Segregation of alloying elements to stabilize θ′ phase interfaces in Al-Cu based alloys

Interactions of alloying elements (Si, Mg, Mn, Zr, Zn) and vacancies with coherent interfaces of θ′ phase in Al-based alloys have been systematically studied by means of ab initio supercell calculations. The interface structure with a half-filled interfacial Cu layer is calculated to be lower in energy (by 0.1 eV per structural vacancy) than the structure with a filled Cu layer; the degree of interface reconstruction depends on the availability of vacancies. The presence of vacancies in the interfacial Cu layer plays a crucial role in the interaction of solutes with coherent θ′ phase interfaces. The solute–interface interaction energies are calculated to be much weaker for elements having closed (Cu, Zn) or empty (Mg, Si) d-electron shells than for d-transition metals (Mn, Zr). To clarify the roles of alloying elements and interface structure in the stability of θ′ phase precipitates, we analyze the solute–interface interactions in terms of electronic-structure and atomic-size contributions to interatomic bonding.