Mosaic dislocation structures in aluminium crystals deformed in multiple slip at 0.5 to 0.8T_M

Deformation microstructures are characterised in high purity aluminium crystals deformed in multiple slip by channel die compression up to strains of 1.5, temperatures of 473 to 773 K, and strain rates of 10(-1) to 10(-3) s(-1). Four single crystal orientations are examined: three orientations corresponding to the stable rolling texture components of polycrystalline f.c.c. metals, C {112} [111], S {421} [112] and B {110} [112] and one recrystallisation component {001} [250]. The deformation microstructures are investigated by different techniques over a wide range of scales and the local orientations have been measured by EBSD (electron back scattered diffraction) and by CBED (convergent beam electron diffraction). The deformation microstructures are subdivided by dislocation boundaries which bound cell blocks oriented at +/- 30 degrees to +/- 55 degrees with respect to the rolling direction. The dislocation boundaries are regularly spaced in two families creating a regular structure of cell blocks whose size is very strain rate and temperature dependent. Such cell blocks are also characterised by lattice rotations of alternating sign (often about the transverse axis). For all crystals, the misorientations between adjacent blocks are of the order of 5 degrees to 10 degrees at epsilon = 0.2. At strains of the order of unity, certain orientations, e.g. C and S, develop local regions of very large misorientations whereas in the B orientation the misorientations do not exceed 10 degrees. The microstructural evolution is analysed within the framework of the LEDS hypothesis and compared to that observed at room temperature. The stability of the mosaic dislocation wall pattern is confirmed by post-deformation anneals.