Pitting behavior of SiCp 2024 Al metal matrix composites

The effects of the volume fraction of SiC particulate reinforcements and th e concentration of chloride ions in solution on the localized corrosion cha racteristics of SiCp/2024 AI metal matrix composites (MMC) were investigate d. A scanning micro reference electrode (SMRE) technique was employed to st udy the dynamic process of pitting initiation and development on the surfac e of the composites at open-circuit potential. Potentiodynamic polarization s were performed to characterize the electrochemical behavior of the MMCs. The morphology of the localized attack on the MMC sample after corrosion te sts were examined by scanning electron microscopy (SEM). The results of ele ctrochemical measurement showed that the composites were less resistant to pit initiation than the corresponding unreinforced metrix alloy. Increase i n the volume fraction of SiCp reinforcement in the SiCp/2024 Al composites resulted in a significant decrease of pitting potential. In situ potential mapping of active centers on the surfaces of the composites revealed that l ocal breakdown of passivity and initiation of micro pitting corrosion could take place even at an open-circuit potential which was more negative than the pitting potential, and the number of active centers on the surfaces of the composites increased as the volume fraction of SiC particulates in MMCs increased. Micro-structural analysis indicated that pitting attack on the composites mainly occurred at SiCp-Al interfaces or inclusions-Al interface s. (C) 1998 Kluwer Academic Publishers.