| Creep age forming is a forming method combined aging and forming simultaneously by taking metal properties of creep. Fundamental creep aging research and creep aging at different technology were carried out by selecting7050aluminum alloy in this paper. The effect of different creep aging temper to the amount of creep deformation, the microstructure and properties were studied by using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and other kinds of testing techniques. The creep activation energy and stress index during the creep aging were calculated according to the obtained experimental data, and then the creep age forming theory and the mechanism were analyzed, the following conclusions were obtained:(1)Two kind of different initial states of creep aging behavior of7050aluminum alloy were revealed. As for the solid solution and quenched samples, the creep activation energy Q=138.2kJ/mol and stress index n=4.47, so the creep aging process is mainly controlled by dislocation climb and grain boundary diffusion. The creep activation energy Q=153.3kJ/mol and stress index n=3.72for the pre-treatment samples, the creep aging mechanism is dislocation viscosity slip.(2) The microstructure and properties evolution rule of creep aging7050aluminum alloy were illustrated. The η’ precipitation phase of creep aging samples precipitate much more, much smaller and distributed more uniformly to those of artificial aging, therefore, the creep aging samples have much higher (about2.5%) tensile strength and yield strength to those of artificial aging. The grain boundary precipitation (GBP) becomes discontinuous and much smaller and the precipitate free zone (PFZ) becomes much narrower to that of artificial aging, thus the creep aging samples have relatively much better exfoliation corrosion resistance and smaller plane anisotropy to that of artificial aging.(3) The influence of creep aging after pre-treated of7050aluminum alloy to the microstructure and properties were illustrated. The tensile strength and yield strength of pre-treatment samples are slightly smaller to those of solution treatment samples, the average tensile strength decreased about1.1%. The creep aging samples after pre-treatment have a large mount of creep aging deformation, the average ultimate mount of creep deformation increased about236%to those of non-pretreated, while the average tensile strength is546.8MPa, the average yield strength is508.6MPa and the elongation is10.8%, therefore the creep aging at150℃/16h condition after pre-treatment are more suitable window for the actual production.(4) The technology of T77temper creep aging of7050aluminum alloy was preliminary explored. The retrogression re-aging (RRA) and retrogression creep re-aging (CRRA) were taken out at the condition of120℃/24h+15℃癈/4h+120℃/24h. Compared with RRA samples, the CRRA samples have much higher strength and much smaller plane anisotropy of fracture toughness, while its exfoliation corrosion is not so good. |
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