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Article

Insight into Microstructure Evolution and Corrosion Mechanisms of K2ZrF6/Al2O3-Doped Hot-Dip Aluminum/Micro-Arc Oxidation Coatings

by
Shuliang Wang
1,*,
Xiaofei Peng
1,
Yi Yang
1,
Shidong Wang
2,3,*,
Mingyu Wu
2,3,
Ping Hu
1 and
Chunyan Fu
1,*
1
School of New Energy and Materials, Southwest Petroleum University, Chengdu 610500, China
2
Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
3
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 2G6, Canada
*
Authors to whom correspondence should be addressed.
Coatings 2023, 13(9), 1543; https://doi.org/10.3390/coatings13091543
Submission received: 16 August 2023 / Revised: 30 August 2023 / Accepted: 31 August 2023 / Published: 4 September 2023
(This article belongs to the Special Issue Microstructure, Friction and Wear, Hardness Properties and Numerical Simulation of Coatings)
Browse Figures
Versions Notes

Abstract

:
In this study, we investigated the impact of K2ZrF6/Al2O3 composite additives on the microstructure evolution and corrosion behavior of ceramic coatings formed through micro-arc oxidation (MAO) treatment on hot-dip aluminum-coated 316L stainless steel surfaces. Our findings revealed the successful preparation of micro-arc oxidation ceramic coatings, presenting a dual-layer structure consisting of a porous micro-arc oxidation ceramic outer layer and a relatively dense/thick hot-dip aluminum inner layer. The incorporation of K2ZrF6/Al2O3 composite additives induced a self-sealing effect on the ceramic coating surface. Optimal coating performance was achieved with a composite additive concentration of 7.5 g/L, resulting in remarkable improvements not only in thickness, hardness, and surface smoothness but also in corrosion resistance. This research introduces a pioneering investigation of K2ZrF6/Al2O3 composite additives in the context of micro-arc oxidation technology, offering fresh perspectives and methodologies for the development of highly corrosion-resistant materials.

1. Introduction

Solar power generation technology, being a pivotal innovation in the field of new energy generation, offers immense promise and research significance due to its attributes of high stability, operational simplicity, safety, and reliability [1,2,3,4,5]. Operating within the realm of solar radiation, a complex natural exposure environment, its effects extend beyond mere temperature and climate to encompass alternating cycles of dryness and humidity, as well as the pervasive presence of pollutants [6,7]. In the pursuit of a consistent electricity supply for solar power generation systems, heat storage technology plays a critical role. The choice of heat storage materials becomes not only a decision but also a determinant of their compliance with heat storage technology standards. Among the commonly utilized options are molten salts, metallic sodium, and high-temperature-resistant concrete. In addition, aluminum-based alloys offer advantages including stability, substantial heat storage capacity, and efficient thermal conductivity, making them particularly suitable for use as heat storage materials. However, elevated temperatures lead to solid-to-liquid phase transitions in these thermal storage aluminum alloys, necessitating the selection of containers characterized by commendable corrosion resistance [8,9]. Presently, container materials primarily include weathering steel and stainless steel. Nevertheless, the prolonged interaction of thermal storage aluminum alloys with containers continues to exhibit pronounced corrosive effects, posing a significant risk of safety incidents and potential disruption of entire solar power generation systems if adequate measures are not taken [10,11,12,13,14,15]. Addressing this impending concern requires the prudent choice of superior container materials or the modification of container interiors to meet the practical process requirements.
In practice, addressing the challenge of severe erosion on container surfaces involves employing surface modification treatments. Among these methods, the application of hot-dip aluminum coating emerges as a robust protective measure [16,17]. The combination of thicker aluminum coatings with micro-arc oxidation (MAO) technology leads to the creation of ceramic coatings that serve as effective barriers against liquid aluminum corrosion [18,19,20]. However, the scope of research and application in this field remains limited, underscoring the urgent practical significance and engineering value of exploring these less-explored areas.
In the realm of MAO investigations, researchers often enhance the fundamental electrolyte by adding specific concentrations of additives to improve the characteristics of ceramic coatings. This strategic inclusion of complex oxides contributes to the formation of coatings with increased density, impressive resistance to wear and corrosion, and overall improved performance [21,22,23,24]. Among them, ZrO2 functions as a high-temperature-resistant oxide with a high melting point, high electrical resistivity, and low thermal expansion coefficient. This makes it an ideal catalyst for enhancing high-temperature and oxidation resistance in metal devices [25,26,27,28,29]. Notable examples include the findings of Zhong et al. [30], which reveal the improved thermal shock resistance of MAO ceramic coatings containing zirconium dioxide, in contrast to the silica coatings formed using the sol–gel method. Similarly, Wang et al. [31] made significant advancements by developing MAO coatings containing ZrTiO4 and m-ZrO2 on the Ti6Al4V alloy, resulting in significantly enhanced oxidation resistance at elevated temperatures. The introduction of the K2ZrF6 compound into the basic electrolyte triggers a transformative chemical reaction within an alkaline solution, leading to the in-situ generation of ZrO2 [32,33].
The efforts exemplified by Askarnia et al. [34] involve the application of composite coatings comprising Al2O3 and ZrO2 particles onto the AZ31 magnesium alloy using MAO technology. This intervention led to a substantial reduction in surface pores, an approximately eight-fold decrease in wear rate, and a noticeable increase in coating hardness. This outcome can be attributed to the improved wettability of the coating, primarily due to Al2O3. Similarly, Soliman et al. [35] conducted MAO experiments by introducing NaF and Al2O3 nano-additives into silicate electrolytes, resulting in a compact coating characterized by minimized roughness, primarily composed of a robust MgO phase that enhances corrosion resistance.
The above literature review suggests that introducing the K2ZrF6/Al2O3 composite additives into the basic electrolyte contributes to the presence of ZrO2 and Al2O3 in the MAO coatings, thus significantly enhancing their performance [34,36,37]. However, to the best of the authors’ knowledge, the impact of different concentrations of K2ZrF6/Al2O3 composite additives on ceramic coatings formed through MAO treatment of hot-dip aluminum-coated 316L stainless steel has not been investigated. Combining an outer high-performance MAO layer with the thicker aluminum layer on the 316L stainless steel has the potential to greatly improve the corrosion resistance of the developed coating system.
This innovative work was conducted using pre-prepared hot-dip aluminized stainless steel samples, optimized MAO process parameters, and a basic electrolyte. Different concentrations of composite additives, characterized by a K2ZrF6/Al2O3 composition ratio of 4/1 and designated as S0, S1, S2, S3, and S4 in ascending order, were introduced. This exploration aims to uncover the effects of varying composite additive concentrations on the characteristics of MAO ceramic coatings. The objective is to determine the optimal concentration of the composite additives that result in the highest performance of ceramic coatings.

2. Materials and Methods

2.1. Material and Coating Preparation

The 316L stainless steel material employed in this work has a dimension of 40 mm × 13 mm × 2 mm. This stainless steel material is produced by Shanxi Taigang Stainless Steel Co., Ltd. (Taiyuan, China). Its chemical composition (obtained through smelting analysis) is presented in Table 1.
Pre-Treatment: The specimens were polished with sandpaper up to #1200 grit, followed by immersion in a 10 g/L NaOH solution at 80 °C for a constant 10 min. Subsequently, the surfaces were rinsed with deionized water. The specimens were then placed in a 15% HCl solution at room temperature for 5 min, followed by rinsing off the residual solution with deionized water. Next, the specimens were immersed in assist-plating agent, 5 wt.% K2ZrF6, at 90 °C for 15 min.
Hot-Dip Aluminum Plating: Prior to commencing the hot-dip aluminum plating experiment, standard GB 9970 aluminum granules were placed in a graphite crucible and heated in a metal melting furnace up to 1000 °C. After complete melting of the aluminum granules, the furnace temperature was lowered to 730 °C for the hot-dip aluminum plating experiment, with NaCl particles used as a covering agent. The 316L stainless steel samples were immersed in the aforementioned molten aluminum for 5 min to prepare the hot-dip aluminum layer. Subsequently, the samples were air-cooled at room temperature. The specimens were then subjected to ultrasonic cleaning for 5 min using a 5% HNO3 + 1% HF solution, followed by ultrasonic cleaning with anhydrous ethanol for 5 min. After air-drying with cold air, the samples were stored in a drying chamber for micro-arc oxidation experiments.
Micro-Arc Oxidation Treatment: The aforementioned hot-dip plated samples underwent micro-arc oxidation treatment subsequently. A combination of silicate and phosphate electrolyte was introduced with K2ZrF6/Al2O3 composite additives at concentrations of 0 g/L (S0; 0.0 g/L K2ZrF6 + 0.0 g/L Al2O3), 2.5 g/L (S1; 2.0 g/L K2ZrF6 + 0.5 g/L Al2O3), 5.0 g/L (S2; 4.0 g/L K2ZrF6 + 1.0 g/L Al2O3), 7.5 g/L (S3; 6.0 g/L K2ZrF6 + 1.5 g/L Al2O3), and 10.0 g/L (S4; 8.0 g/L K2ZrF6 + 2.0 g/L Al2O3), which can be seen in Table 2. The micro-arc oxidation was performed at a frequency of 200 Hz, an oxidation time of 30 min, positive-to-negative duty ratios of 15% to 5%, and a current density of 10 A/dm2.

2.2. Characterization Methods

The micro-arc oxidation ceramic layer’s surface and cross-sectional morphology were observed using a scanning electron microscope (SEM, ZEISS EVO MA15, Carl Zeiss Microscopy GmbH, Jena, Germany). Energy-dispersive X-ray spectroscopy (EDS, OXFORD 20, Carl Zeiss Microscopy GmbH, Jena, Germany) was employed to characterize the element distribution and content of the micro-arc oxidation ceramic layer on both the surface and cross-sectional surface. X-ray diffraction (XRD) analysis was carried out on a DX-2700B diffractometer (Dandong Haoyuan Instrument Co., Ltd., Dandong, China) for phase composition analysis of the micro-arc oxidation ceramic layer. Specific parameters were as follows: Cu target, Kα radiation source, acceleration voltage and current set at 40 kV and 40 mA, respectively, step size of 0.0167°, dwell time of 12 s, approximately 0.1°/min.
The thickness of the aluminum coating under different plating temperatures and times, as well as the thickness of the micro-arc oxidation ceramic layer with varying concentrations of composite additives, was measured using the TT-230 eddy current thickness gauge, with an accuracy of 1 µm. For each test, five random positions on the aluminum-coated surface were selected, and the average of the measurements was taken as the final thickness value. The surface hardness of the micro-arc oxidation ceramic layer doped with different concentrations of composite additives was measured using a digital micro-hardness tester (HXD-1000TMB, Shanghai Taiming Optical Instrument Co., Ltd., Shanghai, China), with a loading force of 100 gf, a holding time of 15 s, and a diamond indenter. Similarly, five random positions on the ceramic layer surface were chosen for each test, and the average of the measurements represented the final hardness value.
The corrosion resistance of the micro-arc oxidation ceramic layer was analyzed using an electrochemical workstation (Reference 3000, Gamry, Philadelphia, PA, USA). Employing the classical three-electrode system, the specimen served as the working electrode, a platinum electrode as the auxiliary electrode, and a saturated calomel electrode as the reference electrode. For electrochemical impedance spectroscopy, the specific technical parameters were as follows: test area of 1 cm2, frequency range from 100 kHz to 0.01 Hz, and amplitude set at ±10 mV. All electrochemical tests were conducted in a 5% NaCl solution at room temperature of 25 °C.

3. Results and Discussion

3.1. Analysis of Oxidation Voltage in Micro-Arc Oxidation Process

Figure 1 demonstrates that the relationship between oxidation voltage and time during the micro-arc oxidation (MAO) experiment exhibits a consistent pattern across various additive concentrations. In the early stage of the MAO process (i.e., 0–3 min), the oxidation voltage rises linearly and rapidly with time, with nearly identical growth rates among different composite additive concentrations. At this phase, the oxidation voltage has not yet reached the critical breakdown voltage, as shown in the image. It is found that gas bubbles begin to emerge around the anode sample, and the temperature gradually ascends. As time elapses (i.e., 3–5 min), the growth rate of the oxidation voltage decelerates. Concurrently, a handful of sparks appear on the sample’s surface, accompanied by an escalation in temperature. Subsequently (i.e., 5–20 min), the oxidation voltage stabilizes at a specific value. This signifies the appearance of numerous volcano-like micropores on the sample’s surface, penetrated by the oxidation voltage, leading to an intensification and brightening of the sparks [38,39].
Moreover, during the MAO process, as the concentration of composite additives increases, the oxidation voltage follows a pattern of initial increase and subsequent decrease. Remarkably, at a concentration of 7.5 g/L, the oxidation voltage reaches its peak at 530 V. This behavior is primarily due to lower additive concentrations at which K2ZrF6 and Al2O3 disperse in the electrolyte. Hydrolysis could lead to the formation of Al(OH)3 and Zr(OH)4 precipitates, which further hinder the movement of charged particles in the electrolyte. This elevation in electrolyte resistance necessitates a higher oxidation voltage to induce surface breakdown [40]. Consequently, within the additive concentration range of 0–7.5 g/L, the oxidation voltage increases proportionally with concentration. However, with a further increase in additive concentration, agglomeration occurs during the formation of the ceramic layer. This obstructs the progression of the MAO process, leading to a slowdown in coating deposition rates and, consequently, a reduction in surface resistance. As a result, when the additive concentration reaches 10 g/L, the oxidation voltage displays a declining trend.

3.2. Microstructure and Elemental Analysis of Micro-Arc Oxidation Ceramic Coatings

Figure 2 presents the surface morphology and elemental distribution of ceramic coatings formed through micro-arc oxidation treatment on hot-dip aluminum-coated 316L stainless steel surfaces, with varying concentrations of K2ZrF6/Al2O3 composite additives introduced into an optimized silicate-phosphate-based electrolyte. As seen in the figures, a layer of micro-arc oxidation ceramic coating was successfully prepared on the surface of the 316L hot-dip aluminum-coated samples, characterized by numerous discharge micropores and a typical volcanic morphology. EDS mapping reveals a relatively uniform distribution of O, Al, and Zr elements in the ceramic coatings, indicating the successful involvement of Zr elements in the formation of the micro-arc oxidation coating. During the micro-arc oxidation process, Zr mainly exists in the form of ZrO2, which has been reported to significantly enhance heat shock resistance and oxidation resistance of micro-arc oxidation coatings [41]. In this work, the addition of K2ZrF6 may induce the generation of ZrO2, possibly following the following mechanism [41]:
K2ZrF6 → 2K+ + ZrF62−
ZrF62− + 4OH− → Zr(OH)4 + 6F−
Zr(OH)4 → ZrO2 + 2H2O
ZrF62− + 4OH− → ZrO2 + 6F− + 2H2O
From Figure 2a, it is evident that at a composite additive concentration of 2.5 g/L, there are larger and numerous discharge micropores on the ceramic coating surface. This is primarily due to the fusion of adjacent micropores during the micro-arc oxidation process, resulting from the abundance of micropores. As the composite additive concentration increases to 5 g/L (Figure 2b), the Al2O3 and K2ZrF6 powders partially fill the micropores, reducing their quantity. This enhances the coating’s surface density and smoothness while generating a small amount of white fusion material. Based on EDS mapping results and previous studies, this white fusion material is mostly composed of silicon–oxygen compounds. Excessive silicon–oxygen compounds can affect the smoothness of the ceramic coating surface. At a composite additive concentration of 7.5 g/L (Figure 2c), the ceramic coating surface becomes smoother, with fewer white fusion materials, and many micropores are covered by fine particles. However, when the composite additive concentration reaches 10 g/L (Figure 2d), more white fusion materials are generated on the ceramic coating surface, and there are more micro-convex regions. This suggests that an excessively high composite additive concentration can reduce the surface smoothness of the ceramic coating and affect the coating’s performance.
According to Table 3, the ceramic coating contains a series of elements including O, Al, P, Zr, and Si. With the increase in composite additive concentration, the Zr content also increases, indicating the increasing involvement of Zr elements in the film-forming process. This confirms the presence of ZrO2 on the coating surface. Additionally, the Si content exhibits a trend of initially decreasing and then increasing. When the composite additive concentration is 7.5 g/L, the Si content is the lowest, at only 0.8 wt.%, consistent with the SEM results mentioned above. This indicates that at this concentration, there are fewer white fusion materials, and the ceramic coating’s surface smoothness and density are optimal.
Figure 3 illustrates the cross-sectional morphology and elemental linear distribution of hot-dip aluminum-coated samples after micro-arc oxidation treatment at different composite additive concentrations. As shown, the coating structure is dense, without distinct porous layers. According to the linear element scanning results, in the vicinity of the outer surface (0–10 µm), the content of Al, Zr, and O is higher. However, beyond this depth, the Al content is high, while the Zr and O contents are lower. This indicates a layered structure of the coating, with the outer layer being rich in Al, Zr, and O, mainly constituting an Al2O3-ZrO2 micro-arc oxidation layer. The inner layer is rich in Al, mainly derived from the hot-dip plating process. Furthermore, Si elements tend to randomly aggregate throughout the entire coating thickness.

3.3. Phase Analysis of Micro-Arc Oxidation Ceramic Coatings

Figure 4 shows the XRD spectra of samples after micro-arc oxidation treatment of hot-dip aluminum-coated 316L stainless steel surfaces with varying concentrations of composite additives. From the graph, it can be observed that the diffraction peaks are mainly attributed to Al and Al2O3 phases. The presence of characteristic peaks of Al indicates that the micro-arc oxidation ceramic coating is relatively thin, allowing X-rays to easily penetrate the ceramic coating during testing and detect the aluminum plating layer on the stainless steel substrate. Additionally, the intensity of the Al characteristic peak is highest in sample S1, indicating a thinner micro-arc oxidation coating and easier detection of the aluminum plating layer by X-rays. As the composite additive concentration increases, the intensity of the Al characteristic peak decreases, suggesting that higher concentrations of composite additives can effectively increase the thickness of the ceramic coating. The Al2O3 phase in the XRD spectra exhibits a single characteristic peak, and the intensity of this peak remains relatively consistent across different additive concentrations. This indicates that its origin is primarily the oxidation of aluminum atoms in the aluminum plating layer during the micro-arc oxidation process, although Al2O3 powder in the additives could also contribute to its presence. Furthermore, no ZrO2 was detected, suggesting that the content of ZrO2 is relatively low and exists only near the surface of the coating, as confirmed by SEM and EDS results. It should be noted that the diffraction peak of Al deviates from the standard position of the Al peak and shifts slightly to the right [37,42,43]. The occurrence of this peak shift phenomenon indicates a distortion in the lattice constant of the Al crystal during the processes of hot-dip coating and micro-arc oxidation [44,45,46]. This phenomenon may be related to the presence of residual stresses, or compounds such as Al2O3, ZrO2, or SiO2. However, the specific reasons for this need further in-depth research.

3.4. Analysis of Thickness and Hardness of Micro-Arc Oxidation Ceramic Coatings

In general, there are two main factors influencing the corrosion resistance of ceramic coatings during the micro-arc oxidation process. Firstly, the microstructure of the ceramic coating’s surface plays a significant role. Variations in the number and non-uniformity of unique volcano-like micropores on the surface of micro-arc oxidation ceramic coatings lead to different probabilities of corrosion ions diffusing through these micropores and reaching the interface of the intermediate layer or substrate. A higher number and larger size of micropores facilitate the diffusion of corrosive ions to the substrate interface, resulting in poorer corrosion resistance [47,48,49,50,51,52,53]. Secondly, the thickness and hardness of the ceramic coating are also important factors affecting the corrosion resistance of composite coatings. Thicker ceramic coatings provide a greater barrier against corrosive ions for the intermediate layer or substrate interface [54]. The hardness of micro-arc oxidation coatings directly impacts their corrosion resistance [55]. A higher coating hardness usually indicates better resistance against scratching, wear, and deformation, thereby reducing the susceptibility of the coating to external erosive forces.
According to Figure 5a, it can be observed that with an increase in the concentration of composite additives, the thickness of the ceramic coating initially increases and then decreases, reaching its maximum value at 7.5 g/L. This indicates that incorporating K2ZrF6/Al2O3 composite additives into the base electrolyte within the range of 0 to 7.5 g/L promotes an increase in the thickness of the ceramic coating. The primary reason for this is that the addition of K2ZrF6/Al2O3 composite additives alters the oxidation voltage during the micro-arc oxidation process, which is directly related to the deposition rate of the coating. Higher oxidation voltage leads to a faster deposition rate and, consequently, a thicker coating, aligning with the conclusions drawn from Figure 1. However, when the concentration of composite additives reaches 10 g/L, the reduction in the thickness of the ceramic coating can be attributed to the uneven diffusion of excessive additives within the electrolyte. This can lead to aggregation and adhesion on the surface of the hot-dip aluminum-coated samples, making it more difficult to breach the aluminum plating layer and impeding the arc discharge during the micro-arc oxidation process, thereby affecting the coating’s deposition rate.
From Figure 5b, it can be seen that the trend in hardness variation of the ceramic coating corresponds closely with the thickness variation trend. This implies that the micro-arc oxidation ceramic layer significantly contributes to the hardness value. When 7.5 g/L of K2ZrF6/Al2O3 composite additives are added, the hardness value of the sample increases from 406HV to 482HV compared to the sample without K2ZrF6/Al2O3 additives. The increase in coating hardness can be attributed to the addition of 7.5 g/L K2ZrF6/Al2O3, which significantly enhances the oxidation voltage during the micro-arc oxidation process as evidenced by Figure 1. This, in turn, provides more oxidation energy, leading to the formation of more hard phases such as Al2O3 and ZrO2. The presence of these hard phases contributes to the improved surface hardness of the coating.

3.5. Electrochemical Response and Corrosion Mechanism Analysis

Electrochemical methods play a crucial role in evaluating the corrosion performance of micro-arc oxidation coatings. These methods simulate the electrochemical processes in real corrosion environments, providing comprehensive and quantitative information about coating corrosion performance [45,52,56,57]. Among these methods, electrochemical impedance spectroscopy (EIS) plays a pivotal role in analyzing the corrosion performance of micro-arc oxidation coatings. EIS data present the electrochemical impedance spectrum of the coating, encompassing various aspects such as charge transfer processes, interfacial reactions, and the formation of corrosion products. These data not only aid in a deeper understanding of corrosion types and degrees but also predict the durability and lifespan of coatings in practical use.
As shown in Figure 6a, Nyquist plots and low-frequency area magnifications of micro-arc oxidized coatings on hot-dip aluminum-coated samples under different composite additive concentrations exhibit similar electrochemical behavior. Generally, the relationship between resistance and capacitance in charge transfer processes can be reflected by the impedance arc in Nyquist plots. The size of the impedance arc’s radius is directly proportional to the corrosion resistance of the sample; a larger radius indicates better corrosion resistance [45,57,58,59]. From the magnified low-frequency area, it can be observed that the impedance arc radius of ceramic coatings on hot-dip aluminum-coated samples increases initially and then decreases with the rise in composite additive concentration. The S3 sample has the largest impedance arc radius, indicating the best corrosion resistance. The corrosion resistance order can be listed as follows: S3 > S4 > S2 > S1 > S0. The poorest corrosion resistance is observed in S0 samples, confirming that the K2ZrF6/Al2O3 composite additives used in this study effectively enhance the corrosion resistance of micro-arc oxidation ceramic coatings.
Figure 6b presents Bode plots of micro-arc oxidized coatings on hot-dip aluminum-coated samples after treatment under different composite additive concentrations. The corrosion resistance of samples can also be evaluated by the magnitude of |Z| at low frequency; larger |Z| values indicate better corrosion resistance. It can be confirmed that the S3 sample exhibits the best corrosion resistance. Additionally, the phase angle and impedance values of all samples change in a similar trend as frequency varies, suggesting that K2ZrF6/Al2O3 composite additives only influence the corrosion resistance of the micro-arc oxidation ceramic coating and do not alter the structural characteristics of the ceramic layer itself [60]. Furthermore, the Bode plots reveal at least two time constant features, corresponding to the ceramic outer layer of the coating and the hot-dip aluminum inner layer, aligning with the cross-sectional analysis results.
Figure 7 illustrates the equivalent circuit diagram of EIS for micro-arc oxidized coatings on hot-dip aluminum-coated samples after treatment under different composite additive concentrations. In the diagram, Rs represents the electrolyte resistance, RP1 and CP1 represent the equivalent resistance and capacitance of the outer layer of the coating, while RP2 and CP2 represent the equivalent resistance and capacitance of the inner layer of the coating. The ZSimpWin impedance spectroscopy fitting software was employed to fit EIS data, and the fitted parameters are presented in Table 4. It can be observed that the fitted resistance RP2 > RP1. This is due to the thicker hot-dip aluminum inner layer, which better resists the corrosion of external corrosive ions, resulting in higher impedance values. Conversely, the micro-arc oxidation outer layer of the coating is thinner and contains certain voids, facilitating the passage of corrosive ions and thus leading to relatively lower impedance values. Nevertheless, research indicates that porous ceramic coatings can exhibit a self-sealing effect during the corrosion process, effectively preventing further corrosion. The self-sealing effect of micro-arc oxidation coatings refers to the ability of small pores on the coating surface to close, enhancing the coating’s sealability and corrosion resistance. Methods for achieving self-sealing pores in micro-arc oxidation coatings generally involve optimizing process parameters, increasing oxide film thickness, implementing secondary treatments, adding pore-sealing agents, utilizing surface treatments, etc. These methods aim to reduce pore formation and promote the self-filling and sealing of internal coating pores, thereby enhancing the sealability and corrosion resistance of the coating. Additionally, the appearance of an additional time constant in the high-frequency position of the Bode plots might be attributed to further self-sealing effects of the coating. Similar reports are found in the literature [61].
With an increase in the concentration of K2ZrF6/Al2O3 composite additives, both RP1 and RP2 show an initial increase followed by a subsequent decrease. The combined value of RP1 and RP2 determines the level of the coating’s resistance to external corrosion. Consequently, the corrosion resistance of the film layer demonstrates an initial improvement, followed by a reduction. The S3 sample exhibits the highest R values, reaching 3240 Ω·cm2 and 7488 Ω·cm2 respectively, indicating the best corrosion resistance among the samples. This suggests that an appropriate amount of K2ZrF6/Al2O3 powder adequately fills the volcano-like micropores on the micro-arc oxidation ceramic coating, reducing the number and size of these pores [56,61,62]. Moreover, the formed phases such as Al2O3 and ZrO2 can obstruct the erosion of corrosive ions, enhancing the corrosion resistance of the ceramic coating [63,64].
In summary, K2ZrF6/Al2O3 composite additives were introduced into the micro-arc oxidation technology field in this investigation, revealing their impact on ceramic coating performance and corrosion resistance. This research not only advances the forefront of micro-arc oxidation technology but also provides new perspectives and methodologies for exploring the realm of material corrosion and protection.

4. Conclusions

This study investigated the influence of introducing different concentrations of K2ZrF6/Al2O3 composite additives into an optimized silicate–phosphate-based electrolyte on the microstructure evolution and corrosion mechanism of ceramic coatings formed on the surface of 316L stainless steel through hot-dip aluminum coating and subsequent micro-arc oxidation (MAO) treatment. The specific conclusions are as follows:
(1) The analysis of oxidation voltage in the micro-arc oxidation process revealed consistent patterns across various additive concentrations of K2ZrF6/Al2O3. However, increasing additive concentrations led to an initial rise and subsequent decline in the stabilized oxidation voltage, with the maximum value found at a concentration of 7.5 g/L.
(2) Micro-arc oxidation ceramic coatings were successfully prepared on the surface of 316L stainless steel hot-dip aluminum-coated samples, forming a dual-layer structure of hot-dip aluminum/micro-arc oxidation ceramic coating. The micro-arc oxidation ceramic coating primarily consisted of Al2O3/ZrO2 and displayed numerous micropores. The addition of K2ZrF6/Al2O3 composite additives resulted in a self-sealing effect on the ceramic coating surface, simultaneously impacting the coating properties. With an increase in composite additive concentration, the thickness and hardness of the ceramic coating showed an initial increase followed by a decrease trend. When the composite additive concentration reached 7.5 g/L, both the thickness and hardness of the ceramic coating reached their maximum values. Additionally, the coating surface became smooth and compact, effectively retarding the penetration of corrosive media and significantly enhancing corrosion resistance.
(3) Electrochemical results supported that the coating on the sample surface exhibited a dual-layer structure, mainly composed of a porous micro-arc oxidation ceramic outer layer and a relatively thick hot-dip aluminum inner layer. When the K2ZrF6/Al2O3 composite additive concentration was 7.5 g/L, the resistance values of both the inner and outer layers reached their maximum values, indicating that the hot-dip aluminum/MAO ceramic coating possessed the best corrosion resistance.

Author Contributions

Conceptualization, S.W. (Shuliang Wang) and S.W. (Shidong Wang); Formal analysis, P.H.; Funding acquisition, S.W. (Shuliang Wang); Investigation, P.H.; Methodology, S.W. (Shuliang Wang) and S.W. (Shidong Wang); Project administration, S.W. (Shuliang Wang); Resources, S.W. (Shuliang Wang); Supervision, S.W. (Shuliang Wang); Validation, X.P. and P.H.; Writing—original draft preparation, X.P. and P.H.; Writing—review and editing, S.W. (Shuliang Wang), X.P., Y.Y., S.W. (Shidong Wang), M.W. and C.F. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Open Fund of Sichuan Shale Gas Efficient Exploitation Advanced Materials Preparation Technology Engineering Research Center, Southwest Petroleum University (Project No. 2022SCYYQKCCL014), P.R. China.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data will be made available on request.

Acknowledgments

The authors express their gratitude for the financial support provided by the Sichuan Shale Gas Efficient Exploitation Advanced Materials Preparation Technology Engineering Research Center, Southwest Petroleum University.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Kennedy, K.M.; Ruggles, T.H.; Rinaldi, K.; Dowling, J.A.; Duan, L.; Caldeira, K.; Lewis, N.S. The role of concentrated solar power with thermal energy storage in least-cost highly reliable electricity systems fully powered by variable renewable energy. Adv. Appl. Energy 2022, 6, 100091. [Google Scholar] [CrossRef]
  2. Zhan, J.; Wang, Z. Solar Thermal Power Generation Technology in a New Generation of Energy System Positioning. Adv. Energy Power Eng. 2018, 6, 1–9. [Google Scholar] [CrossRef]
  3. Singh, G.K. Solar power generation by PV (photovoltaic) technology: A review. Energy 2013, 53, 1–13. [Google Scholar] [CrossRef]
  4. Hayat, M.B.; Ali, D.; Monyake, K.C.; Alagha, L.; Ahmed, N. Solar energy–A look into power generation, challenges, and a solar-powered future. Int. J. Energ Res. 2019, 43, 1049–1067. [Google Scholar] [CrossRef]
  5. Devabhaktuni, V.; Alam, M.; Depuru, S.S.S.R.; Green II, R.C.; Nims, D.; Near, C. Solar energy: Trends and enabling technologies. Renew. Sustain. Energy Rev. 2013, 19, 555–564. [Google Scholar] [CrossRef]
  6. Mummana, S.S.; Anne, S.B.; Vooradi, R. A simple unit specific event based modeling framework for short term scheduling and heat integration of batch plants: Design and optimization of heat storage vessels. Comput. Chem. Eng. 2021, 145, 107155. [Google Scholar] [CrossRef]
  7. Budyko, M.I. The effect of solar radiation variations on the climate of the Earth. Tellus 1969, 21, 611–619. [Google Scholar] [CrossRef]
  8. Maruoka, D.; Sato, K.; Miura, S.; Murakami, T.; Kasai, E. Development of High Temperature Oxidation Resistant Iron-Based Heat Storage Materials for Rapid Carbonization and Pulverization Process of Biomass. Tetsu-to-Hagane 2020, 106, 527–533. [Google Scholar] [CrossRef]
  9. Chatterjee, U.; Bose, S.K.; Roy, S.K. Environmental Degradation of Metals: Corrosion Technology Series/14; CRC Press: Boca Raton, FL, USA, 2001. [Google Scholar]
  10. Czerwinski, F. Thermal Stability of Aluminum Alloys. Materials 2020, 13, 3441. [Google Scholar] [CrossRef]
  11. Zhu, M.; Yi, H.; Lu, J.; Huang, C.; Zhang, H.; Bo, P.; Huang, J. Corrosion of Ni–Fe based alloy in chloride molten salts for concentrating solar power containing aluminum as corrosion inhibitor. Sol. Energ. Mat. Sol. C 2022, 241, 111737. [Google Scholar] [CrossRef]
  12. Wei, G.; Huang, P.; Xu, C.; Liu, D.; Ju, X.; Du, X.; Xing, L.; Yang, Y. Thermophysical property measurements and thermal energy storage capacity analysis of aluminum alloys. Sol. Energy 2016, 137, 66–72. [Google Scholar] [CrossRef]
  13. García-Romero, A.; Delgado, A.; Urresti, A.; Martín, K.; Sala, J.M. Corrosion behaviour of several aluminium alloys in contact with a thermal storage phase change material based on Glauber’s salt. Corros. Sci. 2009, 51, 1263–1272. [Google Scholar] [CrossRef]
  14. Wang, S.; Niazi, H.; Lamborn, L.; Chen, W. Strain-shock-induced early stage high pH stress corrosion crack initiation and growth of pipeline steels. Corros. Sci. 2021, 178, 109056. [Google Scholar] [CrossRef]
  15. Li, M.C.; Wang, S.D.; Ma, R.Y.; Han, P.H.; Bi, H.Y. Effect of cyclic oxidation on electrochemical corrosion of type 409 stainless steel in the simulated muffler condensates. J. Solid State Electrochem. 2012, 16, 3059–3067. [Google Scholar] [CrossRef]
  16. Yao, X.; Xia, S.; Lv, Y.; Yang, W.; Chen, J. Effects of hot dipping temperature on microstructure and mechanical properties of Pb40Sn60 alloy coating on copper wires. Mater. Sci. Eng. A 2021, 810, 140991. [Google Scholar] [CrossRef]
  17. Zhang, G.; Zhang, S.; Song, R.; Cai, C. Effect of Mg and Si contents on hot-dip 55Al-Zn plating: Experimental and molecular dynamics simulation. Mater. Today Commun. 2023, 35, 106131. [Google Scholar] [CrossRef]
  18. Lin, Z.; Wang, T.; Yu, X.; Sun, X.; Yang, H. Functionalization treatment of micro-arc oxidation coatings on magnesium alloys: A review. J. Alloys Compd. 2021, 879, 160453. [Google Scholar] [CrossRef]
  19. Golubkov, P.E.; Pecherskaya, E.A.; Karpanin, O.V.; Shepeleva, Y.V.; Zinchenko, T.O.; Artamonov, D.V. Automation of the micro-arc oxidation process. J. Phys. Conf. Ser. 2017, 917, 092021. [Google Scholar] [CrossRef]
  20. Likhanov, V.A.; Skryabin, M.L. The study of oxide films on the surface of a piston of aluminum alloy after micro-arc oxidation. IOP Conf. Ser. Earth Environ. Sci. 2019, 315, 032045. [Google Scholar] [CrossRef]
  21. Chen, Y.; Wu, L.; Yao, W.; Chen, Y.; Zhong, Z.; Ci, W.; Wu, J.; Xie, Z.; Yuan, Y.; Pan, F. A self-healing corrosion protection coating with graphene oxide carrying 8-hydroxyquinoline doped in layered double hydroxide on a micro-arc oxidation coating. Corros. Sci. 2022, 194, 109941. [Google Scholar] [CrossRef]
  22. Yang, J.; Fang, K.; Xu, K.; Shen, X.; Xu, X. Effect of zinc or copper doping on corrosion resistance and anti-oxidative stress of strontium-based micro-arc oxidation coatings on titanium. Appl. Surf. Sci. 2023, 626, 157229. [Google Scholar] [CrossRef]
  23. Shen, X.; Fang, K.; Ru Yie, K.H.; Zhou, Z.; Shen, Y.; Wu, S.; Zhu, Y.; Deng, Z.; Ma, P.; Ma, J.; et al. High proportion strontium-doped micro-arc oxidation coatings enhance early osseointegration of titanium in osteoporosis by anti-oxidative stress pathway. Bioact. Mater. 2022, 10, 405–419. [Google Scholar] [CrossRef]
  24. Thukkaram, M.; Cools, P.; Nikiforov, A.; Rigole, P.; Coenye, T.; Van Der Voort, P.; Du Laing, G.; Vercruysse, C.; Declercq, H.; Morent, R.; et al. Antibacterial activity of a porous silver doped TiO2 coating on titanium substrates synthesized by plasma electrolytic oxidation. Appl. Surf. Sci. 2020, 500, 144235. [Google Scholar] [CrossRef]
  25. Li, H.; Sun, Y.; Zhang, J. Effect of ZrO2 particle on the performance of micro-arc oxidation coatings on Ti6Al4V. Appl. Surf. Sci. 2015, 342, 183–190. [Google Scholar] [CrossRef]
  26. Fatimah, S.; Kamil, M.P.; Kwon, J.H.; Kaseem, M.; Ko, Y.G. Dual incorporation of SiO2 and ZrO2 nanoparticles into the oxide layer on 6061 Al alloy via plasma electrolytic oxidation: Coating structure and corrosion properties. J. Alloys Compd. 2017, 707, 358–364. [Google Scholar] [CrossRef]
  27. Hu, C.-J.; Hsieh, M.-H. Preparation of ceramic coatings on an Al–Si alloy by the incorporation of ZrO2 particles in microarc oxidation. Surf. Coat. Technol. 2014, 258, 275–283. [Google Scholar] [CrossRef]
  28. Zhong, Y.; Shi, L.; Li, M.; He, F.; He, X. Characterization and thermal shock behavior of composite ceramic coating doped with ZrO2 particles on TC4 by micro-arc oxidation. Appl. Surf. Sci. 2014, 311, 158–163. [Google Scholar] [CrossRef]
  29. Kaseem, M.; Lee, Y.H.; Ko, Y.G. Incorporation of MoO2 and ZrO2 particles into the oxide film formed on 7075 Al alloy via micro-arc oxidation. Mater. Lett. 2016, 182, 260–263. [Google Scholar] [CrossRef]
  30. Liang, J.; Srinivasan, P.B.; Blawert, C.; Dietzel, W. Comparison of electrochemical corrosion behaviour of MgO and ZrO2 coatings on AM50 magnesium alloy formed by plasma electrolytic oxidation. Corros. Sci. 2009, 51, 2483–2492. [Google Scholar] [CrossRef]
  31. Wang, C.; Hao, J.; Xing, Y.; Guo, C.; Chen, H. High temperature oxidation behavior of TiO2+ZrO2 composite ceramic coatings prepared by microarc oxidation on Ti6Al4V alloy. Surf. Coat. Technol. 2015, 261, 201–207. [Google Scholar] [CrossRef]
  32. Selvi, E.; Muhaffel, F.; Yürektürk, Y.; Vanlı, A.S.; Baydoğan, M. Influence of Electrolyte Compositions and Electrical Parameters on Thermal Properties of Micro-Arc Oxidized AZ91 Alloy. J. Mater. Eng. Perform. 2021, 31, 1667–1678. [Google Scholar] [CrossRef]
  33. Malinovschi, V.; Marin, A.; Negrea, D.; Andrei, V.; Coaca, E.; Mihailescu, C.N.; Lungu, C.P. Characterization of Al2O3/ZrO2 composite coatings deposited on Zr-2.5Nb alloy by plasma electrolytic oxidation. Appl. Surf. Sci. 2018, 451, 169–179. [Google Scholar] [CrossRef]
  34. Askarnia, R.; Sobhani, M.; Zare, M.; Aghamohammadi, H.; Staji, H. Incorporation of Al2O3 and ZrO2 ceramics to AZ31 magnesium alloys composite coating using micro-arc oxidation method. J. Mech. Behav. Biomed. 2023, 141, 105784. [Google Scholar] [CrossRef]
  35. Wang, Z.-H.; Zhang, J.-M.; Li, Y.; Bai, L.-J.; Zhang, G.-J. Enhanced corrosion resistance of micro-arc oxidation coated magnesium alloy by superhydrophobic Mg−Al layered double hydroxide coating. Trans. Nonferr. Met. Soc. 2019, 29, 2066–2077. [Google Scholar] [CrossRef]
  36. Xin, S.G.; Le, J.; Song, L.X. The Composition and Hardness of the Coating Containing Zirconia Produced by Micro-Arc Oxidation on Aluminium Alloy. Key Eng Mat 2012, 512, 1082–1088. [Google Scholar] [CrossRef]
  37. Tang, M.; Li, W.; Liu, H.; Zhu, L. Preparation Al2O3/ZrO2 composite coating in an alkaline phosphate electrolyte containing K2ZrF6 on aluminum alloy by microarc oxidation. Appl. Surf. Sci. 2012, 258, 5869–5875. [Google Scholar] [CrossRef]
  38. Li, Z.; Cheng, Y.; Kang, S.-H.; Tu, W.; Cheng, Y. A re-understanding of the breakdown theory from the study of the plasma electrolytic oxidation of a carbon steel—A non-valve metal. Electrochim. Acta 2018, 284, 681–695. [Google Scholar] [CrossRef]
  39. Qi, X.; Jiang, B.; Song, R. Effects of ageing treatment on corrosion behavior of 7075 aluminum alloy coated by micro arc oxidation (MAO). Corros. Sci. 2022, 199, 110164. [Google Scholar] [CrossRef]
  40. Guo, H.; Liu, Z.; Wang, Y.; Li, J. Tribological mechanism of micro-arc oxidation coatings prepared by different electrolyte systems in artificial seawater. Ceram. Int. 2021, 47, 7344–7352. [Google Scholar] [CrossRef]
  41. Yang, W.; Xu, D.; Guo, Q.; Chen, T.; Chen, J. Influence of electrolyte composition on microstructure and properties of coatings formed on pure Ti substrate by micro arc oxidation. Surf. Coat. Technol. 2018, 349, 522–528. [Google Scholar] [CrossRef]
  42. Al Bosta, M.M.; Ma, K.-J.; Chien, H.-H. The effect of MAO processing time on surface properties and low temperature infrared emissivity of ceramic coating on aluminium 6061 alloy. Infrared Phys. Technol. 2013, 60, 323–334. [Google Scholar] [CrossRef]
  43. Lihong, L.; Dejiu, S.; Jingwu, Z.; Jian, S.; Liang, L. Evolution of micro-arc oxidation behaviors of the hot-dipping aluminum coatings on Q235 steel substrate. Appl. Surf. Sci. 2011, 257, 4144–4150. [Google Scholar] [CrossRef]
  44. Song, S.; Chen, B.; Li, H.; Shi, R.; Liu, C.; Yang, B.; de la Fuente, G. Growth behavior and insulation property of the oxide layer during micro-arc oxidation of aluminium in “soft” regime condition. J. Mater. Sci. 2023, 58, 7136–7148. [Google Scholar] [CrossRef]
  45. Wang, S.D.; Xu, D.K.; Wang, B.J.; Sheng, L.Y.; Qiao, Y.X.; Han, E.-H.; Dong, C. Influence of phase dissolution and hydrogen absorption on the stress corrosion cracking behavior of Mg-7% Gd-5% Y-1% Nd-0.5% Zr alloy in 3.5 wt.% NaCl solution. Corros. Sci. 2018, 142, 185–200. [Google Scholar] [CrossRef]
  46. Wang, S.; Chen, L.; Li, Q.; Wang, S.; Wu, M.; Yang, S.; Xiang, D. Effects of Al or Mo Addition on Microstructure and Mechanical Properties of Fe-Rich Nonequiatomic FeCrCoMnNi High-Entropy Alloy. Metals 2022, 12, 191. [Google Scholar] [CrossRef]
  47. Yang, C.; Xu, W.; Meng, X.; Shi, X.; Shao, L.; Zeng, X.; Yang, Z.; Li, S.; Liu, Y.; Xia, X. A pH-responsive hydrophilic controlled release system based on ZIF-8 for self-healing anticorrosion application. Chem. Eng. J. 2021, 415, 128985. [Google Scholar] [CrossRef]
  48. Zhong, F.; He, Y.; Wang, P.; Chen, C.; Wu, Y. Novel pH-responsive self-healing anti-corrosion coating with high barrier and corrosion inhibitor loading based on reduced graphene oxide loaded zeolite imidazole framework. Colloids Surf. A Physicochem. Eng. Asp. 2022, 642, 128641. [Google Scholar] [CrossRef]
  49. Wang, S.; Lamborn, L.; Chevil, K.; Gamboa, E.; Chen, W. Dense and Sparse Stress Corrosion Crack Initiation in an X65 Pipeline Steel with Mill Scale. In Proceedings of the 2020 13th International Pipeline Conference, Virtual, Online, 28–30 September 2020. [Google Scholar]
  50. Wang, S.; Lamborn, L.; Chen, W. Near-neutral pH corrosion and stress corrosion crack initiation of a mill-scaled pipeline steel under the combined effect of oxygen and paint primer. Corros. Sci. 2021, 187, 109511. [Google Scholar] [CrossRef]
  51. Wang, S.; Lamborn, L.; Chevil, K.; Gamboa, E.; Chen, W. On the formation of stress corrosion crack colonies with different crack population. Corros. Sci. 2020, 168, 108592. [Google Scholar] [CrossRef]
  52. Wang, S.; Lamborn, L.; Chevil, K.; Gamboa, E.; Chen, W. Near-neutral pH corrosion of mill-scaled X-65 pipeline steel with paint primer. J. Mater. Sci. Technol. 2020, 49, 166–178. [Google Scholar] [CrossRef]
  53. Peng, Y.; Liu, L.; Wang, S.; Lin, Y.; Sun, Y.; Xia, R. Effect of simulated pore solution on passivation characteristic of P110 steel. J. Petrol. Sci. Eng. 2018, 167, 949–956. [Google Scholar] [CrossRef]
  54. Durdu, S.; Usta, M. Characterization and mechanical properties of coatings on magnesium by micro arc oxidation. Appl. Surf. Sci. 2012, 261, 774–782. [Google Scholar] [CrossRef]
  55. Wang, S.D.; Wu, M.Y.; Xu, D.K.; Han, E.-h. Improving corrosive wear resistance of Mg-Zn-Y-Zr alloys through heat treatment. J. Magnes. Alloys 2023, 11, 1981–1995. [Google Scholar] [CrossRef]
  56. Wang, S.; Yao, M.; He, X.; Wu, B.; Liu, L.; Wang, S.; Wu, M.; Zhang, X.; Xiang, D. Corrosion Evolution of a Concrete/Casing Steel in Simulated Formation Water under Different CO2 Partial Pressures. Int. J. Electrochem. Sci. 2020, 15, 9948–9970. [Google Scholar] [CrossRef]
  57. Wang, S.D.; Xu, D.; Chen, X.; Han, E.; Dong, C. Effect of heat treatment on the corrosion resistance and mechanical properties of an as-forged Mg–Zn–Y–Zr alloy. Corros. Sci. 2015, 92, 228–236. [Google Scholar] [CrossRef]
  58. Zhao, L.; Cui, C.; Wang, Q.; Bu, S. Growth characteristics and corrosion resistance of micro-arc oxidation coating on pure magnesium for biomedical applications. Corros. Sci. 2010, 52, 2228–2234. [Google Scholar] [CrossRef]
  59. Chen, X.W.; Li, M.L.; Zhang, D.F.; Cai, L.P.; Ren, P.; Hu, J.; Liao, D.D. Corrosion resistance of MoS2-modified titanium alloy micro-arc oxidation coating. Surf. Coat. Technol. 2022, 433, 128127. [Google Scholar] [CrossRef]
  60. Yan, Y.; Han, Y.; Li, D.; Huang, J.; Lian, Q.J.A.S.S. Effect of NaAlO2 concentrations on microstructure and corrosion resistance of Al2O3/ZrO2 coatings formed on zirconium by micro-arc oxidation. Appl. Surf. Sci. 2010, 256, 6359–6366. [Google Scholar] [CrossRef]
  61. Liu, C.; Zhang, W.; Xu, T.; Li, H.; Jiang, B.; Miao, X. Preparation and corrosion resistance of a self-sealing hydroxyapatite-MgO coating on magnesium alloy by microarc oxidation. Ceram. Int. 2022, 48, 13676–13683. [Google Scholar] [CrossRef]
  62. Wang, S.; Lamborn, L.; Chevil, K.; Gamboa, E.; Chen, W. Strain-Aging-Assisted Localized Corrosion of a Mill-Scaled X-65 Pipeline Steel. Corrosion 2021, 77, 792–808. [Google Scholar] [CrossRef]
  63. Li, C.; Goei, R.; Li, Y.; Shi, J.; Liu, F.; Li, B.; Gao, Y.; Li, Y.; Li, S.; Tok, A.I.Y. Effect of chromium on erosion-corrosion properties of ZrO2-Al2O3 particles reinforced Fe-based composites in artificial seawater slurries. Corros. Sci. 2022, 198, 110138. [Google Scholar] [CrossRef]
  64. Li, J.; Ma, C.; Wang, J.; Bian, D.; Zhao, Y. Effect of pore content and pH on the corrosion behavior of hydrophobic ceramic coatings. Int. J. Appl. Ceram. Technol. 2023, 20, 1624–1635. [Google Scholar] [CrossRef]
Coatings 13 01543 g001
Figure 1. U-T (oxidation voltage–time) variation curve of hot-dip aluminum plated samples with composite additives at different concentrations during the micro-arc oxidation treatment.
Figure 1. U-T (oxidation voltage–time) variation curve of hot-dip aluminum plated samples with composite additives at different concentrations during the micro-arc oxidation treatment.
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Figure 2. Surface micromorphology and element distribution of ceramic coating on hot-dip aluminized samples after micro-arc oxidation treatment under different composite additive concentrations: (a1) 2.5 g/L; (b1) 5.0 g/L; (c1) 7.5 g/L; (d1) 10 g/L; (a2–d2) is the enlarged image of the corresponding area).
Figure 2. Surface micromorphology and element distribution of ceramic coating on hot-dip aluminized samples after micro-arc oxidation treatment under different composite additive concentrations: (a1) 2.5 g/L; (b1) 5.0 g/L; (c1) 7.5 g/L; (d1) 10 g/L; (a2–d2) is the enlarged image of the corresponding area).
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Figure 3. Cross-sectional morphology and element distribution of hot-dip aluminized samples after micro-arc oxidation treatment under different composite additive concentrations: (a) 2.5 g/L; (b) 5.0 g/L; (c) 7.5 g/L; (d) 10 g/L.
Figure 3. Cross-sectional morphology and element distribution of hot-dip aluminized samples after micro-arc oxidation treatment under different composite additive concentrations: (a) 2.5 g/L; (b) 5.0 g/L; (c) 7.5 g/L; (d) 10 g/L.
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Figure 4. XRD patterns of hot-dip aluminized samples after micro-arc oxidation treatment under different composite additive concentrations.
Figure 4. XRD patterns of hot-dip aluminized samples after micro-arc oxidation treatment under different composite additive concentrations.
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Figure 5. Thickness value (a) and hardness value (b) of ceramic coating on hot-dip aluminum-coated samples after micro-arc oxidation treatment under different composite additive concentrations.
Figure 5. Thickness value (a) and hardness value (b) of ceramic coating on hot-dip aluminum-coated samples after micro-arc oxidation treatment under different composite additive concentrations.
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Figure 6. EIS spectra of micro-arc oxidation coatings on hot-dip aluminum-coated samples treated under different composite additive concentrations: (a) Nyquist plot; (b) Bode plot.
Figure 6. EIS spectra of micro-arc oxidation coatings on hot-dip aluminum-coated samples treated under different composite additive concentrations: (a) Nyquist plot; (b) Bode plot.
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Figure 7. Equivalent circuit diagrams of EIS for micro-arc oxidation coatings on hot-dip aluminum-coated samples treated under varying composite additive concentrations.
Figure 7. Equivalent circuit diagrams of EIS for micro-arc oxidation coatings on hot-dip aluminum-coated samples treated under varying composite additive concentrations.
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Table 1. Main chemical composition of 316L stainless steel (in wt.%).
Table 1. Main chemical composition of 316L stainless steel (in wt.%).
ElementCSiMnSPCrNiMoN
Content0.020.81.50.030.0316.510.82.20.08
Table 2. The concentration of K2ZrF6/Al2O3 composite additives utilized in this work.
Table 2. The concentration of K2ZrF6/Al2O3 composite additives utilized in this work.
ConditionTotal Concentration (g/L)K2ZrF6 (g/L)Al2O3 (g/L)
S00.00.00.0
S12.52.00.5
S25.04.01.0
S37.56.01.5
S410.08.02.0
Table 3. EDS element content on the surface of hot-dip aluminized samples after micro-arc oxidation treatment under different composite additive concentrations.
Table 3. EDS element content on the surface of hot-dip aluminized samples after micro-arc oxidation treatment under different composite additive concentrations.
Composite Additive Concentration (g/L)O (wt.%)Al (wt.%)P (wt.%)Si (wt.%)Zr (wt.%)
2.535.16561.5380.2001.3991.698
5.031.90064.9000.3001.1001.800
7.530.40066.3000.3000.8002.200
10.030.80065.5000.3001.1002.300
Table 4. Fitting results of EIS for micro-arc oxidation coatings on hot-dip aluminum-coated samples treated under different composite additive concentrations.
Table 4. Fitting results of EIS for micro-arc oxidation coatings on hot-dip aluminum-coated samples treated under different composite additive concentrations.
SampleRs (Ω·cm2)Cp1 (F·cm−2)Rp1 (Ω·cm2)Cp2 (F·cm−2)Rp2 (Ω·cm2)
S020.379.707 × 10−5545.33.856 × 10−31134
S114.561.746 × 10−4580.02.871 × 10−31353
S252.132.242 × 10−51473.01.430 × 10−32779
S352.701.263 × 10−53240.06.439 × 10−47488
S418.267.745 × 10−72571.03.112 × 10−53207
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Wang, S.; Peng, X.; Yang, Y.; Wang, S.; Wu, M.; Hu, P.; Fu, C. Insight into Microstructure Evolution and Corrosion Mechanisms of K2ZrF6/Al2O3-Doped Hot-Dip Aluminum/Micro-Arc Oxidation Coatings. Coatings 2023, 13, 1543. https://doi.org/10.3390/coatings13091543

AMA Style

Wang S, Peng X, Yang Y, Wang S, Wu M, Hu P, Fu C. Insight into Microstructure Evolution and Corrosion Mechanisms of K2ZrF6/Al2O3-Doped Hot-Dip Aluminum/Micro-Arc Oxidation Coatings. Coatings. 2023; 13(9):1543. https://doi.org/10.3390/coatings13091543

Chicago/Turabian Style

Wang, Shuliang, Xiaofei Peng, Yi Yang, Shidong Wang, Mingyu Wu, Ping Hu, and Chunyan Fu. 2023. "Insight into Microstructure Evolution and Corrosion Mechanisms of K2ZrF6/Al2O3-Doped Hot-Dip Aluminum/Micro-Arc Oxidation Coatings" Coatings 13, no. 9: 1543. https://doi.org/10.3390/coatings13091543

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