Effect of Sn content on microstructure and boron distribution in Si-Al alloy

Si-Al and Si-Al-Sn alloy melts were used for silicon purification by alloy solidification refining method. The effects of Sn addition on alloy microstructure, eutectic Si morphology, as well as B distribution were investigated using optical microscopy, scanning electron microscopy, electron probe microanalyzer and inductively coupled plasma mass spectrometer. Primary Si and αAl + Si structures with flake-like eutectic Si were found in Si-Al alloy; while an additional structure of αAl + βSn + Si in Si-Al-Sn alloy was found. Si in αAl + Si eutectic had a globular shape, whereas some Si in αAl + βSn + Si eutectic had an octahedral shape. Compared with primary Si, more boron was found to distribute in final solidified phase during the solidification, i.e. αAl + Si for Si-Al system and αAl + βSn + Si for Si-Al-Sn system. The refining ratio of B decreased with increasing Al content in Si-Al alloy melt, while increased with Sn addition using Si-Al-Sn alloy melt.