The Study Of Smelting Technology And Microstructures And Mechanical Properties Of Mg-Li Alloys

Recent, Mg-Li series alloys have become one of the emphases in the field of Mg alloys due to the low density and light Specific Strength and Specific modulus.But this kind of alloy has several Key problems such as easy oxidation,easy cinder inclusion,etc. Additionally, the strength of Mg-Li alloys at room temperature especially at high temperature is low, which limits the application of Mg-Li alloys. So, the key way to promote the application of Mg-Li alloys is to develop new smelting process and enhance the mechanical properties.The foundry and rolling process for Mg-Li alloys is investigated in this thesis. The influence of Al and Ca on the microstructures and mechanical properties of Mg-Li alloys is analyzed by OM, SEM, X-Ray, EDS and tensile tests. The results indicate that it is favor of improving the strength and ductility with lower density at the condition of enhancing the stirring and prolonging the time before casting and using CaF2 as the flux cover. With increasing of solid solution temperature, the strength mechanism evolves from dispersion strength to solid solution strength. And the maximum ductility is obtained at the solid solution temperature of 450K. The maximum of elongation to failure and the ultimate tensile strength of the sheet rolled with the ingots produced by the new smelting process can be up to 40% and 355MPa, respectively. The reasons for the improvement can be owing to the second phase such as AlMg, LiAl and CaMg₂, CaLi₂, which lead to the dispersion strength effect. Moreover, the grain is refined by the element of Ca, which result in fine-grain strength effect. So, it can be concluded that CaF₂ is favor of improving the quality of ingots and the alloying elements of Al and Ca can enhance the mechanical properties of Mg-Li alloys.