Research Progress on Interfacial Evolution and Joint Performance in Dissimilar Al/Mg Friction Stir Welding

Dissimilar Al/Mg structures offer significant potential for lightweight design and complementary performance. However, owing to the limited mutual solid solubility, low eutectic temperature, and high interfacial reactivity of the Al-Mg system, brittle intermetallic compounds, primarily Al 3 Mg 2 and Al 12 Mg 17 , readily form during welding, making the interface the most critical region controlling joint performance. This review focuses on recent progress in the interfacial evolution of dissimilar Al/Mg friction stir welding. Starting from the thermodynamic constraints governing Al-Mg interfacial reactions, it summarizes the formation pathways of typical IMCs, the spatial reconstruction induced by material flow, the evolution of interfacial configurations driven by processing parameters, and interfacial regulation strategies involving interlayers and geometric design. The intrinsic relationship between interfacial state and joint performance is further discussed in conjunction with weld-zone microstructural distribution, local property variations, joint strength, ductility, and fracture behavior. Current studies indicate that the key to improving Al/Mg joint performance does not lie simply in reducing the overall amount of IMCs, but in controlling their formation location, continuity, and spatial distribution, while modifying load transfer and crack propagation paths through material flow regulation and interfacial structure design. Moreover, the post-weld interface is not merely a direct continuation of the original contact surface, but a newly formed microstructural region resulting from the combined effects of material flow, elemental diffusion, and interfacial reactions.