In the process of aluminum and aluminum alloy smelting, hydrogen and oxide inclusions are the main substances that pollute the aluminum melt. Aluminum is quite easy to produce Al2O2 or sub-alumina (AlO2 and AlO) with oxygen. At the same time, it is also easy to absorb gas (H). It accounts for 70-90% of the total amount of gas in the aluminum melt. The main defects in cast aluminum alloys-pores and slag inclusions are caused by solid particles, such as gas and oxides remaining in the alloy. Therefore, for the quality of the melt, not only the correct and reasonable smelting process must be selected, but also the refining and purification treatment of the melt is also important.
There are many methods for refining and purifying aluminum and aluminum alloy melts, mainly including floatation method, flux refining method, melt filtration method, vacuum method and combined method. This article mainly introduces the application of flux refining method in aluminum alloy smelting.
The role of flux
Molten salt flux is widely used in the production of primary aluminum and secondary aluminum to improve the quality of the melt and the recovery rate of metallic aluminum. The flux has four functions:
1. It can change the wettability of the aluminum melt to the oxide (alumina), so that the aluminum melt is easily separated from the oxide (alumina), so that most of the oxide (alumina) enters the flux and reduces the content of oxides in the melt.
2. The melt can change the state of the oxide film on the surface of the melt. This is because it can break the solid and dense oxide film on the surface of the melt into fine particles, which is beneficial to the hydrogen in the melt from the particles of the oxide film. It escapes through the gap and enters the atmosphere.
3. The existence of the flux layer can isolate the contact between the water vapor in the atmosphere and the aluminum melt, make it difficult for hydrogen to enter the aluminum melt, and prevent the melt from oxidizing and burning.
4. The flux can absorb the oxides in the aluminum melt, so that the melt can be purified.
In short, the removal of inclusions by the flux refining agent is mainly achieved by adsorption, dissolution and chemical action with the oxide film and non-metallic inclusions in the melt.