The Study Of Quasicrystal In Mg-Zn-Y Alloy And Appliation Of Quasicrystal Strengthening Magnesium Alloy

Magnesium alloy is one of the lightest materials among the industry application alloys. Magnesium alloys have good strength , particularly, which specific strength are nearly equal to that of aluminium alloys .With good processing property , corrosion resistance,well heat conductivity, damping and electromagnetsim shield properties ,Magnesium alloys are wildly considered to be the advanced industry alloy in future.However , the disadvantage of magnesium alloys are low room temperature strength and poor elevated temperature strength, thus, many workers at present have focused on development of high strength magnesium alloys .Quasicrystal has high hardness and the Young's modulus. Since it has been discovered at 1984, it keeps constantly relation with the alloy strength. If distributing stable quasicrystal particles with appropriate dimension homogeneously in magnesium matrix ,high-strength magnesium alloy can be produced.The stable icosahedral quasicrystal in Mg-Zn-Y system alloy was fist discovered by Luo in 1993 .Later, the researcher found that the quasicrystal has good potential formative ability and it can be formed at a wide component range at a large volume fraction in Mg-Zn-Y system alloy. This alloy system provide a bright way for producing quasicrystal -strengthed magnesium alloys.In the present thesis,the preparation of Mg-Zn-Y quasicrystal,mopholgy evolution,microstructures analysis and structure examination were completed and a high strengthen magnesium alloy strengthened by quasicrystal particles was produced by melt-mixing method. The research results of the paper are as follow:1. The stable icosahedral quasicrystal was successfully prepared in Mg-Zn-Y system alloy by traditional cast method. The quasicrystal was identificated by X ray diffraction and TEM technology to be stable Icosahedral quasicrystal .The quasicrystal composition is calculated to be Mg₂9Zn₆3Y₈ by EDX.2. The solidification process of Mg₃0Zn₆0Y₁0 alloy ,quasicrystal forms by peritectic reaction at 647℃ ,the primary phase composition is7o.6oYi3.o8,which forms about at 723 °C.3. Icosahedral phase has special quasi-structure ,so its growth morphology is different from the common crystal phase. In Mg-Zn-Y system alloy, the morphology of quasicrystal is liable to be petal-like. The six-branches, five-braches, and polygon-like quasicrystal are all observed in the solidification microstructure of Mg-Zn-Y system alloy.4. Alloy composition and cooling rate are major actors depending on the patterns of icosahedral quasicrystal morphology.The more content of low-temperature phases,such as Mg3Zn7 phase, and the slower cooling rate ,the much more easily changing the petal-like to polygon-like morphology by interface energy.5. Through the melt-mixing method ,the main phases in final mixing alloy are a-Mg, Mg2Zn, AI3Z114Y3 which have changed dramatically compared to masteralloys. The tensile test shows that the mixing alloy has ab 200 MPa ,which is higherthan AZ91 alloy . The quasicrystal-strengthed mechanics is attributed to good interface action force between quasicrystal / matrix and dislocation movement hindered by quasicrystal.