Flash-PEO coatings loaded with corrosion inhibitors on AA2024

Abstract

Flash plasma electrolytic oxidation (flash-PEO) with in situ incorporation of inhibitors is explored as a strategy for corrosion protection of 2024 aluminium (Al) alloys. Thin (~5 μm) and energy-efficient coatings were successfully developed on the Al substrate in 100 s treatment time using different electrolytes based on molybdate, stannate, tungstate, vanadate lanthanum or cerium salts additives with and without complexing agent (EDTA). Screening of the optimum combination in search of minimum thickness and best corrosion protective performance was performed using electrochemical impedance spectroscopy (EIS). Coatings based on EDTA-Ce and WO42 were selected and investigated further in comparison with the inhibitor-free phosphate coating in terms of morphology, composition, corrosion behaviour and paint adhesion. EDTA-Ce coating showed excellent paint adhesion and the highest impedance modulus at short immersion times in 3.5 wt% NaCl aqueous solution. Neutral salt spray testing of this coating as a full system comprising an epoxy primer showed no signs of corrosion after 1000 h of exposure.