Investigation of Re-Spot Effects on Mechanical Properties in Resistance Spot Welding of Low Carbon Steel

Resistance spot welding is a widely utilized method for joining metal sheets in the automobile industry. This research studied the mechanical and metallurgical features of welds made of low-carbon steel. Two methods were utilized in implementing welding, single-pulse and second-pulse, to improve the welds' mechanical features. The current of the second pulse was less than the current of the first pulse. The results also demonstrated that the fusion zone in the second pulse consisted of two regions: The primary fusion zone (PFZ) and the second fusion zone formed since the second pulse. The microstructure of the Primary fusion zone is composed of lath martensite and tempered martensite in the second fusion zone (SFZ). It was noticed that the ultimate tensile shear force was 4.36 in a single pulse compared to second-pulse welds, which were 7.46 KN. It was also demonstrated that the hardness magnitudes decreased with the increase of the second pulse current due to the increase in ductility, which negatively impacted the mechanical features.