对新型2198铝锂合金进行Alodine 1200S化学转化处理。采用极化曲线和电化学阻抗谱研究不同转化时间处理前后该合金在3.5% NaCl溶液中的腐蚀破坏过程。根据铬酸盐化学转化处理后铝锂合金的电化学阻抗谱特征, 建立与之相应的电化学等效电路模型, 并分析了化学转化膜的成膜机理。结果表明, 化学转化处理促使铝锂合金的自腐蚀电位和击穿电位正移。化学转化处理的合金Nyquist图低频容抗半径和Bode图阻抗模值大小随化学转化时间延长先增大后减小, 出现极值。转化时间为1 min 30 s时容抗弧和感抗弧半径最大, 阻抗模值最大, 阻抗相位角最接近-90°。转化膜表面可能吸附部分的K3[Fe(CN)6]促进剂和游离的六价铬, 在NaCl溶液中浸泡时, 可能发生局部表面的吸脱附和扩散。

The corrosion properties of 2198 Al-Li alloy and chromate conversion coated 2198 Al-Li alloys with different treating times were studied by polarization curves and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. According to the characteristics of EIS, the electrochemical equivalent circuit was established. The formation mechanism of chromate conversion coating on the alloy was further analyzed. The results showed that Ecorr and Eb of the alloy shifted positively after chromate conversion coating treatment. The radius of capacitive arcs in Nyquist plot increased first and then decreased. The radius of capacitive arcs became the maximum when the treating time was 1 min and 30 second. Under the same condition, the modulus of corrosion resistance became the maximum, and the phase angle of corrosion resistance was the closest to -90°. Few amounts of K3[Fe(CN)6] accelerator and free Cr(Ⅵ) species were adsorbed on the coating surface, and parts of them desorbed and diffused during the immersion process.