Microstructural evolution and fracture mechanisms of steel/Al lap joints by beam oscillation welding with Ni interlayer

This study presents an innovative synergistic strategy that combines laser beam oscillation with a microalloying Ni interlayer to join galvanized steel and aluminum alloy in a lap configuration, effectively addressing the longstanding challenge of brittle intermetallic compounds formation in Fe-Al dissimilar joints. The dynamic interplay between beam oscillation-induced agitation and the microalloying effect of Ni fundamentally reshaped the interfacial metallurgy, facilitating the development of a serrated rather than a blocky interfacial microstructure. Consequently, the interface primarily comprised Fe2Al5, FeAl3, Fe3Ni, AlNi, and Fe2Al5Zn0.4 phases, leading to reduced crack susceptibility and minimized weld seam failure. Notably, this dual-action mechanism resulted in a remarkable enhancement in mechanical performance, with the tensile load increasing by 117.4% (1.08 kN) compared to conventional laser welding, representing a significant improvement in optimizing the strength-ductility balance of steel-aluminum hybrid structures.