## 4 Conclusions  
Commercial pure Mg specimens were processed through ECAP via single pass, two passes, and four passes, along with a variety of routes (A, Bc, and C). The exterior angle (\(\Psi\)) of the split ECAP die was 20\({}^{\circ}\), and both of the adopted ECAP dies had inner channel angles (\(\phi\)) of 90\({}^{\circ}\) and 120\({}^{\circ}\). ML techniques were adopted to estimate the ECAP variables and verify the experimental findings of microstructural evolution, tensile properties, and Vicker's microhardness of ECAP specimens and their AA counterparts. The following conclusions were drawn:  
1. Route Bc is the most effective route in grain refinement. 2. The ECAP die with channel angle of 90\({}^{\circ}\) resulted in higher plastic strain; hence, it is more efficient than the 120\({}^{\circ}\)-die in grain refinement. 3. Processing through 4 Bc resulted in significant grain refinement of 86% compared to the AA condition. 4. The 4 Bc using the 90\({}^{\circ}\)-die produced the most robust texture, which was greater than 26 times random. 5. The grain size demonstrated a strong correlation of \(-\)0.67 with rising number of passes, while \(\phi\) affected the grain size strongly (with 0.83), whereas the route type had the lowest effect on the grain size. 6. When adopting a 90\({}^{\circ}\)-die to accumulate the plastic strain up to 4 Bc, the subsequent HV was indeed 111% higher than that of the AA equivalent. 7. From ML findings, it was clear that the number of passes was the most significant parameter affecting the Mg HV values, whereas ECAP channel angle (\(\phi\)) revealed high correlation factor with HV values as well. 8. The 4 Bc with \(\phi\) = 90\({}^{\circ}\) and 120\({}^{\circ}\) led to a significant increase of \(\sigma_{\rm u}\) by 44.7%% and 35.7%, respectively, compared to the AA counterpart, which can be explained by the significant refinement in the grain size. 9. \(\sigma_{\rm u}\) was affected by the rising number of passes with a strong correlation of 0.81, as revealed in the correlation chart, while affecting ductility moderately with 0.47. 10. The route type weakly affected all four responses of hardness, \(\sigma_{\rm u}\), \(\rm D_{\rm u}\), and grain size. Conceptualization, W.H.E.-G., A.I.A. and M.S. ; methodology, W.H.E.-G., M.O.A. and A.B. ; software, M.S., M.F.A. and F.N.A. ; validation, A.I.A., M.S. and M.K. ; formal analysis, M.F.A. and F.N.A. ; investigation, W.H.E.-G., M.O.A. and A.B. ; resources, A.I.A., M.F.A. and M.O.A. ; data curation, M.S. and M.K. ; writing--original draft preparation, M.K. and M.S. ; writing--review and editing, W.H.E.-G. and A.I.A. ; visualization, A.B. ; supervision, M.O.A. ; project administration, W.H.E.-G., A.I.A. and M.F.A. ; funding acquisition, A.B. All authors have read and agreed to the published version of the manuscript. The Princess Nourah bint Abdulrahman University Researchers Supporting Project number PNURSP2023R230, Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia. Not applicable. **Data Availability Statement:** All the raw data supporting the conclusion of this paper were provided by the authors. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & **Optimized** & \multicolumn{2}{c}{**Training Set**} & \multicolumn{2}{c}{**Testing Set**} \\ \cline{3-6}  & **ML Model** & **RMSE** & **R\({}^{2}\)** & **RMSE** & **R\({}^{2}\)** \\ \hline \(\sigma_{\rm u}\) (MPa) & SVR & 12.91 & 0.797 & 4.253 & 0.929 \\ Ductility & GPR & 0.256 & 0.991 & 2.382 & 0.728 \\ (\(\rm D_{u}\)%) & SVR & 0.358 & 0.982 & 2.047 & 0.799 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Model evaluation metrics of pure Mg ECAP parameters. **Acknowledgments:** The authors acknowledge the Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2023R230), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia, for funding the publication of this project. **Conflicts of Interest:** The authors declare no conflict of interest.