Heterogeneous microstructures and microtextures in cube-oriented al crystals after channel die compression

Abstract

Pure aluminum crystals of cube orientation have been deformed in plane-strain compression to strains of unity using a channel die. The macrostructures and microstructures were characterized in three dimensions by a range of metallographic techniques including optical, scanning, and transmission electron microscopy. Particular attention was paid to quantifying global textures and local variations in crystal orientation by means of X-ray pole figures, automatic electron back-scattered diffraction (EBSD) and semiautomatic transmission electron microscope (TEM) Kikuchi line analysis. Cube crystals are observed to break up into macroscopic deformation bands aligned along the elongation direction and strongly disorientated by rotations mostly, but not uniquely, about the transverse direction. The bands develop deformation substructures of dislocation boundaries or, in certain cases, of intersecting dislocation boundaries which have characteristic microtexture signatures of alternating lattice rotations. The transition regions between the bands are composed of equiaxed dislocation cells which accommodate continuous orientation gradients over distances of about 20 µm. Compared to the behavior of rolled A1 crystals, the macroscopic bands are observed to lie in different planes, but the microscopic subdivisions and microtextures developed in the channel die and in rolling are very similar. The origins of the macroscopic and microscopic subdivisions are discussed in terms of the local deformation modes and slip amplitudes and their relation to the behavior of rolled crystals.