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 solutions. 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, , and Al/graphite which had been passivated in for one week did not pit in for at least one month. Electrochemical impedance spectroscopy (EIS) is a convenient tool for monitoring of the passivation and the corrosion processes.