Assessment of the Al-Bi-Mg system and extrapolation to the Al-Bi-Mg-Sn quaternary system

Abstract

The phase equilibria in the Al-Bi-Mg-Sn quaternary system have been studied using the CALPHAD (CALculation of PHAse Diagram) method. One of the four ternary systems constituting the quarternary system, the Al-Bi-Mg system, is re-assessed by means of the CALPHAD technique and Thermo-Calc software package, in consideration of the associate model for the liquid phase instead of the Modified Quasi-chemical Model used in the literature report. While for the other three ternary systems, the Al-Bi-Sn, the Al-Mg-Sn and the Bi-Mg-Sn systems, the thermodynamic parameters are mainly adopted from the literature reported optimization results with a little modification to the Al-Bi-Sn and the Al-Mg-Sn systems for the compatibility of all the constituent binary systems. The assessment results of the Al-Bi-Mg ternary system are in good agreement with the available experimental phase relations, including the liquidus surface projection and the vertical sections. The thermodynamic database of the Al-Bi-Mg-Sn quaternary system was developed without the consideration of the quaternary interactions and the quaternary compounds. With this newly developed thermodynamic database, the phase equilibria and the solidification processes of the ternary and the quarternary systems are calculated and analyzed.