THE CHARACTERIZATION OF CE-MO-BASED CONVERSION COATINGS ON AL-ALLOYS .2.

Auger Electron Spectroscopy (AES), Rutherford Backscattering Spectrosc opy (RES) and Forward Recoil Spectroscopy (FRS), have been used to stu dy the surface chemistry of a multistep process for the generation of a cerium- and molybdenum-containing conversion coating on aluminium al loys. After standard pretreatment, the conversion coating was produced on 2024-T351 and 6061-T6 Al alloys by (i) treatment for 24 h in air s aturated with water vapour at 100 degrees C, (ii) 2 h in 10 mM Ce(NO3) 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). RES and FRS indicated that the coating generated on both alloys was predominan tly a hydrated aluminium oxide. AES depth profiles confirmed that the cerium was associated with large intermetallics. On 2024 there was Ce detected on the oxide covering the matrix whereas none was detected on the oxide over 6061. Copyright (C) 1996 Elsevier Science Ltd