High Pressure Solidification And Heat Compression Behavior Of Mg-Zn-Y Alloy

In this thesis, Mg-7.50Zn-3.39Y and Mg-7.58Zn-1.68Y alloys have been prepared with the2RRL-M8vacuum resistance smelting furnace. The two kinds of conventional casting alloys were solidified at2GPa and4GPa using CS-IB type hexahedron anvil machine. The heat compression test of conventional casting alloys and high-pressure-solidification alloys was studied by Gleeble-3500thermal/mechanical simulation tester. The microstructure, phase composition and microstructure after heat compression of alloy solidified under different pressures were investigated by metallographic, scanning electronic microscopy (SEM), the energy dispersive spectrometer (EDS) and X-ray diffraction(XRD). Constitutive equations of both conventional casting alloys were constructed.The results showed that the microstructure of conventional casting Mg-7.50Zn-3.39Y and Mg-7.58Zn-1.68Y alloys are consisted of a-Mg matrix and the second phases distributed between dendrite. The a-Mg matrix of Mg-7.50Zn-3.39Y alloy is equiaxed dendrite and the α-Mg matrix of Mg-7.58Zn-1.68Y alloy is "ice" dendrite. The microstructure of alloy solidified under GPa-level pressure is refined significantly, and the higher the pressure is the finer the grain is. The content of Mg-7.50Zn-3.39Y conventional casting alloy from13.56%down to11.24%when solidification pressure is4GPa and the content of Mg-7.58Zn-l.68Y alloy from9.12%down to8.37%.The heat compression stress level and the true strain of peak stress of conventional casting Mg-7.50Zn-3.39Y and Mg-7.58Zn-1.68Y alloys are smaller than high-pressure solidification alloy. When the temperature is250℃and the rape is0.15s-1, the true strain of conventional casting Mg-7.50Zn-3.39Y alloy is0.23when the peak stress is176MPa, the true strain of4GPa-solidified alloy is0.18when the peak stress is215MPa. And the true strain of conventional casting Mg-7.58Zn-1.68Y alloy is0.24when the peak stress is129MPa, the true strain of4GPa-solidified alloy is 0.17when the peak stress is170MPa. Compared with the conventional casting alloy, the quantity of recrystal grains of high-pressure solidification alloy is less, the quantity of slip bands and twin crystal is more.The deformation mechanism of both alloys at low temperature is slip mechanism and twin mechanism, pay slip mechanism at intermediate temperature, climb mechanism at high temperature. As the temperature increases, the ability of grain boundary migration increases, the generation of twin crystal is inhibited, the rate of nucleation recrystal grains increases. The lower deformation temperature is, the fuller dynamic recrystal is. Therefore, the higher temperature and the lower rate is, the less content of twin crystal and the more content of recrystal is, and the higher peak stress is. Constitutive equations of Mg-7.50-Zn3.39Y and Mg7.58-Zn-1.68Y alloy is σm=12.674Inε+182.583and σm=13.158Inε+175.266.