2024铝合金在模拟动态海水/大气界面环境中的局部腐蚀机制

Localized Corrosion Mechanism of 2024 Aluminum Alloy in a Simulated Dynamic Seawater/Air Interface

搭建了由电动推杆、时间继电器及4个腐蚀电化学传感器组成的模拟动态海水/大气界面(简称为水气界面)腐蚀测试平台,综合采用腐蚀电位监测、电化学阻抗谱(EIS)技术、电化学噪声(EN)技术以及表面和截面形貌分析,研究了2024铝合金在模拟动态水气界面区的局部腐蚀行为与机制,并比较了其与全浸区腐蚀行为的差异性。结果表明,动态水气界面区腐蚀产物呈“连续分布”特征,主要是由于试样向上移出水面过程中蚀孔内阳极溶解产生的Al^(3+)流出,与界面区丰富的氧结合生成腐蚀产物;全浸区腐蚀产物分布较为分散。水气界面区随着铝合金浸入和移出水面,腐蚀电位呈现周期性“下降-上升”波动,波动幅值为5~10 mV。全浸区与水气界面区的水线上方由于腐蚀电位较高所以为阴极区,水线下方为阳极区;但腐蚀电位差异不大,因此宏观腐蚀电池作用不明显。EIS结果表明,水气界面区高频容抗弧半径均呈现先增大后减小趋势,界面区的腐蚀产物膜由于覆盖度大,比全浸区的腐蚀产物膜耐蚀性好。EN结果表明,水气界面区电流噪声的波动幅值先减小后增大,表明局部腐蚀敏感性先减小后增大,电流噪声的功率谱密度(PSD)高频线性区斜率均小于-20 dB/dec,表明其腐蚀类型均为局部腐蚀。和全浸区相比,水气界面区的蚀孔尺寸小,孔蚀发展速率较慢,这主要是因为水气界面区的O含量高,O2通过扩散到达蚀孔内部发生还原反应,消耗H+,进而提升蚀孔内的pH值。

A seawater corrosion test platform to simulate the dynamic seawater/air interface is constructed,comprising an electric putter,a time relay,and four corrosion electrochemical sensors.The localized corrosion mechanism of 2024 aluminum alloy in a simulated dynamic seawater/air interface is investigated by corrosion potential monitoring,electrochemical impedance spectroscopy(EIS),electrochemical noise(EN)measurements,and the analysis of the surface and cross-section morphology.The differences in the corrosion behavior at the seawater/air interfacial region and that of full immersion region are discussed.The results showed that the corrosion products at the dynamic seawater/air interfacial region are continuously distributed,which is mainly due to the dissolved Al^(3+)flowing from the pits and reacting with the oxygen in the dynamic seawater/air interfacial region.The distribution of corrosion products in the entire leaching area is more dispersed.As aluminum alloy is immersed and removed from water periodically,the corrosion potential fluctuates periodically with an amplitude of 5-10 mV.Due to the high corrosion potential in the seawater/air interfacial region,the aluminum alloy above the waterline behaves as the cathode,and that below the waterline acts as the anode.However,because of the subtle difference in the corrosion potential,the galvanic corrosion effect is not obvious.The results of EIS revealed that the highfrequency capacitive arc radius of both seawater/air interfacial region and full immersion zone increased first and then decreased,and the corrosion product film in the interface zone had better corrosion resistance than that in the full immersion zone.The results of the EN test showed that the fluctuation amplitude of current noise decreased first and then increased,indicating that the local corrosion sensitivity decreased first and then increased.The slope of the high-frequency linear region of the power spectral density of current noise was less than-20 dB/dec,indicating that the corrosion type was local corrosion.The pit size at the seawater/air interface was much smaller than that in full immersion region,because the oxygen in the seawater/air interface region could be easily reduced within the pits by consuming H+,thereby increasing the pH value within the pits.