基于电化学噪声研究缓蚀剂对AA6063铝合金点蚀的影响

采用电化学噪声(ECN)、电化学阻抗谱(EIS)和极化曲线研究了AA6063 铝合金在3% (w) NaCl 溶液中的亚稳态点蚀萌发和稳态点蚀生长特征, 着重探讨了CeCl₃、Na₂CrO₄、8-羟基喹啉(8-HQ)等三种不同类型缓蚀剂对亚稳态和稳态点蚀的抑制机理. 结果表明: 当铝合金表面阴极相(Al-Si-Fe)周边的Al 基体发生局部溶解后,会导致邻近区域pH值升高(>8.4), 引起Ce(OH)₃在蚀点中心区的阴极相表面优先沉积, 从而抑制局部腐蚀的阴极去极化过程. 随着缓蚀剂浓度的提高, 亚稳态噪声峰的平均积分电量(q)随之递减, 但噪声峰的平均寿命几乎没有变化, 表明Ce³⁺并不能直接加速亚稳态蚀点的修复, 但可降低蚀点内金属Al 的溶解速率. CrO₄^2-不但可加速蚀点修复, 还可降低亚稳态蚀点的形核速率. 8-HQ主要与Al³⁺、Mg²⁺等形成不溶性螯合物并沉积在铝合金表面,提高了铝基体的全面抗腐蚀能力, 但并不能显著提高其耐点蚀能力.

Effect of Inhibitors on Pitting Corrosion of AA6063 Aluminium Alloy Based on Electrochemical Noise

The pitting corrosion of AA6063 aluminum alloy in 3% (w) NaCl solution was investigated by electrochemical noise (ECN), electrochemical impedance spectroscopy (EIS), and polarization curves. Inhibition of nucleation and propagation of metastable pits by inhibitors, such as CeCl₃, Na₂CrO₄, and 8-hydroxyquinoline (8-HQ), was evaluated based on ECN data statistics. It was found that the local pH could be over 8.4 near the cathode phase (Al-Si-Fe) due to dissolution of Al matrix, leading to preferential deposition of Ce(OH)₃ on the surface of the cathode phase, thereby inhibiting the cathodic process of pitting corrosion. The average electric charge (q) of metastable pits decreased with increasing the corrosion inhibitor concentration, but the average lifespan of noise transients remained almost constant, indicating that Ce³⁺ ions did not accelerate the rehabilitation of metastable pits directly, but reduced the dissolution rate of Al inside active pits. However, CrO₄^2- ions not only accelerated the rehabilitation of metastable pits, but also reduced the nucleation rate of the AA6063 aluminum alloy. In contrast, 8-HQ acted as an effective corrosion inhibitor for AA6063 aluminum alloy through formation of insoluble chelate films with Al³⁺ ions and Mg²⁺ ions, but failed to enhance the pitting corrosion resistance of the aluminum alloy.