Method for applying coatings to articles made of valve metals and their alloys

Abstract

The present invention relates to the field of electrochemical applications for coating valve metals such as aluminum, titanium, magnesium and their alloys by means of a micro-arc oxidation (MAO) process, with a wide range of uses not only on new articles but also on articles after operation, in particular for restoring coatings after wear. A method consists in immersing the article in a bath with an aqueous electrolyte solution and carrying out the MAO in a pulsed anodic-cathodic mode. The MAO is carried out by controlling the growth rate of the coating on the edges, corners and center of the article by changing the mode during the application of the coating, using a device in which a charging unit comprises a quasi-resonant converter with a controllable pulse increase in current and voltage working modes. The invention makes it possible to control the coating production rate on different surface areas of the article, making it possible to obtain a coating of uniform thickness on the article or the necessary thickness of its areas.

Description

Technical Field

[0001] The present invention relates to the field of micro-arc oxidation electrochemical coating of valve metals (aluminum, titanium, magnesium) and their alloys. The process has wide application not only on new products but also on products after operation, for example, to restore the coating after wear. Compared with anodizing and other electroplating processes, micro-arc oxidation (MAO) is characterized by shorter coating times and the elimination of numerous operations associated with product surface preparation, such as etching, degreasing, bleaching, and rinsing with hot and cold water. It also significantly simplifies wastewater and spent electrolyte treatment systems, reduces the number of production areas, and reduces water consumption. Background Art

[0002] A method for forming a ceramic coating on metals and alloys comprises an electrolytic cell equipped with a first electrode and filled with an alkaline aqueous electrolyte, wherein the article is immersed in the electrolyte and connected to another electrode, wherein a pulsed current is supplied through the electrode so that the process is carried out in a plasma discharge mode. The specified process comprises the following steps: supplying high-frequency bipolar current pulses having a predetermined frequency range to the electrode; and generating acoustic vibrations in the electrolyte within a given acoustic frequency range, such that the frequency range of the acoustic vibrations overlaps the frequency range of the current pulses (patents WO03083181, C25D11 / 02, and C25D11 / 04, published on October 9, 2003).

[0003] However, according to the data given in the patent, although the formation rate of the MAO coating is high (2-10 μm / min), there is no information about the area of ​​the part to be coated, so it is difficult to estimate the true formation rate of the coating and to which area of ​​the product this rate is related.

[0004] This patent proposes to obtain a low roughness coating (0.6-2.1 μm) by additionally using an acoustic vibration generator, which complicates the installation design and thus increases the cost of the MAO coating technology.

[0005] The disadvantage is also the use of unstable electrolytes, which alkalize quickly and become clogged with reaction products. It is impossible to correct the depleted electrolyte by simply adding the missing components, which leads to a short working time, after which the electrolyte must be emptied and replaced with a new one. When dispersed particles are used in the electrolyte composition, the solution must be constantly stirred to maintain a stable content of the dispersed particles in the electrolyte volume, which also complicates the installation design.

[0006] There is a known method comprising micro-arc oxidation of valve metal products and their alloys in an aqueous electrolyte solution containing sodium dihydrogen phosphate, sodium silicate, potassium cyanide, sodium molybdate in pulsed anodic-cathodic mode (patent RU 2607875, C25D11 / 14, publication date 20.10.2016).

[0007] A disadvantage of this method is the use of alkali metal silicates in the electrolyte. Although the service life of a given electrolyte is longer than with standard silicate electrolytes, the use of small amounts of alkali metal silicates, such as 1 to 10 g / L, can lead to alkalization and clogging with reaction products. Furthermore, this method cannot form a uniform black coating on composite components composed of various aluminum and titanium alloys.

[0008] A known method in the field of electrochemical coating of valve metals and their alloys (patent RU2077612, C25D11 / 02, publication date 20.04.1997) was chosen as a prototype. This method involves oxidation in an alkaline electrolyte in a pulsed anodic-cathodic mode, alternating positive and negative pulses of complex shape, with pulse durations and pauses between them of 100-300 μs, an initial time of 0-7 μs, and anodic current density values ​​ranging from 0 to 800 A / dm 2 It remains constant until 25-50μs, after which it suddenly changes from the initial set value to 80-800A / dm 2 The cathode current density value ranges from 0 to 800A / dm in 0-7μs. 2 Sudden change, remains constant before 25-50μs, then suddenly changes from the initially set value to 50-800A / dm 2 Then from 25-50μs to the end of the pulse, it changes to 80-800A / dm 2 As alkaline electrolytes, 1) aqueous solutions of phosphates, borates, and alkali metal fluorides with a pH of 7-8 are used, as well as 2) solutions containing liquid glass, alkali metal hydroxides, fine powders of oxides, nitrides, metal carbides, and metalloids. The resulting oxide layer is then treated in a solution of a polymer material or ground.

[0009] A drawback of the prototype is the use of high energy concentrations during the initial 0-7 μs, which subsequently disrupt the metal surface, preventing good adhesion of the coating to the metal. The narrow pulse duration of 100-300 μs reduces the effectiveness of controlling the coating's properties. Furthermore, the impact of the high-density current on the electrolyte containing the liquid glass leads to its destruction, making it impossible to repeatedly obtain high-quality coatings in this electrolyte. A further disadvantage is the use of fine powders in the electrolyte that must be constantly kept in suspension, making it difficult to control the concentration of suspended particles in the electrolyte volume. After the current is passed through, the changes in the liquid glass structure do not provide a charge for the suspended particles in solution. All of this leads to a rapid decrease in the formation rate and a loss of coating performance. Summary of the Invention

[0010] The purpose of the present invention is to develop a method for coating products made of valve metals and their alloys, which, thanks to the proposed coating formation algorithm, makes it possible to control the coating formation rate over the entire surface of the article, which makes it possible to obtain coatings with complex physical and mechanical properties.

[0011] The technical result is a control of the speed with which the coating is obtained on various parts of the surface of the article, which in turn allows a coating of uniform thickness to be obtained on the entire surface of the article or on individual parts thereof to be obtained with a desired thickness.

[0012] The technical result is that, by combining this method with the required power source, it is possible to reduce the energy consumption of production and increase the loading area of ​​the covered part.

[0013] The technical achievements also include the realization of the following series of characteristics of the produced coating:

[0014] Roughness of 1.5 μm or less;

[0015] Corrosion resistance is 1000h or higher;

[0016] Hardness of 500HV or higher;

[0017] Wear resistance is 8mg / 1000 times or less;

[0018] The porosity is 17% or less.

[0019] Finished coatings up to 150 μm thick can be obtained using this method, without the need for additional machining to remove loose coating.

[0020] Furthermore, compared to known MAO coating formation methods, this method enables the coating of products with an area ranging from 0.001 to 2000 dm 2 .

[0021] The solution to this problem is to coat the surface of articles made entirely or partially of valve metal or its aluminum, magnesium, or titanium alloys immersed in an aqueous electrolyte solution by micro-arc oxidation in a pulsed anodic-cathodic mode. Unlike the prototype, micro-arc oxidation is carried out in a pulsed anodic-cathodic mode with a voltage of 0 to 1200 V. The pulse duration is 10 to 1000 μs, the pulse repetition frequency is 10 to 1000 Hz, and the pause time between the anodic and cathodic pulses is 0 to 10 ms, controlling the coating growth rate at the face, corner, and center of the treated surface.

[0022] The technical achievement is achieved by using a device that includes a tank with electrolyte and oxide products, a power supply including a control unit, a direct pulse generating unit, a reverse pulse generating unit, a capacitor unit, and a charging unit. The charging unit can charge a large capacitive load without the need for an additional circuit current limiting part. It has a controllable pulse boost quasi-resonant converter with current and voltage working modes ( Figure 1 ).

[0023] This equipment allows the coating of parts to be continued after machining has stopped, achieving the desired thickness and necessary coating properties. Coatings obtained with this equipment do not require additional machining.

[0024] The use of a controlled pulse-boosted quasi-resonant converter makes it possible to eliminate additional current-limiting parts in the circuit, thereby reducing energy losses. A pulse repetition frequency of up to 1000 Hz and a pulse duration of 10 μs are applied to obtain the coating without affecting the quality of the obtained coating, making it possible to obtain a coating with the required roughness and thickness without the need for an acoustic vibration generator. This greatly simplifies the installation design of the MAO, reduces energy consumption, and generally reduces the cost of coating production.

[0025] In order to form a coating with a higher growth rate (vf) on the surface and corners of the article than in the center (vc) (vf>vc), the anodic voltage was set to 350 to 600 V, a pulse duration of 50 to 300 μs, and a pulse repetition frequency of 30 to 500 Hz; the cathodic voltage was set to 0 to 100 V, a pulse duration of 50 to 100 μs, and a pulse repetition frequency of 30 to 500 Hz; the pause time between the anodic and cathodic pulses was 0 to 5 ms; the voltage amplitude was 350 to 500 V, the pulse duration was 50 to 300 ms, and the pulse repetition frequency was The proportion of anode pulses with a voltage amplitude of 30 to 500 Hz and the proportion of cathode pulses with a voltage amplitude of 0 to 50 V, a pulse duration of 50 to 100 μs, and a pulse repetition frequency of 30 to 500 Hz do not exceed 75%; while the proportion of anode pulses with a voltage amplitude of 500 to 600 V, a pulse duration of 50 to 300 μs, and a pulse repetition frequency of 30 to 500 Hz and the proportion of cathode pulses with a voltage amplitude of 0 to 100 V, a pulse duration of 50 to 100 μs, and a pulse repetition frequency of 30 to 500 Hz are at least 25%.

[0026] In order to form a coating (vf) with the same growth rate on the item center (vc) and the item surface (corner), i.e., vf = vc, the anode voltage is set to 200 to 600 V, the pulse duration is 50 to 300 μs, and the pulse repetition frequency is 30 to 100 Hz. The cathode voltage is 0 to 100 V, the pulse duration is 50 to 200 μs, and the pulse repetition frequency is 30 to 100 Hz; the pause time between the anode and cathode pulses is 5 to 8 ms; the proportion of anode pulses with a voltage amplitude of 500 to 600 V, a pulse duration of 50 to 300 μs, and a pulse repetition frequency of 30 to 100 Hz, and the proportion of cathode pulses with a voltage amplitude of 0 to 100 V, a duration of 50 to 200 μs, and a pulse repetition frequency of 30 to 100 Hz do not exceed 50%; and the proportion of anode pulses with a voltage amplitude of 200 to 400 V, a duration of 50 to 300 μs, and a pulse repetition frequency of 30 to 100 Hz, and the proportion of cathode pulses with a voltage amplitude of 100 to 200 V, a duration of 50 to 200 μs, and a pulse repetition frequency of 30 to 100 Hz is at least 50%.

[0027] In order to form a coating where the growth rate at the item center (vc) is higher than that at the item surface and corner (vf), i.e., vf < vc, the anode voltage is set to 300 to 600 V, the pulse duration is 12 to 500 μs, and the pulse frequency is 10 to 1000 Hz. The cathode voltage is 150 to 300 V, the pulse duration is 100 to 200 μs, and the pulse frequency is 10 to 1000 Hz; the pause time between the anode and cathode pulses is 5 to 10 ms; the proportion of anode pulses with a voltage amplitude of 300 to 600 V, a duration of 12 to 100 μs, and a pulse repetition frequency of 10 to 500 Hz, and the proportion of cathode pulses with a voltage amplitude of 150 to 300 V, a duration of 100 to 200 μs, and a pulse repetition frequency of 10 to 500 Hz do not exceed 35%; the proportion of anode pulses with a voltage amplitude of 300 to 600 V, a duration of 100 to 500 μs, and a pulse repetition frequency of 500 Hz to 1000 Hz, and the proportion of cathode pulses with a voltage amplitude of 150 to 300 V, a duration of 200 to 500 μs, and a pulse repetition frequency of 500 to 1000 Hz is at least 65%.

[0028] Therefore, the required process algorithm creates conditions for controlling the coating formation rate on certain parts of the item surface and provides a technical result.

[0029] According to the method of the claims, the coating is carried out by passing an electric current through an item whose surface is completely or partially a valve metal or its alloy and a cathode in contact with the electrolyte. In this case, the cathode is connected to the negative pole of the power supply, while the item is connected to the positive pole of the power supply. Therefore, the item to be coated acts as the anode.

[0030] Any article made directly from valve metals and / or their alloys can serve as anode, as well as articles having elements made from these metals and / or their alloys, primarily housings, various components (stop valves, pump and compressor components, stamping equipment, internal combustion engine components, automotive components, instrument housings, radiators, etc.) in the aerospace, electronics, chemical, oil and gas, automotive, tool, textile, medical and other industries, as well as instrumentation, mechanical engineering, production of building structures, household goods, etc. The list of articles that can be coated by the method of the invention is quite extensive and includes various components made from / or using valve metals and / or their alloys.

[0031] Within the framework of the present invention, the term "valve metal" is understood to mean aluminum, magnesium, and titanium, and the term "valve metal alloy" is understood to mean various alloys of aluminum, magnesium, and titanium. For example, aluminum alloys according to GOST 4784-97, such as D16, D16T, AMC, D16AM, AD31, AMg2, AMgZ, AMg6, V-95, AD31, AD33, etc., or aluminum alloys according to GOST 1583-93, such as AK4, AK5, AK-8, AK-12, etc.; magnesium alloys according to GOST 14957-76, such as MA2-1, MA5, etc.; and magnesium alloys according to GOST 2856-79, such as ML5, etc.; and titanium alloys according to GOST 19807-91, such as VT1-0, VT6, VT14, VT18, VT22, OP4, etc.

[0032] The cathode can be the container containing the electrolyte itself and / or another electrode immersed in the electrolyte solution. Stainless steel and / or aluminum cathodes are preferred. The cathode immersed in the electrolyte solution can have various shapes, depending on the project configuration, such as plates, rods, and / or combinations thereof. The cathode container can have various shapes and sizes depending on the size and configuration of the item being processed.

[0033] In the present invention, according to the above method, the aqueous electrolyte solution can be a slightly alkaline phosphate borate (pH=7-9) electrolyte, a silicate electrolyte (pH=10) or a weakly acidic phosphate ferrite electrolyte (pH=5-6).

[0034] According to the present invention, the temperature of the electrolyte solution is maintained (e.g., by cooling) at 10 to 60° C., preferably 15 to 30° C. At lower temperatures, the rate of coating formation decreases sharply, and at higher temperatures, inferior coatings are formed: high roughness, porosity, and poor adhesion of the coating to the valve metal and / or its alloys.

[0035] During the coating process, the temperature typically increases gradually, so the electrolyte needs to be cooled, for example, by circulating it through a heat exchanger or by including a heat exchanger in the vessel containing the electrolyte and passing cold water through the cooling system.

[0036] Furthermore, the cooling efficiency can be improved by using an electrolyte with nitrogen, oxygen, air or other gases (primarily air) that are inert to the oxidation process of the valve metal and / or its alloys. In addition, the cooling efficiency can be improved by stirring the electrolyte, for example, with a stirrer or by rotating the anode(s) and / or cathode.

[0037] To improve the supply of electrolyte components to the electrode surface and the removal of reaction products, the coating process can be carried out under stirring. In addition, stirring helps to evenly distribute the electrolyte components throughout the container and minimizes temperature gradients, which in turn avoids local overheating of the items and provides a better coating.

[0038] Within the framework of the present invention, stirring can be achieved by bubbling the electrolyte through a gas distribution device (e.g., a perforated tube) immersed in the electrolyte and preferably arranged along the wall of the container in which the electrolyte is located. During the oxidation process of the valve metal and / or its alloy, bubbling is performed using an inert gas, such as nitrogen, oxygen, air, etc., mainly air.

[0039] In the claimed method, coating is carried out at a temperature of 10 to 40°C. DETAILED DESCRIPTION

[0040] The possibility of implementing the claimed invention is demonstrated by examples of its concrete implementation.

[0041] For coating application, use a total area of ​​1.0-100.0dm 2 Plate products and a total area of ​​1700.0dm 2 Radiator made of the following alloys:

[0042] Product 1-D16 aluminum alloy, in line with GOST4784-97 standard;

[0043] Product 2 - AMg6 aluminum alloy, according to GOST4784-97 standard;

[0044] Product 3 - VT1-0 titanium alloy, according to GOST 19807-91 standard;

[0045] Product 4 - ML5 magnesium alloy, according to GOST2856-79 standard;

[0046] Product 5 - AD35 aluminum alloy, according to GOST4784-97 standard;

[0047] Product 6 - AK12 aluminum alloy according to GOST 4784-97 standard.

[0048] The compounds constituting the electrolyte are dissolved in distilled water in the amounts of Examples 1 to 3 at a temperature of 20-25° C. and under constant stirring. Once all the compounds are completely dissolved, the electrolyte is ready for use.

[0049] Before coating, the product is degreased with ethanol and / or acetone and washed with water. If the parts have been washed with oil or cooling mixtures used in metalworking, degreasing is not allowed.

[0050] The electrolyte and electrodes are placed in a container equipped with a stirrer and air distribution system. The product is connected to the positive terminal of a power source. A stainless steel plate is used as the cathode and connected to the negative terminal of the power source. The process is carried out under the specified power source parameters for 10-90 minutes at a temperature of 20°C.

[0051] Table 1 shows the coating conditions.

[0052] Table 2 shows the properties of the coatings obtained.

[0053] Example 1. A well-known example of coating without controlling the processing rate is performed on the surface of a product in a phosphate-borate electrolyte of composition 1: Na2HPO4-40g / l, Na2B4O7-30g / l, NaF-10g / l.

[0054] Example 2. Coating of an article made of D16 aluminum alloy in a phosphate-borate electrolyte of composition 2 without controlling the processing rate of the article surface: Na2HPO4-43 g / l, Na2B4O7-28 g / l, H3BO3-15 g / l, NaF-8 g / l.

[0055] Example 3. Coating of an article made of D16 aluminum alloy in a phosphate-ferrite electrolyte of composition 3 without controlling the processing rate of the article surface: NaH2PO4-18 g / l, K3[Fe(CN)6]-13 g / l, Na2SiO3-2 g / l, Na2MoO4-1.5 g / l.

[0056] Example 4. An article made of AMg6 aluminum alloy is coated in an electrolyte of composition 3, and the processing rate at the surface and center of the article is controlled (vf>vc) (Example 3).

[0057] The anodic voltage was initially 500 V and gradually increased to 600 V, while the cathodic voltage was maintained constant at 50 Hz. The duration of the anodic pulse was 200 μs, the cathodic pulse was 100 μs, with a 1 ms pause between them, and the pulse repetition rate was 70 Hz. The resulting coating had a thickness of 39 μm at the edge of the plate and 30 μm in the center.

[0058] Example 5. In the electrolyte of Component 3, controlling the processing rates at the surface and the center of the article (vf = vc), a coating is applied to an article made of AMg6 aluminum alloy (Example 3).

[0059] The anode voltage at the initial time is 600 V and gradually decreases to 400 V. The cathode voltage at the initial time is 30 V and gradually increases to 100 V. The duration of the anode pulse is 250 μs. The duration of the cathode pulse at the initial time is 100 μs and then increases to 150 μs. The pause between the anode and cathode pulses is 5 ms, and the pulse repetition rate is 30 Hz.

[0060] The thickness of the resulting coating is the same, 30 μm, at the edge and the center of the plate.

[0061] Example 6. In the electrolyte of Component 3, controlling the processing rates at the surface and the center of the article (vf < vc), a coating is applied to an article made of AMg6 aluminum alloy (Example 3).

[0062] The anode voltage at the initial moment is 600 V and gradually decreases to 450 V. The cathode voltage at the initial moment is 200 V and gradually decreases to 100 V. The duration of the anode pulse at the initial moment is 12 μs, the duration of the cathode pulse is 150 μs, the repetition frequency is 500 Hz, with a pause of 0.7 ms in the middle, and then the change in the anode and cathode pulses is up to 200 μs, with a repetition frequency up to 300 Hz. The thickness of the resulting coating is 30 μm at the edge of the plate and 33 μm at the center.

[0063] Example 7. A coating is applied to an article made of VT1-0 titanium alloy in the electrolyte of Component 2 (Example 2), controlling the processing rates at the plate surface and the center (vf > vc). The thickness of the resulting coating is 36 μm at the edge of the plate and 31 μm at the center.

[0064] Example 8. A coating is applied to an article made of ML5 magnesium alloy in the electrolyte of Component 2 (Example 2), controlling the processing rates at the surface and the center of the article (vf > vc). The thickness of the resulting coating is 15 μm at the edge of the article and 14 μm at the center.

[0065] Example 9. A coating is applied to a large-sized article (S = 1700.0 dm 2 ) made of AD35 aluminum alloy in the electrolyte of Component 2 (Example 2), controlling the processing rates at the surface and the center of the article (vf > vc). The thickness of the resulting coating is 21 μm at the edge of the article and 15 μm at the center.

[0066] Example 10. An article made of AK12 aluminum alloy was coated in an electrolyte of composition 3 (Example 3), with controlled processing rates (vf > vc) at the surface and center of the article. The resulting coating had a thickness of 39 μm at the edge and 30 μm at the center.

[0067] Table 1. Electrolyte composition and coating conditions

[0068]

[0069]

[0070] Table 2. Properties of the resulting coatings

[0071]

[0072] The analysis of the obtained results shows that the proposed coating method, combined with the proposed process mode and electrolyte composition, makes it possible to control the coating rate of deformable and cast aluminum, titanium, and magnesium alloy products. As a result, it is possible to obtain a coating with a uniform thickness over the entire surface of the article or to obtain a desired thickness in individual parts of it. The introduction of this micro-arc oxidation coating method in production can ensure high productivity.

Claims

1. A method for forming a coating on an article, the surface of which is made entirely or partially of valve metal or an alloy of valve metal such as aluminum, magnesium or titanium, comprising immersing the substrate in an aqueous electrolyte bath and performing micro-arc oxidation (MAO) in a pulsed anodic-cathodic mode, characterized in that: The MAO is performed using an apparatus having a pulse-driven quasi-resonant boost converter with a charging unit having current and voltage operation modes, with the coating growth rate on the faces and corners being higher than the growth rate in the center of the article; The anode voltage of the device is set to 350 to 500 V and gradually increased to 500 to 600 V, the cathode voltage is kept constant at 0 to 100 V, the duration of the anode pulse is set to 50 to 300 μs, the duration of the cathode pulse is 50 to 100 μs, the pulse repetition frequency is 30 to 500 Hz, and the pause time between the anode and cathode pulses is 0 to 5 ms; The proportion of anodic pulses with a voltage amplitude of 350 to 500 V, a duration of 50 to 300 μs, and a pulse repetition frequency of 30 to 500 Hz and cathodic pulses with a voltage amplitude of 0 to 50 V, a duration of 50 to 100 μs, and a pulse repetition frequency of 30 to 500 Hz shall not exceed 75%. Furthermore, the ratio of the anode pulses with a voltage amplitude of 500 to 600 V, a duration of 50 to 300 μs, and a pulse repetition frequency of 30 to 500 Hz to the cathode pulses with a voltage amplitude of 0 to 100 V, a duration of 50 to 100 μs, and a pulse repetition frequency of 30 Hz to 500 Hz is at least 25%.

2. A method for forming a coating on an article, the surface of which is made entirely or partially of valve metal or an alloy of valve metal such as aluminum, magnesium or titanium, comprising immersing the substrate in an aqueous electrolyte bath and performing micro-arc oxidation (MAO) in a pulsed anodic-cathodic mode, characterized in that: Using an apparatus having a pulse-driven quasi-resonant boost converter with a charging unit having current and voltage operation modes, the MAO is performed at the same growth rate of the coating at the center of the article and at the surface and corners of the article; The anode voltage of the device is set to 500 to 600 V, then gradually changed to 200 to 400 V, and the cathode voltage is set to 0 to 100 V, then gradually changed to 100 to 200 V; the duration of the anode pulse is set to 50 to 300 μs, the duration of the cathode pulse is 50 to 200 μs, the pulse repetition frequency is 30 to 100 Hz, and the pause time between the anode and cathode pulses is 5 to 8 ms; Among them, the proportion of anodic pulses with a voltage amplitude of 500 to 600 V, a duration of 50 to 300 μs, and a pulse repetition frequency of 30 to 100 Hz and cathodic pulses with a voltage amplitude of 0 to 100 V, a duration of 50 to 200 μs, and a pulse repetition frequency of 30 to 100 Hz shall not exceed 50%; Furthermore, the ratio of the anode pulses having a voltage amplitude of 200 to 400 V, a duration of 50 to 300 μs, and a pulse repetition frequency of 30 to 100 Hz to the cathode pulses having a voltage amplitude of 100 to 200 V, a duration of 50 to 200 μs, and a pulse repetition frequency of 30 to 100 Hz is at least 50%.

3. A method for forming a coating on an article, wherein the surface of the article is made entirely or partially of valve metal or an alloy of valve metal such as aluminum, magnesium, or titanium, comprising immersing the article in an aqueous electrolyte solution and performing micro-arc oxidation (MAO) in a pulsed anodic-cathodic mode, wherein: Using a pulse-driven quasi-resonant boost converter having a charging unit with current and voltage operation modes, the MAO coating grows faster in the center of the article than on the surface and corners of the article; The anode voltage of the device is set to 300 to 600 V, and the cathode voltage is set to 150 to 300 V; the duration of the anode pulse is set to 12 to 100 μs, and then gradually changes to 100 to 500 μs; the duration of the cathode pulse is set to 100 to 200 μs, and then gradually changes to 200 to 500 μs; the repetition frequency of the anode pulse is set to 10 to 500 Hz, and then changes to 500 to 1000 Hz, and the repetition frequency of the cathode pulse is set to 10 to 500 Hz, and then changes to 500 to 1000 Hz, and the pause time between the anode and cathode pulses is 5 to 10 ms; The ratio of anodic pulses with a voltage amplitude of 300 to 600 V, a duration of 12 to 100 μs, and a pulse repetition frequency of 10 to 500 Hz to cathodic pulses with a voltage amplitude of 150 to 300 V, a duration of 100 to 200 μs, and a pulse repetition frequency of 10 to 500 Hz does not exceed 35%; The ratio of the anodic pulses having a voltage amplitude of 300 to 600 V, a duration of 100 to 500 μs, and a pulse repetition frequency of 500 to 1000 Hz to the cathodic pulses having a voltage amplitude of 150 to 300 V, a duration of 200 to 500 μs, and a pulse repetition frequency of 500 to 1000 Hz is at least 65%.

4. The method according to any one of claims 1 to 3, characterized in that The cathode is a container made of stainless steel, aluminum or titanium, and its aqueous solution is a slightly alkaline phosphate borate electrolyte with a pH of 7-9 or a slightly acidic phosphate ferrite electrolyte with a pH of 5-6.

5. The method according to any one of claims 1 to 3, characterized in that The formation of the coating layer is performed at a temperature of 10 to 40°C.

6. The method according to any one of claims 1 to 3, characterized in that Nitrogen, oxygen or air is added to the electrolyte aqueous solution.

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