Substructural Alignment during ECAE Processing of an Al-0.1Mg Aluminium Alloy

Yan Huang

doi:10.3390/met6070158

Abstract

An investigation has been carried out into the microstructures developed during the early stages of equal channel angular extrusion (ECAE) in a polycrystalline single-phase Al-0.13Mg alloy, with emphasis on the substructural alignment with respect to the die geometry and the crystallographic slip systems, which is essentially related to the grain refinement and texture development during deformation. The material was processed by ECAE at room temperature to three passes, via a 90° die. Microstructures were examined and characterized by EBSD. It was found that dislocation cell bands and microshear bands were respectively the most characteristic deformation structures of the first and second pass ECAE. Both formed across the whole specimen and to align approximately with the die shear plane, regardless of the orientation of individual grains. This confirmed that substructural alignment was in response to the direction of the maximum resolved shear stress rather than to the crystallographic slip systems. However, a significant fraction of material developed preferred orientations during deformation that allowed the coincidence between the crystallographic slip systems and the simple shear geometry to occur, which governed texture development in the material. The third pass deformation was characterized with the formation of a fibre structure with a significant fraction of high angle boundaries, being aligned at an angle to the extrusion direction, which was determined by the total shear strain applied.

Highlights

Equal channel angular extrusion (ECAE) has become a routine method for severe plastic deformation (SPD) for producing submicron-grained and nanocrystalline metals [1,2,3,4]
The substructural alignment was examined with respect to the deformation geometry and crystallographic orientations of individual grains
The elongation direction of individual cells is in line with the substructural alignment direction they are in, the direction of some cells is more diverse than the overall substructure

Summary

Introduction

Equal channel angular extrusion (ECAE) has become a routine method for severe plastic deformation (SPD) for producing submicron-grained and nanocrystalline metals [1,2,3,4]. Deformation banding due to orientation splitting may occur on top of the grain shape change in response to the strain applied [9]. A unique feature of ECAE is that intensive shear banding often takes place, upon strain path change during repetitive processing [6]. An essential issue is how characteristic deformation structures such as the dislocation boundaries and shear bands are aligned with respect to the die geometry and crystallographic slip planes, which is critical to the understanding of the deformation mechanisms and texture development in the process. Segal [6,7] suggests that grain refinement in ECAE is primarily a result of shear banding parallel to the die shear plane, which is macroscopically oriented in response

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Conclusion