Solute coupling governed complex behaviours of precipitate/matrix interfaces in Al alloys

Precipitation-hardened alloys frequently encounter chemical and thereby structural variations at the precipitate/matrix interfaces, which would inevitably impose a strong impact on subsequent precipitation kinetics. However, an atomistic understanding on coupling of different solute atoms at heterophase interfaces and how it changes the precipitate evolution remains largely elusive. Taken Al-Cu-Li-Mg alloy as a model system, here we reveal complex precipitate/matrix interface behaviours governed by solute coupling, using scanning transmission electron microscopy and first-principles calculations. The pre-segregated solutes at precipitate/matrix interfaces largely modify segregation behaviours of following ones, thus, guiding the atomic arrangement at the interfaces. Such solute coupling effect can shape the heterophase interfaces, catalyse the heterogenous nucleation and evolution of interfacial precipitates, and also alter the atomistic mechanism of precipitate growth. Our findings provide atomistic insight into the complex interface behaviours controlled by solute coupling, which would benefit the design of novel age-hardenable materials through interface engineering.