Hot deformation behavior of 7150 aluminum alloy during compression at elevated temperature

Hot compression tests of 7150 aluminum alloy were preformed on Gleeble-1500 system in the temperature range from 300 °C to 450 °C and at strain rate range from 0.01 s^? 1 to 10 s^? 1, and the associated structural changes were studied by observations of metallographic and transmission electron microscope. The results show that the true stress–true strain curves exhibit a peak stress at a critical strain, after which the flow stresses decrease monotonically until high strains, showing a dynamic flow softening. The peak stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener–Hollomon parameter in the hyperbolic-sine equation with the hot deformation activation energy of 229.75 kJ/mol. In the deformed structures appear the elongated grains with serrations developed in the grain boundaries, decreasing of Z value leads to more adequate proceeding of dynamic recrystallization and coarser recrystallized grains. The subgrains exhibit high-angle sub-boundaries with a certain amount of dislocations and large numbers of dynamic precipitates in subgrain interiors as increasing Z value. The dynamic recovery and recrystallization are the main reasons for the flow softening at low Z value, but the dynamic precipitates and successive dynamic particles coarsening have been assumed to be responsible for the flow softening at high Z value.