The nucleation and growth of Si was 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 promoted 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 number 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 upon subsequent controlled cooling.Influence of Impurity Elements on the Nucleation and Growth of Si in High Purity Melt-Spun Al-Si-Based Alloys. J.H.Li, M.Z.Zarif, G.Dehm, P.Schumacher: Philosophical Magazine, 2012, 92[31], 3789-805