Inclusions and gases in the metal have a significant impact on the strength, fatigue resistance, corrosion resistance, and stress corrosion cracking performance of the material. Effectively controlling the oxidized inclusions in the melt to improve the quality of cast rods and rolled plates has become a common goal pursued by the metallurgical, casting and material industries of all countries. Currently, the ceramic foam filter purification method is widely used to remove inclusions in aluminum alloy melts.
Formation of Inclusions in Aluminum Alloy
Part of the inclusions in aluminum alloy come directly from the charge, and most of them are formed during the smelting and pouring process, mainly oxide inclusions. All the inclusions before casting are called primary oxidation inclusions, which can be divided into two categories according to their size: one is the large inclusions with uneven distribution in the macrostructure, which makes the alloy structure discontinuous and reduces the compactness of the casting. It becomes the source of corrosion and the source of cracks, thereby significantly reducing the strength and plasticity of the alloy; the other type is small
Dispersed inclusions, this kind of inclusions cannot be completely removed after refining, which increases the viscosity of the metal melt and reduces the feeding capacity of the molten aluminum during solidification. The secondary oxidation inclusions are mainly formed during the pouring process. During pouring, the molten aluminum contacts the air, and the oxygen reacts with the aluminum to form oxide inclusions. During the smelting process, the aluminum alloy contacts various components in the furnace gas to generate compounds such as AL2O3. The Al2O3 in the molten aluminum will increase the hydrogen content of the molten aluminum. Therefore, the content of AL2O3 in the molten aluminum has a great influence on the formation of pores in the aluminum casting.
Filter Purification Method
Foam ceramic filtration technology came out in the 1970s and has been rapidly widely used in the United States, Canada, Japan, France, Australia, and Switzerland. It is the most effective way to remove inclusions in the aluminum melt.
In recent years, some new technologies for purifying molten aluminum have been researched at home and abroad, such as vacuum dynamic processing, ultrasonic continuous degassing purification and corundum ceramic filters, which have received very good results. However, these process methods are relatively complicated and costly, and it is difficult for them to be widely promoted in Shangye cattle production. As for the metal filter screen and fiber cloth filtration, only large inclusions in the aluminum alloy melt can be removed, but the inclusions below the micron level cannot be removed, and the metal filter screen will also pollute the aluminum alloy. The use of foam ceramic filter plates can filter out fine inclusions and significantly improve the mechanical properties and appearance quality of the castings.
Principle of Filter Purification Method
The ceramic foam filter plate has a multi-layer network and multi-dimensional through holes, and the holes communicate with each other. When filtering, the molten aluminum carries inclusions and flows along the tortuous channels and pores, and is directly intercepted, adsorbed, deposited, etc. when it comes into contact with the foamed framework of the filter plate. When the melt flows in the hole, the channel of the filter plate is curved, the melt flowing through the channel changes the flow direction, and the inclusions collide with the hole wall anvil and firmly adhere to the hole wall.