Formation of nanometer scale intermetallic phase at interface of aluminum-to-steel spot joint by welding-brazing process

Interfacial microstructure, joint strength and crack propagation passage of fusion weld-brazed IF steel/Al 5754 joints were investigated. Nanometer scale intermetallic τ5 compound layer and needle-like τ6 ternary phase were observed at the interface with a heat input below 0.27 kJ/cm. Joint shear strength of 150-200 MPa was obtained, which resulted from the formation of an ultra-thin ternary intermetallic phase and the lack of the more brittle binary intermetallic phase at the steel/solidified filler alloy interface.