Depending on the use of the final product, the level of cleanliness of the molten metal is different. The thinner the final product is required (easy-open cans, heat sinks, etc.), or the higher the surface quality requirements of high-precision strip foil (PS plate base, mirror decorative board, etc.), the higher the requirements for the cleanliness of the metal melt. So the molten metal processing is important.
During the remelting process, depending on the furnace charge, the clinker such as scrap, trimming, and sheet material is seriously oxidized and contains many kinds of non-metallic inclusions. The most common ones are α-phase alumina powder and MgAl2O4 magnesium-aluminum tip. Spar-based refractory particles (MgAl2O4), oxide films, boride, magnesium oxide and magnesium chloride and other non-metal oxides. Inclusions exceeding the specified content can cause various problems, such as breaking the continuity of the aluminum alloy, forming pores, or breaking the strip.
When aluminum strips are used for PS plate base purposes, they are deformed by rolling, and inclusions will form common blisters on the surface of the final product. In addition, some very hard solid inclusions (such as refractory particles) can damage the surface of the rolling mill roll, leaving repeated marks on the strip and becoming the source of cracks.
Hydrogen has a high solubility in aluminum melt. The hydrogen in the aluminum melt mainly comes from the chemical reaction between aluminum and the moisture in the furnace gas, and part of it comes from the hydrogen in the furnace gas or the air. In addition, aluminum ingots are prone to contact with water vapor in the air when stored in the open air, which is also an important reason for the increase in the air content of the aluminum melt. When slab casting, pay attention to the water content of the environment and the casting temperature. The higher the solution temperature, the greater the solubility of hydrogen in molten aluminum, and it is inevitable that the ingot contains hydrogen.
The influence of hydrogen in the aluminum melt can form defects such as porosity, pores, and white spots during the solidification of the ingot. When the temperature of the ingot increases significantly, from hot rolling to annealing, the above-mentioned pores will form blisters on the surface of the ingot. These pores will crack on the edges of the strip during the rolling process.
In the manufacturing process of the ingot, controlling the cleanliness of the molten metal is a very important part of the manufacturing process. This is why it is necessary to process the alkali metals and inclusions of the melt in the furnace in the different process stages of the aluminum melt processing. Degassing system and filtering equipment are the basic conditions for molten metal processing to obtain clean molten metal.