## 3 Results and Discussion
### Electrochemical Behavior  
When aluminum comes into contact with water, a protective layer of AlOOH forms on its surface [48]; however, when this passive layer comes into contact with chloride ions, anodic disintegration items (i.e., AlOHCl and AlOHCl\({}_{2}\)) develop. These products have a tendency to dissolve in water, thereby promoting the anodic disintegration of the passive film [49]. Figure 3 shows the polarization curve of the as-received Al5083 and ECAP samples in the 3.5% NaCl solution. Table 1 presents the data obtained from these curves using Tafel's extrapolation method. Figure 3: Potentiodynamic polarization curve of the Al5083 alloy in the 3.5% NaCl solution. The curve and the data clearly show that the corrosion resistance property (\(i_{corr}\) value) increases with the increasing passes in the ECAP, compared to the as-received sample. No particular pattern was observed in the case of the corrosion potential (\(E_{corr}\) value). The as-received sample showed the highest \(E_{corr}\) value compared to the ECAP sample, which can be explained by the micrograph given in Figure 2a-d. The grain refinement of this alloy increased after every pass. When grain refinement occurs, it provides more sites to initiate the corrosion (i.e., increases the corrosion rate, which decreases the overall corrosion resistance property). Grain refinement provides more areas for corrosion in two ways: (1) inside the grain boundary and (2) at the grain boundary. The results clearly indicate that with more ECAP passes comes the tendency of corrosion rate increase in the Al alloy, due to grain refinement [50]. Figures 4 and 5 represent the Bode magnitude and the Bode phase plot, respectively, in the 3.5% NaCl solution. The Bode magnitude plot exhibits two separate areas. In the lower- and higher-frequency sections, the Bode magnitude plot illustrates constant log \(\left|\text{Z}\right|\) values vs. log (_f_), indicating a response to the solution resistance. In the broad (0.1-1000.0 Hz) middle-frequency range, the spectra displayed a linear slope of approximately \(-1\). This is a characteristic response of the capacitive behavior of the surface film. The phase angle of the as-received sample approached 70\({}^{\circ}\) in the Bode phase plot at the intermediate frequency range. For the other samples (first, second, and third passes), the phase angle gradually decreased to near 30\({}^{\circ}\), showing a diffusion on the surface that affected the solution resistance and consequently lowered the corrosion resistance. The character of all the Nyquist plots (Figure 6) exhibits almost the same pattern for all the samples. Hence, we may very well presume that the ECAP does not impact the surface character. The Nyquist plots demonstrated two different time constants: (1) one at high frequencies related to a well-defined loop, which can be ascribed to the parallel combination of polarize resistance (\(R_{p}\) \begin{table}
\begin{tabular}{c c c} \hline
**Sample** & \(i_{corr}\) **(A/cm\({}^{2}\))** & \(E_{corr}\) **(V)** \\ \hline Annealed & \(1\times 10^{-6}\) & \(-3.29\times 10^{-1}\) \\ First pass & \(2\times 10^{-5}\) & \(-4.55\times 10^{-1}\) \\ Second pass & \(1\times 10^{-4}\) & \(-5.18\times 10^{-1}\) \\ Third pass & \(3\times 10^{-4}\) & \(-3.59\times 10^{-1}\) \\ \hline \end{tabular}
\end{table} 
Table 1: Potentiodynamic polarization results in the 3.5% NaCl Solution. Figure 4: Electrochemical impedance spectroscope (EIS) log \(\left|\text{Z}\right|\) curve of the Al5083 alloy in 3.5% NaCl solution. and a double-layer constant phase element (\(Q_{dl}\)); and (2) another at low frequencies related to a very dissipated loop, and in some cases, all around a characterized inductive loop. The EIS of these samples was performed in the same NaCl solution. The influence of the grain refinement on the corrosion resistance was also found herein, supporting the above discussions [51].