Effect Of Sn Addition And Heat Treatment Process On Microstructure And Mechanical Properties Of Mg-Zn-Y Alloys Reinforced By Quasicrystal Phase

Magnesium alloy is regarded as the most potential green engineering material in the 21st century.It has been widely used in aerospace,electronic communication,national defense and other important fields.The performance requirements of magnesium alloy are also increasing.The development and application of magnesium alloy with excellent mechanical properties have become the focus of current research.Magnesium alloy containing rare earth has excellent room temperature strength and high temperature creep resistance,but its high cost limits its application.Mg-Zn-Y alloy reinforced by quasicrystal phase is a typical high strength and low rare earth magnesium alloy,which has attracted the attention of researchers at home and abroad.In this paper,based on Mg-Zn-Y alloy,the microstructure and mechanical properties of the alloy were controlled by adding Sn and optimizing the hot treatment process.The morphology,distribution and volume fraction of I-phase in as-cast,as-extruded and as-aged state were studied by OM,SEM and TEM.The transformation of precipitates during solidification due to the addition of Sn was discussed by XRD and DSC.EBSD was used to analyze the texture transformation of the alloy after different pre-deformation.Finally,the ultimate tensile strength,yield strength,elongation and Vickers hardness at room temperature were used to characterize the properties of the alloy.The effects of Sn addition and different hot treatment processes on the microstructure and properties of Mg-Zn-Y alloy reinforced by quasicrystal phase ware studied,and the magnesium alloy with excellent comprehensive mechanical properties was explored to expand the application scope of magnesium alloy.Mg-8Zn-2Y-x Sn(x=0,0.5,1.0 wt.%)alloy was designed.The ingot was obtained by melting.And then the effect of Sn on the as-cast microstructure feature of Mg-8Zn-2Y alloy was studied,especially the effect of Sn addition on the morphology and distribution of quasicrystal phase.The results show that the as-cast microstructure of Mg-8Zn-2Y-x Sn alloy is dendrite like.With the addition of Sn,the secondary dendrite spacing is refined.0.5wt%Sn is the best.The second phase of Mg-8Zn-2Y alloy consists of continuous network?-Mg/W-phase eutectic on the grain boundary and I-phase particles in the matrix,while the compounds on the grain boundary of alloy containing Sn change into?-Mg/I-phase eutectic,and the lamellar spacing is obviously reduced.In addition,a small amount of Sn₃Y₅ was distributed in the matrix.At the same time,the solidification process of Mg-8Zn-2Y-x Sn alloy was analyzed in detail.The microstructure and mechanical properties of Mg-8Zn-2Y-x Sn alloy as-extruded and as-aged were studied.Microstructure of extruded Mg-8Zn-2Y-0.5Sn alloy consists of fine I-phase particles distributed along the extrusion direction,fine dynamic recrystallization grains of submicron and a small number of deformed grains without dynamic recrystallization.The ultimate tensile strength of the alloy increased from352MPa of Mg-8Zn-2Y to 401MPa due to the high volume fraction of I-phase particles and ultrafine dynamic recrystallization grains.When Sn was added to 1.0 wt.%,complete dynamic recrystallization took place,the microstructure became more uniform and better plasticity was obtained.A large number of Mg-Zn phases were precipitated during the aging treatment of Mg-8Zn-2Y-x Sn at 160?,and the mixed structure of Mg-Zn phase and I phase is observed in the aged alloy.The yield strength of Mg-8Zn-2Y-1Sn alloy is increased from 274MPa to 360MPa,and its elongation more than 20%.The solid solution process of Mg-8Zn-2Y alloy was studied.The results show that after solid solution at 420?/24h+445?/10h,the continuous network W-phase eutectic on the grain boundary mostly dissolves into?-Mg,and a small amount of discontinuous W-phase remains on the grain boundary.In addition,the effect of the billet microstructure on the properties and microstructure of the hot-rolled alloy was studied.It is found that the second phase of solution alloy after rolling is mainly fine particles precipitated dynamically during rolling,while the second phase of the alloy directly rolled as cast is mainly a large number of broken long strip particles distributed along the rolling direction.The ultimate tensile strength of as-cast direct rolling alloy is34%higher than that of solution rolling alloy,and the elongation is reduced from 15.1%to 9.5%.The response of pre-compression deformation to age hardening(at 160?)of Mg-8Zn-2Y alloy plate was studied.After 10%compression strain along the TD direction of the plate,the{10 1?2}twinning deformation is initiated,and the microstructure is mostly twinned.At the same time,the c-axis of most of the grains turns to TD direction,and the texture component becomes(0001)//TD.A large number of twin boundaries and high density dislocations provide more nucleation substrates for precipitates.The increased volume fraction of rod-shaped and granular Mg-Zn phases in the matrix and the I-phase particles on the twin boundary make the Mg-8Zn-2Y alloy reach a higher peak hardness.