Study On Rolling Technology Of Mg-9li-2zn Alloys And Their Microstructures And Mechanical Properties

Mg-Li alloy has wide application foreground in the field of aviation, spaceflight and 3C due to its characteristics with low density, high strength to weight ratio and high ductility and so on. But lots of problems still exist for Mg-Li alloy, such as bad heat stability, ability of oxidation resistance and corrosion resistance, which limit the further application of Mg-Li alloy. So, the key to promote the application of Mg-Li alloy is to develop a new smelting process and research the Rolling Process of Mg-Li alloy and analysis the deformation mechanism. It had become the key to extend the application of Mg-Li alloy. The method of combining experimental study and theoretical analysis is used in this thesis.Mg-Li alloy is analyzed by OM,SEM,X-Ray,EDS and tensile tests. The foundry and rolling process for Mg-Li alloy and softening mechanism in the annealing process of Mg-Li alloy are investigated in this thesis. Based on these analyses, determined the process flow of alloys preparation-rolling-heat-treatment. Moreover, the influence of Al and Ca on the microstructures and mechanical properties of Mg-Li alloy is analyzed. The main results are as following:(1) The Mg-9Li-2Zn alloy casting process was studied. Using LiCl+LiF salts as covering agent when melting the alloy could obtain good protective effect.(2) The homogenization treatment of Mg-Li alloy was studied. With solution treatment temperature increasing, the strengthening mechanisms changed from dispersion strengthening to solid solution strengthening gradually, an appropriate prolonging the homogenization treatment time properly is conducive to solid dissolved second phase particle to the grain. Under the experimental conditions, the optimum technological parameters of homogenization treatment process of Mg-9Li-2Zn alloy were as following. The solid solution treatment temperature was 250℃, and heat preservation time was 24 hours. While the best homogenization treatment temperature of Mg-9Li-2Zn-xCa alloy was 300℃and heat preservation time was 24 hours. (3) The rolling temperature and pass reduction of Mg-9Li-2Zn alloy were studied. With the increase of rolling temperature, it occurred with dynamic recrystallization, and alloy grains were refined. The optimum temperature for rolling was 200℃-300℃,and the optimum single pass reduction of cold rolling should be controlled between 20% and 30%。(4) The anneal treatment technology after rolling was studied. And anneal softening mechanism was also confirmed. Annealing could eliminate work-hardening and residual stress formed during the process of cold rolling, to improve alloy deformability. The optimum annealing temperature of Mg-9Li-2Zn was 300℃, and the time was 60min. With the rising of annealing temperature, the hardness of Mg-9Li-2Zn alloy decreased rapidly at the beginning and then kept basically the same. After heat preservation at 300℃for 60 min, the deformation rate of the alloy plate can reach 70% in the subsequent cold rolling(5) Effect of Al and Ca on microstructure and properties of Mg-9Li-2Zn alloy was studied in this paper. The addition of Ca to Mg-9Li-2Zn alloy could increase the mechanical properties of alloy at room temperature, adding 0.1mass% Ca, the tensile strength and yield strength were increased by 19.16% and 17.22% respectively, and elongation was increased by 5.88%.