New Approach for Chromate Free Coatings in Aircraft Applications: Modified Zinc Pigments
Alternatives for the environmentally harmful Cr(VI)-based protective coatings for aluminum alloys are highly demanded, especially for aircraft application a. So far, suitable alternative pigments providing inhibiting effects which are comparable to the performance of chromates have not been found. Well known pigments used in corrosion protection coatings are zinc pigments for steel substrates - offering cathodic protection to the substrate and a densification of the coating due to the volume expansion of its corrosion products. Furthermore, it is generally assumed that zinc corrosion products also offer an inhibiting effect. Due to their lower electrochemical potential zinc does not provide cathodic protection to aluminum substrates. To transfer the positive protection effects of zinc to the application of protective coatings on aluminum substrates, zinc pigments have been successfully modified by alloying with magnesium.