Preparation method for preparing carbonitriding composite coating through liquid-phase plasma permeation and micro-arc oxidation

Abstract

The invention discloses a preparation method for preparing a carbonitriding composite coating through liquid-phase plasma permeation and micro-arc oxidation, and relates to a preparation method of a coating. The invention aims to solve the problem that a coating formed on the surface of a magnesium alloy in the prior art cannot meet high hardness, high wear resistance and high corrosion resistance at the same time. The method comprises: 1, magnesium alloy pretreatment; 2, ultrasonic oil removal; 3, preparing a liquid-phase plasma permeation solution; 4, carrying out liquid-phase plasma permeation treatment; and 5, micro-arc oxidation treatment. According to the prepared carbonitriding composite coating, a carbonitriding layer formed through liquid-phase plasma permeation is combined with a magnesium oxide ceramic membrane generated through micro-arc oxidation, and the surface hardness of the magnesium alloy is remarkably improved; and under the dual effects of the carbonitriding layer and the magnesium oxide ceramic membrane, the hardness and wear resistance of the magnesium alloy are greatly improved, and the corrosion resistance is enhanced. According to the method, the carbonitriding composite coating prepared through liquid-phase plasma permeation and micro-arc oxidation can be obtained.

Description

Technical Field

[0001] The present invention relates to a method for preparing a coating. Background Art

[0002] Magnesium alloys are widely used in the fields of aerospace, automotive lightweighting, and electronic devices due to their low density, high specific strength, and good damping properties. However, the low surface hardness, poor wear resistance, and corrosion resistance of magnesium alloys limit their applications in harsh environments. Existing single surface treatment methods (such as liquid-phase plasma nitriding, carburizing, or micro-arc oxidation) can partially improve the surface properties of magnesium alloys, but it is difficult to simultaneously meet the requirements of high hardness, high wear resistance, and high corrosion resistance.

[0003] Liquid-phase plasma nitriding mainly generates plasma in the liquid phase to infiltrate nitrogen atoms into the surface of magnesium alloys, forming a nitride layer to improve the surface hardness. However, the nitrided layer formed by this method is relatively thin, and it is easy to be damaged in the long-term friction and corrosion environment, resulting in a decrease in wear resistance and corrosion resistance. Although the carburizing process can increase the carbon content on the surface of magnesium alloys and improve the hardness and wear resistance to a certain extent, the improvement effect on corrosion resistance is limited, and the carburizing process has high requirements for temperature and atmosphere control, and the process stability is poor. Micro-arc oxidation uses a high-voltage pulsed power supply in an electrolyte solution to generate micro-arc discharge on the surface of magnesium alloys, forming a ceramic film layer, which can improve the surface hardness and corrosion resistance. However, there are some micropores and cracks in the micro-arc oxidation film layer, and these defects will reduce the denseness of the film layer, making corrosive media easy to penetrate into the substrate and affecting the long-term corrosion resistance.

[0004] The present invention provides an innovative multi-element composite surface treatment technology. By organically combining the liquid-phase plasma carbonitriding process with the micro-arc oxidation technology, the limitations of single surface treatment methods are effectively overcome. This technology first uses the liquid-phase plasma carbonitriding process to modify the surface of magnesium alloys, significantly improving their surface hardness and wear resistance; subsequently, through micro-arc oxidation treatment, a ceramicized oxide film with excellent corrosion resistance is constructed on the strengthened surface. The innovation of this composite treatment technology lies in: on the one hand, it fully exerts the strengthening effect of liquid-phase plasma carbonitriding and the surface modification advantages of micro-arc oxidation. Through the synergistic effect of the two processes, the comprehensive improvement of the surface hardness, wear resistance, and corrosion resistance of magnesium alloys is achieved; on the other hand, during the process implementation, an innovative approach is adopted to use the same micro-arc oxidation power supply. By precisely regulating the electrical parameters and optimizing the electrolyte components, seamless connection of the two treatment processes is achieved, which not only simplifies the equipment configuration but also significantly reduces the production cost. This composite treatment technology that integrates strengthening and modification provides an efficient and economical solution for the comprehensive improvement of the surface properties of magnesium alloys. Summary of the Invention

[0005] The object of the present invention is to solve the problem that the coatings formed on the surface of magnesium alloys in the prior art cannot simultaneously meet the requirements of high hardness, high wear resistance and high corrosion resistance, and to provide a preparation method for carbonitriding composite coatings by liquid-phase plasma immersion and micro-arc oxidation.

[0006] A preparation method for carbonitriding composite coatings by liquid-phase plasma immersion and micro-arc oxidation is specifically completed according to the following steps:

[0007] I. Pretreatment of magnesium alloy:

[0008] The surface of the magnesium alloy is polished to obtain a magnesium alloy with a bright surface.

[0009] II. Ultrasonic degreasing:

[0010] The magnesium alloy with a bright surface is immersed in a degreasing agent at a temperature of 50°C to 60°C, ultrasonically treated for a period of time, taken out, washed, and dried to obtain a degreased magnesium alloy.

[0011] III. Preparation of liquid-phase plasma immersion solution:

[0012] Triethanolamine and glycerol are added to deionized water, and then urea, ammonium nitrate, melamine and potassium hydroxide are added, and ultrasonically treated for a period of time to obtain a liquid-phase plasma immersion solution.

[0013] IV. Liquid-phase plasma immersion treatment:

[0014] First, the graphite electrode and the degreased magnesium alloy are immersed in the liquid-phase plasma immersion solution, then the graphite electrode is connected to the positive pole of the power supply of the micro-arc oxidation device, the degreased magnesium alloy is connected to the negative pole of the power supply of the micro-arc oxidation device, the forward DC mode is set, and the reaction is carried out for a period of time at a forward voltage of 300V to 450V to obtain a magnesium alloy treated by liquid-phase plasma immersion.

[0015] V. Micro-arc oxidation treatment:

[0016] The graphite electrode and the magnesium alloy treated by liquid-phase plasma immersion are immersed in the micro-arc oxidation electrolyte, the graphite electrode is connected to the negative pole of the power supply of the micro-arc oxidation device, the magnesium alloy treated by liquid-phase plasma immersion is connected to the positive pole of the power supply of the micro-arc oxidation device, the constant voltage mode is set, and micro-arc oxidation is carried out for a period of time under the conditions of a constant voltage of 500V to 550V, a duty cycle of 10% to 20%, and a frequency of 100Hz to 500Hz to obtain a carbonitriding composite coating.

[0017] Advantages of the present invention:

[0018] 1. The carbonitriding composite coating prepared by the present invention combines a carbonitriding layer formed by liquid-phase plasma carburizing and a magnesium oxide ceramic film generated by micro-arc oxidation, significantly improving the surface hardness of the magnesium alloy; under the dual action of the carbonitriding layer and the magnesium oxide ceramic film, the hardness, wear resistance and corrosion resistance of the magnesium alloy are greatly improved; moreover, by adjusting the process parameters of liquid-phase plasma carburizing and micro-arc oxidation, the thickness, hardness and properties of the coating can be flexibly controlled;

[0019] 2. The attached drawings of the specification of the present invention Figure 1 show the SEM surface morphology characteristics of the coating under different process treatments; among them, Figure 1 (a) is the microscopic morphology of the carbonitriding composite coating prepared by liquid-phase plasma carburizing and micro-arc oxidation, Figure 1 (b) is the surface structure of the pure micro-arc oxidation ceramic coating. It is found by comparison that the coating prepared by the composite process of liquid-phase plasma carbonitriding and micro-arc oxidation shows significant advantages in the microscopic structure; compared with the single micro-arc oxidation coating in Comparative Example 1, the porosity of the composite coating is reduced by about 45%, and the proportion of closed holes in the hole structure is increased from 35% in the comparative example to 80%; this significant optimization of the microscopic structure is mainly due to the pretreatment effect of the liquid-phase plasma carbonitriding process: First, a dense strengthening layer is formed on the surface of the magnesium alloy during the carbonitriding process, providing a more uniform substrate for subsequent micro-arc oxidation; Second, the introduction of carbon and nitrogen elements changes the surface electrochemical characteristics, making the discharge behavior during the micro-arc oxidation process more uniform and controllable, thus promoting the formation of a dense coating. It is particularly worth noting that the substantial increase in the proportion of closed holes effectively constructs a three-dimensional protection network, and this unique structure can significantly block the penetration path of corrosion media such as Cl - and significantly improve the corrosion resistance of the coating;

[0020] 3. As shown in Table 1 of the present invention, it can be known from the EDS energy spectrum analysis of the coating elements that: compared with the micro-arc oxidation coating, the atomic percentage of carbon element in the carbonitriding composite coating prepared by liquid-phase plasma carburizing and micro-arc oxidation is increased from 10.36% to 15.72%, and the nitrogen element content shows a slight increase, from 3% to 3.38%. This change is closely related to the liquid-phase plasma carburizing process in the composite process. The unique physical and chemical environment created by this treatment process creates more favorable conditions for carbon and nitrogen sources to participate in the construction of the coating, promoting the more sufficient embedding of carbon and nitrogen atoms into the coating structure; further hardness tests show that the average hardness of the coating treated by pure micro-arc oxidation is about 520HV, while the average hardness of the coating prepared by the liquid-phase plasma carburizing / micro-arc oxidation composite process is increased to about 630HV, reflecting the optimization effect of the composite process on the mechanical properties of the coating;

[0021] 4. In the attached drawings of the specification of the present invention Figure 2Presented are the corrosion resistance performance data of the magnesium alloy coating: For the coating treated only by micro-arc oxidation, the corrosion current density is 1.35×10 -6 A / cm 2 ; For the carbonitriding composite coating prepared by liquid-phase plasma infiltration and micro-arc oxidation, the corrosion current density is as low as 1.29×10 -7 A / cm 2 , and the corrosion potential is -1.21V; The comparison shows that the ceramic coating prepared by the composite treatment has about 10 times improved corrosion resistance performance compared with the pure micro-arc oxidation coating, and the corrosion potential shifts positively by 0.11V, significantly strengthening the corrosion resistance performance of the magnesium alloy.

[0022] V. In the attached drawings of the specification of the present invention Figure 3 Shows the thickness diagrams of the coatings under different plasma infiltration conditions. As the plasma infiltration voltage gradually increases, the thickness of the carbonitriding coating gradually increases, and the thickness of the composite coating also increases with the increase of the liquid-phase plasma infiltration voltage; This indicates that the liquid-phase plasma infiltration treatment not only improves the surface hardness of the substrate, but also provides a more uniform substrate for the subsequent micro-arc oxidation treatment, enabling the micro-arc oxidation process to proceed more effectively, thereby forming a thicker composite coating. This increase in thickness not only helps to improve the mechanical properties of the coating, but also enhances its corrosion resistance, because a thicker coating can provide a better physical barrier to prevent the penetration of corrosive media. Description of the Drawings

[0023] Figure 1 Are the microtopographies of the ceramic coatings prepared on the magnesium alloy under different process conditions, where (a) is the carbonitriding composite coating prepared by liquid-phase plasma infiltration and micro-arc oxidation in Example 1, and (b) is the ceramic coating prepared by the micro-arc oxidation process in Comparative Example 1;

[0024] Figure 2 Are the corrosion resistance performances of the ceramic coatings prepared on the magnesium alloy under different process conditions;

[0025] Figure 3 Are the thickness diagrams of the coatings prepared under different plasma infiltration conditions in Examples 1 to 4. Detailed Embodiments

[0026] Detailed Embodiment 1: A preparation method for a carbonitriding composite coating prepared by liquid-phase plasma infiltration and micro-arc oxidation in this embodiment is specifically completed according to the following steps:

[0027] I. Pretreatment of the magnesium alloy:

[0028] Polish the surface of the magnesium alloy to obtain a magnesium alloy with a bright surface;

[0029] II. Ultrasonic degreasing:

[0030] Immerse the magnesium alloy with a bright surface into a degreasing agent at a temperature of 50°C to 60°C, perform ultrasonic treatment for a period of time, take it out, then clean and dry it to obtain the degreased magnesium alloy;

[0031] III. Prepare the liquid-phase plasma infiltration solution:

[0032] Add triethanolamine and glycerol to deionized water, then add urea, ammonium nitrate, melamine, and potassium hydroxide, and perform ultrasonic treatment for a period of time to obtain the liquid-phase plasma infiltration solution;

[0033] IV. Liquid-phase plasma infiltration treatment:

[0034] First, immerse the graphite electrode and the degreased magnesium alloy into the liquid-phase plasma infiltration solution, then connect the graphite electrode to the positive pole of the micro-arc oxidation device power supply, connect the degreased magnesium alloy to the negative pole of the micro-arc oxidation device power supply, set the forward DC mode, and react for a period of time at a forward voltage of 300V to 450V to obtain the magnesium alloy after liquid-phase plasma infiltration treatment;

[0035] V. Micro-arc oxidation treatment:

[0036] Immerse the graphite electrode and the magnesium alloy after liquid-phase plasma infiltration treatment into the micro-arc oxidation electrolyte, connect the graphite electrode to the negative pole of the micro-arc oxidation device power supply, connect the magnesium alloy after liquid-phase plasma infiltration treatment to the positive pole of the micro-arc oxidation device power supply, set the constant voltage mode, and perform micro-arc oxidation for a period of time under the conditions of a constant voltage of 500V to 550V, a duty cycle of 10% to 20%, and a frequency of 100Hz to 500Hz to obtain the carbonitriding composite coating.

[0037] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that in Step 1, the surface of the magnesium alloy is polished successively with 180#, 600#, 1000#, and 2000# SiC sandpapers to obtain the magnesium alloy with a bright surface; the size of the magnesium alloy described in Step 1 is 200mm×20mm×2mm. Other steps are the same as those in Specific Embodiment 1.

[0038] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is that the degreasing agent described in Step 2 is composed of octylphenol polyoxyethylene ether, absolute ethanol, trisodium phosphate, potassium hydroxide, and water, where the concentration of octylphenol polyoxyethylene ether is 2g / L to 3g / L, the concentration of absolute ethanol is 100mL / L to 150mL / L, the concentration of trisodium phosphate is 10g / L to 20g / L, and the concentration of potassium hydroxide is 10g / L to 15g / L. Other steps are the same as those in Specific Embodiment 1 or 2.

[0039] Embodiment 4: The difference between this embodiment and any one of Embodiments 1 to 3 is that: in Step 2, the power of the ultrasonic treatment is 100W - 200W, and the time of the ultrasonic treatment is 10min - 20min. Other steps are the same as those in Embodiments 1 to 3.

[0040] Embodiment 5: The difference between this embodiment and any one of Embodiments 1 to 4 is that: in Step 3, the volume ratio of triethanolamine, glycerol, and deionized water is (150 - 200):(50 - 100):(700 - 800). Other steps are the same as those in Embodiments 1 to 4.

[0041] Embodiment 6: The difference between this embodiment and any one of Embodiments 1 to 5 is that: in Step 3, the mass ratio of urea, ammonium nitrate, melamine, and potassium hydroxide is 10:10:(1 - 2):(5 - 6); in Step 3, the mass ratio of urea to the volume of deionized water is 10g:(700 - 800). Other steps are the same as those in Embodiments 1 to 5.

[0042] Embodiment 7: The difference between this embodiment and any one of Embodiments 1 to 6 is that: in Step 3, the power of the ultrasonic treatment is 100W - 200W, and the time of the ultrasonic treatment is 10min - 20min. Other steps are the same as those in Embodiments 1 to 6.

[0043] Embodiment 8: The difference between this embodiment and any one of Embodiments 1 to 7 is that: in Step 4, the reaction time under a forward voltage of 300V - 450V is 20min - 30min. Other steps are the same as those in Embodiments 1 to 7.

[0044] Embodiment 9: The difference between this embodiment and any one of Embodiments 1 to 8 is that: in Step 5, the time of micro-arc oxidation is 30min - 40min. Other steps are the same as those in Embodiments 1 to 8.

[0045] Embodiment 10: The difference between this embodiment and any one of Embodiments 1 to 9 is that: in Step 5, the micro-arc oxidation electrolyte is composed of sodium hexametaphosphate, triethanolamine, sodium glycerophosphate, disodium ethylenediaminetetraacetate, sodium fluoride, and water, wherein the concentration of sodium hexametaphosphate is 15g / L - 20g / L, the concentration of triethanolamine is 50mL / L - 100mL / L, the concentration of sodium glycerophosphate is 4g / L - 6g / L, the concentration of disodium ethylenediaminetetraacetate is 1g / L - 5g / L, and the concentration of sodium fluoride is 1g / L - 3g / L. Other steps are the same as those in Embodiments 1 to 9.

[0046] The following examples are used to verify the beneficial effects of the present invention:

[0047] Example 1: A preparation method for a carbonitriding composite coating prepared by liquid-phase plasma penetration and micro-arc oxidation is specifically completed according to the following steps:

[0048] I. Pretreatment of magnesium alloy:

[0049] The surface of the magnesium alloy is polished to obtain a magnesium alloy with a bright surface.

[0050] In step I, the surface of the magnesium alloy is polished successively with 180#, 600#, 1000#, and 2000# SiC sandpapers to obtain a magnesium alloy with a bright surface.

[0051] The size of the magnesium alloy described in step I is 200 mm × 20 mm × 2 mm.

[0052] II. Ultrasonic degreasing:

[0053] The magnesium alloy with a bright surface is immersed in a degreasing agent at a temperature of 55°C, ultrasonically treated for 10 min at an ultrasonic power of 100 W, taken out, washed, and dried with an electric hair dryer to obtain a degreased magnesium alloy.

[0054] The degreasing agent described in step II is composed of octylphenol polyoxyethylene ether, anhydrous ethanol, trisodium phosphate, potassium hydroxide, and water, where the concentration of octylphenol polyoxyethylene ether is 3 g / L, the concentration of anhydrous ethanol is 100 mL / L, the concentration of trisodium phosphate is 10 g / L, and the concentration of potassium hydroxide is 10 g / L.

[0055] III. Preparation of liquid-phase plasma penetration solution:

[0056] 200 mL of triethanolamine and 100 mL of glycerol are added to 700 mL of deionized water, and then 10 g of urea, 10 g of ammonium nitrate, 1.5 g of melamine, and 5 g of potassium hydroxide are added, and ultrasonically treated for 10 min at an ultrasonic power of 100 W to obtain a liquid-phase plasma penetration solution.

[0057] IV. Liquid-phase plasma penetration treatment:

[0058] First, the graphite electrode and the degreased magnesium alloy are immersed in the liquid-phase plasma penetration solution, then the graphite electrode is connected to the positive pole of the power supply of the micro-arc oxidation device, the degreased magnesium alloy is connected to the negative pole of the power supply of the micro-arc oxidation device, the forward DC mode is set, and the reaction is carried out for 20 min at a forward voltage of 400 V to obtain a magnesium alloy treated by liquid-phase plasma penetration.

[0059] V. Micro-arc oxidation treatment:

[0060] Immerse the graphite electrode and the magnesium alloy treated by liquid-phase plasma infiltration into the micro-arc oxidation electrolyte. Connect the graphite electrode to the negative pole of the power supply of the micro-arc oxidation device, and connect the magnesium alloy treated by liquid-phase plasma infiltration to the positive pole of the power supply of the micro-arc oxidation device. Set the forward DC mode, and perform micro-arc oxidation for 30 minutes under the conditions of a constant voltage of 500 V, a duty cycle of 10%, and a frequency of 100 Hz to obtain a carbonitriding composite coating;

[0061] The micro-arc oxidation electrolyte described in step five is composed of sodium hexametaphosphate, triethanolamine, sodium glycerophosphate, disodium ethylenediaminetetraacetate, sodium fluoride and water. Among them, the concentration of sodium hexametaphosphate is 15 g / L, the concentration of triethanolamine is 50 mL / L, the concentration of sodium glycerophosphate is 4 g / L, the concentration of disodium ethylenediaminetetraacetate is 1 g / L, and the concentration of sodium fluoride is 1 g / L.

[0062] Comparative Example 1: The ceramic coating prepared by the micro-arc oxidation process is specifically completed according to the following steps:

[0063] I. Pretreatment of magnesium alloy:

[0064] Grind and polish the surface of the magnesium alloy to obtain a magnesium alloy with a bright surface;

[0065] In step one, use 180#, 600#, 1000#, and 2000# SiC sandpapers to grind and polish the surface of the magnesium alloy in sequence to obtain a magnesium alloy with a bright surface;

[0066] The size of the magnesium alloy described in step one is 200 mm × 20 mm × 2 mm;

[0067] II. Ultrasonic degreasing:

[0068] Immerse the magnesium alloy with a bright surface into the degreasing agent at a temperature of 55 °C, perform ultrasonic treatment for 10 minutes at an ultrasonic power of 100 W, take it out and then wash it, and dry it with an electric hair dryer to obtain the degreased magnesium alloy;

[0069] The degreasing agent described in step two is composed of octylphenol polyoxyethylene ether, absolute ethanol, trisodium phosphate, potassium hydroxide and water. Among them, the concentration of octylphenol polyoxyethylene ether is 3 g / L, the concentration of absolute ethanol is 100 mL / L, the concentration of trisodium phosphate is 10 g / L, and the concentration of potassium hydroxide is 10 g / L;

[0070] III. Micro-arc oxidation treatment:

[0071] Immerse the graphite electrode and the degreased magnesium alloy into the micro-arc oxidation electrolyte. Connect the graphite electrode to the negative pole of the power supply of the micro-arc oxidation device, and connect the degreased magnesium alloy to the positive pole of the power supply of the micro-arc oxidation device. Set the forward DC mode and perform micro-arc oxidation for 30 min under the conditions of a constant voltage of 500 V, a duty cycle of 10%, and a frequency of 100 Hz to obtain a ceramic coating.

[0072] The micro-arc oxidation electrolyte described in step 3 is composed of sodium hexametaphosphate, triethanolamine, sodium glycerophosphate, disodium ethylenediaminetetraacetate, sodium fluoride, and water. Among them, the concentration of sodium hexametaphosphate is 15 g / L, the concentration of triethanolamine is 50 mL / L, the concentration of sodium glycerophosphate is 4 g / L, the concentration of disodium ethylenediaminetetraacetate is 1 g / L, and the concentration of sodium fluoride is 1 g / L.

[0073] Example 2: The difference between this example and Example 1 is that in step 4, the reaction is carried out at a forward voltage of 300 V for 20 min. Other steps and parameters are the same as those in Example 1.

[0074] Example 3: The difference between this example and Example 1 is that in step 4, the reaction is carried out at a forward voltage of 350 V for 20 min. Other steps and parameters are the same as those in Example 1.

[0075] Example 4: The difference between this example and Example 1 is that in step 4, the reaction is carried out at a forward voltage of 450 V for 20 min. Other steps and parameters are the same as those in Example 1.

[0076] Figure 1 are the micro-morphologies of the ceramic coatings prepared on the magnesium alloy under different process conditions. Among them, (a) is the carbonitriding composite coating prepared by liquid-phase plasma carbo-nitriding and micro-arc oxidation in Example 1, and (b) is the ceramic coating prepared by the micro-arc oxidation process in Comparative Example 1.

[0077] From Figure 1 it can be seen that: The experimental results of Example 1 show that the coating prepared by the composite process of liquid-phase plasma carbo-nitriding and micro-arc oxidation exhibits significant advantages in the micro-structure. Compared with the single micro-arc oxidation coating in Comparative Example 1, the porosity of the composite coating is reduced by about 45%, and the proportion of closed holes in the hole structure increases from 35% in the comparative example to 80%. The significant optimization of this micro-structure is mainly due to the pretreatment effect of the liquid-phase plasma carbo-nitriding process: First, a dense strengthening layer is formed on the surface of the magnesium alloy during the carbo-nitriding process, providing a more uniform substrate for the subsequent micro-arc oxidation; Second, the introduction of carbon and nitrogen elements changes the surface electrochemical characteristics, making the discharge behavior during the micro-arc oxidation process more uniform and controllable, thus promoting the formation of a dense coating. It is particularly worth noting that the substantial increase in the proportion of closed holes effectively constructs a three-dimensional stereoscopic protection network. This unique structure can significantly block Cl -The penetration paths of corrosive media are equivalent, significantly enhancing the corrosion resistance of the coating.

[0078] Table 1 shows the elemental ratios of the ceramic coatings prepared on magnesium alloys under different process conditions;

[0079] Table 1

[0080]

[0081]

[0082] Figure 2 is the corrosion resistance of the ceramic coatings prepared on magnesium alloys under different process conditions.

[0083] From Figure 2 it can be seen that for the coating only treated by micro-arc oxidation, the corrosion current density is 1.35×10 -6 A / cm 2 ; for the carbonitriding composite coating prepared by liquid-phase plasma infiltration and micro-arc oxidation, the corrosion current density is as low as 1.29×10 -7 A / cm 2 , and the corrosion potential is -1.21V; the comparison shows that the corrosion resistance of the ceramic coating prepared by the composite treatment is about 10 times higher than that of the pure micro-arc oxidation coating, and the corrosion potential shifts positively by 0.11V, significantly enhancing the corrosion resistance of the magnesium alloy. This result fully confirms the synergistic effect of liquid-phase plasma carbonitriding and micro-arc oxidation technologies, not only optimizing the coating structure but also essentially improving the long-term protection performance of the coating.

[0084] Figure 3 is the coating thickness diagram of the coatings prepared under different plasma infiltration conditions in Examples 1 to 4;

[0085] The thickness of the coatings prepared under different liquid-phase plasma infiltration voltage conditions is shown in Figure 3; the red part in the figure represents the thickness of the liquid-phase plasma infiltration coating. From Figure 3 it can be seen that as the liquid-phase plasma infiltration voltage gradually increases, its thickness gradually increases, and the thickness of the prepared composite coating also increases accordingly. Specifically, when the voltage increases from 300V to 450V, the thickness of the liquid-phase plasma infiltration coating shows an obvious upward trend. This trend indicates that a higher voltage can promote more plasma to participate in the reaction, thus forming a thicker infiltration layer on the surface of the magnesium alloy. In addition, the thickness of the composite coating also increases with the increase of the liquid-phase plasma infiltration voltage. This shows that the liquid-phase plasma infiltration treatment not only improves the surface hardness of the substrate but also provides a more uniform substrate for the subsequent micro-arc oxidation treatment, enabling the micro-arc oxidation process to proceed more effectively, thereby forming a thicker composite coating.

Claims

1. A method for preparing a carbonitriding composite coating by liquid phase plasma ionization and micro-arc oxidation, characterized in that The preparation method is specifically completed according to the following steps:

1. Magnesium alloy pretreatment: Grinding and polishing the surface of the magnesium alloy to obtain a magnesium alloy with a bright surface; 2. Ultrasonic oil removal: The magnesium alloy with bright surface is immersed in a degreasing agent with a temperature of 50°C to 60°C, subjected to ultrasonic treatment for a period of time, taken out, cleaned, and dried to obtain the degreasing magnesium alloy; 3. Preparation of liquid phase plasma ionization solution: Triethanolamine and glycerol are added to deionized water, and then urea, ammonium nitrate, melamine and potassium hydroxide are added, and ultrasonic treatment is performed for a period of time to obtain a liquid phase isopyrolysis solution; 4. Liquid phase plasma ionization treatment: Firstly, a graphite electrode and a degreased magnesium alloy are immersed in a liquid phase plasma diffusion solution, and then the graphite electrode is connected to the positive electrode of a power supply of a micro-arc oxidation device, and the degreased magnesium alloy is connected to the negative electrode of the power supply of the micro-arc oxidation device, and a forward DC mode is set, and a forward voltage of 300V to 450V is reacted for a period of time to obtain a magnesium alloy treated by liquid phase plasma diffusion; 5. Micro-arc oxidation treatment: A graphite electrode and a magnesium alloy treated by liquid phase plasma diffusion are immersed in a micro-arc oxidation electrolyte, the graphite electrode is connected to the negative electrode of a power supply of a micro-arc oxidation device, the magnesium alloy treated by liquid phase plasma diffusion is connected to the positive electrode of the power supply of the micro-arc oxidation device, a constant voltage mode is set, and micro-arc oxidation is performed for a period of time under the conditions of a constant voltage of 500V to 550V, a duty cycle of 10% to 20%, and a frequency of 100Hz to 500Hz to obtain a carbonitriding composite coating.

2. The method for preparing a carbonitriding composite coating by liquid phase plasma ionization and micro-arc oxidation according to claim 1, characterized in that In step 1, the surface of the magnesium alloy is polished using 180#, 600#, 1000#, and 2000# SiC sandpaper in sequence to obtain a magnesium alloy with a bright surface; the size of the magnesium alloy described in step 1 is 200mm×20mm×2mm.

3. The method for preparing a carbonitriding composite coating by liquid phase plasma ionization and micro-arc oxidation according to claim 1, characterized in that The degreasing agent described in step 2 is composed of octylphenol polyoxyethylene ether, anhydrous ethanol, trisodium phosphate, potassium hydroxide and water, wherein the concentration of octylphenol polyoxyethylene ether is 2g / L~3g / L, the concentration of anhydrous ethanol is 100mL / L~150mL / L, the concentration of trisodium phosphate is 10g / L~20g / L, and the concentration of potassium hydroxide is 10g / L~15g / L.

4. The method for preparing a carbonitriding composite coating by liquid phase plasma ionization and micro-arc oxidation according to claim 1, characterized in that The power of the ultrasonic treatment in step 2 is 100W to 200W, and the time of the ultrasonic treatment is 10min to 20min.

5. The method for preparing a carbonitriding composite coating by liquid phase plasma ionization and micro-arc oxidation according to claim 1, characterized in that The volume ratio of triethanolamine, propylene glycol and deionized water described in step 3 is (150-200):(50-100):(700-800).

6. The method for preparing a carbonitriding composite coating by liquid phase plasma ionization and micro-arc oxidation according to claim 1, characterized in that The mass ratio of urea, ammonium nitrate, melamine and potassium hydroxide described in step 3 is 10:10:(1-2):(5-6); the volume ratio of the mass of urea described in step 3 to deionized water is 10g:(700-800).

7. The method for preparing a carbonitriding composite coating by liquid phase plasma ionization and micro-arc oxidation according to claim 1, characterized in that The power of the ultrasonic treatment described in step 3 is 100W to 200W, and the time of the ultrasonic treatment is 10min to 20min.

8. The method for preparing a carbonitriding composite coating by liquid phase plasma nitriding and micro-arc oxidation according to claim 1, characterized in that In step 4, the reaction time at a forward voltage of 300V to 450V is 20min to 30min.

9. The method for preparing a carbonitriding composite coating by liquid phase plasma ionization and micro-arc oxidation according to claim 1, characterized in that The time of the micro-arc oxidation described in step 5 is 30 min to 40 min.

10. The method for preparing a carbonitriding composite coating by liquid phase plasma ionization and micro-arc oxidation according to claim 1, characterized in that The micro-arc oxidation electrolyte described in step five is composed of sodium hexametaphosphate, triethanolamine, sodium glycerophosphate, disodium ethylenediaminetetraacetic acid, sodium fluoride and water, wherein the concentration of sodium hexametaphosphate is 15g / L~20g / L, the concentration of triethanolamine is 50mL / L~100mL / L, the concentration of sodium glycerophosphate is 4g / L~6g / L, the concentration of disodium ethylenediaminetetraacetic acid is 1g / L~5g / L, and the concentration of sodium fluoride is 1g / L~3g / L.

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