Journal of Japan Institute of Light Metals
Online ISSN : 1880-8018
Print ISSN : 0451-5994
ISSN-L : 0451-5994
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Volume 64, Issue 6
Displaying 1-5 of 5 articles from this issue
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RESEARCH ARTICLE
  • Effects of aging conditions on creep behavior of an Al–Mg–Si alloy
    Makoto Ando, Akio Niikura, Yoshikazu Suzuki, Goroh Itoh
    Article type: RESEARCH ARTICLE
    2014 Volume 64 Issue 6 Pages 229-234
    Published: June 30, 2014
    Released on J-STAGE: July 30, 2014
    DOIhttps://doi.org/10.2464/jilm.64.229
    JOURNAL FREE ACCESS
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    Creep behavior of an Al–0.3%Mg–0.5%Si alloy affected by aging condition was investigated to obtain fundamental knowledge on the thermal stability in the service temperature range for the precipitation-hardened aluminum heat-exchanger. The alloy was aged at 175°C for 3 h (under-aged; the specimen will be termed “UA specimen”) and 24 h (peak-aged; “PA specimen”), after solution treatment. These specimens were subjected to creep testing at temperatures of 150°C and 200°C. When the creep temperature was 150°C, the UA specimen showed a lower creep rate than that of the PA specimen. On the other hand, when the creep temperature was 200°C, both specimens showed almost the same creep rate. In accordance with the higher creep resistance, TEM images demonstrated that fine precipitates were formed in the UA specimen, but not in the PA specimen, during creep testing at 150°C. These results suggest that the higher creep resistance of the UA specimen is derived from the dynamic precipitation, probably transition from clusters to needle-shaped precipitates, during creep deformation that increases the numerical density of the precipitates because the testing temperature is lower than the aging temperature. When the creep temperature is 200°C, higher than the aging temperature, however, the dynamic precipitation does not increase the numerical density of the precipitates, since the UA specimen as well as PA specimen is immediately over-aged at an early stage of the testing.
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  • Effect of aging precipitates on the bendability of an Al–Mg–Si alloy
    Hidetaka Nakanishi, Mineo Asano, Hideo Yoshida
    Article type: RESEARCH ARTICLE
    2014 Volume 64 Issue 6 Pages 235-240
    Published: June 30, 2014
    Released on J-STAGE: July 30, 2014
    DOIhttps://doi.org/10.2464/jilm.64.235
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    Al–Mg–Si alloys are usually applied a T4 temper as the plate material for automobile bodies, because of necessity of a high bake hardening property. Many reports about the improvement in the bendability of Al–Mg–Si alloys applied a T4 temper has been published, because they easily crack during the hemming process. On the other hand, Al–Mg–Si alloys applied T6 and T7 tempers are used for the material of wiring plates and heat radiation devices. A high electrical conductivity and good bendability are necessary for these devices. In this paper, the effect of the aging conditions on the bendability was investigated. As a result, the bendability at the T6 temper significantly decreased. The bendability under the aging temper, and over the aging temper was better than that at the T6 temper. Specimens treated by natural-aging at high temperature before the T6 temper easily cracked during the bending test. It was postulated that the formation of shear bands was significant and the bendability decreased during the bending test under the high density and finely β″ phase precipitate conditions.
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  • Effect of severe plastic deformation on mechanical properties and microstructure in 7075 aluminum alloy
    Shigeru Kuramoto, Kayo Horibuchi, Ichiro Aoi, Keiichiro Oh-ishi
    Article type: RESEARCH ARTICLE
    2014 Volume 64 Issue 6 Pages 241-248
    Published: June 30, 2014
    Released on J-STAGE: July 30, 2014
    DOIhttps://doi.org/10.2464/jilm.64.241
    JOURNAL FREE ACCESS
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    The commercial Al–Zn–Mg–Cu base 7075 alloy has been reported to have significantly high tensile strength after high-pressure torsion (HPT) process, one of the typical methods of severe plastic deformation. This strengthening can be attributed to high dislocation density, grain refinement, nano-scale solute clustering in the interior of grains, and/or solute segregation to grain boundaries. However, the details in the strengthening mechanism remain unknown. In the present study, transmission electron microscopy (TEM) analysis has been made to characterize the change in microstructure during HPT. Disc specimens of 10 mm diameter and 1 mm thick were machined from extruded bar of commercial 7075 alloy, and solution treated for 5 h at 480°C. The solution treated specimen was subjected to HPT process under compression stress of 2 GPa and rotation speed of 1 rpm for 10 turns. The TEM analyses were made on the specimen taken from the place 2.5 mm apart from disc center. Localized concentrations of solute atoms to grain boundaries are observed in the HPTed specimen. The strengthening mechanism will be discussed in relation to the observed changes in deformation microstructure.
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