Abstract
Localized corrosion formed on an Al-based metal-matrix composite (MMC) reinforced with 40 wt% Si particles in an air-exposed 0.5 M Na2SO4 solution. Scanning vibrating electrode technique revealed that the net currents over the localized corrosion region were cathodic. Scanning ion-selective electrode technique revealed that the solution near the localized corrosion region was alkalized. Scanning electron microscopy indicated that corrosion initiated around Fe-containing intermetallic particles, which serve as cathodic sites. It is hypothesized that during the processing of the Al/Si MMC, inter-diffusion causes Al atoms to diffuse into Si particles forming a layer of highly p-doped Si at the Al/Si interface. Thus, following the immersion of the MMC into the Na2SO4 solution, at the sites adjacent to the Fe-containing intermetallic particles where the Al matrix dissolved, highly p-doped Si surfaces were exposed to the solution. The highly p-doped surfaces can therefore serve as cathodic sites and exacerbate corrosion.
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