Microstructural evolution and mechanical performance of laser-welded aluminum alloy/steel joints with a multi-component interlayer

• The introduction of a multi-element interlayer significantly enhanced the mechanical performance of the Al/steel joint. • A refined interfacial microstructure was achieved, featuring multiple intermetallic phases and dispersed nanocrystals. • The joint exhibited excellent ductility, with bending tests showing no cracking. • Fracture analysis indicated that cracks initiated within the intermetallic layer and propagated along weld seam, resulting in a mixed brittle-ductile failure mode The introduction of an Al 80 Mg 14 Zn 2.5 Cu 2.5 Si 1.0 interlayer significantly enhances the mechanical performance of laser-welded Al/steel joints, increasing the tensile strength to 147±3 MPa and improving plasticity, as evidenced by crack-free bending at 127°. This enhancement results from the formation of a refined interfacial microstructure comprising a thin Fe-Al intermetallic layer and nanocrystals dispersed within Fe 18 Al 78 amorphous phases. Lattice mismatch analysis reveals a low mismatch at the ƞ-Fe 2 Al 5 /Fe interface and a high mismatch at the ƞ-Fe 2 Al 5 /Fe 18 Al 78 interface, suggesting that fracture initiates within the ƞ-Fe 2 Al 5 layer and propagates along the ƞ-Fe 2 Al 5 /Fe 18 Al 78 interface toward the weld seam, ultimately leading to a mixed brittle-ductile fracture mode.