Study of θ’ precipitation behavior in Al-Cu-Cd alloys by phase-field modeling

The θ’(Al₂Cu) precipitation behavior of Al-Cu-Cd alloys was investigated by phase-field simulations. Due to the formation of Cu-Cd-vacancy clusters, the diffusion of Cu in the Al matrix is replaced by the movement of the clusters. Thus the diffusion model was modified and the diffusion coefficient of Cu-Cd-vacancy clusters was used in the new model. Moreover, the interfacial energy of θ’ phase is reduced by the Cd atoms segregation at the α(Al)/θ’ interface. Therefore, multiple combinations of coherent and semi-coherent interfacial energies were compared regarding the growth kinetics of θ’ phase in the simulation. The results indicated that the variation of the diameter-to-thickness ratio of θ’ phase primarily depended on the coherent interfacial energy. And the equilibrium diameter was a monotonically increasing function of the diameter-thickness ratio. Appropriate coherent and semi-coherent interfacial energies were obtained based on a comparison of the diameter-thickness ratio between the phase-field simulations and experimental data. The yield strength was calculated considering the morphology of the θ’ phases and was validated by experimental results for different Al-Cu-Cd alloys.