Resistance spot welding of Mg to electro-galvanized steel with hot-dip galvanized steel interlayer

An AZ31 magnesium alloy and electro-galvanized DP600 steel were joined via resistance spot welding (RSW) with a hot-dip galvanized Q235 steel interlayer, and the microstructure and tensile properties of the weld joint with and without the interlayer were compared. The tensile properties of the weld joint with the interlayer were superior to the joint without the interlayer. With the optimal welding parameters, the peak load increased by 30% and the energy absorption was twice that of the traditional RSW joint. During welding, the hot-dip zinc coating on the interlayer melted and was squeezed out of the welding zone under the electrode force, where it assembled out of the nugget to form a soldered region. This soldered region acted as a mechanical seal, which improved the solid-state bonding and braze-welding in the weld joint. This mechanical seal effect cannot form during RSW without an interlayer because the thin and compact characteristics of the electro-galvanized zinc coating make it difficult to squeeze out.