Ag segregation and interfacial characterization of the hexagonal β(Mg2Si)-phase in Al-Mg-Si-Ag alloy

This study investigates the interface characteristics of the hexagonal β(Mg₂Si)-phase in Al-Mg-Si-Ag alloys, providing novel insights into its orientation relationship, interfacial conditions, misfit, and Ag segregation with the Al matrix. Using optical microscopy (OM), focused ion beam (FIB), and scanning transmission electron microscopy (STEM), we clarified the role of three distinct facets {111} Al // {111} hex.β , {122} Al // {110} hex.β , and {112} Al // {111} hex.β in determining the stability and properties of the hexagonal β(Mg₂Si)-phase. Unlike the conventional β(Mg₂Si)-phase with a {100} Al habit plane, the hexagonal β-phase was found on the {111}Al habit plane, exhibiting a new orientation relationship [{111} Al // {111} hex.β , < 110> Al // < 110> hex.β ]. Ag segregation was notably observed at the interfaces of these facets, with varying concentrations influencing interfacial coherency and strain. These findings not only advance our understanding of microstructural evolution in Al-Mg-Si alloys but also provide a foundation for tailoring material properties through interface engineering. The results offer critical insights for optimizing alloy compositions and heat treatments to enhance mechanical properties and performance in practical applications.