## 3 Results  
### Microstructure Observation and Elemental Content Analysis Results  
Figure 5 shows the SEM images of the morphologies of the B4C and K2 TiF6 particles and their corresponding EDS spectra. The SEM image of B4C shows a polyhedral morphology of particles, with sizes mostly ranging from 0.5 to 2 \(\upmu\)m, and the finer particles displaying more defined angular facets. Figure 4: Dimensions (in mm) according to ASTM E8 [31] and appearance of prepared and tested tensile test specimens. Figure 5: SEM images and EDS spectra of boron carbide (B4C) and potassium hexafluorotitanate (K2 TiF6) particles. The particles exhibit sharp edges and corners, reflecting the high hardness and brittle nature of B4C. The SEM morphology of K2 TiF6 particles, with sizes ranging from 50 to 150 \(\upmu\)m, reveals a well-defined, angular structure with a smooth surface. The smoothness of the particle surface indicates minimal surface oxidation or degradation. The particles exhibit a relatively uniform size distribution within the specified range. Some particles show slight variations in shape, but the overall distribution remains homogeneous, characteristic of well-synthesized K2 TiF6 crystals. The chemical composition of B4C indicates that it contains 67.2 \(\pm\) 0.3% B and 26.6 \(\pm\) 0.3% C with O, Fe, and Si impurities. The purity of the powder was \(\sim\) 94%. The EDS chemical composition of the K2 TiF6 additive indicated that it contains 30.3 \(\pm\) 0.1% K, 17.2 \(\pm\) 0.1% Ti, and 52.6 \(\pm\) 0.1% F.  
Figure 6 presents the LM images, while Figure 7 displays the SEM images and EDS spectra of specimens S1, S1-HT, S2, and S2-HT. There was similarity between the LM and SEM images. The bright colors in the LM images correspond to the initial \(\alpha\)-Al matrix, whereas the dark inclusions in specimens S1 and S1-HT are likely to be air oxygen (O) and/or crucible carbon (C) inclusions accidentally deposited on the observation surface. The results of the elemental content analysis, namely, EDS spectra of the full map of specimens S1 and S1-HT presented in Figure 7, confirm the presence of these elements. The presence of oxygen and carbon in pure aluminum is typical in EDS analysis, and inclusions such as Al4C3 and Al2O3 are commonly found after the melting and casting process without filtering [35]. The degree of protection from the external atmosphere during stir casting affects the increase in O concentration. Various techniques can improve this protection, such as an inert atmosphere and vacuum assistance. However, it is not the purpose of this study to provide such protection, and, generally, the technical aspects of casting are of secondary importance here, although attempts were made during casting to limit the exposure to the external atmosphere by closing the crucible from above. Figure 6: LM images of the S1, S1-HT, S2, and S2-HT specimens. The dark recesses in the SEM images show relatively minor evidence of micropores, reflecting the reasonably good quality of the stirring and ultrasonic treatment processes. The particle size distribution, primarily ranging from 0.5 to 2 \(\upmu\)m, indicates that the stir-casting process successfully integrates fine ceramic particles into the aluminum matrix. Nevertheless, micropores and agglomerated/clustered B\({}_{4}\)C particles are observed in the S2 and S2-HT composites because of the very low particle dispersity of B\({}_{4}\)C particles, making them vulnerable to particle agglomeration effects [36]. The absence of large voids or cracks at the interface suggests that the stir-casting process has effectively minimized defects typically associated with particle-matrix bonding, such as poor wetting or delamination. In contrast to specimens S1 and S1-HT, specimens S2 and S2-HT exhibit a fine interdendritic grain structure and the presence of additives  
Figure 7: SEM images and EDS spectra of the S1, S1-HT, S2, and S2-HT specimens.