Active protective PEO coatings on AA2024: Role of voltage on in-situ LDH growth

Abstract

Four voltage-controlled plasma electrolytic oxidation (PEO) coatings were developed on AA2024 aluminum alloy at 350 V, 400 V, 450 V and 500 V. Zn–Al LDH layer was in situ grown and loaded with corrosion inhibitor (vanadate) on the coatings to provide active protection to the PEO layers. The structure, morphology and composition of PEO coatings without and with LDH-NO3 and LDH-VOx were investigated using SEM, EDS, XRD and GDOES. Coatings formed at higher voltages (thicker and more stable) reveal a decrease of LDH flakes on the surface. The corrosion behavior and the effectiveness of LDH formation and inhibitor intercalation were also studied. Electrochemical impedance spectroscopy and scanning vibrating electrode techniques have shown a remarkable increase in the corrosion resistance of the LDH-inhibitor treated sample in comparison with PEO coated AA2024 specimen.