Thermodynamic descriptions of ternary Al–Si–Yb system and their application to understand solidification behaviors of Yb-modified Al–Si alloys

In this paper, thermodynamic descriptions of binary Si–Yb and ternary Al–Si-Yb system were assessed using the CALculation of PHAse Diagram (CALPHAD) technique, from which insights to the solidification behaviors of Yb-modified Al–Si alloys were attained. Firstly, all the experimental phase equilibria and thermodynamic properties in binary Si–Yb and ternary Al–Si-Yb systems were critically evaluated. Based on evaluated experimental data in the literature, the thermodynamic parameters of binary Si–Yb system were then updated, resulting in a better agreement with the experimental phase equilibrium data in Si-rich part than the previous assessment in the literature. Afterward, the thermodynamic descriptions of ternary Al–Si-Yb system were established on the basis of thermodynamic parameters of three boundary binaries, and their reliability was verified by comprehensively comparing the predicted thermodynamic properties/solidified behaviors with the literature data. Finally, the Scheil-Gulliver solidification simulations of different Yb-modified Al–Si alloys were conducted, from which the effect of Yb additions on the solidification sequences, phase transition temperatures, and phases/structures fractions in Al–Si-Yb alloys was analyzed.