静水压力对超纯Al/超纯Fe电偶中超纯Al腐蚀行为的影响

Effect of Hydrostatic Pressure on Corrosion Behavior of Ultra Pure Al Coupled with Ultra Pure Fe

采用动电位极化和电化学噪声方法在3.5%NaCl中研究了静水压力对超纯Al/超纯Fe电偶中超纯Al腐蚀行为的影响。利用离散小波变换去除噪声信号的直流漂移,然后进行散粒噪声和随机分析;利用HilbertHuang变换对噪声信号做时频分析;用SEM观察腐蚀试样的表面形貌;用有限元方法模拟压力分布。结果表明,不同静水压力下超纯Al在3.5%NaCl溶液中皆自钝化,与超纯Fe偶合后发生点蚀。随静水压力的升高,超纯Al/超纯Fe的电偶电位逐渐降低,电偶电流逐渐增大。静水压力越高,经电偶腐蚀后超纯Al表面形成的点蚀坑尺寸越小且分布更加均匀。静水压力的提高加速了电偶腐蚀中超纯Al的点蚀孕育速率,但抑制了点蚀生长概率,降低了局部腐蚀倾向。静水压力为常压时,点蚀可沿水平、竖直方向扩展;在静水压力存在的条件下,点蚀更易于沿水平方向扩展。

Hydrostatic pressure was one of the critical factors affecting deep-sea corrosion. Theoretical research showed that increasing hydrostatic pressure could improve the activity of metal materials, increase the difference in activity between coupled metal materials, and aggravate the galvanic corrosion.At present, there were many researches on the corrosion behavior of metallic materials under hydrostatic pressure, but there were few researches on the influence of hydrostatic pressure on the corrosion behav-ior of metal materials. Due to the requirements of structure and performance in the marine environment,equipment components with different electrochemical properties must be connected. In such a harsh environment, galvanic corrosion would obviously accelerate. Therefore, it was very necessary to study the galvanic corrosion behavior of metallic materials under the condition of the deep sea. Fe-based alloys and Al-based alloys have been widely used in the marine environment, and there have been many studies on corrosion of Fe-based alloys and Al-based alloys in the deep-sea environment. As a result of single composition and structure, taking ultra-pure Al and ultra-pure Fe as the research object, the influence of phase, inclusion and other factors on corrosion behavior under hydrostatic pressure could be avoided,which was helpful to clarify the influence of hydrostatic pressure on corrosion behavior of ultrapure Al coupled with ultra-pure Fe. The influence of hydrostatic pressure on the corrosion behavior of ultrapure Al coupled with ultrapure Fe was studied in 3.5%Na Cl using electrodynamic polarization and electrochemical noise. The discrete wavelet transform was utilized to remove the direct current drift of noise signal,and then the stochastic analysis based on the shot noise theory was carried out. The Hilbert-Huang transform was utilized to analyze the time-frequency characteristics of the noise signal. The surface morphology of corrosion samples was observed by SEM. The pressure distribution was simulated by finite element method. The results showed that the ultrapure Al was self-passivation in 3.5%Na Cl solution under different hydrostatic pressures, pitting corrosion occurred after coupling with ultrapure Fe. With the increase of hydrostatic pressure, the galvanic potential of coupled ultrapure Al and ultrapure Fe decreased gradually,and the galvanic current increased gradually. The increase of hydrostatic pressure accelerated the pitting generation rate of ultrapure Al in galvanic corrosion, but inhibited the growth probability of pitting corrosion and reduced the tendency of local corrosion. When hydrostatic pressure was atmospheric, pitting corrosion could expand along the horizontal and vertical directions. In the presence of hydrostatic pressure, pitting corrosion was easier to expand along the horizontal direction.