A transient effect in grain-boundary migration during recrystallization in aluminum

Abstract

The growth of grains during early stages of recrystallization at 65°, 100° and 187°C in 99.99 + % pure aluminum rods extruded at sub-zero temperatures has been studied. Two stages of growth were noted for grains whose crystallographic orientations may be described as a scattered 〈114̄〉 - 〈012〉 with respect to the fiber axis of the rod. A transient-growth stage occurred at early times and was characterized by very high boundary migration rates initially which decreased by 10 5 during isothermal annealing. The ensuing growth was characterized by a slow, steady-state boundary velocity. The duration of transient growth depended on the annealing temperature being longer at the lower temperatures. The grain diameter reached during transient growth was larger the higher was the temperature of annealing. Pre-annealing at 24°C reduced the grain diameter achieved on subsequent annealing at 100°C. The X-ray line breadth of cold work recovered 20% during the transient-growth period at 100°C. Two possible interpretations of the observed transient effects are discussed. These involve the role of residual impurities and the excess vacancies generated by plastic deformation.