Effect Of Heat Treatment On Microstructure And Mechanical Properties Of Mg-Li Eutectic Alloy

Recent studies have shown that Mg-Li alloy as the lightest metal structural material had broad application prospects in aerospace and other fields.In this paper,Mg-7.3Li eutectic alloy is taken as the research object.The effect of heat treatment on the microstructure and mechanical properties of Mg-Li eutectic alloy is studied by changing the heat treatment parameters such as heat treatment temperature and holding time.Firstly,the effect of heat treatment with/without temperature gradient on the microstructure of binary Mg-Li eutectic alloy is studied.The evolution of microstructure and mechanical properties of the alloy after thermal stabilization at different thermal stabilization times is studied,and the microstructure evolution of the alloy caused by solute diffusion in the alloy is explained by establishing an analytical model.In addition,the relationship between the microstructure and mechanical properties of binary alloys is obtained by heat treatment without temperature gradient.Due to the low strength of binary Mg-Li alloy,in this paper,different alloying elements(Al and Ca/Al and Y)are added,and the microstructure of the alloy is regulated by heat treatment to further improve the mechanical properties of the alloy.Compared with Mg-7.3Li binary eutectic alloy,the microstructure of Mg-7.3Li-4Al-7Ca alloy is significantly refined and the Al₄Ca phase and(Mg,Al)₂Ca eutectic appear after the addition of Al and Ca elements.Then,the alloy is heated at250?,300?,350?and 400?for 30min,60min and 120min,respectively.Among them,after holding at 400?for 120min,the number of lamellar eutectic in the alloy decreases and the distribution of precipitates is uniform.Thus,the combined effect of solid solution strengthening and dispersion strengthening is the best,and the tensile strength of the alloy reaches 161MPa,which is 25.7%higher than that of as-cast alloy and 36.4%higher than that of binary alloy.Compared with Mg-7.3Li binary eutectic alloy,Al₂Y precipitates appeared in the microstructure of Mg-6.3Li-3.5Al-3Y alloy after adding Al and Y elements.Then,the alloy is heated at 250?,300?,350?and 400?for 30min,60min and 120min,respectively.After holding at 350?for 60min,the volume fraction of Al₂Y precipitates in the alloy decreases,the size reaches the minimum and the distribution is uniform.Therefore,the combined effect of solution strengthening and dispersion strengthening is the best,and the tensile strength of the alloy reaches 181MPa,which is 36.1%higher than that of as-cast alloy and 53.4%higher than that of binary alloy.