Corrosion Performance of Al-base Metal-Matrix-Composites (MMC)

Abstract

This paper deals with SCC and pitting corrosion resistance of 6061 and 7075 Al-base metal-matrix composites (MMC) manufactured by using the squeeze casting methods in the laboratory. SiC-whisker, Al₂O₃ and carbon fibers are used as reinforcements. SSRT can be applied to evaluate the MMC's resistance to SCC. Resistance of MMC to pitting corrosion can be determined by potentio-dynamic polarization to measure pitting potential. Transmission-electron-microscopy (TEM) can be used for observation of interfacial layers formed between the metal-matrix and reinforcements. When MMC is polarized in 3.5% NaCl solution, changes occurs in cathodic reaction due to the effect on the interfacial layers between the reinforcement fibers and the matrix. It can be found, however, that reinforcement fibers in MMC have no effect on the development of pitting and SCC susceptibility of MMC unless their conductivities are not shown. In other words, chemical composition and heat-treatments applicable to improve the localized corrosion performance of 6061 and 7075 Al-alloys are still effective to increase the localized corrosion resistance of MMC despite the difference in the critical stress of SCC.