用时域法EIS评估LY12CZ铝合金的膜下腐蚀

通过对表面带有硫酸阳极化膜和H06－1012H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，logGg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。

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

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.