Simultaneously overcoming metallurgical bonding and brittle intermetallic compounds of Al/Mg interface produced by compound casting through a novel HEA/Ni coating

A high-strength Al/Mg bimetallic composite was successfully fabricated using lost foam compound casting combined with a novel FeCoNiCrCu/Ni (HEA/Ni) composite coating as an intermediate layer. This study focused on the microstructure, mechanical properties, and strengthening mechanism at the Al/Mg interface after treatment with this composite coating. Results indicate that the introduction of the HEA/Ni composite coating transforms the originally brittle intermetallic compound interface layer into a multicomponent diffusion layer. This novel interface comprises a continuous AlxFeCoNiCrCu body-centered cubic (BCC) structural layer, a residual high-entropy alloy layer, and a magnesium solid solution layer containing Mg 2 Ni eutectic structures. Compared to the continuous, thick brittle Al 3 Mg 2 and Al 12 Mg 17 layers formed upon direct contact between aluminum and magnesium, the residual high-entropy alloy layer effectively suppresses mutual diffusion between aluminum and magnesium. Furthermore, the nickel coating not only resolves the diffusion reaction challenge between magnesium and the high-entropy layer but also promotes finer Mg 2 Ni particles with more uniform distribution within the reaction layer. This significantly enhances the interfacial bonding performance between the dissimilar aluminum and magnesium metals. After applying the HEA/Ni composite coating, the shear strength of the Al/Mg bimetal reached 73.63 MPa, representing a 132.05% increase compared to the untreated bimetal.