The mechanism of corrosion inhibition by chromate conversion coatings from X-ray absorption near edge spectroscopy (xanes)

Abstract X-Ray absorption spectra of chromate conversion coatings on Al 2024-T3 and 3003-H14 have been obtained as a function of processing time and environmental exposure. The spectra reveal the presence of a significant ratio of unreacted hexavalent chromium in the chromate conversion coatings which decays with the time of exposure in air-equilibrated 0.5 M NaCl. These results suggest that the unique corrosion-protective property of chromated Al lies in the presence of a source of the hexavalent chromium species as an active inhibiting species.