Microstructure and properties of Mg–Ca–Zn alloy for thermal energy storage

Mg-based alloys with a suitable phase change temperature, high phase change latent heat and excellent compatibility with Fe are currently the research hotspot in the field of latent heat storage. Herein, based on the Pandat software calculations, five different Mg–Ca–Zn alloys have been designed by changing Ca or Zn content. It's found that Mg–15Ca–30Zn alloy exhibits a suitable phase change temperature, a high heat storage value, a small solid-liquid coexistence temperature range, and leading to ease of processing according to the results of Pandat solidification simulation. Subsequently, the microstructure, thermophysical properties and high-temperature oxidation properties of Mg–Ca–Zn alloys were systematically investigated. The experimental results revealed that the Mg–Ca–Zn alloys are mainly composed of primary α-Mg phase, Mg2Ca phase, MgZn phase and Ca2Mg6Zn3 phase. The melting enthalpy of Mg–15Ca–30Zn alloy (eutectic alloy) is the highest among these five alloys due to high volume of α-Mg + Mg2Ca + MgZn + Ca2Mg6Zn3 eutectic structure and Ca2Mg6Zn3 ternary phases with high binding energy, whereas Mg–15Ca–40Zn alloy exhibits a large heat storage value per unit volume. The results of high-temperature oxidation experiments indicate that Mg–15Ca–30Zn and Mg–15Ca–40Zn alloys have good oxidation resistance at 350 °C due to the dense oxide layer of CaO + ZnO with good protection, and the oxidation resistance of Mg–15Ca–40Zn alloy is better than that of Mg–15Ca–30Zn alloy at 400 °C due to the increase of highly dense ZnO (1 < PBR <2) content. The obtained results confirm the suitability of the studied metal alloys for latent heat energy storage.