Thermal characteristics of Mg-Zn-Mn alloys with high specific strength and high thermal conductivity

The temperature and concentration dependence of thermal diffusivity, specific heat, density, thermal expansion, and thermal conductivity of as-cast and heat-treated (T4 and T6) Mg-[x] wt.% Zn-1 wt.% Mn (x = 3, 5, and 8) (Mg-Zn-Mn) alloys were investigated over temperatures ranging from 20 °C to 300 °C, and the results were correlated with the respective microstructures of the alloys. The thermal conductivity of the Mg-Zn-Mn alloys decreased remarkably with increasing Zn composition but exponentially increased with increasing temperature. The thermal diffusivity and thermal conductivity of alloys subjected to T4 and T6 heat treatments were higher than those of as-cast alloys. The dissolution of Mg-Zn phases with α-Mn precipitates from the Mg matrix contributed to the improvement in thermal conductivity of T4 Mg-Zn-Mn alloys. The thermal conductivity and the atomic sizes of solute atoms were closely related. In Mg-Zn-Mn alloy, the addition of Zn atoms to the Mg matrix had smaller effects on thermal conductivity, while the addition of Mn atoms caused considerable lattice distortions and thus significantly affected thermal conductivity. T6 aging treatment improved their thermal heat transfer characteristics due to the decrease in amount of dissolved Zn by precipitation.