Journal of Japan Foundry Engineering Society
Online ISSN : 2185-5374
Print ISSN : 1342-0429
ISSN-L : 1342-0429
Volume 81, Issue 10
Displaying 1-4 of 4 articles from this issue
  • Kanako Taga, Yuta Fukui, Yoshiki Tsunekawa, Masahiro Okumiya
    2009 Volume 81 Issue 10 Pages 469-474
    Published: October 25, 2009
    Released on J-STAGE: August 12, 2014
    JOURNAL FREE ACCESS
      Ultrasonic vibration is applied to various molten metal processes for such purposes as (1) improving wettability, (2) promoting liquid adhesion at vibrating surface and (3) promoting sono-solidification like grain refinement. The present study is focused on sono-solidification with acoustic cavitation in hypereutectic Al-18mass%Si alloy. An equilibrium microstructure composed of primary silicon and coupled eutectic α-Al/Si phases is generally observed in Al-18mass%Si alloy. However, non-equilibrium α-Al solid solution grains develop along with equilibrium phases in the sono-solidification. That is, during the sono-solidification of Al-18mass%Si alloy, non-equilibrium α-Al grains crystallize near the ultrasonic radiator before reaching the eutectic temperature of 577℃, in addition to the refined primary silicon grains. Ultrasound in molten Al-Si alloys exhibits two outstanding behaviors of cavitation bubbling and acoustic streaming, which cause the crystallization of α-Al grains in hypereutectic Al-Si alloy. It is known that high pressures of over 1GPa generated by collapse of cavitation bubbles lead not only to increase in the eutectic temperature, but also higher silicon content at the eutectic point in Al-Si alloy. With chemical analyses of EPMA, non-equilibrium α-Al grains are characterized by higher silicon content compared with that of primary α-Al grains in hypoeutectic Al-7masst%Si alloy. Consequently, non-equilibrium α-Al nuclei are crystallized at collapsed cavitation bubble sites before reaching the eutectic temperature and they are dispersed throughout the billet due to acoustic streaming.
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  • Shotaro Masuda, Hiroyuki Toda, Shunzo Aoyama, Shin Orii, Shoji Ueda, M ...
    2009 Volume 81 Issue 10 Pages 475-481
    Published: October 25, 2009
    Released on J-STAGE: August 12, 2014
    JOURNAL FREE ACCESS
      Usually, aluminum die-cast alloys are used with casting surface, therefore it can be assumed that defects exist in the sub-surface regions. These defects are largely neglected in conventional evaluations as these regions are removed before testing. In the present study, fatigue tests were performed using specimens with casting surface. Fatigue life was statistically analyzed, and synchrotron radiation X-ray microtomography was also applied to visualize surface defects in 3D together with the in-situ observation of crack initiation. The results revealed that specimens with shorter fatigue lives exhibit aligned micropores of approximately 10μm in diameter in a sub-surface region, which inevitably cause premature fatigue crack initiation. The in-situ observation clearly revealed fatigue crack initiation at agglomerated micropores.
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  • Makoto Miyake, Yasuhiro Hoshiyama, Hidekazu Miyake
    2009 Volume 81 Issue 10 Pages 482-488
    Published: October 25, 2009
    Released on J-STAGE: August 12, 2014
    JOURNAL FREE ACCESS
      A color-etching method has been proposed to reveal the austenite microstructure that precipitates during eutectic solidification of spheroidal graphite cast iron. In fact, the color-etched microstructure corresponds to a phase with a dendritic, or a layer, shape encompassing the spheroidal graphite. To clarify the identity of this color-etched microstructure, we compared the microstructure ?which had been interrupted-quenched during eutectic solidification with a normally solidified microstructure obtained at the same cooling rate.
      The results show that the color-etched microstructure corresponds to the austenite phase at the middle stage of eutectic solidification. The occurrence of color-etched microstructure was also observed in some commercial castings. Austenite dendrites with various morphologies were observed in every spheroidal graphite cast iron sample. With castings of the same shape, the dendrite structure was found to vary ; Some castings had small dispersed austenite dendrite structures, while others are seen to increase to bulky sizes, suggesting that this hidden austenite dendrite structure affects fluidity during the eutectic solidification process and manifests itself in castability as shrinkage behavior.
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