Transformation Of Quasicrystal And Long-Period Order Structure In Magnesium Alloy

In this paper, Mg-based LOPS alloys and quasicrystalline alloys and their composites were prepared by copper mould casting. The microstructures and phase constituent were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Transmission Electron Microscope (TEM). The mechanical properties of the alloys were tested by universal electronic material testing machine, and the fracture surfaces were analyzed by SEM. The influence of Zn/Y ratio of the alloy on the phase composition and the influence of microstructure and phase composition on the mechanical properties of alloys were investigated. The conclusions were obtained as follows:1) In the Mg-4Ni-Zn-Y alloy, when Zn/Y ratio is less than 0.625, the internal enhanced phase of alloy is Mg12ZnY; when Zn/Y ratio is greater than 2.5, the enhanced phase isMg3Zn6Y, when Zn/Y ratio is between 0.625 and 2.5, the two enhanced phases both exist. With the Zn/Y ratio increase, needle long-period phase reduce and are dispersed gradually, quasi-crystalline phase, when the Zn/Y ratio reaches 0.625, quasicrystals appear and present a growing trend.2) In the Mg-4Ni-Zn-Y alloy, the yield strength increases and then decreases with Zn/Y ratio. Mg89Ni4Zn5Y2 alloy, which has the largest, has a minimum yield strength. Mg9o.8Ni4Zn2Y3.2 alloy and Mg83Ni4Zn5Y8 alloy, which have the same Zn/Y ratio, showed different yield strength, because of the differences of the content of the internal second phase.3) In Mg87-xNi8Zn5Yx (x=2,4,8) series alloys, content of amorphous phase will decrease with increasing content of Y, Mg79Ni8Zn5Y8 alloy has the highest ultimate tensile strength, it can achieve 812MPa, while Mg83Ni8Zn5Y4 alloy has the maximum plastic deformation, it can achieve 9%.4) Compared to Mg87Ni4Zn5Y4 alloy and Mg83Ni8Zn5Y4 alloy, with the increase of Ni, the long-period phases decrease, quasi-crystalline phase and a-Mg phase increase. Mg87Ni4Zn5Y4 alloy shows a better plasticity and strength than Mg83Ni8Zn5Y4 alloy. The compressive strength and plasticity of Mg87Ni4Zn5Y4 alloy are 656MPa and 17% respectively. 5) In the series of Mg81Ni8Zn9-xY2+x(x= 0,2,4) alloys, with the increase of Y, the content of amorphous alloy increases. Mg81Ni8Zn9Y2 alloy and Mg81Ni8Zn5Y6 alloy both have higher strength and better ductility. The fracture strength and elongation of two alloys are 580MPa/4.5% and 571MPa/8%, respectively.