2018 Fiscal Year Annual Research Report
Mg-希土類結晶および非晶質合金の作製とその力学特性調査
| Project/Area Number |
18F18733
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| Research Institution | Tohoku University |
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Principal Investigator |
加藤 秀実 東北大学, 金属材料研究所, 教授 (80323096)
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| Co-Investigator(Kenkyū-buntansha) |
ZHANG DEPING 東北大学, 金属材料研究所, 外国人特別研究員
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| Project Period (FY) |
2018-11-09 – 2021-03-31
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| Keywords | Rear earth / Heat treatment / Age hardening / Strengthening mechanism / Phase structure |
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| Outline of Annual Research Achievements |
RE-Zr master alloys were well prepared by arc-melting furnace under the argon atmosphere because of the high melting point of RE (Sm, Yb, Ho) and Zr elements. Magnesium is a very active element and volatilizes easily, then, Mg-4Sm/Ho-xYb-Zr (x=0, 1, 2, 3) alloy were produced by induction melting in a circulating argon atmosphere at lower temperature avoiding volatilization of Mg with skillful operating induction melting furnace. The quality is generally less than 40 grams due to the limitation of the furnace body. The composition of the alloys were determined by EDS test and the dimension of alloy sample is processed by mechanical processing equipment. The as-cast samples were characterized by metallography, SEM and XRD to observe the grain size and the type of the intermetallic compounds. Analysis results and EDS mappings of elements show that components of as-cast alloys meet the requirements and are more uniformly distributed without segregation. SEM images reveal that the microstructures are mainly composed of equiaxed dendrites α-Mg grains and eutectic particles and more RE addition corresponds to better grain refinement effect. XRD indicates that these eutectic phases are Mg-RE intermetallic compounds located at grain boundaries. The determination of the structure of specific intermetallic compounds needs to be identified by TEM transmission characterization in the next step.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Commercial WE43 (Mg-Y-Nd-Zr) alloy is a typical example of successful application in Mg-RE-Zr series alloy. Mg-4Sm/Ho-xYb-Zr (x=0, 1, 2, 3) alloy in progress have a low cost and relatively high performance compared with WE43. Due to the different melting points of elements, alloys are prepared in two steps. The first step is to melt high melting point RE and Zr elements into master alloy by arc-melting furnace. Then, the Mg element with low melting point and the RE-Zr master alloy are melted by induction furnace at lower temperatures.This ensures that the alloy can be prepared according to the specified composition and avoided the disadvantage of magnesium volatilization. The demand for alloys is large because alloys require subsequently a series of different tests and characterizations.
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| Strategy for Future Research Activity |
Heat treatment process parameters are explored under different temperature and time conditions by using muffle furnace. Age hardening curve of samples is determined by hardness test under different state conditions. The alloy samples with different contents and different states are characterized by metallography, SEM, XRD, TEM and EBSD. By these means, we will attempt to research and find the orientation relationships between the Mg matrix and precipitates related with transformation mechanism and phase structure. It is an important factor to produce abundant, fine and uniform equilibrium phase particles in the matrix of Mg-RE-Zr alloys after solution aging heat treatment. During next period, Prof. Zhang will use advanced facilities effectively of IMR to conduct a further research.
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