Abstract
To analyze the effect of lithium and microstructure on the pitting corrosion behavior of aluminum alloys, three types of aluminum alloys were studied via scanning electron microscopy, transmission electron microscopy, electrochemical polarization, and by immersion tests coupled with in-situ observation of pitting and statistical analysis of pit depths measured by surface profilometry. It was found that, with increasing lithium content, the resistance to pitting corrosion was enhanced and the passive range was enlarged. In-situ observation revealed that the development of pitting corrosion exhibited three stages, including an initial slow nucleation stage (Stage I), a fast development stage (Stage II), and a stabilized growth stage (Stage III). Higher lithium content contributed to shorter time periods of Stages I and II, resulting in faster pitting evolution and a higher number of pits. However, the pits were generally shallower for the specimen with the highest lithium content, which is in agreement with the results of the electrochemical analysis.
Highlights
The primary driving force for research and development on aviation aluminum alloys is to reduce the weight of aircraft [1,2,3,4]
Abundant studies have shown that the addition of Li can change the microstructures of Al alloys dramatically [2,3,7,19,20,21,22], especially for the precipitated phases induced by Li addition
According to Li et al [16,26,27], the θ0 phase usually acts as the cathode compared to the matrix, while T1 and T2 are anodic to the alloy base, indicating that further addition of lithium can change the initiation behavior of pitting corrosion
Summary
The primary driving force for research and development on aviation aluminum alloys is to reduce the weight of aircraft [1,2,3,4]. The amount, size, location, and chemistry of precipitated phases show significant effects on the pitting corrosion behavior of aluminum alloys [8,15,16,17,18]. The addition of lithium to 0.5 wt.% facilitates the precipitation of θ0 (Al2 Cu) phase with a refined dispersion in the matrix of 2xxx series aluminum alloys, while higher lithium content (1.0 wt.%) results in the formation of T1 (Al2 CuLi) as the dominant precipitant [23]. According to Li et al [16,26,27], the θ0 phase usually acts as the cathode compared to the matrix, while T1 and T2 are anodic to the alloy base, indicating that further addition of lithium can change the initiation behavior of pitting corrosion. This work will be followed by further analysis using the point defect model in the second part of this series
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