OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 1 2025 Fig. 9. Theoretical and measured density versus weight percent of reinforcing component Fig. 10. Percentage of porosity in specimens versus weight percent of reinforcing component density of the composites increases linearly with increasing concentration of added TiO2 nanoparticles. Experimentally measured density values are lower than the theoretical ones. Analysis of the density data allowed for the estimation of composite porosity. Fig. 10 illustrates the effect of TiO2 nanoparticle concentration on the porosity of Al-7Si alloy-based composites. It is evident that as the concentration of TiO2 nanoparticles increases, the porosity of the composites also increases. MMC with a TiO2 nanoparticles content of 2 wt. % had the porosity of 0.56 %, while at 6 wt. %, it increased to 1.23 %. The increase in porosity is associated with the formation of pore nuclei on the surface of the reinforcing particles and its agglomeration at high concentrations [40–42]. M. Kok [43] notes that porosity is a common phenomenon in the production of MMCs due to the prolonged particle feeding and increased surface area in contact with air, which is due to the small particle size. However, in this study, optimization of process parameters and careful control of wettability improved particles wettability and bonding force between the TiO2 nanoparticles and the Al-7Si-based alloy, and reduced composite porosity. According to Mattli et al. [44], the density of
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