Influence of Corrosion Products on Corrosion Behavior of Cut Edges of Galvanized Coatings/Q235 Carbon Steel

doi:10.11902/1005.4537.2025.225

Journal of Chinese Society for Corrosion and protection

2026, Vol. 46

Issue (3): 703-716 DOI: 10.11902/1005.4537.2025.225

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Influence of Corrosion Products on Corrosion Behavior of Cut Edges of Galvanized Coatings/Q235 Carbon Steel

LI Yongkun, ZHOU Jiashun, WANG Youbin(

), GAO Feng, WANG Xinpeng, TANG Hongqun

School of Resources, Environment and Materials, Guangxi University, Nanning 530004, China

Cite this article:

LI Yongkun, ZHOU Jiashun, WANG Youbin, GAO Feng, WANG Xinpeng, TANG Hongqun. Influence of Corrosion Products on Corrosion Behavior of Cut Edges of Galvanized Coatings/Q235 Carbon Steel. Journal of Chinese Society for Corrosion and protection, 2026, 46(3): 703-716.

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Abstract

Zn-based eutectic alloy coatings with high corrosion resistance and sacrificial anode protection performance are widely used for corrosion protection of steel. During the usage process, galvanized steel plates are often subjected to cutting or shaping operations, which can cause the galvanized coating and/or the steel substrate at the cutting edge to be exposed to environmental corrosion. Then, how the steel substrate at the cutting edge is corroded, and how the adjacent galvanized layer or its corrosion products will affect the corrosion behavior of the steel substrate, are all topics worthy of study. Herein, the corrosion behavior of cut edge of galvanized coatings of pure Zn, Zn-3Mg, Zn-5Al, and Zn-4Al-3Mg/Q235 carbon steel was studied. First the galvanized steels were cut into cylindrical samples, and sealed using epoxy resin, leaving only one cut-edge surface free and polished. The samples were immersed in a 5% (mass fraction) NaCl solution for corrosion testing; meanwhile another part of samples were subjected to salt spray testing. The microstructure of samples, morphology and phase constituents of corrosion products were characterized by means of field emission scanning electron microscope with energy dispersive spectrometer, 3D microscope, X-ray diffractometer. Besides, the micro-area corrosion behavior of the cut edges of different galvanized coatings was characterized by scanning electrochemical microscopy (SECM). Results show that the corrosion products are distributed both on the coating at the cut edge area and on the steel substrate near the coating. The corrosion products on the Zn and Zn-3Mg coatings were mainly simonkolleite, and on the steel substrate were mainly Zn₅(OH)₈Cl₂ and hydrozincite (Zn₅(OH)₆(CO₃)₂). For Zn-5Al and Zn-4Al-3Mg coatings, the main corrosion products were layered double hydroxide (Zn₆Al₂(OH)₁₆CO₃·4H₂O), Zn₅(OH)₈Cl₂, and Zn₅(OH)₆(CO₃)₂·H₂O. Scanning electrochemical microscope measurements revealed that initially, the feedback currents of Zn-Al and Zn-Al-Mg coatings were higher than those of Zn. Over time, the feedback currents of Zn-Al and Zn-Al-Mg coatings decreased to levels below those of Zn. The feedback current on the surface of the coating and the surface of the steel substrate far away from the side of the coating are larger, while the feedback current on the surface of the steel substrate close to the side of the coating is smaller. Overall, both the feedback current and the current depression decreased with the corrosion time. Salt spray corrosion tests showed that the average weight loss rate of cut edges is 1.04 × 10^-2, 9.88 × 10^-3, 5.73 × 10^-3, and 5.21 × 10^-3 g·m^-1·h^-1 for that with coatings of pure Zn, Zn-Mg, Zn-Al, and Zn-Al-Mg respectively. Among others, the corrosion resistance of the cut-edge with Zn-4Al-3Mg coating is the best. The corrosion product layer of Zn-4Al-3Mg coating is compact with higher content of protective products, Zn₅(OH)₈Cl₂ and Zn₆Al₂(OH)₁₆CO₃·4H₂O, provides a synergistic protective effect. The good protective performance of the corrosion products layer makes the Zn-Al-Mg coating show superior long-term corrosion resistance.

Key words: Zn-based eutectic alloys corrosion products cutting-edge corrosion localized corrosion localized electrochemistry corrosion behavior

Received: 15 July 2025 32134.14.1005.4537.2025.225

ZTFLH:

TG178.44

Fund: National Natural Science Foundation of China(52461011);Guangxi Science and Technology Project(AA24263065);China Postdoctoral Science Foundation(2023MD744187)

Corresponding Authors: WANG Youbin, E-mail: wangyoubin@gxu.edu.cn

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	LI Yongkun
	ZHOU Jiashun
	WANG Youbin
	GAO Feng
	WANG Xinpeng
	TANG Hongqun

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https://www.jcscp.org/EN/10.11902/1005.4537.2025.225 OR https://www.jcscp.org/EN/Y2026/V46/I3/703

Table1 Chemical composition of the prepared Zn alloys　　　(mass fraction / %)

Fig.1 Schematic diagram of (a) the cut edge of the coating (top view) and (b) immersion of plated cut edge

Fig.2 SEM images of Zn (a), Zn-Mg (b), Zn-Al (c) and Zn-Al-Mg (d) coatings

Table 2 EDS elemental analysis results for the marked spots in Fig.2　　　(atomic fraction / %)

Fig.3 SEM images of the cut edges of Zn (a), Zn-Mg (b), Zn-Al (c), Zn-Al-Mg (d) coatings after immersion in 5%NaCl solution for 6 h

Table 3 EDS elemental analysis results for the marked spots in Fig.3　　　(atomic fraction / %)

Fig.4 Distribution of corrosion products at the cut edges Zn (a), Zn-Mg (b), Zn-Al (c) and Zn-Al-Mg (d) coatings after immersion in 5%NaCl solution for 0.5 h (a1-d1), 2 h (a2-d2), 4 h (a3-d3) and 6 h (a4-d4)

Fig.5 SECM line-scan curves at the cut edges of Zn (a), Zn-Mg (b), Zn-Al (c) and Zn-Al-Mg (d) coatings after immersion in 5%NaCl solution for different time

Fig.6 SECM maps of the cut edges of Zn (a), Zn-Mg (b), Zn-Al (c) and Zn-Al-Mg (d) coatings after immersion in 5%NaCl solution for 0.5 h (a1-d1), 2 h (a2-d2) and 6 h (a3-d3)

Fig.7 XRD patterns (a, b) of coatings after salt spray corrosion for 24 h

Fig.8 Average mass loss rates for the cut edge samples of different coatings after neutral salt spray for 24 h

Fig.9 SEM cross-sectional images and corresponding EDS surface scans of Zn (a), Zn-Mg (b), Zn-Al (c), and Zn-Al-Mg (d) coatings after salt spray corrosion for 168 h

Table 4 EDS elemental analysis results for the marked spots in Fig.9　　　(atomic fraction / %)

Fig.10 Corrosion morphology of the cut edges of Zn (a), Zn-Mg (b), Zn-Al (c) and Zn-Al-Mg (d) coatings after salt spray corrosion for 24 h

Fig.11 Schematic diagram of the cut edge corrosion process of Zn (a), Zn-Mg (b), Zn-Al (c) and Zn-Al-Mg (d) coatings

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