Segregation of Alloying Elements to Stabilize Teta Prime 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 calculations. The interface structure with a filled interfacial Cu layer is calculated to be lower in energy than the structure with a half-filled Cu layer (by 0.1 eV per structural vacancy), which implies that a temperature-induced reconstruction of the interface may take place. The presence of vacancies in the interfacial Cu layer structure plays a crucial role in the interaction of solutes with a coherent θ′ phase interface. 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.