## 2 Materials and Methods
### Procedure for Manufacturing AMCs  
A schematic representation of the AMCs manufacturing procedure is shown in Figure 2. Before starting the ultrasonic-assisted stir casting process, the graphite crucibles were preheated in a PM-5 muffle furnace (Plavka.Pro, Korolev, Russia) at a relatively low temperature of 200 \({}^{\circ}\)C. To remove all possible moisture, the casting steel split mold, designed to produce cast specimens as round rods with a diameter of \(\sim\)25 mm and a length of \(\sim\)220 mm, was preheated in a muffle furnace to a temperature of 300 \({}^{\circ}\)C. Pure aluminum blocks in crucibles and microsilica powders loaded in steel cups were preheated to 450 \({}^{\circ}\)C in a muffle furnace chamber to improve mixing and wetting, and reduce thermal shock. Heating was performed at a low rate of temperature increase of 3.75 \({}^{\circ}\)C/min, which ensured smooth heating for 2 h.  
The first two specimens, S1 and S1-HT (where HT means heat-treated), were unreinforced pure aluminum specimens, with S1 cast without heat treatment and S1-HT cast with T6 heat treatment. These specimens were cast (by gravity casting) without ultrasonic-assisted stir casting for comparison with the reinforced materials. The second two specimens, S2 and S2-HT, were minorly reinforced (\(\sim\)0.36 %wt) microsilica specimens prepared by ultrasonic-assisted stir casting. These specimens were prepared in a JC-S  
Figure 2: Schematic representation of the AMC manufacturing procedure.  
220-4 electric resistance furnace (Zibo JC Eco-Tech Co., Ltd., Zibo, Shandong, China) with a power of 5 kW and maximum temperature of 1200 \(\pm\) 1 \({}^{\circ}\)C, equipped with a K-type chromel-alumel thermocouple to monitor the temperature. Before operation, the furnace was preheated to 750 \({}^{\circ}\)C and maintained at a set level throughout the process to provide the required stable thermal conditions. Maintaining this temperature ensures the uniform heating of the materials and minimizes thermal fluctuations that could affect the experimental results or product quality. Ultrasonic-assisted stir casting (Figure 2) involves two key steps to improve the distribution and integration of reinforcing particles in the aluminum matrix: mechanical and ultrasonic stirring. Mechanical stirring was performed using a four-blade steel impeller with a rotational speed of approximately 600 \(\pm\) 3 rpm. A vortex was created and maintained for 7-10 min to ensure uniform distribution of microsilica particles in the melt. Microsilica particles were gradually fed into the vortex using a steel spoon (feed rate \(\sim\) 1 g/min). A JH-LRT30 ultrasonic system (Hangzhou Precision Machinery Co., Ltd., Hangzhou, China) operating at 20.5-20.6 kHz and 2 kW was used for the ultrasonic stirring. This was performed for 20 min, after which the material was poured into a preheated steel casting mold to homogenize the melt. Consequently, cast specimens of AMCs were obtained as cylindrical rods with a diameter of \(\sim\)25 mm and a length of \(\sim\)220 mm. After cooling, some specimens were subjected to T6 heat treatment [33], resulting in S1-HT and S2-HT specimens. Heat treatment included solution hardening and artificial aging. For solution hardening, the specimens were heated in a muffle furnace at 520 \({}^{\circ}\)C for 120 min and then quickly cooled in water to fix the structure. Artificial aging was performed by heating the specimens to 180 \({}^{\circ}\)C and holding them at that temperature for 12 h, after which they were cooled to room temperature in air. After the heat treatment and cooling, mechanical wet cutting of the specimens was performed to obtain separate parts (without external shrinkage) for further study and performance analysis of the obtained composites (Figure 3).