Aluminum containing cryolite melts in the melting process of aluminum and aluminum alloy. In order to prevent the oxidation of the melt and remove the inclusions in the melt, flux is usually added to achieve the purpose. The former is to remove a layer of flux called covering agent on the melt surface and form a dense liquid layer with a certain thickness after melting, which can prevent the infiltration of oxygen, so as to prevent the oxidation of aluminum and significantly reduce the burning loss of aluminum. The latter is to add a certain amount of refining agent into the melt, which can separate Al2O3 and other inclusions from the aluminum melt and float on the melt together to form slag to be removed, and can absorb a certain amount of hydrogen in the melt, Therefore, the refining agent has the dual functions of impurity removal and hydrogen removal.

The covering agent and refining agent of aluminum and aluminum alloy melt are mostly composed of chlorine salt and fluorine salt, and some also contain cryolite (Na3AlF6). However, due to the high price, it does not contain potassium cryolite koji (kalf4). The commonly used No. 1 covering agent is composed of 40-50kcl, 25-35nacl and 18-26na3alf6. It is a powdered flux containing cryolite, with a density of about 2.3 kg / M and a melting point of about 670 ℃. Due to the increase of interfacial tension between cryolite, aluminum melt and flux, the volatility and hygroscopicity of flux are reduced, and the covering layer becomes more.

In principle, potassium cryolite (kalf4) can be used to replace all cryolite in the flux to obtain better coverage and refining effect. However, potassium cryolite is expensive, so it is better not to use potassium cryolite in terms of cost performance. Generally, the melting capacity of chloride salt to alumina is very small, which is 1% - 2%. If cryolite is added, the melting ability of flux to alumina will be greatly enhanced.