Effect of Different Loading Conditions on Corrosion Damage Behavior of 7050 Aluminum Alloy under Synergistic Effect of Marine Atmospheric Environment and Tensile Fatigue Load

As the structural material of the marine equipment superstructure, the corrosion damage behavior of high strength aluminum alloy can be attributed to the interaction of thin electrolyte film corrosion of marine atmospheric environment and fatigue load. At present, researches on the interaction between corrosion environment and fatigue load mainly focus on corrosion fatigue crack propagation and fatigue life, and the corrosion condition is mainly solution immersion environment. However, atmospheric corrosion is carried out in a thin electrolyte film. The development of the corrosion process and its secondary effects and the affecting factors of which are very different from those in the solution. This work aims to study the effect of different stress loading conditions on the corrosion damage behavior of 7050 aluminum alloy under the synergistic effect of marine atmospheric environment and tensile fatigue load. The outdoor actual marine atmosphere in Wanning test site was used as the thin electrolyte film corrosion environment for 7050 alloy, and the self-designed fatigue load test device was utilized to apply different tensile fatigue loads at the same time. A sinusoidal stress waveform was employed to the specimen with a frequency of 10 Hz, and the maximum stress was 30% of the yield stress. The stress ratios of the fatigue load were 0.1 and 0.06. The stress loading periods included two ways: one was to load the stress once a month for 1 800 s each time; the other was to load the stress once a week for 450 s each time. It intended to study the effects of stress ratio and stress loading period on the corrosion rate, corrosion morphology, fatigue property and fracture morphology of 7050 alloy under the synergistic effect. The microstructure of 7050 alloy was characterized by a spot of irregularly shaped second phase particles and their surface distribution was not very homogenous. The grain boundary morphology of 7050 alloy was flat, and the grain was elongated along the rolling direction. All 7050 alloy specimens suffered pitting corrosion and intergranular corrosion under the synergistic effect of marine atmospheric environment and tensile fatigue load. The corrosion product layers of specimens under the dynamic stress condition were less compact and had many superficial cracks on them. Under the condition of loading stress once a month, the maximum corrosion depths of specimens with 0.1 stress ratio and 0.06 stress ratio were 40.1 μm and 46.5 μm, respectively, while the maximum corrosion depth of specimens with stress loaded weekly was 41.2 μm. The corrosion rates of specimens loaded monthly and with 0.06 stress ratio were significantly higher than those of specimens loaded monthly and with 0.1 stress ratio, and specimens in the former case were more prone to corrosion fatigue fracture. The fractures of all specimens showed fatigue fracture characteristics. The crack sources were located on the surface of the alloys and propagated radioactively to the core. Thus it can be inferred that the decrease in the stress loading period and stress ratio will significantly accelerate the corrosion damage process of 7050 aluminum alloy under the synergistic effect and reduce its anti-fatigue performance. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.