PITTING AND PASSIVATION OF AL-ALLOYS AND AL-BASED METAL MATRIX COMPOSITES

Pitting and crevice corrosion of Al alloys and Al-based metal matrix composites can be detected by characteristic changes of the impedance spectra in the low frequency region. A pitting model has been developed which is in agreement with the experimental data. A fitting procedure has been used to analyze a large amount of data which have been obtained for as-received samples and samples which had been passivated in CeCl3solutions. This chemical passivation process produces surfaces which are very resistant to localized corrosion. The chemical passivation process provides a valuable alternative to chromate conversion coatings. Al 6061, Al/SiC, and AL/graphite which had been passivated in CeCl3for one week did not pit in 0.5NNaCl for at least one month. Electrochemical impedance spectroscopy (EIS) is a convenient tool for monitoring of the passivation and the corrosion processes. © 1990, The Electrochemical Society, Inc. All rights reserved.