The Research On Preparation Process, Microstructures And Properties Of Mg-14Li-X Series Alloy

Recently, Mg-Li series alloys have become one of the emphases in the field of Mg alloys due to the low density, high 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 especially at high temperature is low, which limits the application of Mg-Li alloys. So, the key to promote the application of Mg-Li alloys is to develop a new smelting process and enhance their 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 main results are as following:(1)The foundry process of LAl41 Mg-Li alloy was studied. Using CaF₂+LiCl+LiF admixture as flux cover can achieve good protective action, and the material mechanical properties are enhanced by the refined grain process which happened with the Ca element produced during the chemical reaction between CaF₂ and the melting. The preferable pouring temperature is 993K, and the mold temperature is 573K.(2)The solid solution of LAl41 Mg-Li alloy was studied. 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. Prolonging the solid solution time properly benefits the progress during which the second phase dissolving into the grain. The preferable solid solution temperature is 453K, and the heat preservation time is 6h.(3)The rolling process of Mg-14%Li Mg-Li alloy was studied. According to experiment results of room rolling Mg-14%Li Mg-Li alloy, the material mechanical properties are enhanced, as cast condition tensile strength is 165MPa and rolling condition tensile strength maximum is 235MPa, at the same time, its extensibility accretes from 13.5 percent to 48 percent. With the temperature rising,its extensibility is at all times rising. The extensibility is improved by pressing reduction accretion and manufacturing refined grain.(4) With joining a little Al element, Al intermetallic compounds exist in basal body grain boundary and grain inner. Room temperature tensile strength is improved by refined graph and distributing equably. A little Ca element is joined by flux cover CaF₂ and refines structures, and improves its tensile strength and extensibility. But, with the Ca element accretion, its properties decline.