## 3 Results and Discussion
### Structure and Hardness
The grains are primarily separated by quite perfect rectilinear high-angle boundaries, and this was confirmed by the ring-like nature of the selected-area electron diffraction pattern with a lot of discrete point reflections (Figure 7c) and dark-field images obtained in the matrix reflections (Figure 7b). The bright-field images show non-uniform deformation-induced contrast inside certain grains, which indicates a high degree of internal stress (Figure 7a). On the other hand, the absence of an internal substructure and the accumulation of dislocations inside the grains, as well as the rather fine, perfect high-angle boundaries, indicate a rather equilibrium-consistent UFG structure that apparently formed via low-temperature dynamic recrystallization. The absence of precipitates inside the grains and the absence of reflections other than those of Al on the selective area electron diffraction pattern show that the decomposition of the supersaturated Al solid solution and the precipitation of hardening phases did not occur under HPT at n = 10. The lattice period of the Al matrix in the deformed composite and the matrix alloy was determined in order to assess the possibility of oversaturated solid solution formation under HPT. It is known that the accuracy of determining the lattice period depends on the measurement error of the interplanar distance and the accuracy of finding the diffraction angle (\(\theta\)). Taking this into account, the precision determination of the lattice period of the Al matrix in the deformed AlFeGn composite and deformed AlFe alloy was carried out by measuring the interplanar distances of the HKL [331] and [420] planes at diffraction angles 20 equal to 112 and 115\({}^{\circ}\), respectively. The lattice periods averaged over two values are shown in Figure 2.0 According to [36], iron being in solid solution reduces the aluminum lattice period: 1 wt.%Fe reduces it by 0.005 A. By knowing the change in the Al lattice period under deformation (\(\Delta\)a = a(n=0) - a(n=10)), one can calculate the amount of iron that passes into solid solution under HPT. The grating periods averaged over two values of the Al solid solution are shown in Figure 2.1 \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Graphene Content, wt.\%**} & \multicolumn{4}{c}{**Number of Revolutions, n**} \\ \cline{2-6}  & **0** & **5** & **10** & **\(\Delta\)a, Å** & **Fe Content, wt.\%** \\ \cline{2-6}  & & **a, Å** & & & \\ \hline
0 & 4.0490 \(\pm\) 0.0002 & 4.0478 \(\pm\) 0.0001 & 4.0466 \(\pm\) 0.0001 & 0.0024 & 0.48 \\ \hline
0.12 & 4.0491 \(\pm\) 0.0002 & 4.0470 \(\pm\) 0.0002 & 4.0454 \(\pm\) 0.0002 & 0.0037 & 0.74 \\ \hline \end{tabular}
\end{table} 
Table 2: Lattice periods of the Al matrix before and after HPT. Figure 8: Grain–subgrain size distribution of AlFeGn composite after HPT, n = 10. The calculations show that the content of iron in the Al solid solution of the AlFe alloy was 0.48%, while in the composite, it rose to 0.74%. Thus, SPD not only leads to grain refinement but also results in the deformation-induced dissolution of disperse iron aluminides and the formation of supersaturated Al solid solutions. Such structural features contribute to the strength of the materials, which was pointed out more than once in experimental studies using SPD methods [16; 17; 18]. This strengthening is achieved via the sum of contributions from various structural mechanisms, i.e., the grain-boundary (the Hall-Petch relationship), dispersion (the Orowan mechanism), dislocation (proportional to the dislocation density), and solid solution (proportional to the content of the alloying element in the Al solid solution). Figure 9 shows the behavior of the hardness of the samples of different compositions under HPT with different numbers of revolutions (n). The data obtained indicate that the hardness increased sharply after HPT by n = 5; with a higher degree of deformation, the hardness growth declines.