The Mechanisms of Resistance Spot Welding of Magnesium to Steel

A novel technology has been developed for the resistance spot welding (RSW) of magnesium to steel producing joint strength as high as 95 pct of that of Mg to a Mg joint. The mechanisms of the dissimilar joining have been investigated using mechanical testing and metallurgical examination employing scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The results show that the mechanisms of joining during RSW of a magnesium alloy to Zn-coated steel involve braze welding, solid-state bonding, and soldering. The joint formation in comparison of RSW of Zn-coated steel with steel, Au-plated Ni, and bare Ni sheets is discussed. A possible expansion of this technology also is suggested.