Hot Deformation Behavior Of High Strength Aluminum Alloys

7000-series and2000-series aluminum alloys are all belong to high-strengthaluminum alloys, they are used extensively in aviation and aerospace, both of the alloysare called "unweldable metal". The problem of welding difficult of the two alloys hasbeen resolved by Friction Stir Welding (FSW). The welding temperature and plastic flowof the weld metal is very important for weld formation quality in actual welding process,so investigations of the hot deformation behavior is useful for taking insight of weldingprocess optimization and welding mechanism.By thermo-simulation, hot deformation behaviors of7050and2024aluminum alloyswas investigated by the use of Gleeble-3500simulator with hot tensile and compressiontests. From the curves of flow stress vs. strain, the flowing behaviors of both alloys all aresignificantly affected by strain rate and deformation temperature. Overall, the flow stressdecreases with increasing deformation temperature and decreasing strain rate.For the tensile deformation, the deformation temperature and strain rate on the impactof metal plasticity was discussed by reduction of area and elongation and metallographicobservation, meanwhile, thermal deformation constitutive equation was established. Theresult show that the ductility of the two alloys increases with increasing deformationtemperature and decreasing strain rate. The hot deformation activation energy (Q) issmaller than2024aluminum alloy, this indicates that7050aluminum alloy is more easierfor dynamic recrystallization. In the experimental conditions, the main softeningmechanism of7050aluminum alloy is dynamic recrystallization and400℃is best forductility, the main softening mechanism of2024aluminum alloys is dynamic recovery,and there is no ductility peak.For the compress deformation, we also established thermal deformation constitutiveequation. Based on dynamic materials model (DMM) and Prasad's instability criterion, wegot strain rate sensitivity (m) and the efficiency of power dissipation (η) and flowinstability zone, the processing maps were finished finally. The suitable hot workingprocesses can be got using processing maps combined with metallographic observation. The microstructure inhomogeneity caused by different strain distribution was discussed,the results show that dynamic recrystallization of7050aluminum alloys is occurred in400℃low strain rates, it is good for hot working. For2024aluminum alloys, materialfalls into unstable region when strain rate is low and the temperature is between250~300℃; there is peak of efficiency of power dissipation when temperature is over400℃, it is good for hot working. Under this condition, dynamic recovery is the mainmechanism.