Study On The Structure And Properties Of Mg-Gd-Y-Zn-Si Magnesium Alloy With High Elastic Modulus

In recent years,aerospace weapons and equipment have put forward higher requirements for the stability and lightweight of load-bearing parts.The tensile strength of magnesium alloy at room temperature can reach more than 450 MPa and the elastic modulus is only about 45 GPa,showing an obvious "strength-modulus" mismatch problem,resulting in significant elastic deformation of magnesium alloy parts under high stress,which seriously affects the service effect.Therefore,the development of high elastic modulus magnesium alloy is of great significance for the upgrading of aerospace weapons and equipment.In view of the above problems,based on the widely used high-strength and heatresistant Mg-Gd-Y-Zn magnesium alloy,the reinforcing phases are formed in situ by adding silicon to the melt,and the uniform distribution and refinement of the reinforcing phases are realized by near liquidus mechanical stirring and blending melting;The evolution of microstructure and properties of the new alloys in as cast,homogenized,extruded and aged states was systematically studied by means of ICP,OM,SEM,TEM,resonance instrument,nano indentation and mechanical properties at room temperature.The characteristics of volume fraction and size distribution of reinforcing phase were mainly revealed.The specific results are as follows:Three kinds of VW75-xZn-ySi（x=0,0,2,y=1,2,2,wt.%）alloys（1Si,2Si,2Zn2Zi alloys for short）were prepared by ordinary mold casting+liquid stirring method.The reinforced phases were seriously precipitated and cluster.XRD shows that the high modulus reinforcing phases are YSi and Gd5Si3.The average particle size of the reinforced phase particles of the three alloys is 5.7 μm、4.1 μm and 3.5 μm respectively.After extrusion,the reinforced phase distribution of the three alloys is more uniform,and the reinforced phases of 1Si and 2Si alloys is broken and refined to 3.4 respectively μm and 3.7 μm.The average particle size of 2Zn-2Zi alloy is still 3.5 μm.After adding Si and Zn,the elastic modulus of magnesium alloy is improved with the formation of RE-Si phase.The area fraction of reinforcing phases at the bottom of 2Zn-2Si ingot is 8.5%,2Si alloy is 8.4%,1Si alloy is 5.7%,and the elastic modulus is further improved because of LPSO phase.The elastic modulus at the bottom of 2Zn-2Si ingot is the largest,which is 48.7 GPa.After extrusion deformation,the volume fraction of reinforcing phase particles increases,and the elastic modulus of alloy increases,and 2Zn-2Si is 51.5 GPa,T5 treatment has little effect on the elastic modulus of the alloy.The T5 elastic modulus of 2Zn-2Si alloy is 53.4 GPa.After adding Si and Zn,the content of solid solution rare earth in the alloy matrix decreases,resulting in the weakening of precipitation strengthening effect.The T5 tensile strength,yield strength and elongation of 2Zn-2Si alloy are 239 MPa,145 MPa and 6.5%respectively,and the tensile strength is about 128 MPa lower than that of 1Si alloy.In order to improve the mechanical properties of Mg-RE-Zn-Si high modulus magnesium alloy and solve the settlement and cluster of reinforcing phases,Mg-10Gd-8Y1Zn-2Si alloy was prepared by mold casting and near liquidus mechanical stirring.Near liquidus stirring greatly promoted the uniform distribution of reinforcing phases.After extrusion deformation,the reinforcing phase particles were broken and refined to 0.9 μm.The average volume fraction is 12.9%and the length ratio is 1.12.The dynamic elastic modulus of the alloy as extruded is 52 GPa.The nano indentation experiment shows that the average elastic modulus of high modulus particles is 147.5 GPa.Combined with Halpin-Tsai model,the calculated elastic modulus of the alloy as extruded is 50.8 GPa,with an error of 3.4%compared with the experimental value.The alloy reaches the peak hardness at 200℃/26 h.The room temperature tensile properties of T5 state:the tensile strength is 377 MPa,the yield strength is 275 MPa and the elongation is 2%.Mg-10Gd-8Y-1 Zn-2Si ingots were prepared by double doping method and near liquidus mechanical stirring.Compared with simple near liquidus stirring,the double doping method greatly refined the size of the strengthening phase and significantly improved the T5 state strength of the extruded material.After extrusion deformation,the reinforced phase particles are broken and refined to 0.7 μm.The volume fraction is 9.05%and the average aspect ratio is 1.10.Combined with Halpin-Tsai model,the elastic modulus is 54.2 GPa,the experimental value is 52.4 GPa,and the error is 3.4%.The alloy reaches peak aging at 200℃/24 h.The room temperature tensile properties of T5 state:tensile strength 415 MPa,yield strength 349 MPa,elongation 1.5%,and elastic modulus 53.3 GPa.