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Volume 47, Issue 9
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RESEARCH REPORT
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Masakazu NIIKURA, Kohei HASEGAWA, Takeshi FUJITA, Shinji MITAO, Naotak ...1997 Volume 47 Issue 9 Pages 469-474
Published: 1997
Released on J-STAGE: March 30, 2007
JOURNAL FREE ACCESSEffect of strain rate and Mg content on elongation and serration behavior was studied in pure aluminum and Al–Mg alloy sheets with Mg content up to 6.5%. Elongation increased monotonously with strain rate in pure aluminum, but Mg–containing alloys showed a minimum elongation at a strain rate of about 1 s−1. The elongation decrease with strain rate in a strain rate range below the minimum was much sharper and the elongation increase in a range above the minimum was less abrupt in alloys with Mg content of 4~6% than in alloys with Mg content of 2~3%. Consequently, although the alloys with high Mg content showed higher elongation in ordinary static tensile testing, the alloys with low Mg content exhibited higher elongation in dynamic condition which was considered closer to press forming of automobile body panels. Serration amplitude in load-displacement curves decreased with increasing strain rate and decreasing Mg content. The low-Mg alloys exhibited no serration in dynamic condition at a strain rate of about 1 s−1, while the high-Mg alloys still showed serration to a certain extent. The observed phenomena were discussed based on dynamic strain aging, dynamic recovery, and temperature rise during the testing by adiabatic deformation.View full abstractDownload PDF (1387K) -
Yasuhiro UETANI, Kenji MATSUDA, Tohru KATAYAMA, Seichi RENGAKUJI, Fuji ...1997 Volume 47 Issue 9 Pages 475-480
Published: 1997
Released on J-STAGE: March 30, 2007
JOURNAL FREE ACCESSSpecimens of an Al–1.0 mass%Mg2Si–0.34 mass%Si alloy which had been aged at temperatures ranging between 423 and 573 K up to peak-aged condition were tensile-tested at a room temperature. Localized deformation behavior near grain boundaries on the specimen surface was observed with a scanning tunneling microscope. With increasing aging temperature from 423 to 573 K, elongation increased from 0.4% to about 10% and the fracture mode changed from intergranular to transgranular fracture. For aging temperatures of 473 K and below, fold formations was explicable in terms of the magnitude and the direction of the maximum resolved shear stress (Fmax) on a grain boundary plane. In contrast, in the specimen aged at 573 K where elongation appreciably increased and transgranular fracture occurred, the displacement of scratch line and the step at the grain boundary were not always generated at all the grain boundaries that had a large magnitude and suitable direction of Fmax. In this specimen, two types of folds were observed: one was developed with increasing amount of deformation and the other was not developed. The increased elongation of this specimen was attributed to relatively low frequency of markedly developed folds.View full abstractDownload PDF (1186K) -
Masayoshi OZAWA, Kouei YOSHIHARA, Tadashi MOMONO, Hiroshi G. KATAYAMA1997 Volume 47 Issue 9 Pages 481-486
Published: 1997
Released on J-STAGE: March 30, 2007
JOURNAL FREE ACCESSProduction of Al2O3 particle/Al–4.5 mass%Cu alloy composite was attempted by the transient liquid phase (TLP) sintering in hot pressing. As a result, the CuAl2 (θ-phase), which formed finely and continuously at the grain boundary in the Al–4.5 mass%Cu alloy, disappeared by the addition of Al2O3 particle. The mechanical properties of the TLP-sintered composites were superior to those of solid-phase-sintered composites. It is clear that the bonding strength between Al2O3 particle and matrix exerts a great effect on the tensile strength of the TLP sintered composites. The sintering process of Al2O3/Al–4.5mass%Cu mixed powder by TLP sintering was accelerated compared with that by solid phase sintering. From the experimental results mentioned above, TLP sintering was confirmed to be effective to produce metal matrix composites.View full abstractDownload PDF (921K) -
Hisamichi KIMURA, Akihisa INOUE, Kenichiro SASAMORI, Yoshihito KAWAMUR ...1997 Volume 47 Issue 9 Pages 487-492
Published: 1997
Released on J-STAGE: March 30, 2007
JOURNAL FREE ACCESSMechanical grinding (MG) of gas atomized Al–7.9 mass%V–4mass%Fe alloy powder was performed for various times up to 396 ks with a low energy ball mill. The bulk material with a size of φ8 mm × 300 mm was made of the powder subjected to MG for 72 ks (72 ks–MG powder) by warm extrusion. The gas atomized powder has a spherical shape with an average diameter of about 31 μm and the structure consists of Al, icosahedral and Al11V phases. The 72 ks–MG powder has a flattened spherical morphology and the structure consists of icosahedral and Al phases. The extruded bulk material of the 72 ks–MG powder also consists of icosahedral and Al phases and has a high packing density of approximately 100%. The tensile strength (σUTS), plastic elongation (εP), Vickers hardness (HV) and Young's modulus at room temperature for the extruded bulk alloy are 588 MPa, 3.5%, 180 and 83.4 GPa, respectively, and the σUTS, εP and HV at 573 K are 306 MPa, 3.2% and 90, respectively. Thus, the bulk material is concluded to have high stiffiness and high elevated-temperature strength.View full abstractDownload PDF (1006K) -
Kenji MATSUDA, Hiroshi GAMADA, Kaname FUJII, Tomoo YOSHIDA, Tatsuo SAT ...1997 Volume 47 Issue 9 Pages 493-499
Published: 1997
Released on J-STAGE: March 30, 2007
JOURNAL FREE ACCESSHigh resolution electron microscopy (HRTEM) was performed for an aged Al–1.0 mass%Mg2Si alloy to clarify the morphology and crystal system of the precipitates that occur prior to the β' intermediate phase. At the early stage of aging, there observed a number of precipitates with irregular arrangement of bright dots in their cross-sections of the HRTEM images. With increasing aging time, the precipitates with the irregular arrangement of bright dots (the random type) decrease and the precipitates with the parallelogram network arrangement of bright dots in their cross-sections (the parallelogram type) begin to increase. The parallelograms have interior angles between 62° and 89°. The 30% of them had a fixed angle of 75° (the 75° parallelogram type). In the over aging condition, the number density of the parallelogram type precipitates decrease, and the β' intermediate phase becomes predominant. There are three types of precursory precipitates, the random, the parallelogram and the 75° parallelogram types, prior to the β' phase at all aging temperatures investigated in Al–0.6 mass%Mg2Si, Al–1.0 mass%Mg2Si and Al–1.6 mass%Mg2Si alloys. The compositional region, where the above three types of precipitates are observed, is in good agreement with the previously reported region for G.P. (2) zone in the equilibrium phase diagram of the Al–Mg2Si pseudo-binary alloy.View full abstractDownload PDF (1704K) -
Takayoshi FUJINO, Katsutaro OKUMURA, Hayao NOGUCHI1997 Volume 47 Issue 9 Pages 500-505
Published: 1997
Released on J-STAGE: March 30, 2007
JOURNAL FREE ACCESSHydroxide solution of alkaline-earth metal is easy to form carbonate by absorbing carbon dioxide in air. This absorption was able to be prevented simply by setting carbon fluoride membrane on the liquid surface. In the present investigation, anodization of aluminum was done by this method in barium hydroxide bath. The properties of the anodized film were compared with those produced in other alkaline baths such as sodium carbonate and sodium hydrate baths and in sulfuric acid baths. Furthermore, sodium aluminate acid and sodium tetraborate were added to barium hydroxide bath in order to improve hardness and abrasion resistance of the soft film produced in alkali, and the effects were examined. As a result, the films obtained in barium hydroxide baths were superior to those with the same thickness (8 μm) obtained in sodium hydrate and sodium carbonate baths in the hardness and the resistance to alkali corrosion. Among all the films tested, the film obtained in sodium-tetraborate-added barium hydroxide bath was found to have the highest hardness and greatest alkali resistance. These properties were attributable to the formation of fine cell structure from SEM observation of the film surface, and were thought to be related to the composition ratio of Al and O and the film density. From the results of an EPMA analysis and surface roughness measurement, the addition of sodium tetraborate was found to suppress the dissolution of the formed film, and also to reduce the unevenness of the film surface.View full abstractDownload PDF (756K)
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