Microstructures and Morphology Evolution of Icosahedral Phase of As-cast Mg_(67.4)Zn_(28.9)Y_(3.7) Ternary Alloy Subjected to the Pouring Temperature

摘要

The microstructure,chemical composition and morphology evolution of icosahedral quasicrystalline phase of Mg67.4Zn28.9Y3.7 ternary alloy were investigated in detail at different pouring temperatures by X-ray diffraction(XRD),scanning electron microscopy(SEM) and energy-dispersive spectrum(EDS).Low interfacial energy favors the formation of I-phase.The experimental results show that the primary I-phase reveals petal-shaped with five and six branches,where each branch has facetted growth morphology with the size ranging from 50 to 100 μm.As the temperature decreases,the polygon-shaped I-phase forms,attributed to the decomposition of branch of petal-shaped I-phase,and then it grows bigger and some of the fine polygons join together to form large polygons.Besides these,(α-Mg+I-phase) eutectic structures disappear and the relative amount of Mg7Zn3 phase increases as the pouring temperature decreases.The chemical composition and morphology evolution of I-phase were also discussed.