Influence of impurity elements on the nucleation and growth of Si in high purity melt-spun Al–Si-based alloys

Abstract

The nucleation and growth of Si has been investigated by TEM in a series of high purity melt spun Al–5Si (wt%)-based alloys with a trace addition of Fe and Sr. In the as-melt-spun condition, some twinned Si particles were found to form directly from the liquid along the grain boundary. The addition of Sr into Al–5Si-based alloys promotes the twinning of Si particles on the grain boundary and the formation of Si precipitates in the α-Al matrix. The majority of plate-shaped and truncated pyramid-shaped Si precipitates were also found to nucleate and grow along {111}_α-Al planes from supersaturated solid solution in the α-Al matrix. In contrast, controlled slow cooling decreased the amount of Si precipitates, while the size of the Si precipitates increased. The orientation relationship between these Si precipitates and the α-Al matrix still remained cube to cube. The β-Al₅FeSi intermetallic was also observed, depending on subsequent controlled cooling.

Keywords:

• Al–Si alloy
• precipitation
• TEM
• melt spinning
• impurity effect

Acknowledgements

JL gratefully acknowledges Gabriele Moser and Dr Boriana Rashkova for their help with TEM sample preparation at the Erich Schmid Institute of Materials Science of the Austrian Academy of Science. MZZ acknowledges financial support from the Higher Education Commission (HEC) of Pakistan and cooperation from the OEAD.