Experimental and parametric study on the dissimilar joining of Mg/steel sheet by a low power resistance spot welding machine

The use of dissimilar structures is increasingly attracting attention in various industries, particularly the automotive sector. Metals such as magnesium and aluminum play a significant role in reducing vehicle body weight, which contributes to lower fuel consumption and decreased air pollution. While low-power spot welding machines are commonly available in some industries, their application for magnesium resistance spot welding (RSW) remains limited. This study investigates the effects of key RSW parameters on joining dissimilar sheets: AZ31B magnesium alloy sheets with a thickness of 2 mm and electro-galvanized steel sheets (St14) with a thickness of 1 mm, using a low-power spot welding machine. Three critical parameters – welding time, electrode force, and welding current – were selected for the study. Additionally, the depth of the spot weld indentation was examined. Tensile shear testing was employed to evaluate the joint strength, and the response surface method (RSM) was used to design and conduct the experiments. The results indicate that using a DC welding machine operating at a current of 19 kA, 18 welding cycles, and an electrode force of 170 dN, an acceptable joint strength of approximately 5000 N was achieved through diffusion bonding. Under these conditions, the indentation depth on the magnesium side was measured to be approximately 1.2 mm. and the failure mode observed in the welded samples was identified as interfacial fracture.