Pressure effects on thermodynamics and diffusion behaviors in Al-Zn-Mg-Cu alloys: Integrated CALPHAD modeling and applications

Pressure critically governs thermodynamic equilibria and transport in materials. While the effects of pressure on thermodynamics and diffusion behaviors in simple systems are well studied, predicting and controlling pressure-driven behaviors in complex multicomponent systems remains challenging. In this paper, insights into effect of pressure on thermodynamic and diffusion behaviors in Al-Zn-Mg-Cu alloys were gained. Firstly, a critical thermodynamic assessment of the quaternary Al-Zn-Mg-Cu system under pressure was carried out, incorporating available pressure-related experimental data. Then, an atomic mobility model for multicomponent alloys under pressure was developed, extending our previous binary alloy frameworks, to evaluate pressure-dependent atomic mobilities in face-centered cubic (fcc) Al-Zn-Mg-Cu alloys. The reliability of model and related descriptions was validated against experimental phase equilibria, solidification behaviors, diffusivities, composition profiles, and diffusion paths. Finally, leveraging CALPHAD tools, the pressure-dependent descriptions were applied to simulate the particle dissolution and precipitation growth during high-pressure heat treatment (HPHT) of Al-Zn-Mg-Cu alloys. This enabled the establishment of quantitative linkages among pressure, temperature, time, and microstructure, facilitating the optimization of HPHT parameters. The approach provides a predictive framework for tailoring pressure-mediated thermodynamics and diffusion behaviors in complex alloys, advancing the design of advanced alloys under extreme conditions.