Interfacial microstructure and strength of steel/aluminum alloy lap joint fabricated by magnetic pressure seam welding

Lap joining of low carbon steel (SPCC)/A6111 aluminum alloy was carried out using the magnetic pressure seam welding method. Interfacial microstructure, in particular, an intermediate layer formed at the weld interface was precisely examined using TEM. Tensile tests were also performed for the lap joints. Lap joining was successfully attained in several microseconds with no temperature increase. Weld interface of the lap joint showed wavy morphology and the intermediate layer was observed along the wavy interface. These microstructures are similar to that of the explosive weld lap joint. TEM observation revealed that the intermediate layers consist of fine aluminum grains (around 100 nm) and more finely dispersed intermetallic particles. A6111 matrix close to the weld interface also exhibited extremely refined grain structure. The bonding strength of the joint was quite high and it failed at the parent plate. The multi-phase intermediate layer and grain-refined aluminum layer are considered to be the origin of high interfacial bonding strength of the lap joint.