Dissimilar spot welding joints of AZ31-443 ferritic stainless steel with cover plate

摘要

Magnesium alloy AZ31B sheets and 443 ferritic stainless steel were welded using the technique of resistance spot welding with cover plates under relatively low welding current condition. The interface layer can produce, and the molten Mg can wet the surface of the interface layer of Fe-Al intermetallic compound. Metallurgical study of spot joints shows the cracks situated in only sideway of AZ31 weldment in nugget under long welding time. The cause of cracks considering the Fe-Mg equilibrium phase diagram is associated with the possible thermal behavior of various elements in nugget during spot welding process. The almost amount of reaction product FeAl3 somewhere near the interface can produce almost vertical tension stress, resulting in parallel crack. The tensile strength of the spot joint increases at first and decreases afterward.