Effect of alternating magnetic field on microstructure and performance for dissimilar welding-brazing of galvanized steel to 6061 aluminum alloy in an overlapping configuration

•The evolution of interfacial compounds under different magnetic fields was deeply explored.•Formation mechanism of HAZ cracking in steel/Al joints was also clarified.•It may be applied to achieve high performance joints of dissimilar materials in manufacturing. In this work, we presented laser welding-brazing of Al/steel dissimilar alloys with alternating magnetic field augmentation. Interfacial microstructures, element distribution and mechanical properties of the joints welded at different magnetic field frequencies were carefully investigated. Formation mechanism of HAZ cracking was also discussed. The results showed that Zn element in the filler metal promoted the occurrence of Fe2 (Al, Zn)5 phase instead of Fe-Al intermetallic compounds at the steel interface, which greatly improved interfacial performance. Columnar crystals at the Al interface were broken into fine dendrites with the aid of the electromagnetic force in the molten metal. Zn-rich products at grain boundaries weakened the cohesions between grains and increased the crack susceptibility. It has been also found that formation of HAZ cracking mainly goes through four stages involving crack inoculation, crack nucleation stage, crack initiation and crack growth. The tensile force and elongation of welded joints subjected to an alternating magnetic field can be increased by 126% and 144%, respectively, compared to that of joints laser welded in the shortage of a magnetic field. Significant improvement in joint performance is attributed to the precipitation of Fe2 (Al, Zn)5 phase and transformation of interface shape.