腐蚀对新型高强度铝合金疲劳裂纹萌生机制及扩展行为的作用

根据编制的某机场环境加速试验谱，通过腐蚀试验模拟飞机服役过程中遭受的潮湿空气、盐雾、二氧化硫、酸雨和干/湿交变等严酷条件的侵蚀作用，采用飞机主承力结构新型高强度铝合金7B04-T74，制备单边缺口拉伸(Single edge notch tension, SENT)试样进行预腐蚀和疲劳试验，分析不同程度腐蚀损伤对疲劳裂纹萌生、裂纹扩展行为和疲劳寿命的影响，揭示腐蚀对裂纹萌生及扩展行为的作用机理。结果表明，在腐蚀初期，疲劳裂纹萌生源主要为单个蚀孔，裂纹扩展路径较为平直；随着腐蚀程度的加重，在多个蚀孔处同时萌生多条小疲劳裂纹，萌生疲劳裂纹的蚀孔具有隧道效应，扩展路径不规则，形成“之”字形裂纹；疲劳裂纹萌生机制是材料第二相与腐蚀损伤之间相互竞争的结果；腐蚀导致疲劳寿命显著降低，尤其是裂纹萌生寿命，腐蚀12年试验件裂纹萌生寿命仅为未腐蚀试验件裂纹萌生寿命的2.2%。

Effect of Corrosion Damage on Fatigue Crack Initiation Mechanism and Growth Behavior of High Strength Aluminum Alloy

Corrosion damage are simulated through accelerated corrosion testing based on the complied environment spectrum, as result of high humidity atmosphere, salt fog, sulfur dioxide, acid rain and dry/wet alternation for aircraft structure during service. Prior corrosion and fatigue experiments are conducted for single edge notched specimen machined from 7B04-T74 advanced high strength aluminum alloy of aircraft critical structure. And the influence of different corrosion damage on fatigue crack initiation and propagation behavior is analyzed, as well as crack growth rate and fatigue life, to find the mechanism of corrosion damage on fatigue behavior. The results indicate that crack initiation site is mainly single pit in early corrosion stage, and the crack follows a relatively straight path. While the corrosion damage grows more severely, multiple small cracks initiate from several pits and there is obvious tunneling effect beneath pits, cracks follow zigzag path. The material microstructures compete with corrosion pits as crack origins. Corrosion damage seriously decreases fatigue life of aluminum alloy. Fatigue crack initiation life with corrosion damage equivalent to 12 years is only 2.2% of that without damage, which indicates crack initiation life is especially sensitive to corrosion damage.