الفهرس 
Aluminum and its AlloysOnly 14 pages are availabe for public view
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Abstract
Hypereutectic aluminum-silicon (Al-Si)alloys are widely used in the automobile and aerospace industries because of their low density, good strength, excellent wear, good corrosion resistance, low coefficient of thermal expansion and are fully recyclable. They are used in applications, which require a combination of lightweight and high strength, such as liner-less engine blocks, pistons, and pumps. However, all of these previously desirable properties of hypereutectic Al-Si alloys depend on the characteristics of their cast microstructures, namely secondary dendrite cell size or arm spacing, the size morphology or shape and the distribution of eutectic and primary Si particles. The morphology of primary silicon particles can be complex, such as plate-like, star-shaped, polygonal, blocky, and feathery varying with solidification conditions, alloying elements, and chemical composition.
In the present thesis, the eutectic Al–13 wt. % Si and hypereutectic Al-16 wt. % Si were prepared by using permanent mould casting technique. The effect of the cooling technique during solidification on the cast microstructure, mechanical properties, and electrical conductivity of Al-Si alloys was investigated by using the conventional water-cooled and air-cooled methods. The mechanical properties such as the yield stress, tensile strength, hardness, and impact energy were measured at various cooling methods. Microstructure with scanning electron microscope (SEM) and Energy dispersive spectrometer (EDS) analysis of Al-Si alloys have been studied. In addition, the hardness after solution treatment at 529 °C for 2 h and artificial ageing at various temperatures 180 °C and 210° C for aging time 2- 10 h was measured.
In addition, the mechanical properties of the hypereutectic Al-16% Si alloy with the introduction of zinc oxide (ZnO) nanoparticles (NPs) at varies concentrations of ZnO NPs (0.5, 1, 1.5 and 3% wt.) synthesized by simple sol gel technique were examined.
The results show an enhancement in the mechanical and electrical properties for the eutectic Al-13 wt. % Si and hypereutectic Al-16 wt. % Si alloys for the water-cooled over the air-cooled technique. In addition, the largest value of the impact energy (4.91 J) was obtained for the eutectic Al-13 wt. % Si alloys compared to the hypereutectic Al-16 wt. % Si alloys at (3.09 J) for water-cooled medium. The total solidification time (TST) of Al 13% wt. Si was longer than that time for the hypereutectic Al 16% wt. Si at various cooling mediums. The maximum tensile strength and hardness (148 MPa, 84 HRD) were given for the hypereutectic alloy using water-cooling .
Aging studies of Al-Si alloys with aging temperatures 180 ºC and 210 ºC show that the hardness values increased as the silicon content increases. For hypereutectic Al-16 wt. % Si at aging temperature 180 ºC and aging time 4 h by using water-cooled technique, it was observed that the maximum hardness value reached 100 HRD compared with 87 HRD for the eutectic Al-13 wt. % Si alloy.
The microstructure of the synthesized ZnO NPs reflects the formation of the wurtzite-type ZnO and the average crystallite size was around 35 nm. The addition of ZnO nanoparticle to hypereutectic Al-16 wt. % Si alloy enhanced the mechanical properties such as the tensile strength and impact energy) through the control of Si-morphology. The maximum tensile strength and impact energy of this alloy was 200 MPa and 5.38 J, respectively, at 3 wt. % of ZnO nanoparticles. This enhancement in the mechanical properties can be attributed to the decomposition and dissolution of the nano-oxide particles in aluminum alloy melt and grain growth restriction with the resultant grain refining effect.