THE CHARACTERIZATION OF CE-MO-BASED CONVERSION COATINGS ON AL-ALLOYS .1.

Scanning Electron Microscopy (SEM), X-Ray Photo-electron Spectroscopy (XPS) and Scanning Auger Electron Spectroscopy (AES) have been used to study the surface chemistry of a multistep process for the generation of cerium- and molybdenum-containing conversion coatings on aluminium alloys. After standard pretreatment, the conversion coating was produ ced on 2024-T351 and 6061-T6 Al alloys by (i) treatment for 24 h in ai r saturated with water vapour at 100 degrees C, (ii) 2 h in 10 mM Ce(N O3)3 at 90-100 degrees C, (iii) 2 h in 5 mM CeCl3 at 90-100 degrees C and (iv) anodic polarisation for 2 h in Na2MoO4 at 500 mV (SCE). XPS i ndicated that the coating generated on both alloys was predominantly a hydrated aluminium oxide. It appeared from SEM and Scanning AES that the cerium was concentrated locally on the oxide. XPS indicated that t he cerium was present in a mixture of Ce(III) and Ce(IV) oxidation sta tes. Many of these cerium rich areas were associated with the constitu ent particles (large intermetallics). Mo(VI) was detected with XPS and there was evidence from SEM and AES to suggest that there was local e nrichment of Mo around the intermetallic particles. Copyright (C) 1996 Elsevier Science Ltd