Thermodynamic description of multi-component multi-phase alloys and its application to the solidification process

Abstract

Metallic materials in engineering applications are mostly multi-component and multi-phase alloys. In this work, the solute partition behavior and its influence on the solidification process of multi-component alloys were studied in detail based on the CALPHAD technology. A complete thermodynamic model for the accurate calculation of the partition coefficients in solidification process was described. The model is applied to Al–Si–Mg ternary alloy, and the predicted partition coefficients were compared with some former experimental data. Good agreement between the calculation results and the experimental data demonstrates the validity of the present model. The variation of solute partition coefficient of both Si and Mg is studied in dendritic solidification process of Al–Si–Mg alloys. It is found that the partition coefficient changes greatly during solidification process. By coupling CALPHAD method with micro scale solidification model, the predicted solidification path for different composition or cooling rates and the eutectic fraction of Al–Si–Mg alloys agree well with the experimental results. The conventional theory of constrained dendrite growth for binary alloys is extended to multi-component alloys based on the CALPHAD method with considerations of the solute interactions, through which the primary dendrite spacing is estimated.