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

Abstract

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.