An experimental set-up was designed for measuring the fatigue crack propagation rate of A7N01 aluminum alloy welded joint using fatigue test system. The microstructure of welded joint was analyzed by an optical microscope, and the morphology of fatigue fracture was studied by an election scanning microscope. The results show that the microstructure of parent metal is the aging rolled structure by the α(Al) matrix, coarse first phase, secondary disperse strengthening phase and some inclusions. The microstructure of HAZ is the α(Al) matrix with some un-soluble microstructure. The microstructure of weld seam is the α(Al) matrix with divorced eutectic phase. The fatigue crack propagation characteristic is different due to different microstructures and different scale second phase precipitates of welded joint. The fatigue crack propagation rate increases with the increase of stress ratio. The discordant plastic deformation between the second phase precipitate and matrix in the crack tip plastic region can promote the propagation of fatigue crack and affect growth rate of it.%使用疲劳试验机测试A7N01铝合金焊接接头的疲劳裂纹扩展速率,采用光学显微镜对焊接接头的显微组织进行分析,使用扫描电镜对疲劳断口形貌进行研究.结果表明:母材的显微组织为时效状态的α(Al)基体与粗大一次相、弥散二次强化相以及少量的夹杂物构成的轧制状态组织；热影响区的显微组织为α(Al)基体以及少量未固溶的一次相组织,焊缝的显微组织为α(A1)基体与离异共晶组织.焊接接头的显微组织以及第二相粒子尺度不同导致了疲劳裂纹扩展特性不同.随着应力比的增加,疲劳裂纹扩展速率均呈增大趋势.裂纹尖端塑性区内的第二相粒子与基体的不协调塑性变形可促进疲劳裂纹的扩展,影响疲劳裂纹的扩展速率.
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