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In this work, the use of ZrO2 nanocoating in aluminum substrates, generated by controlled electrochemical chronoamperometry in hexafluorozirconic acid solutions (H2ZrF6·5H2O), resulted in a lower porous films than that obtained by chemical conversion coating. After the application of an epoxy coating, long-term cyclic immersion corrosion tests and scratch tests proved the superior protection of the dual system and the coating lifespan, thanks to the enhanced adhesion of ZrO2 intermediate layer and the organic coating. As zirconium-based electrolytes are considered more friendly bath if compared to that of other conversion coating processes, like chromating, phosphating or anodizing processes, the study opens new insights to the protection of structural metals in sectors such as automotive, naval and aerospace industries. The main advantages are the employment of lightweight intermediate pre-treatment (nanoscale), compared to conventional ones (microscale), and reduction of waste slurry (electrolyte bath free of additives). [ABSTRACT FROM AUTHOR]

Herein, the influence of the substrate in the formation of zirconium oxide monolayer, from an aqueous hexafluorozirconic acid solution, by chemical conversion and by electro-assisted deposition, has been approached. The nanoscale dimensions of the ZrO2 film is affected by the substrate nature and roughness. This study evidenced that the mechanism of Zr-EAD is dependent on the potential applied and on the substrate composition, whereas conversion coating is uniquely dependent on the adsorption reaction time. The zirconium oxide based nanofilms were more homogenous in AA2024 substrates if compared to pure Al grade (AA1100). It was justified by the high content of Cu alloying element present in the grain boundaries of the latter. Such intermetallic active sites favor the obtaining of ZrO2 films, as demonstrated by XPS and AFM results. From a mechanistic point of view, the electrochemical reactions take place simultaneously with the conventional chemical conversion process driven by ions diffusion. Such findings will bring new perspectives for the generation of controlled oxide coatings in modified electrodes used, as for example, in the construction of battery cells; in automotive and in aerospace industries, to replace micrometric layers of zinc phosphate by light-weight zirconium oxide nanometric ones. This study is particularly addressed for the reduction of industrial waste by applying green bath solutions without the need of auxiliary compounds and using lightweight ceramic materials. [ABSTRACT FROM AUTHOR]