用循环极化曲线研究Al和铝合金的点蚀行为

通过循环极化确定纯Al和Al-7Zn-0.1Sn-0.015Ga (质量分数,%) 合金在3.5%NaCl溶液中的自腐蚀电位E_corr、点蚀电位E_pit、点蚀转变电位E_ptp和保护电位E_rp,并通过Al和铝合金在这些特征电位的点蚀形貌研究了它们的点蚀行为及点蚀扩展机理。结果表明：在点蚀电位时开始出现点蚀坑,随着电位升高点蚀坑迅速向横向和纵向扩展直至保护电位；纯Al的点蚀坑为窄而深的方形点蚀形貌,蚀坑内部为粗糙的结晶状结构,且表面出现明显的丝状腐蚀。Al-7Zn-0.1Sn-0.015Ga合金的点蚀形貌为宽而浅的圆形腐蚀坑,蚀坑内部比较光滑,且丝状腐蚀消失。合金元素能明显活化合金,降低点蚀坑深度,改善其腐蚀形貌。

Characterization of Pitting Behavior of Pure Al and Al-7Zn-0.1Sn-0.015Ga Alloy by Cyclic Polarization Technique

Pitting corrosion behavior of pure Al and Al-7Zn-0.1Sn-0.015Ga (mass fraction, %) alloy in 3.5%NaCl solution was studied by cyclic polarization technique in terms of characteristics of corrosion potential E_corr, pitting potential E_pit, pitting transition potential E_ptp and repassivation potential E_rp. While the corrosion morphology of them was investigated by scanning electron microscopy (SEM). The results showed that pits initiate at the pitting potential, they grow quickly both in depth and diameter with the increasing potential until the protective potential. Pits formed on pure Al are narrow and deep square pits, the inner wall of which exhibits rough crystalline structure with a filament corrosion like surface. While pits on Al-7Zn-0.1Sn-0.015Ga alloy are wide and shallow circular pits, with relatively smooth wall but without the filament corrosion like feature. Alloying elements can significantly activate the alloy, reduce its pitting depth, and thus alter the corrosion morphology.