###### Abstract
First, many industrial wastes contain high concentrations of metal oxides and other components with high hardness and thermal stress resistance, which contribute to a significant increase in the mechanical strength and wear resistance. Second, industrial wastes solve the acute environmental problems associated with their high toxicity, processing complexity, and long decomposition times. Such materials in the production of AMCs make it possible to minimize the volume of waste to be disposed and significantly reduce their negative impact on the environment. Agricultural wastes, despite their availability and low cost, have limited strength, low thermal stability, and low compatibility with aluminum matrices. In addition, their processing for use in AMCs requires additional efforts to remove organic impurities and ensure stable performance, which reduces the cost-effectiveness. Thus, industrial wastes are best for reinforcing aluminum matrices, combining the advantages of high performance while solving environmental problems. One promising but poorly researched waste for reinforcing aluminum materials is ultrafine spherical powder microsilica (silica fume), a byproduct of silicon or ferrosilicon production consisting of particles less than 1 um in diameter. Microsilica is an amorphous non-crystalline polymorph of silicon dioxide (SiO\({}_{2}\)) and has several valuable properties, such as high pozzolanic activity, high dispersibility, low density, high isotropic strength, increased heat resistance, and corrosive resistance. These characteristics make microsilica a demanded raw material for the production of various construction materials, composites, and other materials worldwide [24], including in Kazakhstan [25; 26], which is one of the world's largest producers of silicon [27] and ferrosilicon [28]. Despite the significant industrial and scientific interest in using microsilica, analysis of existing publications has revealed insufficient studies on its application in technologies for obtaining AMCsby stir casting. [PERSON] et al. [29] investigated the structure and properties of A356-microsilica composite using large microsilica particles ranging from 15 \(\upmu\)m to 24 \(\upmu\)m in size. The introduction of microsilica increases the hardness and wear resistance of the composites. However, a modified compocasting process is required to achieve optimal performance. In another study, [PERSON] et al. [30] used flotation-treated amorphous microsilica to produce hypoeutectic and hypereutectic Al-Si alloys based on commercially pure aluminum. The approaches developed by the authors were efficient; however, they cannot be fully classified as stir-casting technologies because the objectives of this research were somewhat different, and the main focus was on methods for producing Al-Si alloys rather than on the development of composite materials. Additionally, the incorporation of nanoparticles into Al alloys has been shown to substantially improve their mechanical and structural properties through nanoscale reinforcement mechanisms [31; 32]. These findings further emphasize the importance of exploring alternative reinforcing materials, such as ultrafine microsilica, to develop cost-effective and high-performance AMCs. The aim of this study is to investigate the potential of using ultrafine microsilica particles as a minor reinforcing material in AMCs produced via ultrasonic-assisted stir casting, with supplementary T6 heat treatment [33]. This study seeks to overcome challenges associated with the low strength of pure aluminum [34; 35] and the difficulties of processing nanoscale reinforcing particles, while ensuring cost-effectiveness and environmental sustainability. The novelty of the work lies in the following aspects:  
* Application of ultrafine microsilica: While microsilica has been explored in other studies, this research uniquely focuses on ultrafine microsilica particles (<200 nm) as a minor reinforcement (~0.36 wt%) in AMCs, which remains an underexplored approach.