The role of fly-ash and rice-hull-ash in preventing the degradation of hybrid Al/SiC<inf>p</inf> composites prepared from recycled aluminum

The use fly-ash (FA) and rice-hull-ash (RHA) offers the potential for the manufacture of hybrid Al/SiCp/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 SiCp reinforcements when the composites are processed with aluminum in molten state. Experimentally, MgAl2O4 is formed in situ during the infiltration of SiCp-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 SiCp 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.