Growth morphology of primary silicon in cast Al-Si alloys and the mechanism of concentric growth

Faceted growth of primary silicon crystals in cast hypereutectic aluminium- silicon alloys is studied by measurement of spacings between successive gro wth traces observed in microsections. A general equation, derived to specif y conditions for stable growth of silicon crystal, is supported by spacing measurements. Some examples of departures from stable silicon growth are st udied. Three stages in the development of faceted crystal growth are recogn ized, changing from spheroidal to faceted to unstable with increasing cryst al diameter. (C) 1999 Elsevier Science B.V. All rights reserved.