THE USE OF FLY-ASH AND RICE-HULL-ASH IN Al/SiC_p COMPOSITES: A COMPARATIVE STUDY OF THE CORROSION AND MECHANICAL BEHAVIOR

摘要

The corrosion characteristics and mechanical behavior of Al/SiC_p/spinel composites prepared by reactive infiltration with fly-ash (FA) and rice-hull ash (RHA) -both with recycled aluminum- were investigated. MgAl_2O_4 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 SiC_p dissolution and the subsequent formation of the unwanted Al_4C_3. However, FA-composites are susceptible to corrosion via formation of Al_4C_3 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 Mg_2Si 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 MgAl_2O_4 morphologies. While RHA composites exhibit higher surface hardness than FA composites, the latter display a higher modulus of rupture.