J. Mater. Sci. Technol. ›› 2010, Vol. 26 ›› Issue (12): 1089-1097.

• Research Articles • 上一篇    下一篇

Eutectic solidification in near-eutectic Al-Si casting alloys

廖恒成 1,1,吴申庆2,丁科1,毕娟娟1,张敏3,席晓1   

  1. 1. 东南大学
    2. 南京东南大学材料科学与工程系
    3. 西安理工大学
  • 收稿日期:2009-08-26 修回日期:2009-12-15 出版日期:2010-12-31 发布日期:2010-12-21
  • 通讯作者: 廖恒成
  • 基金资助:

    铝硅合金共晶凝固模式与微孔形成间关系规律的研究

Eutectic Solidification in Near-eutectic Al-Si Casting Alloys

H.C. Liao, M. Zhang, J.J. Bi, K. Ding, X. Xi, S.Q. Wu   

  1. School of Materials Science and Engineering, Southeast University; Jiangsu Key Laboratory for Advanced Metallic Materials, Nanjing 211198, China
  • Received:2009-08-26 Revised:2009-12-15 Online:2010-12-31 Published:2010-12-21
  • Contact: Hengcheng LIAO
  • Supported by:

    the National Natural Science Foundation of China under Grant No. 50771031 and the Research Foundation of Southeast University under Grant No. XJ0612238

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摘要： Eutectic solidification in near-eutectic Al-13.0%Si casting alloys was investigated using thermal analysis and microstructure characterization. In unmodified alloy, dual eutectic structures were observed. The coarse eutectic (dendrite-like Al + coarse Si flakes) is formed at a temperature above the equilibrium temperature of eutectic (Al+Si) reaction (577oC). The coarse eutectic (CE) grains nucleate from the primary silicon particles formed earlier due to local enrichment of silicon solute and grow in a divorced mode between the dendritic Al phase and large silicon flakes. The fine eutectic (FE) grains nucleate late on other potential sites activated by melt undercooling and grow in coupled-growing mode with the silicon crystals as fine flakes. The formation of the fine eutectic grains is in favor in the alloys containing boron because of a great number of potential nucleation sites from boron-containing particles. Addition of strontium to the alloys restrains completely the formation of primary silicon particles and limits the nucleation of the coarse eutectic. This is because the eutectic point has moved far enough to make the alloy, at this composition (Al-13%Si), hypo-eutectic. Cooling rate during solidification has an important influence on the formation of these two eutectics.

关键词: Al-Si alloy, eutectic, solidification, dual eutectic grains, grain refinement

Abstract: Eutectic solidification in near-eutectic Al-13 wt pct Si casting alloys and the effect of trace addition of boron or strontium on it have been investigated using thermal analysis and microstructural characterization. In unmodified alloy, dual eutectic structure has been observed. The coarse eutectic (dendrite-like Al+ coarse Si flakes) is formed above the equilibrium temperature of eutectic (Al+Si) reaction (577°C). The coarse eutectic (CE) grains nucleate from the primary silicon particles formed earlier due to local enrichment of silicon solute and grow in a divorced mode between the dendritic Al phase and large silicon flakes. The fine eutectic (FE) grains nucleate later on other potential sites activated by melt undercooling and grow in coupled-growing mode with the silicon crystals as fine flakes. The formation of the FE grains is favored in the alloys containing boron because of a great number of potential nucleation sites being added from boron-containing particles. Addition of strontium to the alloys restrains completely the formation of primary silicon particles and hence limits the nucleation of the CE. This is because the eutectic point has moved far enough to make the alloy, at this composition (Al-13 wt pct Si), hypo-eutectic. Local cooling rate during solidification has an important influence on competition formation of these two eutectics.

Key words: Al-Si alloy, Eutectic, Solidification, Dual eutectic grains, Grain refinement