Improvement of protection performance of Mg-rich epoxy coating on AZ91D magnesium alloy by DC anodic oxidation

An anodic oxidation film was fabricated on an AZ91D magnesium (Mg) alloy via simple direct current anodic oxidation. The effects of the anodic oxidation film on the protection performance of a Mg-rich primer on this alloy, were determined. In addition to the barrier effect of the films, the holes in the film enhanced the mechanical interlocking between the primer and the film. This yielded a significant increase in the adhesion of the primer, on the AZ91D substrate by the film. The results of electrochemical measurements and scratch testing suggested that the film significantly prolongs the lifetime of the primer and the composite coating system provides excellent protection for the alloy. The mechanisms governing the effect of the film on the protection performance of the primer were discussed.