Significantly improved bonding strength of Al/Mg bimetallic interface by compound casting via FeCoNiCrCu high entropy alloy coating

FeCoNiCrCu high entropy alloy (HEA) coating was introduced into the interface of Al/Mg bimetal prepared by a compound casting in order to improve the bonding strength of the Al/Mg bimetal. With the application of the FeCoNiCrCu HEA coating, the HEA coating greatly inhibited the diffusion between Al and Mg, and the Al and HEA tended to form a new solid solution structure. The brittle Al-Mg intermetallic compounds were significantly reduced, leading to a remarkable decrease in interface thickness, only 9.86 % of the original interface. The Al/Mg bimetal formed a complex interface of Al3Mg2+Mg2Si/AlxFeCoNiCrCu+FeCoNiCrCu+ Mg2Ni mixed phases/δ-Mg+Al12Mg17 eutectic structure. Molecular dynamics simulations further confirmed that adding FeCoNiCrCu HEA coating effectively hindered the diffusion between Al and Mg and prevented the formation of the Al-Mg intermetallic compounds. The shear strength increased from 30.62 MPa to 50.47 MPa, increasing by 64.83%, owing to the remarkable decrease of the Al-Mg intermetallic compounds and the generation of the Mg2Ni mixed phases in the interface. The fracture of the bimetal with the HEA coating occurred between the HEA coating and δ-Mg+Al12Mg17 eutectic with a certain plastic deformation, while the fracture of the bimetal without HEA coating was located in Al3Mg2 layer, showing an obvious brittle fracture.