Effect Of High Pressure On Microstructures And Mechanical Properties Of Mg-Zn-Y Alloys Reinforced By Quasicrystals

The super-high pressure can modify the solidification mechanism of alloys,which results in variation of microstructures and mechanical properties.The present paper has chosen four Mg-3.64Zn-1.63Y(wt%),Mg-8.65Zn-1.56Y(wt%),Mg-14.09Zn-1.52Y(wt%)and Mg-9.96Zn-2.10Y(wt%)as-cast alloys to conduct high pressure solidification experiments with CS-IB Cubic Hydraulic Pressure Machine and meanwhile high pressure experiments of Mg-9.96Zn-2.10Y(wt%)alloy at 2,4,6 GPa were performed attached to high pressure experiments with different cooling rate at constant 4 GPa;The microstructures and phases composition of above several alloys were observed and identified respectively by means of OM,SEM,EDS and XRD.The Vicker-hardness and room temperature compression properties of above normal and high-pressure alloys were examined with almighty WDW3100 tester and FM-ARS9000 micro-hardness tester.The heat compression experiments of Mg-9.96Zn-2.10Y(wt%)alloy were conducted on the Gleeble-3500 heat/stress simulation experimental device to investigate the effect of the microstructures change brought about by pressure on heat flow deformation behavior.The results indicate that the as-cast microstructures of all four alloys are coarsened and shown to be inhomogeneous.And the secondary phases are characterized with thick netted-connect.However,microstructures under high pressure are refined and grain sizes are uniform.The secondary phases in Mg-3.64Zn-1.63Y(wt%)?Mg-8.65Zn-1.56Y(wt%)and Mg-9.96Zn-2.10Y(wt%)alloy are all distributed with thin and dispersion gradually as the solidification pressure increases,especially secondary phases under 4,5 or 6 GPa disperse in matrix uniformly.But most of the secondary phases are observed with continuous net in Mg-14.09Zn-1.52Y(wt%)alloy solidified under high pressure with the decrease of disperse particle-secondary phases.The solid solubilities of Zn in the four alloys increase with increasing pressure.The faster the cooling rate of the high pressure solidification alloy is,the thinner the microstructure of alloy is.As to the mechanical properties of alloy,the average hardness of other three alloys increases gradually with the elevation of pressure except for Mg-9.96Zn-2.10Y(wt%)alloy.The hardness of Mg-9.96Zn-2.10Y(wt%)increases first and then decreases with hardnessvalue of 6 GPa being lower than that of 4 GPa.The ultimate compression strength of four alloys increases gradually.And the reduction ratio of Mg-14.09Zn-1.52Y(wt%)alloy decreases gradually,but the reduction ratio of other three alloys elevates by degrees.Under constant pressure condition the hardness and the ultimate compression strength of studied alloys increases with the increase of content of solute atoms on the whole.For example,the hardness values of the as-cast Mg-3.64Zn-1.63Y(wt%),Mg-8.65Zn-1.56Y(wt%),Mg-9.96Zn-2.10Y(wt%)and Mg-14.09Zn-1.52Y(wt%)are53.43,63.35,68.37 and 77.84 HV respectively and the ultimate compression strengths of that are 252.93,333.89,344.82 and 372.14 MPa,the hardness values of the above order alloys under 4 GPa are 85.47,105.63,112.54 and 131.29 HV and the ultimate compression strengths of that are 350.88,407.54,456.23 and 555.58 MPa.