부산대학교 도서관

The intermediate temperature deformation behavior and microstructural evolution of a spray formed 7075 Al alloy were performed at temperatures 60–120 °C with strain rates 0.00001–0.1 s−1. The results reveal that the softening mechanism of the intermediate temperature deformation is dynamic recovery (DRV), which can be quantitated by Zener-Hollomon (Z) parameter. The constitutive equation can reasonably predict the stress-strain behavior of the alloy at intermediate temperatures. The activation energy is related to the deformation process and the interactions of the substructure, the average value is 140.1 kJ/mol. The higher efficiency of power dissipation in the processing map is related to the DRV at lower deformation temperatures. The optimum processing domain is located at the temperature of 90–120 °C and strain rate of 0.006–0.1 s−1 with a power dissipation efficiency range of 20%–40%. The processing parameters of the intermediate temperature deformation should be strictly controlled according to the strain. The uniform microstructure of 7075 alloys obtained by spray forming is crucial to overcome the disadvantage of poor deformability. The inferior coordinated deformation facilitates crack propagation at low strain rates. The high-density dislocation provides adequate nucleation sites for dynamic precipitation. The level of dynamic restoration facilitates the transformation from low angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs). The dislocations move to the grain/sub-grain boundary to form dislocation walls at low temperatures. The contribution to the stress from grain boundary (13.2–17.7 MPa), nanoscale precipitates (65.7–191.5 MPa), and dislocation (5.9–23.4 MPa) increases the difficulty of deformation. The deformation process at higher temperatures (105–120 °C) can be facilitated by the dissolution and coarsening of the nanoscale precipitates, and dislocation motion at the grain boundary.