Study on microstructure and mechanical properties of Mg‐6Sn‐1Ca and Mg‐7Sn‐1Ca dissimilar magnesium alloys by resistance spot welding

This study investigated the resistance spot welding performance of 1.5 mm thick Mg‐6Sn‐1Ca and Mg‐7Sn‐1Ca magnesium alloys, focusing on the effects of welding current (12 kA to 16 kA) on tensile properties, hardness, fracture morphology, microstructure, and nugget diameter. Optical microscopy and scanning electron microscopy were employed for characterization. The results indicate that the Vickers hardness of Mg‐6Sn‐1Ca was highest in the nugget zone, followed by the heat affected zone, and lowest in the base metal, with the overall hardness peaking at 14 kA. For Mg‐7Sn‐1Ca, the hardness was highest in the base metal and lowest in the nugget zone at 12 kA to 14 kA, while at 16 kA, the nugget zone hardness became the highest and the base metal hardness the lowest. Both alloys exhibited brittle fracture characteristics, with coarse grains in the heat affected zone and finer grains in the nugget zone, while the base metal consisted of fine equiaxed grains. As the welding current increased, the grains in the nugget zone coarsened, and the nugget diameter reached its maximum at 14 kA, decreasing at 16 kA. This research provides a foundation for optimizing the resistance spot welding process of dissimilar magnesium alloys.