Characterisation of unsealed anodic oxide layers on aluminium

The inhibiting effect of unsealed anodic oxide layers on filiform corrosion (FFC) was studied. This was done by means of impedance measurements, polar isation measurements and accelerated corrosion tests (Lockheed test). The e lectrochemical measurements indicate that both the porous layer and the bar rier layer contribute to an enhanced corrosion resistance. In the Lockheed test, the specimens with a porous layer, did not show FFC. The specimens wi th a barrier layer revealed first a decrease of the number of filaments but after a certain point it increased. In contrast to this, the corroded area of the filaments showed a gradual decrease with increasing barrier layer t hickness.