THE USE OF A GASEOUS MIXTURE CONTAINING Ar, SiF_4, Cl_2 AND SF_6 FOR THE MELT TREATMENT OF ALUMINUM-SILICON-COPPER ALLOYS

摘要

The melt treatment of Al-Si-Cu alloys has been carried out for many years on an industrial scale, to achieve a high melt quality. In the specific case of element removal from the melt, many different techniques and chemical products have been employed, with many variations in performance; from very low to very high efficiencies. Na_2SiF_6 has been reported as one of the most efficient compounds to remove magnesium from liquid aluminum alloys. However, it has been established that this compound decomposes into NaF and SiF_4 prior to reacting with the dissolved magnesium. In this work, the use of a mixture of gases containing Ar, SiF_4, Cl_2 and SF_6, for the liquid treatment of aluminum alloys is reported. A gas mixture containing a low concentration of SiF_4 had the best performance. After the treatment, the alloy exhibited low porosity, small inclusions content and low final magnesium content.