###### Abstract  
In this work, we studied the effect of thermal exposure on the microstructure and mechanical properties of an Al-5 wt.% TiO\({}_{2}\) composite material with additions of 5 wt.% Cu and 2 wt.% stearic acid as a process control agent (PCA), obtained by mechanical alloying. The composite was processed in a ball mill for 10 h. Composite granules were consolidated by hot pressing at 400 \({}^{\circ}\)C. SEM, XRD, and DSC analyses were used to study the microstructure, phase composition, and thermal behavior, respectively. Studies showed that the hot pressing of the material with copper addition leads to the precipitation of Al\({}_{2}\)Cu particles from the supersaturated solid solution and a decrease in the microhardness to 233 HV in comparison with the as-milled state (291 HV). In the material with a PCA additive, on the other hand, the microhardness increases from 162 to 187 HV due to the formation of aluminum carbide nanoparticles. In both cases, no reduction reaction products were found. At the same time, the Al-STIO\({}_{2}\)-2 PCA material after hot pressing shows a more stable grain structure than the Al-STIO\({}_{2}\)-5 Cu material. In addition, the compressive strength at 300 \({}^{\circ}\)C of the former material is 1.7 times higher than that of the latter one. mechanical alloying; composite; aluminum; stearic acid; titanium dioxide; hot pressing +
Footnote †: journal: Applied  
interfacial shear stress, and the Orowan strengthening effect caused by the resistance of closely spaced fine hard particles to the free movement of dislocations [1,26]. An important factor in the manufacture of dispersion-strengthened composites is the size of the strengthening particles. For example, it was shown [27] that the mechanical strength of aluminum composites could be increased by 20% if the size of the reinforcement particles was reduced from a micrometer to a nanometer scale. Various methods are used to obtain aluminum composites, such as ultrasonic casting [28], gas pressure infiltration [29], injection molding [30,31], semi-solid mechanical stirring [32], and mechanical alloying [33]. However, if liquid-phase methods are used for producing composite materials, the presence of contaminants on the particle surfaces hinders wetting by aluminum melt [34,35] which leads to a weakening of interface bonding and, as a result, a decrease in strength. In addition, when liquid phase processes are used, there is a difference in density between the matrix melt and the reinforcing particles, which prevents their even distribution. On the other hand, powder metallurgy methods deliver a significant increase in strength parameters [36, 37, 38]. An effective way to obtain dispersion-strengthened metal-matrix composites is the method of mechanical alloying (MA) related to powder metallurgy. This process avoids some disadvantages (e.g., segregation phenomena) typical of composites produced by liquid processes. When this phenomenon occurs, the distribution of alloy elements is not uniform, which may degrade the mechanical properties. On the other hand, the MA method can be used to obtain homogeneous nanocomposites due to the high degree of microstructure refinement. The essence of the MA technique lies in the processing of a metal powder together with one or more alloying components. In this process, composite granules are formed with a uniform composition and ultrafine microstructure due to complex physical processes. [39, 40, 41]. Hence, the method is unique because the process occurs entirely in the solid state. This method differs in that the powder components are not only homogeneously mixed but also significantly dispersed due to the severe plastic deformation accompanying the process. Severe plastic deformation leads to a dramatic increase in the density of crystalline defects. In this case, a homogeneous and, as a rule, nanocrystalline structure forms and is preserved at elevated temperatures [42, 43, 44].