Segregation Behavior of Metal Impurities During Al-Si Melt Directional Solidification with an Open Ended Crucible

The distribution characteristic and segregation behavior of metal impurities during directional solidification of Al-20Si, Al-30Si and Al-40Si alloys have been investigated. The morphologies of the alloys and impurity phases were observed by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. The concentration profiles of representative metal impurities Al, Fe and Ti were measured by inductively coupled plasma optical emission spectrometry. The results indicate that the metal impurities segregate into the eutectic Al-Si melt during the growth of primary Si flakes and gradually segregate towards the top of each ingot during directional solidification. A concept of apparent segregation coefficient is proposed to characterize the segregation behavior of impurity elements. The apparent segregation coefficients of metal impurities decrease with increase in solidification temperature of the Al-Si alloys.