Processing maps for hot deformation of the extruded 7075 aluminum alloy bar: Anisotropy of hot workability

The flow stress behavior of 7075 aluminum alloy was investigated by carrying out hot-compression tests on extruded bars with loading directions at 0°, 45° and 90° to the axis of the bars, which were, respectively, named 0°, 45° and 90° specimens. The tests were undertaken using a Gleeble-1500 thermal simulation machine in the temperatures range of 320–480 °C and strain rates range of 0.001–1 s−1. The resulting microstructures were examined and the crystal textures were analyzed. It was found that the flow stresses for the 0° specimens were always the highest and those for the 45° specimens the lowest. The apparent activation energy for 0°, 45° and 90° specimens were calculated to be 143.4 kJ mol−1, 147.4 kJ mol−1 and 146.5 kJ mol−1, respectively, which is close to that for lattice self-diffusion (142 kJ mol−1) for pure aluminum. The processing maps for all specimen orientations were built at a strain of 0.7. The main characteristic of the three power dissipation maps were found to be similar. There was one instability deformation domain in the temperature range of 320–340 °C and strain rate range of 0.18–1 s−1 for the 0° and 90° specimens, while no instability deformation domain was observed for the 45° specimens. According to the processing maps and microstructural observations, the optimum hot-working parameters for the extruded 7075 alloy bars of all the three orientations were determined to be at a temperature of 480 °C and at a strain rate of 0.1 s−1. The characteristics of the flow stresses and deformation maps were explained in terms of the elongated grains and the texture.