A study on modification mechanism by Sr in Al-Si eutectic alloy.

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  • SONG Kikyung
    Waseda University
  • FUJII Hidetoshi
    Department of Materials Science and Engineering, Faculty of Science and Engineering, Waseda University
  • NAKAE Hideo
    Department of Materials Science and Engineering, Faculty of Science and Engineering, Waseda University
  • YAMAURA Hideki
    Hitachi Metals Ltd.

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  • Al-Si共晶合金におけるSrによるSiの微細化機構への一考察
  • Al Si キョウショウ ゴウキン ニ オケル Sr ニ ヨル Si ノ ビサ

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Abstract

The effect of Sr content and solidification rate on the morphology of the Si phase in the Al-Si eutectic alloy were investigated using a unidirectional solidification method. A critical quantity of Sr for the modification was found between 0.004 and 0.07mass%. When more Sr than the critical quantity was added, the Si phases were modified at a solidification rate of R ≤ 4mm/h, while the Si phases were coarsened at a solidification rate of R ≥ 2mm/h. When the solidification rate is very low, any addition of Sr coarsens the Si phase without modification effect. The reduction of Si/liquid interfacial free energy by addition of Sr allows Si phase to grow with an instinctive shape as the leading phase. In these circumstances, the adsorption of Sr on Si phases plays an essential role. That is, when the solidification rate is very low, adsorbed Sr can not prevent Si phase from growing and therefore Si phase becomes coarse. On the other hand, when the solidification rate is high, adsorbed Sr prevents Si phase from growing on the fastgrowing faces and the Si phase is modified.

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