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

TAN Xiaoming;ZHANG Danfeng;BIAN Guixue;CHEN Yueliang;Department of Aeronautical Mechanical Engineering,Qingdao Branch, Naval Aeronautical Engineering University;  
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.
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