Strain hardening and microstructure evolution of channel-die compressed aluminium bicrystals

The different types of strain heterogeneities developed in pure aluminium bicrystals during plane strain compression have been characterized by advanced metallographic techniques over several length scales. Bicrystals, with three grain orientation combinations (one hard/soft, and two stable/unstable) containing grain boundaries perpendicular to the compression axis, were deformed up to strains of 1.5 at 77 K and their deformation substructure investigated by optical microscopy, high resolution EBSD and transmission electron microscopy. At the macroscopic scale the hard/soft combination develops major strain variations as the softer grain flows out over the harder grain. This is consistent with finite element simulations of bicrystal deformation using the appropriate individual grain hardening laws and leads to a large transition zone near the boundary. At the microscopic level, the grains of the other combinations behave essentially as single crystals under the same deformation conditions, in particular with respect to the deformation substructure and microtexture distributions. It is concluded that for most grain pair combinations of deformed bicrystals the individual grain orientations play a dominant role in deformation substructure development as a consequence of their dependence on slip system interactions.