Abstract

This work focuses on the experimental investigation of the ternary Mg-Al-Ca system using Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and metallographic techniques. Twenty one samples were chosen in the critical regions with the guidance of the phase diagrams developed by thermodynamic modeling. The DSC has permitted real time measurement of the temperature and enthalpy of the phase transformations. The experimental results were compared with thermodynamic calculations using the phase assemblage diagrams and vertical sections. The thermodynamic calculations are consistent with the experimental results in some samples, especially in the solidus temperature, whereas discrepancy was observed in several cases especially in the liqudus phase transformation temperature. This suggests that Mg-Al-Ca system should be reoptimised considering the new experimental findings. Nevertheless, the phases that were identified with the XRD and metallographic techniques show agreement with thermodynamic modeling. One of the invariant transformations predicted by thermodynamic modeling was verified experimentally and found to occur at 512{493}C and the composition is close to 10.8 at.% Ca 79.5 at.% Mg and 9.7 at.% Al. In this study, a new phase region was found close to the Mg-Al side and a new ternary solid solution (Mg 2 Ca) was confirmed