Joining thin galvanized low carbon steel sheet to AA6056-T4 by resistance spot welding and adhesive weld bounding

Abstract

Multimaterial assemblies made by resistance spot welding (RSW) process offer a cost-efficient lightweight solution for automotive body-in-white production. However, joining different materials, such as steel (Fe) and aluminum (Al), brings issues due to their different physical properties and low weldability. The present work investigated the evolution of the weld between a thin galvanized low carbon steel sheet and an AA6056-T4 aluminum alloy from macroscopic observations to the evolution of the intermetallic compound layer (IMC) during RSW. Comparisons between homogeneous Al-Al RSW, Fe-Al RSW and Fe-Al adhesive weld bonding for different mechanical solicitations were also realized. Observations showed that the interface for short welding periods is composed of a thin and discontinuous IMC layer. The interface also presents defects that facilitate crack initiation and propagation, leading to an interfacial fracture mode. The different mechanical tests carried out demonstrated that the Al-Al and Fe-Al welds reached a similar maximum tensile load under the shear–tensile test. However, Fe-Al assemblies under cross-tensile test showed poor mechanical properties. The use of an adhesive layer with an Fe-Al spot weld seems to be a potential solution, as it is easily implementable on production lines and improves the mechanical properties of Fe-Al assemblies.