Welding Defects Occurrence and Their Effects on Weld Quality in Resistance Spot Welding of AHSS Steel

An investigation was made on the weldability of DP600 steel. Influences of electrode force, welding current and welding time on welding defects occurrence were discussed. Metallographic analysis and tensile-shear tests were implemented for weld quality detections. Weld quality dependency on welding defects was studied. It was found that welding defects were easy to occur during spot welding process of DP600 steel, which could be explained by its rich chemistry. Lower electrode force, larger welding current and longer welding time all contributed to the easy occurrence of welding defects. HAZ softening caused by martensite tempering was observed under strong welding parameters. For interfacial failure, welding defects effects on weld quality should not be underestimated. As to pullout failure, the effect of expulsion on weld quality was not that significant as suggested by other researches. In the end, a method was introduced to predict peak load and maximum tensile-shear displacement for pullout failure.