Covering flux is used for smelting and casting. It has strong surface tension, not easy to rupture, good protection, long duration, with strong absorption to hydrogen oxidation inclusions and not easy produce flux impurities.
The combination of magnesium and potassium chlorides provides the low melting eutectic，while the fluoride provides the surface wettability and chemical reactivity with magnesium oxide to cause sufficient removal. MgO increases the viscosity of flux. The barium compound provides the density requirement for the salt to effectively mix with the magnesium and then settle out at the bottom of the crucible.