Effect of Corrosion Morphology on Electrochemical Impedance Spectroscopy Characteristics of Mg-alloy

doi:10.11902/1005.4537.2025.011

Journal of Chinese Society for Corrosion and protection

2025, Vol. 45

Issue (6): 1589-1598 DOI: 10.11902/1005.4537.2025.011

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Effect of Corrosion Morphology on Electrochemical Impedance Spectroscopy Characteristics of Mg-alloy

XU Shiyuan¹, MENG Xin², YANG Yazhang¹, LIU Chen¹, ZHANG Zhao³, FANG Xiaozu¹(

)

1 Ningbo branch of Chinese Academy of Ordnance Science, Ningbo 315000, China
2 Chongqing Tiema Industrial Group Co. Ltd. , Chongqing 400000, China
3 Department of Chemistry, Zhejiang University, Hangzhou 310000, China

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XU Shiyuan, MENG Xin, YANG Yazhang, LIU Chen, ZHANG Zhao, FANG Xiaozu. Effect of Corrosion Morphology on Electrochemical Impedance Spectroscopy Characteristics of Mg-alloy. Journal of Chinese Society for Corrosion and protection, 2025, 45(6): 1589-1598.

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Abstract

In order to investigate the formation mechanism of dual inductive loops in electrochemical impedance spectroscopy (EIS) of Mg-alloy, the corrosion behavior in 3.5% (mass fraction) NaCl solution of pure Mg (exhibiting uniform corrosion) and AZ31 Mg-alloy (predominantly undergoing localized corrosion) was comparatively assessed. After immersion in 3.5% (mass fraction) NaCl solution for 24 h, the EIS test results revealed that the pure Mg did not exhibit dual inductive loops. However, the dual inductive loops can be observed for AZ31 Mg-alloy. Morphological analysis further demonstrated that the pure Mg did experience uniform corrosion. However, AZ31 Mg-alloy suffered from both filiform corrosion and pitting corrosion. The different propagation mechanism of filiform corrosion and pitting corrosion led to the formation of non-uniform corrosion morphology. The test results of EIS and corrosion morphology established that the formation of double induction loops for AZ31 Mg-alloy is related to the non-uniform corrosion morphology.

Key words: Mg-alloys corrosion EIS corrosion morphology

Received: 06 January 2025 32134.14.1005.4537.2025.011

ZTFLH:

T146.2

Fund: Ningbo Youth Science and Technology Innovation Leading Talents Project(2024QL010);China Innovation Challenge (Ningbo) Major Project(2023T001)

Corresponding Authors: FANG Xiaozu, E-mail: nbbkycorrosion2024@163.com

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	XU Shiyuan
	MENG Xin
	YANG Yazhang
	LIU Chen
	ZHANG Zhao
	FANG Xiaozu

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https://www.jcscp.org/EN/10.11902/1005.4537.2025.011 OR https://www.jcscp.org/EN/Y2025/V45/I6/1589

Table 1 Composition of the pure Mg and AZ31 Mg-alloy for experiments

Fig.1 Backscattering photographs of pure Mg and AZ31 Mg-alloy samples: (a, b) pure Mg samples, (b) morphology with high magnification of region 1, (c) AZ31 Mg-alloy samples, (d) morphology with high magnification of region 2

Table 2 EDS results of different areas of AZ31 Mg-alloy

Fig.2 EIS results of pure Mg and AZ31 Mg-alloy samples after immersion in 3.5%NaCl solution for 24 h: (a) Nyquist plot of pure Mg samples, (b) Nyquist plot of AZ31 Mg-alloy samples, (c) frequency-phase angle plot, (d) frequency-modulus plot

Fig.3 Optical photos of pure Mg and AZ31 Mg-alloy samples after immersion in 3.5%NaCl solution for 24 h: (a) pure Mg sample, (b) AZ31 Mg-alloy sample

Fig.4 SEM of the corrosion morphology of pure Mg-alloy: (a) surface film morphology, (b) the morphology with high magnification of region 3, (c) matrix morphology after corrosion products removed, (d) the morphology with high magnification of region 4

Fig.5 Corrosion morphology of AZ31 Mg-alloy samples after removal of corrosion products: (a) 3D morphology, (b, c) SEM of pitting corrosion area, (d, e) SEM of filiform corrosion area

Fig.6 Cross section of AZ31 Mg-alloy sample after immersion in 3.5%NaCl solution for 24 h: (a) SEM of filiform corrosion area, (b) SEM of pitting corrosion area

Table 3 EDS test results of corrosion products of pure magnesium and AZ31 Mg-alloy samples

Fig.7 XRD pattern results of pure Mg and AZ31 Mg-alloy corrosion products

Fig.8 Equivalent circuits of pure Mg samples (a) and AZ31 Mg-alloy samples (b)

Fig.9 SEM of corrosion morphology of AZ31 Mg-alloy samples after 10 min immersion: (a) AZ31 Mg-alloy samples after removal of corrosion products, (b) the morphology with high magnification of region 5, (c) the morphology with high magnification of region 6

Fig.10 SEM of corrosion morphology of AZ31 Mg-alloy samples after 30 min immersion: (a) AZ31 Mg-alloy samples after removal of corrosion products, (b) the morphology with high magnification of region 7, (c) the morphology with high magnification of region 8

Fig.11 Schematic diagram of the AZ31 Mg-alloy corrosion process

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