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MECHANISM OF GRAIN REFINEMENT IN ALUMINIUM ALLOYS IN THE PROCESS OF HYDROSTATIC EXTRUSION

Malgorzata Lewandowska

Warsaw University of Technology, Faculty of Materials Science and Engineering (InMat), Wołoska 141, Warszawa 02-507, Poland

Abstract

Hydrostatic extrusion (HE) is one of the methods that enable relatively high strains. Its unique features are three-axial compressive stresses within the billet and high strain rates. This results in a rapid processing under high pressure and may provide a new opportunity for suppressing recovery and possible grain growth in heavily deformed materials. This work describes the microstructure evolutions and mechanisms of grain refinement in aluminium alloys processed by this deformation method.
The materials used in this study represent different series of aluminium alloys and include heat-treatable (2XXX and 7XXX series) and non heat-treatable (1XXX series) alloys. The microstructure observations were performed by using TEM and SEM techniques. Next, the revealed microstructures were described quantitatively in terms of the grain size and shape. The distributions of misorientations between neighbouring grains were also calculated on the basis of crystallographic orientations of the grains measured from Kikuchi lines obtained in TEM.
It has been found that the processing by HE results in a significant grain refinement and the formation of large fraction of deformation induced high angle grain boundaries (HAGBs). From the quantitative analysis of the material microstructure and grain boundary characteristics, the contribution of different mechanisms of grain refinement (e.g. continuous dynamic recrystallization, grain rotation) was analysed. These results were compared to aluminium alloys processed by other severe plastic deformation methods. Moreover, one of the aspects of microstructural analysis was the evolution of size, shape and distribution of second phase particles (precipitates and intermetallics). Their influence on the process of grain refinement and HAGB distribution was discussed.

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MECHANISM OF GRAIN REFINEMENT IN ALUMINIUM ALLOYS IN THE PROCESS OF HYDROSTATIC EXTRUSION

Presentation: oral at E-MRS Fall Meeting 2005, Symposium I, by Malgorzata Lewandowska See On-line Journal of E-MRS Fall Meeting 2005 Submitted: 2005-05-17 07:41 Revised: 2009-06-07 00:44

Presentation: oral at E-MRS Fall Meeting 2005, Symposium I, by Malgorzata Lewandowska
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-05-17 07:41 Revised: 2009-06-07 00:44