| Abstract:The aging creep forming is a new technology developed for the manufacture of large integral panel component. This technique is a forming method allowing forming and aging taking place at the same time, which takes advantage of the creep properties of the metal and aging hardening characteristics.2524aluminum alloy is the best choice for a new generation of aircraft skin material. In order to better predict the creep behavior, the rebound law, strengthening phase precipitation and mechanical properties of the components in the complex environment of stress and heat treatment, mechanical test, hardness and conductivity test, TEM microstructure analysis, data regression analysis and finite element simulation were adopted with usage of self-developed tooling, to carry out researches on the property of the stress and the influence which is imposed on2524aluminum alloy creep by using the prescription system. The thesis’s research works mainly include the following aspects:1. A series of experiments, which were concerned with creep deformation behavior, creep mechanism, material properties and microstructure evolution law, were carried out, hence the following conclusions were drawn:①Through the calculation and analysis of the2524aluminum alloy creep curves, we found that, after entering the second stage, the creep strain value under compressive stress is twice of that under tensile stress. We also got the apparent activation energy and the stress exponent, thus concluded that, the creep mechanism of2524aluminum alloy under tensile stress was mainly controlled by the dislocation slip process, while that under compressive stress state was mainly controlled by grain boundary sliding process.②The test research on the properties of the creep aging material sample is carried out. The optimum process system of alloy under tensile stress:experimental stress of180MPa, the experimental temperature of190℃, aging time12h. The comparison of physical properties under two stress state found that, under the same conditions, the hardness and conductivity of the alloy, which has been tested in creep process under compressive state, is slightly higher than that under tensile stress.③Micro-structural analysis using TEM has been carried out to do further research. The results found that the2524aluminum alloy’s intragranular precipitates got in creep aging process were in larger quantities and got evener distribution in comparison with that got in zero stress process. Meanwhile, the results also found that the2524aluminum alloy’s intragranular precipitates got in creep aging process under compressive stress state were finer and got evener distribution in contrast with that got under tensile stress state. At grain boundary, the band width of the precipitate free zone is narrow, and the precipitated phase is distributed discontinuously.2. Based on experimental creep deformation curves, hybrid particle swarm algorithm were used to establish the creep aging constitutive equations under tensile and compressive stress. And the error analysis results shows that the theoretical fitting curves are in agreement with the experimental curves.3. Based on the establishment of the constitutive equations under tensile and compressive stress, the springback law of typical panel member dealt with creep aging process was predicted, and relevant experimental verification was done. The results show that the constitutive models including both stress state can better describe the panel components’creep age forming process, and the accuracy of springback prediction using comprehensive constitutive model higher then the tension stress constitutive model. |
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