Removal of impurity silicon from molten aluminum alloy with compound method

When aluminum product scrap is recycled as melting material, it is essential to control impurity elements entering the molten metal from scrap for quality assurance. To date, in order to prevent entry of impurity elements into the molten metal from scrap, solid-phase selection and liquid-phase refining have been used. When an eye is placed on the liquidphase refining, a segregation process is adopted for manufacturing of high-purity metal, but presently, any process for removing impurity elements from the molten metal obtained by melting scrap has not yet been put in practical use. Therefore, this report places an eye on the so-called compound method. In this method, proper elements were added to the molten metal to form intermetallic compounds with impurity elements to be removed. The impurity elements were removed by removing the compounds from the molten metal. A special attention was placed on silicon as an impurity element to be removed and for an element to be added to form intermetallic compounds, calcium was chosen based on the value of standard free energy of formation ΔG⁰ of binary compounds containing silicon. With these elements, at least, Ca₂Si and CaSi₂Al₂ are found to form as intermetallic compounds and the silicon concentration in the molten metal is reduced by about 50% in relative values.