Study on Weldability and Mechanical Properties of RSW Annular-Nugget Joint. Part 1 — FEM and Characterization Results

The weldability of DP780 steel using resistance spot welding (RSW) was studied by comparing a new ring conductive electrode (RSW-R) and a spherical electrode (RSW-S). The mechanism of the RSW process of annular-nugget on the weldability was analyzed by examining the joint’s current density and thermal field. Finite element analysis revealed that under RSW-R conditions, the annular conductive area expanded the contact area of the faying surface and reduced the nugget’s current density. This characteristic effectively mitigated the risk of expulsion associated with high heat input rates and excessively high liquid metal temperatures while enhancing energy utilization. Mechanical property tests demonstrated that variations in heat input efficiency during nugget growth affected the weldability range, with the annular-nugget joints achieving a 1.5-fold increase in range compared to RSW-S. In addition, when using RSW-R, a larger nugget diameter was achieved with less Joule heating. The maximum nugget diameter increased by 17.38%, and the indentation depth was significantly reduced by 48.65% compared to RSW-S.