Refining of molten aluminum refers to the removal of gases and inclusions in the aluminum alloy. Because the two processes of aluminum alloy smelting and refining are mostly combined, these two processes are called refining in production practice. Since the gas in aluminum alloy is mainly hydrogen, degassing means mainly removing hydrogen.
At present, the main method of refining of molten aluminum is to produce a large amount of gas by refining agent in the aluminum alloy. The bubble body may be the internal chemical reaction of the aluminum liquid, or part of the refined degassing agent is added directly using the principle of partial pressure to dissolve in the aluminum hydrogen The particles diffuse toward the bubble. At this time, the partial pressure of the bubble is zero and the specific gravity of the bubble is lighter. When the bubble rises to the surface of the molten aluminum, the bubble bursts and the hydrogen escapes into the atmosphere, finally achieving the purpose of removing the hydrogen. The principle of slag removal is the same as that of degassing, “slag removal is the basis of degassing”.
Although the density of solid alumina is similar to that of molten aluminum, it takes a long enough time to reach the bottom of the crucible after entering the molten aluminum. However, the oxide film formed after the aluminum water is oxidized has only a large number of pores with large diameters that are dense in contact with the aluminum water. The surface area is large, and the adsorption tends to float upward. Therefore, the specific gravity difference between this oxide film and the aluminum water is small. When it is mixed into the melt, the floating and sinking speed is very slow, and it is difficult to remove from the aluminum water, forming pores and inclusions in the casting. Therefore, the key to transferring aluminum water is to minimize mixing and minimize the contact between aluminum water and air.
The most commonly used method to eliminate pinholes in aluminum alloy castings is the flux refining of molten aluminum method. The most commonly used flux is to degas with chloride salts and chlorides during the melting process. When using chloride salts and chloride degassing agents for degassing, use a bell jar press the degassing agent into the bottom of the crucible 100m and move it at a constant speed. In order to prevent the aluminum liquid from splashing in large quantities, the degassing agent can be added in batches, and the degassing is completed and the slagging is completed, and it is allowed to stand for a specified time. For other metal fluxes, the refining operation is the same.
