## 3 Results and Discussions
### Coating Corrosion Resistance  
The data from the linear polarization measurements are presented in Table 6, and the polarization curves of treated and untreated aluminum samples are shown in Figure 7. In the figures, E\({}_{\text{corr}}\) and j\({}_{\text{corr}}\) represent the corrosion potential and corrosion current density, respectively. Additionally, E\({}_{\text{pit}}\) indicates the potential where a breakdown of the anodic layer occurs and localized corrosion (pitting) begins. The corrosion rate (CR) in mm/year is presented in Table 6 and is calculated using Equation (3). \[CR=\frac{3.27\times 10^{-3}\times j_{corr}\times W}{\rho} \tag{3}\]  
where CR is the corrosion rate (mm/year); j\({}_{\text{corr}}\) is the corrosion current density (A/cm\({}^{2}\)); W is the equivalent mass of the material studied (according to ASTM G102: 2015 [48]), and \(\rho\) is the specific mass of the material studied (g/cm\({}^{3}\)). In general, it is observed that the PEO treatment made the aluminum sample much more corrosion-resistant compared to the untreated sample, both in terms of nobility (corrosion potential, E\({}_{\text{corr}}\)) and corrosion rate (current density, j\({}_{\text{corr}}\)). A higher potential on the \(y\)-axis indicates a greater ability of material, with less interaction with the aggressive environment. Moreover, being more shifted to the left on the \(x\)-axis (Log (i)) of the graph indicates higher corrosion resistance [2; 49; 50]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **E\({}_{\text{corr}}\) (V)** & **j\({}_{\text{corr}}\) (A/cm\({}^{2}\))** & **E\({}_{\text{pit}}\) (V)** & **CR (mm/Year)** \\ \hline AA2024 & \(-\)0.64 & 7.4 \(\times\) 10\({}^{-5}\) & \(-\)0.55 & 9.6 \(\times\) 10\({}^{-2}\) \\ AA2024 (PEO) & \(-\)0.47 & 1.1 \(\times\) 10\({}^{-7}\) & + 0.85 & 1.5 \(\times\) 10\({}^{-4}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Corrosion potential (E\({}_{\text{corr}}\)), corrosion current density (j\({}_{\text{corr}}\)), pit corrosion (E\({}_{\text{pit}}\)), and corrosion rate (CR). Figure 7: Polarization curves of the AA2024 aluminum alloy with and without PEO treatment, with orange arrows indicating the breaking point of the coatings (Epit). The data from Table 6 and Figure 7 demonstrate that the PEO treatment significantly increased the corrosion resistance of the AA2024 aluminum alloy. The pitting potential (E\({}_{\text{pit}}\)) indicates the oxide layer's durability until its breakdown. In the untreated sample, the rupture points were subtle, around \(-0.55\) V, with subsequent attempts at passivation. In contrast, the PEO-treated sample exhibited a more pronounced pitting potential at \(+0.85\) V, characterized by a clear breakdown of the anodic curve and a sudden increase in corrosion current density [2; 19; 51]. The PEO treatment on the AA2024-O alloy significantly increased its corrosion resistance, with a reduction in corrosion rate of approximately 99.84% compared to the untreated sample (Equation (4)). \[Reduction\;CR\;=\;\frac{(CR\;AA2024\;untreated\;-CR\;AA2024\;treated)}{CR\;AA2 024\;untreated}\times 100 \tag{4}\]  
This improvement in resistance is attributed to the formation of an oxide layer acting as a barrier, consistent with findings from other studies demonstrating that PEO treatments indeed decrease the corrosion rate in aluminum alloys [52; 53]. The noise observed at the end of the polarization curve corrosion test may indicate an attempt at repassivation of the alloy, reflecting changes in the surface state as it tries to form a protective layer. However, the test interruption due to the equipment reaching its \"overlay\" suggests that the continuous scanning method may have introduced inaccuracies. Continuous sweeps can distort the half-sweep curve, affecting corrosion potential and current density. Furthermore, traditional analysis techniques can introduce errors, especially in small ranges of superpotentials.