Impurities in aluminum alloy melt contain more or less gas, various non-metallic inclusions, and other harmful metals. The presence of these impurities will directly affect the quality of aluminum alloy, causing ingots such as porosity, pores, slag inclusions, etc. Defects in turn have adverse effects on the mechanical properties, processing properties, corrosion resistance, surface treatment properties and product appearance of downstream processed products. In order to overcome the above-mentioned adverse effects, melt purification in the aluminum alloy casting production becomes extremely important. Alkali removal from aluminum alloy melt is an important part of the melt purification. At the same time, for the production method of direct batching of electrolytic aluminum liquid, it becomes very necessary to remove alkali.
Impurities in Aluminum Alloy Melt
The source of the alkali metal in the aluminum melt is in the production of aluminum alloy melting and casting. The alkali metal mainly refers to the elements of lithium, sodium, and potassium.
The sources of the alkali metals are mainly the following ways.
- Aluminum for raw materials.
- In aluminum alloy casting production, the electrolytic aluminum liquid or remelted aluminum ingots used are all from electrolytic aluminum plants.
- Na. In the electrolytic aluminum production process, the use of sodium-containing media such as cryolite (Na3AIF6) and sodium fluoride (NaF), so that there is a certain content of sodium in the electrolytic aluminum liquid, the content can reach 80ppm, and the sodium content in actual production is controlled at 30 ~60ppm; the sodium content in aluminum ingots for remelting is generally 8-15ppm, and individually reaches 23pm.
- Li. In the production of electrolytic aluminum, additives such as CaF, LF and MgF2 are added to improve the chemical, physical or electrochemical properties of the electrolyte. At the same time, in most cases, there is a small amount of Ca, L and Mg in the electrolytic aluminum raw material alumina itself.
- K. Mainly from impurities in raw materials and auxiliary materials in electrolytic aluminum production. Most commonly used refining agents for aluminum alloys contain metallic sodium and potassium ions, and the main components of the refining agent are Na3AF6, NaCl, KCl and a small amount of NaF.