| At present,one of the hottest topics in heat storage research is phase change heat storage technology,which is effectively used in solar energy development,energy saving in the built environment and waste heat and waste heat recovery.Phase change heat storage materials are the key carriers of heat storage technology,which can effectively save energy and improve energy utilization.However,in the development and utilization of high-temperature solar energy,its own characteristics such as discontinuity,dispersion,and inhomogeneity greatly limit the engineering application of phase change heat storage materials.Therefore,seeking suitable energy storage methods and media to utilize solar energy has become a hot research topic around the world.In this thesis,the research and exploration of magnesium-based metal heat storage alloys are carried out,and we tried to use Pandat phase diagram software to calculate and design the composition points of Mg-Ca-Zn phase change heat storage alloys.At the same time,the calculation of the total heat and temperature of the alloy is carried out through the solidification simulation module.The density and phase transformation parameters of the alloy were determined according to the archimedes drainage method and DSC experiments,and then supplemented by XRD,SEM and EDS experiments,the microstructure of the alloy samples was observed.The effects of the addition of Ca and Zn elements on the microstructure and physical parameters of Mg-Ca-Zn alloys were analyzed and discussed.Finally,the heat storage alloys with better comprehensive properties were selected to study and test the high temperature oxidation resistance.The main conclusions are as follows:(1)The Mg-Ca-Zn alloy is mainly composed of a large number of primary α-Mg phases and α-Mg+Mg2Ca+MgZn+Ca2Mg6Zn3 eutectic structure.By adjusting the content of Zn and Ca,compared with the matrix structure of other alloys,the matrix structure of Mg-15Ca30Zn alloy is obviously refined,the relative proportion of eutectic structure is increased,and the microstructure is obviously improved,and its eutectic structure shape is mostly cells and chains.(2)The phase change heat storage value of Mg-15Ca-30Zn alloy is the highest,which corresponds to the eutectic point,while the heat storage per unit volume of Mg-15Ca-40Z alloy is the largest.The alloy has a higher heat storage value of phase transition,which may be due to the higher proportion of eutectic α-Mg+Mg2Ca+MgZn+ Ca2Mg6Zn3 structure and the higher concentration of Ca2Mg6Zn ternary phase with high binding energy.(3)Compared with the experimental values,the simulated calculated values of phase transition temperature and heat can provide a certain reference value.The heat storage capacity of the alloy is an important parameter,but other factors need to be considered.According to the calculation results of solidification simulation,the Mg-15Ca-30Zn alloy has a small solid-liquid coexistence temperature range,is easy to process,and has a high heat storage value.(4)The Mg-15Ca-30Zn and Mg-15Ca-40Zn alloys exhibited excellent oxidation resistance at 350℃ due to the good protective effect of the dense oxide layer of CaO+ZnO,while the oxidation resistance of Mg-15Ca-40Zn alloy at a relatively high temperature(400℃)is better than that of Mg-15Ca-30Zn alloy,which is mainly due to the presence of a higher content of dense zinc oxide in Mg-15Ca-40Zn(1<PBR<2).(5)Base on the investigated properties of five Mg-Ca-Zn alloys,the Mg-15Ca-30Zn and Mg-15Ca-40Zn alloys have suitable phase change temperature,high melting enthalpy and heat storage density,and exhibit good oxidation resistance at 350℃,which are therefore expected to be used as heat storage. |
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