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Yo Kojima
Nagaoka University of Technology
225Publications
28H-index
2,923Citations
Publications 225
Newest
Naritoshi Aoyagi2
Estimated H-index: 2
,
Shigeharu Kamado38
Estimated H-index: 38
(Nagaoka University of Technology),
Yo Kojima28
Estimated H-index: 28
(Nagaoka University of Technology)
Porous aluminum alloy has been developed by powder metallurgy route using Spark plasma sintering (SPS) technique. Sintered material was produced by SPS system after getting the mixture of Al-12Si alloy and titanium hydride powders. Porous materials are prepared under various process conditions, and the pore morphology was investigated. Compression test is performed at crosshead speed of 1mm/min, 10mm/min and 100mm/min with no lubricant. The compression strength, σC i.e. plateau stress was estima...
Source Cite
L.B. Tong5
Estimated H-index: 5
(Nagaoka University of Technology),
M.Y. Zheng31
Estimated H-index: 31
(Harbin Institute of Technology)
+ 4 AuthorsYo Kojima28
Estimated H-index: 28
(Nagaoka University of Technology)
Abstract Mg–5.25 wt.% Zn–0.6 wt.% Ca alloy was subjected to equal channel angular pressing (ECAP) at 250 °C using route A, Bc and C, respectively, in order to investigate the effect of shearing strain path on microstructure, texture and mechanical properties. Route Bc was the most effective in grain refinement and generating high angle grain boundaries, while route A was the least effective. Different textures were developed when a different ECAP route was applied. After ECAP using route A, the ...
49 Citations Source Cite
S.W. Xu10
Estimated H-index: 10
(Nagaoka University of Technology),
N. Matsumoto5
Estimated H-index: 5
(Nagaoka University of Technology)
+ 2 AuthorsYo Kojima28
Estimated H-index: 28
(Nagaoka University of Technology)
Abstract Hot compression tests were performed on the as-cast and aged Mg–9Al–1Zn (AZ91) alloy specimens at temperature of 300 °C to investigate the influence of pre-aging treatment on microstructure and mechanical properties of the hot compressed AZ91 alloy. The results show that the pre-aging treatment can be effective in increasing the precipitation number of Mg 17 Al 12 phase and enlarging the discontinuous precipitates area, in which the dynamic recrystallization (DRX) occurs with discontinu...
18 Citations Source Cite
L.B. Tong5
Estimated H-index: 5
(Nagaoka University of Technology),
Mingyi Zheng14
Estimated H-index: 14
(Harbin Institute of Technology)
+ 5 AuthorsYo Kojima28
Estimated H-index: 28
(Nagaoka University of Technology)
Abstract An ultrafine-grained (UFG) Mg–5.12 wt.% Zn–0.32 wt.% Ca alloy with an average grain size of 0.7 μm was produced by subjecting the as-extruded alloy to equal channel angular pressing (ECAP) for 4 passes at 250 °C. The fine secondary phase restricted the dynamic recrystallized (DRXed) grain growth during the ECAP processing, resulting in a remarkable grain refinement. A new texture was formed in the ECAPed Mg alloy with the {0 0 0 2} plane inclined at an angle of 58° relative to the extru...
45 Citations Source Cite
2009 in Scripta MaterialiaIF: 4.16
S.W. Xu21
Estimated H-index: 21
(Nagaoka University of Technology),
N. Matsumoto5
Estimated H-index: 5
(Nagaoka University of Technology)
+ 2 AuthorsYo Kojima28
Estimated H-index: 28
(Nagaoka University of Technology)
Twin dynamic recrystallization (DRX) occurs during the hot compression of AZ91 alloy with precipitation of Mg 17 Al 12 phase at the newly formed DRXed grain boundaries. The pinning effect of the Mg 17 Al 12 precipitates is greatly influenced by compression temperature, resulting in compression temperature having a stronger influence than strain rate on DRXed grain size. The conventional relationship between DRXed grain size and the Zener–Hollomon parameter breaks down as the pinning effect of th...
66 Citations Source Cite
S.W. Xu21
Estimated H-index: 21
(Nagaoka University of Technology),
N. Matsumoto5
Estimated H-index: 5
(Nagaoka University of Technology)
+ 2 AuthorsYo Kojima28
Estimated H-index: 28
(Nagaoka University of Technology)
Abstract During hot compression, Mg 17 Al 12 (β) precipitates show strong influence on the microstructural changes of 415 °C-24 h homogenized AZ91 alloy. When compressed at 300 °C and 350 °C, dynamic recrystallization (DRX) only occurs near grain boundaries with discontinuous β precipitate pinning at the newly DRXed grain boundaries. With increasing compression temperature and decreasing strain rate, the β-precipitating region expands; however, the amount of pinning precipitates decreases, resul...
60 Citations Source Cite
S.W. Xu10
Estimated H-index: 10
(Nagaoka University of Technology),
N. Matsumoto5
Estimated H-index: 5
(Nagaoka University of Technology)
+ 3 AuthorsYo Kojima28
Estimated H-index: 28
(Nagaoka University of Technology)
Abstract In order to choose the appropriate process parameters for further thermo-mechanical processes, high temperature tensile tests of as-cast Mg–Al–Ca alloys containing 1, 4 and 7% of total amount of Al and Ca (denoted as AX1, AX4 and AX7, respectively), where Al:Ca = 29:26, were examined. During the tensile test, the Mg 2 Ca and (Mg, Al) 2 Ca compounds contribute to not only grain refining but also become crack initiation sites and lower the ductility, thus the AX4 alloy exhibits the best d...
46 Citations Source Cite
S.W. Xu10
Estimated H-index: 10
(Nagaoka University of Technology),
Shigeharu Kamado38
Estimated H-index: 38
(Nagaoka University of Technology)
+ 2 AuthorsYo Kojima28
Estimated H-index: 28
(Nagaoka University of Technology)
Abstract Dynamic recrystallization (DRX) behavior of as-cast AZ91 magnesium alloy during hot compression at 300 °C and the strain rate of 0.2 s −1 was systematically investigated by electron backscattering diffraction (EBSD) analysis. Twin DRX and continuous DRX (CDRX) are observed in grains and near grain boundaries, respectively. Original coarse grains are firstly divided by primary { 1 0 1 ¯ 2 } tensile twins and { 1 0 1 ¯ 1 } compression twins, and then { 1 0 1 ¯ 1 }–{ 1 0 1 ¯ 2 } double twi...
100 Citations Source Cite
Hanlin Ding10
Estimated H-index: 10
(Shanghai Jiao Tong University),
Liufa Liu11
Estimated H-index: 11
(Shanghai Jiao Tong University)
+ 2 AuthorsYo Kojima28
Estimated H-index: 28
(Nagaoka University of Technology)
In this paper, the flow behavior of the magnesium alloy AZ91 during hot compression with dynamic recrystallization (DRX) is studied by the electron back-scattered diffraction pattern (EBSP) method and a two-dimensional cellular automata (CA) simulation. The flow behavior characteristics of the alloy during compression are studied and analyzed in detail. The influence of second phase particles on the accumulation of dislocation and the migration of grain boundaries during the compression process ...
10 Citations Source Cite
2009 in Scripta MaterialiaIF: 4.16
Kentaro Yamada4
Estimated H-index: 4
(Nagaoka University of Technology),
Hiroaki Hoshikawa2
Estimated H-index: 2
(Nagaoka University of Technology)
+ 4 AuthorsYo Kojima28
Estimated H-index: 28
(Nagaoka University of Technology)
The addition of 0.25–0.5 at.% of Ag to Mg–3.4Gd–0.1Zr (at.%) alloy significantly enhances the age-hardening response, particularly in underaged conditions. The peak-aged Mg–3.4Gd–0.5Ag–0.1Zr alloy exhibits an extremely high ultimate strength, of above 410 MPa. The plate precipitates are formed on the basal plane of the matrix with a high number density in underaged conditions and co-exist with β′ phase in the peak-aged condition. The co-precipitation effectively contributes to the strengthening ...
56 Citations Source Cite
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