| Project/Area Number |
09555212
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 展開研究 |
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| Research Field |
Structural/Functional materials
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
NEMOTO Minoru Kyushu Univ., Dpt.Mater.Sci.& Eng., prof., 工学部, 教授 (90005265)
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| Co-Investigator(Kenkyū-buntansha) |
TOINO Harumichi Nippon Light Metal Co.Ltd., R&D Center, Manager, 技術開発本部・製品化技術室, 主任研究員
OH-ISHI Keiichiro Kyushu Univ., Dpt.Mater.Sci.& Eng., Ass., 工学部, 助手 (70294890)
HORITA Zenji Kyushu Univ., Dpt.Mater.Sci.& Eng., Ass.Prof., 工学部, 助教授 (20173643)
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| Project Period (FY) |
1997 – 1998
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| Keywords | superplasticity / equal-channel angular pressing / microstructural evolution / ultrafine grain sizes / aluminum alloys / intense straining / grain growth / TEM |
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| Research Abstract |
The equal-channel angular (ECA) pressing is capable of introducing an ultrafine grain size into bulk materials and the precise nature of the microstructure is dependent upon the total strain introduced by the pressing, temperature and speed of pressing. When the strain is sufficiently high, it is possible to achieve very high tensile ductilities at high strain rates. It is noted that the use of different processing routes provides an opportunity to alter the shearing planes and shear directions within the sample and therefore to modify, in a favorable manner, the microstructures induced by ECA pressing. It is known that the combination of shear in three dimensional way is effective to increase the amount of misorientation formed during each pressing. The attained grain size is as small as 1.2 micrometers even in high purity aluminum. When the alloying elements are added, the attained grain size reduced appreciably. To increase the elevated temperature stability of fine grain size, whic
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h is a prerequisite for attaining high strain rate superplasticity, a fine dispersion of particles is required. The present results provide a very clear demonstration of refinement of grain size and resultant advantageous high strain rate superplasticity which may be achieved by ECA pressing and microstructural control in a typical commercial Al-Mg-Li-Zr alloy where precipitates are present to retain the ultrafine grain sizes even at high temperatures where diffusion is rapid. Similar grain refinement and high strain rate superplasticity are achieved also in a commercial Al-2004 alloy known as Supral 100 with a chemical composition of Al-6% Cu-0.4% Zr. Furthermore, the exceptionally high strain rate superplasticity of the Al-3%Mg-0.2%Sc alloy was achieved by ECA pressing at room temperature without the use of any intermediate heating. In the Al-Mg-Sc alloy, the migration of grain boundaries are suppressed by the fine dispersion Al_3 Sc phase and then enhancing the grain boundary sliding and the matrix is solution strengthened by Mg suppressing the dislocation glide in the grains. The present work also provides the potential for substantially increasing the viability of superplastic forming in the metal forming industry. Less
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