The rapid development of modern industry requires products with good mechanical properties and light weight, and thus, the application of Al and its alloy attracts a great deal of attention. However, the production of Al products is surely associated with melting process, in which the formation of oxide inclusions and the absorption of gases like hydrogen are inevitable owing to the oxygen and water vapor in the air. These impurities in molten aluminum have unfavorable influence on the quality of aluminum products. These defects are found in melting and casting processes and therefore, it is of great significance to investigate the influence of inclusions and gas in molten aluminum on the quality of aluminum products and to develop a refining method to remove them.
In order to remove inclusions and gas in molten aluminum, several methods are being used. Among them, refining by solid refining agents is considered most effective from the viewpoint of process operation and economical effectiveness. For solid refining agent, alkaline metal salts in the type of chloride including NaCl and KCl are widely used, and fluorides including NaF, AlF3, MgF2, Na3AlF6, CaF2, Na2SiF6, NaBFO4, etc. are also used.
Many researchers reported the composition of chloride-fluoride system refining agents, and most of them focused on the removal of oxide inclusions. However, there are few investigations related to the appropriate composition of refining agents and the changes in their melting point for the removal of gas, which greatly affect the mechanical performance of pure aluminum products like aluminum sheet.
Sin Hyok, a section head at the Faculty of Metallic Engineering, selected a chloride-fluoride system refining agent as a solid refining agent for removing oxide inclusions and gases to investigate the acting mechanism of each component and determine the optimal composition ratio, and estimated the adaptability of the new agent by measuring its melting point.
The chlorides were NaCl and KCl and the fluorides were Na2SiF6 and NaF, and the optimal ratio of NaCl, KCl, Na2SiF6 and NaF was about 44, 33, 12 and 11%, respectively.