Tem Study of Recrystallization in Ultra-Fine Grain AA3104 Alloy Processed by High-Pressure Torsion

Abstract

AbstractThe effect of annealing on the microstructure and the texture development was investigated in a particle containing AA3104 aluminium alloy. The samples were processed at room temperature by high-pressure torsion (HPT) up to ten turns. The nucleation of new grains was analyzed by a transmission electron microscope equipped with a system for local orientation measurements and a heating holder.The shear deformation induces a decrease of the grain size. After the first two turns of the HPT processing the initial structure of large grains was ‘transformed’ into a structure of fine cells/grains with the diameter of a few tens of nanometers. In the central areas of the samples the elongated shape of the cells/grains was observed up to six turns. For higher deformations, this structural inhomogeneity was totally removed and only the equiaxed grains were observed. The crystal lattice of small grains rotates in such a way that the <111> direction is parallel to the compression axis. After annealing the structure coarsened. Nevertheless, after primary recrystallization, the structure was still composed of relatively fine and equiaxed grains of a similar size. In most of the observed cases the size of the recrystallized grains in the areas close to and far from the large second phase particles was similar. The recrystallization leads to the creation of new texture components. The new grain orientations lost the positions typically observed in the deformed state and showed the tendency for the coincidence of the <100> crystallographic directions with the compression axis.