Influence of Phosphorous Content on Eutectic Modification in Al-Si Alloy

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  • Al-Si共晶合金の共晶組織改良処理に及ぼすりん含有量の影響
  • Al Si キョウショウ ゴウキン ノ キョウショウ ソシキ カイリョウ ショリ ニ オヨボス リンガンユウリョウ ノ エイキョウ

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Abstract

In order to examine eutectic solidification in Al-Si alloy, the role of the purity of Al-Si alloy and the eutectic modification agent, strontium or sodium, on eutectic solidification sequences was investigated by a technique of quenching during eutectic reaction. <br>  If Al-Si alloy contains more than a few ppm of phosphorous (commercial purity alloys), eutectic cells in Al-Si alloy melt grow on centrally-located polygonal silicon which nucleates on AlP particles. However, nucleation of eutectic cells tends to be difficult within the melt with sodium addition due to low phosphorous content, even though the sample is made of identical commercial purity start materials. In the case of samples containing little phosphorous, eutectic phases tend to nucleate on the mold surface and grow in the opposite direction of the heat flow. <br>  Addition of strontium or sodium results in the morphology of eutectic silicon, which acts as the leading phase of eutectic coupled growth and promotes transition from plate to fiber (coral) shape with decreased anisotropy. This causes eutectic aluminum to grow according to the crystal orientation of the eutectic silicon in unmodified melt, but grow freely with subgrain formations in modified melt. <br>  These results reveal that eutectic solidification of Al-Si alloy is controlled by the nucleation frequency of eutectic cells depending on phosphorous content and decrease in the anisotropy of eutectic silicon due to modification.

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