Preparation, microstructure and thermal properties of MgBi alloys as phase change materials for thermal energy storage

Comparing with Al-based phase change material, Mg-based phase change material is getting more and more attention due to its high corrosion resistance with encapsulation materials based on iron. This study focuses on the characterization of Mg36%Bi, Mg54%Bi and Mg60%Bi (wt. %) alloys as phase change materials for thermal energy storage at high temperature. The phase compositions, microstructure and phase change temperatures were investigated by X-ray diffusion (XRD), electron probe micro-analysis (EPMA) and differential scanning calorimeter (DSC) analysis, respectively. The results indicates that the microstructure of Mg36%Bi and Mg54%Bi alloys are mainly composed of α-Mg matrix and α-Mg + Mg3Bi2 eutectic phases, Mg60%Bi alloy are mainly composed of the Mg3Bi2 phase and α-MgMg3Bi2 eutectic phases. The melting enthalpies of Mg36%Bi, Mg54%Bi and Mg60%Bi alloys are 138.2, 180.5 and 48.7 J/g, with the phase change temperatures of 547.6, 546.3 and 548.1 °C, respectively. The Mg54%Bi alloy has the highest melting enthalpy in three alloys. The main reason may be that it has more proportion of α-Mg + Mg3Bi2 eutectic phases. The thermal expansion of three alloys increases with increasing temperature. The values of the thermal conductivity decrease with increasing Bi content. Besides, the activation energy of Mg54%Bi was calculated by multiple DSC technology.