Papers by Author: Kenji Matsuda

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Authors: Azusa Furihata, Kenji Matsuda, Junya Nakamura, Susumu Ikeno, Yasuhiro Uetani
Abstract: In this work, the age-hardening of Al- 1.0 mass% Mg2Si- 0.4 mass% Mg – 0.5 mass% Ag (ex.Mg-Ag alloy) alloy has been investigated. It showed increase of hardness and age-hardening response. Precipitates in this alloy aged at 523 K have been observed by high resolution transmission electron microscopy (HRTEM) and classified into five types based on characteristics in their HRTEM images.
Authors: Seung Won Lee, Daichi Akama, Z. Horita, Tetsuya Masuda, Shoichi Hirosawa, Kenji Matsuda
Abstract: This study presents an application of high-pressure torsion (HPT) to an Al-Li-Cu-Mg alloy (2091). The alloy was subjected to solid solution treatment at 505oC for 30 minutes and was processed by HPT under 6 GPa for 5 revolutions at room temperature. The hardness increased with straining and saturated to a constant level at 225 Hv. Aging was undertaken on the HPT-processed alloy at 100, 150 and 190oC for the total periods up to 9.3 days. The aging treatment led to a further increase in the hardness to ~275 Hv. It is shown that the simultaneous strengthening of the alloy due to grain refinement and age hardening was successfully achieved by application of HPT and subsequent aging treatment. The enhancement of the strength is prominent when compared with the application of a conventional rolling process.
Authors: Tomoatsu Murakami, Kenji Matsuda, Takeshi Nagai, Junya Nakamura, Tokimasa Kawabata, Susumu Ikeno
Abstract: It is known that Al-Mg-Ge alloy shows the similar precipitation sequence to Al-Mg-Si alloy, and its equilibrium phase is β-Mg2Ge according to its phase diagram. In this study, the precipitation sequence of Al-Mg-Ge alloys containing different contents of Mg2Ge has been investigated by hardness test, TEM and HRTEM observation to understand the effect of Mg2Ge contents on age-hardening behavior of the alloys. The hardness of as-quenched and peak-aged samples have been improved by increasing Mg2Ge contents. The precipitates in the peak-aged samples have been classified into some metastable phases, such as the β’-phase and parallelogram-type precipitate by HRTEM observation. The relative frequency of these precipitates in the is has been changed with Mg2Ge contents.
Authors: Daichi Akama, Z. Horita, Kenji Matsuda, Shoichi Hirosawa
Abstract: This research investigates simultaneous strengthening by grain refinement and fine precipitation in age-hardenable Al-Mg-Si alloys containing an additional element of either Ag, Cu, Pt or Pd. The alloys were solution-treated and processed by high-pressure torsion (HPT) at room temperature under a pressure of 6 GPa. They were aged at a temperature of 373 K for up to a total period of 6.7 hours. Vickers microhardness was measured after selected periods of aging and the microstructures were observed by transmission electron microscopy. It was found that, in all alloys, the grain sizes after HPT were refined to 300-400 nm and there were significant increases in the hardness through the HPT processing. The hardness was further increased by the subsequent ageing treatment, confirming the simultaneous strengthening by grain refinement and fine precipitation. However, the aging behavior was different depending on the alloying compositions.
Authors: Masaya Nishikubo, Kenji Matsuda, Yoshihisa Oe, Jyunya Nakamura, Susumu Ikeno
Abstract: In this study, the aging behaviour of several Al-Mg-Si alloys (Al-Mg-Si-Cu , Al-Mg-Si-Ag and Al-Mg-Si-Cu-Ag) has been investigated by hardness tests and TEM observations. Comparing the age-hardening rate in the early period of these alloys, the alloys with Cu or/and Ag addition are faster than that of the base alloy, and the aging time to reach the maximum hardness of the alloys with Cu or/and Ag addition is shorter than that of the base alloy.Therefore the aging behaviour of that alloys has been investigated by TEM observations to understand the effect of Cu, Ag and Cu+Ag additions on aging precipitation.
Authors: Kaname Fujii, Tokimasa Kawabata, Kenji Matsuda, Susumu Ikeno
Abstract: Changes in the mechanical properties on AZ91 Mg alloy cast into sand mold caused by heat-treatment and its microstructure were investigated by the tensile test and observation using optical and scanning electron microscopes, and chemical composition analysis. Tensile test results show that the specimens aged at 441K have larger elongation than those of aged at 489K, although they had same proof stress. The fracture surface observation reveal the cleavage fracture of aged specimen caused by the nodular structure as well as the formation of micro void around the coarse spheroidal Al-Mn-(Fe) phase.
Authors: Kenji Matsuda, Susumu Ikeno, Tatsuo Sato, Akihiko Kamio
Authors: Kenji Matsuda, Junya Nakamura, Yoshio Nakamura, Tatsuo Sato, Susumu Ikeno
Abstract: The crystal structure of metastable phase in Ag added Al-Mg-Si alloy was investigated by comparing the β’-phases in Al-Mg-Si alloy without Ag, using images of high resolution transmission electron microscope (HRTEM), selected area electron diffraction patterns (SADPs) and an energy dispersive X-ray spectroscopy (EDS). SADPs and HRTEM images obtained from metastable phase in the Ag added Al-Mg-Si alloy showed similar to those of β’-phase in Al-Mg-Si alloy without Ag and had different lattice spacings because of the effect of Ag. According to our careful analysis on obtained HRTEM images and SADPs, it includes more complicated crystal lattice of distorted hexagons.
Authors: Katsumi Watanabe, Kenji Matsuda, Tokimasa Kawabata, Susumu Ikeno
Abstract: Magnesium alloys have received considerable attention because of their lightweight and recyclability. AM-series and AZ-series Mg-Al alloys have been used for industrial products widely, particularly for AM-series alloys because of better toughness and impact absorption properties than AZ-series alloys. The Mg17Al12 intermetallic compound is the only precipitate formed during ageing after the solution heart treatment. Discontinuous precipitates exist in grain boundary randomly, and continuous precipitates exist in the matrix. However, there is few report about the orientation relationship between the discontinuous precipitates and the matrix. The purpose of this study is to investigate the orientation relationship between the discontinuous precipitates and the matrix of AM-series magnesium alloys. Hardness measurement, SEM observation, the electron backscattered diffraction (EBSD) techniques were preformed in order to understand the relationship between the discontinuous precipitate and crystallographic orientation of grains in AM-series magnesium alloy. TEM samples with discontinuous precipitates were prepared using the focused ion beam (FIB). And TEM observation was performed to investigate the discontinuous precipitates and crystallographic orientation in the matrix.
Authors: Kenji Matsuda, Tokimasa Kawabata, Yasuhiro Uetani, Susumu Ikeno
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