Influence of electrode shape and material on shear force and microstructure of resistance spot welded AZ80 magnesium alloy

Resistance spot welding of AZ80 magnesium alloy is challenging owing to limited understanding of how electrode design and welding parameters interact to influence joint microstructure and strength. This study investigates the effects of electrode shape and material on the shear force and microstructure of resistance spot-welded AZ80 magnesium alloy. Three electrode shapes (A, R, and P) and two electrode materials (ZrCrCu and Al2O3Cu) were analyzed at welding currents of 13 kA and 17 kA. Nugget size and failure modes were also examined. The results demonstrate that electrode shape and material significantly affect welding heat, nugget size, and joint strength. The fusion zone (FZ) area increased due to the combined effects of welding current, electrode shape, and material. Higher welding heat modified the FZ boundary microstructure, transitioning from cellular morphologies to columnar dendrites, and eventually to equiaxed dendrites, thereby enhancing joint strength. The highest shear force was observed with an R-shaped ZrCrCu electrode at a welding current of 17 kA. However, excessive welding heat reduced the FZ area due to molten metal expulsion. It also promoted the growth of the brittle β-Mg17Al12 phase in the coarse grain heat-affected zone (CGHAZ), shifting the fracture pattern from nugget pull-out to through-thickness in the base metal and decreasing joint strength. This study concludes that selecting appropriate electrodes can mitigate β-Mg17Al12 phase growth in the CGHAZ, highlighting the importance of optimizing welding parameters for improved joint quality in AZ80 magnesium alloy welding.