Evolution Of Microstructure?Texture And Mechanical Property In Mg-Y Alloys During Equalchannel Angular Pressing

Magnesium(Mg)alloys have broad application prospect in transportation and aerospace industried due to its lower density,higher specific strength and specific stiffness.However,widespread use of Mg alloys was limited by its poor strength and formability in room temperature.The alloying and grain refinement were the effective way to improve strength and plasticity.Latest results have been reported that Y addition is expected to weaken basal texture for good ductility.Meanwhile solution strengthening is introduced to improve strength in Mg alloys.Grain refinement can both improve strength and plasticity at the same time.Equal-channel angular pressing(ECAP)is used to refine grains effectively by severe deformation introduced.ECAP is one kind of methods to prepare bulk ultra-fined grain materials effectively.Now the investigations of strong basal texture Mg-Al and Mg-Zn alloys during ECAP are systematic and extensive.Nevertheless,fewer systematic results about ECAP of weak basal texture Mg alloys with Re elements have been reported.This article investigated the microstructure,texture and mechanical property evolution of as-extrusion and as-cast Mg-Y alloys by different ECAP procedures.The main results are as follows:1.The addition of Y element(0-5 wt.%)reduced grain size of both pre-extruded and ascast Mg-Y alloys.Meanwhile strengths were improved at RT tensile.The microstructure of as-cast Mg and Mg-1Y alloy consist of columnar grains,while equal-axed grains in as-cast Mg-5Y alloy.2.The reducing temperature from 400? to 300? can result in lower grain sizes and microstructure homogeneity in constant temperature ECAP process.The increasing passes make strain accumulated,and make microstructure more and more homogeneous by DRX.The increasing content of Y improve thermos-stability of Mg-Y alloy in ECAP process.3.The homogeneous microstructure with an average grain size of 6.1 ?m was obtained in pre-extruded Mg-1Y by reduced temperature ECAP.However crack occurred in low temperature(300?)by constant temperature ECAP.4.ECAP make basal pole of pre-extruded Mg-Y alloy more random.The weaker basal texture is in favor of activation of basal slip system.Compared to pre-extruded Mg-5Y,the strength and plasticity were improved by 300?-4P ECAP process.The UTS(306.4 MPa)increased by 5.6%,the YS(273.9 MPa)increased by 9.8% and the EL(23.9%)increased by 60.4%.The effect of ECAP on mechanical property in Mg-Y alloys is combined action of texture weakening and fine-grain strengthening.Hardness after ECAP reduced with increasing grain size.5.With increasing passes and increasing Y content,grain size decrease in cast Mg-Y alloy by reduced temperature ECAP.For cast Mg-1Y,crack occurred in 4passes,which indicated the plasticity of cast Mg-1Y weaker than cast Mg and Mg-5Y.6.ECAP make hardness increase with passed and all ECAPed hardness are greater than that of as-cast.Compared to as-cast Mg-5Y,both of strength and plastic are improved by ECAP 4passes.YS(225.6 MPa)increased by 405.8%,EL(16.6%)increased by 33.9%,which are similar to pre-extruded Mg-5Y bar.