## 3 Results and Discussion
### Impact of ECAP Processing Factors
#### 3.2.1 Microstructure Evolution
Results showed that 2A led to a reduction in grain size of 73.3% relative to the AA equivalent, with the limit of grain sizes between 0.56 \(\upmu\)m to 22.62 \(\upmu\)m and a mean grain size of 1.69 \(\upmu\)m. It can be seen in Figure 4b that, post-ECAP processing with 2 Bc, the region of refined grains grew while the region of coarse grains shrank. Following two passes, the grain size varied from 4.41 \(\upmu\)m to 9.29 \(\upmu\)m, with a mean of 1.49 \(\upmu\)m; this was mostly attributable to the rise throughout the induced strain. Grain sizes varied from 0.677 \(\upmu\)m to 11.052 \(\upmu\)m, with a mean grain size of 1.574 \(\upmu\)m following 2C processing, suggesting that 2C decreased mean grain size by 75.1% relative to the AA equivalent, which is depicted in Figure 4c. Based on these results, it was evident that route Bc was superior to routes C and A for producing UFG-equiaxed grains, while route A produced grains that were far more extended. Figure 4 and Table 2 revealed that the mean size of the grain was smallest for the grains produced by route Bc, preceded by route C, and then route A using the 90\({}^{\circ}\)-die. For Mg billets processed through the 120\({}^{\circ}\)-die, as depicted clearly in Figure 4d, processing via 2A led to bimodality in the structure, with the UFG existing alongside prolonged coarse grains. In comparison to its AA equivalent, the grain size resulted from 2A was refined by 72.3%, varying from 0.68 \(\upmu\)m up to 24.79 \(\upmu\)m with a mean grain size of 1.75 \(\upmu\)m. Furthermore, following 2 Bc, nevertheless, the mean grain size was 1.89 \(\upmu\)m, varying from 0.5 \(\upmu\)m up to 22.73 \(\upmu\)m, as depicted in Figure 4e. Strain buildup during the two passes showed a rise in the UFG regions, while diminishing the coarse grain regions, which is consistent with the results from the 90\({}^{\circ}\)-die. For instance, 2C processing led to a 69.4% refinement of the mean grain size of pure Mg relative to its AA equivalent, as displayed in Table 2.  
The (0001) pole figures in AA condition and the ECAP-processed pure Mg with a 90\({}^{\circ}\)-die and 120\({}^{\circ}\)-die are depicted in Figure 5. Figure 5a reveals that the AA texture was a prominent (0001) <uvtw> fiber texture, with the intense (0001) poles oriented in alignment inclined in relation to the ED. Crystallographically, ECAP processing resulted mostly in the simple shear texture, with the shear plane in alignment at 45 degrees with respect to the ED. When plastically deforming hcp metals, the optimal simple shear texture relied heavily on the presence of active slip systems; unlike fcc and bcc crystal structures, hcp crystals only had a restricted amount of slip systems, including basal (0001)<11-20>, prismatic (10-10)<11-20>, or pyramidal [10-11]<11-20> slip [65; 68; 69]. Figure 4: IPF orientation map comparable to ED for pure Mg processed 2A (**a**,**d**), 2 Bc (**b**,**e**), and 2C (**c**,**f**) using the 90\({}^{\circ}\)-die (**a**–**c**) and 120\({}^{\circ}\)-die (**d**–**f**). Figure 5: _Cont._  
Figure 5b shows that following a single pass of ECAP through the 90\({}^{\circ}\)-die, the texture had been twisted nearly 45 degrees about the ED. This is important because it reflected the impact of the initial ECAP pass, which activated the basal slip. As a result of applying 1P, the texture intensity of AA dropped from a maximum of 24.26 to around 9.59 times random, as depicted in Figure 5b. In the initial pass through shear deformation, there were fewer active slip systems, which clearly weakened the texture [64]. A quite robust texture was developed following 1P using the 120\({}^{\circ}\)-die at roughly 23.22 times random, whereas the texture constituents were substantially twisted about the ED.