## 3 Results and Discussion  
According to our previous study [65], the process of MA of Al-5 TiO\({}_{2}\) composites with additions of copper and stearic acid occurs in different ways. For example, the addition of 5 wt.% Cu contributes to the effective MA of aluminum with titanium oxide from the beginning of milling, while the addition of PCA postpones this process. The presence of stearic acid in the material during milling leads to the suppression of particle welding, which is necessary for the formation of composite granules. This is because stearic acid is \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Initial Composition** & **Preparation Method** & **Final Phase Composition** & **Hardness** & \begin{tabular}{c} **Strength** \\ **(Compressive/** \\ **Tensile/Bending)** \\ \end{tabular} & **Ref.** \\ \hline Al–15\%SiC–(4–12) wt.\% & mixing + sintering & Al, TiO\({}_{2}\), SiC & 45–75 HV & — & [20] \\ TiO\({}_{2}\) & stir casting & Al, TiO\({}_{2}\) & 42–83 HB & \(\sigma_{\text{UTS}}\) = 185–450 MPa & [21] \\ \hline AA6063–(6–18) vol.\% TiO\({}_{2}\) & friction stir processing & Al, TiO\({}_{2}\) & 80–142 HV & \(\sigma_{\text{UTS}}\) = 250–325 MPa & [23] \\ \hline Al–16, 32 wt.\% TiO\({}_{2}\) & MA + sintering & Al, Al\({}_{2}\)O\({}_{3}\), Al\({}_{3}\)Ti & 139 HV (max) & \(\sigma_{\text{UCS}}\) = 375 MPa (max.) & [51] \\ \hline Al–10 wt.\% TiO\({}_{2}\) & \begin{tabular}{c} mixing + sintering: \\ SPS \\ conventional \\ microwave \\ \end{tabular} & \begin{tabular}{c} Al, TiO\({}_{2}\) \\ Al, Al\({}_{3}\)Ti, TiO\({}_{2}\) \\ Al, Al\({}_{3}\)Ti \\ Al, Al\({}_{3}\)Ti \\ \end{tabular} & \
\begin{tabular}{c} 134 HV \\ 92 HV \\ 234 HV \\ \end{tabular} &
\begin{tabular}{c} \(\sigma_{\text{UBS}}\) = 161 MPa \\ 92 HV \\ \end{tabular} & [25] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._adsorbed by the surface of the Al particles, resulting in a lubricating effect. For the material with the Cu addition, the welding stage develops intensively already after 1 h of milling. However, both processed materials reach the same steady state after 10 h.  
Figure 1 shows images of granules of Al-5 TiO\({}_{2}\) composite materials with additions of stearic acid and copper obtained after 10 h of MA. In both cases, the formed particles have a uniform size and an equiaxial shape. The average particle size for the Al-5 TiO\({}_{2}\)-2 PCA material is about 140 \(\upmu\)m, and for the Al-5 TiO\({}_{2}\)-5 Cu material, it is 100 \(\upmu\)m. Thus, adding copper makes it possible to obtain a finer powder. Figure 2 shows the DSC curves of the studied materials. Three exothermic peaks are visible on each of them, but their nature has some differences. To interpret them, we studied the microhardness of the cold-pressed powders as a function of the annealing temperature. The results are shown in Figure 3. For this study, the powders were compacted into tablets 10 mm in diameter and subjected to successive annealing at 200 to 500 \({}^{\circ}\)C with a holding time of 1 h at each temperature. Before measuring the microhardness, the tablets were carefully polished on sandpaper to a minimum fineness. Figure 1: Morphology of composite granules containing **(a)** 2% stearic acid and **(b)** 5% Cu after 10 h of milling. Figure 2: DSC curves of composite powders with additions of **(a)** 2% stearic acid and **(b)** 5% Cu. As can be seen from Figure 3, the microhardness of Al-5 TiO\({}_{2}\)-5 Cu granules after MA (291 HV) is significantly higher than that of Al-5 TiO\({}_{2}\)-2 PCA (162 HV), which is due to the effect of the solid-solution strengthening of aluminum by copper [67]. In addition, with an increase in the annealing temperature, starting at 200 \({}^{\circ}\)C, the microhardness of the material with the addition of PCA increases gradually, reaching a peak at 400 \({}^{\circ}\)C. With a subsequent increase in temperature, the microhardness decreases. The material with the addition of copper behaves somewhat differently.