The aluminum casting flux chemical composition is mostly halogen salts, which are heterogeneous inclusions relative to the aluminum melt. After the melt purification is completed, it must be allowed to stand for a period of time to float or settle, and then separate from the aluminum liquid.
Taking Na3AlF6 and Na2SiF6 as examples, Na3AlF6 produces the following reactions in aluminum melt:
Na3AlF6 is characterized by a relatively high melting point and low hygroscopicity. The decomposition products reduce the wettability of the interface between solid alumina and aluminum melt, which is easy to separate from aluminum and promote the drying of slag. However, too much fluoride will cause a violent exothermic reaction and produce a large amount of toxic gas. Na3AlF6 can adsorb and dissolve Al2O3, and can increase the surface tension in contact with the aluminum melt and promote the separation from the aluminum melt.
The AlF3 produced by the reaction can remove alkaline earth elements such as Ca and Na in the aluminum melt (the reaction formula is as follows).
The decomposition reaction of Na2SiF6 in the aluminum melt is as follows:
The NaF generated by the reaction can corrode the metal body on the Al2O3-Al interface, mechanically detach the oxide film, and dissolve it into the flux, thereby purifying it, and releasing a small amount of Na for deterioration. The generated SiF4 volatilizes into gas and partially removes it.
Na2SiF6 and Al2O3 produce the following reactions:
The resulting Na3AlF6 has the effect of adsorbing Al2O3, and can also be combined with SiO2 to form a massive slag, which is easy to strip off.
With the advancement of aluminum alloy processing technology and the development of aluminum alloy flux purification technology, some new characteristics have been presented in the preparation of flux and its performance requirements, which not only put forward higher requirements on the purification effect, but also impose higher requirements on the flux itself.
At present, the purification treatment of aluminum melt has higher and higher requirements for purification, and the complex configuration of flux components increases the possibility of the second pollution of the aluminum melt and the environment by the flux itself. The configuration of the flux composition is as simple as possible, which is the only way to solve the side effects of the flux.