含初始缺陷铝合金结构的寿命评估方法大多需要用到裂纹扩展深度这一难以直接测得的参数，为了找到其与表面裂纹长度之间的关系，对预腐蚀7A09铝合金进行疲劳试验，并利用扫描电镜结合能谱仪进行疲劳断口分析，发现了腐蚀坑处萌生裂纹沿着深度方向的扩展规律。结果表明：7A09铝合金的疲劳断口多呈脆性断裂特征，富集的增强相反而会成为脆性相，降低材料的塑性变形能力；对于单一裂纹源主导的疲劳断裂，其内部扩展深度与表面裂纹长度之间存在线性关系，通过检测构件中裂纹的表面长度可以获得其扩展深度，对于结构剩余寿命的估算具有参考价值；对于多源疲劳，裂纹扩展长度与深度间无确定的关系。。

The present fatigue life evaluation approach for aluminum alloy containing defects is based on depth extension of crack which is hidden inside and hard to be directly obtained. In order to find the relation between depth extension and surface cracks length, fatigue experiment was carried out on aluminum alloy 7A09 with prior corrosion damage, and propagation rules of corrosion pit cracks along depth direction was found by analyzing the fatigue fracture by using scanning electron microscope and energy disperse microscope. Results indicate that the fatigue fratography exhibits brittle fracture morphology, and the accumulation of the second phase particles will inversely enhance embrittlement by reducing plasticity. For fracture dominated by solo crack, the depth extension and the surface length of crack displays a linear relationship which provide a way to evaluate depth extension of a crack based on the detectable surface length, which is valuable to residual life prediction of structure. For multiple fatigue, there is uncertain relation between extension length and depth of crack.