Molecular dynamic simulation has been done to determine the dynamic and local structure of liquid alumina at 3000 K. Fourteen different systems at densities ranging from 2.5 to 4.5 g cm −3 was prepared by compressing the low-density melt. Two kinds of pore aggregation, pore cluster and pore tube, were examined. Clear evidence was found of structural transformation from a tetrahedral to an octahedral network. For a low-density system there was a large pore tube, which involved 93% of oxygen-vacancy-like pores and spread over the whole simulation cell. Conversely, in a high-density system the largest pore tube contained less than 1% of all oxygen-vacancy-like pores. A similar trend also was observed for other pore kinds such as aluminium-vacancy-like pores and large pore clusters. The diffusion constants significantly decreased in the region of the structural transformation. The diffusion mechanism in low-and high-density systems was examined and is discussed here.

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Equal channel angular pressing (ECAP) is a viable forming procedure to extrude material by use of specially designed channel dies without a substantial change in geometry and to make an ultrafine grained material by imposing severe plastic deformation. Because the evolution of microstructures and the mechanical properties of the deformed material are directly related to the amount of plastic deformation, the understanding of the phenomenon associated with strain development is very important in the ECAP process. The plastic deformation behaviour during pressing is governed mainly by die geometry (channel sizes, a channel angle and corner angles), material properties (strength and hardening behaviour) and process variables (temperature, lubrication and deformation speed). There is a need for modelling techniques which may permit a wider study of the effects observed for better process control and the understanding of process related phenomena. In this study, we describe a range of our continuum modelling results of the ECAP process in order to illustrate the modelling applicability. Firstly, the finite element results of ECAP modelling for various geometric factors are described. Secondly, the inhomogeneous deformation due to the hardening property of the material is explained. Lastly, modelling the temperature field coupled with stress as a typical process variable in ECAP is presented.