Influences of Te, Ba, Ce and Bi on the Formation of Modified Structure and Mechanical Properties in Eutectic Al-Si Cast Alloys

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  • 共晶 Al-Si 系鋳造合金の改良組織生成と機械的性質に及ぼす Te，Ba，Ce 及び Bi の影響
  • キョウショウ Al Siケイ チュウゾウ ゴウキン ノ カイリョウ ソシキ セ

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  The aim of this investigation is the clarification of the influences of additional elements (M) both on the refinement of eutectic silicon and on the improvement of mechanical properties and the mechanism of refinement of eutectic silicon in Al-Si cast alloys. Te, Ba, Ce and Bi are chosen as modifier elements because these elements have characteristics common with the other elements used as modifier elements in the past. Further, more improvement of mechanical properties has been tried by the simultaneous addition of 1 % Cu and 1 % Mg to the Si-refined Al-Si alloys. All these additional elements have the effect of refinement of eutectic silicon. The mechanism of refinement may be as follows. During Al-Si-M ternary eutectic solidification, a large number of silicon crystals are nucleated preferentially in the boundaries between pre-existing phases such as AlxMy compounds which are formed through preceding Al-M binary eutectic reactions. The growth of their nuclei is hindered and suppressed by their pre-existing phases such as AlxMy compounds, which results in the refinement of eutectic silicon. As for the mechanical properties, the addition of Te is most effective for the improvement of strength and elongation. In the Bi-added alloys containing 1 % Cu and 1 % Mg, tensile strength of 362 MPa, Brinell hardness of 94 and elongation of 10 % are achieved in heat-treated state. It is suggested that the improvements of toughness in these Al-Si cast alloys may correspond to the change of orbital energy in DV-Xα molecular orbital calculation by the addition of Te, Sb or Bi to aluminium clusters.

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