characteristic of CFRP matrix tearing failure, and the maximum drawing load of joint reaches 2500 N. However, when the melting depth increases to the thickness of steel plate, the heat effect on CFRP plate becomes severe, and the bond between the resin and carbon fiber wire in base material is destroyed, which deteriorates the performance of steel/CFRP joint.