The rapid development of modern industry requires products with good mechanical properties and light weight and thus, the application of Al and its alloys attracts a great deal of attention. Inclusions and gas in molten aluminum decrease its fluidity and make its structure rough to decrease the castability and serve as the source of crack. Also, they decrease the workability and surface finish, and especially it is unfavorable to the toughness and fatigue strength. Therefore, there have been many researches to remove these inclusions and gas.
A researcher prepared KCl-NaCl-NaF-Na2AlF6 system refining agent and estimated the refining efficiency by measuring the density of aluminum to determine the effective composition of KCl-NaCl-NaF-Na2AlF6 system. Some components of KCl-NaCl-NaF-Na2AlF6 generate gas for removing gas, but their main refining action is the absorption of oxide inclusions. In other words, the hydrogen removal effect is not so high. Therefore, it is necessary to select and use an additive to increase the amount of generated gas for improving the hydrogen removal effect.
Ri Hyok, a researcher at the Faculty of Metallic Engineering, selected an additive to improve the refining efficiency of NaCl-KCl-Na2SiF6-NaF system-compound refining agent for gas impurities in molten aluminum for continuous casting, and determined its amount.
Based on the relationship between the partial pressure and the chemical potential of refining gas and those of the hydrogen in molten aluminum, he induced a formula for determining the amount of additives. He conducted a metallic microscope analysis of newly-refined aluminum to confirm the refining efficiency.
He found that the amount of NaNO3 which was selected as an additive is 0.2% of that of refined aluminum and at that time the amount of carbon is 0.1%.
You can find his paper “Improvement of the Refining Effect of NaCl-KCl-Na2AlF6-NaF System-Refining Agent for Gas by Adding NaNO3” in “Proceedings of KUTIC-2025”.