INFLUENCE OF THE MICROSTRUCTURE ON THE NUCLEATION AND GROWTH OF CHROMATE CONVERSION COATINGS ON ALUMINUM ALLOYS

摘要

The intermetallic particles present on the surface of aluminum alloys strongly affect the nucleation, growth and final properties of eliromate conversion coating (CCC). Coupons of AA2024-T3 were immersed in a commercial chromate bath (Alodine 1200) for different times and after different surface pre-treatments. By means of Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Atomic Force Microscopy (AFM) the roles played by the intermetallics on the nucleation and growth mechanisms of CCC could be distinguished and the influence of the surface preparation procedure was also highlighted. The removal of the intermetallic particles and of any eventual copper surface enrichment are necessary conditions to obtain a dense, homogeneous and protective chromate film.