Cryogenic Performance Of Lightweight High Entropy Alloys

High entropy alloy is a new alloy system with muti principal elements and high configurational entropy,which exhibit unique properties compared with conventional alloys in recent researches.Typical high entropy alloys composed of 3d transiton elements such as Fe Co Ni Cr Mn have great mechanical properties at cryogenic temperature.However,most of them have high density and high cost,which is hard to meet the demand of lightweight in the field of aeronautics,astronautics,energy and transportation.Hence,based on lightweight elements Al,Li and Mg,this thesis designs and prepares four lightweight high entropy alloys Al₈₀Li₁₀Mg₁₀,Al₈₀Li₅Mg₅Cu₅Zn_4.97Zr_0.03,Al₇₆Li_9.5Mg_9.5Cu_2.5Zn_2.47Zr_0.03 and Al_77.6Li_9.7Mg_9.7Cu_1.5Zn_1.47Zr_0.03(at.%).Microstructures,precipitations and mechanical behaviors of lightweight high entropy alloys are studied by means of modern analysis.Main conclusions are reached as below:1.It is found that Cu,Zn and Zr elements have significant effects on the volume fraction of precipitates at grain boundaries and average grain size in as-cast microstructure.2.The volume fraction of precipitates in the grain boundaries and average grain size have a great effect on the tensile strength of Al-Li-Mg alloy.After heat treatment,the tensile strength decreases due to the volume fraction of precipitated phase decreases and the grain size increases.293K,compared with the as-cast samples,the fracture strength of Al₈₀Li₁₀Mg₁₀,Al₈₀Li₅Mg₅Cu₅Zn_4.97Zr_0.03,Al₇₆Li_9.5Mg_9.5Cu_2.5Zn_2.47Zr_0.03 and Al_77.6Li_9.7Mg_9.7Cu_1.5Zn_1.47Zr_0.03 reduced by 17.7%,49.8%,23.1%and 38.5%respectively.3.The lower the temperature,the higher the toughness of the lightweight high entropy alloys.The tensile strength and yield strength of Al_77.6Li_9.7Mg_9.7Cu_1.5Zn_1.47Zr_0.03at 123K were 228.9 MPa and 187.9 MPa respectively,which were increased by 8.1%and 18.6%compared with room temperature.