The corrosion characteristics and mechanical behavior of Al/SiCp/spinel composites prepared by reactive infiltration with fly-ash (FA) and rice-hull ash (RHA) -both with recycled aluminum- were investigated. MgAl2O4 is formed in situ during infiltration 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. However, FA-composites are susceptible to corrosion via formation of Al4C3 by the interaction of native carbon in FA with liquid aluminum. The foremost corrosion mechanism in both types of composites is attributed to microgalvanic coupling between the intermetallic Mg2Si and the matrix. Microstructure and mechanical characterization show that FA- and RHA-composites possess mechanical properties that are significantly different and that this behavior is due to the original ash and MgAl2O4 morphologies. While RHA composites exhibit higher surface hardness than FA composites, the latter display a higher modulus of rupture.
Al/SiCp composites; fly ash; rice hull ash
