Journal of Japan Institute of Light Metals
Online ISSN : 1880-8018
Print ISSN : 0451-5994
ISSN-L : 0451-5994
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Volume 47, Issue 2
Displaying 1-9 of 9 articles from this issue
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RESEARCH REPORT
  • Modeling of primary solidification of hypereutectic Al–Si alloy with dynamic undercooling
    Tatsuya OHMI, Kiyotaka MATSUURA, Masayuki KUDOH, Youichi ITOH
    1997 Volume 47 Issue 2 Pages 71-77
    Published: 1997
    Released on J-STAGE: March 30, 2007
    DOIhttps://doi.org/10.2464/jilm.47.71
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    A simplified numerical model is proposed to simulate the crystallization behavior of facet primary crystals of a hypereutectic Al–Si alloy. The alloy is assumed to be solidified in a cooling medium which is at a given temperature, TB. The obtained results are summarized as follows: (1) The average crystal size, d3, decreases as cooling rate, R, increases. When R exceeds a critical level, however, d3 begins to converge to a constant value which depends on TB. (2) The average crystal size depends on the maximum undercooling degree of the liquid phase, ΔTLM. (3) The value of ΔTLM is nearly equal to ΔTm which corresponds to the undercooling degree at the apparent onset of crystallization which is detected from the cooling curve.
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  • Effects of the addition of Cu and Mg on the machinability of hyper-eutectic Al–Si system alloys
    Takio TANAKA, Shinsaku HANASAKI
    1997 Volume 47 Issue 2 Pages 78-83
    Published: 1997
    Released on J-STAGE: March 30, 2007
    DOIhttps://doi.org/10.2464/jilm.47.78
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    In turning of hyper-eutectic Al–Si system casting alloy, it is desirable to add Cu less than about 0.5% and as little Mg as possible in that alloy for the tool wear, because the tool wear remarkably increases by adding Cu or Mg to that alloy. While, in that alloy (JIS AC9A or AC9B) containing both of Cu and Mg each 0.5~1.5%, the refinement of primary silicon in that alloy by casting to a metallic mold having larger cooling rate during solidification than a sand mold, and use of cutting oil in turning of that alloy are very effective in decreasing the tool wear. The finished surface roughness of that alloy is effectively improved and the size of chip becomes remarkably fine by adding Cu or Mg.
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  • Structures and mechanical properties of rapidly solidified Mg–Y based alloys
    Satoshi HANAWA, Makoto SUGAMATA, Junichi KANEKO
    1997 Volume 47 Issue 2 Pages 84-89
    Published: 1997
    Released on J-STAGE: March 30, 2007
    DOIhttps://doi.org/10.2464/jilm.47.84
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    Rapidly solidified flakes of Mg–Y based alloys with or without ternary additions of Ca and Zn were prepared by atomizing the alloys melt and subsequent splat-quenching onto a single copper roll. Ternary alloying additions were 3 mass% Ca for Mg–5 mass% Y alloy and 2 mass% Zn for Mg–10 mass% Y alloy. The flakes were consolidated by cold pressing and hot extrusion. In as rapidly solidified flakes of the Mg–Y binary alloys, extended solid solubility of Y was obtained in the Mg matrix because of high cooling rate of rapid solidification. But, fine dendric structures, the arm spacing of which was approximately 4 μm, were observed in rapidly solidified flakes of the ternary alloys. After consolidation, fine dispersion of intermetallic compounds was observed in all the extruded P/M materials. Those compounds consisted of Mg24Y5 in binary alloys, and Mg24Y5, Mg2Ca or Mg12YZn in the ternary alloys. As-extruded P/M materials of Mg–10 mass%Y and Mg–10 mass%Y–2 mass%Zn alloys showed no remarkable softening after annealing at 573 K. Mg–10 mass%Y–2 mass%Zn alloy showed the highest tensile strength of 520 MPa at room temperature and 440 MPa at 473 K. However, the tensile strength of all the P/M materials dropped below 80 MPa at 573 K.
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  • Microstructures and coarsening behavior of silicon particles in P/M Al–Si–Cu–Mg alloys containing Fe and Ni
    Rodinei M. GOMES, Tatsuo SATO, Akihiko KAMIO
    1997 Volume 47 Issue 2 Pages 90-97
    Published: 1997
    Released on J-STAGE: March 30, 2007
    DOIhttps://doi.org/10.2464/jilm.47.90
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    The microstructures and coarsening behavior of silicon particles in Al–Si–Cu–Mg alloys containing 5 mass% of Fe or 7.5 mass% of Ni produced by a powder metallurgy technique were investigated by means of optical and transmission electron microscopy. The effects of Fe or Ni on the coarsening of silicon particles have been examined for specimens annealed at 723, 778 and 793 K in relation to hardness and proof stress changes. Through TEM observations β–AlFeSi, β'–AlFeSi, Al16(MnFe)4Si3, AlCu2Fe7 and Al3Fe phases are found to be present in the Fe containing alloy, while Al3Ni and Al3Ni2 are detected in the Ni containing alloy. The mechanism of coarsening of silicon particles was discussed on the basis of the Lifshitz-Slyosov-Wagner theory (LSW theory). The activation energy for the coarsening of silicon particles in the alloys containing Fe or Ni is larger than that in the Fe-free or Ni-free alloy. The size distribution of Si particle is better described by the log-normal distribution, which is different from that expected from the LSW theory. The intermetallic compounds containing Fe or Ni effectively retard the coarsening of silicon particles, as well as increase the proof stress of the alloys.
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  • Effects of grain size and dendrite arm spacing on tensile properties of continuous-cast 6061 aluminum alloy billets
    Tomokazu YAMASHITA, Tooru WATANABE, Kou NAKAHIRA, Kenji MATSUDA, Hiros ...
    1997 Volume 47 Issue 2 Pages 98-103
    Published: 1997
    Released on J-STAGE: March 30, 2007
    DOIhttps://doi.org/10.2464/jilm.47.98
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    A method to control grain size and DAS (secondary dendrite arm spacing) independently was established by the vertical semi-continuous casting process with a heat insulating mold, and the effects of grain size and DAS on the tensile properties of 6061 aluminum alloy billets were investigated. The grain size and DAS were controlled by changing casting rate and additional amount of a grain refiner. The Hall-Petch relation is obtained between grain size and 0.2% proof stress, but it's not obtained between DAS and 0.2% proof stress. DAS affects significantly the elongation, and the elongation increases as DAS decreases, but the effect of DAS on the elongation diminishes as a homogenization proceeds.
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  • Effect of grain size on localized deformation near grain boundaries in Al–1 mass%Mg2Si base alloys
    Yasuhiro UETANI, Tohru KATAYAMA, Kenji MATSUDA, Kiyoshi TERAYAMA, Susu ...
    1997 Volume 47 Issue 2 Pages 104-109
    Published: 1997
    Released on J-STAGE: March 30, 2007
    DOIhttps://doi.org/10.2464/jilm.47.104
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    Localized deformation near grain boundaries in Al–1 mass%Mg2Si–0.4 mass%Si alloys with and without 0.14 mass% Mn were investigated by scanning tunneling microscopy in relation to the grain size. Test pieces with gage length of 18 mm and width of 6 mm were cut from cold-rolled sheets, solutionized at 848 K, water-quenched peak-aged at 423 K and finally deformed in tension at room temperature at a strain rate of 1.86×1O−4s−1. The average grain size of the Mn-bearing and Mn-free alloys was 60 (small-grained) and 400 μm (large-grained) after heat treatment, respectively. Although elongation was increased upto about 8% strain by the manganese addition, the small-grained specimen had an intergranular fracture surface as well as the large-grained one. Fold formation mechanism in the small-grained specimen seemed to be the same as that in the large-grained specimen, and small surface cracks were observed occasionally at the grain boundaries having folds. In the small-grained specimen, step height at some grain boundaries attained a large value of about 1.5 μm. Frequencies of fold formation in the large-grained specimen reached to about 40% of all triple points in the gage area, while it was only about 10% in the small-grained specimen.
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  • Effect of heat-treatment condition on the occurrence of serrations in an Al–6 mass%Zn alloy
    Teruto KANADANI, Kazuki YOSHIOKA, Tsutomu TASHIRO
    1997 Volume 47 Issue 2 Pages 110-113
    Published: 1997
    Released on J-STAGE: March 30, 2007
    DOIhttps://doi.org/10.2464/jilm.47.110
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    The eflfect of heat-treatment conditions on occurrence of serration in an Al–6 mass%Zn alloy was investigated. The specimen was aged for each time within 2600 ks mainly at 293 K after water-quenching from temperatures (TQ) ranging from 473 K to 853 K, and then tensile-tested at room temperature (293 K). The lower the TQ was and the shorter the aging time was, the more easily the serration occurred. As a result, in the case of TQ=473 K, the serration occurred even after aging for a long time such as 2600 ks, while in the case of TQ=773 K, the serration did not occur independent of aging conditions. Also, the serration occurred when specimens were furnace-cooled from 773 K to room temperature. From these results and those obtained by means of electrical resistivity measurements, it is considered that the serration in this alloy occurs when small GP zones such as Guinier radius under 1 nm or some solute clusters are formed.
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