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铁道科学与工程学报

JOURNAL OF RAILWAY SCIENCE AND ENGINEERING

Vol. 15    No. 6    December 2005

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Evaluation of pitting corrosion of Al-Mg-Mn-Sc-Zr alloy in EXCO solution by EIS
PENG Yong-yi(彭勇宜)1,2, YIN Zhi-min(尹志民)2, LI San-hua(黎三华)1 

1. School of Physics Science and Technology, Central South University,
 Changsha 410083, China; 
2. School of Materials Science and Engineering, Central South University, 
Changsha 410083, China

Abstract: In order to evaluate the degree and severity of Al-Mg-Mn-Sc-Zr alloy in exfoliation corrosion(EXCO) solution quickly and nondestructively, electrochemical impedance spectroscopy(EIS) technique was employed. The Al-Mg-Mn-Sc-Zr alloy suffers pitting corrosion in the EXCO solution. During pit incubation, the Nyquist diagram is composed of a depressed capacitive arc at high-mediate frequency and an inductive arc at low frequency. The inductive arc fades with immersion time, and the beginning of pitting corrosion and the appearance of two capacitive arcs have simultaneity. During pit propagation, the Nyquist diagram is composed of two overlapped capacitive arcs. As time goes on, two time constants are more clearly distinguished. The high frequency and low frequency capacitive arc are aroused by passive surface and new interface, respectively. An equivalent circuit is designed to fit EIS, and the experimental results and the fitted results have good correspondence. The degree and severity of pitting corrosion can be obtained by the features of EIS and comparing the fitted values of parameters at different times.

 

Key words:  Al-Mg-Mn-Sc-Zr alloy; EXCO solution; pitting corrosion; EIS

ISSN 1672-7029
CN 43-1423/U

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