EXTENDED ABSTRACT: The diffusivity and concentration of vacancies have strong influences on the precipitation behavior of age-hardening precipitates in aluminum alloys. In this work, the impacts of substitutional solute atoms on vacancy diffusion in dilute alloys are quantitatively studied by using atomistic kinetic Monte Carlo (KMC) simulations. Based on the detailed diffusion behavior revealed by KMC, a physics-based analytic model is derived to quantify the vacancy diffusivity in dilute alloys. With the vibrational frequency and migration enthalpy of vacancy and binding energy of solute-vacancy pairs obtained from ffrst-principles calculations, the analytical model can precisely predict the vacancy diffusivity. Furthermore, a numerical model is developed to simulate the spatial evolution of non-equilibrium excess vacancies across grains during cooling from solution treatment and during ageing heat treatments of multicomponent aluminum alloys. In the model, the annihilation rates of excess vacancies at grain boundaries and at dislocation jogs have been derived based on a rigorous description of the annihilation mechanisms of vacancies. The model is successfully applied to interpret the age hardening behaviors of experimental alloys subjected to different thermomechanical processing conditions. The above models help to reach a deeper understanding of the roles of excess vacancies and impurity atoms in precipitation kinetics of age hardening aluminum alloys.

Keywords: Vacancies; Diffusion; Thermodynamics; Kinetics; Aluminum alloys; KMC simulations; DFT calculations.