Kinetic Monte Carlo Simulations for Solute Clustering in Multicomponent Al Alloys

High-strength 7000 series Al (Al-Mg-Zn-based) alloys have severe formability limitations due to fast precipitate kinetics at room temperature (natural aging). This is primarily a result of the nucleation and growth of solute clusters and Guinier-Preston (GP) zones. In this work, solute clustering kinetics in multicomponent Al alloys is simulated with a newly developed kinetic Monte Carlo (kMC) simulation framework. An accurate surrogate model was constructed based on first-principles calculations to accurately and efficiently predict vacancy migration energy barriers and migration energetic driving force on the fly as a function of the local lattice occupations. The model was implemented in kMC simulations to investigate solute clustering kinetics in Al-Mg-Zn-based alloys at different temperatures and cooling rates. Our results reveal that solute clusters nucleate rapidly at medium temperatures (400-600K), even at fast cooling rates (>100 K/s), thereby providing nuclei for fast natural aging. Additionally, the nuclei would exhibit different Zn-Mg ratios and short-range order as temperatures drop below 400K. Furthermore, our time-independent canonical Monte Carlo thermodynamic simulations also confirmed the presence of different solute clustering phases at varying temperatures.