The process of aluminum flux purification for the dissolution, combination and adsorption of melt inclusions is based on the basic premise. The flux becomes a liquid phase in the melt, that is, the flux is required to be in a molten state during the purification process, not a solid phase. Therefore, the primary factor to be considered in flux preparation is to make the melting point of the flux lower than the melting point of the liquidus of the aluminum melt. Under normal atmospheric pressure, the melting point of aluminum is about 660°C, and the liquidus temperature of the aluminum alloy melt with the addition of alloying elements also changes with the composition of the alloy, mostly above 660°C.
When the aluminum casting flux meets the solid slag inclusion on the surface of the aluminum melt or inside the aluminum melt, the physical properties of the slag particles will be changed, and the slag inclusion on the surface and inside of the aluminum melt will be separated from the aluminum melt together with the flux and removed. On the surface of the aluminum melt, the removal of suspended slag by the flux depends on the mutual surface tension relationship between the three interfaces of the flux, the aluminum melt and the air; while the slag inclusion in the aluminum melt, the removal by the flux depends on the flux and the aluminum melt. The mutual surface tension relationship between the interface of solid and solid slag inclusions.
How to realize the low melting point physical properties of the flux and create a low melting point environment for the refining process through the composition design of the flux is one of the basic problems in preparing the flux.
The working principle of aluminum flux purification is to achieve the purpose of purification by adsorbing and dissolving the oxide inclusions in the aluminum melt and the hydrogen adsorbed on it, and floating to the surface of the aluminum liquid through the density difference. The flux removal and purification process is a complex multiphase process, which is restricted by many factors, the most important of which is the thermodynamic and kinetic conditions of purification.