| With the increasing demand of lightweight, longevity, high reliability and extreme service performance of the modern aeronautic and astronautic equipments, the manufacturing of high performance complex integral components is one of the most important technical routes to realize the rapid development of aeronautic and astronautic equipments. Creep-aging forming, which combines the creep forming and artificial aging, has recently been selected as the most promising manufacturing process to form complex integral components. Due to the insufficient in theoretical research, the creep-aging behaviors of a commercial7075aluminum alloy are studied in this dissertation to provide some theoretical directions to the forming of the high performance complete integral components. The results and achievements of the dissertation are as follows:(1) The creep-aging behaviors of7075aluminum alloy are studied by uniaxial tensile creep experiments, and the effects of creep-aging processing parameters on the creep-aging behaviors of the studied aluminum alloy are discussed. Results show that the creep-aging behaviors of the studied7075aluminum alloy are sensitive to the creep-aging temperature and applied stress. The creep strain increases with the increase of creep-aging temperature and applied stress. A constitutive equation is established to describe the variation of creep strain with the creep-aging temperature and applied stress. A good agreement between the predicted and measured creep strains shows that the established creep constitutive model can give an accurate and precise estimate of the creep behaviors of the studied Al-Zn-Mg-Cu alloy.(2) The effects of creep-aging processing on the microstructural evolution of the studied7075aluminum alloy are studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Results show that coarse insoluble precipitates (Al7Cu2Fe and Mg2Si) and intermediate precipitates (Al18Mg3Cr2and Al3Zr precipitates) are found in the aluminum matrix, and the effects of creep-aging processing on the coarse insoluble precipitates and intermediate precipitates are not obvious. The main aging precipitates are η’ and η phases, and the aging precipitates grow up with the increase of creep-aging temperature and applied stress. With the increase of creep-aging temperature and applied stress, the precipitates are discontinuously distributed on the grain boundary and the width of precipitate free zone increases simultaneously. Compared with the stress-free aging, creep-aging can refine the aging the precipitates and narrow the width of precipitate free zone.(3) The effects of creep-aging processing on the corrosion resistance of7075aluminum alloy are discussed. It is found that the creep-aging temperature and applied stress can change the sizes and distribution of aging precipitates, which results in the increase of the corrosion resistance. The corrosion resistance of7075aluminum alloy is sensitive to the creep-aging processing parameters. With the increase of creep-aging temperature, the corrosion resistance first increases and then decreases within the tested condition. Furthermore, the best corrosion resistance appears when the creep-aging temperature is393K. Meanwhile, the corrosion resistance increases with the increase of applied stress, and when the applied stress is230MPa, the studied alloy has the best corrosion resistance.(4) In conclusion, when the creep-aging temperature is393K, the size and distribution of aging precipitates are reasonable, and the studied7075aluminum alloy has good corrosion resistance, which is suitable for manufacturing the high performance light alloy integral panels. |
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