Study on laser/DP-MIG hybrid welding-brazing of aluminum to Al-Si coated boron steel

Abstract The aluminum-steel hybrid assemblies would simultaneously reach the engineering aim to reduce weight and improve fuel efficiency. However, it is of great challenge to join aluminum to steel due to the great difference in thermal properties and the formation of IMC. In this work, a better joint between aluminum and Al-Si coated boron steel was successfully achieved using laser/DP-MIG hybrid welding-brazing. The examinations of welding appearance, macrostructure, interface microstructure, and tensile tests were carried out. The laser/DP-MIG hybrid welding-brazing could simultaneously strengthen metallurgic bonding and wettability compared to conventional MIG joint. The plasma characteristics of laser/DP-MIG hybrid source contributes to suppress the formation and growth of IMC. Three phases and its formation mechanism were demonstrated in detail: τ5-Fe2Al8Si, θ-Fe(Al,Si)3, and η-Fe2(Al,Si)5. The average joint strength of laser/DP-MIG was 271.8 N/mm whereas that of conventional MIG was 138.4 N/mm. The substantial adhesion area at the brazing interface and the brittle IMC is the two main factors in determining the tensile strength.