By preventing the formation of metal oxides, flux enables the solder to adhere to the clean metal surface, rather than forming beads, as it would on an oxidized surface. The role of flux is typically dual: dissolving the oxides already present on the metal surface, which facilitates wetting by molten metal, and acting as an oxygen barrier by coating the hot surface, preventing its oxidation.įor example, tin-lead solder attaches very well to copper, but poorly to the various oxides of copper, which form quickly at soldering temperatures. In high-temperature metal joining processes ( welding, brazing and soldering), flux is a substance that is nearly inert at room temperature, but which becomes strongly reducing at elevated temperatures, preventing oxidation of the base and filler materials. 6.2 Metal salts as flux in hot corrosion.6.1 Fluxes for soldering certain metals.In some applications molten flux also serves as a heat-transfer medium, facilitating heating of the joint by the soldering tool or molten solder. įluxes are also used in foundries for removing impurities from molten nonferrous metals such as aluminium, or for adding desirable trace elements such as titanium.Īs cleaning agents, fluxes facilitate soldering, brazing, and welding by removing oxidation from the metals to be joined. These agents served various functions, the simplest being a reducing agent, which prevented oxides from forming on the surface of the molten metal, while others absorbed impurities into the slag, which could be scraped off the molten metal. Iron ore was also used as a flux in the smelting of copper. Some of the earliest known fluxes were sodium carbonate, potash, charcoal, coke, borax, lime, lead sulfide and certain minerals containing phosphorus. They are used in both extractive metallurgy and metal joining. Fluxes may have more than one function at a time. In metallurgy, a flux (derived from Latin fluxus meaning "flow") is a chemical cleaning agent, flowing agent, or purifying agent. Wire freshly coated with solder, still immersed in molten rosin flux
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