HIGH-RESOLUTION SEM STUDIES OF CHROMATE CONVERSION COATINGS

Scanning electron microscope studies have shown that chromate paint pretreatment of aluminum resulted in the deposition of a film comprising layers of spherical-shaped particles. On alkali-etched substrates the particle size varied from between 60 nm to less than 10 nm. The larger particles tended to occur either in some of the larger pits on the surface or in the vicinity of intermetallic particles. Uniformly sized 50 to 60 nm particles were deposited on the surface of a polished substrate. Penetration of organic resins into the particulate surfaces may contribute towards the good paint and lacquer adhesion resulting from the pretreatment process.