Spot welding of aluminium clad steel to steel or aluminium: Joining steel to aluminium with an intermediate layer (1st report)

Abstract

Summary This paper describes an investigation of the resistance spot weldability of aluminium clad steel sheet to steel or aluminium sheet as well as joining of a steel to an aluminium sheet with an aluminium clad steel sheet as an intermediate layer. The clad steel sheet was produced by hot‐rolling of steel and aluminium sheet by a direct resistance heating process. The mechanical properties of the clad steel sheet were between those of the steel and aluminium sheet, and the peel strength was satisfactorily high. The materials used in spot welding were a 0.8 mm thick EDDQ steel sheet, a 1.0 mm thick aluminium‐magnesium alloy sheet, and a 0.8 mm thick clad steel sheet which had an aluminium/steel thickness ratio of 1.1:1. Spot welding of steel sheet to the steel side of the clad steel sheet and aluminium sheet to the aluminium side of the clad steel sheet was successful. Spot welding of steel sheet to aluminium sheet using the clad steel sheet as an intermediate layer was also successful. The spot welding thermal cycle, however, led to a thin intermetallic compound layer being formed at the steel/aluminium interface of the clad steel sheet. The suitable welding current ranged between the values suitable for steel to steel and aluminium to aluminium. The tensile shear strength and U‐tension strength of steel/clad‐aluminium joints were higher than those of steel‐aluminium direct joints and near those of aluminium‐aluminium joints. These mechanical test results suggest that the presence of an intermetallic compound layer at the steel/aluminium interface of the clad steel sheets is not detrimental to the strength of the steel‐clad‐aluminium joints. The fracture mode of these joints varied with the welding current.