Microstructure and properties of laser spiral spot welding and resistance spot welding DC06 galvanized steel joints

The law of laser spiral spot welding and resistance spot welding process on DC06 galvanized steel joints forming, microstructure, and mechanical properties (microhardness and shear properties) was comparative studyed. The results show that both processes can obtain well-formed welded joints, the microstructure of the laser spiral welded head is mainly ferrite (F) and a small amount of carburized body (Fe₃C); the microstructure of the resistance spot welded head is mainly bainite (B) and ferrite (F). Due to uneven heat dissipation inside and outside, the laser spiral spot welding nucleus formed in the center of the equiaxed crystals of low hardness, surrounded by columnar crystals with obvious orientation, hardness values of 130 − 160 HV; resistance spot welding nucleus area cold rate is similar, no obvious hardness gradient, hardness in about 190 HV. The laser spiral spot welding tensile shear load is 10.14 kN, which is 13.02% higher than the resistance spot welding 8.82 kN. The failure form of the joint was analyzed and found that the failure forms of laser spiral spot welding and resistance spot welding were tear-out types and pull-out type respectively. Finally, the effect of lap gap and zinc coating on the mechanical properties of laser spiral joint welds is also discussed.