Corrosion study of ceria coatings on AA6060 aluminum alloy obtained by cathodic electrodeposition: Effect of deposition potential

Abstract

Among potential replacements for chromates, cerium-based conversion coatings (CeCCs) have been identified as leading candidates, showing a good promise as environmentally compliant corrosion inhibitors on Al alloys. In this work, CeCCs were synthesized on M6060 by electrolytic deposition (ELD), a well-suited method for the fabrication of films with controllable properties, at low processing temperature and cost. The CeCCs were deposited at room temperature from Ce(NO3)(3) solution, applying different cathodic potentials (-1.1, -1.4 and -1.6 V vs. SCE) for different deposition times between 5 and 20 min. Structural, morphological and compositional properties of the films were characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy coupled with energy dispersive spectroscopy. Ceria films were nanostructured, exhibiting a cubic fluorite structure. From corrosion perspective, the quality of CeCCs was evaluated in 0.5 M NaCI solution via electrochemical impedance spectroscopy and linear sweep voltammetry. As shown, the coating corrosion quality is the interplay between deposition potential and deposition time. The highest potential led to highly cracked films of poor adherence, even at the shortest deposition time, which disqualified them from any corrosion protection application. The lowest potential (-1.1 V) produced crack-free coatings, but longer times (>= 10 min) were needed to provide the protective layer formation. The best corrosion protection offered CeCCs prepared at -1.4 V. The highest R-p (582 k Omega cm(2)) and the smallest CPE (12.6 . 10(-6) s(n) Omega(-1) cm) were obtained at 20 min deposition time. However, from economical point of view, 10 min deposition is a promising choice. These CeCCs also improved pitting corrosion resistance owing to homogeneous microstructure and sufficient thickness.