The use of flux

If the brazing operation is not filled with inert gas or in an environment of reduction reaction (ie a furnace), the flux must prevent the formation of oxides when the metal is heated. The flux can also clean the contaminants on the soldering surface. The application of flux can be in the following forms, including slurry, liquid, powder, or prefabricated solder paste that combines flux and solder metal powder. The flux can also be coated on the outer layer of the electrode and embedded in the core of the wire. In these two cases, the free flux will enter the weld bead along with the molten filler metal during heating and joining. Excessive flux should be removed at the end of soldering, because the flux residue in the weld bead can cause corrosion and hinder surface treatment and weld bead inspection. Phosphorus-containing alloy solder is self-fluxing during copper-to-copper welding. The general selection of fluxes is based on their performance on the base metal. In order to be effective, the chemical properties of the flux must take into account both the properties of the base material and the filler material. Self-fluxing alloy phosphorous fillers will produce brittle phosphides, and self-fluxing alloy phosphorus fillers such as those used for welding iron or nickel will produce brittle phosphides. As a general rule, longer soldering cycles should use less flux than shorter soldering operations.