Corrosion Behavior of Zn-2.0Al-1.5Mg Coatings in Simulated Marine Atmosphere
GU Tianzhen1,2,3, LIU Yuwei1,3(), PENG Can1,2,3, ZHANG Peng4, WANG Zhenyao1,3(), WANG Chuan1,3, MA Cheng4, CAO Hongwei4
1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2 School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China 3 Liaoning Shenyang Soil and Atmosphere Corrosion of Materials National Observation and Research Station, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 4 HBIS Group Technology Research Institute, Shijiazhuang 050023, China
Cite this article:
GU Tianzhen, LIU Yuwei, PENG Can, ZHANG Peng, WANG Zhenyao, WANG Chuan, MA Cheng, CAO Hongwei. Corrosion Behavior of Zn-2.0Al-1.5Mg Coatings in Simulated Marine Atmosphere. Acta Metall Sin, 2025, 61(2): 278-286.
As the service environment changes, the widely used galvanized coating faces challenges due to its overly thick coating and insufficient corrosion resistance. Zn-2.0Al-1.5Mg coatings have emerged as an alternative to conventional galvanizing because of their excellent corrosion resistance and are extensively used in buildings, home appliances, and automobiles in harsh environments. The marine environment, known for its high corrosiveness, faces considerable material corrosion problems. Highly resistant materials, such as Zn-2.0Al-1.5Mg coating, stainless steel, have found applications in the marine environment. However, the development period of Zn-2.0Al-1.5Mg coating is short, and further research is required to determine its suitability for highly corrosive marine atmospheric environments. Consequently, the laboratory dry-wet alternating cycle corrosion test method, corrosion mass loss, SEM, XRD, EIS, and potentiodynamic polarization were used to investigate the corrosion behavior (e.g., corrosion kinetics, corrosion product evolution, corrosion morphology, and electrochemical behavior) of Zn-2.0Al-1.5Mg coatings in a simulated marine atmosphere. Results show that the initial corrosion product is ZnO at 168 h, with Zn5(OH)8Cl2·H2O appearing after 168 h of corrosion cycles (336, 504, 672, 840, and 1848 h). The emergence of ZnO at 168 h is attributed to the shortened dry-wet alternating cycle time, while that of Zn(OH)2·0.5H2O at 1848 h is attributed to the depletion of Mg or Al elements. The corrosion rate of Zn-2.0Al-1.5Mg coatings in the simulated marine atmosphere exhibited an M-shaped curve over time, closely related to the evolution of corrosion products. Between 0 and 840 h, the corrosion rate increased, except for a decrease between 336 and 504 h; this trend may be attributed to the disappearance of ZnO and an increase in the amount of Zn5(OH)8Cl2·H2O. Combined with the electrochemical results, it is speculated that the corrosion will accelerate with further exposure after 1848 h.
Corresponding Authors:
LIU Yuwei, associate professor, Tel: (024)23893544, E-mail: ywliu12s@imr.ac.cn; WANG Zhenyao, professor, Tel: (024)23893544, E-mail: zhywang@imr.ac.cn
Fig.1 Mass losses (a) and average corrosion rates (b) of Zn-2.0Al-1.5Mg coating in the simulated marine atmosphere at different time (V—corrosion rate, t—corrosion time)
Fig.2 XRD spectra of Zn-2.0Al-1.5Mg coating in the simulated marine atmosphere at different time
Fig.3 Macromorphologies of Zn-2.0Al-1.5Mg coating in the simulated marine atmosphere at different time (a) 168 h (b) 840 h (c) 1848 h
Fig.4 Surface SEM images of Zn-2.0Al-1.5Mg coating in the simulated marine atmosphere at different time (a) 168 h (b) 336 h (c) 504 h (d) 672 h (e) 840 h (f) 1848 h
Fig.5 Cross-sectional SEM images of Zn-2.0Al-1.5Mg coating in the simulated marine atmosphere at different time (a) 168 h (b) 336 h (c) 504 h (d) 672 h (e) 840 h (f) 1848 h
Fig.6 SEM image and corresponding EDS mappings of elements of Zn-2.0Al-1.5Mg coating in the simulated marine atmosphere at 1848 h
Fig.7 Potentiodynamic curves of Zn-2.0Al-1.5Mg coating in the simulated marine atmosphere at different time (E—potential, i—current density, SCE—saturated calomel electrode)
Fig.8 Corrosion current density (icorr) of Zn-2.0Al-1.5Mg coating obtains by Tafel extrapolation after different exposure periods
Fig.9 Nyquist (a) and Bode (b) diagrams of Zn-2.0Al-1.5Mg coating in the simulated marine atmosphere at different time (Z'—impedance real part, Z"—impedance imaginary part, Z—impedance)
Fig.10 Equivalent circuit of EIS (Rs—electrolyte resistance, Rr—rust layer resistance, Rct—charge transfer resistance, Qr—rust layer capacitance, Qdl—double layer capacitance, EIS—electrical impedance spectroscopy)
Time
h
Rs
Ω·cm2
Qr
Rr
Ω·cm2
Qdl
Rct
Ω·cm2
Chi-squared
Rp (= Rr + Rct)
Ω·cm2
yr
Ω-1·cm-2·S
nr
ydl
Ω-1·cm-2·S
ndl
0
4.33 × 101
1.30 × 10-5
6.56 × 10-1
7.20 × 103
6.26 × 10-5
9.71 × 10-1
6.44 × 103
9.29 × 10-3
1.36 × 104
168
5.05 × 101
1.48 × 10-5
6.81 × 10-1
8.26 × 102
2.05 × 10-3
5.23 × 10-1
8.94 × 102
5.87 × 10-3
1.72 × 103
336
8.53 × 10-4
2.02 × 10-5
4.65 × 10-1
2.31 × 102
6.74 × 10-7
9.60 × 10-1
2.87 × 104
2.39 × 10-2
2.89 × 104
504
2.51 × 101
1.07 × 10-5
6.95 × 10-1
2.84 × 103
1.19 × 10-4
6.36 × 10-1
5.52 × 103
7.11 × 10-3
8.36 × 103
672
4.21 × 10-3
3.03 × 10-5
4.58 × 10-1
7.89 × 102
2.09 × 10-7
1.00 × 100
6.33 × 103
6.47 × 10-3
7.12 × 103
840
3.07 × 101
1.77 × 10-5
5.50 × 10-1
5.52 × 103
4.13 × 10-4
8.78 × 10-1
4.59 × 103
4.34 × 10-2
1.01 × 104
1848
3.14 × 10-23
1.51 × 10-3
8.38 × 10-2
4.70 × 10-19
4.63 × 10-7
7.34 × 10-1
5.95 × 102
7.36 × 10-4
5.95 × 102
Table 1 Impedance parameters of Zn-2.0Al-1.5Mg coating after being fitted
Fig.11 Variations of 1/ Rp after different corrosion periods
Fig.12 Variations of the equilibrium concentration of chloride solution () of NaCl solution with different relative humidities[37]
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