Research On Microstructure And Mechanical Properties Of Mg-7.0Zn-0.7Y-1.0Ce-0.3Zr Alloy By Rolling Process

Mg-Zn-Y series alloys are widely used in industrial production as a relatively cheap deformed magnesium alloy.However,the magnesium alloy of this series has low strength and poor plasticity.Therefore,the introduction of effective strengthening phase through alloy composition design,coupled with extrusion and rolling process,can improve its structure and performance,which can provide theoretical basis and technical support for the development of high-strength and toughness rare earth magnesium alloy plates.For this reason,as-cast Mg-7.0 Zn-0.7Y-1.0Ce-0.3Zr alloy were prepared by traditional gravity casting.After solid solution treatment,the extrusion plate was prepared by hot extrusion,and then the solid solution and extrusion plates were rolled respectivly.By means of OM,SEM,TEM,EBSD and XRD,the microstructure of the alloy in different states was compared and analyzed.The hardness and tensile mechanical properties of the alloy were tested at room temperature and the toughening mechanism was discussed.The main conclusions are as follows:(1)The microstxucture of as-cast Mg-7.0Zn-0:7Y-1.0Ce-0.3Zr alloy is composed of a-Mg matrix,MgZn2 phase,I-Mg3Zn6Y quasicrystal phase and Mgl:sZn9.sCe3 phase.The hardness,ultimate tensile strength,yield strength and elongation of the as-cast alloy are 61.2 HVi;?190 MPa,78 MPa and 4.5%,respectively.After solution treatment at 400'C for 8 h,the phase composition do not change,but the volume fraction of the second phase decrease in the structure,and the grains are obviously coarsened.The hardness,ultimate tensile strength,yield strength and elongation of the solid solution treated alloy are 56.4 HV10,185 MPa and 83 MPa and 6%,respectively.(2)The optimal solid solution and rolling scheme is:425? rolling to 70%deformation.The rolled microstructure has obvious morphologic characteristics.Dynamic recrystallization is observed in all the alloys with grain size ranging from 6 to 10?m.The ultimate tensile strength and yield strength of the alloy increased to 282 and 252 MPa,respectively,and the yield ratio increase from 0.45 to 0.89,but the elongation decrease from 6%to 2%.(3)After hot extrusion at 420?,the alloy phase composition does not change and presente equiaxial crystal morphology.At the same time,the morphology of the second phase change significantly,with the aggregation of large block phase,long strip phase and large network phase completely disappearing.The morphology of the second phase change into small block and small particle phase,and the second phase is linearly distributed along the extrusion direction.The comprehensive mechanical properties are improved significantly.The ultimate tensile strength and yield strength increase from 185 and 83 MPa to 262 and 178 MPa,respectively.Elongation increase from 6%to 15%;The yield to strength ratio increase from 0.45 to 0.68.(4)The optimal extruding and rolling scheme is:425? rolling to 85%deformation.The rolling structure is equiaxed grain,which is the result of dynamic recrystallization.The grain size of the alloy is 4-9?m,and the second phase content is the largest.The tensile strength and yield strength increased to 318 and 280 MPa respectively,the yield ratio increase from 0.68 to 0.90,and the elongation decrease to 10%.(5)After hot rolling,severe plastic deformation occurs and the degree of dynamic recrystallization deepens with the increase of rolling temperature and deformation.The more complete the dynamic recrystallization,the finer and more uniform the grain.The mechanical properties of the alloy are improved by working hardening,second phase hardening and fine grain hardening.