Composite coating for marine atmospheric environment and preparation method thereof

Abstract

The invention relates to a micro-arc oxidation composite coating for a marine atmospheric environment and a preparation method of the micro-arc oxidation composite coating, and belongs to the technical field of metal material surface treatment. The preparation method comprises the following steps: treating a base material which is a magnesium alloy; the treated base material is placed in electrolyte to be subjected to micro-arc oxidation treatment; and finally, magnetron sputtering is carried out on the base material subjected to micro-arc oxidation treatment. The composite coating is prepared on the base material and sequentially comprises a micro-arc oxidation layer and a magnetron sputtering layer. The micro-arc oxidation layer achieves a hole sealing effect through magnetron sputtering; meanwhile, the roughness and porosity of the surface of the micro-arc oxidation layer are improved, the porosity is 22.0% or below, the impermeability of the composite coating is remarkably improved, and therefore the corrosion resistance of the micro-arc oxidation layer is comprehensively improved, and technical support is provided for further application of light alloy in ocean engineering equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material surface treatment, and in particular to a composite coating for marine atmospheric environment and a preparation method thereof. Background Art

[0002] The marine atmosphere is characterized by high humidity, high salinity, and a rich diversity of marine microorganisms. The large amount of salts such as sodium chloride dissolved in seawater forms an electrolyte solution film on metal surfaces. This, combined with oxidants such as oxygen, triggers electrochemical corrosion of the metal. This corrosion phenomenon is particularly severe for various metal structures exposed to the marine atmosphere, such as ships, offshore platforms, and coastal facilities. Corrosion not only causes direct wear and tear on metal materials, reducing their mechanical properties and structural integrity, but can also lead to equipment failures, safety incidents, increased maintenance costs, and downtime, resulting in significant economic losses for marine engineering and related industries.

[0003] Micro-arc oxidation, an emerging surface treatment technology, has garnered widespread attention in the field of metal corrosion protection in recent years. This technology builds upon conventional anodizing by increasing the operating voltage, causing the oxide film on the metal surface to undergo micro-arc discharge in an electrolyte. During this micro-arc discharge process, the transient high temperature and high pressure create an in-situ oxide film with ceramic properties on the metal surface. This film exhibits high hardness, excellent wear resistance, and a certain degree of corrosion resistance. It also bonds tightly to the metal substrate, eliminating the adhesion issues associated with traditional coatings.

[0004] However, due to its porous structure, high porosity, and numerous cracks, the long-term corrosion resistance of simple micro-arc oxidation coatings in marine atmospheric environments still needs to be improved. In particular, its protective effect is limited when facing complex and changing marine climate conditions and long-term seawater erosion. Therefore, it is necessary to improve or compositely treat the micro-arc oxidation coating to reduce its surface porosity and achieve a pore sealing effect, thereby improving its corrosion resistance in marine environments. Summary of the Invention

[0005] In view of the above analysis, the present invention aims to provide a micro-arc oxidation composite coating for use in marine atmospheric environment and a preparation method thereof, so as to solve the problem of poor corrosion resistance of existing micro-arc oxidation coatings.

[0006] In one aspect, the present invention provides a method for preparing a composite coating for use in a marine atmospheric environment, comprising the following steps:

[0007] S1: treating a substrate, wherein the substrate is a magnesium alloy;

[0008] S2: prepare electrolyte;

[0009] S3: placing the treated substrate in an electrolyte for micro-arc oxidation treatment;

[0010] S4: Finally, magnetron sputtering is performed on the substrate after micro-arc oxidation treatment;

[0011] A composite coating is prepared on a substrate, which comprises a micro-arc oxidation layer and a magnetron sputtering layer in sequence.

[0012] Furthermore, the magnesium alloy is az31b or az91.

[0013] Furthermore, in step S4, the temperature of the magnetron sputtering is 25°C-30°C.

[0014] Furthermore, in step S4, pre-sputtering is first performed, and then magnetron sputtering is performed; the pre-sputtering time is 80-120s, the magnetron sputtering time is 500-600s, the magnetron sputtering power is 80-100w, and the turntable speed is 5-7r / min.

[0015] Furthermore, in step S4, an aluminum oxide target is used to coat the surface of the magnesium alloy micro-arc oxidation layer by magnetron sputtering.

[0016] Furthermore, in step S3, a double pulse power supply is used to perform micro-arc oxidation on the surface of the substrate; the micro-arc oxidation process parameters are: a current density of 3-5A / dm 2 , frequency is 1500-2500Hz, duty cycle is 10%-30%, temperature is 20℃-40℃, and time is 2-3min.

[0017] Furthermore, in step S2, when preparing the electrolyte, 8-12 g of sodium silicate, 1-3 g of sodium hydroxide and 1-3 g of sodium fluoride are added to each liter of deionized water.

[0018] Furthermore, in step S1, the substrate is treated in the following steps: degreasing and cleaning, grinding and polishing, ultrasonic cleaning, and drying;

[0019] The grinding and polishing process is to use 200#, 400#, 800#, 1200#, and 2000# SiC sandpaper to grind the substrate surface step by step.

[0020] Furthermore, the thickness of the composite coating is 20 μm-22 μm.

[0021] On the other hand, the present invention provides a composite coating for use in a marine atmospheric environment, which is obtained by the preparation method described in the present invention. The composite coating includes a micro-arc oxidation layer and a magnetron sputtering layer.

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] 1. In the present invention, a magnesium alloy substrate needs to be treated, then placed in an electrolyte for micro-arc oxidation treatment, and finally subjected to magnetron sputtering treatment. Magnetron sputtering is used to achieve a pore-sealing effect in the micro-arc oxidation layer. At the same time, the surface roughness and porosity of the micro-arc oxidation layer are improved, with the porosity below 22.0%, and the impermeability of the composite coating is significantly enhanced. This comprehensively improves the corrosion resistance of the micro-arc oxidation layer, providing technical support for the further application of light alloys in marine engineering equipment.

[0024] 2. The present invention forms a composite coating on a magnesium alloy substrate, comprising a micro-arc oxidation layer and a magnetron sputtering layer. The micro-arc oxidation layer has a porous structure, and aluminum oxide is filled into the porous structure of the micro-arc oxidation layer by magnetron sputtering. At this time, the micro-arc oxidation layer and the magnetron sputtering layer have excellent bonding strength due to interlocking, preventing the composite coating from falling off, thereby increasing the service life of the composite coating;

[0025] 3. The present invention coats an aluminum oxide layer on the micro-arc oxide layer by magnetron sputtering, namely, a magnetron sputtering layer. During use, a passivation film with high chemical stability is formed, which can improve corrosion resistance.

[0026] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0028] Figure 1 Schematic diagram of the structure of the micro-arc oxidation composite coating;

[0029] Figure 2 The surface morphology of the composite coating of Example 1 under a scanning electron microscope;

[0030] Figure 3 The surface morphology of the composite coating of Comparative Example 1 under a scanning electron microscope;

[0031] Figure 4 is the potentiodynamic polarization curve obtained by testing in 3.5wt.% NaCl solution;

[0032] Reference numerals:

[0033] 1. Substrate; 2. Micro-arc oxidation layer; 3. Magnetron sputtering layer. DETAILED DESCRIPTION

[0034] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0035] Various metal structures, especially light alloys, are used in ships, offshore platforms, coastal facilities, and other equipment. However, when light alloys come into contact with the marine atmosphere, they can cause electrochemical corrosion, leading to direct loss of the metal material and reducing its mechanical properties and structural integrity.

[0036] To improve the corrosion resistance of light alloys, micro-arc oxidation (MAO) is performed on their surfaces. This technology builds upon conventional anodizing by increasing the operating voltage to induce micro-arc discharges in the electrolyte. During this micro-arc discharge process, the instantaneous high temperature and high pressure create an in-situ ceramic-like MAO film on the metal surface. This MAO film exhibits high hardness, excellent wear resistance, and a certain degree of corrosion resistance.

[0037] However, due to its porous structure, high porosity and numerous cracks, the long-term corrosion resistance of the micro-arc oxidation coating in the marine atmospheric environment still needs to be improved. Especially when facing complex and changeable marine climate conditions and long-term seawater erosion, its protective effect has certain limitations.

[0038] Therefore, the present invention provides a method for preparing a composite coating for use in a marine atmospheric environment, comprising the following steps:

[0039] S1: treating a substrate, wherein the substrate is a magnesium alloy;

[0040] S2: prepare electrolyte;

[0041] S3: placing the treated substrate in an electrolyte for micro-arc oxidation treatment;

[0042] S4: Finally, magnetron sputtering is performed on the substrate after micro-arc oxidation treatment;

[0043] A composite coating is prepared on a substrate, which comprises a micro-arc oxidation layer and a magnetron sputtering layer in sequence.

[0044] Compared with the existing technology, the preparation method provided by the present invention requires the treatment of the magnesium alloy substrate, which is then placed in an electrolyte for micro-arc oxidation treatment, and finally subjected to magnetron sputtering treatment. Magnetron sputtering is used to achieve the effect of sealing the micro-arc oxidation layer; at the same time, the surface roughness and porosity of the micro-arc oxidation layer are improved, and the impermeability of the composite coating is significantly improved, thereby comprehensively improving the corrosion resistance of the micro-arc oxidation layer and providing technical support for the further application of light alloys in marine engineering equipment.

[0045] Specifically, in step S1, the substrate is treated in the following order: degreasing and cleaning, grinding and polishing, ultrasonic cleaning, and drying;

[0046] The grinding process is to use 200#, 400#, 800#, 1200#, and 2000# SiC sandpaper to grind the substrate surface step by step.

[0047] It should be noted that polishing the substrate before micro-arc oxidation can effectively remove surface oxides and oil stains, making the resulting film more uniform and smooth, making it easier to undergo micro-arc oxidation and magnetron sputtering treatments, obtaining a smaller porosity, and improving corrosion resistance.

[0048] Specifically, in step S2, when preparing the electrolyte, 8-12 g of sodium silicate, 1-3 g of sodium hydroxide and 1-3 g of sodium fluoride are added to each liter of deionized water.

[0049] It should be noted that in preparing the electrolyte, sodium silicate, sodium hydroxide and sodium fluoride are added to deionized water and stirred evenly. The concentration of sodium silicate in the electrolyte is 8-12 g / L, the concentration of sodium hydroxide is 1-3 g / L, and the concentration of sodium fluoride is 1-3 g / L.

[0050] In the present invention, the electrolyte acts as a conductive medium to promote the electrochemical reaction between the substrate and the electrode, and through ion conduction, a closed loop is formed to drive the oxidation reaction required for micro-arc discharge. At the same time, the active ions in the electrolyte (such as SiO3 2- 、F - ) will also participate in the formation of oxide film.

[0051] Specifically, in step S3, a double pulse power supply is used to perform micro-arc oxidation on the surface of the substrate; the micro-arc oxidation process parameters are: a current density of 3-5A / dm 2 , frequency is 1500-2500Hz, duty cycle is 10%-30%, temperature is 20℃-40℃, and time is 2-3min.

[0052] It should be noted that there is a significant mutual influence between micro-arc oxidation and magnetron sputtering, especially in the synergy between surface morphology and film layer combination. If micro-arc oxidation parameters such as voltage, electrolyte composition, and processing time are not properly controlled, the porosity of the film may be too high or unevenly distributed, forming a rough and porous surface structure. This high porosity will not only weaken the uniform deposition of target atoms during magnetron sputtering, but also reduce the adhesion and density of the sputtered film due to stress concentration at the edge of the hole or residual electrolyte contaminants, and even cause the film layer to crack or peel off. At the same time, the residual microcracks or loose areas in the micro-arc oxidation film layer may become nucleation points for defects in the magnetron sputtering film, further affecting its corrosion resistance. Therefore, optimizing the micro-arc oxidation process to control porosity and surface flatness is the key to ensuring the quality of subsequent magnetron sputtering films.

[0053] In the present invention, the micro-arc oxidation process parameters have different effects on the performance of the micro-arc oxidation film. Among them, the duty cycle is 10%-30%, such as 10%, 12%, 15%, 18%, 20%, 21%, 23%, 25%, 29% or 30%; the frequency is controlled at 1500-2500Hz, such as 1500Hz, 1600Hz, 1700Hz, 1800Hz, 2000Hz, 2200Hz or 2500Hz. The micro-arc oxidation film prepared at too high or too low a frequency is looser and has larger pore size; the current density is 3-5A / dm 2 , such as 3A / dm 2 , 4A / dm 2 or 5A / dm 2 A lower current density will loosen the film, while a higher current density will cause localized ablation, making the film surface uneven. The temperature is 20°C-40°C, such as 20°C, 22°C, 25°C, 27°C, 29°C, 30°C, 31°C, 35°C, 36°C, 38°C, or 40°C. Higher temperatures will hinder film formation and affect film quality. The time should be controlled within 2-3 minutes. A shorter time will result in a thinner film. However, there is an upper limit to the film thickness. Once the upper limit is reached, the thickness cannot be increased even if the time is extended.

[0054] Specifically, in step S4, pre-sputtering is first performed, and then magnetron sputtering is performed; the pre-sputtering time is 80-120s, the magnetron sputtering time is 500-600s, the magnetron sputtering power is 80-100w, and the turntable speed is 5-7r / min.

[0055] It should be noted that in the present invention, the control of parameters during the magnetron sputtering process directly affects the performance of the final product. For example, the time of magnetron sputtering is controlled at 500-600s, which can be 500s, 520s, 530s, 550s, 570s, 580s or 600s; a higher sputtering time will lead to increased surface roughness, and a lower sputtering time will result in a thinner coating, which will not be able to play a protective role. Similarly, the power of magnetron sputtering is controlled at 80-100w, which can be 80w, 83w, 86w, 88w, 90w, 94w, 96w or 100w; a higher power will also lead to increased grain size and increased surface roughness, and a lower sputtering power will result in a too thin coating, which will also not be able to play an effective protective role.

[0056] Specifically, in step S4, an aluminum oxide target with a diameter of 80 μm is used to coat the surface of the magnesium alloy micro-arc oxidation layer by magnetron sputtering.

[0057] It should be noted that in the present invention, a magnetron sputtering layer, namely an aluminum oxide film, is formed on the micro-arc oxide layer by using aluminum oxide as a target material for magnetron sputtering. As a passivation film, the aluminum oxide film effectively resists corrosion and exhibits good compatibility with the micro-arc oxide layer. This not only improves bonding strength but also seals the micro-arc oxide layer, resulting in a lower porosity and, in turn, higher corrosion resistance, effectively extending the protection period.

[0058] Specifically, in step S4, the temperature of the magnetron sputtering is 25°C-30°C.

[0059] Specifically, the magnesium alloy is az31b or az91.

[0060] It should be noted that AZ31B and AZ91 are both AZ series magnesium alloys, the main alloying elements of which are aluminum (Al) and zinc (Zn). The aluminum content is relatively high, and they have low density characteristics, with a specific gravity of about 1.78-1.8.

[0061] The present invention provides a composite coating for use in a marine atmospheric environment, which is obtained by the preparation method of the present invention. The composite coating comprises a micro-arc oxidation layer and a magnetron sputtering layer, and the thickness of the composite coating is 20 μm-22 μm.

[0062] It should be noted that the present invention forms a composite coating on a magnesium alloy substrate, which includes a micro-arc oxidation layer and a magnetron sputtering layer. The micro-arc oxidation layer has a porous structure, and aluminum oxide is filled into the porous structure of the micro-arc oxidation layer by magnetron sputtering. At this time, the micro-arc oxidation layer and the magnetron sputtering layer have excellent bonding force due to interlocking, which prevents the composite coating from falling off, thereby improving the service life of the composite coating.

[0063] The present invention coats an aluminum oxide layer on the micro-arc oxide layer by magnetron sputtering, namely, a magnetron sputtering layer. During use, a passivation film with high chemical stability is formed, which can improve corrosion resistance.

[0064] In order to more clearly describe the present invention, it is further illustrated by the following examples and comparative examples.

[0065] Example 1

[0066] The preparation method of the composite coating comprises the following steps:

[0067] S1: treating a substrate, wherein the substrate is a magnesium alloy;

[0068] The az31b magnesium alloy substrate was degreased and cleaned with a degreasing agent, and then the surface of the az31b magnesium alloy was polished step by step using SiC sandpaper of different sizes (200#, 400#, 800#, 1200#, 2000#). The polished az31b magnesium alloy was ultrasonically cleaned for 3 minutes using ethanol and other cleaning agents, and then dried with hot air.

[0069] S2: prepare electrolyte; the concentration of sodium silicate in the electrolyte is 10g / L, the concentration of sodium hydroxide is 2g / L, and the concentration of sodium fluoride is 2g / L;

[0070] S3: placing the treated substrate in an electrolyte for micro-arc oxidation treatment;

[0071] Using a pulse power supply in constant voltage mode, the micro-arc oxidation process parameters are as follows: current density is 4A / dm 2 , stirring speed is 200 rpm, frequency is 2000 Hz, duty cycle is 20%, temperature is 40 ° C, and time is 2 min;

[0072] S4: Finally, magnetron sputtering is performed on the substrate after micro-arc oxidation treatment; an aluminum oxide target with a diameter of 80 mm is pre-sputtered first, and then magnetron sputtered, and the surface of the magnesium alloy micro-arc oxidation layer is coated by magnetron sputtering;

[0073] The temperature of magnetron sputtering is 25° C., the time of pre-sputtering is 100 s, the time of magnetron sputtering is 600 s, the power of magnetron sputtering is 100 W, and the rotation speed of the turntable is 7 r / min.

[0074] A composite coating is prepared on a substrate, which includes a micro-arc oxidation layer and a magnetron sputtering layer in sequence. The thickness of the composite coating is 20 μm.

[0075] Example 2

[0076] The preparation process of Example 2 is substantially the same as that of Example 1, except that in step S3 of Example 2, the micro-arc oxidation process parameters are as follows: the current density is 5A / dm 2 , frequency is 2500Hz, duty cycle is 30%, temperature is 40℃, and time is 3min.

[0077] Example 3

[0078] The preparation process of Example 3 is substantially the same as that of Example 1, except that in step S3 of Example 3, the micro-arc oxidation process parameters are as follows: the current density is 3A / dm 2 , frequency is 1500Hz, duty cycle is 10%, temperature is 20℃, and time is 2min.

[0079] Example 4

[0080] The preparation process of Example 4 is substantially the same as that of Example 1, except that, in step S4 of Example 4, the temperature of magnetron sputtering is 25°C, the time of pre-sputtering is 100s, the time of magnetron sputtering is 550s, the power of magnetron sputtering is 90w, and the turntable speed is 6r / min.

[0081] Example 5

[0082] The preparation process of Example 5 is substantially the same as that of Example 1, except that, in step S4 of Example 5, the temperature of magnetron sputtering is 25°C, the time of pre-sputtering is 100s, the time of magnetron sputtering is 500s, the power of magnetron sputtering is 80w, and the turntable speed is 5r / min.

[0083] Comparative Example 1

[0084] The preparation process of Comparative Example 1 is substantially the same as that of Example 1, except that step S4 is not included in Comparative Example 1.

[0085] Comparative Example 2

[0086] The preparation process of Comparative Example 2 is substantially the same as that of Example 1, except that in step S3 of Comparative Example 2, the micro-arc oxidation process parameters are as follows: the current density is 2A / dm 2 , frequency is 1000Hz, duty cycle is 5%, temperature is 45℃, and time is 30s.

[0087] Comparative Example 3

[0088] The preparation process of Comparative Example 3 is substantially the same as that of Example 1, except that in Comparative Example 3, the temperature of magnetron sputtering is 35° C., the time of pre-sputtering is 150 s, the time of magnetron sputtering is 400 s, and the power of magnetron sputtering is 120 W.

[0089] Performance testing

[0090] The above examples and comparative examples were subjected to performance tests, mainly including corrosion current, corrosion potential, and porosity. The test results are shown in Table 1.

[0091] Table 1 Performance test results

[0092] Group log(i / A) Corrosion potential (V) Porosity% Example 1 -8.4732 -0.2787 14.285 Example 2 -8.1384 -0.3528 16.863 Example 3 -8.2287 -0.5039 17.543 Example 4 -8.5001 -0.5681 19.453 Example 5 -8.3621 -0.3956 21.523 Comparative Example 1 -7.6700 -0.8382 28.960 Comparative Example 2 -6.8052 -0.9909 26.245 Comparative Example 3 -6.2159 -1.1242 25.822

[0093] Combined with Examples 1-5 and Comparative Examples 1-3 and with reference to Tables 1 and Figure 1-4 It can be seen that the preparation method provided in this example, through micro-arc oxidation and magnetron sputtering treatment, forms a composite coating on the magnesium alloy substrate, namely a micro-arc oxidation layer and a magnetron sputtering layer. The thickness of the composite coating ranges from 20 μm to 22 μm. Testing shows that the composite coatings obtained in Examples 1-5 have a porosity of 14-22%, a corrosion potential above -0.6, and a log(i / A) below -8, indicating good corrosion resistance.

[0094] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a composite coating for marine atmospheric environment, characterized in that: The following steps are involved: S1: treating a substrate, wherein the substrate is a magnesium alloy; S2: prepare electrolyte; S3: placing the treated substrate in an electrolyte for micro-arc oxidation treatment; S4: finally, magnetron sputtering is performed on the substrate after micro-arc oxidation treatment; A composite coating is prepared on a substrate, which comprises a micro-arc oxidation layer and a magnetron sputtering layer in sequence.

2. The method for preparing a composite coating for marine atmospheric environment according to claim 1, characterized in that: The magnesium alloy is az31b or az91.

3. The method for preparing a composite coating for marine atmospheric environment according to claim 1, characterized in that: In step S4, the temperature of the magnetron sputtering is 25°C-30°C.

4. The method for preparing a composite coating for marine atmospheric environment according to claim 1, characterized in that: In step S4, pre-sputtering is first performed, and then magnetron sputtering is performed; the pre-sputtering time is 80-120s, the magnetron sputtering time is 500-600s, the magnetron sputtering power is 80-100w, and the turntable speed is 5-7r / min.

5. The method for preparing a composite coating for marine atmospheric environment according to claim 1, characterized in that: In step S4, an aluminum oxide target is used to coat the surface of the magnesium alloy micro-arc oxidation layer by magnetron sputtering.

6. The method for preparing a composite coating for marine atmospheric environment according to claim 1, characterized in that: In step S3, a double pulse power supply is used to perform micro-arc oxidation on the surface of the substrate; the micro-arc oxidation process parameters are: a current density of 3-5A / dm 2 , frequency is 1500-2500Hz, duty cycle is 10%-30%, temperature is 20℃-40℃, and time is 2-3min.

7. The method for preparing a composite coating for marine atmospheric environment according to claim 1, characterized in that: In step S2, when preparing the electrolyte, 8-12 g of sodium silicate, 1-3 g of sodium hydroxide and 1-3 g of sodium fluoride are added to each liter of deionized water.

8. The method for preparing a composite coating for marine atmospheric environment according to claim 1, characterized in that: In step S1, the substrate is treated in the following order: degreasing and cleaning, grinding and polishing, ultrasonic cleaning, and drying; The grinding and polishing process is to use 200#, 400#, 800#, 1200#, and 2000# SiC sandpaper to grind the substrate surface step by step.

9. The method for preparing a composite coating for marine atmospheric environment according to claim 1, characterized in that: The thickness of the composite coating is 20 μm-22 μm.

10. A composite coating for use in a marine atmospheric environment, characterized in that: The composite coating is obtained by the preparation method according to any one of claims 1 to 9, wherein the composite coating comprises a micro-arc oxidation layer and a magnetron sputtering layer.

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