Localized Corrosion Induced in Graphite/Aluminum Metal-Matrix Composites byResidual Microstructural Chloride

摘要

Graphite/Aluminum (G/Al) metal-matrix composites (MMCs) manufactured using thetitanium-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. Corrosion behavior of G/Al MMC precursor wires and plates made of diffusion-bonded packs of precursor wires was investigated in this study. In chloride-free sodium sulfate solutions, severe pitting of the wire-wire diffusion bonds was observed to coincide with distinct pitting regimes in anodic polarization diagrams of the G/Al MMC plates. The pitting of the diffusion bond regions disbonded the precursor wires, and caused the plates to exfoliate. Pitting was found to be induced by residual microstructural chloride, which originated from the Ti-B VD method. This work suggests that the exfoliation of G/Al MMC plates should be eliminated by producing composites with halide-free microstructures. (aw)