Interaction of Fe‐Containing, Secondary Al–Si Alloy with Oxide and Carbon‐Containing Ceramics for Fe Removal

Fe is a detrimental impurity element in secondary, i.e., recycled, Al–Si cast alloys for castability and mechanical properties. Fe removal can be achieved by binding Fe into Fe‐containing, primary particles and removing these from the, thus, Fe‐depleted Al–Si alloy melt. Expanding the application of filters beyond the removal of nonmetallic inclusions to increase the Fe‐removal efficiency can contribute to production of high‐quality, secondary Al–Si alloys. The usability of Al₂O₃, 3Al₂O₃ · 2SiO₂, MgAl₂O₄, Al₂O₃–C, and SiC filter materials in contact with Al7.1Si, Al7.1Si1.5Fe, and Al7.1Si0.75Fe0.75Mn alloys is evaluated in sessile‐drop and crucible experiments regarding wettability, chemical interaction, nucleation, particle formation, and the subsequent effect on the alloy composition. The Al–Si melts in contact with Al₂O₃ act as nonreactive, low‐wetting reference systems. MgAl₂O₄ and SiO₂ in 3Al₂O₃ · 2SiO₂ are reduced, forming low‐wetting Al₂O₃, whereas Mg and Si enrich in the droplet. In contact with SiC and Al₂O₃–C, a thin layer of high‐wetting Al₄C₃ is formed. In case of Al₂O₃–C, primary Fe‐containing particles are specifically attached to the Al₄C₃ layer, which is associated with oriented growth of that layer. The remaining Fe content in the melt is 0.9 at% and beneficial kinetic effects for the Fe removal are suggested.