Subgrain Coalescence and the Nucleation of Recrystallization of Grain Boundaries in Aluminium

An experimental study has been made of recrystallization processes which have been initiated at grain boundaries in aluminium samples. The samples had an initial grain size of between 30 and 130 $\mu $m and were deformed 50% by rolling before annealing at 573 K. The microstructures developed in the region of the grain boundaries, after annealing times chosen just to initiate recrystallization, have been investigated with transmission electron microscopy. A major part of the investigation has been the identification of a number of different types of potential recrystallization nuclei at these sites. It has been established that the formation of most of these recrystallization nuclei involves modifications to the subgrain structures adjacent to grain boundaries. A model is developed for the formation of recrystallization nuclei at grain boundaries by processes involving subgrain coalescence. The microstructures predicted by the model are in accord with those observed experimentally.