Multiscale Modeling of Solute Clustering Kinetics during Quenching and Aging in Al-Zn-Mg-based Alloys

High-strength 7000 series Al (Al-Mg-Zn-based) alloys face significant formability challenges due to the rapid nucleation and growth of solute clusters and Guinier-Preston (GP) zones during quenching and subsequent natural aging at room temperature. This study investigates these kinetic behaviors through both experimental and computational approaches. In situ transmission electron microscopy (TEM) with controlled heating, quenching at varying cooling rates, and natural aging revealed the immediate formation of solute clusters post-quench and the nucleation of GP-II zones near clusters within the first ~10 minutes of aging. Large-scale lattice kinetic Monte Carlo (kMC) simulations, using an accurate surrogate model for vacancy migration barriers, confirmed that solute clustering predominantly occurs during quenching. A simplified potential energy landscape model was developed to approximate cluster energetics, validated by kMC simulations. Results indicate a transition in vacancy trapping behavior—from size-dependent growth in energy basins for small clusters to size-insensitive behavior in larger clusters, governed by random walk dynamics. By coupling Markov chain predictions with singular approximations, we estimated effective cluster binding energies, enabling improved predictions of excess vacancy concentrations in the Al matrix. These predictions are critical for modeling solute diffusivities and informing continuum-scale models of diffusion-controlled phenomena such as nucleation, growth, and coarsening during precipitation.