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谷 啓貴, 青葉 知弥, 小林 正和, 高橋 明宏, 三浦 博己2017 年 67 巻 8 号 p. 355-360
発行日: 2017/08/30
公開日: 2017/09/30
ジャーナル フリーA hot-extruded AZ80 magnesium (Mg) alloy was multi-directionally forged (Multi-Directionally Forged/MDFed) under decreasing temperature conditions from 673 K down to 433 K to cumulative strain of ΣΔε=5.6 (i.e., 7 passes of MDFing) at maximum. The initial average grain size of 20.1 µm was gradually reduced with increasing cumulative strain and average grain size of 0.4 µm could be attained at cumulative strain of ΣΔε=5.6. The Charpy impact tests of MDFed AZ80Mg alloys having various grain sizes were carried out. The impact value first increased up to ΣΔε=0.8, however, it particularly and gradually decreased with increasing cumulative strain over ΣΔε=1.6. Fracture surfaces of the hot-extruded and the MDFed samples to ΣΔε=0.8 exhibited dimples indicating occurrence of ductile fracture. The MDFed samples to ΣΔε=3.2–5.6, however, showed rather flat appearances indicating occurrence of brittle fracture. Because bumps, which sizes were corresponding to grain sizes, were observed on the flat fracture surfaces, it is suggested that cracks propagated along grain boundaries. That is, crack propagation along grain boundaries resulted in the decrease in the impact value, and therefore, it gradually decreased with grain size.
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水口 隆, 伊藤 勉, 木村 耕太, 栗坂 登紀子, 大藤 弘明, 木村 正樹2017 年 67 巻 8 号 p. 361-366
発行日: 2017/08/30
公開日: 2017/09/30
ジャーナル フリーThis work investigated the microstructural evolution occurring during high-temperature tensile tests (743 K, strain rate 1×10−3 s−1) of a friction stir processed polycrystalline solid solution 5083 aluminum alloy, along with the effect of the microstructure change on the room-temperature mechanical properties. Grain refinement was effectively achieved in the stir zone, with the mean observed grain size less than 10 µm. The nominal stress–nominal strain curve indicated that the flow stress drastically increased until a maximum stress value at which point fracture occurred. The value of elongation to failure exceeded 300%; this high ductility can be referred to as superplastic-like elongation. The area fraction of cavity increased with increasing strain. Room-temperature tensile tests at a strain rate of 1×10−3 s−1 revealed that the strength and ductility decreased with an increasing area fraction of cavity, and that the extent to which the strength and ductility are affected depends on the cavity.
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金武 直幸2017 年 67 巻 8 号 p. 369-376
発行日: 2017/08/30
公開日: 2017/11/30
ジャーナル フリーPDF形式でダウンロード (2441K)
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