الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The present investigation focusing on studying the microstructural changes and mechanical characteristics of A356/Al2O3 Metal Matrix Nano Composites (MMNCs) fabricated using two techniques, typically, stir casting (SC) technique and a combination of stir casting and cooling slope casting (SC/CSC) techniques. The A356 Al alloy was reinforced with Al2O3 nanoparticles having average size of 50 nm. The effect of the volume fraction of the Al2O3 nanoparticles on the microstructural and mechanical characteristics of A356/Al2O3 MMNCs fabricated using the aforementioned techniques were evaluated. Moreover, the effect of water-cooling on the microstructure and mechanical properties of A356/Al2O3 MMNCs fabricated using SC/CSC technique was also evaluated. The results revealed that the monolithic as-cast A356 Al alloy exhibited lower porosity content than A356/Al2O3 MMNCs produced by either SC or SC/CSC techniques. However, the nanocomposites fabricated using SC showed lower porosity content than those fabricated using SC/CSC technique. The A356/Al2O3 MMNCs fabricated using SC/CSC technique with water-cooling exhibited higher porosity than those fabricated without water-cooling. Generally, the average grain size of the primary -Al grains for A356/Al2O3 MMNCs produced by SC was lower than those fabricated using SC/CSC technique. However, the water-cooled A356/Al2O3 MMNCs fabricated using SC/CSC technique exhibited lower average size of the -Al grains in comparison with those fabricated without water-cooling. Increasing the volume fraction of the Al2O3 nanoparticles up to 1 vol.-% reduces the average grain size of the A356/Al2O3 MMNCs. Such observation was noticed for A356/Al2O3 MMNCs ingots produced using SC and SC/CSC techniques. Both of the A356 monolithic alloy and the A356/Al2O3 MMNCs produced using SC and SC/CSC techniques exhibited practically the same shape factor. The A356/Al2O3 MMNCs produced using SC and SC/CSC techniques exhibited lower hardness values than the A356 monolithic alloy. However, the A356/Al2O3 MMNCs fabricated using SC/CSC technique exhibited higher hardness values than those fabricated using SC technique. The MMNCs fabricated using SC/CSC technique with water-cooling showed slightly higher hardness values as compared with those fabricated without water-cooling. Increasing the volume fraction of the Al2O3 nanoparticles increases the hardness of the A356/Al2O3 MMNCs. The A356/Al2O3 MMNCs produced using SC and SC/CSC techniques exhibited lower ultimate tensile strength than that of the monolithic A356 as-cast alloy. The A356/Al2O3 MMNCs fabricated using SC/CSC exhibited lower ultimate tensile strength values than those fabricated using A356/Al2O3 MMNCs fabricated using SC technique. Generally, increasing the vol.-% of Al2O3 nanoparticles was found to be reduce the tensile strength of the MMNCs.