OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 1 2025 For particle-reinforced MMCs, the molten metal stirring method is the most often used technique. In order to achieve homogenous mixing, this technique requires careful control of several manufacturing parameters, such as molten metal temperature, stirring time, continuous and uniform rate of reinforcement component addition to the mixture, and stirring speed [13]. The molten metal stirring method offers several advantages, including simplicity, low processing costs, ease of matrix structure control, and the production of near-net shape components. However, a significant challenge encountered when using this method is the poor wettability of ceramic particles, necessitating special measures to ensure adequate bonding between the reinforcing particles and the matrix. Addressing this challenge is essential for achieving high-quality component bonding and improving the overall performance characteristics of the composite materials [3, 9]. TiO2 is a prominent example of a ceramic material widely used in MMCs and possessing significant potential as a reinforcing component for aluminum composites. Aluminum alloys reinforced with TiO2 are characterized by enhanced hardness, making these materials promising for a wide range of applications, including electronic devices, automotive parts, and aerospace components. The improved mechanical properties of the material provide enhanced stability and durability in demanding operating conditions, such as high temperatures or corrosive environments. It is confirmed that incorporating TiO2 into aluminum effectively improves the mechanical properties and hardness of aluminum alloys, expanding its application possibilities [4, 15, 16, 17]. In their study, Nassar et al. evaluated the mechanical, wear, and structural characteristics of an Al/TiO2 nanocomposite produced by powder metallurgy. The results demonstrated a uniform distribution of TiO2 nanoparticles within the Al matrix and a low porosity. It is established that with increasing content of nanoscale TiO2, the yield strength, wear resistance, ultimate tensile strength, and hardness of the nanocomposite increased [2]. It should be noted that TiO2, like most ceramic materials, exhibits poor wettability with molten aluminum [18–20]. Several methods have been developed to address this issue and improve the wetting of reinforcing particles by the matrix. These include the addition of reaction-active particles, such as magnesium, heat treatment of ceramic particles, and the application of metallic coatings [4, 19]. The cooling rate of a casting is influenced by factors such as mold wall thickness, pouring temperature, and the heat accumulation capacity of the casting mold [21–23]. Increasing the cooling rate has a significant influence on the as-cast structure, leading to grain refinement and modification of the matrix structure [24, 25]. This, in turn, affects the mechanical characteristics, increases the tendency to chill formation, and results in increased hardness, but may reduce strength and impair the machinability of castings. The eutectoid transformation following solidification also influences the microstructure of the as-cast alloy [25, 26]. The purpose of the current study is to investigate the influence of mold wall thickness during the solidification process on the microstructure and mechanical properties of the Al- 7Si alloy matrix. In addition, the objective of this study is to develop a comprehensive understanding of the properties and potential of Al- 7Si alloy-based composites reinforced with TiO2 particles for its application in high-stress structural components. To achieve these objectives, the following tasks were addressed: – the influence of the mass fraction of the hardening component TiO2 on the density, hardness, and wear resistance of the composites was investigated; – a metallographic analysis was performed on the microstructure formed in the Al- 7Si alloy after casting using multi-wall thickness steel mold; – the microhardness and average grain size were determined in the obtained alloy samples cast into steel molds with different wall thickness. Methods In this study, a hypoeutectic Al-7Si alloy was used as the matrix material for the composites. The chemical composition of the alloy is shown in Table 1. TiO2 particles with the size of about 80 nm were used as reinforcement. Fig. 1 shows the results of qualitative X-ray diffraction (XRD) analysis of the TiO2 nanopowder used as the reinforcing material in this investigation. The mass fraction of TiO2 nanoparticles
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