The invention relates to a process for brazing metallic materials, an aqueous flux suspension and a novel flux for use in a brazing process and a preparation process for the novel flux.
During brazing, metal materials are joined at a temperature of above 500.degree. C. with the aid of a molten additional metal (solder). The melting point of the solder is lower than the melting point of the materials, so that the solder joints of many metals can be separated in a nondestructive manner by melting the solder again.
During soldering, oxides and other interfering top layers on the metal surface present a problem: the surface must be metallically pure so that a satisfactory solder joint forms. This is achieved using fluxes, which are generally brushed on, sprayed on or applied as a solder covering on the material.
Fluxes based on alkali metal salts, preferably potassium salts, of complex aluminum fluorides are particularly suitable, for example for brazing light metal materials, in particular alloyed (for example with magnesium) or unalloyed aluminum materials, since they are non-corrosive and non-hygroscopic. Fluxes of this type which are, for example, mixtures of KAlF.sub.4 and K.sub.3 AlF.sub.6 or mixtures of KAlF.sub.4 and K.sub.2 AlF.sub.5 are already known, and the last mentioned compound can optionally be present as the hydrate.
The surface-cleaning action of a flux is evident from, inter alia, the fact that, after melting, the solder runs on the surface of the component or of the components. The better the surface of the component has been cleaned by the flux, the more readily the solder runs on that surface.