Phase Formation in Mg-Sn Alloys Modified by Ca and Ce

Thermodynamic descriptions are developed for the ternary Mg-Ce-Sn and the quaternary Mg-Ca-Ce-Sn systems by combining the Calphad method with experimental investigations on selected key samples. Ten ternary and six quaternary alloy samples were prepared from the elements in sealed Ta-capsules and studied by differential thermal, microstructural and x-ray diffraction analyses. These data were used together with the scarce literature data to develop and/or validate the thermodynamic descriptions and the calculated phase diagrams in the Mg-rich regions. Phase formation and microstructure development is also compared with solidification simulations under equilibrium and Scheil conditions. The ternary MgSnCe compound is found to be extremely stable. In the quaternary Mg-Ca-Ce-Sn system it exhibits very large solid solubility of Ca and exists as a single solid phase up to the known intermetallic solution phase range MgSnCa-Ca2Sn, all exhibiting the same crystal structure. These features result in significant complexity of phase equilibria in quaternary Mg-rich alloys.