Spatially resolved microchemical analysis of chromate-conversion-coated aluminum alloy AA2024-T3

The corrosion of aerospace aluminum alloys has been linked to the electrochemical behavior and chemical composition of constituent intermetallic compounds (IMCs). In this study, secondary ion mass spectrometry (SIMS), x-ray photoelectron spectroscopy (XPS), synchrotron infrared microspectrometry (SIRMS) and x-ray absorption near-edge structure spectroscopy (XANES) were used to characterize chromate conversion coatings (CCCs) formed on AA2024-T3 sheet and cast IMC analogs. The nascent surface film formed on IMC and matrix surfaces was characterized to reveal the influence of microstructure on CCC structure and composition. Copper-rich regions were found on the outermost CCC surface. Intermetallic compounds rich in Cu were found to be surface depleted of Cr and enriched in CN from the ferricyanide present in the CCC as an accelerator compound. By distinguishing particle morphology and chemistry, SIMS data demonstrated that heterogeneities in CCC composition were associated with IMCs. Copyright (C) 2002 John Wiley Sons, Ltd.