用时域法EIS评估LY12CZ铝合金的膜下腐蚀

STUDY ON EVALUATION FOR UNDER-FILM CORROSION OF COATED 2024T3 ALUMINUM ALLOY WITH EIS BY TIME DOMAIN METHOD

通过对表面带有硫酸阳极化膜和H0 6 - 10 12H航空环氧底漆的LY12CZ铝合金型材进行剥蚀敏感性加速腐蚀试验 (EXCO) ,采用时域法Laplace转换EIS和截面金相观察来衡量铝合金的膜下腐蚀 .结果表明 :时域法EIS测出的试样Rd、Cg 能够评估膜下腐蚀的损伤程度 ;不同膜下腐蚀形态对应着不同的Rd、Cg 的范围 .Rd 和Cg 随腐蚀时间的变化趋势可以反映基体金属点蚀的萌生、漆膜鼓泡和基体出现剥蚀的历程 .大量平行数据的统计分析表明 :logRd 符合Gumbel分布 ,logCg 符合正态分布 ;由于logRd 服从Gumbel分布 ,故可以根据小面积试样的logRd 值 ,对大面积试样腐蚀最严重处的状况有所估计 .大面积试样在EXCO溶液中浸泡时 ,其logRd 随时间呈指数下降 .

In this article,EIS by Laplace transform time domain method was used to evaluate under-film corrosion of coated 2024T3 aluminum alloy.EXCO immersion test,optical microscope observation and statistic method were also employed.Results show that EIS by time domain method is a quick,nondestructive and quantitative method to detect under-film corrosion of 2024T3 Al alloy.The low frequency impedance ( R d),high frequency capacitance ( C g) can be treated as indicators of under-film corrosion.Correlation was established between R d and C g and corrosion states.Statistical analysis show that log( R d) match Gumbel distribution and log( C g) correspond to normal distribution.Investigations show that different corrosion states have different dynamic rules.If only pitting occurs on the specimen, R d and C g fluctuates.When the exfoliation happens, R d will decrease and C g will increase with time.Log( R d),which reflect the most severe corrosion in large-scale specimen,will decrease exponentially with time in EXCO solution.