Abstract
Following on the results presented in the first part of this study, the focus of attention now shifts to the influence of different deposition sequences and heat treatment temperatures on the production of multilayered conversion coatings of silica and boehmite on 1020 carbon steel, aiming the improvement of the anticorrosive performance of alumina coatings in a saline medium. Thus, conversion coatings composed by different deposition sequences of two xerogel films (boehmite/silica and silica/boehmite films), were evaluated by SEM and XRD after heat treatment. After covering these multilayered conversion coatings containing silica and boehmite with alumina film, the systems were characterized by electrochemical impedance spectroscopy in NaCl 0.5 mol L−1 solution. Both kinds of multilayered conversion coatings improved the anticorrosive performance of the alumina film in the aggressive medium, independent of the coating arrangement and the heat treatment temperature used. Moreover, this parameter affected the composition and morphology of both kinds of conversion coatings, directly influencing on the anticorrosive properties of the final coating systems. Among all of the systems studied in the present work, the one produced using silica/boehmite deposition sequence and heat-treated at 600 °C showed the most significant improvement in the corrosion protection of steel in a saline medium.
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