Of Mg-8li-y Alloys Organizational Structure And Mechanical Performance

Mg-Li alloy also is known as lightweight alIoy,the density of magnesium is 1.738 g/cm³,as well as lithium of 0.538 g/cm³,adding lithium to magnesium, which reduces the density of magnesium alloy,improve the stability and plastic,make it to be more outstanding performance lightweight structural materials.It not only has the density of smaller,but also has a high strength, stiffness ratio and excellent anti-vibration properties and the ability to penetrate high-energy particles,in particular its deformation(forging of)better than other magnesium alloy,so it be used in weapons,aerospace,automotive,electronics,and other fields.At the present time,deforming Mg alloy has been extensively used in modern aerospace plane,but it is initial step in cast Mg-Li alloy study.Based on detail reviews of the progress of Mg-Li alloys,the heat treatment process of the cast Mg-8Li-xY was studied.Vacuum melting method and heat treatment method,were carried out together.The effects of the heat treatment process and heat treatment processing parameters on the microstructure and mechanical properties of the testing cast Mg-8Li-Y alloys have been investigated by means of mechanical property measurement,optical microscopy,scanning electron microscopy and micro hardness tester,respectively.Influence on microstructure and mechanical properties of the test Mg-8Li-Y alloys caused by different heat treatment process has been studied.Influence degree of heat treatment processing parameters such as solution temperature,solution time,ageing temperature and ageing time on microstructure and performance of the testing Mg-8Li-Y alloys has been analyzed. Similarly,heat treatment strengthening mechanism of cast Mg-8Li-Y alloy has also been discussed.The main results are as follows:1.The Mg-6.84Li cast alloy is mainly composed byβ-Li phase andα-Mg phase which is elongated strips.2.Heat Treatment can be greatly enhanced Mg-6.84Li alloy tensile and yield strength,with the increase of temperature quenching,Mg-6.84Li alloy tensile strength,yield strength gradually increased,the elongation rate decreased gradually. 3.Mg-6.84Li and Mg-8Li-xY alloys in the process of heat treatment will be a singleαphase in the surface segregation,when the heating rate greater than 10℃/ min,the temperature at 300℃above,the Alloy will be found theα-phase surface segregation.4.Alloy in the encloSed space of heat treatment process,the specimen surface area and sealed air ratio greater than 1 / 40(mm-1)can make a surface segregationαphase,the cooling rate have a certain degree of influence about densification ofαphase,cooling the faster,the better.5.Y can be refinedαphase structure to a certain extent of the Mg-Li alloy;with the increase of the Y content of the alloy in a major organizational change,a new hardening generation ofγ-phase will be found;When the Y in more than 6 wt%,a large number ofγmeet enrichment in the grain boundary,network structure formed;when Y in 10 wt%,the alloy of theα-Mg disappear.6.Y has effectively improved the Mg-Li alloy of the tensile strength,yield strength;When the Y in the amount of 4 wt%,the tensile strength of the alloys increased 17.5%with 43.4%elongation,there was a relatively good mechanical properties.7.Mg-8Li-Y alloys have better mechanical properties with 500℃heat treatment,Mg-8Li-2Y alloy has the highest tensile strength of 211 MPa after quenching treatment,comparing to cast achieved an increase of 71%,while its elongation at 15.6%;This is a great significance for achieving engineering materials.8.With increasing temperature quenching(300℃to 500℃),Mg andγ(Mg₂₄Y₅)to theβphase increase in the solution,along with the lattice constantβphase,the reduction of hardening alloy hardness increase;When quenching temperature rises to 500℃,with the solution degrees andγ(Mg₂₄Y₅)of the circular spherical uniform distribution,the alloy tensile strength increase sharp.9.After aging at 150℃for 24 hours,grain will grow up,Mg and Y in theβphase solution decreases,αandγphase will precipitate along withβphase grain boundary,all which lead alloy tensile strength and elongation decreased.