| Magnesium lithium alloy is the lowest density of structural metal materials.Compared with other structural materials,magnesium lithium alloy has the advantages of high specific stiffness,high specific strength,easy recovery and easy cutting.It has wide application prospects in the fields of electronics,automobile and national defense,but the strength of Mg-Li alloy is not high and the thermal stability is poor.The results show that the yield strength of Mg-Li is lower than 100 MPa at room temperature,and the tensile strength is generally lower than 120 MPa.This greatly limits the application of Mg Li alloys in many fields,especially as structural materials.Therefore,it is necessary to improve the mechanical properties of Mg-Li alloy by alloying and processing.Al element and Sn element can be used as alloying elements to improve the mechanical properties of Mg-Li alloy.In this paper,Mg-6Li-xAl-0.8Sn(x=0,1,3,5)alloy with different Al content was prepared on the basis of Mg-Li-Sn alloy.By using optical microscope(OM),scanning electron microscopy(SEM),X-ray diffraction(XRD)and sans CMT-5105 electronic universal testing machine for casting,solid solution state and extruded Mg-6Li-x Al-0.8Sn alloy microstructure observation and mechanical properties test,the conclusions are as follows:(1)As cast Mg-6Li-0.8Sn alloy is composed of Mg2 Sn and Li2 MgSn.After adding Al element,the matrix of Mg-6Li-xAl-0.8Sn(x=1,3,5)alloy is composed of α-Mg and β-Li phase.When 1% Al was added,the new compounds Mg17Al12 and LiMgAl2 were appear.Mg17Al12 was mainly distributed in the α/β boundaries,and LiMgAl2 was mainly distributed in the β phase.When the Al content is 3%,the second phase alloy in the transition from Mg17Al12 phase to AlLi phase and LiMgAl2 phase,lamellar AlLi phase distribution in β phase.When the content of Al increased to 9%,with the disappearance of the Li MgAl2 phase in the alloy,the second phase of the alloy was mainly distributed in the Al Li phase on the phase and the bulk Mg2 Sn and Li2 MgSn.(2)The addition of Al can obviously improve the strength of as cast Mg-6Li-0.8Sn alloy.With the increase of Al content,the tensile strength of the alloy increases firstly.When the content of Al is greater than 3%,the tensile strength of the alloy decreases slowly.When the content of Al is 3%,the tensile strength of the alloy reaches the maximum value of 173.1Mpa.The yield strength of the alloy has been increasing always.When the content of Al is 5%,the yield strength of the alloy reaches the maximum value of 152.3Mpa.Compared with the Mg-6Li-0.8Sn alloy without Al addition,the increase was 67.6% and 170.5%,respectively.(3)Mg-6Li-0.8Sn solid solution alloy still consists of α-Mg、Mg2Sn and Li2 MgSn,but the intensity of the diffraction peaks of Mg2 Sn phase and Li2 MgSn phase decreased,with the addition of Al elements,Mg-6Li-1Al-0.8Sn alloy after heat treatment phase composition changes,When the content of Al was 3%,the diffraction peak of Mg17Al12 phase disappeared,completely soluble in beta phase.When the content of Al was 3% and 5%,the peak intensity of AlLi phase in Mg-6Li-x Al-0.8Sn(x=3,x=5)alloy after heat treatment did not change obviously.(4)The as cast and solid solution treatment of Mg-6Li-x Al-0.8Sn alloy in the α and β phase hardness with the increase of Al content showed a rising trend,and after solution treatment of α and β phase when the content of Al is 5% reaches its maximum value,respectively 88.6HV and 92.1 HV.The hardness of α-Mg phase in Mg-6Li-1Al-0.8Sn alloy was improved by 15.6HV,the hardness of β-Li phase was increased by 29.7HV,and the increase rate was 31.2% and 69.4%,respectively.(5)After extrusion deformation,the grain size of Mg-6Li-x Al-0.8Sn alloy is obviously refined,the second phase distribution is more uniform and the overall mechanical properties of the alloy are improved remarkably.The extruded Mg-6Li-1Al-0.8Sn alloy has the best comprehensive mechanical properties.With the elongation of 30.5%,the tensile strength of 201.2MPa is still high. |
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