The role of fly-ash and rice-hull-ash in preventing the degradation of hybrid Al/SiCp composites prepared from recycled aluminum

The use fly-ash (FA) and rice-hull-ash (RHA) offers the potential for the manufacture of hybrid Al/SiC_p/spinel composites via reactive infiltration, both with recycled aluminum. The main reason behind this statement is the beneficial role that both waste materials play in preventing the degradation of SiC_p reinforcements when the composites are processed with aluminum in molten state. Experimentally, MgAl₂O₄ is formed in situ during the infiltration of SiC_p-preforms in the temperature range 1050-1150 °C for 50-70 min in argon atmosphere at a pressure slightly above to that of the atmospheric pressure. Results reveal that both FA and RHA help in preventing SiC_p dissolution and the subsequent formation of the unwanted Al₄C₃; and although FA-composites still might be susceptible to corrosion via Al₄C ₃ -by the interaction of native carbon in FA with liquid aluminum-a proper FA treatment significantly mitigates its deleterious effect. Primary corrosion mechanisms and strategies to overcome the potential degradation effects are outlined.