Enhanced corrosion and tribocorrosion behavior of plasma electrolytic oxidized coatings on 5052 aluminum alloy with addition of pullulan to silicate electrolyte

Plasma electrolytic oxidation (PEO) ceramic coatings were fabricated on a 5052 aluminum (Al) alloy using a silicate-based electrolyte with the pullulan addition, and the effects of different pullulan concentrations on the corrosion and tribocorrosion resistance of the coatings were investigated. The morphology, chemical composition, phase structure, and mechanical properties of the coatings were observed via scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and scratching. The corrosion and tribocorrosion properties were evaluated via electrochemical tests and tribocorrosion tests in a 3.5 wt% NaCl solution, respectively. As a result of the pullulan addition, the phase structure of the coatings was slightly affected, but their microstructure and mechanical properties were significantly altered. The PEO coating displayed the smallest pore size and densest structure at a concentration of pullulan addition of 1.0 g/L. The corrosion current density of PEO coating was 2.41 x 10-8 A/cm2, which was two orders of magnitude lower than that of the Al alloy substrate. In addition, under tribocorrosion conditions, the wear rate of PEO coating was only 4.6 x 10-6 mm3N-1m-1, which was 91.8 % lower than that of the substrate, indicating excellent corrosion and tribocorrosion resistance. This study provides guidelines for the devel-opment of a sustainable and eco-friendly corrosion inhibitor for PEO coatings on Al alloys.(c) 2023 Elsevier B.V. All rights reserved.