XPS AND SEM CHARACTERIZATION OF HYDRATED CERIUM OXIDE CONVERSION COATINGS

Cerium-rich conversion coatings have been deposited onto aluminium 2024-T351 alloy by immersion into a solution containing 10 g L(-1) CeCl3 and 1% H2O2 in a process described as 'cerating'. Prior to deposition the alloy had been prepared either by using a standard chemical pretreatment used for aerospace alloys before conversion coating or by polishing. X-ray photoelectron spectroscopy and scanning electron microscopy have been used to characterize these cerium-containing conversion coatings. It was found that, during deposition, hydrated cerium oxide initially covered the intermetallics present in the alloy surface and then covered the surface generally. Deposition continued over the intermetallics throughout the conversion coating process, resulting in thick, heavily-cracked regions considerably greater than the average thickness of the film (>0.3 mu m). Elsewhere the coating was generally up to 0.2 mu m thick, and appeared to comprised of deposited particles around 100 nm in size.