Experimental Investigation of Resistance Spot Welding of Ultrathin IF Steel Sheets

Resistance Spot Welding (RSW) is a powerful tool for overlap joint of thin sheets. The welding procedure contributes to affecting the electrical, thermal and mechanical properties of the sheets. In this article, resistance spot welding of ultrathin IF steel sheets (0.67 mm thickness) have been studied. The IF steel sheets were welded by different welding currents (65, 70, 80, 90 and 100 A). The microstructure of the samples was observed using an optical microscope and the tensile test has been carried out to determine the joint strength and fracture mode. The microstructural observations showed that the grain size increase in the fusion zone by increasing the welding current and the heat-affected zone experienced recrystallization and small equiaxed grains were formed in the heat-affected zone. The base metal keeps its high hardness value from the work-hardening induced by the previous rolling process. Best joint strength was obtained at 80 A welding current (2600 N). The fracture mode changes from partial interfacial failure (at lower welding current) to the pullout with tearing of the sheets (at higher welding current).