In this paper, the optimum fluoride component in the multifunctional refining flux used for recycling aluminum scrap was determined. Theoretical analysis of solid fluxing shows that strong stripping ability of oxide layer on aluminum surface for the flux and appropriate interfacial tensions between Al melt / inclusion (o-_M-I), flux / inclusion (o-_F-I), and flux / Al melt (o-_F-M) are indispensable for making the flux achieve the properties of covering, drossing, and cleaning simultaneously. In term of four preliminarily selected fluoride salts, i.e., KF, AlF₃, K₃AlF₆ and KAlF₄, the results of interfacial tension measurements indicates that, combined addition of A-type fluoride (KF) and B-type fluoride (AlF₃, K₃AlF₆ and KAlF₄) to equimolar NaCl-KCl can just offset the shortage of single addition of KF which means worsening the separating effect of flux from melt surface and weakening the wettability of flux on the inclusions due to the lower o-_F-M and the higher o-_F-I respectively. Additionally, coalescence behaviors of aluminum droplets in molten fluxes reveals that, KF, K₃AlF₆ or KAlF₄ possesses stronger stripping ability of oxide layer, while the stripping ability of oxide layer for AlF₃ is weaker. Ultimately, the combination of KF with K₃AlF₆ or/and KAlF₄ is ascertained to be an optimum selection for fluoride component in the multifunctional refining flux.

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