We've investigated the effect of preliminary Al substrate treatment on the deposition and corrosionprotection ability of thin, conversion cerium oxide layers formed in solutions containing Ce 3+ and Cu 2+ ions. The cerium oxide layers and their corrosion protection behaviour were investigated by SEM, EDS, XPS, and model polarization E-lg i and It chronoamperometric curves. We report on the structure, morphology, chemical composition and the state of the elements in the conversion layers, as well as the thickness and distribution of the elements up to the "conversion layer"/"aluminium substrate" interphase boundary. The preliminary treatment of the Al substrate, as well as the presence of Cu 2+ , both substantially influence the thickness, composition and protective ability of the formed ceria and alumina mixed conversion layers. All these features are related to changes in the ratio of the formed AlOOH (~Al 2 O 3 .H 2 O), Ce(OH) 3 (~Ce 2 O 3) and Ce(OH) 4 (~CeO 2) on the modified Al surface, which are affected by the preliminary treatment of the Al substrate and presence of Cu 2+ ions in the immersion treatment solution based on Ce 3+ ions.

Systematic studies were carried out with respect to the elucidation of the role of additional “post-treatment” immersion phosphate processing on conversion corrosion protective ceria coatings CCOC deposited on aluminium Al 1050. Thereupon, the influence of various compositions of the CCOC as well as the conditions of such treatment were studied, based on solutions of Na3PO4 or NH4H2PO4. The results obtained with respect to the corrosion behavior, respectively the corresponding changes in the chemical composition of the studied corrosion-protective systems, give us the reason to suppose that the phosphate layers formed on the CCOC play the role of not only protective barrier coating, but they also change the kinetics of the conjugated electrochemical reactions characterizing the corrosion of aluminium. Key words: aluminum, pre-treatment, cerium-containing conversion films, corrosion

No abstract

Abstract. It is known that there is special interest in the contemporary investigations on conversion treatment of aluminum aimed at promoting its corrosion stability, which is focused on electrolytes on the basis of salts of metals belonging to the group of rare-earth elements. Their application is especially attractive, as it enables a successful substitution of the presently applied highly efficient, but at the same time toxic Cr 6+ -containing electrolytes. The present paper presents a study on the influence of the preliminary alkaline activation and acidic de-oxidation of the aluminum surface on the processes of immersion formation of protective cerium oxides films on Al 1050. The results obtained show that their deposition from simple electrolytes (containing only salts of Ce 3+ ions) on the Al surface, treated only in alkaline solution, occurs at a higher rate, which leads to preparing thicker oxide films having a better protective ability. In the cases when the formation of oxide films is realized in a complex electrolyte (containing salts of Ce 3+ and Cu 2+ ions), better results are obtained with respect to the morphology and protective action of cerium oxides film on samples that have been consecutively activated in alkaline solution and deoxidized in acidic solution.Electrochemical investigations were carried out in a model corrosion medium (0.1 M NaCl); it was shown that the cerium protective films, deposited by immersion, have a cathodic character with regard to the aluminum support and inhibit the occurrence of the depolarizing corrosion process -the reaction of oxygen reduction.