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Article

Research on Dynamic Marine Atmospheric Corrosion Behavior of AZ31 Magnesium Alloy

by
Ying Wang
1,2,
Weichen Xu
1,2,
Xiutong Wang
1,2,
Quantong Jiang
1,2,
Yantao Li
1,2,
Yanliang Huang
1,2 and
Lihui Yang
1,2,*
1
Key Laboratory of Marine Environmental Corrosion and Bio-Fouling, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
2
Open Studio for Marine Corrosion and Protection, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266237, China
*
Author to whom correspondence should be addressed.
Metals 2022, 12(11), 1886; https://doi.org/10.3390/met12111886
Submission received: 12 October 2022 / Revised: 31 October 2022 / Accepted: 2 November 2022 / Published: 4 November 2022
(This article belongs to the Special Issue Preparation and Processing Technology of Advanced Magnesium Alloys)
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Abstract

:
The dynamic marine atmospheric corrosion behavior of AZ31 magnesium alloy was investigated in situ exposed on the deck of marine scientific research vessel for 1 year. The marine scientific research vessel carried out five voyages from the coast of China to the western Pacific Ocean, while the navigation track and environmental data were collected and analyzed. The corrosion rate and characteristics were evaluated by using weight loss tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. The corrosion rate from weight loss values was 52.23 μm∙y−1 after exposure for 1 year, which was several times higher than that of the static field exposure test in marine atmospheric environment of other reported literature. The main corrosion products were Mg5(CO3)4(OH)2·4H2O, MgCO3·3H2O and Mg2(OH)3Cl·4H2O. The corrosion was initiated from pitting corrosion and evolved into general corrosion gradually. The serious corrosion maybe due to the harsh corrosive environment with alternating changes in temperature and relative humidity caused by multiple longitude and latitude changes, and particularly high deposition rate of chloride during voyage, which was nearly twenty times that on the coast of China. This study provides effective data for the application of magnesium alloy in shipboard aircraft and other equipment, and provides a reference for indoor simulation experiments.

1. Introduction

As the lightest structural metals, magnesium alloys possess good machinability and high thermal conductivity, which have been widely used in marine equipment, shipboard aircraft, and other fields [1,2,3,4,5,6]. However, magnesium alloys are susceptible to corrosion due to the high chemical and electrochemical activity, which limits its application, especially in corrosive atmospheric environments [7,8].
Many researchers have conducted a series of studies about the influence of environmental factors on magnesium alloys. Esmaily et al. [9] reported that atmospheric corrosion of Mg–Al alloy AM50 was strongly reduced with decreasing temperature. The research of Merino et al. [10] showed that corrosion attack of Mg and Mg–Al alloy under the salt fog test increased with increasing temperature. The relative humidity also affects the corrosion behavior of magnesium alloys significantly. The study of Lebozec et al. [11] showed that when the relative humidity increased from 75% to 95%, the corrosion rate of Mg–Al alloy AZ91D and AM50 increased accordingly. In addition to temperature and relative humidity, aggressive ions such as Cl−, accelerate the atmospheric corrosion process of magnesium alloys obviously, especially in high relative humidity environment. Jönsson et al. [12] studied the corrosion behavior of Mg–Al alloy AZ91D, which was exposed in humid air at 95% relative humidity (RH) with deposition of 70 μg/cm2 NaCl. The results showed that the corrosion attack starts at locations with higher NaCl contents. However, most research on the atmospheric corrosion process of magnesium alloys has performed tests in simulated environment [13,14,15,16,17,18,19] that cannot fully simulate the synergistic effect of real atmospheric environmental factors.
Recently, some further studies on atmospheric corrosion of magnesium alloys have been conducted on the basis of exposure tests in actual atmospheric environments. Jönsson et al. [20] reported that the corrosion rate of AZ91D exposed in the marine atmospheric environment of 3–5 m from Atlantic shore Brest France was 4.2 μm/a, exposed in the rural atmospheric environment of 100 km west of Stockholm was 2.2 μm/a, and urban atmospheric environments of Stockholm was 1.8 μm/a. Liao et al. [21] found that the corrosion rate of AZ31B in the marine atmospheric environment (Shimizu, Japan) was much higher than that in urban areas (Osaka, Japan). These results indicated that magnesium alloys suffered more serious corrosion in the marine atmospheric environment.
There have been few studies of the corrosion behavior of magnesium alloys in dynamic marine atmospheric environment, and current research on atmospheric corrosion behavior of magnesium alloys were conducted with static field exposure test at permanent location, such as the coast or island. In contrast to static field exposure tests, marine equipment in application is mostly mobile in the ocean, and the harsh corrosive environment with high relative humidity, high deposition rate of chloride [22] and alternating changes in temperature and relative humidity caused by multiple longitude and latitude changes may affect the corrosion behavior of magnesium alloys. The corrosion behavior of magnesium alloy in the dynamic marine atmosphere environment of real ocean voyage has not been widely reported, and the dynamic marine atmospheric exposure experiment is a necessary complement to static exposure experiments and simulated atmospheric environments, and can provide effective data for the corrosion behavior research of magnesium alloys in the marine atmospheric environment.
In this work, the corrosion behavior of AZ31 magnesium alloys in the dynamic marine atmosphere during ocean voyage was studied through the atmospheric exposure experiment on the deck of Research Vessel KEXUE. In addition, the corrosion characteristics were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. This study provides effective data for the application of magnesium alloy in shipboard aircraft and other equipment.

2. Materials and Methods

2.1. Material Preparation

The specimen in this work was as-extruded AZ31 magnesium alloy, the extrusion temperature was 350 °C. The chemical composition was as listed in Table 1. Specimens for field exposure test were all 100 mm × 50 mm × 3 mm. All specimens were ground with 800 grit emery papers, degreased with acetone, dried with flowing air and weighed. Four replicate metal samples were retrieved from the exposure site after 1, 3, 6 and 12 months. Three replicas were used to determine weight loss of specimens, and the other one was used to analyze the corrosion morphology, corrosion products.

2.2. Dynamic Natural Environment Exposure Test

The dynamic natural environment exposure test was carried out on the open deck of the Research Vessel KEXUE of the Institute of Oceanology, Chinese Academy of Sciences (Qingdao, China). As is shown in Figure 1a,b, the specimens of AZ31 magnesium alloy (as circled in red in Figure 1) were installed on the test rack with the angle of 45° horizontal to the deck. The cumulative atmospheric exposure time was 1 year. As is shown in Figure 1c, the navigation range was around China offshore (Qingdao, China) to the western Pacific.

2.3. Determination Method for Natural Environmental Factors

The temperature, relative humidity (RH) and wind speed were measured by the automatic weather station of Research Vessel KEXUE.
The determination method for the deposition rate of chloride at the exposure test site described below was based on GJB 8894.1-2017. A double-layer medical gauze used to collect chloride ions with an area of 100 cm2 was exposed at the exposure site for 7 days. Three parallel specimens of the gauze were collected each time. The collected gauze was fully cleaned, and the chloride ions concentration in the solution was measured.

2.4. Corrosion Rate Measurements

The corrosion rate was measured by weight loss measurements, and the corrosion products were removed by immersion in 200 g/L CrO3 + 10 g/L AgNO3 for 10 min at 25 °C, and then the samples were rinsed with distilled water and alcohol, dried and weighted.
The weight loss of AZ31 magnesium after exposure for different periods was calculated by using the following equation:
C = (w0 − w1)/S
where C is the weight loss of the metal due to corrosion, w0 is the original weight, w1 is the final weighted, S is the surface area.
The corrosion rate of AZ31 magnesium after exposure for different periods was calculated by using the following equation:
v = (w0 − w1)/(S·T·ρ)
where v is the corrosion rates of the metal due to corrosion, w0 is the original weight, w1 is the final weight, S is the surface area, T is the experimental time, ρ is the density.

2.5. Corrosion Products Analysis

Corrosion morphology of corrosion products was observed by scanning electron microscope (Regulus 8100, HITACHI, Tokyo, Japan) and Laser confocal scanning microscopy (OLS5000, Olympus, Tokyo, Japan). Phase composition was analyzed by X-ray diffraction (Ultime IV, Rigaku, Tokyo, Japan), and the element types and valence states of the corrosion products were analyzed by X-ray photoelectron spectroscopy (ESCALAB 250Xi, Thermo, Waltham, MA, USA).

2.6. Electrochemical Measurements

Electrochemical measurements were performed with a electrochemical workstation (PARSTAT 4000, Princeton Applied Research, Oak Ridge, TN, USA) in 3.5% NaCl solution in a conventional three-electrode cell, where the magnesium alloy specimen was the working electrode, saturated calomel electrode was the reference electrode and Pt foil was the counter electrode. The test system was always in a steady state with no stirring. The working electrode surface was covered with silicone rubber to leave an exposed area of 1.0 cm2. Prior to testing, the working electrode was stabilized for about 30 min with open circuit potential measurement. Potentiodynamic polarization test was measured in the range of ±0.5 V vs. the open circuit potential with the scan rate 1 mV/s. All the measurements were performed at ambient temperature (25 ± 2 °C) and repeated at least three times to maintain the reproducibility.

3. Results

3.1. The Environment of Field Exposure

The exposure environment of the specimens is the deck of the Research Vessel KEXUE, which is quite different from the static field exposure test at permanent locations such as the coast or islands reported in other studies.
Firstly, the duration of navigation in the western Pacific Ocean accounted for most of exposure time. During the exposure period, the proportion of the time of dynamic state (navigation in western Pacific Ocean) was 58.1%, and static state (stopping at Qingdao) was 41.9%. The ratio of the dynamic state and static state of exposure was about 3:2, which is more consistent with the real application environment of magnesium alloys in marine equipment.
Secondly, the Research Vessel KEXUE went to the western Pacific Ocean to carry out a series of scientific investigations, and traveled between Qingdao and the western Pacific five times during the exposure period, experiencing large changes in temperature during four of them. During the exposure period, the average temperature in western Pacific Ocean was about 29 °C, the average relative humidity was about 78%. In Qingdao, the annual average temperature was 14.4 °C, and the lowest temperature was below 0 °C in winter. The annual average relative humidity was 75.0%. Figure 2 shows the daily average temperature and relative humidity at exposure test site during voyage. As is shown in Figure 2, after exposure for 3 months, the Research Vessel KEXUE returned to Qingdao from the western Pacific Ocean with a hot and humid environment, while at that time it was winter in Qingdao, so the temperature and relative humidity of the exposure site changed significantly. A few days later, the Research Vessel KEXUE went to the western Pacific, and the temperature and relative humidity rose again. The changes in temperature and relative humidity in other voyages were similar. In static exposure tests, only the change in season causes the slow change of temperature and humidity, but the specimens exposed on the deck experience rapid change of temperature and humidity several times in one year. The circulation of temperature change may cause more serious corrosion [23].
Thirdly, the specimens exposed on the deck were subjected to the severe marine environment. Table 2 shows the range and average value of environment factor during the exposure period. Figure 3 shows the proportion of different range of temperature, relative humidity, deposition rate of chloride and wind speed during the ocean voyage, according to the hourly average value. Table 3 shows the range and average value of environment factor during ocean voyage. The temperature was higher than average temperature (26 °C) for most of the time, the maximum humidity was 97%, and the maximum wind speed was above 20 m/s. It is worth noting that during ocean voyage, the deposition rate of chloride was extremely high, and was above 100 mg/m2 d most of time, and the highest value was above 1100 mg/m2 d. The deposition rate of chloride was much higher than the value reported in other research measured in the static marine atmospheric exposure test, as shown in Table 4.
Table
Table 2. The range and average value of environment factor during exposure period.
Table 2. The range and average value of environment factor during exposure period.
Environment FactorT
(°C)		RH
(%)		Cl−
(mg/m2d)		Wind Speed
(m/s)
Range−0.9~33.118~9763.9~1130.00~20.2
Average value21.175.4232.45.2
Table
Table 3. The range and average value of environment factors during ocean voyage.
Table 3. The range and average value of environment factors during ocean voyage.
Environment FactorT
(°C)		RH
(%)		Cl−
(mg/m2d)		Wind Speed
(m/s)
Range−0.9~33.118~9763.9~1130.00.2~20.2
Average value26.075.7380.46.8
Table
Table 4. The deposition rate of chloride in static marine atmospheric exposure test.
Table 4. The deposition rate of chloride in static marine atmospheric exposure test.
LocationClimate TypeDeposition Rate of Chloride (mg/m2d)
The Gulf of Mexico [24]subtropical monsoon110~311
Zhanjiang, coastal of China [25]subtropical monsoon100~600
Xisha Islands, China [22]tropical marine climate64.39
Qingdao, coastal of China [26]temperate monsoon25
Shimizu, coastal of Japan [21]temperate monsoon4.2
It has been reported that chloride ions and relative humidity in the marine atmosphere significantly impact the corrosion processes of magnesium alloy [10,12,27]. Many studies illustrate the well-known corrosiveness of NaCl towards Mg alloys, and NaCl can form aqueous solution by absorbing water at RH > 75% [9]. As shown in Figure 3, the proportion of time when RH > 75% was 56%, which indicated that AZ31 magnesium alloy was covered by the thin electrolyte layer of high concentration of Cl− for more than half of the time during the ocean voyage. The thin electrolyte layer covering the surface of specimens provided the reaction environment for the electrochemical reaction during the corrosion process and made large areas on the surface become electrochemically connected.
Additionally, the chemical and electrochemical reactions involved in the anodic and cathodic reactions are thermally activated [28,29], and the effect of high temperature may also accelerate the anodic and cathodic reactions during ocean voyage.
Considering the synergistic effect of high temperature, high humidity, and high deposition rate of chloride, AZ31 magnesium alloy may suffer severe corrosion in hash dynamic marine exposure test compared with the static field exposure test at permanent location during ocean voyage.

3.2. Corrosion Rate

The weight loss of specimens exposed to the marine atmospheric environment during ocean voyage is shown in Figure 4. For the first month of the exposure period, the corrosion rate was 29.81 μm∙y−1. However, after exposure for 3 months, the slope of the curve of weight loss increased significantly. In addition, then the weight loss of specimens increased at the similar rate with the elapse of exposure time. After exposure for 1 year, the corrosion rate was 52.23 μm∙y−1, which was significantly higher compared with other static exposure studies. It was almost 3 times higher than that of the Xisha Islands [22] and 1.6 times higher than that of the Shimizu, Japan [21]. This means that AZ31 magnesium alloy suffered more serious corrosion in dynamic marine atmospheric environment.
Figure 5 shows the monthly average values of temperature, relative humidity and deposition of chloride ion during exposure time. It can be seen that relative humidity and the deposition of chloride ion remained at high level. In addition, at the beginning of exposure, the deposition of chloride ion increased continuously, the maximum value appeared at the time of exposure for 3 months, almost 2 times higher than that of the first month. Therefore, the corrosion rate of AZ31 magnesium alloy increased significantly after exposure for 3 months. During the following exposure period, the AZ31 magnesium alloy was covered by thin electrolyte layer of high concentration of chloride ion in most of time under the high relative humidity and high deposition of chloride ion. Therefore, the corrosion rate of specimens remained at a high level.

3.3. Surface Morphology Analysis

Figure 6 shows the surface appearance of AZ31 magnesium alloy specimens with corrosion products and without corrosion products after exposure for different periods in dynamic marine environment of ocean voyage. The specimens lost their metallic luster after exposure for 1 month, and many corrosion products formed on the surface. After exposure for 12 months, the whole surface of specimens was covered by corrosion products. After removing the corrosion products, we found that the amount of corrosion pits increased, and the corrosion pits connected with each other continuously with the elapse of exposure time.
Figure 7 displays the SEM of AZ31 magnesium alloy specimens exposed for different periods in the marine environment. A trace amount of corrosion products appeared on the surfaces of AZ31 magnesium alloy specimen after exposure for 1 month. After removing corrosion products, it can be seen that there were obvious corrosion pits on the surface of AZ31 magnesium alloy (as pointed by the arrow in Figure 7b). After exposure for 3 months, corrosion pits increased, and corrosion products completely covered the whole surface. After exposure for 6 months, a large number of corrosion products gathered on the surface of the specimens, part of surface of specimen appeared the detachment of corrosion products (as circled in red in Figure 7a), and corrosion pits connected with each other (as circled in red in Figure 7b). After exposure for 12 months, thick corrosion product layers covered the whole surface of specimen with cracks.
Figure 8 shows SEM images of the cross-section of AZ31 magnesium alloy specimens exposed for 12 months in dynamic marine environment of ocean voyage. After exposure for 12 months, a corrosion product layer with a thickness of more than 50 μm was formed on the surface of specimens. However, it could also be seen that there were some small cracks in corrosion product layer. The thin electrolyte layer of high concentration of Cl− might permeate into the matrix through these cracks, which might weaken the protection of corrosion products.
Figure 9 shows the laser confocal scanning microscopy (LCSM) analysis of AZ31 magnesium alloy specimens exposed for different periods in marine environment. The maximum pit depth presented a significant increase with prolonged exposure time. The maximum pit depth of specimens after exposure for 1, 3, 6 and 12 months were 44.213 μm, 63.048 μm, 172.344 μm and 276.366 μm, respectively. The research of Cui et al. [22] showed that the deepest pits of AZ31 magnesium alloy exposed on Xisha Island, with a tropical marine climate, after exposure for 1,3 and 6 months were all in the order of 30 ± 3 μm. The value of pit depth of AZ31 magnesium alloy exposed in dynamic marine atmospheric environment was significantly higher compared with other static exposure studies.
The analysis of the surface morphologies shows that the corrosion of AZ31 magnesium alloy was influenced by dynamic marine environment significantly. At the beginning of exposure, the corrosion products were formed at active sites under the corrosiveness of chloride ion. After exposure for 3 months, the average deposition rate of chloride ion was highest (in Figure 5). Under the synergistic effect of high temperature, high relative humidity and high deposition rate of chloride ion, a lot of corrosion products were formed on the surface of specimens after exposure for 3 months. After exposure for 6 months, specimens experienced temperature difference caused by ocean voyage from Qingdao to the western Pacific several times. The volume changes in the matrix and the corrosion product layer was different when temperature changed rapidly. Therefore, there was obvious stress at the interface between matrix and the corrosion product layer, which accelerated the detachment of corrosion products and the formation of cracks. The change in temperature and hash environment factor such as high wind speed and storm damaged the integrity of corrosion product layer seriously. As discussed in Section 3.1, the specimens were covered by a thin electrolyte layer of high concentration of chloride ions in most of time during ocean voyage. Therefore, the solution contained chloride ions that had stubbornly penetrated into the corrosion product layer through destroyed area of corrosion product layer, causing the amount and depth of the local corrosion to increase continually. With the extension of exposure time, more and more corrosion pits connected with each other, leading to the general corrosion and expansion of corrosion to the matrix.

3.4. Corrosion Product Analysis

The composition of corrosion products can be analyzed by XRD [30]. Figure 10 shows the composition of corrosion products formed on AZ31 magnesium alloy after exposure for 12 months. The results showed that the main corrosion products generated on AZ31 magnesium alloy were carbonate-containing compounds Mg5(CO3)4(OH)2·4H2O (JCPDS 25-0513) [31] and MgCO3·3H2O(JCPDS 70-1433) [32], and chloride-containing compound Mg2(OH)3Cl·4H2O (JCPDS 07-0412) [33]. This indicates that CO2 and Cl− participated in the corrosion process.
Figure 11 shows the XPS spectrum of corrosion products formed on AZ31 magnesium alloy exposed for 12 months in the marine environment of ocean voyage. The element C existed as CO32−, C-O, C=O and C-H or C-O, and carbon-containing pollutants existed on the surface of specimens. The element O existed as CO32− and OH−. The ratio of CO32− and OH− in the corrosion products was about 5.5:1, which indicated that CO2 participated in the corrosion reaction process in the hot and humid environment and there were a large amount of CO32−containing compounds in the corrosion products. This was consistent with the results of XRD. As shown in Table 5, the proportion of Cl 2p was 12.69%. Combined with the previous analysis of XRD and the high deposition rate of chloride, the Cl 2p in the whole-range spectra was due to chlorine-containing corrosion products and the deposition of chloride ions.

3.5. Electrochemical Behavior Analysis

Figure 12 shows the polarization curves of AZ31 magnesium alloy matrix and after exposure for 12 months. The corrosion potential and current density are listed in Table 6. Compared with the AZ31 matrix, the specimens after exposed for 12 months showed a current density decreasing and a positive shift of corrosion potential. The current density decreased about one order of magnitude. This indicates that the corrosion products generated on the surface of specimens might impede the ion diffusion process [34]. With the extension of exposure, more and more corrosion products were generated on surface of the specimens under the synergistic effect of high temperature, high relative humidity and the high deposition rate of chloride ion, making the plugging effect of the corrosion product layer more obvious.

4. Discussion

Figure 13 shows the corrosion process schematic of AZ31 magnesium alloy during exposure in the dynamic marine atmosphere.
During the initial stage of the reaction, chloride ions attached to the defects on the specimen surface and reacted with magnesium substrate and magnesium corrosion products, and destroyed the integrity of the surface. The thin electrolyte layer of high chloride ion concentration covered on the surface of specimens provides the reaction environment for the electrochemical reaction and make large areas on the surface become electrochemically connected, the corrosion occurs rapidly, and corrosion products are generated on the surface.
The degradation of AZ31 magnesium alloy was dominated by the chemical reaction process including oxidation and hydration reactions at the beginning [9].
Anodic reaction:
Mg→Mg2+ + 2e−
Cathodic reaction:
2H2O + 2e−→2OH− + H2
With the extension of exposure time, the location of local corrosion increased, Cl− diffused into the matrix through corrosion pits, and the anodic reaction taken place inside the magnesium alloy matrix, which induced deep pits in specimens. At the same time, cathodic reaction had taken place on the specimen surface to generate OH−, which could combine with Mg2+ to form magnesium hydroxide and magnesium hydroxyl-carbonate layer.
According to the phase diagram of the system MgO / CO2/H2O [35], brucite reacted with CO2 to form MgCO3 as follows [15]:
Mg(OH)2 + CO2→MgCO3 + H2O
CO2 reacted with H2O to form HCO3−, and then reacted with brucite [22]:
5Mg(OH)2 + 4HCO3− + nH2O →Mg5(CO3)4(OH)2·4H2O + 4OH
Brucite reacted with H+, Cl− and H2O to form Mg2Cl(OH)3 as follows [36]:
2Mg(OH)2 + H++Cl− + 3H2O →Mg2Cl(OH)3·4H2O
With the extension of exposure time, the location of local corrosion increased under the continuous action of high temperature and the thin electrolyte layer of high chloride ion concentration, the corrosion pits continuously sprout on the surface and connect with each other, the specimen evolved into general corrosion. Due to the synergistic action of the change of temperature, high wind speed and storms, corrosion products were peeled off from specimens, and all these harsh dynamic environmental factors accelerated the corrosion process.

5. Conclusions

The effect of the dynamic marine atmospheric environment on the corrosion process of AZ31 magnesium was investigated in this work. The results of this study are applicable to the coastal areas of China and the Pacific Ocean marine environment, and could provide effective data for the application of magnesium alloys in carrier plane during ocean voyage. The results can be summarized as follows:
  • The corrosion rate of AZ31 magnesium alloy after exposure for 1 year in dynamic marine atmospheric environment ocean voyage was 52.23 μm∙y−1, the maximum depth of corrosion pits was 276.366 μm, which is much higher than that of other research studied with static field exposure test at permanent location in marine environment. After exposure for 1 year, the main corrosion products were Mg5(CO3)4(OH)2·4H2O, MgCO3·3H2O and Mg2(OH)3Cl·4H2O. The corrosion was initiated from pitting corrosion and evolved into general corrosion.
  • The dynamic marine atmospheric environment is hash, with high temperature, high relative humidity and high deposition rate of chloride. The average temperature was 26.0 °C. The relative humidity was 75.7%, the proportion of time when RH > 75% was 56%. The average deposition rate of chloride ion was 380.4 mg/m2d.
  • The synergistic effect of high relative humidity and chloride ion plays an important role in the corrosion process of AZ31 magnesium alloy. During ocean voyage, the AZ31 magnesium alloy was covered by thin electrolyte layer of high concentration of chloride ion in most of time, which accelerated the corrosion of AZ31 magnesium alloy significantly.

Author Contributions

Conceptualization, L.Y.; methodology, W.X.; investigation, Q.J.; resources, L.Y.; data curation, X.W.; writing—original draft preparation, Y.W.; writing—review and editing, Y.H. and L.Y.; supervision, Y.L.; funding acquisition, L.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Science and Technology Resources Investigation Program of China (Grant No. 2019FY101400), Overseas Science and education cooperation center deployment project (No. 121311KYSB20210005) and Wenhai Program of the S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology (Qingdao) (NO. 2021WHZZB2304).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is available from the corresponding author by request.

Acknowledgments

Data Support from Institute of Oceanology of the Chinese Academy of Sciences Marine Science Data Center (MSDC: http://msdc.qdio.ac.cn/). The data and samples were collected by RV KEXUE.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The dynamic natural environment exposure test environment. (a) Test rack A, (b) test rack B, (c) navigation range.
Figure 1. The dynamic natural environment exposure test environment. (a) Test rack A, (b) test rack B, (c) navigation range.
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Figure 2. Daily average temperature and relative humidity at exposure test site during voyage: (a) temperature, (b) relative humidity.
Figure 2. Daily average temperature and relative humidity at exposure test site during voyage: (a) temperature, (b) relative humidity.
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Figure 3. The proportion of environment factors during ocean voyage. (a) Temperature, (b) relative humidity, (c) wind speed, (d) deposition rate of chloride.
Figure 3. The proportion of environment factors during ocean voyage. (a) Temperature, (b) relative humidity, (c) wind speed, (d) deposition rate of chloride.
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Figure 4. The weight loss of AZ31 magnesium alloy in the marine atmospheric environment during ocean voyage.
Figure 4. The weight loss of AZ31 magnesium alloy in the marine atmospheric environment during ocean voyage.
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Figure 5. The monthly average values of temperature, relative humidity, and deposition of chloride ion during exposure time. (a) Temperature, (b) relative humidity and (c) chloride ion deposition rate.
Figure 5. The monthly average values of temperature, relative humidity, and deposition of chloride ion during exposure time. (a) Temperature, (b) relative humidity and (c) chloride ion deposition rate.
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Figure 6. Surface appearance of AZ31 magnesium alloy specimens exposed for different periods in marine environment of ocean voyage: (a) with corrosion products, (b) without corrosion products.
Figure 6. Surface appearance of AZ31 magnesium alloy specimens exposed for different periods in marine environment of ocean voyage: (a) with corrosion products, (b) without corrosion products.
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Figure 7. SEM images of the surface of AZ31 magnesium alloy specimens with corrosion products exposed for different periods in marine environment of ocean voyage: (a) with corrosion products, (b) without corrosion products.
Figure 7. SEM images of the surface of AZ31 magnesium alloy specimens with corrosion products exposed for different periods in marine environment of ocean voyage: (a) with corrosion products, (b) without corrosion products.
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Figure 8. SEM images of the cross-section of AZ31 magnesium alloy specimens exposed for 12 months in dynamic marine environment of ocean voyage.
Figure 8. SEM images of the cross-section of AZ31 magnesium alloy specimens exposed for 12 months in dynamic marine environment of ocean voyage.
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Figure 9. Laser confocal scanning microscopy (LCSM) of AZ31 magnesium alloy specimens without corrosion products exposed for different periods in marine environment of ocean voyage. (a) 1 month, (b) 3 months, (c) 6 months, (d) 12 months.
Figure 9. Laser confocal scanning microscopy (LCSM) of AZ31 magnesium alloy specimens without corrosion products exposed for different periods in marine environment of ocean voyage. (a) 1 month, (b) 3 months, (c) 6 months, (d) 12 months.
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Figure 10. XRD patterns of AZ31 magnesium alloy: (a) corrosion products, (b) matrix.
Figure 10. XRD patterns of AZ31 magnesium alloy: (a) corrosion products, (b) matrix.
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Figure 11. The XPS binding energy spectrum of corrosion products formed on AZ31 magnesium alloy exposed for 12 months in the marine environment of ocean voyage: (a) narrow scan spectrum of C 1s, (b) narrow scan spectrum of O 1s, (c) whole spectrum, (d) proportion of the different states of element O.
Figure 11. The XPS binding energy spectrum of corrosion products formed on AZ31 magnesium alloy exposed for 12 months in the marine environment of ocean voyage: (a) narrow scan spectrum of C 1s, (b) narrow scan spectrum of O 1s, (c) whole spectrum, (d) proportion of the different states of element O.
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Figure 12. The polarization curves of AZ31 magnesium alloy matrix and specimen after exposure for 12 months in marine environment of ocean voyage.
Figure 12. The polarization curves of AZ31 magnesium alloy matrix and specimen after exposure for 12 months in marine environment of ocean voyage.
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Figure 13. The corrosion process schematic of AZ31 magnesium alloy.
Figure 13. The corrosion process schematic of AZ31 magnesium alloy.
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Table
Table 1. The nominal chemical composition of AZ31 magnesium alloys (wt. %).
Table 1. The nominal chemical composition of AZ31 magnesium alloys (wt. %).
MaterialAlZnMnSiFeCuNiMg
AZ313.190.810.300.0250.0060.0020.0006Bal.
Table
Table 5. The XPS analysis of the corrosion products formed on AZ31 magnesium alloy exposed for 12 months.
Table 5. The XPS analysis of the corrosion products formed on AZ31 magnesium alloy exposed for 12 months.
ElementS 2pCl 2pC 1sO 1sMg 2pZn 2p
Atomic %1.9912.6929.641.7113.70.3
Table
Table 6. The corrosion potentials (Ecorr) and corrosion current density (icorr) obtained from anodic polarization curves of AZ31 magnesium alloy.
Table 6. The corrosion potentials (Ecorr) and corrosion current density (icorr) obtained from anodic polarization curves of AZ31 magnesium alloy.
SpecimensPotential
(Ecorr /V)		Corrosion Current Density
(icorr /Acm−2)
Matrix−1.5321.054 × 10−4
12 months−1.5082.984 × 10−5
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Wang, Y.; Xu, W.; Wang, X.; Jiang, Q.; Li, Y.; Huang, Y.; Yang, L. Research on Dynamic Marine Atmospheric Corrosion Behavior of AZ31 Magnesium Alloy. Metals 2022, 12, 1886. https://doi.org/10.3390/met12111886

AMA Style

Wang Y, Xu W, Wang X, Jiang Q, Li Y, Huang Y, Yang L. Research on Dynamic Marine Atmospheric Corrosion Behavior of AZ31 Magnesium Alloy. Metals. 2022; 12(11):1886. https://doi.org/10.3390/met12111886

Chicago/Turabian Style

Wang, Ying, Weichen Xu, Xiutong Wang, Quantong Jiang, Yantao Li, Yanliang Huang, and Lihui Yang. 2022. "Research on Dynamic Marine Atmospheric Corrosion Behavior of AZ31 Magnesium Alloy" Metals 12, no. 11: 1886. https://doi.org/10.3390/met12111886

APA Style

Wang, Y., Xu, W., Wang, X., Jiang, Q., Li, Y., Huang, Y., & Yang, L. (2022). Research on Dynamic Marine Atmospheric Corrosion Behavior of AZ31 Magnesium Alloy. Metals, 12(11), 1886. https://doi.org/10.3390/met12111886

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