The Formation Mechanism and Characterization of Al-Si Master Alloys from Sodium Fluosilicate

Abstract

A modified Al-Si alloy containing up to 15 wt.% Si has been obtained from the reaction of sodium fluosilicate (Na₂SiF₆) with molten aluminum. This work attempted to estimate the mechanism of the reaction of Na₂SiF₆ with molten aluminum to produce Al-Si alloys. The effect of temperature, Na₂SiF₆/Al Wt ratio and reaction time on the formation of Al-Si alloy were investigated. The thermodynamic data, kinetic and rate of the reaction were studied. The results showed the possibility of the reaction between Na₂SiF₆ and molten aluminum thermodynamically, and that this reaction might be controlled chemically. The current study aims to optimize the factors that affecting the preparation of a modified Al-Si alloy from a reduction of sodium fluosilicate using molten aluminium. Temperature 950 ^oC, reaction time 20 – 25 min and Na₂SiF₆/Al Wt ratio related to the applied Si percentage. The prepared alloys could be modified due to the presence of Na₂SiF₆ in the used material as a source of sodium in response to modifying the produced Al-Si alloys. The microstructure by using LOM, SEM, and EDX proved that the needle-like silicon converts to fine fibrous. The volume fraction of primary Si reduces and the eutectic point moves to a higher silicon concentration. The modification improves the wear characteristics and increases the tensile and hardness.