An investigation on rivet plug laser welding of hybrid joints between high-strength steel and aluminum alloy

Lightweight materials such as high-strength steel and aluminum alloys are expected to be extensively applied in vehicle body structures. However, the deformation of high-strength steel is difficult, and the reflectivity of aluminum alloy is high, in addition, some problems such as the generation of brittle Fe-Al compounds exist in direct welding of steel/aluminum. In this paper, a reliable hybrid joint between high-strength steel and aluminum alloy is acquired by a novel joining method of rivet plug laser welding (RPLW). The work piece is rotated by the displacement device, and laser beam is oscillated in a straight line by the galvanometer mechanism. The steel/steel metallurgical interface is obtained by controlling the energy distribution of laser beam based on the coupling of rotation and oscillation. The steel/aluminum riveting interface is acquired through the interference fit between the prefabricated hole of aluminum alloy plate and steel rivet. Thus, traditional steel/ aluminum metallurgical joint is transformed into hybrid joint consisting of steel/steel metallurgy joint area (SSA) and steel/aluminum riveting area (SAA). Microstructure and properties of RPLW hybrid joints are analyzed, and laser energy distribution, temperature and flow field of joints are simulated. The results showed that some defects are avoided in SSA and the sealed connection is obtained in SAA. The tensile-shear strength of RPLW hybrid joint reaches 329.27 MPa at the optimal parameter, which is comparable to that of the aluminum alloy base metal. Nevertheless, the un-fused, cracks appear in SAA, or the reduced connection width and the coarse grain in SSA, which will deteriorate the hybrid joint performance.