基于扫描Kelvin探针和FT-IR的7B04铝合金/涂层体系丝状腐蚀研究

Investigation of filiform corrosion of coated 7B04 aluminum alloy by scanning Kelvin probe and FTIR

摘要:

对7B04铝合金进行硫酸或铬酸阳极氧化后再喷涂底漆或底漆+面漆，从而制备四类试样，而后开展标准丝状腐蚀试验，利用扫描 Kelvin 探针（SKP）和傅里叶变换红外光谱（FT-IR）技术对7B04铝合金/涂层体系的腐蚀行为和机理进行研究。光学显微镜观察发现四类试样上腐蚀丝的数量较少，且长度不超过3 mm，表明四类试样均具有较好的耐蚀性。SKP测试结果表明，四类试样跨划痕区域的伏打电位随试验时间的变化规律相似，划痕处与周围的涂层-金属界面之间的电位差引起丝状腐蚀的发生，腐蚀机理为阳极破坏；单个腐蚀丝的伏打电位值朝着头部降低，朝着尾部升高，头部和尾部之间的电位差促进腐蚀丝的传播。FT-IR分析显示丝状腐蚀产物的成分主要为Al(OH)3 、Al2O3和AlCl3及其部分水解产物，发生的电化学反应类似于7B04铝合金在氯离子作用下的点蚀过程。对比分析结果表明两种阳极氧化方式对丝状腐蚀的影响差异性较小。

Abstract:

Four types of samples were obtained by anodizing 7B04 aluminum alloy with sulfuric acid or chromic acid and then spraying primer or primer and topcoat. Then a standard filiform corrosion test was carried out and the corrosion behavior and mechanism of 7B04 aluminum alloy/coating systems were investigated by scanning Kelvin probe and Fourier transform infrared spectroscopy (FT-IR). Optical microscope observations reveal that the number of filaments on the four types of samples is small, and the length is no more than 3 mm, indicating that the four types of specimens all have good corrosion resistance. The results of SKP tests show that the variation of Volta potential of the scribe mark and adjacent area with the test time is similar among the four kinds of samples. The potential difference between the scribe mark and the adjacent coating-metal interface causes the occurrence of filiform corrosion, and the corrosion mechanism is anodic undermining. The Volta potential of a single filament decreases towards the head and increased towards the tail, and the potential difference between the head and the tail promotes the propagation of the filament. The results of FT-IR show that the main components of corrosion products at the scribe mark and under the filament are Al(OH)3, Al2O3, AlCl3，and its partially hydrolyzed products. The main chemical reactions in the filiform corrosion are similar to the pitting corrosion of 7B04 aluminum alloy under the erosion of chloride ion. Comparative analysis shows that the influence of two anodic oxidation modes on filiform corrosion is less different