Journal of Japan Institute of Light Metals
Online ISSN : 1880-8018
Print ISSN : 0451-5994
ISSN-L : 0451-5994
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Volume 61, Issue 4
Displaying 1-6 of 6 articles from this issue
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RESEARCH REPORT
  • Development of in-situ measuring methods for mechanical properties on semi-solid aluminum alloy
    Hiroyuki Chiba, Toru Ueki, Takanari Toriyama, Itaru Endo, Takamitsu Ko ...
    Article type: Research Report
    2011 Volume 61 Issue 4 Pages 135-141
    Published: April 30, 2011
    Released on J-STAGE: May 31, 2011
    DOIhttps://doi.org/10.2464/jilm.61.135
    JOURNAL FREE ACCESS
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    It is necessary to obtain the mechanical properties of semi-solid alloy in order to predict the occurrence of solidification cracking, one of the serious casting defects of aluminum alloy die-casting and DC casting, by computer simulation. New in-situ measuring method for mechanical properties on semi-solid aluminum alloy by horizontal tensile test, based on that of Oya and Kitaoka et al., was developed. The strain was determined by measuring the displacement between dendrites defined as the makers. Influence of gage length on the fracture strain was clarified. Fracture strain and tensile strength of semi-solid Al–7mass%Si alloy were obtained.
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  • Formation and growth of tin whiskers on aluminum–tin alloys
    Koji Murakami, Makoto Hino, Yutaka Mitooka, Teruto Kanadani
    Article type: Research Report
    2011 Volume 61 Issue 4 Pages 142-148
    Published: April 30, 2011
    Released on J-STAGE: May 31, 2011
    DOIhttps://doi.org/10.2464/jilm.61.142
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    In order to clarify the mechanism of formation and growth of nodules and whiskers on the leads used in aluminum electrolytic capacitors, aluminum–tin binary alloys were subjected to the investigation as the model alloys for the joints in the leads. The concentration of tin in the binary alloys was 1, 5 or 10 at%. The alloy of 10 at% tin showed the largest number of nodules or whiskers on its polished surface after keeping under ambient conditions for 7.8 Ms. Many whiskers whose length were more than several tens of micrometers were observed in the case of the alloy of 5 at% tin. The alloy of 1 at% tin showed few nodules or whiskers. Growth of nodules and whiskers is caused by difusion of tin atoms from the strained or unstable areas into the stable ones or the root grains. Then, the extrusion toward the surface at the root grains develops nodules and whiskers. As a prevention measure of whiskers, selective etching of the aluminum phase using a solution of sodium hydroxide was confirmed to be successful. Thus the aluminum phase was thought to form a non-uniform distribution of strain in the tin phase. This acts as the driving force in difusion of tin atoms.
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  • Refinement of primary silicon of hypereutectic Al–Si alloys by ultrasonic radiation and its application for die castings
    Kazuhiro Oda, Sergey Komarov, Yasuo Ishiwata
    Article type: Research Report
    2011 Volume 61 Issue 4 Pages 149-154
    Published: April 30, 2011
    Released on J-STAGE: May 31, 2011
    DOIhttps://doi.org/10.2464/jilm.61.149
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    The study purpose is to investigate effects of ultrasonic radiation on refinement of primary Si crystals of hypereutectic Al–Si alloys and to examine the refining effect in die casting. The ultrasonic refining effect was examined by using Al–Si alloys without or with addition of phosphorus. The experiments included melting of alloy in a crucible, radiation of ultrasound into the melt at temperatures at least 60 K higher than the Si crystallization temperature, holding of the melt for 20–80 s and pouring of it into a Cu mold by gravity casting. The refining effect was found to be dependent on P content and holding time. The EPMA investigation revealed that the ultrasonic radiation increases the number of AlP particles acting as heterogeneous sites for the primary Si nucleation. The refining effect was significant at the holding time of 20–50 s. Then, based on the above results, the radiation conditions for the die casting were determined. A key point of the conditions was that the refining effect and melt fluidity are kept at the desired level for a period after the radiation. Microstructural investigation showed considerable refinement of primary Si crystals and Al–Fe–Mn–Si compounds. The ultrasonically treated die castings exhibited an improved tensile strength.
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  • Near-surface nanocomposite structure on commercial purity aluminum induced by fine particle bombardment
    Norio Nakamura, Shin-ichi Takagi
    Article type: Research Report
    2011 Volume 61 Issue 4 Pages 155-159
    Published: April 30, 2011
    Released on J-STAGE: May 31, 2011
    DOIhttps://doi.org/10.2464/jilm.61.155
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    Commercial purity aluminum (A1070) was subjected to fine particle bombardment (FPB) with 1.0 mass% carbon steel and pure nickel projectile particles. Nanocomposite structures formed at the near-surface region, which contained refined aluminum grains of less than 100 nm in diameter and dispersed projectile fragments several tens of nanometer to several micrometer in size. Beneath the nanocomposite structure was found a fine-grained matrix with approximately 1-μm-diameter grains. Observation of the microstructural transition at the near-surface region suggested that the nanocomposite structures developed via severe plastic deformation (SPD), accompanied by a folding and imposing of the convex part of the surface, and by mechanical mixing with the fragments of the projectile particles. The nanocomposite structures exhibited high hardness values of approximately HV200, which are superior to those of extra-super duralumin (A7075-T6). The relationship between the grain size and hardness value in the structures corresponds well to the Hall–Petch relationship extrapolated from previous studies. Therefore, the increase in hardness is thought to be mainly the result of grain refinement strengthening.
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