Treatment process for compounding ceramic film layer on surface of magnesium alloy, corresponding magnesium alloy and application

Abstract

The invention relates to the technical field of magnesium alloy surface treatment, in particular to a treatment process for a magnesium alloy surface composite ceramic film layer, a corresponding magnesium alloy and application. The treatment process comprises the following treatment steps that a to-be-treated workpiece is pretreated; preparing a mixed electrolytic solution containing silicon nitride nanoparticles; the workpiece is placed in the mixed electrolytic solution, plasma electrolytic oxidation treatment is carried out with the workpiece as an anode and stainless steel as a cathode, and a composite ceramic film layer is formed on the surface of the workpiece; by forming the composite ceramic layer containing the silicon nitride nanoparticles on the surface of the magnesium alloy workpiece, the friction resistance of the magnesium alloy is improved, under the synergistic effect of sodium fluosilicate in the mixed electrolytic solution, the corrosion resistance of the magnesium alloy is greatly improved, and the application stability of the magnesium alloy in a severe environment is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloy surface treatment, and in particular to a treatment process for a composite ceramic film layer on the surface of a magnesium alloy, a corresponding magnesium alloy and an application thereof. Background Art

[0002] Magnesium is one of the least dense structural metals on earth, with a density of about 1.74 g / cm 3 , which makes magnesium alloy one of the lightest engineering metal materials. Magnesium alloy is not only lightweight, but also has high strength, high stiffness, good shock absorption performance and excellent machining performance. These characteristics make magnesium alloy have broad application prospects in aerospace, automobile manufacturing, electronic products and other fields. For example, in the aerospace field, magnesium alloy can be used to manufacture aircraft structural parts, engine parts, etc.; in the automobile manufacturing field, magnesium alloy can be used to manufacture body frames, suspension systems and other parts.

[0003] Suspension arms made of magnesium alloy have good strength and rigidity, which can effectively reduce the weight of the vehicle and improve the response speed and comfort of the suspension system. However, due to the active chemical properties of magnesium, it is easy to oxidize in the air to form a loose oxide film, which cannot effectively prevent further corrosion, resulting in relatively poor corrosion resistance and easy corrosion in humid or acidic environments.

[0004] In addition, the surface hardness of magnesium alloy is low, which is easy to cause wear and scratch during use, and thus the wear resistance is also poor. These defects greatly limit the application of magnesium alloy in the field of automobile suspension arms.

[0005] As a key component of the automobile suspension system, the suspension arm is often subjected to impact and vibration from the road, and is often exposed to harsh environments such as moisture and salt spray, and is easily affected by chemical corrosion. If the friction and corrosion resistance of the magnesium alloy cannot be improved, the structural strength and load-bearing capacity of the suspension arm will decrease, affecting driving stability. Summary of the invention

[0006] In view of the problem in the prior art that traditional magnesium alloys are difficult to maintain high corrosion resistance and wear resistance in harsh environments such as vibration and humidity, the present invention provides a treatment process for a composite ceramic film layer on the surface of a magnesium alloy, a corresponding magnesium alloy and its application.

[0007] The first object of the present invention is to provide a treatment process for a composite ceramic film layer on a magnesium alloy surface, comprising the following treatment steps:

[0008] S1: pre-processing the workpiece to be processed;

[0009] S2: preparing a mixed electrolyte solution containing functional nanoparticles;

[0010] S3: placing the workpiece in a mixed electrolytic solution, using the workpiece as an anode and the stainless steel material as a cathode for plasma electrolytic oxidation treatment to form a composite ceramic film layer on the surface of the workpiece.

[0011] The surface of the workpiece to be processed is treated by combining electrolytic oxidation and plasma technology. The ion beam generated by high-energy plasma is used to make the electrolyte react chemically with the workpiece surface, thereby forming a dense and uniform composite ceramic film layer with functional nanoparticles on the workpiece surface. The film surface is dense and uniform, which improves the overall friction resistance of the material, and effectively prevents the erosion of the workpiece by corrosive media, improves the mechanical properties of the workpiece, and extends the service life of the workpiece.

[0012] Specifically, the functional nanoparticles include silicon nitride nanoparticles.

[0013] By using silicon nitride nanoparticles with high hardness and low reactivity as functional particles. During the plasma electrolytic oxidation process, due to the high temperature and high energy generated by arc discharge, a part of the silicon nitride nanoparticles can penetrate the coating and enter the interior of the coating, forming a stronger chemical bond with the magnesium alloy matrix, significantly improving the overall strength and toughness of the material, reducing interface defects, and thus enhancing the adhesion of the film layer. Another part of the silicon nitride nanoparticles will adhere to the surface of the coating, improving the mechanical interlocking force between the film layer and the matrix, so that the film layer can effectively resist wear, reduce material loss, and show excellent wear resistance in a friction environment; at the same time, the silicon nitride particles in the film layer can reduce the intrusion of corrosive media, reduce oxidation and corrosion of the matrix workpiece, and improve the corrosion resistance of the workpiece.

[0014] Specifically, the particle size of the silicon nitride nanoparticles is 15 to 30 nm.

[0015] Silicon nitride nanoparticles with a size of 15 to 30 nm can easily enter the surface and internal pores of the coating, thereby increasing the thickness of the film layer and enhancing the overall mechanical properties and mechanical properties of the workpiece. When the particle size of silicon nitride nanoparticles exceeds 30 nm, during the plasma electrolytic oxidation process, on the one hand, due to the drastic temperature change, thermal stress will be generated inside the material. At this time, if the silicon nitride nanoparticles exceed 30 nm, they will be embedded in the surface of the workpiece to form tiny holes or defects, generating corresponding stress. When superimposed with thermal stress, it will exceed the material's bearing capacity, and microcracks will form on the coating surface, which will affect the overall mechanical properties of the workpiece.

[0016] Specifically, the mixed electrolytic solution of S2 includes 12-18 g / L of sodium sulfate, 8-12 g / L of sodium hydroxide, 6-10 g / L of potassium fluoride, 6-10 g / L of propanol, and 1-3 g / L of silicon nitride nanoparticles.

[0017] By adopting the above technical solution, when the concentration of silicon nitride nanoparticles is 1 to 3 g / L, the coating has a good growth effect. During the micro-discharge stage of plasma electrolytic oxidation treatment, the coating thickness increases due to the reaction of silicon nitride nanoparticles with molten oxides. As the concentration of silicon nitride nanoparticles increases, the reaction rate with molten oxides accelerates. The excessively fast reaction rate makes the internal structure of the coating uneven. At the same time, the increase in coating thickness is accompanied by the concentration of thermal stress, especially during the cooling process. This stress concentration may lead to the formation of cracks inside the coating or between the coating and the substrate, thereby affecting the overall performance of the coating and then affecting the adhesion and corrosion resistance of the coating.

[0018] Specifically, the mixed electrolytic solution of S2 also includes 1 to 3 g / L of sodium fluorosilicate.

[0019] After exploring the effects of various electrolyte concentrations in the mixed electrolyte solution, especially silicon nitride nanoparticles on the friction resistance and corrosion resistance of the composite ceramic film layer, the inventors unexpectedly discovered that with the gradual increase in silicon nitride concentration, the surface roughness of the coating also increases. Although moderate roughness helps to enhance the adhesion of the coating, an overly rough surface may become the starting point of corrosion, especially in a salt spray environment. That is to say, within a certain range, the corrosion resistance first increases and then weakens with the increase in silicon nitride concentration. For this reason, the inventors cleverly introduced a specific electrolyte, sodium fluorosilicate, and compounded it with the existing system mixed electrolyte, which not only significantly optimized the compounding effect, but also showed a synergistic effect with silicon nitride nanoparticles to improve corrosion resistance.

[0020] Sodium fluorosilicate decomposes in the electrolyte to generate silicate ions (SiF6 3- ) and fluoride ion (F - These ions react with magnesium ions (Mg 2+ ) reacts to form a protective ceramic film rich in magnesium fluoride (MgF2) and magnesium oxide (MgO) in the film layer. The composite ceramic film layer has the function of blocking the direct contact between the corrosive medium (such as moisture, oxygen, etc.) and the magnesium alloy substrate. At the same time, the protective ceramic film rich in magnesium fluoride (MgF2) and magnesium oxide (MgO) has good chemical stability to prevent further corrosion of the composite ceramic film layer.

[0021] When sodium fluorosilicate and silicon nitride nanoparticles coexist in the electrolyte, the two show a significant synergistic effect. On the one hand, the protective film layer formed by sodium fluorosilicate provides a good substrate for the embedding of silicon nitride nanoparticles; on the other hand, the addition of silicon nitride nanoparticles further enhances the mechanical strength and wear resistance of the film layer, while improving its density and corrosion resistance by filling the tiny pores in the film layer. In addition, silicon nitride nanoparticles themselves have good chemical stability and low thermal expansion coefficient, which helps to maintain the structural stability of the ceramic film layer under temperature changes or mechanical stress, and reduce the risk of corrosion caused by cracking of the film layer.

[0022] Specifically, during the step S3, the temperature of the mixed electrolyte is maintained at 20±2°C.

[0023] Specifically, during the plasma electrolytic oxidation treatment process, the constant current is 5 to 6A, the duty cycle is 25% to 35%, the frequency is 1000 to 1350 Hz, and the oxidation time is 12 to 20 minutes.

[0024] In the present invention, the magnitude of the constant current directly affects the growth rate of the film layer and the quality and performance of the final film layer. A constant current lower than 5A is not conducive to the passivation of the substrate surface in the early stage of oxidation, while a constant current higher than 6A may lead to severe oxidation, which may easily lead to loose film layer or even local ablation, affecting the quality of the film layer.

[0025] Moreover, during the plasma electrolytic oxidation treatment process, when the duty cycle is lower than 25%, the breakdown voltage and the discharge arc space density can be increased, and the arc intensity can be reduced; when the duty cycle is higher than 35%, it will cause an increase in current density, thereby increasing the film-forming reaction rate, but it will also lead to an increase in roughness, affecting the tribological properties of the composite ceramic film layer.

[0026] Specifically, the conductivity of the mixed electrolytic solution is 49.00-55.00 mS / cm, the termination voltage is 410-460 V, and the pH value is 11.20-13.80.

[0027] The second object of the present invention is to provide a magnesium alloy with a composite ceramic film layer, wherein the magnesium alloy is treated by the treatment process as described in claims 1 to 8 to form a magnesium alloy with a composite ceramic film layer on the surface of the workpiece, wherein the thickness of the composite ceramic film layer is 18.50 to 32.50 μm, the microhardness of the magnesium alloy is 264 to 313 HV0.2, and the corrosion current density is 9.87×10 -7 ~1.22×10 -6 A×cm -2 The wear rate is 9.93×10 -5 ~1.05×10 -4 .

[0028] The third object of the present invention is to provide a magnesium alloy device used in an automobile suspension arm, wherein the surface of the magnesium alloy device has a composite ceramic film layer, and the composite ceramic film layer is formed by processing using the process described in any one of claims 1 to 8.

[0029] Beneficial effects:

[0030] The present invention forms a composite ceramic layer containing silicon nitride nanoparticles on the surface of a magnesium alloy workpiece to improve the friction resistance of the magnesium alloy. Under the synergistic effect of sodium fluorosilicate in a mixed electrolytic solution, the corrosion resistance of the magnesium alloy is greatly improved, and the stability of the magnesium alloy in harsh environments is increased.

[0031] Sodium fluorosilicate is introduced into the mixed electrolytic solution. The decomposition products of sodium fluorosilicate can be evenly deposited on the surface of the magnesium alloy, which helps to evenly distribute silicon nitride nanoparticles, avoiding uneven protective performance of the film layer due to local excessive thickness or thinness during the film formation process. A uniform film layer structure is crucial to improving overall corrosion resistance.

[0032] Due to the penetration and adhesion of silicon nitride nanoparticles during the plasma electrolytic oxidation process, the growth rate and thickness of the composite ceramic film layer are enhanced; and the embedding and melting process enhances the interfacial bonding between the composite ceramic film layer and the magnesium alloy matrix, improves the adhesion of the composite ceramic film layer and ensures that it is not easy to fall off when subjected to external forces. At the same time, the addition of sodium fluorosilicate promotes the formation of a denser and more uniform composite ceramic film layer. Under the combined action of the two, in the process of forming a composite ceramic film layer with strong adhesion, it can effectively reduce microscopic defects and pores, enhance friction resistance, reduce the penetration of corrosive media, enhance the overall friction resistance and corrosion resistance, and maintain the long-term protection effect of magnesium alloy workpieces.

[0033] The treatment process of the composite ceramic film layer on the surface of the magnesium alloy of the present invention has simple steps, is easy to operate, does not require complicated equipment and expensive materials, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a scanning electron microscope image of the lower surface of sample 2. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The raw materials used in the embodiments of the present invention can all be purchased directly from the market.

[0037] The magnesium alloy workpiece can be AZ31, AZ91, AZ61, AZ60 or MB8 as specified in the standard GB / T5153-1985. The present invention mainly describes the technical solution of the present invention by taking MB8 alloy as the workpiece. The size of the MB8 alloy workpiece selected by the present invention is 20×15×5mm 3 and 30×30×5mm 3 The workpiece is pre-processed first, and the pre-processing steps include:

[0038] First, use degreasing liquid to degrease the surface of the workpiece for 5 to 10 minutes, then use clean water to remove the degreasing liquid on the surface of the workpiece and dry it with cold air;

[0039] The dried workpiece is then polished, which involves continuous grinding using sandpaper of different grits, including 400, 800, 1000 and 1500 grit sandpaper;

[0040] The sample was then placed in deionized water for ultrasonic treatment for 10 min and finally dried under cold air conditions to complete the pretreatment steps of the workpiece to be processed.

[0041] After the sample has completed the above pretreatment steps, it enters the preparation of the example.

[0042] It should be noted here that the base solution of the mixed electrolyte of the present invention includes electrolytes in the following concentration range: sodium sulfate 12-18 g / L, sodium hydroxide 8-12 g / L, potassium fluoride 6-10 g / L, propanol 6-10 g / L, and various combinations of the above electrolytes within the concentration range are within the protection scope of the present invention.

[0043] Use multiple sizes of 20×15×5mm 3 The magnesium alloy workpieces and multiple sizes of 30×30×5mm 3 The magnesium alloy workpiece is processed as in the following embodiment to provide workpieces of different sizes for various performance tests.

[0044] Example 1

[0045] Preparation of mixed electrolyte: 15g sodium sulfate, 10g sodium hydroxide, 8g potassium fluoride and 8g propanol were added to 1L deionized water in sequence, and the solution was dispersed by a high-speed homogenizer for 10 minutes until it was uniform and transparent to obtain a basic electrolyte solution; then 1g silicon nitride nanoparticles with a particle size of 15nm were introduced into the basic electrolyte solution, ultrasonically oscillated for 30 minutes, and finally the entire solution was transferred to a working tank, and a water circulation system was used to continuously stir the working tank to obtain a mixed electrolyte solution.

[0046] Surface treatment: Place the workpiece that has completed the pretreatment step in a mixed electrolytic solution, with the workpiece as the anode, the anode is fixed to the workpiece through aluminum equipotential bolts, and the cathode is connected to the stainless steel material for plasma electrolytic oxidation treatment;

[0047] During the treatment process, the applied constant current was 6A, the duty cycle was set to 30%, the frequency was 1200 Hz, and the treatment time was 15 minutes. The whole process used a water circulation system with a stirring and cooling mechanism to maintain the mixed electrolyte temperature at an ambient temperature of 18 to 22°C to form a composite ceramic film layer on the workpiece surface.

[0048] During the treatment process, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Example 1 was recorded as 54.00±0.78mS / cm, the end voltage was 415±3V, and the pH value was 12.50±0.09.

[0049] Example 2

[0050] Preparation of mixed electrolyte: 12g sodium sulfate, 8g sodium hydroxide, 9g potassium fluoride and 6g propanol were added to 1L deionized water in sequence, and the solution was dispersed by a high-speed homogenizer for 10 minutes until it was uniform and transparent to obtain a basic electrolyte solution; then 1g silicon nitride nanoparticles with a particle size of 15nm were introduced into the basic electrolyte solution, ultrasonically oscillated for 30 minutes, and finally the entire solution was transferred to a working tank, and a water circulation system was used to continuously stir the working tank to obtain a mixed electrolyte solution.

[0051] Surface treatment: Place the workpiece that has completed the pretreatment step in a mixed electrolytic solution, with the workpiece as the anode, the anode is fixed to the workpiece through aluminum equipotential bolts, and the cathode is connected to the stainless steel material for plasma electrolytic oxidation treatment;

[0052] During the treatment process, the applied constant current was 5A, the duty cycle was set to 25%, the frequency was 1300 Hz, and the treatment time was 12 minutes. The whole process used a water circulation system with a stirring and cooling mechanism to maintain the mixed electrolyte temperature at an ambient temperature of 18 to 22°C to form a composite ceramic film layer on the workpiece surface.

[0053] During the treatment process, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Example 2 was recorded as 54.21±0.65 mS / cm, the end voltage was 420±4 V, and the pH value was 12.18±0.10.

[0054] Example 3

[0055] Preparation of mixed electrolyte: 18g sodium sulfate, 12g sodium hydroxide, 10g potassium fluoride and 10g propanol were added to 1L deionized water in sequence, and the solution was dispersed by a high-speed homogenizer for 10 minutes until it was uniform and transparent to obtain a basic electrolyte solution; then 1g silicon nitride nanoparticles with a particle size of 15nm were introduced into the basic electrolyte solution, ultrasonically oscillated for 30 minutes, and finally the entire solution was transferred to a working tank, and a water circulation system was used to continuously stir the working tank to obtain a mixed electrolyte solution.

[0056] Surface treatment: Place the workpiece that has completed the pretreatment step in a mixed electrolytic solution, with the workpiece as the anode, the anode is fixed to the workpiece through aluminum equipotential bolts, and the cathode is connected to the stainless steel material for plasma electrolytic oxidation treatment;

[0057] During the treatment process, the applied constant current was 5A, the duty cycle was set to 35%, the frequency was 1000 Hz, and the treatment time was 20 minutes. The whole process used a water circulation system with a stirring and cooling mechanism to maintain the mixed electrolyte temperature at an ambient temperature of 18 to 22°C to form a composite ceramic film layer on the workpiece surface.

[0058] During the treatment process, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Example 3 was recorded as 55.32±0.70 mS / cm, the end voltage was 423±3 V, and the pH value was 13.40±0.09.

[0059] Example 4

[0060] The difference between this embodiment and embodiment 1 is that the mass of silicon nitride nanoparticles introduced into the mixed electrolyte in this embodiment is different. In this embodiment, 2 g of silicon nitride nanoparticles with a particle size of 15 nm are introduced. After the basic electrolyte solution is introduced, the ultrasonic oscillation time is extended to 35 minutes.

[0061] During the treatment process, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Example 4 was recorded as 53.64±0.60 mS / cm, the termination voltage was 420±4 V, and the pH value was 13.08±0.10.

[0062] Example 5

[0063] The difference between this embodiment and embodiment 1 is that the mass of silicon nitride nanoparticles introduced into the mixed electrolyte in this embodiment is different. In this embodiment, 3 g of silicon nitride nanoparticles with a particle size of 15 nm are introduced. After the basic electrolyte solution is introduced, the ultrasonic oscillation time is extended to 40 minutes.

[0064] During the treatment process, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Example 5 was recorded as 53.89±0.55 mS / cm, the end voltage was 425±5 V, and the pH value was 13.12±0.08.

[0065] Example 6

[0066] The difference between this embodiment and embodiment 4 is that the particle size of the silicon nitride nanoparticles introduced into the mixed electrolyte in this embodiment is different. The particle size of the silicon nitride nanoparticles used in this embodiment is 25 nm.

[0067] During the treatment process, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Example 6 was recorded as 54.18±0.45 mS / cm, the end voltage was 425±5 V, and the pH value was 13.33±0.10.

[0068] Example 7

[0069] The difference between this embodiment and embodiment 4 is that the particle size of the silicon nitride nanoparticles introduced into the mixed electrolyte in this embodiment is different. The particle size of the silicon nitride nanoparticles used in this embodiment is 30 nm.

[0070] During the treatment process, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Example 7 was recorded as 53.11±0.25 mS / cm, the end voltage was 420±5 V, and the pH value was 12.88±0.10.

[0071] Example 8

[0072] The difference between this embodiment and embodiment 6 is that the mixed electrolytic solution of this embodiment further includes 1 g / L of sodium fluorosilicate. During the preparation process, 1 g / L of sodium fluorosilicate is first added to 1 L of deionized water, and then 18 g of sodium sulfate, 12 g of sodium hydroxide, 10 g of potassium fluoride, 10 g of propanol and other electrolytes are added in sequence, and other operation steps remain unchanged.

[0073] During the treatment process, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Example 8 was recorded as 53.61±0.60 mS / cm, the termination voltage was 445±4 V, and the pH value was 12.18±0.09.

[0074] Example 9

[0075] The difference between this embodiment and embodiment 6 is that the mixed electrolytic solution of this embodiment further includes 2 g / L of sodium fluorosilicate.

[0076] During the treatment process, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Example 9 was recorded as 54.21±0.65 mS / cm, the end voltage was 440±4 V, and the pH value was 11.72±0.10.

[0077] Example 10

[0078] The difference between this embodiment and embodiment 6 is that the mixed electrolytic solution of this embodiment further includes 3 g / L of sodium fluorosilicate.

[0079] During the treatment process, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Example 10 was recorded as 55.21±0.25 mS / cm, the termination voltage was 442±4 V, and the pH value was 11.61±0.08.

[0080] Comparative Example 1

[0081] The difference between this comparative example and the embodiment is that the mixed electrolytic solution of this comparative example does not include silicon nitride nanoparticles, and the other components and operation steps are the same as those of embodiment 1.

[0082] During the treatment of Comparative Example 1, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Comparative Example 1 was recorded as 52.25±0.82 mS / cm, the termination voltage was 420±4 V, and the pH value was 12.55±0.10.

[0083] Comparative Example 2

[0084] The difference between this comparative example and Example 1 is that the parameters in the plasma electrolytic oxidation process of this comparative example are different from those of Example 1. The specific process parameters are as follows:

[0085] During the plasma electrolytic oxidation treatment, the applied constant current was 7A, the duty cycle was set to 40%, the frequency was 1350 Hz, and the treatment time was 10 minutes. The entire process used a water circulation system with a stirring and cooling mechanism to maintain the mixed electrolyte temperature at an ambient temperature of 18 to 22°C to form a composite ceramic film layer on the workpiece surface.

[0086] During the treatment process, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Example 1 was recorded as 53.20±0.62 mS / cm, the end voltage was 425±4 V, and the pH value was 12.50±0.10.

[0087] Comparative Example 3

[0088] The difference between this comparative example and Example 1 is that this comparative example uses 1 g of silicon carbide nanoparticles with a particle size of 15 nm instead of 1 g of silicon nitride nanoparticles with a particle size of 15 nm for testing, and other components and operating steps are the same as those in Example 1.

[0089] During the treatment process, the pH value of the electrolyte was measured using a PHS-3C pH meter, and the conductivity was measured using a DDS-307A conductivity meter. The conductivity of Example 1 was recorded as 54.22±0.76 mS / cm, the end voltage was 420±4 V, and the pH value was 12.40±0.10.

[0090] Performance Testing

[0091] The workpieces of Examples 1 to 10 that have been surface treated are recorded as Samples 1 to 10, and the workpieces of Comparative Examples 1 to 3 that have been surface treated are recorded as Comparative Samples 1 to 3. Performance characterization of Samples 1 to 10: Energy decomposition spectroscopy (EDS) analysis of Samples 1 to 10 treated with plasma electrolytic oxidation was performed using a Tescan Mira 4 field emission microscope (SEM), and the presence of magnesium, oxygen, nitrogen and fluorine in the composite ceramic coating was determined through EDS element mapping.

[0092] Samples 1 to 10 and comparative samples 1 to 3 were tested for thickness, hardness, corrosion resistance, friction resistance, etc. The specific testing methods are as follows:

[0093] Film thickness: A micro 2500 digital eddy current thickness gauge was used to measure the thickness of the composite ceramic film. A sample with a size of 20×15×5mm was randomly selected. 3 The thickness of the samples was measured, 10 random measuring points were selected on the front and back of the workpiece after the plasma electrolytic oxidation surface treatment, and the average hardness of the composite ceramic film layer was calculated.

[0094] Film hardness: measured using a microhardness tester with dimensions of 20×15×5mm 3 The sample size is 30×30×5mm 3 The microhardness of the samples was measured and the average film hardness was calculated.

[0095] Corrosion resistance: Neutral salt spray test (GB / T10125-2021) was carried out on samples of two sizes respectively. After 720h test, if there is no rust on the surface of the sample, it is qualified, otherwise it is unqualified.

[0096] At the same time, the electrochemical properties of the film layer of the sample were tested (GB / T40299-2021).

[0097] Friction resistance: Randomly select a sample with a size of 20×15×5mm 3The wear amount of samples was measured (GB / T12444-2006).

[0098] The performance test results are shown in the following table.

[0099]

[0100] After testing samples 1 to 10, the thickness of the composite ceramic film layer on the upper and lower surfaces (the lower surface facing the bottom of the electrolyte) of samples 1 to 10 is different, and the lower surface is 2 to 3 μm thicker than the upper surface. The reason for this difference is that the electrolyte concentration at the bottom of the mixed electrolyte is high during the plasma electrolytic oxidation process, resulting in a thicker film layer on the lower surface side.

[0101] Compared with the comparative sample 1, the average thickness of the silicon nitride nanoparticles increased by 6 to 20 μm, indicating that the silicon nitride nanoparticles promoted the growth of the coating. In addition, the effects of silicon nitride nanoparticles of different concentrations and different particle sizes on the growth of the coating are also different.

[0102] Combination Figure 1 It can be seen that the cross section of sample 2 treated with plasma electrolytic oxidation shows a double-layer structure of the composite ceramic film layer, including a loose outer layer and a dense inner layer. During the plasma electrolytic oxidation treatment, the coating undergoes a cyclic growth process, including the stages of "decomposition-melting-sintering-coating formation".

[0103] The increase in film thickness is mainly due to two factors. A portion of silicon nitride nanoparticles penetrate the coating under the high temperature and high energy generated by arc discharge, filling the pores and cracks inside the coating, thereby increasing the thickness of the coating and improving its density and uniformity; another portion of silicon nitride nanoparticles adhere to the surface of the coating, enhancing the bonding force between the coating and the substrate through physical adsorption or chemical bonding. These adhered nanoparticles also serve as a matrix for subsequent coating growth, promoting further thickening of the coating. This allows smaller-sized silicon nitride nanoparticles to easily enter the micron-sized pores on the surface of the coating, further improving the coating thickness and performance.

[0104] In addition, during the micro-discharge process, the coating thickness increases due to the reaction of silicon nitride nanoparticles with molten magnesium oxide, resulting in the formation of magnesium silicate phase. When the concentration is 2g / L silicon nitride nanoparticles, the thickness increases significantly, while when the concentration increases further, the thickness decreases. This is because the increase in the concentration of silicon nitride nanoparticles will cause serious damage to the inner layer. A large amount of silicon nitride nanoparticles are transported through the discharge sparks with reduced intensity, and the attenuated sparks are not enough to catalyze the energy required for the reaction of silicon nitride nanoparticles with the workpiece surface, thereby generating defects and damaging the structural integrity of the inner layer that has been formed. Defects may become a path for corrosive media, affecting the overall corrosion resistance of the sample, which is also consistent with the relevant detection data of the electrochemical reaction between comparison sample 1 and samples 1 to 3 in the table, such as low-frequency impedance modulus and corrosion current density.

[0105] Combined with the data in comparison sample 1, samples 1 to 3 and the table, the addition of silicon nitride nanoparticles has a significant effect on the friction coefficient and wear rate, and the formation of the composite ceramic film layer significantly improves the wear resistance of the sample; and from the friction coefficient and wear rate data of samples 4 to 5 and samples 6 to 7, the particle size of silicon nitride nanoparticles and the concentration in the mixed electrolyte solution have different degrees of influence.

[0106] Therefore, although silicon nitride nanoparticles are high-hardness materials with friction resistance, how to introduce them into magnesium alloys for surface treatment and maintain excellent corrosion resistance in addition to friction resistance in the surface layer is a key difficulty in the field of magnesium alloy surface treatment.

[0107] The present invention overcomes the incompatibility problem between friction resistance and corrosion resistance by introducing sodium fluorosilicate into the mixed electrolytic solution. Combining the corrosion current density, corrosion potential and low-frequency impedance modulus test data of sample 8 and sample 6, the additional addition of 1g / L of sodium fluorosilicate into the electrolytic solution of sample 8 significantly improves the overall corrosion resistance of sample 8.

[0108] Since the magnesium alloy of the composite ceramic film layer prepared by the present invention has excellent friction resistance and corrosion resistance, it can meet the requirements for application in automobile suspension arms.

[0109] It should be understood that the above embodiments are exemplary and are not intended to include all possible implementations included in the claims. Various modifications and changes may be made on the basis of the above embodiments without departing from the scope of the present disclosure. Similarly, the various technical features of the above embodiments may be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only express several implementations of the present invention and do not limit the scope of protection of the patent of the present invention.

Claims

1. A process for treating a composite ceramic film layer on the surface of a magnesium alloy, characterized in that: The processing steps include: S1: pre-processing the workpiece to be processed; S2: preparing a mixed electrolyte solution containing functional nanoparticles; S3: placing the workpiece in a mixed electrolytic solution, using the workpiece as an anode and the stainless steel material as a cathode for plasma electrolytic oxidation treatment to form a composite ceramic film layer on the surface of the workpiece.

2. The process for treating a composite ceramic film layer on a magnesium alloy surface according to claim 1, characterized in that: The functional nanoparticles include silicon nitride nanoparticles.

3. The process for treating a composite ceramic film layer on the surface of a magnesium alloy according to claim 2, characterized in that: The particle size of the silicon nitride nanoparticles is 15-30 nm.

4. The process for treating a composite ceramic film layer on the surface of a magnesium alloy according to claim 3, characterized in that: The mixed electrolytic solution of S2 includes 12-18 g / L of sodium sulfate, 8-12 g / L of sodium hydroxide, 6-10 g / L of potassium fluoride, 6-10 g / L of propanol, and 1-3 g / L of silicon nitride nanoparticles.

5. The process for treating a composite ceramic film layer on the surface of a magnesium alloy according to claim 4, characterized in that: The mixed electrolytic solution of S2 also includes 1-3 g / L of sodium fluorosilicate.

6. The process for treating a composite ceramic film layer on the surface of a magnesium alloy according to claim 1, characterized in that: During the S3 step, the temperature of the mixed electrolyte is maintained at 20±2°C.

7. The process for treating a composite ceramic film layer on the surface of a magnesium alloy according to claim 1, characterized in that: During the plasma electrolytic oxidation treatment process, the constant current is 5 to 6A, the duty cycle is 25% to 35%, the frequency is 1000 to 1350 Hz, and the oxidation time is 12 to 20 minutes.

8. The process for treating a composite ceramic film layer on the surface of a magnesium alloy according to claim 7, characterized in that: The mixed electrolytic solution has an electrical conductivity of 49.00 to 55.00 mS / cm, a termination voltage of 410 to 460 V, and a pH value of 11.20 to 13.

80.

9. A magnesium alloy with a composite ceramic film layer, characterized in that: The magnesium alloy is treated by the treatment process as claimed in claims 1 to 8 to form a magnesium alloy with a composite ceramic film layer on the surface of the workpiece, the thickness of the composite ceramic film layer is 18.50 to 32.50 μm, the microhardness of the magnesium alloy is 264 to 313 HV0.2, and the corrosion current density is 9.87×10 -7 ~1.22×10 -6 A×cm -2 The wear rate is 9.93×10 -5 ~1.05×10 -4 .

10. A magnesium alloy device used in an automobile suspension arm, wherein the surface of the magnesium alloy device has a composite ceramic film layer, and the composite ceramic film layer is formed by processing according to any one of claims 1 to 8.

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