Hot deformation behavior and dynamic softening mechanisms of hot-extruded Al-Cu-Mg-Ag-Mn-Zr-Ti alloy

The hot deformation behavior of the Al-4.96Cu-0.96Mg-0.63Ag-0.57Mn-0.13Zr-0.02Ti alloy was investigated by hot compression experiments performed on a Gleeble 3500 thermal simulation tester. The temperature and strain rate were controlled in the range of 573–773 K and 0.001 s−1-1 s−1 for thermal processing. The true stress-true strain curve shows that the flow stress decreases with the higher deformation temperature, and lower strain rate. When the strain rate is large, the dynamic softening effect in the alloy is difficult to offset the work hardening caused by the entanglement of high-density dislocations, so that the peak stress of the alloy reaches the peak value at a large strain. The Arrhenius equation with Zener-Hollomon parameter (Z) is established, and the hot deformation activation energy of the alloy is 147.906 kJ/mol. It can be seen from the thermal processing map that the alloy is prone to plastic deformation instability at low temperature and high strain rate. The high energy dissipation zone (deformation temperature is 740–773 K, strain rate is 0.001–0.004 s−1) is the best processing parameter area. The results of EBSD and TEM show that there are fewer recrystallized grains in the microstructure obtained under the deformation conditions in the instability region, while many deformed grains exist and dislocation density are large, and dynamic recovery (DRV) is the dominant dynamic softening mechanism. However, due to the higher temperature and lower strain rate in the optimal processing parameters region, dynamic recrystallization (DRX) mainly occurs, resulting in more recrystallized grains, less dislocations and fewer low angle grain boundaries.