Study on thermophysical performance of Mg-Bi-Sn phase-change alloys for high temperature thermal energy storage

Mg-based alloys are potential high temperature phase change materials for thermal energy storage due to their high melting enthalpy, high thermal conductivity and excellent compatibility with Fe-based containment materials. This work mainly focuses on studying the microstructure and thermophysical characterization of Mg-Bi-Sn alloys phase change materials with 4 different components and their thermal energy storage performance. The experimental results show that the Mg-33Bi-17Sn, Mg-39Bi-17Sn and Mg-45Bi-17Sn alloys mainly consist of primary alpha-Mg phase and alpha-Mg + Mg2Sn + Mg3Bi2 eutectic structure, and the Mg-33Bi-23Sn alloy mainly consist of primary alpha-Mg phase, primary Mg2Sn + Mg3Bi2 phases and alpha-Mg + Mg2Sn + Mg3Bi2 eutectic structure. Their melting enthalpies are respectively 18.5 J/g, 168.8 J/g, 106.3 J/g and 140.3 J/g, while their melting temperatures are about 515 degrees C-525 degrees C. As from the results, the Mg-39Bi-17Sn alloy obtains the highest melting enthalpy, which attributes to its higher proportion of eutectic alpha-Mg + Mg2Sn + Mg3Bi2 structure. However, the Mg-45Bi-17Sn alloy shows the highest thermal conductivity. In addition, the melting point of Mg-39Bi-17Sn alloys increase by about 1.8 degrees C, and the melting enthalpy decreases by about 4.2% after 300 thermal cycling. Based on all results, the Mg-39Bi-17Sn alloy shows with great thermalphsycial performance and is expected to be used as thermal energy storage material.