(1. 中南大学 粉末冶金研究院，长沙 410083；
2. 中南大学 材料科学与工程学院，长沙 410083；
3. 中南大学 有色金属材料科学与工程教育部重点实验室，长沙 410083)
摘 要: 通过金相显微镜(OM)、取向分布函数(ODF)及扫描电镜(SEM)研究25 mm厚7475-T7351铝合金板材的疲劳性能和裂纹扩展速率。结果表明：板材的疲劳强度存在各向异性，横向疲劳强度为300 MPa，纵向疲劳强度为310 MPa，疲劳寿命均大于1×107 cycle。板材在Kt=1、应力比R=0.1和应力强度幅度？K=30 MPa·m1/2条件下，纵向疲劳裂纹扩展速率da/dN为2.73×10-3~4.41×10-3 mm/cycle，横向疲劳裂纹扩展速率da/dN为5.76×10-3~8.22×10-3 mm/cycle。疲劳裂纹主要在次表面的含O、Na、Cl非金属夹杂物处及粗大第二相处萌生，在疲劳裂纹扩展区可观察到大量疲劳条带，在瞬时断裂区，断口呈小韧窝和解理断裂的混合形貌。
关键字: 7475铝合金；疲劳性能；各向异性；裂纹扩展速率
（1. Powder Metallurgy Research Institute, Central South University, Changsha 410083, China;
2. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
3. Key Laboratory of Nonferrous Materials Science and Engineering, Ministry of Education,
Central South University, Changsha 410083, China）
Abstract:The optical microscopy, orientation distribution function and scanning electron microscopy were used to investigate the fatigue properties and the rate of fatigue crack growth of 7475-T7351 alloy plate with thickness of 25 mm. The results show that the fatigue strength is anisotropic for the plate, it is 300 MPa along the transverse direction and 310 MPa along the longitudinal direction, respectively, and the fatigue life is longer than 1×107 cycle. Under the conditions of Kt=1, stress ratio R=0.1 and stress intensity factor amplitude ？K=30 MPa·m1/2, the fatigue crack growth rate da/dN along the longitudinal and transverse direction are 2.73×10-3-4.41×10-3 mm/cycle and 5.76×10-3-8.22×10-3 mm/cycle, respectively. The fatigue cracks mainly initiate on the non-metallic inclusions containing O, Na, Cl and coarse second phase on the sub-surface. A large number of striations are observed in the fatigue propagation zone, and a mixture of small dimples and cleavage is observed on the fracture surface in the fatigue fracture zone.
Key words: 7475 aluminum alloy; fatigue property; anisotropy; fatigue crack growth rate
