The Formation of Dislocation Structure and Nucleation ofRecrystallized Grains in an Aluminum Single Crystal

Abstract

strain free grains and their subsequent growth at the expense of the deformed matrix. These recrystalli.ation nuclei or newly formed grains usually emerge in regions ofhigh lattice curvature, where the orientation changes with a steep gradient from one matrix orientation to another. These regions were found first in a deformed Si-Fe single crystal to be consisted of finely banded structural elements, hence the name transition band (or rnicrobands) was given to these regions[I,2]. Later studies on heavily rolled copper and aluminum polycrystals also found similar regions oflarge lattice curvature believed to be the sites ofnucleation ofcube oriented grains[3,4]. However, the spatial distribution ofmicrostructure and orientation which develops in polycrystalline copper and aluminum after large reductions is very complex and has not at all been characterised. This complication adds to the uncertainties over the nature ofthe nucleation sites for recrystallised grains, and is particular for the formation of the cube oriented recrystallised grains in heavily deformed copper and aluminum that develops a strong cube texture upon recrystallisation. The present investigation was undertaken in an attempt to give further understanding on the origin of the cube texture in fcc metals. An aluminum single crystal with an initial orientation of (001)[110] was used. It is known that this orientation is unstable. Upon rolling deformation the crystal rotates about its 110] axis in the transverse direction (TD) toward the (112)[111 and (112)[ 1 111 orientations which are characteristic ofthe copper type rolling texture. Thedevelopment ofthe dislocationsubstructure inconnection with texturalchanges, as afunction ofstrain in channel die compression, and the orientation aspects ofnucleation duringrecrystallisation that leads to the formation ofthe recrystallisation texture, have been studied in considerable detail.