## 3 Results and Discussion
It is known the factors influencing DRX are: (a) stacking fault energy (SEF, \(\gamma_{SFE}\)); (b) initial grain size; (c) thermo-mechanical processing conditions; and (d) second-phase particles [27]. Material stacking fault energy has a considerable impact on the DRX [36]. During hot deformation of materials with high SFE, such as aluminium, due to the effective DRV, CDRX is often observed. Subgrain structures with LAGBs are formed at more significant deformations and gradually transformed into high-angle grain bound-state materials. Figure 8: TEM bright field micrograph of the annealed specimens after FSP with powder addition. Figure 7: XRD patterns of both the rolled and the annealed specimens after FSP. aries (HAGBs) [37]. During high-temperature deformation, it is usual to observe the development of a homogeneous microstructure [27]. As a result, the micro-shear and deformation bands become less significant compared to cold deformation. Under these conditions, CDRX occurs by the continuous pile-up of dislocations into LAGBs, which raises their misorientation. In due course, HAGBs are created when misorientation angles exceed a critical value \(\theta_{c}\) (\(\theta_{c}\) = 15\({}^{\circ}\)) [38]. As mentioned above, the nanosized particles (Al\({}_{13}\)Fe\({}_{4}\) and Al\({}_{2}\)O\({}_{3}\)) are formed during reactive FSP, acting as reinforcements. These particles also have an essential role in recrystallisation. They are inclined to hinder boundary movement and decrease the rate of recrystallisation and grain growth through a Zener pinning mechanism. After a certain deformation level due to the action of small second-phase particles, the (sub)boundaries are pinned. On the other hand, the entrapment of dislocations within boundaries increases the dislocation density, and the lattice's local strain close to particles enhances the fraction of HAGBs. Since in the reactive FSP, precipitation co-occurs during DRX, the driving force of recrystallisation and the Zener pinning mechanism proceed over time. However, as demonstrated in Figure 10, grains are slightly smaller in the nanocomposite fabricated on the annealed base metal compared to the nanocomposite grain size processed on the rolled base metal. Therefore, it can be concluded that, in addition to the effect of \(\gamma_{SFE}\) and nanoparticles on grain refinement, the initial particle size also affects the final structure. As mentioned before, one of the factors influencing microstructure evolution during DRX is the initial grain size. The previous study reveals that the grain boundaries act as primary nucleation sites for the new grains [39; 40]. Therefore, fine primary grain size provides more nucleation sites. Under a significant strain deformation, the kinetics of grain refinement can notably accelerate by reducing the initial grain size; therefore, the development of misorientation for LAGBs is quicker [41]. As illustrated in Figure 10, the nanocomposites fabricated on the annealed sample have a finer structure. This observation reveals the influence of pre-stored strain energy on the grain growth after dynamic recrystallisation. During the FSP of rolled alloy, there is competition between the grain structure refinement and recovery mechanisms. Figure 9: HAADF imaging, EDS mapping, and selected area diffraction pattern of particles in the fabricated hybrid nanocomposite. The kernel average misorientation (KAM) or local misorientation histogram of the rolled and annealed specimens following FSP with powder addition is shown in Figure 6.0 These specimens were obtained in the middle of the cross-section of the samples. KAM is correlated to the average misorientation between a point and its closest neighbours that are also part of the same grain. KAM is connected to misorientation of less than \(5^{\circ}\). The local plastic strain in specimens was therefore evaluated using the KAM histogram. According to Figure 11, the annealed specimen had higher kernel values than the rolled sample. Figure 12 displays the KAM value versus relative frequency.