Electrochemical reduction of Al(III) and Si(IV) in the NaF-AlF3-Al2O3-SiO2 molten salt system and preparation of homogeneous Al-Si alloys by molten salt electrolysis

Abstract

The segregation of aluminum-silicon alloys directly impacts the mechanical and chemical properties of the alloys, Therefore, homogenization of alloys is of great significance for alloys. This study initially investigated the electrochemical behavior of aluminum (III) and silicon (IV) during the preparation of aluminum-silicon (Al-Si) alloys in NaF-AlF₃-Al₂O₃-SiO₂ molten salts through cyclic voltammetry and steady-state polarization. The results revealed that Al₂O₃ underwent one-step reduction to Al, whereas SiO₂ underwent a two-step reduction process to Si. In addition, electrolysis experiments were carried out in a NaF-AlF₃-Al₂O₃-SiO₂-5wt%CaF₂-1wt%MgF₂-2wt%LiF molten salt system with molecular ratio of 2.4. These experiments involved variations in current density, electrolysis time, Al₂O₃ and SiO₂ additions. It is worth noting that under the conditions of current density of 0.7 A/cm², electrolysis time of 2 h, and silica addition of 2 %, the reduction rate of silicon reached a maximum value of 72.57 %, at which time the silicon in the aluminum-silicon alloys showed a dendritic structure, which was uniformly distributed throughout the entire alloy, and the segregation of the alloy was effectively avoided.