Effects of silicon content on the separation and purification of primary silicon from hypereutectic aluminum–silicon alloy by alternating electromagnetic directional solidification

Abstract

Hypereutectic aluminum (Al)–silicon (Si) alloys with different Si contents were used to evaluate the effects of Si content on separation and purification by alternating electromagnetic directional solidification (AEM–DS) at 3 kHz. A relatively high pulling speed of 40 µm/s was used for improved energy efficiency. After cooling, samples underwent AEM–DS, and efficient separation was obtained. The Si content in Si-rich areas exceeded 85 wt.% (considerably higher than the content in others) and exhibited not a slight relevance with the original Si contents in the hypereutectic Al–Si alloy. With regard to purification, impurities— particularly metallic impurities (Fe, Ti, and Ca)—can be removed to a low level. Electron probe microanalysis (EPMA) indicated that B content was lower in the Si-rich area than in the Al–Si alloy, suggesting that the segregation of B in solid primary Si was higher than that in Al–Si melt during AEM–DS. Moreover, the contents of metallic impurities (Fe, Ti, and Ca) and B decreased when the initial Si content in the Al–Si melt decreased. This finding was attributed to a lower silicon content, which indicated a lower melt temperature, thus allowing segregation at a lower temperature.