预时效后微变形对7050铝合金疲劳性能影响

Effect of micro deformation after pre-aging on fatigue properties of 7050 aluminum alloy

为了研究预时效后微变形对7050铝合金疲劳性能的影响,首先对预时效后的试样进行微变形,随后对变形后的试样进行120℃时效10 h的处理。使用光学显微镜、扫描电镜和疲劳试验机等分析了7050铝合金在不同时效状态下的微观组织和疲劳性能。结果表明:7050铝合金在不同热处理状态下微观断口形貌具有很大的差异性。退火再回归时效(RRA)处理的试样在应力幅为250 MPa和400 MPa下的裂纹扩展区形貌为羽毛形状结构,瞬断区形貌为微孔聚集型断裂。预时效后微变形处理的试样在应力幅为250 MPa下的瞬断区形貌为准解理断裂,在400 MPa下瞬断区为微孔聚集型断裂和准解理断裂的混合形貌。预时效有助于细小GP区的产生,微变形处理使得位错产生,GP区和位错的协同作用导致更均匀的变形,能够降低应力集中从而提高7050铝合金的疲劳性能,在应力幅为250 MPa时其疲劳周期N_(f)=5448685周。

In order to study the effect of micro deformation after pre aging on fatigue properties of 7050 aluminum alloy,the pre aged samples were first micro deformed,and then the deformed samples were aged at 120℃for 10 h.Microstructure and fatigue properties of the 7050 aluminum alloy under different aging conditions were analyzed by means of optical microscope,scanning electron microscopy and fatigue testing machine.The results show that the microscopic fracture surface morphology of the 7050 aluminum alloy is very different under different heat treatment conditions.The morphology of the crack propagation zone of the retrogression and re-aged(RRA)samples under the stress amplitudes of 250 MPa and 400 MPa is feather shaped structure,and the morphology of the transient fracture zone is microporous aggregation fracture.The morphology of the transient fracture zone of the sample after micro deformation treatment after pre aging is quasi cleavage fracture under the stress amplitude of 250 MPa,and the transient fracture zone is a mixed morphology of microporous aggregation fracture and quasi cleavage fracture under the stress amplitude of 400 MPa.Pre-aging contributes to the generation of fine GP area,micro deformation treatment makes dislocations occur,the synergistic effect of GP area and dislocations leads to more uniform deformation,which can reduce stress concentration and improve the fatigue performance of the 7050 aluminum alloy,and when the stress amplitude is 250 MPa,its fatigue cycle N_(f)=5448685 weeks.