## 3 Results and Discussion  
The anodizing parameters, and more precisely the process time and the anodizing current value, were selected in such a way that the differences between the thickness of individual samples were as small as possible (constant value of the electrical charge density). The averaged values of the thickness measurements of the layers are presented in Table 3. The maximum differences between the thickness values of the oxide layers are in the range of 5 \(\upmu\)m.  
The structures of oxide layer surfaces consist of a thin barrier layer, adhering directly to the surface of the aluminum alloy and the surface layer. The barrier layer is formulated first on the surface of the aluminum alloy. It is not porous, the current conducts only in its thinner places, and its thickness is small and amounts to \(0.5\div 2\%\) of the total layer thickness. The surface layer (Figure 1) shows a column-fibrous structure, oriented along the direction of layer growth due to the influence of the electric field in the electrochemical process. The aluminum oxide fibers are arranged parallel to each other forming free spaces between them, which are a migration channel of oxygen ions connecting with the material of the anode. Both the fiber diameters and dimensions of the space between the fibers depend on the parameters employed in the anodizing process (mainly electrolyte temperature and current density). Parallel alignment of the oxide fibers is obtained only when a substrate of high purity is used. Using aluminum alloys as the substrate of the oxide layer distorts the fibers, which are arranged in an irregular way and are directed at different angles. The results of research on the nanostructures of the Al\({}_{2}\)O\({}_{3}\) layers obtained at different formation process temperatures are presented in Figure 1.  
3D isometric visualizations of the layer surfaces are aimed at visualizing the measurement results for the surface geometric structure and the largest deviations from an even surface. Figure 2 presents the surface geometric structure for all tested layers. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & **A** & **B** & **C** & **D** & **E** & **F** \\ \hline Thickness [\(\mu\)m] & 51.3 & 53.0 & 48.0 & 50.4 & 50.9 & 52.0 \\ Deviation [\(\mu\)m] & 0.9 & 1.3 & 1.2 & 0.6 & 0.8 & 1.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Juxtaposition of oxide layer thicknesses. Figure 1: Cross-sectional image of columnar-fibrous structure of oxide layers produced at current density of 2 A/dm\({}^{2}\) in electrolyte at temperatures of: (**a**) 293; (**b**) 298; (**c**) 303 K.  
Table 4 shows the basic stereometric parameters of the amplitude group. The average arithmetic deviation of roughness, \(Sa\), and the average square deviation of roughness, \(Sq\), indicate a low surface roughness of the oxide coatings produced using the electrochemical method. These parameters change within a very small range. However, it can be noticed that as the temperature of the electrolyte in which the layers were produced grows, the value of parameters \(Sa\) and \(Sq\) increases. The maximum height of surface elevation, \(Sp\), had the lowest value (1.28 \(\upmu\)m) for Sample F, while the highest value of \(Sp\) (5.82 \(\upmu\)m) was measured for Sample E. When analyzing the \(Sp\) parameter values, no correlation can be seen between the production conditions and the value of the maximum height of the surface elevations. Parameter \(Sv\), which defines the maximum depth of the surface cavity, had the lowest  
Figure 2: Top view of oxide layer surfaces (3D) (designations of samples in Table 1). value (1.168 \(\upmu\)m) for Sample E, while having the highest (4.368 \(\upmu\)m) for Sample G. It can be concluded that parameter \(Sv\) decreases as the current density increases for each of the temperatures. It is evident that the parameter values increase with an increase in the electrolyte temperature.