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

Abstract

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.