Effect of welding current on microstructure and properties of 2GPa press-hardened steel joints by RSW

In the present study, the resistance spot welding (RSW) test was carried out on 1.5-mm-thick 2GPa press-hardened steel (PHS1800) using medium-frequency welding machines. The effects of welding current (6–10 kA) on the microstructure and mechanical properties of welded joints were investigated. The results indicated that with the increase in welding current, the nugget diameter and electrode indentation depth of the welded joint increased. However, obvious splash occurred at 10 kA. Under different welding current conditions, the microstructures of the tempering zone in each part of the welded joints were different, resulting in an increase in the softening degree in the softened zone accompanying the increase in the welding current. When the welding current was 9 kA, the tensile-shear strength reached a maximum value of 22 kN. The failure mode of the welded joints was partial interfacial failure when the welding current was less than 7 kA. In addition, the failure mode of welded joints was pullout failure when the welding current was greater than or equal to 7 kA. However, the fracture morphology of all samples was a typical ductile fracture. The critical nugget size (D_cr) was set at 5t^0.5(where t is the sheet thickness) to ensure that the sample failure mode was pullout failure. The peak load of the welded joints in both failure modes was not affected by the softened zone of the heat-affected zone.