The properties and uses of fluxes in molten aluminum processing

Gaseous and solid fluxes play an important role in the degassing, demagging, and fluxing of aluminum and its alloys. Inert as well as reactive gases, or hexachloroethane, may be used to remove dissolved hydrogen and sodium. Magnesium may be removed by chlorine or an aluminum-fluoride-containing flux. Fluxes based on a KCl-NaCl mixture may be used to cover and protect the metal from oxidation. To recover aluminum from dresses, a more reactive flux containing cryolite or some other fluoride may be used. In this article, the thermodynamics af aluminum melting and refining are analyzed in terms of the behavior of sodium, magnesium, and calcium. The coalescence of aluminum drops in salt fluxes improves with fluoride additions. With increasing MgCl2 contents in the flux, the effects of NaF and KF additions become much less pronounced.