Static softening behavior and modeling of an Al-Cu-Mg-Zr alloy with various pre-precipitation microstructures during multistage hot deformation

The complex precipitates have been found to work on the hot workability of heat treatable Al alloys considerably. In this work, to include the functions of interrupted holding following multistage hot working, double-stage hot compression tests were performed on an Al-Cu-Mg-Zr alloy with different pre-precipitation microstructures which were tailored through air cooling, water quenching and furnace cooling after solution heat treatment. Microstructural characterizations and physically-based modeling were employed to investigate the static softening behaviors during interval holding. The results indicated that static softening fraction increased with rising deformation temperature, strain rate and holding time. Under the same deformation conditions, the furnace-cooled alloy presented the highest static softening, while the lowest in water-quenched alloy. Particularly, double plateaus were presented in the static softening curve of water-quenched alloy when deformed at 300 degrees C and 0.1 s(-1), which was interpreted by static recovery, static precipitation and its coarsening as well as the complete depletion of stored strain energy during post-deformation holding. When deformed at 450 degrees C and 0.1 s(-1), higher static softening fraction and longer plateaus were observed in all alloy specimens due to the remarkable static recovery within a very short holding time after first-pass deformation. In addition, the established recovery model could generally rationalize the experimental results, and the direct static softening contribution of precipitates coarsening was indicated to be slight according to the results of integrated model.