Protection of aluminum alloys from filiform corrosion by low-temperature plasma interface engineering

This study investigates the filiform corrosion resistance of chromate-free coating systems fabricated on aluminum alloys by low-temperature plasma interface engineering. The aluminum alloys investigated include AA2024-T3 ([2B]), AA7075-T6 ([7B]), Alclad AA2024-T3 ([2A]), plate stock AA2124-T851([2P]), plate stock AA7050-T7451 ([7P]), and ion vapor deposition (IVD) Al-coated AA2024-T3 ([2I]), IVD Al-coated plate stock AA2124-T851([2PI]), IVD Al-coated plate stock AA7050-T7451 ([7PI]). Direct current (DC) cathodic plasma processes including plasma treatment and plasma deposition were used to create the water-insensitive adhesion of organic coatings to aluminum alloys. With appropriate application to aluminum alloys, DC cathodic plasma coatings of trimethylsilane (TMS) combined with argon plasma post-treatment provided tenacious and water-insensitive adhesion between the water-borne, chromate-free spray primers and aluminum substrates. These chromate-free coating systems, when tested by filiform corrosion test, showed superb resistance to filiform corrosion. Filiform corrosion test was found to be a good measure of water sensitivity of the coating interfaces.