Investigation of the microstructure and tensile properties of dual-phase steels of different strength levels joined by resistance spot welding

In this study, DP600/DP1000 and DP600/DP1200 resistance spot welding processes were performed. Welding applications were carried out at 7 kA constant welding current and 5 different electrode pressures (2, 3, 4, 5 and 6 Bar). The study focused on microstructural analysis, microhardness and tensile-shear testing. It was found that the welds consisted of 3 distinct regions. The microstructure differed between the regions. The volume fraction of martensite increased in the weld metal. As the electrode pressure decreased, the tensile-shear force increased for both joint types. The failures occurred on the DP600 side. The pull-out type failure occurred in all joints. Hardness values increased from base metal to weld metal in all parameters.