*3.4.2 Effect of grain size and distribution of secondary phases on corrosion behavior*

**Figure 15** depicts the polarization plots for AZ80 and AZ91 Mg alloys processed with die A at 598 K. From **Figure 15(a)** it was observed that the anodic branches of the unprocessed and processed AZ80 specimen showing the continuous active dissolution of the metal this indicate that AZ80 Mg alloy exhibit poor passivity [30]. Although, Ecorr values of ECAP processed AZ80 Mg alloys are significantly shifted to the less negative potentials and highly reduced the magnitude of Icorr after 2 passes.

**Figure 14.** *Corrosion rate vs. ECAP die.*

A similar observation was made by Ambat et al. [31]. Further, the polarization plot of the 4P ECAPed with 900 die exhibits a corrosion potential of −1.375 VSCE this is higher than corrosion potential of other ECAP passes. This indicates that AZ80 Mg alloy processed with 900 die sample has higher pitting corrosion resistance. Moreover, polarization results specify that the ECAPed AZ80 Mg processed with 900 die has nobler Ecorr values. Further, the potentiodynamic polarization curves of as-received and ECAPed AZ91 Mg specimens in 3.5 wt.% NaCl was also shown in **Figure 16(b)**. The experimental results revealed that the Ecorr, corrosion potential of 4P-ECAPed AZ91 Mg alloys was −1.453VSCE, which was less negative compared with the as-received alloy and other ECAP passes (**Figure 16(b)**). This phenomenon specifies that the cathodic reaction was more difficult in fine-grained Mg alloys compared to the coarse grain alloy. Therefore, with the ECAP, the corrosion potential

#### **Figure 15.**

*Polarization curves of Mg alloys processed through die A (a) ECAPed AZ80 Mg alloys and (b) ECAPed AZ91 Mg alloys.*
