A CALPHAD thermodynamic model for multicomponent alloys under pressure and its application in pressurized solidified Al–Si–Mg alloys

Abstract

High pressure technology has been utilized as an important means to regulate phase structure and improve the properties/performance of alloys. The CALPHAD approach based on accurate databases has great advantages in efficient alloy design. However, the application of CALPHAD in high pressure field is hindered by the lack of reliable thermodynamic model/database for multicomponent alloys under pressure. In this paper, a phenomenologically thermodynamic model for multicomponent alloys under pressure is first developed by separating the contribution into two parts, one is at atmosphere pressure and the other is caused by an increase in pressure, and then successfully applied to establish the pressure-dependent thermodynamic database of ternary Al–Si–Mg system. The calculated phase equilibria/thermodynamic properties of pressure dependence in related alloys are in good agreement with the limited experimental data in the literature, validating the reliability of the obtained thermodynamic database. After that, a CALPHAD design framework for pressurized solidified alloys is proposed by integrating the present pressure-dependent thermodynamic model/database, CALPHAD-type calculations/simulations, and previously developed high-throughput calculation platform Malac-Distmas. Such a framework is finally applied to predict the pressurized solidification and high pressure heat treatment behaviors in different Al–Si–Mg alloys. The predicted microstructure, phase transitions and phase equilibria after pressurized solidification and high pressure heat treatment are consistent with the experimental data. Furthermore, the insights into effect of pressure on the thermodynamic essence of alloys are gained, which may definitely facilitate the advancement of alloy design under high pressure technology.