Fluxes are special blends of typically solid, inorganic compounds designed for degassing, demagging, cleaning, grain refining, and/or chemistry modification of molten aluminium alloys and other purposes. Fluxes are usually added during the melting, holding or degassing of aluminium to furnaces, crucibles, ladles, or other aluminium vessels. Flux raw-material quality, addition method and product form can all affect efficiency. A flux recipe varies depending on its purpose and other process variables, such as alloy and temperature.
In general, salt fluxes fall into one of seven main categories:
- Covering—provide physical barrier to oxidization
- Cleaning—remove oxides suspended in the melt
- Drossing—promote separation of the aluminium from the dross layer
- Refining—react with certain metallic elements in the aluminium (Mg, Ca, Li, Na, K)
- Wall Cleaning—contain compounds to remove oxide buildup; often gunned
- Grain Refining—refines grain structure in final cast parts (i.e. smaller grains)
- Eutectic Modifier—similar to grain refiner, but refines crystalline structure in alloy
The flux recipe depends on the desired application of the flux, and flux recipes can provide insight into their purpose.
- Form low melting, high fluidity compounds within molten metals
- Generate anions capable of reacting to form desired reactants
- Absorb, agglomerate or float reaction products (especially if injected)