Microstructure transformations in the heat-treated Mg–Zn–Y alloy

•We examine the microstructures of Mg–Zn–Y under two different cooling rates.•We discuss the growth mechanism of Mg–Zn–Y quasicrystal.•We discuss the phase transformations during different heat treatments. Mg–Zn–Y icosahedral quasicrystals have been prepared from the Mg63.5Zn34Y2.5 (at.%) alloy by c...

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Bibliographic Details
Published in:Journal of alloys and compounds 2013-11, Vol.577, p.498-506
Main Authors: Geng, Jiwei, Teng, Xinying, Zhou, Guorong, Zhao, Degang
Format: Article
Language:English
Subjects:
Alloy steels
Condensed matter: structure, mechanical and thermal properties
Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
Cooling rate
Copper
Cross-disciplinary physics: materials science
rheology
Diffusion in solids
Exact sciences and technology
Heat treatment
Icosahedral phase
Magnesium base alloys
Materials science
Mg–Zn–Y alloy
Microstructure
Molds
Partitioning
Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
Phase transformation
Physics
Quasicrystal
Quasicrystals
Semi-periodic solids
Structure of solids and liquids
crystallography
Transformations
Transport properties of condensed matter (nonelectronic)
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Summary:•We examine the microstructures of Mg–Zn–Y under two different cooling rates.•We discuss the growth mechanism of Mg–Zn–Y quasicrystal.•We discuss the phase transformations during different heat treatments. Mg–Zn–Y icosahedral quasicrystals have been prepared from the Mg63.5Zn34Y2.5 (at.%) alloy by copper and steel molds casting respectively. The phase transformations under different heat treatments have been investigated successively. Although the cooling rates of the two samples are quite different, the icosahedral quasicrystalline (I-phase) can precipitate from liquid directly almost at the same temperature. The eutectic structure (α-Mg+I-phase) forms at the later stage, while the Mg7Zn3 phase forms under a larger cooling rate (copper mold). Moreover, with a lower cooling speed, micro shrinkage cavities and cracks are easily caused by solute partitioning at the edge of petals-like I-phase. The volume fraction of I-phase is effectively increased after heat treatment at 350°C for 50h because I-phase can grow further in a facet manner during the heat treatment process. The I-phase in the Mg63.5Zn34Y2.5 alloy is thermodynamically unstable at 420°C, and therefore transformations of the I-phase to the W or H-phase occur due to slow transformation kinetics and low thermodynamics driving force. In addition, few decagonal quasicrystalline phases (D-phases) can form on the I-phase/Mg7Zn3 interface. Atomic diffusion and concentration also play a crucial role in these transformations.
ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2013.07.009