Abstract: Modification with sodium is an important processing to improve mechanical properties of Al-Si alloys. However, conflicts remained in previous hypotheses about the mechanism of modification with sodium and the adsorption of sodium on the face of silicon phase has not been detected though the opinion that modification was caused by the adsorption is the most acceptable. In this paper, a new technique in which single crystal silicon seeds were inserted into the melts of Al-22% Si alloys modified with sodium was advanced to study the growth of silicon phase in the alloy. It was showed that modification with sodium affected both nucleation and growth of eutectic silicon. Adsorption of sodium on the faces of the seeds was detected with x-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy. Mechanism of modification with sodium was discussed with the results of the present experiment.

Key words: Al-Si合金, Na吸附, 变质, 表面分析, 机理, 晶体生长