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 processthe reaction of oxygen reduction.

The corrosion-protective influence of eco-friendly ceria conversion coatings deposited on Al-1050 alloy, additionally treated in mixed NaH₂PO₄ and Ca(NO₃)₂ solution, was studied. The main aim of this work was to investigate how the obtained mixed systems of coatings eliminates the negative role of cracks and pores on the surface formed after deposition only of ceria coating. For this purpose, the growth structure, main components and corrosion resistance of the so formed protective systems were investigated by SEM, EDS, XRD, XPS and electrochemical (PDP, Rp, etc.) methods. The results obtained show that the basic components of the conversion layers (before and after exposure in model corrosion media) are characterized by Al₂O₃, Al(OH)₃, CePO₄ and Ca₅(PO₄)₃(OH). Based on these results, the optimal conditions of immersion treatment(s) of Al substrate are established. At these regimes, the relationship of co-deposited Ce³⁺, PO₄³⁺ and Ca²⁺-containing components of the conversion layers determine the maximum values of their polarization resistance—a basic criterion for corrosion protection of Al. This effect is related to the formation of fill out of the defects of the conversion coatings and additional Ca₅(PO₄)₃(OH), CePO₄ AlPO₄ and Al(OH)₃ deposits, leading to the decrease of the corrosion rate.

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

This investigation presents results on the improvement of the corrosion-protective effect of consecutive sealing treatments of anodized Al 1050 (Al_Anod). The treatments were performed in cerium-containing and mixed NaH₂PO₄ + Ca(NO₃)₂ solutions. The changes of the surface morphology, structure and chemical composition, chemical state of the elements, and basic corrosion parameters of the studied systems were investigated by SEM, EDXS, XRD, XPS, and a complex of electrochemical techniques (PDP, E_OCP vs. timeplot, chronoamperometric transients, Rp and CR at E_OCP, etc.). The results obtained show that the basic components of the obtained sealing conversion layers (before and after exposure to model Cl⁻-containing corrosion media) are characterized by Ca₁₀(PO₄)₆(OH)₂, AlO(OH), CePO₄, and CeAlO₃ (after the corrosion tests, they are converted to insoluble Me-PO₃ and Me-P₄O₁₀). We conclude that the observed decrease in the corrosion rate of Al and the corresponding increase in the polarization resistance are accomplished by the two-step sealing treatment, which fills up the Al_Anod pores with insoluble deposits.

Important from exploitation point of view mechanical properties of single-layer, double-layer, and mixed alumina and ceria films and their stainless steel (SS) substrate were investigated by means of nanoindentation experiments. As a result, we obtained the experimental load–displacement curves and calculated the indentation hardness (H_IT) and indentation modulus (E_IT), by means of Oliver and Pharr approximation method. Numerical simulations of the process of nanoindentation by means of finite element method were performed as well, in order to obtain more information about the plastic properties of the investigated films. The obtained results show that the mixed Al₂O₃+Ce₂O₃ film, obtained at dominant concentration of cerium ions in the working electrolyte, has the highest indentation hardness and modulus, followed by the single Ce₂O₃-CeO₂ film, the mixed Al₂O₃+Ce₂O₃ film, obtained at dominant concentration of aluminum ions in the working electrolyte, the double Ce₂O₃-CeO₂/Al₂O₃ layer, and single Al₂O₃ layer.