Study on microstructure and mechanical properties of resistance spot welded joints Of DP800/Q235 steels for automobile

Abstract In this paper, the resistance spot welding experiment of DP800/Q235 dissimilar steel with 2mm thickness was carried out. The hardness test, tensile property evaluation, and microstructure analysis of the welded joint were performed. The results show that the weld surface is well formed, the heat input increases, and the core diameter increases. The microstructure of the molten core zone is lath martensite, ferrite, and a small amount of Weissner structure; the HAZ on the DP800 side is martensite, ferrite, and a small amount of Weissner structure; and the HAZ on the Q235 side is martensite and ferrite. When the process parameters are 9kA, 32cyc, and 0.4MPa, the maximum tensile shear is 18.30kN, and the fracture mode is ductile or mixed ductile and brittle fracture. The hardness of the weld core zone is the highest, and the hardness of the heat-affected zone decreases.