The ultimate goal of modeling precipitation in Al alloys is to predict strength and other properties as a function of alloy composition and thermomechanical processing history via the intermediary of microstructure modeling. We have selected precipitation of q’ in Al-4 wt% Cu as our test system because of the extensive microstructure data to be found in the literature, and we have selected the phase field approach as our primary modeling technique.
Theta’ forms as shear-resistant plates with orientation relationship (100)q’ || (100)a between precipitate and a matrix. The plate is coherent with the fcc matrix on the broad face, with low interface energy, but it is semi-coherent on the edge with high interface energy. The phase field model is based on Kim’s approach[1] and includes elastic energy associated with the lattice mismatch between phases, anisotropic interface energy and anisotropic interface mobility, in addition to standard Gibbs energy functions and diffusivity. The effect of these parameters on morphology and growth rate of q’ precipitates and on diffusion flux around the precipitates is studied in two and three dimensions.
[1]S.G. Kim, W.T. Kim, and T. Suzuki, Phys. Rev. E, Vol. 60, p. 7186, (1999).