Geometrically necessary dislocations distribution in face-centred cubic alloy with varied grain size

Abstract

The evolution of geometrically necessary dislocation (GND) distribution in the deformed 6061 alloy is studied with electron back scatter diffraction (EBSD) and transmission electron microscope (TEM). In dynamic recrystallized state, the average GND density is 8.70 × 1014 m−2 with grain size ~30 μm. In annealed state, the average GND density decreases by an order of magnitude, from 6.81 × 1015 to 7.32 × 1013 m−2 (annealing temperature from 200 to 500 °C) accompanied by increasing grain size. Moreover, the sample has greatest ductility with lowest GND density. According to the tendency of dislocations in TEM, GND gradually migrate from near (200) plane to near (220) plane with increasing annealing temperature. Additionally, GND mainly concentrate on the grain boundaries in the deformed state, and the GND distribution is more homogenous after annealing. It is shown that the GND density is related to the grain boundary type and misorientation angle between adjacent grains. The relationship between average GND density and grain size is approximately parabolic.