## 3 Results and Dissscussion
### Morphological Analysis  
Morphological analysis highlights how the SiC particles were actually embedded in the aluminum alloy metallic base, for each research variant. It is worth mentioning that the first two variants (V\({}_{1}\), V\({}_{2}\)) both individual SiC particles and SiC agglomerations were concentrated in the interior surface of the casted muffs. This phenomenon is rather unexpected. Due to the formation of SiC agglomerations air bubbles appear in their rear. This fact leads to the decrease of the density of the agglomerations below the density of the alloy thus resulting in its displacement inwards. The density ratio for the liquid alloy and SiC particles (2.6/3.1) is in favor of concentrating the silicon carbide on the outer surface of the cylindrical samples. This behavior of the SiC particles was confirmed only in the case of the composite bush molded in the third process (V\({}_{3}\)). The corresponding metallographic images for each analyzed variant are presented as follows: V\({}_{1}\)--Figure 4; V\({}_{2}\)--Figure 5; V\({}_{3}\)--Figure 6.  
Figure 3: Presence of copper on the surface of the SiC particle observed. (**a**) By optical microscope, (**b**) by SEM analysis, (**c**) by EDS. Figure 4: SiC particles distribution within the metallic base alloy — V\({}_{1}\). (**a**) Central embedded SiC particle (\(\times\)200), (**b**) Cu on a SiC particle (\(\times\)500), (**c**) SiC particles agglomeration (\(\times\)200), (**d**) SiC particles agglomeration (\(\times\)200). Figure 5: SiC distribution in the metallic base — V\({}_{2}\). (**a**) Central embedded SiC particle (\(\times\)200), (**b**) Cu on a SiC particle (\(\times\)500), (**c**) SiC particles agglomeration (\(\times\)200), (**d**) SiC particle embedded at sample surface (\(\times\)200). For the V1 method the SiC particles coated with a thin layer of Cu were preheated at 900 \({}^{\circ}\)C and introduced as such in the metallic mass. Due to the preheating stage the particles started to conglomerate and formed lumps that were not crushed afterwards. As a result, the SiC particles were not evenly distributed. Instead, some agglomerations appear in certain areas of the samples (Figure 4c). As an effect of the centrifugal casting, certain agglomerations were dispersed, thus well-embedded single particles also appear in the sample (Figure 4a). The use of activated particles (covered with a thin layer of Cu) is clearly highlighted in Figure 4b where the presence of copper is very well observed. The activated SiC particles show a good adhesion to the metal mass, which is proved by the fact that, although the samples were processed with abrasive paper, the particles were not removed from the surface (Figure 4d). Within the V2 variant of the process, the SiC particles were preheated at 900 \({}^{\circ}\)C and similar to V1 method, lumps appeared as a result of the agglomeration process. In order to avoid having particles agglomerations in the final composite material, the preheated SiC lumps were crushed, which resulted in a much more uniform dispersion of them in the sample volume, even in the areas with high density of embedded particles (Figure 5c). The existence of the thin layer of Cu on the surface of the particles favored their incorporation process in the metal matrix even for single particles (Figure 5a). The use of SiC particles covered with a consistent layer of Cu has the effect of an increased embedding in the base metal mass, as it can be observed from Figure 5b. Variant V2 also ensures a good adhesion of the particles to the sample surface even in the situation of a small contact surface (Figure 5d). For the V3 method, the introduction of SiC particles was performed at room temperature, without preheating. It can be easily observed that most SiC particles are uniformly dispersed in the metal mass of aluminum alloy. This is explained by the fact that without the heating stage, as a source of conglomeration processes, the particles remained dispersed.