Preparation And Study Of Novel Mg-xLi-5Al-5Ca-(Zn) Alloys

Magnesium lithium alloy is the lightest metal structural material because of its advantages of low density,high specific strength and stiffness,good shock absorption and easy cutting,and so on.However,Mg-Li alloys have some disadvantages,such as low strength,poor corrosion resistance and high temperature resistance,which limit its application.Their mechanical strength and corrosion resistance can be improved by alloying and processing technology.For example,Al can improve corrosion resistance,Ca can enhance flame retardant performance and rare earth elements can enhance the mechanical properties.Mg-Li alloys with excellent comprehensive performance and low cost are still rare.In this paper,low cost elements AI,Ca and Zn were chose.Mg-5Li-5Al-5Ca alloy,Mg-5Li-5Al-5Ca-2Zn alloy and Mg-8Li-5Al-5Ca alloy were designed and prepared.Their performance is improved by extrusion and rolling process.The microstructure,mechanical properties,corrosion resistance and flame retardant properties of the alloy were studied.The results show that:The second phase of Mg-xLi-5Al-5Ca(-2Zn)alloys with Ca/Al?1 are mainly Al2Ca.The difference is that the matrix of Mg-5Li-5Al-5Ca and Mg-5Li-5Al-5Ca-2Zn are single phase of a-Mg,while the Mg-8Li-5Al-5Ca alloy matrix is a-Mg and ?-Li.The as cast microstructure is the matrix surrounded by lamellar Al2Ca.After extrusion,the alloys exhibit typical fibrous tissue and crystal grain was obviously fine because of the dynamic recrystallization.The mechanical properties of alloy were improved obviously after extrusion deformation.The yield strength and tensile strength were the highest among Mg-5Li-5Al-5Ca,Mg-5Li-5Al-5Ca-2Zn and Mg-8Li-5Al-5Ca,which were 151MPa and 215MPa,respectively.The Mg-5Li-5Al-5Ca-2Zn alloy has the best plasticity and its elongation is 21%.The strength of the three alloys is better than that of the common Mg-Li alloys.When the Mg-5Li-5Al-5Ca alloy was extruded and rolled at different reduction rates,no cracking occurred.When the rolling reduction ratio was 80%,the surface morphology was still intact,indicating its excellent ability of plastic deformation.Both the yield strength and tensile strength of the alloy increased with the extrusion rolling process.The strength of the alloy increased with the decrease of rolling reduction ratio and the tensile strength was up to 243MPa.The corrosion resistance of Mg-8Li-5Al-5Ca alloy is good,and it increases with the increase of extrusion ratio.After extrusion,the small ?-Li crystal had a lower initial corrosion potential and charge transfer resistance.The granular streamline Al2Ca and the small size grain produced more grain boundaries,so the effect of corrosion inhibition was more obvious.The flame retardancy of Mg-8Li-5 Al-5Ca alloy is better than that of many other commercial magnesium alloys.Its ignition point can reach 721 ? because of protection function of high temperature Al2Ca phase and dense films cross-linked by MgO,Al2O3 and CaO.