兩段脈衝電阻點銲對雙相鋼DP980之影響

Multi-step resistance spot welding is an emerging method for the automotive industry that is distinct from conventional one-step resistance spot welding. In this study, one- and two-step resistance spot welding processes were interrogated with respect to tensile-shear tests, weld nugget sizes, hardness distributions, microstructures, and failure modes for different welding parameters. Experimental results reveal that welding nugget size for two-step resistance spot welding was larger than that for one-step resistance spot welding regardless of the welding current. The tensile shear load capacity and the fracture energy for two-step resistance spot welding were better than that for one-step resistance spot welding at lower welding currents. By comparison, at higher welding currents, the tensile shear load capacity and fracture energy were identical for both welding processes because of softening that arises from the higher heat input. Analyses of hardness and microstructure demonstrated that the weldments softened in the partially melted and sub-critical heat-affected zones. Failure mode also depended on the number of pulses that were applied. This study establishes that two-step resistance spot welding increases the extent of softening and alters mechanical properties versus one-step welding due to the greater heat input in the two-step process, especially at higher welding currents.