New Methods of Obtaining Al–Si Alloys Using Amorphous Microsilica

Abstract

The work presents the calculations of enthalpy of formation as well as Gibbs energy of reduction of silicon dioxide by aluminum. This way, the possibility of producing Al–Si alloys using amorphous silica fume has been established. The influence of alloying additives and impurities on the silicon reduction process has been determined. The possibility of using magnesium as a surface-active additive, which allows for the removal of oxygen from the surface of dispersed particles and the reduction of silicon, has been demonstrated. Effective methods for producing hypoeutectic and hypereutectic Al–Si alloys using amorphous silica fume have been developed. Alloys with a silicon content exceeding 6 wt% were obtained by blowing preheated (t = 300 °C) amorphous silica fume into the aluminum melt (t = 900 °C) along with the stream of argon followed by intense mixing. Alloys with a silicon content exceeding 16 wt% were manufactured by induction melting of a silicon-containing mixture (60% SiO2, 40% Al + 20% 3NaF·2AlF3) subjected to the presintering (t = 800 °C) when the amorphous silica fume was reduced to crystalline silicon. It has been established that crystalline silicon, which is formed during the roasting of the tableted burden (as a result of reactions in solid phases), is smoothly absorbed by the aluminum melt. Aluminum oxide, obtained during the redox reaction, dissolves in cryolite, after which aluminum and silicon are fused together and transferred to the melt. Industrial implementation of the proposed methods will result in the improved efficiency of the existing process of manufacturing Al–Si alloys, as the energy-intensive stage of the crystalline silicon production is partially excluded, as well as reduce adverse environmental impact.