Effects Of Y, Sc And Zr Addition On Microstructure And Mechanical Properties Of Mg-14Li-3Al Alloy

Magnesium and magnesium alloys are the lightest metal structural materials used today.It has the characteristics of low density,high specific strength and specific stiffness,excellent mechanical properties,good thermal conductivity and excellent electromagnetic shielding performance,but its strength is low,which restricts it to become a common structural material.So people add different alloying elements in pure magnesium to improve their performance.In this paper,microalloyed magnesium-lithium alloy ingot was prepared by vacuum melting.By adding alloying elements of Y,Sc and Zr to Mg-14Li-3Al alloy,these alloying elements react with Al to form as many secondary phases as possible to improve the mechanical properties of the alloys.Deformation strengthening of the as-cast alloy was realized by hot rolling.The microstructure of the alloy was studied by means of metallographic microscope,X-ray diffractometer and scanning electron microscope.The mechanical properties of the alloy were tested by universal electronic tensile machine and microhardness tester.The main contents and results of the study were as follows:Themicrostructureandmechanicalpropertiesofas-cast Mg-14Li-3Al-1Y-0.2xSc-0.1xZr alloy were studied by adding 5 different components of Y,Sc and Zr in Mg-14Li-3Al alloy.Then the as-cast Mg-14Li-3Al-1Y-0.2xSc-0.1xZr alloy was hot rolled at 200°C.The microstructure of the alloy was observed and the mechanical properties of the alloy were tested.The relationship between microstructure and mechanical properties was investigated.The addition of Y,Sc and Zr in the as-cast Mg-14Li-3Al alloy can reduce the average grain size and form new precipitates.Y and Sc can react with Al to form Al₃Sc-Al₂Y composite particles in the alloy.As the amount of rare earth addition increases,the precipitation of Al₃Sc-Al₂Y composite particles in the alloy also increases.There is also a phase containing AlSc2 in the alloy containing rare earth elements 1Y-0.2Sc-0.1Zr,1Y-0.4Sc-0.2Zr and 1Y-1.0Sc-0.5Zr.When Zr content is less than 0.4%,Zr is all dissolved in the matrix.When Zr content is equal to 0.5%,the Zr begins to segregate.The addition of rare earth elements increases the strength and hardness of as-cast Mg-14Li-3Al alloy,but decreases its plasticity.The reasons for increasing the strength of as-cast alloys are solid solution strengthening,fine-grained strengthening,and dispersion strengthening of precipitates.The reason for reducing the plasticity of alloy by adding rare earth elements is that slag inclusion and defect are inevitably introduced in the process of melting alloy.The solid solution of rare earth elements and the formation of the second phase lead to the stress concentration and defect in the alloy,which leads to the decline of the plasticity.After hot rolling at 200 degree,the strength and hardness of the as-cast Mg-14Li-3Al-1Y-0.2xSc-0.1xZr alloy plate were obviously improved,and the plasticity was polished up.Finally,the tensile strength of the alloy with the best comprehensive mechanical properties reached 186 MPa,51 MPa higher than that of the cast Mg-14Li-3Al alloy,the yield strength reached 171MPa,51 MPa higher than that of the cast Mg-14Li-3Al alloy,and the elongation reached 24.8%,which was 6.2 points higher than that of the cast Mg-14Li-3Al alloy.The maximum tensile strength of the alloy reached 202MPa,the yield strength reached188MPa,the elongation reached 24.8%,and the hardness value reached 72HV0.2.