Effect of high entropy alloy as the interlayer on the interfacial microstructure and mechanical property of Al/steel bimetal by compound casting

Abstract

Al/steel bimetal prepared by compound casting process exhibits an increasing application prospect in the lightweight field due to the combination of the advantages of Al alloy with steel materials. Unfortunately, a large number of hard and brittle Al–Fe intermetallic compounds (IMCs) are prone to form at the interface, resulting in insufficient interfacial bonding strength of Al/steel bimetal. Therefore, in the present work, the typical CoCrFeNiMn high entropy alloy (HEA) coating fabricated by laser cladding technique was used as the interlayer of Al/steel bimetal to suppress the Al–Fe IMCs. The results showed that the reaction layer of Al/steel bimetal with HEA interlayer first forms Al5Co2 rather than Al5Fe2 phases compared with the as-cast bimetal. More importantly, the Al5Co2 phase layer consists of nanocrystals. Besides, the elements like Cr, Ni and Mn are uniformly distributed into the reaction layer and no IMCs are detected. This contributes to a reduction in the grain size of Al5Fe2 phase. Although the characteristic of brittle with respect to Al5Co2 compound, the interfacial bonding strength of bimestal is improved by 33% compared with that of the as-cast bimetal, attributing to the fact that the nanocrystals formed at the interface make the surface energy and defect size increase in terms of Griffith's theory. In short, laser cladded CoCrFeNiMn HEA coating provides a new choice for the interlayer selection of Al/steel bimetal.