Strained coherent interface energy of the Guinier–Preston II phase in Al–Cu during stress aging

θ″-phase, with a formal stoichiometry of Al3Cu, is a coherent, metastable precipitate (GP-II) phase commonly found in Al-based aerospace alloys. In this paper, we employed a first-principles based method to study the energetics of the Al/θ″ interface as response to external strains. The potential effects of temperature, Cu activity, and different strain modes on interface energy (γ Al/θ″) were systematically investigated. Calculations show that (i) an unstrained γ Al/θ″ always increases with temperature: as temperature increases from T = 298 to 498 K, γ Al/θ″ increases by ~9.0 %; (ii) γ Al/θ″ is more sensitive to compressive strains than to tensile strains of the same magnitude. In particular, for a parallel compressive strain increasing from 0 to 2 % at a typical aging temperature, γ Al/θ″ decreases by ~6.6 %, while a vertical compressive strain of 2 % has a slightly stronger impact by decreasing γ Al/θ″ by ~9.6 %. Different influences of applied strain/stress on the formation energies of different orientated interfaces can be further exaggerated by the Poisson effect, and eventually affect the preferential precipitation orientation of θ″ in the matrix.