Macroscopic and microscopic subdivison of a cold–rolled aluminium single crystal of cubic orientation

Abstract

An aluminium single crystal of cube orientation has been rolled to 15, 30 and 50% reductions under controlled homogeneous rolling conditions. The deformation structure of the rolled specimens was investigated by both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) over several scales of magnification. The local crystallographic orientations have been measured by an automatic electron back scattering patterns (EBSP) technique and a semiautomatic TEM method. Orientation image maps based on the local orientation data have been used to reveal the evolution of the deformation structure during rolling. It is observed that by an opposite rotation around transverse direction (TD) the crystal was subdivided into four macroscopic bands, termed matrix bands in the present paper, which are parallel to the rolling plane. Between the four bands there are three transition bands in which the orientation changes continuously from that of a matrix band to that of the adjoining one. A model based on the idea of location–dependent shear strain caused by geometric and friction effects together with a plasticity analysis has been used to explain the macroscopic subdivision of the crystal. In addition to the macroscopic subdivision, a microscopic subdivision by the formation of cell–blocks within the matrix bands and a cell structure within transition bands has also been observed. A difference related to shear amplitude difference between the active slip systems changing continuously across the crystal has been observed. Both the macroscopic orientation of the dislocation boundaries and the misorientation angles and axes across dislocation boundaries are analysed and it is found that Frank9s formula is a useful tool in analysing the dislocation boundaries formed during deformation.