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The dispersion characteristics of the nano-sized Y2O3 powders in molten aluminum were investigated from the viewpoint of changes in microstructure and mechanical property as a function of oxide contents. As the solidification structure, the oxide nanoparticles dispersed in the columnar crystal was mainly segregated on the grain boundary, whereas the oxide nanoparticles dispersed in the equiaxed crystal was uniformly dispersed on both grain boundary and inside the crystal. The most uniform dispersion of oxide nanoparticles was observed at Y2O3 content of 2 mass%. As Y2O3 content of 3 mass%, the size of oxide nanoparticles in metal matrix increased due to the particle aggregation, as confirmed by SEM analysis. Moreover, it was found that the mechanical properties such as hardness and tensile strength were improved at Y2O3 content of 2 mass%, indicating the well-dispersion of nano-sized Y2O3 powders in cast aluminum. The hardness was increased by 1.2 times up to 57 HV and tensile strength was increased by 1.55 times up to 80 MPa, compared with the case of pure aluminum. However, at Y2O3 content of 3.0 mass%, tensile strength was sharply decreased by 0.6 times due to aggregation of oxide nanoparticles, while the hardness was increased to 57 HV, which is the same as the case of Y2O3 content of 2.0 mass%. [doi:10.2320/matertrans.M2010166]

Effect of Oxide Dispersion on Dendritic Grain Growth Characteristics of Cast Aluminum Alloy