LOCALIZED CORROSION INDUCED IN GRAPHITE ALUMINUM METAL-MATRIX COMPOSITES BY RESIDUAL MICROSTRUCTURAL CHLORIDE

Graphite fiber/aluminum (G/A) metal-matrix composites (MMCs) manufactured using the titanium-boron vapor deposit (Ti-B VD) method were found susceptible to localized corrosion in chloride-free sodium sulfate solutions in which Al should be passive. G/Al MMC precursor wires and plates made of diffusion-bonded packs of precursor wires were investigated in this study. When G/Al MMC plates were exposed to chloride-free sodium sulfate solutions, pitting regimes were visible in the anodic polarization diagrams. Accordingly, wire-wire diffusion bonds were severely pitted, causing disbonding of precursor wires that led to the exfoliation of plates. The pitting was was found to be caused by residual microstructural chloride originating from the Ti-B VD method. This work suggests that the exfoliation of G/Al MMC plates could be prevented by producing composites with halide-free microstructures.