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 degrees, 450 degrees and 90 degrees to the axis of the bars, which were, respectively, named 0 degrees, 45 degrees and 90 degrees specimens. The tests were undertaken using a Gleeble-1500 thermal simulation machine in the temperatures range of 320-480 degrees 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 degrees specimens were always the highest and those for the 45 degrees specimens the lowest. The apparent activation energy for 0 degrees, 450 degrees and 90 degrees 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 degrees C and strain rate range of 0.18-1 s(-1) for the 0 degrees and 90 degrees specimens, while no instability deformation domain was observed for the 45 degrees 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 degrees 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. (C) 2014 Elsevier B.V. All rights reserved.