OVERVIEW NO 93 - ON THE ORIGIN OF RECRYSTALLIZATION TEXTURES IN ALUMINUM

The electron back scattering pattern technique (EBSP) in SEM has been applied to follow in detail the orientation aspects of the nucleation and growth of recrystallization in cold rolled aluminium. The investigation includes both high purity metal and a commercial grade. The cube- and Goss-oriented recrystallized grains nucleate from transition bands. In the cube case these bands are found in the Cu-and ND-rotated-Cu deformation texture components while the Goss bands have been identified in the brass texture component. Shear bands in the S-deformation component have been identified as nucleation sites for recrystallization. The orientation inside the bands is also S (complementary to the matrix), causing the S-orientation to reappear as a recrystallization texture component. These types of deformation heterogeneities and others are frequently associated with a 40-degrees <111> orientation relationship to the surrounding matrix, making this specific orientation relationship primarily a property to be associated with the oriented nucleation concept. Isolated examples of a true 40-degrees <111> growth selection due to the rapid growth of <111>-tilt-boundaries have been observed. A characteristic aspect in these cases is a growth selection from a planar transformation front. From a careful literature review as well as from experimental observations no direct evidence has been found in support of the hypothesis that 40-degrees <111> grains, when uniformly distributed in space, have a transformation rate potential exceeding that of grains belonging to other texture components. No growth selection has been found in the special case of the growth of cube oriented grains.