## 3 Results and Discussion
The enhanced tensile strength in S2 and S2-HT is attributed to the reinforcement effect of ultrafine microsilica, which acts as a barrier to dislocation movement, while T6 heat treatment further refines the matrix grain structure, improving strength and ductility. Notably, S2-HT specimens exhibited a significant reduction in porosity (Figure 6), resulting in superior elongation at break. The enhanced microhardness (Figure 7) is also consistent with the uniform reinforcement distribution and reduced defect density. These results demonstrate a clear correlation between the microstructure features--such as particle dispersion, reduced porosity, and improved interface bonding--and the mechanical performance of the composites, confirming the effectiveness of the applied processing methods. The developed AMCs reinforced with microsilica have good mechanical properties, which opens possibilities for further use in forming processes such as caliber rolling [37; 38]. Rolling processes require materials that combine good ductility for deformation and high strength for durability under the operating conditions [54; 55; 56]. T6 heat treatment makes it possible to optimize the structural and mechanical properties of composites, making them suitable for further cold or hot rolling operations and expanding their application range in the production of rolled products and structural elements. The mechanical properties of the AMCs reinforced with ultrafine microsilica particles are intricately connected to strain localization mechanisms [57]. The uniform dispersion of microsilica particles within the aluminum matrix, achieved through ultrasonic-assisted stir casting, significantly influences strain distribution. Microsilica particles act as barriers to dislocation motion, creating localized stress concentrations around particle-matrix interfaces. This phenomenon not only enhances strength but also increases the likelihood of strain localization, as observed in the significant improvement of UTS by 59.7% compared to unreinforced aluminum. Additionally, T6 heat treatment improves ductility by reducing residual stresses and refining grain structures. The recrystallized grains and enhanced matrix-particle adhesion lead to a more homogenous strain distribution, mitigating the adverse effects of strain localization. For the heat-treated composite (S2-HT), strain hardening is counterbalanced by the improved particle-matrix interaction, resulting in a notable increase in elongation (60.3%). This balance between localized strengthening and ductility suggests an effective interplay between microsilica reinforcement and matrix plasticity. Furthermore, strain localization effects are evident in the stress-strain behavior. The composites exhibit higher yield strength (YS) due to constrained plastic deformation within grains. However, the presence of microsilica clusters introduces microcracks at stress concentration sites, slightly compromising ductility in the absence of heat treatment. The synergy of microsilica reinforcement and T6 treatment minimizes such localized failures, thereby optimizing the composite's mechanical performance for forming applications. The enhancement in ductility after T6 heat treatment is attributed to multiple microstructural modifications. First, solution treatment at 520 \({}^{\circ}\)C promotes the dissolution of secondary phases into the aluminum matrix, leading to a more homogeneous structure. Quenching preserves this dissolved state, reducing microstructural defects such as segregation and promoting finer grain structures due to recrystallization. Subsequent artificial aging facilitates the precipitation of fine, uniformly distributed strengthening phases, which hinder dislocation motion and enhance plastic deformation capability. Additionally, the refinement of grain boundaries during heat treatment reduces internal stresses and improves ductility by promoting grain boundary sliding.