Solidification and microstructure of as-cast Mg65Zn32Y3 quasicrystal alloy

Stable icosahedral quasicrystal with a nominal composition of Mg30Zn60Y10 (at%) was prepared by an as-cast method. Applying X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques, the equilibrium solidification microstructures of Mg65Zn32Y3 (at%) quasicrystal alloy in Mg-rich corner of the Mg-Zn-Y system was investigated. Since resistivity is one of the physical properties sensitive to structures, it is suggested that there is a reversible temperature-induced solid-liquid structural transition. Quasicrystal possesses quasi-periodic lattice structure and especial electronic structure, which indicates the resistivity of Mg65Zn32Y3 quasicrystal alloy will change greatly during the melting or solidification processes. The temperature dependence on resistivity exhibits a clear turning point. Measuring resistivity-temperature curve (rho-T curve) and comparing with differential scanning calorimetry (DSC) first time, a study on the solidification process of quasicrystal was carried out. The icosahedral quasicrystalline phase (I-phase) surrounded by eutectic microstructure (alpha-Mg+decagonal quasicrystalline phase (D-phase)) is reported first time. During the solidification process, the I-phase is formed at about 423 degrees C undergoing a peritectic reaction, and decagonal quasicrystal eutectic microstructure is formed at the later stage. The phase involved in this peritectic reaction has a composition of Mg28.93M46.62Y24.35 (W-phase). Furthermore, the quasicrystals with various characteristics morphologies exist some degree micro-segregation. And the microsegregation phenomenon in rod-like quasicrystalline phase is more serious than that in petals-like quasicrystalline phase. (c) 2013 Elsevier B.V. All rights reserved.