Modification of AlSi alloys with sodium

Effect of sodium on the solidification process of high purity Al-12 wt% Si alloys and the epitaxial growth of Si phase from (111)Si or (100)Si substrate has been studied by means of thermal analysis, microscopy, X-ray photoelectron spectroscopy and Auger electron spectroscopy. Results show that normal modification with Na has little influence on the eutectic arrest temperature, melting point, latent heat of freeze and heat of fusion of the Al-12 wt% Si alloy, and that Na adsorbs on (111)Si and affects both nucleation and growth of the Si. Kinetic features and mechanism of the modification are discussed and it is suggested that modification of AlSi eutectic with Na is a kinetic problem rather than a thermodynamic one and the transition of growth morphology of eutectic Si from platelike to fibrous results from the effects of Na on the nucleation and growth of both Al and Si phase. © 1991.