Journal of Japan Institute of Light Metals
Online ISSN : 1880-8018
Print ISSN : 0451-5994
ISSN-L : 0451-5994
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Volume 62, Issue 5
Displaying 1-6 of 6 articles from this issue
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RESEARCH ARTICLE
  • Formation of zincate films on binary aluminum alloys and adhesion of electroless Ni–P plated films
    Koji Murakami, Makoto Hino, Masashi Ushio, Daichi Yokomizo, Teruto Kan ...
    Article type: Research Article
    2012 Volume 62 Issue 5 Pages 199-205
    Published: May 30, 2012
    Released on J-STAGE: June 30, 2012
    DOIhttps://doi.org/10.2464/jilm.62.199
    JOURNAL FREE ACCESS
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    Formation of zincate films and adhesion of electroless nickel-phosphorus plated films were studied for binary aluminum alloys of Al–2at%Mn, Al–2at%Fe, Al–2at%Cu, Al–2at%Zn and high-purity aluminum (99.999 mass%). Precipitation mode of zinc in the zincate treatmens greatly varied according to the alloying elements in the substrates. In the cases of the first and the second zincate treatments for Al–Mn, Al–Fe and high-purity aluminum, zinc precipitated excessively, then, porous films of zinc repeatedly fell off the substrate. The surfaces of Al–Cu and Al–Zn alloys were immediately coated by uniform zincate films in the first and the second zincate treatments. Precip-itation of zinc is considered to be uniform if the oxide film on a substrate dissolves uniformly and rapidly in the zincate solution. When electroless nickel-phosphorus plating was conducted after the second zincate treatment of Al–Mn and Al–Fe alloys, the plated films easily peeled off. Those on Al–Cu and Al–Zn alloys showed excellent adhesion, and dimple patterns of the substrates were observed on the partly peeled areas. The poor adhesion is thought to be caused because the excess zinc dissolves at the beginning of the plating and generates hydrogen gas, then, gaps are formed between the plated films and the substrates.
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  • Intergranular corrosion susceptibility for Al–Mn–Cu alloys subjected to heat treatment at 180°C after brazing process
    Yoshiyuki Oya, Satoshi Tanaka, Junji Ninomiya, Takeyoshi Doko, Yoichi ...
    Article type: Research Article
    2012 Volume 62 Issue 5 Pages 206-211
    Published: May 30, 2012
    Released on J-STAGE: June 30, 2012
    DOIhttps://doi.org/10.2464/jilm.62.206
    JOURNAL FREE ACCESS
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    The alternation of an air-conditioner refrigerant from a freon-based refrigerant to CO2 is proposed. A maximum temperature in the CO2 heat-exchange cycle approaches to 180°C after brazing, which might affect susceptibility to intergranular corrosion. In this work, the intergranular corrosion susceptibility of Al–Mn–Cu alloys heat treated at 180°C after brazing was investigated. In both of the heat treated and non-treated Al–Mn–Cu alloys, Al–Cu intermetallic compounds were observed at grain boundaries, while in the non-treated Al–Mn–Cu alloys, Al–Mn intermetallic compounds also existed at the grain boundaries, being in contact with the Al–Cu compounds. The observation indicates that the Al–Mn compounds promote precipitation of the Al–Cu compounds at the grain boundaries. It also means development of Cu depleted zone along the grain boundaries. However, the intergranular corrosion susceptibility was decreased when the heat-treatment time become longer because Cu solid solubility in the grains decreased down to the same level of the Cu depleted zone. With the Mn concentration, the decreasing rate is accelerated and the time needed to show no susceptibility is shortened.
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  • Effects of constituent elements on hydrogen embrittlement resistance of 6061 aluminum alloy in fatigue tests
    Koji Ichitani, Katsumi Koyama
    Article type: Research Article
    2012 Volume 62 Issue 5 Pages 212-218
    Published: May 30, 2012
    Released on J-STAGE: June 30, 2012
    DOIhttps://doi.org/10.2464/jilm.62.212
    JOURNAL FREE ACCESS
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    Fatigue tests under controlled experimental humidity were conducted to reveal the effects of constituent elements on hydrogen embrittlement resistance of 6061 aluminum alloy. Under a humidified air condition hydrogen atoms are generated through a reaction between successively exposed aluminum alloy surface and vapor water, and then the hydrogen embrittlement of the alloy can be studied by controlling experimental humidity. Although a standard 6061 alloy showed no hydrogen embrittlement under humidified air condition, Al–Mg–Si ternary alloy of the same Mg and Si content as the standard 6061 alloy had a much shorter fatigue life under humidified air condition than under dry nitrogen gas condition, and showed significant hydrogen embrittlement. The higher hydrogen embrittlement resistance of the 6061 alloy than the ternary alloy was attributed to constituent elements of Cu and Cr in the 6061 alloy. The observation of fatigue fracture surfaces suggested that Cu addition decreased hydrogen embrittlement sensitivity of the alloy itself and Cr addition decreased sensitivity for intergranular cracking through refinement of the grain structure.
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