Papers by Author: Guang Yin Yuan

Abstract: In recent years, bulk metallic glasses (BMGs) have received considerable attention due to their unique mechanical properties. However, the deformation of BMGs is highly localized in a few shear bands so that many of them exhibit poor plasticity. As such, more and more researchers have focused on improving the plasticity by in-situ or ex-situ introducing of nanoor micro-scale crystalline phases into the metallic glassy matrix in order to formation of multiple shear bands.

Abstract: The microstructure and mechanical properties of Mg95.9Zn3.5Gd0.6 and Mg94.4Zn3.5Gd0.6Cu1.5 alloys reinforced by icosahedral quasicrystalline phase (I-phase) and Laves phase has been studied after extrusion at 573K. Extrusion can significantly refined the I-phase and Laves phase, and the strengthening effect of I-phase and Laves phase has been analyzed. Large volume of icosahedral phase in Mg95.9Zn3.5Gd0.6 has important role in its high UTS and elongation due to strong bonding effect at the I-phase/matrix interface for low interface energy. The Laves phase with cubic topological and close-packed structure in Mg94.4Zn3.5Gd0.6Cu1.5 alloy result in the higher heat resistance at elevated temperatures.

Abstract: The present work studied the precipitate microstructures in as-cast Mg-Zn-Y-Zr alloys. The experimental result showed that there is significant number of small precipitates within the grains besides the icosahedral quasicrystals along the grain boundaries. Among these precipitates, a new phase has been identified. The new phase displays square morphologies with the size in the range of 200 nm to 2 μm. According to the energy dispersive spectrometer (EDS), this phase could be a metallic Y-riched compound. The diffraction patterns can be indexed with an f.c.c. structure with the lattice parameter a = 0.52±0.1 nm. The structure does not agree with any precipitate structures that have been reported from the previous studies of Mg-Zn-Y alloys.

Abstract: This paper investigates the microstructure, mechanical properties and creep behavior of Mg–Al–Ca alloys with different Ca content. SEM and EDAX analyses show that the dominant second phase in the as-cast Mg–Al–Ca alloys is Al2Ca, which distributes at the grain boundaries and disperses in the grain interior as well. Both the elevated tensile strength and the creep resistance of Mg–Al–Ca alloys obviously increased with increasing Ca at high temperature. TEM analyses reveal that finer Al2Ca particles with an average size of 0.02 µm precipitated dynamically during the creep process. Selected area electron diffraction (SAD) patterns show that the dynamic Al2Ca precipitates have a coherent interface with matrix as (0110) Mg // (220) Al2Ca, [2110] Mg // [112] Al2Ca. The strengthening mechanism of Mg–Al–Ca alloys at elevated temperature was discussed.

Abstract: Mg-8Zn-4Al-xY base alloys containing an icosahedral quasicrystal phase (i-phase) as a main strengthening phase were prepared by casting into a copper mould at moderate cooling rates. The Y addition was effective for decreasing the size of i-phase and the more homogeneousness of its dispersed state. The mechanical properties at room temperature were much superior to those of AZ91 alloy. The creep tests indicated a promising high temperature creep resistance of the quasicrystal-reinforced Mg-Zn-Al-Y cast alloy. The dislocation characteristic in crept specimens which containing i-phase and no i-phase was analyzed and strengthening mechanism was discussed.