(1. 中南大學 粉末冶金研究院，長沙 410083；
2. 中南大學 材料科學與工程學院，長沙 410083；
3. 中南大學 有色金屬材料科學與工程教育部重點實驗室，長沙 410083)
摘 要: 通過金相顯微鏡(OM)、取向分布函數(ODF)及掃描電鏡(SEM)研究25 mm厚7475-T7351鋁合金板材的疲勞性能和裂紋擴展速率。結果表明：板材的疲勞強度存在各向異性，橫向疲勞強度為300 MPa，縱向疲勞強度為310 MPa，疲勞壽命均大于1×107 cycle。板材在Kt=1、應力比R=0.1和應力強度幅度？K=30 MPa·m1/2條件下，縱向疲勞裂紋擴展速率da/dN為2.73×10-3~4.41×10-3 mm/cycle，橫向疲勞裂紋擴展速率da/dN為5.76×10-3~8.22×10-3 mm/cycle。疲勞裂紋主要在次表面的含O、Na、Cl非金屬夾雜物處及粗大第二相處萌生，在疲勞裂紋擴展區(qū)可觀察到大量疲勞條帶，在瞬時斷裂區(qū)，斷口呈小韌窩和解理斷裂的混合形貌。
關鍵字: 7475鋁合金；疲勞性能；各向異性；裂紋擴展速率
（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
