OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 1 2025 was varied and set to 0, 2, 4, and 6 %. A specially designed and built electric muffle furnace simplified the composite fabrication process. Fig. 2 summarizes the process flow for manufacturing the Al-% Si alloy specimens and nanocomposites. For the experiment, 400 g of the Al-% Si alloy was charged into a crucible, which was then placed in an electric resistance furnace. The molten Al- 7Si alloy was then cast into lowcarbon steel molds with wall thicknesses of 8, 12, and 29 mm to fabricate samples for studying the influence of mold wall thickness on structure and properties. Nanocomposite samples with an Al- 7Si alloy matrix and TiO2 particles as the reinforcing material were fabricated using a separate steel mold with a wall thickness of 7.5 mm as illustrated in Fig. 2. The TiO2 particles were introduced into the melt at a constant rate of 5 g/min. After the particle addition was complete, the melt was stirred for 5 minutes at a speed of 450 rpm. To enhance the wettability between the reinforcing component and the matrix, 1 % magnesium was added to the melt. Before being dispersed in the melt, the TiO2 particles were also preheated at 700 °C for 2 hours to improve its wettability. After fabrication the as-cast specimens were ready for further examination of its mechanical properties and microstructure. The metallographic specimens were subjected to sequential grinding and polishing using SiC abrasive papers with grit sizes ranging from 150 to 1,200. To reveal the microstructural components, the samples were etched using a solution that contained 75 ml HCl, 25 ml HNO3, 5 ml HF, and 25 ml H2O. An optical microscope and a scanning electron microscope (SEM) were used at various points on the specimen surface to analyze the microstructure. Grain size determination was performed according to ASTM E112. Microhardness was measured on a VHS-1000 microhardness tester using a load of 100 g, utilizing ground and polished specimens. Wear tests were conducted on a pin-on-disc tribometer. The specimens were subjected to loads of 10 N and 20 N while sliding against a 200 mm diameter steel disk at a constant speed of 1 m/s with sliding distances of 350 m and 700 m. The bulk density of Al- 7Si matrix composites Chemical composition of A356 alloy used as the matrix in the MMCs Chemical contents of elements, % Al Si Mg Mn Cu Zn Ni Fe bal. 7.1 0.5 0.01 0.316 0.04 0.01 0.14 Fig. 1. Result of qualitative XRD analysis of nano-titanium oxide (TiO2) Ta b l e 1
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