During industrial thermomechanical processing such
as forging, rolling or extrusion, the strain rate, strain
and temperature in the work piece are changing contin-
uously. It has been reported in recent work on Al–Mg
alloys [1–5] that change in strain rate has a significant
effect on the evolution of dislocation substructure and
subsequent recrystallisation behaviour. Unlike flow
stress, which obeys a mechanical equation of state, the
evolution of dislocation substructures and subsequent
recrystallisation behaviour show more complex be-
haviour with strain, as shown in Fig. 1. As described
elsewhere [6–8], the flow stress in plastic deformation is
determined mainly by mobile dislocations and recrys-
tallisation behaviour is dominated by total stored en-
ergy and its distribution. The total stored energy can be
calculated from total dislocation density rtot=ri+rb,
where ri is the internal dislocation density and rb is the
boundary dislocation density. rb can be calculated in
terms of the misorientation (u) and spacing (d) of
dislocation walls (equiaxed subgrain or elongated mi-
croband boundaries) as: