| During plastic forming, the stress states are different in different positions of formed parts. The flow behavior and microstructure evolution behavior will be different because of the different stress states. The researches on the flow behavior and microstructure evolution behavior under different stress states will be conductive to improve the forming process and control the forming quality. In this paper, the basic mechanism performance tests and metallographic observation tests were carried out on the 2024 aluminum alloy sheets to study the difference of flow behavior and microstructure evolution behavior during the process of tension deformation and compression deformation. The main contents are as follows:By the uniaxial tensile tests and compression tests along the rolling direction using universal material testing machine Zwick/Roell Z020, the flow behavior of 2024 aluminum alloy sheets under different stress states were studied first. The results show that the yield stress in tensile tests is bigger than in compression tests under the same deformation conditions. Under the two stress states, temperature and strain rate have more impact on the flow stress. The flow stress decreases with the increasing of temperature. During the low temperature stage, the flow behavior is less affected by the strain rate. With the increasing of temperature, the influence of stain rate on flow stress increases.The stress-strain constitutive models of tensile tests and compression tests had been established. The results show that the thermal deformation activation energy of tensile tests is smaller than that of compression tests. This phenomenon is related to the microstructure evolution behavior. Because of the recrystallization phenomenon, compression deformation process needs to consume more energy.The hot processing maps of tension tests and compression tests were established based on the power dissipation principles and the criterion of instability proposed by Prasad. The hot processing maps show that the instability areas of tension tests and compression tests are appeared in the region of high temperature and high strain rate, the maximum power dissipation rate are in high temperature and low strain rate area. And the maximum power dissipation rate of tensile tests is smaller than that of compression tests, which illustrates the dynamic recrystallization phenomenon is more likely to occur under the compression stress state.The metallographic observation tests and EBSD observation tests were carried out on the specimens after tensile tests and compression tests in order to study the difference of microstructure evolution in stretched specimens and compressed specimens. The EBSD grain boundary maps shows that there is not obvious recrystallization phenomenon in stretched specimen when the temperature is 450 ? and the strain rate is 0.001 s-1, under the same deformation condition, the recrystallization phenomenon happened fully in compressed specimen. The grain morphology difference is suggested to result from the different movement behavior of grain boundaries, including their migration, sliding and transformation from low-angle boundaries to high-angle boundaries.The model of grain size of compression deformation was established based on the Sellars model. Having not the detailed information of recrystallized grains in tension deformation, another phenomenological model was proposed to use in the modeling of grain size. Taking no account of the formation process of recrystallized grains, the new model coincides with the experimental results. |
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