Metallurgical and Materials Transactions A

, Volume 39, Issue 10, pp 2435–2448 | Cite as

Effect of Strontium and Phosphorus on Eutectic Al-Si Nucleation and Formation of β-Al5FeSi in Hypoeutectic Al-Si Foundry Alloys

  • Y.H. Cho
  • H.-C. Lee
  • K.H. Oh
  • A.K. Dahle


The present investigation was carried out on hypoeutectic Al-Si alloys containing two levels of Fe, 0.5 and 1.1 wt pct, and Sr in the range of 30 to 500 ppm. The addition of Sr in excess of 100 ppm significantly reduced the number of eutectic grains and also resulted in the formation of polygonal-shaped Al2Si2Sr intermetallics. Transmission electron microscopy studies revealed that the Al2Si2Sr phase surrounded the P-rich particles. This may suggest that the otherwise potent nuclei for the Al-Si eutectic, aluminum phosphide (AlP), become poisoned or deactivated by the formation of the Al2Si2Sr phase around the particles. At the high-Fe level (1.1 wt pct Fe), pre-eutectic formation of β-Al5FeSi platelets further reduced the number of eutectic Al-Si nucleation events. It is proposed that both eutectic silicon and β-Al5FeSi are preferentially nucleated on AlP particles. Nucleation of eutectic silicon, therefore, becomes more difficult when it is preceded by the formation of Al2Si2Sr or β-Al5FeSi, because fewer nuclei are available to nucleate silicon. Addition of up to 60 ppm P to the alloys increased the formation temperature of the β-Al5FeSi platelets but did not significantly alter the size, whereas the addition of Sr decreased the β-Al5FeSi nucleation temperature by reducing the potency of the AlP particles.


Eutectic Silicon Unmodified Alloy Aluminum Phosphide Eutectic Nucleation 
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The authors thank Ms. H.K. Kang for her help in EPMA analysis and Mr. D.H. Kim for the preparation of TEM using FIB. The authors also thank Drs. S. McDonald and K. Nogita, University of Queensland, for their help in lab experiments and many valuable discussions.


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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2008

Authors and Affiliations

  1. 1.Department of Materials Science and EngineeringSeoul National UniversitySeoulKorea
  2. 2.Division of Materials EngineeringThe University of QueenslandBrisbaneAustralia

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