Fabrication and characterization of Al-7Si alloy matrix nanocomposite by stir casting technique using multi-wall thickness steel mold

Introduction. The Al-7Si is considered one of the key aluminum alloys due to its favorable combinations of casting and mechanical properties. Metal matrix composites (MMCs) reinforced with ceramic particles are widely used in high-tech industries such as military, automotive, aerospace, and electrical engineering. The purposes of this study are threefold: (1) to investigate the feasibility of producing composite materials based on the Al-7Si alloy reinforced with varying amounts of TiO2 nanoparticles using a stir casting technique; (2) to investigate the effect of mold wall thickness on the microstructure and mechanical properties of the Al-7Si alloy during solidification; and (3) to analyze the influence of the reinforcing component content on the mechanical properties and wear resistance of the resulting composite materials. Methodology. Metal matrix composite materials based on the Al-7Si alloy, containing 0, 2, 4, and 6 wt. % TiO2 nanoparticles, were fabricated using a stir casting technique. Cylindrical specimens with a diameter of 15 mm and a length of 18 mm were prepared for metallographic and mechanical testing. Results and discussion. It is found that the solidification rate increases with increasing mold wall thickness. This leads to an increase in the cooling rate and, consequently, to the formation of a finer-grained structure. The microstructure of the casting demonstrates a change in grain size from fine to coarse when transitioning from the outer surface (adjacent to the inner mold wall) to the inner part of the casting. As a result, the microhardness near the inner mold wall is higher. Density measurements indicate that composites with a higher amount of reinforcing particles exhibit greater porosity. Furthermore, the results of hardness and wear tests reveal that an increase in the TiO2 particle content leads to increased hardness and a significant reduction in the wear rate of the composite materials.