Authors: KeeHyun Kim
Publish Date: 2014/04/02
Volume: 45, Issue: 8, Pages: 3650-3660
Abstract
Hightemperature oxidation of molten aluminum was investigated by highresolution electron microscopes in order to determine the possibility of heterogeneous nucleation of aluminum grains on oxide for the grain refinement and structural uniformity of intensively meltsheared aluminum alloys Highresolution observations detect initial amorphous phase and gammaalumina phase and show fine clusters with size of about 150 to 200 nm composed of extremely fine aluminum grains and gammaalumina or amorphous aluminum oxide Furthermore highresolution lattice images and diffraction patterns show no orientation relationship although there is a specific orientation between gammaalumina and aluminum along 111110 with high potency of heterogeneous nucleation The volumetric shrinkage by the transformation of gamma into alphaalumina causes the surface oxide films to repeatedly rupture and leads to the creation of channels to the base melt surface for further oxidation of fresh metal Based on the observations the mechanism of hightemperature oxidation of molten aluminum and formation of the fine clusters as well as the possibility of the heterogeneous nucleation of aluminum grains are discussedThe author thanks Dr WD Griffiths University of Birmingham for valuable discussions on the results and Professor Z Fan and Dr Y Wang Brunel University and Ms E Hinton University of Birmingham for supplying the material for investigation The authors particularly thank the EPSRC Centre for Innovative Manufacturing in Liquid Metal Engineering EP/H026177/1 for financial support
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