Study on Flow Stress and Microstructure Evolution of 7050 Alloy During Hot Plastic Deformation

7050 alloy at different strain rates,deformation temperature and reduction rate under the upsetting test was measured by thermal simulation testing machine Gleeble-1500.The true stress-true strain curve under different temperatures(250 ℃,325 ℃,400 ℃,475℃)and strain rate deformation(0.01,0.1,1,10 s-1) were obtained.The influence of thermoplastic deformation conditions on the alloy flow stress was studied.The results show that the lower the deformation temperature,and the higher the strain rate,the greater the flow stress.The flow stress at the initial stage of deformation increases with deformation increasing,which can reach the approximate steady state flow limit.The microstructure evolution of the alloy under high temperature thermoplastic deformation was studied by combining with metallurgical test methods and optical microscopy.The relationships between deformation parameters and microstructure evolution in the process of the thermoplastic deformation was analyzed by combining with pressure processing theory.The results confirm that changing the pressure temperature,reduction rate and pressure rate can effectively change the volume fraction of dynamic recrystallization and dynamic recrystallization grain size.The effect of reduction rate on the alloy dynamic recrystallization is obvious.Different dynamic recrystallization starting temperature corresponds to different amounts of deformation.