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Citation: Pan, J.; Wang, Y.; Yang, L.;
Li, W.; Yang, D.; Dou, B.; Hu, C.; Lin,
X. Effect of UV Irradiation on the
Alternating Wet and Dry Corrosion
Behavior of Galvanized Steel in
Sodium Chloride Solution. Crystals
2023,13, 1195. https://doi.org/
10.3390/cryst13081195
Academic Editor: Petros Koutsoukos
Received: 30 June 2023
Revised: 24 July 2023
Accepted: 28 July 2023
Published: 1 August 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
crystals
Article
Effect of UV Irradiation on the Alternating Wet and Dry
Corrosion Behavior of Galvanized Steel in Sodium
Chloride Solution
Jilin Pan 1, Yuhao Wang 2, Liang Yang 2, Weiguang Li 1, Dan Yang 2, Baojie Dou 2 ,3 ,* , Chun Hu 2
and Xiuzhou Lin 2, 3,*
1Sichuan Chengdu Soil Environmental Materials Corrosion National Observation and Research Station,
Chengdu 610062, China; panjilin@126.com (J.P.)
2School of Materials Science and Engineering, Sichuan University of Science & Engineering,
Zigong 643000, China
3Material Corrosion and Protection Key Laboratory of Sichuan Province, Sichuan University of
Science & Engineering, Zigong 643000, China
*Correspondence: baojiedou@suse.edu.cn (B.D.); linxiuzhou@suse.edu.cn (X.L.)
Abstract:
In this paper, the corrosion performance of galvanized steel was investigated in a simulated
marine environment, under UV irradiation coupling with an alternating wet and dry cycle in a
NaCl solution. The surface morphology, composition, and corrosion performance of galvanized steel
before and after different alternating wet and dry corrosion under UV irradiation were investigated.
The results show that the corrosion current density gradually increases and the corrosion resistance
decreases as a function of the alternating wet and dry corrosion cycles. Meanwhile, UV irradiation
accelerates the increase in the corrosion current density and the decrease in the corrosion resistance.
In addition, the corrosion product ZnO shows a semiconductor property, and the photo-induced
electrons and holes produced under UV can participate in the corrosion reaction and promote
the formation of loose corrosion products Zn(OH)
2
, Zn
5
(OH)
8
Cl
2
, and Al
2
Cl
3
(OH)
5·
4H
2
O, thus
accelerating the corrosion of galvanized steel in the atmosphere environment.
Keywords:
marine environment; temperature; ultraviolet radiation; wet/dry alternation; hot-dip
galvanized steel
1. Introduction
The marine environment is rich in resources, and the exploitation of the sea has become
a hot topic. However, offshore equipment is extremely vulnerable to corrosion damage
due to the complexity of the marine environment. Apart from the chloride corrosion, the
equipment normally bears marine atmospheric corrosion under light radiation, splash, and
wave-induced alternating wet and dry action, as well as wind, rain, waves, and currents
of mechanical impact [
1
]. Galvanized steel is widely used in offshore vessels, oil rigs,
island equipment, sewage pipes, and cross-sea bridges due to its high strength and low
cost [
2
–
5
]. Therefore, the investigation of the effect of marine environmental factors on
galvanized steel plays an important role in evaluating the service life of equipment in the
marine environment.
Atmospheric corrosion is essentially an electrochemical corrosion process of materials
in the dry/wet cycle under a thin electrolyte layer, variation of temperature, relative
humidity (RH), rainfall, salt particles, and frequency of wet/dry cycling [
6
–
8
]. In the
last few decades, many efforts have declared that temperature and RH have a significant
effect on the corrosion performance of metal via variations in the physical and chemical
state of the atmosphere/metal interface layer [
9
–
12
]. The salt particles in the air form
droplets or electrolyte layers on the metal surface, formed when the temperature drops
and RH rises. However, the droplets or the thickness of electrolyte layers decrease when
Crystals 2023,13, 1195. https://doi.org/10.3390/cryst13081195 https://www.mdpi.com/journal/crystals
Crystals 2023,13, 1195 2 of 13
the temperature rises and the RH drops [
11
]. According to Fick’s law, variations in the
thickness of electrolyte layers affect the dissolution and diffusion of oxygen, resulting in
different corrosion kinetics of metals [
13
]. The investigation demonstrated the corrosion
rate under a thin electrolyte layer was much higher than that of the sample immersed in
the solution, because of the accelerated dissolution and diffusion of oxygen in the thin
electrolyte layer [
14
,
15
]. Meanwhile, the effect of temperature on the corrosion behavior of
low-alloy steel in the marine atmosphere shows that the increase in temperature not only
promotes the transport of aggressive ions Cl
−
and the formation of local corrosion but also
affects the solubility of oxygen gas in the thin electrolyte layer [12].
UV irradiation is also an indispensable factor affecting the corrosion of metal in the
atmosphere corrosion when the metals are exposed to sunlight; the 2% ultraviolet (UV) in
sunlight has a critical effect [
16
]. Many studies have confirmed that UV irradiation can affect
the corrosion process of metals in the atmosphere. Song et al. [
17
] found that UV irradiation
significantly increased the atmospheric corrosion rate and the positive optical voltage of
carbon steel when they investigated the influence of UV irradiation on the atmospheric
corrosion of Q235 carbon steel induced by NaCl. Liu et al. [
18
] also found the corrosion
rate of carbon steel increased with the increase in temperature from 30 to 60 centigrade in
the high-humidity tropical marine atmosphere. The effect of UV illumination on carbon
steel was closely related to environmental temperature; the higher the environmental
temperature, the greater the impact. A combination of electrochemical and spectroscopic
techniques was built to study the corrosion behavior of Cu-Sn-pb ternary bronze under
UV light; the results indicated that UV/visible illumination had a significant effect on the
corrosion behavior of bronze covered with oxide films, and that visible light irradiation
accelerated the dissolution rate of Cu and Pb and promoted the growth of corrosion layers
on the bronze surface [
16
]. The study of the photoelectric cathodic protection performance
of a coating system on stainless steel suggests that it has some corrosion protection after
exposure to UV light [
19
]. TiO
2
-coated steel revealed the corrosion rate increased due to the
active oxygen generated by photoelectrochemical reaction under UV light [
20
]. The effect
of UV irradiation on the corrosion of zinc was also investigated. Results show that UV
irradiation apparently affected the atmospheric corrosion morphology and corrosion rate of
zinc. Moreover, the corrosion products have a semiconductor property: the photo-induced
electrons and holes produced under UV light which can participate in the corrosion reaction
and affect the atmospheric corrosion rate of zinc [21–23].
Although the effect of UV on zinc and steel has been investigated, the investigation
of the UV effect on galvanized steel is still very limited. The chemical composition and
microstructures of galvanized steel are different from zinc and steel. The galvanization
process with a molten 0.1–1 at% Al-Zn bath results in an outer layer (Zn-Al coating) and an
intermetallic film in the form of Fe
2
Al
5
Znx (0 < x < 1). Therefore, the degradation behavior
of galvanized steel in wet/dry alternating corrosion environments with UV irradiation
might be different. For this purpose, a wet/dry alternating corrosion test system coupled
with UV irradiation was built to evaluate the degradation process of galvanized steel in a
simulated marine atmosphere environment. The effect of UV irradiation on the variation
of structure, composition, and corrosion electrochemical behavior of galvanized steel was
systematically studied.
2. Materials and Methods
2.1. Materials
A commercial hot-dip Q345B galvanized steel was supplied by Shanghai Casting
Enterprise Industrial Co., Ltd., Shanghai, China. The galvanized steel was cut into spec-
imens measuring 45 mm
×
35 mm
×
5 mm using a wire cutter, and then a 3 mm hole
was perforated in the middle of one side (as shown in Figure S1a). The specimens were
degreased with acetone, rinsed with deionized water, and dried in cold air.
Crystals 2023,13, 1195 3 of 13
2.2. Alternating Corrosion Test System
Based on the temperature, humidity, and heat test chamber, a dry and wet alternating
corrosion test system coupled with UV irradiation was built to simulate the dry and wet
alternating corrosion state of galvanized steel in the marine environment, as shown in
Figure 1. The corrosion medium was 3.5 wt.% NaCl solution, the test temperature was
45 ±1◦C
, the dry and wet ratio was 1:1 (1 cycle was 4 h, recorded as 1 T), the wet treatment
was full immersion, the distance between the UV and the sample was 600 mm, and the
dry treatment was placed under UV irradiation at a 250 mm distance. The UV irradiation
was provided by a 15 W quartz UV lamp, a UV spectral range of 200–330 nm, and the UV
irradiation intensity on the sample surface was 0.11 mV/cm−2.
Crystals 2023, 13, x FOR PEER REVIEW 3 of 13
perforated in the middle of one side (as shown in Figure S1a). The specimens were de-
greased with acetone, rinsed with deionized water, and dried in cold air.
2.2. Alternating Corrosion Test System
Based on the temperature, humidity, and heat test chamber, a dry and wet alternating
corrosion test system coupled with UV irradiation was built to simulate the dry and wet
alternating corrosion state of galvanized steel in the marine environment, as shown in
Figure 1. The corrosion medium was 3.5 wt.% NaCl solution, the test temperature was 45
± 1 °C, the dry and wet ratio was 1:1 (1 cycle was 4 h, recorded as 1 T), the wet treatment
was full immersion, the distance between the UV and the sample was 600 mm, and the
dry treatment was placed under UV irradiation at a 250 mm distance. The UV irradiation
was provided by a 15 W quar UV lamp, a UV spectral range of 200–330 nm, and the UV
irradiation intensity on the sample surface was 0.11 mV/cm−2.
Figure 1. Schematic diagram of the wet/dry alternating corrosion test system.
2.3. Characterization
Potentiodynamic polarization curves (PDP) and electrochemical impedance spec-
troscopy (EIS) were used to evaluate the corrosion performance of the galvanized steel by
an electrochemical workstation (CHI660D, Wuhan, China), with a conventional three-
electrode cell, platinum plate as the counter electrode, a saturated calomel electrode (SCE)
as the reference electrode, and the galvanized steel as the working electrode. Before the
testing, the corrosion test system was left to stand for 30 min, and the open circuit potential
(OCP) was recorded for 600 s. The PDP test ranged from −0.3 V vs. OCP to 1.5 V vs. SCE,
and the scanning rate was 1 mV/s. EIS test was performed at frequencies ranging from 100
kHz to 10 mHz by using a 10 mV amplitude sinusoidal voltage at OCP. The data were
fied using ZSimpWin3.5 software. The PDP and EIS measurements were carried out
three times to ensure the repeatability of the measurements.
The morphology of the galvanized steels before and after different dry and wet alter-
nating corrosion tests were characterized by scanning electron microscopy (SEM, S4800,
Hitachi, Tokyo, Japan) with an energy dispersive spectroscopy (EDS, X-MaxN, Oxford,
Figure 1. Schematic diagram of the wet/dry alternating corrosion test system.
2.3. Characterization
Potentiodynamic polarization curves (PDP) and electrochemical impedance spec-
troscopy (EIS) were used to evaluate the corrosion performance of the galvanized steel
by an electrochemical workstation (CHI660D, Wuhan, China), with a conventional three-
electrode cell, platinum plate as the counter electrode, a saturated calomel electrode (SCE)
as the reference electrode, and the galvanized steel as the working electrode. Before the
testing, the corrosion test system was left to stand for 30 min, and the open circuit potential
(OCP) was recorded for 600 s. The PDP test ranged from
−
0.3 V vs. OCP to 1.5 V vs. SCE,
and the scanning rate was 1 mV/s. EIS test was performed at frequencies ranging from
100 kHz to 10 mHz by using a 10 mV amplitude sinusoidal voltage at OCP. The data were
fitted using ZSimpWin3.5 software. The PDP and EIS measurements were carried out three
times to ensure the repeatability of the measurements.
The morphology of the galvanized steels before and after different dry and wet
alternating corrosion tests were characterized by scanning electron microscopy (SEM, S4800,
Hitachi, Tokyo, Japan) with an energy dispersive spectroscopy (EDS, X-MaxN, Oxford,
UK). The crystalline structure of the samples was investigated by X-ray diffraction (XRD,
D8 ADVANCE, BRUKER, Ettlingen, Germany) with Cu-Kαradiation (λ= 0.15406 nm).
Crystals 2023,13, 1195 4 of 13
3. Results
3.1. Electrochemical Behaviors
Potentiodynamic polarization measurement has been widely used to evaluate the
anti-corrosion performances of metal and coated metals [
24
,
25
]. Figure 2shows the po-
tentiodynamic polarization curves of galvanized steel after different cycles of alternating
wet/dry corrosion with and without UV irradiation. After different cycles of corrosion,
the corrosion potential of the specimens under UV irradiation was more negative and the
corrosion current density was also greater, indicating that the galvanized steel was much
easier to corrode under UV irradiation than that of the samples without UV irradiation.
Meanwhile, it is clearly revealed that the corrosion of galvanized steel under UV is much
more serious than that of galvanized steel without UV, as shown in the polarization curves
of the sample with and without UV in the same cycles of corrosion (Figure S2).
Crystals 2023, 13, x FOR PEER REVIEW 4 of 13
UK). The crystalline structure of the samples was investigated by X-ray diffraction (XRD,
D8 ADVANCE, BRUKER, Elingen, Germany) with Cu-Kα radiation (λ = 0.15406 nm).
3. Results
3.1. Electrochemical Behaviors
Potentiodynamic polarization measurement has been widely used to evaluate the
anti-corrosion performances of metal and coated metals [24,25]. Figure 2 shows the poten-
tiodynamic polarization curves of galvanized steel after different cycles of alternating
wet/dry corrosion with and without UV irradiation. After different cycles of corrosion, the
corrosion potential of the specimens under UV irradiation was more negative and the cor-
rosion current density was also greater, indicating that the galvanized steel was much
easier to corrode under UV irradiation than that of the samples without UV irradiation.
Meanwhile, it is clearly revealed that the corrosion of galvanized steel under UV is much
more serious than that of galvanized steel without UV, as shown in the polarization curves
of the sample with and without UV in the same cycles of corrosion (Figure S2).
Figure 2. Polarization curves of galvanized steel after different cycles of corrosion in 3.5% wt.% NaCl
solution (a) without UV; (b) with UV.
In order to compare the corrosion rate of galvanized steel, the corrosion potential
(E
corr
) and corrosion current density (i
corr
) were calculated from the polarization curves, as
shown in Figure 3. From Figure 3a, the corrosion potential of the galvanized steel without
UV decreased dramatically and reached a stable value with the increase in the cycles of
corrosion. The corrosion potential of the specimen under UV shows a trend of first de-
creasing and then gradually increasing with the increase in the cycles, reaching a mini-
mum value of −1.233 V at 5 T. The corrosion potential of the specimens under UV irradia-
tion is more negative than that without UV irradiation. One interpretation is, in the at-
mosphere environment, zinc can form ZnO, which has a typical semiconductor property
that can promote the formation of photoelectrons and migration to the surface of the gal-
vanized steel resulting in a shift of corrosion potential to a negative direction under UV.
Generally, the more negative the corrosion potential, the more prone the metal is to cor-
rode [26]. Therefore, galvanized steel is easier to corrode under UV irradiation than the
samples without UV. Figure 3b shows the corrosion current density of the specimen with
and without UV irradiation. As for the sample without UV, the corrosion current density
increased from 2.24 × 10
−7
A·cm
−2
to the maximum of 6.23 × 10
−6
A·cm
−2
after 10 T cycles of
corrosion; however, the corrosion current density of the specimen with UV irradiation
increased from 2.22 × 10
−7
A·cm
−2
to the maximum of 5.76 × 10
−5
A·cm
−2
after 10 T cycles of
corrosion and kept at approximately 5.00 × 10
−5
A·cm
−2
after 10 T cycles of corrosion. The
corrosion current density of the specimen with UV irradiation was larger than that with-
out UV irradiation. As described in a previous study, photoelectrons promote the
Figure 2.
Polarization curves of galvanized steel after different cycles of corrosion in 3.5% wt.% NaCl
solution (a) without UV; (b) with UV.
In order to compare the corrosion rate of galvanized steel, the corrosion potential
(E
corr
) and corrosion current density (i
corr
) were calculated from the polarization curves,
as shown in Figure 3. From Figure 3a, the corrosion potential of the galvanized steel
without UV decreased dramatically and reached a stable value with the increase in the
cycles of corrosion. The corrosion potential of the specimen under UV shows a trend of
first decreasing and then gradually increasing with the increase in the cycles, reaching
a minimum value of
−
1.233 V at 5 T. The corrosion potential of the specimens under
UV irradiation is more negative than that without UV irradiation. One interpretation is,
in the atmosphere environment, zinc can form ZnO, which has a typical semiconductor
property that can promote the formation of photoelectrons and migration to the surface of
the galvanized steel resulting in a shift of corrosion potential to a negative direction under
UV. Generally, the more negative the corrosion potential, the more prone the metal is to
corrode [
26
]. Therefore, galvanized steel is easier to corrode under UV irradiation than
the samples without UV. Figure 3b shows the corrosion current density of the specimen
with and without UV irradiation. As for the sample without UV, the corrosion current
density increased from 2.24
×
10
−7
A
·
cm
−2
to the maximum of 6.23
×
10
−6
A
·
cm
−2
after
10 T cycles of corrosion; however, the corrosion current density of the specimen with UV
irradiation increased from 2.22
×
10
−7
A
·
cm
−2
to the maximum of 5.76
×
10
−5
A
·
cm
−2
after 10 T cycles of corrosion and kept at approximately 5.00
×
10
−5
A
·
cm
−2
after 10 T
cycles of corrosion. The corrosion current density of the specimen with UV irradiation was
larger than that without UV irradiation. As described in a previous study, photoelectrons
promote the generation of active oxygen to increase the corrosion of galvanized steel,
resulting in a high corrosion current density under UV [
20
]. Figure S3 shows the Mott–
Schottky (M-S) of the galvanized steels after different cycles of corrosion. After 1 T cycle of
Crystals 2023,13, 1195 5 of 13
corrosion, galvanized steels with and without UV show a typical positive slope, indicating
that both surface samples are n-type semiconductors. The sample without UV shows a
similar semiconductor property from 1 T to 10 T, but the semiconductor property of the
sample gradually decreased after 16 T, which might be attributed to an increase in corrosion
resulting in zinc oxide conversion to zinc hydroxide. However, the semiconductor property
of the galvanized steels with UV declines or even disappears after 3 T cycle corrosion.
Under UV, ZnO on the surface of galvanized steel will prove that the formation of photo-
induced electrons and holes participate in the corrosion reaction and then promote the
formation of loose corrosion products, such as Zn(OH)
2
, Zn
5
(OH)
8
Cl
2
, Al
2
Cl
3
(OH)
5·
4H
2
O,
which accelerate the corrosion of galvanized steel. From the above analysis, UV irradiation
will accelerate the corrosion process of galvanized steel in a simulated marine atmosphere.
Crystals 2023, 13, x FOR PEER REVIEW 5 of 13
generation of active oxygen to increase the corrosion of galvanized steel, resulting in a
high corrosion current density under UV [20]. Figure S3 shows the Mo–Schoky (M-S)
of the galvanized steels after different cycles of corrosion. After 1 T cycle of corrosion,
galvanized steels with and without UV show a typical positive slope, indicating that both
surface samples are n-type semiconductors. The sample without UV shows a similar sem-
iconductor property from 1 T to 10 T, but the semiconductor property of the sample grad-
ually decreased after 16 T, which might be aributed to an increase in corrosion resulting
in zinc oxide conversion to zinc hydroxide. However, the semiconductor property of the
galvanized steels with UV declines or even disappears after 3 T cycle corrosion. Under
UV, ZnO on the surface of galvanized steel will prove that the formation of photo-induced
electrons and holes participate in the corrosion reaction and then promote the formation
of loose corrosion products, such as Zn(OH)
2
, Zn
5
(OH)
8
Cl
2
, Al
2
Cl
3
(OH)
5
·4H
2
O, which ac-
celerate the corrosion of galvanized steel. From the above analysis, UV irradiation will
accelerate the corrosion process of galvanized steel in a simulated marine atmosphere.
Figure 3. (a) Corrosion potential and (b) corrosion current density of galvanized steel after different
cycles of corrosion in 3.5% wt.% NaCl solution with and without UV, and the total corrosion time is
180 h.
EIS was employed to evaluate the corrosion resistance and analyze the anti-corrosion
mechanism of galvanized steel. Figures 4 and 5 show the EIS curves of galvanized steel
after different cycles of corrosion with and without UV. As shown in Figure 4a, the im-
pedance modulus of galvanized steel without UV decreased gradually with the increase
in cycles of immersion, and the capacitive arc gradually decreased, as shown in Figure 4b,
indicating the corrosion resistance of galvanized steel decreased as a function of the cor-
rosion cycles. Meanwhile, there are two-time constants appearing, which were aributed
to the zinc coating and the electrochemical corrosion reaction at the solution/zinc coating
interface. The EIS data can be demonstrated by a physical model shown in Figure 6. R
s
is
the solution resistance; R
c
and Q
c
are the coating resistance and capacitance, respectively;
and R
ct
and Q
dl
are the charge transfer resistance and capacitance, respectively [27]. From
Figure 4c, as for the sample with UV, the impedance modulus of galvanized steel de-
creased dramatically from 10
4
Ω·cm
2
at 1 T to 1.81 × 10
4
Ω·cm
2
at 3 T and decreased with
the increase in the cycles of immersion. The capacitive arc shifted to low frequency, sug-
gesting the composition of the corroded galvanized steel has a significant change due to
some special reaction occurring under UV.
Figure 3.
(
a
) Corrosion potential and (
b
) corrosion current density of galvanized steel after different
cycles of corrosion in 3.5% wt.% NaCl solution with and without UV, and the total corrosion time is
180 h.
EIS was employed to evaluate the corrosion resistance and analyze the anti-corrosion
mechanism of galvanized steel. Figures 4and 5show the EIS curves of galvanized steel after
different cycles of corrosion with and without UV. As shown in Figure 4a, the impedance
modulus of galvanized steel without UV decreased gradually with the increase in cycles of
immersion, and the capacitive arc gradually decreased, as shown in Figure 4b, indicating
the corrosion resistance of galvanized steel decreased as a function of the corrosion cycles.
Meanwhile, there are two-time constants appearing, which were attributed to the zinc
coating and the electrochemical corrosion reaction at the solution/zinc coating interface.
The EIS data can be demonstrated by a physical model shown in Figure 6.R
s
is the
solution resistance; R
c
and Q
c
are the coating resistance and capacitance, respectively; and
R
ct
and Q
dl
are the charge transfer resistance and capacitance, respectively [
27
]. From
Figure 4c, as for the sample with UV, the impedance modulus of galvanized steel decreased
dramatically from 10
4Ω·
cm
2
at 1 T to 1.81
×
10
4Ω·
cm
2
at 3 T and decreased with the
increase in the cycles of immersion. The capacitive arc shifted to low frequency, suggesting
the composition of the corroded galvanized steel has a significant change due to some
special reaction occurring under UV.
Crystals 2023,13, 1195 6 of 13
Crystals 2023, 13, x FOR PEER REVIEW 6 of 13
Figure 4. EIS curves of galvanized steel after different cycles of corrosion in 3.5% wt.% NaCl solution
(a,b) without UV and (c,d) with UV.
01x10
4
2x10
4
3x10
4
0
1x10
4
2x10
4
3x10
4
1T without UV
1T
with UV
fitting
−
Z'' (Ω·cm
2
)
Z' (Ω·cm
2
)
(b)
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
10
2
10
3
10
4
25T without UV
25T with UV
fitting
|Z|
(
Ω
⋅
cm
2
)
Frequency (Hz)
−
phase
(
°
)
(c)
-10
0
10
20
30
40
50
60
70
Figure 4.
EIS curves of galvanized steel after different cycles of corrosion in 3.5% wt.% NaCl solution
(a,b) without UV and (c,d) with UV.
Crystals 2023, 13, x FOR PEER REVIEW 6 of 13
Figure 4. EIS curves of galvanized steel after different cycles of corrosion in 3.5% wt.% NaCl solution
(a,b) without UV and (c,d) with UV.
01x10
4
2x10
4
3x10
4
0
1x10
4
2x10
4
3x10
4
1T without UV
1T
with UV
fitting
−
Z'' (Ω·cm
2
)
Z' (Ω·cm
2
)
(b)
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
10
2
10
3
10
4
25T without UV
25T with UV
fitting
|Z|
(
Ω
⋅
cm
2
)
Frequency (Hz)
−
phase
(
°
)
(c)
-10
0
10
20
30
40
50
60
70
Figure 5. Cont.
Crystals 2023,13, 1195 7 of 13
Crystals 2023, 13, x FOR PEER REVIEW 7 of 13
Figure 5. EIS curves of galvanized steel after different cycles of corrosion in 3.5% wt.% NaCl solution
without and with UV (a,b) 1 T, (c,d) 25 T, and (e,f) 46 T.
Figure 6. Fiing equivalent circuit model of electrochemical impedance spectroscopy.
Figure 5 shows a comparison of the EIS curves with and without UV for the same
corrosion cycle. The EIS curves with and without UV at cycle 1 T are very similar; how-
ever, with the extension of the corrosion cycle, the EIS curves change significantly and the
impedance modulus at 0.01 Hz decreases sharply with UV, indicating that UV exacerbates
the damage to the galvanized coating, leading to a sharp reduction in corrosion resistance.
Meanwhile, the phase constant in the plots of the galvanized steel shift to a low frequency,
suggesting the composition of the galvanized steel has a significant difference under UV.
This result should be aributed to the formation of ZnO with the semiconductor property,
which changes the reaction on galvanized steel under UV. The composition of the corro-
sion products on galvanized steel will be detected by XRD to further verify the reaction.
In order to analyze the anti-corrosion mechanism of galvanized steel, this study used
the equivalent circuit model (Figure 6) to fit the impedance data. Figure 7 shows the R
ct
and R
c
of galvanized steel after different cycles of corrosion in 3.5 wt.% NaCl solution
without and with UV. R
ct
, which is inversely proportional to corrosion rate, is a parameter
representing the resistance of the electron transfer across the metal surface. The higher R
ct
is, the more difficult the corrosion reaction, and hence the lower the corrosion rate [25]. As
shown in Figure 7a, the R
ct
values of galvanized steel without UV are higher than the sam-
ples with UV. The results indicate that UV accelerates the electron transfer on the surface
of galvanized steel, and then increases the corrosion rate of galvanized steel.
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
10
2
10
3
10
4
46T without UV
46T with UV
fitting
|Z|
(
Ω
⋅
cm
2
)
Frequency (Hz)
−
phase
(
°
)
(e)
-10
0
10
20
30
40
50
60
70
Figure 5.
EIS curves of galvanized steel after different cycles of corrosion in 3.5% wt.% NaCl solution
without and with UV (a,b)1T,(c,d) 25 T, and (e,f) 46 T.
Crystals 2023, 13, x FOR PEER REVIEW 7 of 13
Figure 5. EIS curves of galvanized steel after different cycles of corrosion in 3.5% wt.% NaCl solution
without and with UV (a,b) 1 T, (c,d) 25 T, and (e,f) 46 T.
Figure 6. Fiing equivalent circuit model of electrochemical impedance spectroscopy.
Figure 5 shows a comparison of the EIS curves with and without UV for the same
corrosion cycle. The EIS curves with and without UV at cycle 1 T are very similar; how-
ever, with the extension of the corrosion cycle, the EIS curves change significantly and the
impedance modulus at 0.01 Hz decreases sharply with UV, indicating that UV exacerbates
the damage to the galvanized coating, leading to a sharp reduction in corrosion resistance.
Meanwhile, the phase constant in the plots of the galvanized steel shift to a low frequency,
suggesting the composition of the galvanized steel has a significant difference under UV.
This result should be aributed to the formation of ZnO with the semiconductor property,
which changes the reaction on galvanized steel under UV. The composition of the corro-
sion products on galvanized steel will be detected by XRD to further verify the reaction.
In order to analyze the anti-corrosion mechanism of galvanized steel, this study used
the equivalent circuit model (Figure 6) to fit the impedance data. Figure 7 shows the R
ct
and R
c
of galvanized steel after different cycles of corrosion in 3.5 wt.% NaCl solution
without and with UV. R
ct
, which is inversely proportional to corrosion rate, is a parameter
representing the resistance of the electron transfer across the metal surface. The higher R
ct
is, the more difficult the corrosion reaction, and hence the lower the corrosion rate [25]. As
shown in Figure 7a, the R
ct
values of galvanized steel without UV are higher than the sam-
ples with UV. The results indicate that UV accelerates the electron transfer on the surface
of galvanized steel, and then increases the corrosion rate of galvanized steel.
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
10
5
10
2
10
3
10
4
46T without UV
46T with UV
fitting
|Z|
(
Ω
⋅
cm
2
)
Frequency (Hz)
−
phase
(
°
)
(e)
-10
0
10
20
30
40
50
60
70
Figure 6. Fitting equivalent circuit model of electrochemical impedance spectroscopy.
Figure 5shows a comparison of the EIS curves with and without UV for the same
corrosion cycle. The EIS curves with and without UV at cycle 1 T are very similar; however,
with the extension of the corrosion cycle, the EIS curves change significantly and the
impedance modulus at 0.01 Hz decreases sharply with UV, indicating that UV exacerbates
the damage to the galvanized coating, leading to a sharp reduction in corrosion resistance.
Meanwhile, the phase constant in the plots of the galvanized steel shift to a low frequency,
suggesting the composition of the galvanized steel has a significant difference under UV.
This result should be attributed to the formation of ZnO with the semiconductor property,
which changes the reaction on galvanized steel under UV. The composition of the corrosion
products on galvanized steel will be detected by XRD to further verify the reaction.
In order to analyze the anti-corrosion mechanism of galvanized steel, this study used
the equivalent circuit model (Figure 6) to fit the impedance data. Figure 7shows the R
ct
and R
c
of galvanized steel after different cycles of corrosion in 3.5 wt.% NaCl solution
without and with UV. R
ct
, which is inversely proportional to corrosion rate, is a parameter
representing the resistance of the electron transfer across the metal surface. The higher R
ct
is, the more difficult the corrosion reaction, and hence the lower the corrosion rate [
25
].
As shown in Figure 7a, the R
ct
values of galvanized steel without UV are higher than
the samples with UV. The results indicate that UV accelerates the electron transfer on the
surface of galvanized steel, and then increases the corrosion rate of galvanized steel.
R
c
can be used as the parameter to reflect the barrier property of zinc coating to
corrosive agents [
28
]. It can be found in Figure 7b that the R
c
value of galvanized steel
without UV is much higher than the sample with UV before 5 T corrosion cycle, and
the R
c
value decreased dramatically, indicating that the zinc coating has a good barrier
property to corrosive agents at the beginning, but this decreases due to the corrosion
reaction that occurred on the coating. Polarization and EIS data suggest that UV will affect
the corrosion reaction on galvanized steel and accelerate the corrosion rate. Using SEM and
XRD, we further analyze the structure and composition of galvanized steel in the different
corrosion cycles.
Crystals 2023,13, 1195 8 of 13
Crystals 2023, 13, x FOR PEER REVIEW 8 of 13
Figure 7. (a) Rct and (b) Rc of galvanized steel after different cycles of corrosion in 3.5% wt.% NaCl
solution without and with UV.
Rc can be used as the parameter to reflect the barrier property of zinc coating to cor-
rosive agents [28]. It can be found in Figure 7b that the Rc value of galvanized steel without
UV is much higher than the sample with UV before 5 T corrosion cycle, and the Rc value
decreased dramatically, indicating that the zinc coating has a good barrier property to
corrosive agents at the beginning, but this decreases due to the corrosion reaction that
occurred on the coating. Polarization and EIS data suggest that UV will affect the corro-
sion reaction on galvanized steel and accelerate the corrosion rate. Using SEM and XRD,
we further analyze the structure and composition of galvanized steel in the different cor-
rosion cycles.
3.2. Structure and Composition
The corrosion morphology of the galvanized steel after different cycles was further
analyzed using SEM and EDS; the results are shown in Figure 8 and Table 1. From Figure
8, the corrosion products on the surface of the galvanized steel with and without UV in-
creased with the increase in corrosion cycles. Meanwhile, the corrosion products on the
surface of the galvanized steel with UV was much more than that of the samples without
UV after 1 T, 10 T, and 25 T. For 46 T, the corrosion products on the surface of the galva-
nized steel with UV were looser than those of the sample without UV, but it is difficult to
distinguish the number of corrosion products. Therefore, EDS was performed on the gal-
vanized steel after the 46 T experiment. Most of the corrosion products on the sample
without UV were Zn and 12.87% O, indicating the corrosion products mainly might be
oxide and hydroxide compounds. However, 28.47% O was detected on the surface of the
galvanized steel with UV, suggesting much more zinc oxide and zinc hydroxide were
formed. Meanwhile, 12.89% Cl elements were also detected, indicating the corrosion of
galvanized steel with UV is more serious than that of the sample without UV, and new
corrosion products might form under UV. These results indicated that UV irradiation not
only accelerated the corrosion of galvanized steel, but also changed the corrosion process
of galvanized steel, and the composition of corrosion products changed significantly. XRD
was used to further analyze the structure of corrosion products to illustrate the degrada-
tion mechanism of galvanized steel under UV.
5 1015202530354045
0.0
5.0x10
3
1.0x10
4
1.5x10
4
2.0x10
4
without UV
with UV
Cycles
R
ct
(
Ω⋅
cm
2
)
(a)
5 1015202530354045
0
1x10
4
2x10
4
3x10
4
4x10
4
5x10
4
6x10
4
without UV
with UV
Cycles
R
c
(
Ω⋅
cm
2
)
(b)
Figure 7.
(
a
)R
ct
and (
b
)R
c
of galvanized steel after different cycles of corrosion in 3.5% wt.% NaCl
solution without and with UV.
3.2. Structure and Composition
The corrosion morphology of the galvanized steel after different cycles was further
analyzed using SEM and EDS; the results are shown in Figure 8and Table 1. From Figure 8,
the corrosion products on the surface of the galvanized steel with and without UV increased
with the increase in corrosion cycles. Meanwhile, the corrosion products on the surface of
the galvanized steel with UV was much more than that of the samples without UV after
1 T, 10 T, and 25 T. For 46 T, the corrosion products on the surface of the galvanized steel
with UV were looser than those of the sample without UV, but it is difficult to distinguish
the number of corrosion products. Therefore, EDS was performed on the galvanized steel
after the 46 T experiment. Most of the corrosion products on the sample without UV were
Zn and 12.87% O, indicating the corrosion products mainly might be oxide and hydroxide
compounds. However, 28.47% O was detected on the surface of the galvanized steel with
UV, suggesting much more zinc oxide and zinc hydroxide were formed. Meanwhile, 12.89%
Cl elements were also detected, indicating the corrosion of galvanized steel with UV is
more serious than that of the sample without UV, and new corrosion products might form
under UV. These results indicated that UV irradiation not only accelerated the corrosion
of galvanized steel, but also changed the corrosion process of galvanized steel, and the
composition of corrosion products changed significantly. XRD was used to further analyze
the structure of corrosion products to illustrate the degradation mechanism of galvanized
steel under UV.
Crystals 2023, 13, x FOR PEER REVIEW 9 of 13
Figure 8. SEM of galvanized steel after immersion in 3.5% wt.% NaCl solution without and with UV
for 1 T, 10 T, 25 T, and 46 T.
Tab le 1. Results of EDS analysis of galvanized steel after immersion in 3.5% wt.% NaCl solution
with and without UV for 46 T.
Elements (W%) Zn O Cl Al Other
Without UV 86.52 12.87 0.13 0.45 0.03
With UV 58.43 28.47 12.89 0.04 0.17
The composition of the corrosion products on galvanized steel was characterized us-
ing XRD. As shown in Figure 9, as for the galvanized steel without UV, there was only a
few ZnO formed on the galvanized steel after 1 T alternating wet/dry corrosion. The peak
of ZnO increased slightly as a function of the immersion corrosion cycle. In contrast, the
corrosion products of galvanized steel with UV showed significant diversity. Apart from
the ZnO, Zn
5
(OH)
8
Cl
2
H
2
O (Simonkolleite) appeared at approximately 10° after 1 T of cor-
rosion, indicating a new reaction occurred under UV [29]. Meanwhile, the peak of ZnO
was higher than that of the sample without UV, declaring that UV accelerates the corro-
sion of the zinc coating. After 25 T corrosion cycles, FeOCl, AlOCl, and Al
2
Cl
3
(OH)
5
·4H
2
O
appeared, indicating that the aggressive agents penetrated the zinc coating to the Fe
2
Al
5
intermetallic layer, even to the matrix [29]. SEM and XRD results further verify that UV
irradiation can change the corrosion reaction on galvanized steel.
0 102030405060708090
♣
♣
♦
Intensity (a.u.)
2θ (degree)
10T with UV
10T without UV
♣
♣
♣
♦♦
♣ Zn
♣ ZnO
♦ Zn5(OH)8Cl2H2O
♣
(b)
♦
♦
♣
♣
♦♣♣
♦
♦
♣
♣
Figure 8.
SEM of galvanized steel after immersion in 3.5% wt.% NaCl solution without and with UV
for 1 T, 10 T, 25 T, and 46 T.
Crystals 2023,13, 1195 9 of 13
Table 1.
Results of EDS analysis of galvanized steel after immersion in 3.5% wt.% NaCl solution with
and without UV for 46 T.
Elements (W%) Zn O Cl Al Other
Without UV 86.52 12.87 0.13 0.45 0.03
With UV 58.43 28.47 12.89 0.04 0.17
The composition of the corrosion products on galvanized steel was characterized
using XRD. As shown in Figure 9, as for the galvanized steel without UV, there was only
a few ZnO formed on the galvanized steel after 1 T alternating wet/dry corrosion. The
peak of ZnO increased slightly as a function of the immersion corrosion cycle. In contrast,
the corrosion products of galvanized steel with UV showed significant diversity. Apart
from the ZnO, Zn
5
(OH)
8
Cl
2
H
2
O (Simonkolleite) appeared at approximately 10
◦
after 1 T of
corrosion, indicating a new reaction occurred under UV [
29
]. Meanwhile, the peak of ZnO
was higher than that of the sample without UV, declaring that UV accelerates the corrosion
of the zinc coating. After 25 T corrosion cycles, FeOCl, AlOCl, and Al
2
Cl
3
(OH)
5·
4H
2
O
appeared, indicating that the aggressive agents penetrated the zinc coating to the Fe
2
Al
5
intermetallic layer, even to the matrix [
29
]. SEM and XRD results further verify that UV
irradiation can change the corrosion reaction on galvanized steel.
Crystals 2023, 13, x FOR PEER REVIEW 9 of 13
Figure 8. SEM of galvanized steel after immersion in 3.5% wt.% NaCl solution without and with UV
for 1 T, 10 T, 25 T, and 46 T.
Tabl e 1. Results of EDS analysis of galvanized steel after immersion in 3.5% wt.% NaCl solution
with and without UV for 46 T.
Elements (W%) Zn O Cl Al Other
Without UV 86.52 12.87 0.13 0.45 0.03
With UV 58.43 28.47 12.89 0.04 0.17
The composition of the corrosion products on galvanized steel was characterized us-
ing XRD. As shown in Figure 9, as for the galvanized steel without UV, there was only a
few ZnO formed on the galvanized steel after 1 T alternating wet/dry corrosion. The peak
of ZnO increased slightly as a function of the immersion corrosion cycle. In contrast, the
corrosion products of galvanized steel with UV showed significant diversity. Apart from
the ZnO, Zn
5
(OH)
8
Cl
2
H
2
O (Simonkolleite) appeared at approximately 10° after 1 T of cor-
rosion, indicating a new reaction occurred under UV [29]. Meanwhile, the peak of ZnO
was higher than that of the sample without UV, declaring that UV accelerates the corro-
sion of the zinc coating. After 25 T corrosion cycles, FeOCl, AlOCl, and Al
2
Cl
3
(OH)
5
·4H
2
O
appeared, indicating that the aggressive agents penetrated the zinc coating to the Fe
2
Al
5
intermetallic layer, even to the matrix [29]. SEM and XRD results further verify that UV
irradiation can change the corrosion reaction on galvanized steel.
0 102030405060708090
♣
♣
♦
Intensity (a.u.)
2θ (degree)
10T with UV
10T without UV
♣
♣
♣
♦♦
♣ Zn
♣ ZnO
♦ Zn5(OH)8Cl2H2O
♣
(b)
♦
♦
♣
♣
♦♣♣
♦
♦
♣
♣
Crystals 2023, 13, x FOR PEER REVIEW 10 of 13
Figure 9. XRD spectrum of galvanized steel after immersion in 3.5% wt.% NaCl solution with and
without UV (a) 1 T; (b) 10 T; (c) 25 T; and (d) 46 T.
3.3. Corrosion Mechanism
Based on the above results, the corrosion mechanism diagrams of galvanized steel in
a simulated marine environment, under UV irradiation coupling with an alternating wet
and dry in a NaCl solution, are proposed and presented in Figure 10. According to our
previous study, the galvanization process with a molten 0.1–1 at% Al-Zn bath resulted in
an outer layer (Zn-Al coating), and an intermetallic film (20–50 nm) formed between the
zinc coating and the steel substrate, presumably in the form of Fe2Al5 Znx (0 < x < 1), which
can inhibit the formation of Fe-Zn intermetallic phase or “outbursts” that are detrimental
to the mechanical properties of the final coating [30].
Figure 10. Corrosion mechanism of galvanized steel in an alternating wet and dry cycle NaCl solu-
tion (a) without UV; (b) with UV.
As shown in Figure 10a, in a neutral NaCl solution, the Zn-rich phase is more active
than the Al-rich phase; consequently, Zn2+ ions formed in an anodic reaction (in Equation
(1)), whilst a cathodic reaction (O2 reduction as shown in Equation (2)) occurred on the Al-
rich phase. Zn2+ ions reacted with the OH− from the cathodic reaction resulting in Zn(OH)2.
The Zn(OH)2 will transfer to ZnO because of the unstable of Zn(OH)2 (Equation (3)).
0 102030405060708090
Δ
♦
♥
♣
♣
25T with UV
25T without UV
♣
♣
Zn
♣ ZnO
♦ Zn
5
(OH)
8
Cl
2
H
2
O
Δ FeOCl
♥ Al
2
Cl
3
(OH)
5
4H
2
O
♣
♣
♣
♣
♣
♣
♣
♣
♣
♣
♣
♣
♦
♥ ♦♦♦
♥
♦♣
Δ
Δ
(c)
Intensity (a.u.)
2θ (degree)
0 102030405060708090
Δ
♦
♣
♣
46T with UV
46T without UV
♣
♣
♣
♣ Zn
♣ ZnO
♦ Zn
5
(OH)
8
Cl
2
H
2
O
Δ FeOCl
♦ AlOCl
♣
♣
♣
♣
♣
♦♦
♦♦♦
♦
♣
Δ
♣
♦Δ
♣♣
♣
♦
2θ (degree)
Intensity (a.u.)
(d)
Figure 9.
XRD spectrum of galvanized steel after immersion in 3.5% wt.% NaCl solution with and
without UV (a)1T;(b) 10 T; (c) 25 T; and (d) 46 T.
3.3. Corrosion Mechanism
Based on the above results, the corrosion mechanism diagrams of galvanized steel in
a simulated marine environment, under UV irradiation coupling with an alternating wet
and dry in a NaCl solution, are proposed and presented in Figure 10. According to our
Crystals 2023,13, 1195 10 of 13
previous study, the galvanization process with a molten 0.1–1 at% Al-Zn bath resulted in an
outer layer (Zn-Al coating), and an intermetallic film (20–50 nm) formed between the zinc
coating and the steel substrate, presumably in the form of Fe
2
Al
5
Zn
x
(0 < x < 1), which can
inhibit the formation of Fe-Zn intermetallic phase or “outbursts” that are detrimental to the
mechanical properties of the final coating [30].
Crystals 2023, 13, x FOR PEER REVIEW 10 of 13
Figure 9. XRD spectrum of galvanized steel after immersion in 3.5% wt.% NaCl solution with and
without UV (a) 1 T; (b) 10 T; (c) 25 T; and (d) 46 T.
3.3. Corrosion Mechanism
Based on the above results, the corrosion mechanism diagrams of galvanized steel in
a simulated marine environment, under UV irradiation coupling with an alternating wet
and dry in a NaCl solution, are proposed and presented in Figure 10. According to our
previous study, the galvanization process with a molten 0.1–1 at% Al-Zn bath resulted in
an outer layer (Zn-Al coating), and an intermetallic film (20–50 nm) formed between the
zinc coating and the steel substrate, presumably in the form of Fe2Al5 Znx (0 < x < 1), which
can inhibit the formation of Fe-Zn intermetallic phase or “outbursts” that are detrimental
to the mechanical properties of the final coating [30].
Figure 10. Corrosion mechanism of galvanized steel in an alternating wet and dry cycle NaCl solu-
tion (a) without UV; (b) with UV.
As shown in Figure 10a, in a neutral NaCl solution, the Zn-rich phase is more active
than the Al-rich phase; consequently, Zn2+ ions formed in an anodic reaction (in Equation
(1)), whilst a cathodic reaction (O2 reduction as shown in Equation (2)) occurred on the Al-
rich phase. Zn2+ ions reacted with the OH− from the cathodic reaction resulting in Zn(OH)2.
The Zn(OH)2 will transfer to ZnO because of the unstable of Zn(OH)2 (Equation (3)).
0 102030405060708090
Δ
♦
♥
♣
♣
25T with UV
25T without UV
♣
♣
Zn
♣ ZnO
♦ Zn
5
(OH)
8
Cl
2
H
2
O
Δ FeOCl
♥ Al
2
Cl
3
(OH)
5
4H
2
O
♣
♣
♣
♣
♣
♣
♣
♣
♣
♣
♣
♣
♦
♥ ♦♦♦
♥
♦♣
Δ
Δ
(c)
Intensity (a.u.)
2θ (degree)
0 102030405060708090
Δ
♦
♣
♣
46T with UV
46T without UV
♣
♣
♣
♣ Zn
♣ ZnO
♦ Zn
5
(OH)
8
Cl
2
H
2
O
Δ FeOCl
♦ AlOCl
♣
♣
♣
♣
♣
♦♦
♦♦♦
♦
♣
Δ
♣
♦Δ
♣♣
♣
♦
2θ (degree)
Intensity (a.u.)
(d)
Figure 10.
Corrosion mechanism of galvanized steel in an alternating wet and dry cycle NaCl solution
(a) without UV; (b) with UV.
As shown in Figure 10a, in a neutral NaCl solution, the Zn-rich phase is more ac-
tive than the Al-rich phase; consequently, Zn
2+
ions formed in an anodic reaction (in
Equation (1)
), whilst a cathodic reaction (O
2
reduction as shown in Equation (2)) occurred
on the Al-rich phase. Zn
2+
ions reacted with the OH
−
from the cathodic reaction result-
ing in Zn(OH)
2
. The Zn(OH)
2
will transfer to ZnO because of the unstable of Zn(OH)
2
(
Equation (3)
). Meanwhile, Al will dissolve to Al(OH)
4−
(Equation (4)) because of the
increase in OH−from O2reduction [29,31].
Zn →Zn2+ + 2e−(1)
O2+ 2H2O + 4e−→4OH−(2)
Zn2+ + 2OH−→Zn(OH)2(or ZnO + H2O) (3)
Al + 4OH−→Al(OH)4
−+ 3e−(4)
However, under UV, the corrosion that occurs on the surface of galvanized steel is
more complex and the corrosion products are numerous. According to the report, apart
from ZnO, other compounds of zinc were produced on the surface of galvanized steel and
the corrosion rates accelerated because of the photo-induced electrons and holes produced
under UV [
21
]. This phenomenon was also detected in this study (Figure 9); Zn
5
(OH)
8
Cl
2
was detected on the surface of galvanized steel under UV (Equation (5)):
5Zn2+ + 8OH−+ 2Cl−→Zn5(OH)8Cl2(5)
Crystals 2023,13, 1195 11 of 13
With the enhancement of the corrosion reaction on the sample, Cl
−
aggressively
reaches the Fe
2
Al
5
intermetallic film, and the intermetallic layer reacts with Cl
−
to form
Fe
2+
and Al
3+
, and then transfers to FeOCl and Al
2
Cl
3
(OH)
5·
4H
2
O or AlOCl under the
UV catalytic. When the Cl
−
reached the Fe matrix, the Zn-Al coating gradually lost its
protective ability.
Fe →Fe2+ + 2e−(6)
Al →Al3+ + 3e−(7)
2Al3+ + 5OH−+ 3Cl−+ 4H2O→Al2Cl3(OH)5·4H2O (8)
2Fe2+ + O2+ 2Cl−→2FeOCl (9)
2Al2+ + O2+ 2Cl−→2AlOCl (10)
By the above analysis, under UV irradiation, the corrosion process of galvanized steel
can be divided into three stages: (I) Zn-Al coating reacts with Cl
−
aggressive agents, H
2
O
and O
2,
to form ZnO or Zn(OH), Zn
5
(OH)
8
Cl
2
; (II) Fe
2
Al
5
intermetallic layer reacts to
form FeOCl and Al
2
Cl
3
(OH)
5·
4H
2
O or AlOCl after Cl
−
aggressive agents penetrate the
Zn-Al coating; (III) Cl
−
aggressive agents reach the steel substrate and start to dissolve.
UV has an important role in atmosphere corrosion, which can accelerate the destruction
of the galvanized layer on the surface of Q345B, accelerating the corrosion medium into
the substrate, resulting in the destruction of the galvanized layer and a certain degree of
corrosion of Q345B.
4. Conclusions
In this work, a wet/dry alternating corrosion test system coupled with UV irradiation
was built to evaluate the degradation process of galvanized steel in a simulated marine
atmosphere environment.
(1)
The polarization and impedance results show the corrosion of galvanized steel in-
creased as a function of the accelerating wet/dry corrosion cycles. The corrosion of
galvanized steel under UV is more serious than that of galvanized steel without UV
in the same corrosion cycles, which is explained by the formation of semiconductor
ZnO to accelerate the corrosion process under UV.
(2)
In the NaCl solution, the Zn-Al coating reacts to form ZnO and Al(OH)
4−
. The
corrosion reaction gradually occurs, and corrosion products increase as a function of
accelerating wet/dry corrosion cycles without UV irradiation. However, under UV
irradiation, ZnO in galvanized corrosion products has semiconductor properties and
the photovoltaic effect, promoting the formation of loose corrosion products Zn(OH)
2
,
Zn
5
(OH)
8
Cl
2
, and Al
2
Cl
3
(OH)
5·
4H
2
O, thus accelerating the corrosion of galvanized
steel.
Supplementary Materials:
The following supporting information can be downloaded at:
https://www.mdpi.com/article/10.3390/cryst13081195/s1, Figure S1: (a) Photo of the galvanized
steel sample; (b) Photo of the wet/dry alternating corrosion test system; Figure S2: Polarization curves
of galvanized steel with and without UV after different wet and dry corrosion cycles of corrosion in
3.5% wt.% NaCl solution (a) 1 T; (b) 3 T; (c) 5 T; (d) 10 T; (e) 16 T; (f) 25 T; (g) 36 T; (h) 46 T; Figure S3:
Mott-Schottky plots of galvanized steel with and without UV after different wet and dry corrosion
cycles of corrosion in 3.5% wt.% NaCl solution (a) 1 T; (b) 3 T; (c) 5 T; (d) 10 T; (e) 16 T; (f) 25 T; (g) 36 T;
(h) 46 T.
Crystals 2023,13, 1195 12 of 13
Author Contributions:
Conceptualization, J.P. and X.L.; methodology, L.Y. and Y.W.; software,
D.Y.; validation, W.L., D.Y. and C.H.; formal analysis, Y.W., B.D. and X.L.; investigation, L.Y. and
Y.W.; resources, B.D. and X.L.; data curation, B.D.; writing—original draft preparation, J.P. and
Y.W.; writing—review and editing, B.D. and X.L.; visualization, B.D.; supervision, X.L.; project
administration, B.D. and X.L.; funding acquisition, J.P., B.D. and X.L. All authors have read and
agreed to the published version of the manuscript.
Funding:
This work was supported by the National Natural Science Foundation of China (No.
51901146), Key Research and Development Projects of Sichuan Provincial (2021YFG0246), and Na-
tional Science and Technology Resources Investigation Program of China (Grant No. 2021FY100603).
Data Availability Statement:
The raw/processed data required to reproduce these findings can be
obtained through contacting the corresponding authors.
Conflicts of Interest: The authors declare no conflict of interest.
References
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Gao, J.; Hu, W.; Wang, R.; Li, X. Study on a multifactor coupling accelerated test method for anticorrosive coatings in marine
atmospheric environments. Polym. Test. 2021,100, 107259. [CrossRef]
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