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, 3Al(2)O(3) center dot 2SiO(2), 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 3Al(2)O(3) center dot 2SiO(2) 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.