Study On The Phase Transformations And Equilibria Of Low-Y Side In Ternary Mg-Zn-Y System

Magnesium alloy,as one of the lightest metal structure material,is widlely applied in aviation,military,transportation and 3C industries.However,the applications of Mg alloys are restricted due to their poor ductility and creep resistance.It shows that there is a stable two phase coexisting region consists of ?-Mg and I phase.And quasicrystal reinforced high strength magnesium alloys can be produced,with some volume fraction of quasicrystal evenly distributed in the magnesium matrix.It provides a new way to improve the performance of magnesium alloy.And alloy design needs the support of related information of quasicrystal phase equilibrium.The related quasicrysal phase transformations and equilibria in ternary Mg-Zn-Y systerm alloy are studied in this paper by SEM,EPMA,XRD,DSC and TEM,determining low Y part at 400?,450?,475? isothermal section diagram,with the conclusions as follows:The stability of the hexagonal structure Z phase,icosahedral quasicrystal,hexagonal structure H phase and face-centered cubic W phase coexisting with a-Mg solid solution in the low-Y side of Mg-Zn-Y system are different.Among them,the stability of W phase is the highest,followed by H phase and icosahedron quasicrystal I phase.Also,the stability of the worst is Z.The I phase can coexist with ?-Mg solid solution up to 448.8?C and the eutectic reaction?-Mg+I?Liq occurs.Also,the ternary peritectic reaction I+?-Mg?Liq+W occurs.The Z phase can coexist with ?-Mg solid solution up to 344.1 ?.Above this temperature,the hexagonal structure Z phase transform to icosahedral quasicrystal.Futhermore,the W phase can transform to H phase at 339.5 ?.There exist four three-phase regions consisting of I+H+a-Mg,I+liquid+a-Mg,H+W+a-Mg,Z+Zn2Mg+liquid in the isothermal section of low-Y side in Mg-Zn-Y system at 400?.The two-phase region a-Mg+I phase exists between I+H+a-Mg and I+liquid+a-Mg.In this two-phase region,the Zn/Y<6.76 and>5.87.When Zn/Y<3.77,1 phase does not exist and W phase appears.Meanwhile,the W+I tie-line not stable at 400 ?.When Zn/Y>6.76,the system is in liquid-state phase equilibrium.There exist a three-phase region of W phase + liquid + ?-Mg in the low-Y side of Mg-Zn-Y alloys at 450? and 475 ? isothermal section.Comparing to 400 ? isothermal section,the Y content in the liquid phase varies from 0.6%to 3.4%.Till 475 ?,the solubility of Y atoms up to 6.6%.