Recrystallization nucleation mechanism along boundaries in hot deformed Al bicrystals

The orientation dependency of strain induced boundary migration (SIBM) has been studied on 99.995% purity aluminium bicrystals deformed in hot plane strain compression. Four bicrystal combinations were chosen to represent some typical grain boundaries in hot rolled aluminium, i.e. boundaries between a grain of S {142}<211> orientation and adjacent grains with cube, Cu {112}<111>, Bs {011}<112> or another S variant orientation. The bicrystals were deformed in a channel die to true strains of ∼1.5 at 300–400°C and then annealed for short periods to allow grain boundary movement, usually by SIBM. The microstructural changes were followed by channelling contrast SEM and EBSD microtexture measurements. The stored energies of the individual grains were estimated from measurements of the average cell size and misorientation using the Read Shockley expression for the sub-boundary energies; typical values range from ∼10 to 50 kJ m−3. SIBM occurs extensively in bicrystals containing boundaries with the 40° <111> orientation relation. Grain boundaries in other bicrystals either scarcely move or, in the case of the S/Bs combination, become nucleation sites for near-cube germs. The boundary mobilities – as deduced from the local driving forces and the migration distances – are compared with previous data from deformed polycrystals.