Composition templating for heterogeneous nucleation of intermetallic compounds

Refinement of intermetallic compounds (IMCs) through enhancing heterogeneous nucleation during casting process is an important approach to improve the properties of aluminium alloys, which greatly increases the economy value of recycled Al-alloys. However, heterogeneous nucleation of IMCs is inherently more difficult than that of a pure metal or a solid solution. It requires not only creation of a crystal structure but also the positioning of 2 or more different types of atoms in the lattice with specific composition close to that of the nucleated IMCs. Previous understanding on heterogeneous nucleation is based on structural templating, usually considering the small lattice misfit at the interface between the nucleating solid and substrate. In this work, we proposed a hypothesis and demonstrated that composition templating plays a critical role in heterogeneous nucleation of IMCs. The experimental results revealed that segregation of Fe atoms on the AlB₂ surface, i.e., the Fe modified AlB₂ particle, provides the required composition templating and hence enhances heterogeneous nucleation of α-Al₁₅(Fe, Mn)₃Si₂, resulting in a significant refinement of the α-Al₁₅(Fe, Mn)₃Si₂ particles in an Al-5 Mg-2Si-1.0Mn-1.2Fe alloy.