Scrap melters have to deal with ever-increasing levels of undesirable elements and impurities. An important issue in recycling Al scrap is to control such impurities, especially Fe, which may lead to the formation of detrimental phases, such as β-Al9Fe2Si2. One approach is to add Mn (sometimes with Cr) to form Fe-containing α-Al15Si2Mn4, which suppresses the formation of the detrimental phases and can be separated from the melt.
Thermo-Calc can be used to understand the chemical reactions and predict the Mn addition and processing temperature. The figure shows that adding Mn to scrap reduces the Fe content but increases the Mn content. The optimal Mn addition can be determined based on a compromise, which depends on the desired alloy composition.