Resistance spot welding of mild steel to Al-Mg alloy

Abstract

We tried to join steel to Al-Mg alloy using a resistance spot welding method. The effect of Mg in Al-Mg alloy on the strength and the interfacial microstructure of the joint was investigated. Additionally, the effect of an insert metal of commercially pure aluminum, which was put into the bonding interface, on the joint strength was investigated. The following results were obtained. The cross tensile strength of a joint between SS400 steel and commercially pure aluminum (SS400/Al) was high and fracture occurred in the aluminum base metal. However, the strength of a joint between SS400 and Al-Mg aluminum alloy was remarkably low and less than 30% of that of the SS400/Al joint. An intermetallic compound layer developed so thickly at the bonded interface of the SS400/Al-Mg alloy joint that the joint strength decreased. The intermetallic compound layer developed more thickly as Mg content in the Al-Mg alloy increased. Using an insert metal of commercially pure aluminum containing little Mg successfully improved the strength of the SS400/Al-Mg alloy joint and the strength was equivalent to that of the base metal.