This paper deals with the resistance spot weldability of an aluminum clad steel sheet to a steel or an aluminum sheet, and the dissimilar metal joining of a steel to an aluminum sheet with an aluminum clad sheet as an intermediate layer. The clad sheet was produced by hot rolling of steel and aluminum sheets with a direct resistance heating process. The mechanical properties of the clad sheet were between those of the steel and the aluminum sheet, and the peel strength was satisfactorily high.
Materials used in spot welding were a 0.8 mm-thick EDDQ steel sheet, a 1.0 mm-thick aluminum-magnesium alloy sheet and the 0.8 mm-thick clad sheet which has a thickness ratio of aluminum/steel 1.1. The spot welding of the steel sheet to the steel side of the clad sheet and the aluminum sheet to the aluminum side of the clad sheet were successful. The spot welding of the steel sheet to the aluminum sheet by using the clad sheet as intermediate layer was also successful. However, thin intermetallic compound layer was formed at the steel/aluminum interface of the clad sheet due to the spot welding thermal cycle. The suitable welding current ranged between the values suitable for steel to steel and for aluminum to aluminum.
The tensile shear strength and the U-tension strength of steel-clad-aluminum joints were higher than those of steel-aluminum direct joints and close to those of aluminum-aluminum joints. These results from mechanical tests suggest that the existence of intermetallic compound layers at steel/aluminum interfaces of the clad sheets were not detrimental to the strength of the steel-clad-aluminum joints. The fracture mode of these joints varied with the welding current.