Preparation And Research On Microstructure And Properties Of Mg-8Li-xAl-0.5Ca Alloys

Mg-Li alloy is the lightest structural metallic materials with many advantages,such as high specific strength,high specific stiffness,electromagnetic shielding and thermal conductivity.It has wide application prospect in industry.However,the problems of low strength and poor plasticity of Mg-Li alloys greatly limit it wide application in many fields.Addition of alloying elements in mg-Li alloys is an important strengthening method,and Al elements are commonly used as strengthening elements in mg-Li alloys.Therefore,Mg-8Li-xAl-0.5Ca alloy was prepared by adding different content of Al element on the basis of Mg-Li-Ca alloy in this paper and system to study the effect of Al element on microstructure and properties of Mg-8Li-x Al-0.5Ca alloy.In this study,different content of Al element was added on the basis of Mg-Li-Ca alloy,and a new Mg-8Li-xAl-0.5Ca alloy was prepared by infiltration method.The microstructure and mechanical properties of as cast and extruded alloys were studied respectively.The following conclusions are drawn:(1)The as-cast Mg-8Li-0.5Ca alloy is mainly composed of α-Mg phase,β-Li phase and granular Mg2 Ca phase.With the increase of Al element in the alloy,the number of α-Mg phase increases first and then decreases.When the content of Al in the alloy is 3%,the granular Mg2 Ca phase in the alloy is replaced by the fishbone like Al2 Ca phase.When the content of Al in the alloy increases to 6%,the lamellar AlLi phase and the granular MgAl Li2 phase appear in the alloy.When the content of Al in the alloy reaches 9%,the lamellar AlLi phase increases further.(2)The mechanical properties of as-cast Mg-8Li-x Al-0.5Ca alloy shows:With the increase of the content of Al,the tensile strength and yield strength of the alloy increased first and then decreased and the elongation rate decreased with the increase of Al content in the alloy.The maximum tensile strength and yield strength of as-cast Mg-8Li-3Al-0.5Ca alloy were 150.5MPa and 110.8Mpa,respectively.Compared with the as-cast Mg-8Li-0.5Ca alloy without the addition of Al,the growth rates were 22.9% and 34.1%,respectively.(3)The grain size of the as cast alloy was obviously refined and the segregation was not obvious after extrution.The α-Mg phase and β-Li phase was elongated to fibrous along the extrusion direction.The small equiaxed grains appear in the α-Mg phase and β-Li phase.The fishbone like Al2 Ca in the alloy was crushed into a granular distribution along the extrusion direction.The lamellar Al Li phase was broken into small particles distributed at grain boundaries and phase boundaries.(4)The mechanical properties of extruded Mg-8Li-xAl-0.5Ca alloy shows:Compared to the as cast alloy,the tensile strength,yield strength and elongation of the extruded alloy are greatly improved.The extruded Mg-8Li-6Al-0.5Ca alloy has the best comprehensive performance,the tensile strength,yield strength and elongation are 251.2MPa and 220.6MPa,23.5%.The mechanical properties of the alloy have been greatly improved by extrusion deformation.