All issues
Volume 58, Issue 8
Displaying 1-6 of 6 articles from this issue
- |<
- <
- 1
- >
- >|
RESEARCH REPORT
-
Satoru SATO, Yasunori HARADA, Hiroto SASAKI, Naoki ISHIBASHI, Mitsuru ...Article type: Research Report
2008 Volume 58 Issue 8 Pages 363-367
Published: August 30, 2008
Released on J-STAGE: September 30, 2008
JOURNAL FREE ACCESSIn order to achieve an efficient mass-production system, a new semi-liquid casting process was developed that can produce a semi-liquid slurry, in individual metallic vessels, for each casting shot. In this research, the effect of heat treatment conditions was investigated on the mechanical properties and microstructures of stepped casting samples made by the new semi-liquid casting process and compared with that of squeeze cast samples. The semi-liquid castings showed a larger elongation and a slightly lower strength than squeeze castings. The larger elongation is due to the finer eutectic silicon structures formed under the higher cooling rate of semi-liquid slurry. The lower strength is considered to be the effect of the lower magnesium content in the primary-crystallized alpha phase. Castings made by the semi-liquid casting process seem to contain more Al–Si–Fe–Mg compounds, thus more magnesium is consumed to form these compounds than squeeze castings.View full abstractDownload PDF (2606K) -
Hiroki ADACHI, Yusuke YAMAMOTO, Hidetaka NAKANISHI, Tetsuo AIDA, Manab ...Article type: Research Report
2008 Volume 58 Issue 8 Pages 368-374
Published: August 30, 2008
Released on J-STAGE: September 30, 2008
JOURNAL FREE ACCESSPowder metallurgy was used to supersaturate a 7000 series of aluminum alloys with 0.4, 0.8 and 1.5 mass% Sc. Al3Sc particles were precipitated in high density upon applied heat treatment at 773 K. During subsequent hot extrusion, continuous dynamic recrystallization (DRX) occurred and fine DRX grains with a diameter of 1 μm formed. The 1.5 mass%Sc alloy achieved the greatest number of DRX grains. Interestingly, the number of DRX grains observed for the 0.8 mass% Sc alloy was almost the same as that observed for the 0.4 mass% Sc alloy, although the amount of Sc added was two times larger. Continuous DRX occurs only under conditions in which the grain boundary mobility is low; therefore, the number of DRX grains is strongly related to the pinning force on the initial grain boundary exerted by Al3Sc particles. When the pinning force was calculated from the diameter of Al3Sc particles (measured by TEM), the number of DRX grains was determined to be proportional to the calculated pinning force. However, in the case of 0.8 and 1.5 Sc alloys, the Al3Sc particle diameter was twice that obtained at the maximum pinning force (dmax). Thus, it is possible to promote continuous DRX by decreasing the Al3Sc particle diameter in 0.8 and 1.5 Sc alloys. Lowering the rate of heating prior to heat treatment for degassing was found to reduce the critical nucleus size for precipitation of Al3Sc particles as well the diameter of Al3Sc particles. Thus, the pinning force increased in 0.8 Sc and 1.5 Sc alloys, and the number of DRX grains also increased, as expected.View full abstractDownload PDF (2617K) -
Tatsushi ASAHINA, Hidenori ISHIHARA, Hidetaka ASOH, Sachiko ONOArticle type: Research Report
2008 Volume 58 Issue 8 Pages 375-380
Published: August 30, 2008
Released on J-STAGE: September 30, 2008
JOURNAL FREE ACCESSPore nucleation and growth processes of anodic oxide films formed on aluminum substrate were investigated by atomic force microscopy with focusing on the crystal orientation and surface topography of aluminum substrate. Nanotopographies of electropolished aluminum were extremely affected by the crystal orientation of aluminum substrate. For as-received aluminum, regularly aligned striped structure appeared after electropolishing. On the other hand, aluminum substrate annealed at 300°C exhibited isotropic hexagonal cell structure. From X-ray diffraction patterns, it was confirmed that the preferential crystal orientation of aluminum was changed from (110) to (100) when annealing temperature was higher than 300°C. In the initial stage of anodization, specific nanotopography of electropolished aluminum surface was served as the initiation sites for pore generation, and accordingly it influenced cell arrangement. Using planarized aluminum with less than 0.3 nm asperities, however, a large number of fine pores initiated on the oxide film surface. Thus, the growth of anodic oxide films was seriously influenced by the surface topography of aluminum substrate.View full abstractDownload PDF (2502K) -
Koji MURAKAMI, Makoto HINO, Minoru HIRAMATSU, Kiyomichi NAKAI, Sengo K ...Article type: Research Report
2008 Volume 58 Issue 8 Pages 381-387
Published: August 30, 2008
Released on J-STAGE: September 30, 2008
JOURNAL FREE ACCESSMechanism of corrosion protection obtained by anodization for die-cast plates of ASTM AZ91D (Mg–9 mass%Al–0.7 mass%Zn) magnesium alloy has been studied. Anodization was conducted by conventional Dow17 which utilizes chromium oxide (VI), ammonium fluoride and phosphoric acid, and by environment-friendly Anomag whose electrolyte consists of phosphate and ammonium salt. The anodized surface obtained in Dow17 showed local corrosion in salt spray test (SST) after ~500 ks to form corrosion products consisting of magnesium hydroxides. On the other hand, the surface anodized in Anomag was covered with amorphous film, showed only discoloring in SST and corrosion product was scarcely observed. When the anodized surfaces were trenched with ceramic knife to form locally exposed substrate, corrosion product was formed on the trench in the case of Dow17, but corrosion was well suppressed by formation of new type of protective film in the case of Anomag. Anodic polarization curves indicate that the surface anodized in Dow17 is protected by passive substances through which electrolyte can easily reach the substrate, and that in Anomag show sacrificial function where the anodized layer dissolves quite slowly into the electrolyte prior to the substrate. The excellent corrosion protectivity obtained in Anomag is considered to be based on the formation of a new type of protective film as well as sacrificial function of the original amorphous anodized layer.View full abstractDownload PDF (4110K) -
Kenji MATSUDA, Junji TSUKIYAMA, Yasuhiro UETANI, Susumu IKENOArticle type: Research Report
2008 Volume 58 Issue 8 Pages 388-394
Published: August 30, 2008
Released on J-STAGE: September 30, 2008
JOURNAL FREE ACCESSGrain boundary fracture was studied in tensile test for peak-aged balanced and excess Si Al–Mg2Si alloys. The route of crack propagation for intergranular fracture in these alloys was considered by Schmid factor (S.F.) and stress transmission factor (Nij) by crystal orientation to tensile axis. The texture of these alloys before tensile test was recrystallized textures, and there were no significant difference of initial texture between these alloys. Fractured grain boundaries has been classified into the following four groups:
· Group A: Larger difference in S.F. than 0.05 and higher Nij than 0.5.
· Group B: Larger difference in S.F. than 0.05 and lower Nij than 0.5.
· Group C: Smaller difference in S.F. than 0.05 and higher Nij. than 0.5.
· Group D: Smaller difference in S.F. than 0.05 and lower Nij than 0.5.
The cracking was influenced by the grain boundary with larger difference in S.F. and lower Nij in the balanced alloy. The propagation of cracks was influenced by grain boundaries of group B, C, or D with the angles from 60° to 90° to the tensile axis. The cracking and propagation of cracks occurred all together in excess Si alloy at the same time as beginning of tensile test, and grain boundaries in this alloy mostly fractured in the group D with the angle of 30°–90° to the tensile axis.View full abstractDownload PDF (4939K)
REVIEW
-
Tomoya WATANABE, Ryosuke KIMURA, Takashi NAKAZAWA, Hiroyuki CHIBA, Soh ...Article type: Review
2008 Volume 58 Issue 8 Pages 395-405
Published: August 30, 2008
Released on J-STAGE: November 30, 2008
JOURNAL FREE ACCESSDownload PDF (1852K)
- |<
- <
- 1
- >
- >|