## 3 Results and Discussion
### Impact of ECAP Processing Factors
#### 3.2.1 Microstructure Evolution
By comparing the microstructures produced utilizing the 90\({}^{\circ}\) die angle (Figure 3a) and following 1P (Figure 3b), it could be seen that the latter had fewer fine grain regions, whereas the former had more AA with coarse grain regions. The reason for this could be explained by the fact that the 120\({}^{\circ}\) die angle caused far less strain on its first pass than the 90\({}^{\circ}\) die angle did. Grain sizes following 1P varied between 1.1 um and 24.8 um, averaging 2.62 um. Figure 2: IPF orientation map for pure Mg in its AA condition, IPF coloring triangle, red: (001); blue: (120); green: (010). After undergoing ECAP processing, the grain size resulting from 4 Bc (through the 90\({}^{\circ}\)-die) was more refined, varying from 0.21 \(\upmu\)m to 7.14 \(\upmu\)m with a mean of 0.88 \(\upmu\)m, as depicted in Figure 3c. Without the five separate slip systems necessary for homogenous plasticity, local shearing close to the grain boundaries led to the gradual lattice twists that refined the grains [49]. Equivalent results were obtained by [PERSON] and [PERSON] [48] following the processing of pure Mg into four passes, which led to a mean particle size of 1.75 \(\upmu\)m. Another research looked into 4 and 12 passes of ECAP processing on A291 Mg alloy, where they found that only four passes were sufficient to produce the desired homogeneous microstructure, which was distinguished by consistent and fine equiaxed grains having a mean grain size of 7 \(\upmu\)m, which was explained thoroughly by [PERSON] et al. [64]. For the 120\({}^{\circ}\)-die, increases in the regions with structural fine grains could be seen with augmenting the passes; at 4 Bc, the microstructure consisted mainly of fine recrystallized equiaxed grains. Furthermore, the grain size following 4 Bc resulted in a range extending from 0.81 \(\upmu\)m to 6.5 \(\upmu\)m, showing a mean value of 1.89 \(\upmu\)m, as depicted in Figure 3d. The grain size of pure Mg processed using ECAP for multiple passes is often significantly reduced. According to studies [65], ECAP processing of Mg leads to continuous dynamic recovery and recrystallization (CDRR). It was discovered by [PERSON] and [PERSON] [66] that the ECAP could process pure Mg with as many as eight passes at varying temperatures. Refined grains with the necklace structure were reported to have formed as a consequence of the CDRR in all settings studied. Nevertheless, [PERSON] et al. [67] looked at the effects of ECAP processing on the grain size. The results of the ECAP processing of the grain size were also reported in the literature. Figure 3: IPF orientation map comparable to ED for pure Mg processed 1P (**a**,**b**) and 4 Bc (**c**,**d**) using the 90\({}^{\circ}\)-die (**a**,**c**) and 120\({}^{\circ}\)-die (**b**,**d**). processing on Mg-Al-Ca-Mn alloys with a variety of Mg\({}_{2}\)Ca morphologies for as many as 12 passes, both as-cast and as-homogenized. Following four passes, they had a grain structure that was a combination of coarse and fine grains; following eight passes, it was more uniform; but then following 12 passes, it was completely uniform. To investigate the effect of route type on the microstructural evolution of pure Mg, other samples of pure Mg were ECAP-processed with 120\({}^{\circ}\) and 90\({}^{\circ}\) die angles over two passes of different routes A, Bc, and C, as shown in Figure 4. After the AA sample was processed with a 90\({}^{\circ}\)-die for two passes, fine grains started occupying the microstructural area; however, there were still some big grains, though they had been badly distorted. Moreover, the remaining coarse grains maintained their symmetry and uniformity. Figure 4a demonstrates that as plastic strain increased with augmenting the passes, fine grain regions increased in the case of two passes, while the coarse ones decreased during processing through route A.