A method for preparing a micro-arc oxidation electrolyte and micro-arc oxidation film for magnesium alloy surface treatment

Abstract

This invention provides a micro-arc oxidation electrolyte for magnesium alloy surface treatment and a method for preparing a micro-arc oxidation film. The micro-arc oxidation electrolyte is an aqueous solution containing sodium silicate, sodium hydroxide, potassium fluoride, and titanium boron carbon nitride conductive nanoparticles; or, an aqueous solution containing sodium silicate, potassium hydroxide, potassium fluoride, and titanium boron carbon nitride conductive nanoparticles. This invention also discloses a method for preparing a micro-arc oxidation film using the aforementioned micro-arc oxidation electrolyte for magnesium alloy surface treatment. The micro-arc oxidation electrolyte of this invention contains conductive ceramic nanoparticles—titanium boron carbon nitride conductive nanoparticles. Using these nanoparticles to perform a micro-arc oxidation reaction on the magnesium alloy surface can improve the microstructure of the micro-arc oxidation film, while simultaneously enhancing the corrosion resistance and wear resistance of the magnesium alloy after micro-arc oxidation treatment, significantly improving the surface protection capability of the magnesium alloy, and extending its service life.

Description

TECHNICAL FIELD

[0001] The present application relates to the surface modification technology of metal materials, and in particular to a magnesium alloy surface treatment micro-arc oxidation electrolyte and a preparation method of a micro-arc oxidation film layer. BACKGROUND

[0002] Magnesium alloys are widely used in aerospace, digital 3C and automobile manufacturing fields due to their low density, high specific strength and excellent electromagnetic shielding properties. However, the standard potential of magnesium element (-2.37 V) is low, which leads to the magnesium alloy being easily corroded in corrosive media. In addition, the oxide produced by the corrosion of the magnesium alloy is loose and porous, and cannot act as an effective physical barrier layer to isolate the corrosive medium. At the same time, compared with other metals such as steel and aluminum alloy, the hardness of the magnesium alloy is relatively low, which leads to its poor wear resistance. The low corrosion resistance and wear resistance seriously limit the large-scale engineering application of the magnesium alloy. Therefore, it is urgent to develop an effective surface treatment process to simultaneously improve the corrosion resistance and wear resistance of the magnesium alloy.

[0003] Micro-arc oxidation is a new technology for growing ceramic film layers on the surface of metals in situ. The ceramic film layers prepared by the technology have high chemical stability and excellent corrosion resistance and wear resistance, and have broad application prospects in the field of magnesium alloy corrosion and protection. However, during the preparation of the micro-arc oxidation film layer, continuous and strong sparks and gas are generated on the surface of the magnesium alloy, which leads to a large number of micropore and microcrack defects on the surface, and these defects provide channels for the corrosive medium, which adversely affects the corrosion resistance and wear resistance of the magnesium alloy.

[0004] The magnesium alloy micro-arc oxidation technology needs to regulate relevant parameters during application, including the electrolyte formula, power parameters (voltage, current, duty cycle, etc.). Among them, the formula of the electrolyte is an important key parameter, which greatly affects the structure and corrosion resistance, wear resistance and other properties of the surface film layer of the magnesium alloy. The existing micro-arc oxidation electrolyte includes: (1) the components of the alkaline phosphate system include sodium phosphate (Na3PO4), sodium dihydrogen phosphate (NaH2PO4), etc.; (2) the silicate system usually contains sodium silicate (Na2SiO2) or potassium silicate (K2SiO3) in the silicate electrolyte; (3) the borate electrolyte contains boric acid (H3BO3) or other borate; (4) the alkali metal hydroxide system mainly contains sodium hydroxide (NaOH) or potassium hydroxide (KOH). They have the following shortcomings to varying degrees: the generated oxide film is soft, has poor corrosion resistance and wear resistance, is easily damaged in a friction or mechanical wear environment, and limits its application in high wear environments. SUMMARY

[0005] The purpose of this invention is to address the problems of poor corrosion resistance and wear resistance in existing micro-arc oxidation electrolytes by proposing a micro-arc oxidation electrolyte for magnesium alloy surface treatment. This electrolyte contains conductive ceramic nanoparticles, which can improve the microstructure of the micro-arc oxidation film on the magnesium alloy surface by performing a micro-arc oxidation reaction on the magnesium alloy surface. At the same time, it enhances the corrosion resistance and wear resistance of the magnesium alloy after micro-arc oxidation treatment, significantly improves the surface protection capability of the magnesium alloy, and extends the service life of the magnesium alloy.

[0006] It should be noted that, in this invention, unless otherwise specified, the specific meaning of "comprising" in relation to composition and description includes both open-ended meanings such as "comprising," "including," etc., and closed-ended meanings such as "composed of," "consisting of," etc., and similar meanings.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a micro-arc oxidation electrolyte for magnesium alloy surface treatment, which is an aqueous solution containing sodium silicate, sodium hydroxide, potassium fluoride, and titanium boron carbon nitride conductive nanoparticles; wherein the content of sodium silicate is 8-12 g / L, the content of sodium hydroxide is 6-10 g / L, the content of potassium fluoride is 3-7 g / L, and the content of titanium boron carbon nitride conductive nanoparticles is 1.5-4 g / L;

[0008] Alternatively, it may be an aqueous solution containing sodium silicate, potassium hydroxide, potassium fluoride, and titanium boron carbon nitride conductive nanoparticles; wherein the content of sodium silicate is 6-8 g / L, the content of potassium hydroxide is 1-4 g / L, the content of potassium fluoride is 3-5 g / L, and the content of titanium boron carbon nitride conductive nanoceramics is 1.5-4 g / L.

[0009] Further, the titanium boron carbon nitride conductive nanoparticles are TiBCN, comprising the following components by mass percentage: 0.01–0.3% B, 3–7% C, 4–8% N, with the balance being Ti. Preferably, the mass ratio of the TiBCN is 0.001B:0.04C:0.06N:0.899Ti.

[0010] Furthermore, the particle size of the titanium boron carbon nitride conductive nanoparticles is 10–1000 nm.

[0011] Furthermore, the titanium boron carbon nitride conductive nanoparticles are prepared by the following method: Ti powder is placed in a stainless steel container, boronizing agent is used to fill the voids in the container, and then the stainless steel container is sealed and placed in a pit-type heating furnace for heating at a temperature of 760℃~800℃ for 4-6 hours. After the heating is completed, air cooling or furnace cooling is performed to obtain micron-sized TiBCN powder. Subsequently, the micron-sized TiBCN powder is used to prepare titanium boron carbon nitride conductive nanoceramics using mechanical spheroidizing technology.

[0012] Further, the preferred content of sodium silicate is 9.5-10 g / L, the preferred content of sodium hydroxide is 7.5-8.5 g / L, the preferred content of potassium fluoride is 4.5-5.5 g / L, and the preferred content of titanium boron carbon nitrogen conductive nanoparticles is 2-3.5 g / L.

[0013] Further, the preferred content of sodium silicate is 6.5-7 g / L, the preferred content of potassium hydroxide is 2.5-3 g / L, the preferred content of potassium fluoride is 2.5-3 g / L, and the preferred content of titanium boron carbon nitride conductive nanoceramics is 2-3.5 g / L.

[0014] Another objective of this invention discloses a method for preparing a micro-arc oxidation electrolyte for magnesium alloy surface treatment, comprising the following steps: mixing sodium silicate, sodium hydroxide, potassium fluoride, titanium boron carbon nitrogen conductive nanoparticles and deionized water according to a weight ratio to prepare a magnesium alloy surface treatment micro-arc oxidation electrolyte.

[0015] Furthermore, the mixture is subjected to ultrasonic dispersion treatment.

[0016] Furthermore, the ultrasound duration is 30–90 min, and the temperature is 20–40 °C.

[0017] Another objective of this invention is to disclose the use of a magnesium alloy surface treatment micro-arc oxidation electrolyte in the field of micro-arc oxidation film preparation.

[0018] Another object of the present invention discloses a method for preparing a micro-arc oxidation film, comprising the following steps:

[0019] Step (1) Magnesium alloy pretreatment;

[0020] Step (2) uses a magnesium alloy surface treatment micro-arc oxidation electrolyte to perform a micro-arc oxidation reaction on the magnesium alloy surface, and prepares a micro-arc oxidation film layer on the magnesium alloy surface, thereby obtaining a magnesium alloy micro-arc oxidation sheet with high corrosion resistance and wear resistance.

[0021] Furthermore, the pretreatment in step (1) includes grinding, cleaning, alkaline washing and drying.

[0022] Furthermore, the cleaning process employs ultrasonic cleaning with distilled water and alcohol.

[0023] Furthermore, the alkaline solution used for alkaline washing is an aqueous solution containing 30-60 g / L sodium phosphate and 40-60 g / L sodium hydroxide, the alkaline washing temperature is 55-65°C, and the alkaline washing time is 5-15 min.

[0024] Furthermore, the micro-arc oxidation reaction is conducted in a constant voltage mode, with an AC voltage of 250–400V, a pulse frequency of 400–500Hz, an oxidation time of 3–5 min, a duty cycle of 3%–10%, and an oxidation temperature of 20–42℃. Preferably, the AC voltage is 300V, the pulse frequency is 500Hz, the oxidation time is 3 min, the duty cycle is 5%, and the oxidation temperature is 20–42℃.

[0025] Furthermore, the micro-arc oxidation reaction is performed in constant current mode, with a direct current of 0.3–0.6 A / dm². 2 The pulse frequency is 400–500 Hz, the duty cycle is 3–10%, the oxidation time is 3–5 min, and the oxidation temperature is 20–42℃. The preferred constant current mode is 0.5 A / dm³ DC. 2 The pulse frequency is 500Hz, the duty cycle is 4%, the oxidation time is 5min, and the oxidation temperature is 20-42℃.

[0026] Furthermore, the time for the micro-arc oxidation reaction in step (2) is 3 to 10 minutes.

[0027] Furthermore, the thickness of the micro-arc oxidation film layer in step (2) is 10–50 μm.

[0028] Further, after obtaining the magnesium alloy sheet with a high corrosion resistance and wear resistance protective layer in step (2), the micro-arc oxidation sheet is cleaned and dried.

[0029] Furthermore, the drying temperature is 60-80℃.

[0030] The method for preparing the micro-arc oxidation electrolyte and micro-arc oxidation film layer for magnesium alloy surface treatment of the present invention has the following advantages compared with the prior art:

[0031] 1) The micro-arc oxidation electrolyte for magnesium alloy surface treatment of the present invention introduces titanium boron carbon nitride conductive ceramic nanoparticles into a conventional silicate electrolyte system. The porosity and pore size ratio of the micro-arc oxidation surface are significantly reduced compared with those without titanium boron carbon nitride nanoparticles, and the hardness and wear resistance of the micro-arc oxidation film are significantly improved.

[0032] 2) The micro-arc oxidation electrolyte for magnesium alloy surface treatment of the present invention is easy to prepare, has a long service life, and causes little environmental pollution.

[0033] 3) The film prepared by the micro-arc oxidation electrolyte for magnesium alloy surface treatment of the present invention has a uniform, dense surface and excellent corrosion resistance, which can greatly improve the surface protection capability of magnesium alloy and extend the service life of magnesium alloy.

[0034] 4) The formulation of the micro-arc oxidation electrolyte for magnesium alloy surface treatment and the preparation process of the micro-arc oxidation film layer of the present invention have great application prospects in the field of magnesium alloy surface protection. Attached Figure Description

[0035] Figure 1 This is a scanning electron microscope (SEM) image of the conductive nanoparticles titanium boron carbon nitrogen in Example 1.

[0036] Figure 2 Image a is a scanning electron microscope (SEM) image of the micro-arc oxidation film layer without titanium boron carbon nitride conductive nanoparticles in Comparative Example 1, and image b is a scanning electron microscope (SEM) image of the micro-arc oxidation film layer with titanium boron carbon nitride conductive nanoparticles added in Example 1.

[0037] Figure 3 In Figure a, it is a cross-sectional view of the micro-arc oxidation film layer without the addition of titanium boron carbon nitride conductive nanoparticles in Comparative Example 1, and in Figure b, it is a cross-sectional view of the micro-arc oxidation film layer with the addition of titanium boron carbon nitride conductive nanoparticles in Example 1.

[0038] Figure 4 Electrochemical impedance spectral modulus data for micro-arc oxidation films with / without titanium boron carbon nitride conductive nanoparticles on magnesium alloy substrates, where 1 is the magnesium alloy substrate, 2 is the micro-arc oxidation film without titanium boron carbon nitride conductive nanoparticles in Comparative Example 1, and 3 is the micro-arc oxidation film with titanium boron carbon nitride conductive nanoparticles in Example 1.

[0039] Figure 5 The macroscopic morphology of the micro-arc oxide film layer with and without titanium boron carbon nitride conductive nanoparticles after steel wool tribology test is shown in the left figure as Comparative Example 1 and the right figure as Example 1.

[0040] Figure 6 The Vickers hardness of LA81 magnesium-lithium alloy and micro-arc oxidation films with different contents of titanium-boron-carbon-nitrogen conductive nanoparticles is measured. Detailed Implementation

[0041] The present invention will be further described below with reference to embodiments. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0042] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0043] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0044] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0045] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0046] In this specification, the terms "optional" or "optional" are used to indicate the use or omission of certain substances, components, procedures, application conditions, etc.

[0047] In this instruction manual, when "room temperature" or "room temperature" is used, the temperature can be 15-25℃.

[0048] Unless otherwise specified, all reagents or instruments used in this instruction manual are commercially available products.

[0049] This invention provides a method for preparing a micro-arc oxidation electrolyte and a micro-arc oxidation film for magnesium alloy surface treatment, comprising the following steps:

[0050] (1) Pretreatment of magnesium alloy surface: grinding, cleaning and alkaline washing of magnesium alloy;

[0051] (2) Preparation of micro-arc oxidation electrolyte for magnesium alloy surface treatment: Add conductive titanium boron carbon nitrogen nanoparticles to conventional silicate electrolyte;

[0052] (3) Perform micro-arc oxidation treatment on the pretreated magnesium alloy to prepare a micro-arc oxidation film on the surface of the magnesium alloy.

[0053] (4) Post-treatment of magnesium alloy after micro-arc oxidation: rinse and dry the micro-arc oxidation film.

[0054] This invention prepares a micro-arc oxidation film on the surface of magnesium alloys, which can effectively resist the erosion of corrosive media in corrosive environments and improve its surface wear resistance. Using the micro-arc oxidation electrolyte for magnesium alloy surface treatment according to this invention, the porosity and pore size ratio of the micro-arc oxidized surface are significantly reduced compared to the surface without added nanoparticles, while the hardness and wear resistance of the micro-arc oxidized surface are significantly improved. The film surface is uniform and dense, exhibiting excellent corrosion resistance.

[0055] The present invention does not have any special limitation on the source of the magnesium alloy, which can be obtained by preparation methods well known to those skilled in the art.

[0056] The present invention preferably pre-treats the magnesium alloy before use; the pre-treatment is preferably performed sequentially by grinding, cleaning, alkaline washing, and drying. Pre-treatment of the magnesium alloy by the present invention can remove stains and oxide layers from the surface of the magnesium alloy, thereby improving the quality of the micro-arc oxide film.

[0057] The present invention does not have any special limitations on the operation of polishing the magnesium alloy surface with silicon carbide sandpaper of 100#, 400#, 800#, 1500# and 2000# in sequence, and any polishing operation known to those skilled in the art can be used.

[0058] In this invention, the alkaline solution used in the alkaline washing process is preferably 30-60 g / L sodium phosphate and 40-60 g / L sodium hydroxide, with an operating temperature of 50-70°C and a washing time of 5-15 min. More preferably, it is 45 g / L sodium phosphate and 50 g / L sodium hydroxide, with an operating temperature of 60°C and a washing time of 10 min. This invention does not impose any special limitations on the preparation method of the electrolyte; any preparation method well-known to those skilled in the art can be used.

[0059] In this invention, the electrolyte used to prepare the micro-arc oxidation film is preferably sodium hydroxide 7.5-8.5 g / L, sodium silicate 9.5-10.5 g / L, potassium fluoride 4.5-5.5 g / L, titanium boron carbon nitride conductive nanoceramics 1.5-4 g / L and water, more preferably sodium hydroxide 8 g / L, sodium silicate 10 g / L, potassium fluoride 5 g / L, titanium boron carbon nitride conductive nanoceramics 2.5 g / L and water.

[0060] This invention involves ultrasonically dispersing an electrolyte containing titanium-boron-carbon-nitrogen conductive nanoparticles. The ultrasonic treatment time is 30–120 minutes, and the ultrasonic temperature is room temperature. This invention does not specify a particular type of ultrasonic equipment; any instrument or equipment well-known to those skilled in the art can be used.

[0061] In this invention, the electrical parameters used for preparing the micro-arc oxidation film can be of two types. The first is a constant voltage mode: preferably, AC 250–400V, pulse frequency 400–500Hz, oxidation time 3–5 min, duty cycle 3%–10%, and oxidation temperature 30–42℃; more preferably, AC 300V, pulse frequency 500Hz, oxidation time 3 min, duty cycle 5%, and oxidation temperature 20–42℃. Alternatively, the second preferred mode is a constant current mode with DC 0.5A / dm². 2 The pulse frequency is 400–500 Hz, the duty cycle is 3–10%, the oxidation time is 3–5 min, and the oxidation temperature is 30–42 °C. More preferably, a constant current mode with a DC current of 0.5 A / dm is used. 2 The pulse frequency is 500Hz, the duty cycle is 4%, the oxidation time is 5min, and the oxidation temperature is 20-42℃.

[0062] In this invention, the drying is carried out in an oven at a temperature of 60°C. This invention does not specify a particular model of vacuum oven; any instrument or equipment well-known to those skilled in the art can be used.

[0063] Example 1:

[0064] This embodiment provides a method for preparing a micro-arc oxidation film, including the following steps:

[0065] The surface of the AZ31B magnesium alloy was successively polished with silicon carbide sandpaper of grades 100, 400, 800, 1500, and 2000. Then, the surface was ultrasonically cleaned with distilled water and alcohol to degrease and remove contaminants. Next, the AZ31 magnesium alloy was placed in a solution of 45 g / L sodium phosphate and 50 g / L sodium hydroxide and alkaline-washed at 60°C for 10 minutes. Afterward, the surface was ultrasonically cleaned with alcohol, and finally dried in a 60°C oven for 30 minutes.

[0066] In this embodiment, the micro-arc oxidation electrolyte for magnesium alloy surface treatment uses a silicate electrolyte system, wherein the electrolyte contains 8 g / L sodium hydroxide, 10 g / L sodium silicate, 5 g / L potassium fluoride, 2.5 g / L titanium boron carbon nitride conductive nano-ceramics, and deionized water. Subsequently, the prepared micro-arc oxidation electrolyte is subjected to ultrasonic dispersion treatment for 1 hour at a temperature of 25°C.

[0067] Then, AZ31 magnesium alloy was subjected to micro-arc oxidation in a magnesium alloy surface treatment micro-arc oxidation electrolyte to prepare a micro-arc oxidation film on the surface; the process parameters for the micro-arc oxidation method were: 5A / dm 2 The alternating current was 500 Hz, the pulse frequency was 4%, the oxidation time was 5 min, and the initial temperature of the electrolyte was 25 ℃.

[0068] The micro-arc oxidation film was post-treated by washing with distilled water and alcohol in sequence, and then dried in an oven at 60°C to obtain a micro-arc oxidation film with a thickness of 24 μm.

[0069] Figure 1 This is a scanning electron microscope (SEM) image of the conductive titanium boron carbon nitride nanoparticles in Example 1. It can be seen that the TBCN nanoparticles have a regular polygonal shape and a size of approximately 500 nanometers.

[0070] Example 2:

[0071] This embodiment provides a method for preparing a micro-arc oxidation film, including the following steps:

[0072] The surface of LA81 magnesium-lithium alloy (chemical composition: Mg-8Li-1Al) was successively polished with 100#, 400#, 800#, 1500#, and 2000# silicon carbide sandpaper. Then, the surface was ultrasonically cleaned with distilled water and alcohol to degrease and remove contaminants. Next, the LA81 magnesium-lithium alloy was placed in a 45g / L sodium phosphate and 50g / L sodium hydroxide solution and alkaline-washed at 60℃ for 10 minutes. Afterward, the surface was ultrasonically cleaned with alcohol, and finally dried in a 60℃ oven for 30 minutes.

[0073] In this embodiment, the micro-arc oxidation electrolyte for magnesium alloy surface treatment uses a silicate electrolyte system, wherein the electrolyte system contains 8 g / L sodium hydroxide, 10 g / L sodium silicate, 5 g / L potassium fluoride, 2.5 g / L titanium boron carbon nitride conductive nano-ceramics, and deionized water. Subsequently, the prepared micro-arc oxidation electrolyte is subjected to ultrasonic dispersion treatment for 1 hour, and the initial temperature of the electrolyte at the start of the micro-arc oxidation treatment is 25°C.

[0074] Then, the magnesium-lithium alloy was subjected to micro-arc oxidation in the micro-arc oxidation electrolyte of the magnesium alloy surface treatment in this embodiment to prepare a micro-arc oxidation film layer on the surface. The process parameters of the micro-arc oxidation process are: 300V AC power, 500Hz pulse frequency, duty cycle of 5%, oxidation time of 5min, and initial electrolyte temperature of 25℃.

[0075] The micro-arc oxidation film was post-treated by washing it with distilled water and alcohol in sequence, and then dried in an oven at 60°C to obtain a micro-arc oxidation film with a thickness of 15 μm.

[0076] Example 3:

[0077] This embodiment provides a method for preparing a micro-arc oxidation film, including the following steps:

[0078] The surface of the LA81 magnesium-lithium alloy was successively polished with 100#, 400#, 800#, 1500#, and 2000# silicon carbide sandpaper. Then, the surface was ultrasonically cleaned with distilled water and alcohol to degrease and remove contaminants. Next, the LA81 magnesium-lithium alloy was placed in a solution of 45 g / L sodium phosphate and 50 g / L sodium hydroxide and alkaline-washed at 60°C for 10 minutes. Afterward, the surface was ultrasonically cleaned with alcohol, and finally dried in a 60°C oven for 30 minutes.

[0079] In this embodiment, the micro-arc oxidation electrolyte for magnesium alloy surface treatment uses a silicate electrolyte system, wherein the electrolyte system contains 8 g / L sodium hydroxide, 10 g / L sodium silicate, 5 g / L potassium fluoride, 2.5 g / L titanium boron carbon nitride conductive nano-ceramics, and deionized water. Subsequently, the prepared micro-arc oxidation electrolyte is ultrasonically dispersed for 1 hour at a temperature of 25°C.

[0080] Then, the magnesium-lithium alloy was subjected to micro-arc oxidation in a magnesium alloy surface treatment micro-arc oxidation electrolyte to prepare a micro-arc oxidation film on the surface; the process parameters for the micro-arc oxidation process were: 5 A / dm 2 The alternating current was 500 Hz, the pulse frequency was 4%, the oxidation time was 5 min, and the initial temperature of the electrolyte was 25 ℃.

[0081] The micro-arc oxidation film was post-treated by washing it with distilled water and alcohol in sequence, and then dried in an oven at 60°C to obtain a micro-arc oxidation film with a thickness of 20.7 μm.

[0082] Example 4

[0083] This embodiment provides a method for preparing a micro-arc oxidation film, including the following steps:

[0084] The surface of the LA81 magnesium-lithium alloy was successively polished with 100#, 400#, 800#, 1500#, and 2000# silicon carbide sandpaper. Then, the surface was ultrasonically cleaned with distilled water and alcohol to degrease and remove contaminants. Next, the LA81 magnesium-lithium alloy was placed in a solution of 45 g / L sodium phosphate and 50 g / L sodium hydroxide and alkaline-washed at 60°C for 10 minutes. Afterward, the surface was ultrasonically cleaned with alcohol, and finally dried in a 60°C oven for 30 minutes.

[0085] In this embodiment, the micro-arc oxidation electrolyte for magnesium alloy surface treatment uses a silicate electrolyte system. Electrolyte system 1 contains 8 g / L sodium hydroxide, 10 g / L sodium silicate, 5 g / L potassium fluoride, 1 g / L titanium boron carbon nitride conductive nanoceramics, and deionized water. Electrolyte system 2 contains 8 g / L sodium hydroxide, 10 g / L sodium silicate, 5 g / L potassium fluoride, 4 g / L titanium boron carbon nitride conductive nanoceramics, and deionized water. The prepared micro-arc oxidation electrolyte is then ultrasonically dispersed for 1 hour at a temperature of 25°C.

[0086] Then, the magnesium-lithium alloy was subjected to micro-arc oxidation in magnesium alloy surface treatment micro-arc oxidation electrolyte 1 and micro-arc oxidation electrolyte 2 to prepare a micro-arc oxidation film layer on the surface. The process parameters of the micro-arc oxidation process are: AC current of 5A / dm2, pulse frequency of 500Hz, duty cycle of 4%, oxidation time of 5min, and initial electrolyte temperature of 25℃.

[0087] The micro-arc oxidation film was post-treated by washing with distilled water and alcohol in sequence, drying in an oven at 60°C, and obtaining a fragmented micro-arc oxidation film with a thickness of 40 μm in electrolyte 1 and a micro-arc oxidation film with a thickness of 30 μm in electrolyte 2.

[0088] The titanium boron carbon nitride conductive nanoceramics described in Examples 1-4 are all the same, namely TiBCN1.

[0089] The method for preparing titanium-boron-carbon-nitrogen conductive nanoceramics includes the following steps:

[0090] Preparation method of TiBCN1: 25g of Ti powder is placed in a stainless steel container, and boronizing agent is used to fill the voids in the container. The stainless steel container is then sealed and placed in a pit-type heating furnace for heating at 800℃ for 5 hours. After the heating is completed, air cooling or furnace cooling is performed to obtain micron-sized TiBCN powder. Subsequently, the micron-sized TiBCN powder is used to prepare titanium boron carbon nitride conductive nanoceramics using mechanical spheroidization technology. The TiBCN ratio is 0.001B:0.04C:0.06N:0.899Ti, and the particle size of the titanium boron carbon nitride conductive nanoparticles is 10-1000nm.

[0091] Preparation method of TiBCN2: 25g of Ti powder is placed in a stainless steel container, and boronizing agent is used to fill the voids in the container. 10g of charcoal is added to the boronizing agent as the carbon source in the conductive nanoparticles. The stainless steel container is then sealed and placed in a pit-type heating furnace for heating at 800℃ for 5 hours. After the heating is completed, it is air-cooled or furnace-cooled to obtain micron-sized TiBCN powder. Subsequently, the micron-sized TiBCN powder is used to prepare titanium boron carbon nitride conductive nanoceramics using mechanical spheroidization technology. The TiBCN ratio is 0.001B:0.16C:0.04N:0.799Ti, and the particle size of the titanium boron carbon nitride conductive nanoparticles is 10-1000nm.

[0092] Compare with Example 1

[0093] This comparative example is identical to Example 1 except that it does not contain titanium boron carbon nitride conductive nanoparticles.

[0094] Figure 2 Image a shows a scanning electron microscope (SEM) image of the micro-arc oxidation film layer without titanium boron carbon nitride conductive nanoparticles in Comparative Example 1, while image b shows a scanning electron microscope (SEM) image of the micro-arc oxidation film layer with titanium boron carbon nitride conductive nanoparticles in Example 1. It can be seen that after adding titanium boron carbon nitride conductive nanoparticles, the number and size of pores in the micro-arc oxidation film layer are significantly reduced, with the micropore diameter decreasing from approximately 10 micrometers in the initial state to 2–3 micrometers.

[0095] Figure 3 Image a shows a cross-sectional view of the micro-arc oxidation film layer without the addition of titanium boron carbon nitride conductive nanoparticles in Comparative Example 1, and image b shows a cross-sectional view of the micro-arc oxidation film layer with the addition of titanium boron carbon nitride conductive nanoparticles in Example 1. It can be seen that after adding titanium boron carbon nitride conductive nanoparticles, the coating thickness decreased from the initial 30.7 micrometers to 20.1 micrometers. The coating is more dense and uniform, and the number of pores and the pore size ratio are significantly reduced. Compared with the micro-arc oxidation coating without the addition of titanium boron carbon nitride conductive nanoparticles, no obvious easily corroded through-pores are observed. This morphology is more conducive to the corrosion protection of the coating.

[0096] Figure 4The data show the electrochemical impedance spectral modulus values ​​of micro-arc oxidation films on magnesium alloy substrates with and without titanium boron carbon nitride conductive nanoparticles, where 1 represents the magnesium alloy substrate, 2 represents the micro-arc oxidation film without titanium boron carbon nitride conductive nanoparticles in Comparative Example 1, and 3 represents the micro-arc oxidation film with titanium boron carbon nitride conductive nanoparticles in Example 1. It is evident that the impedance modulus of the micro-arc oxidation film with added titanium boron carbon nitride conductive nanoparticles is significantly greater than that without, indicating that the addition of conductive nanoparticles improves the corrosion resistance of the film.

[0097] Figure 5 The macroscopic morphology of the micro-arc oxidation film layers with and without titanium boron carbon nitride conductive nanoparticles after steel wool tribology tests is shown in the left figure (Comparative Example 1) and the right figure (Example 1). It can be seen that the surface of the micro-arc oxidation film layer without conductive nanoparticles has obvious deep scratches, exposing the metal substrate in some areas. In contrast, the surface of the micro-arc oxidation film layer with added conductive nanoparticles shows no exposed metal substrate. These results indicate that adding titanium boron carbon nitride conductive nanoparticles can significantly improve the tribological resistance of the film layer.

[0098] Figure 6 The Vickers hardness of the LA81 magnesium-lithium alloy and micro-arc oxidation films with different contents of titanium-boron-carbon-nitrogen conductive nanoparticles in Example 1 are shown. It can be seen that the Vickers hardness of the micro-arc oxidation film without conductive nanoparticles is 225 Hv, while the Vickers hardness of the micro-arc oxidation film with 2.5g of conductive nanoparticles added in Example 1 increases to 325 Hv. The results indicate that adding conductive nanoparticles can improve the hardness of the film.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A magnesium alloy surface treatment micro-arc oxidation electrolyte, characterized in that, The water solution comprises sodium silicate, sodium hydroxide, potassium fluoride and titanium boron carbon nitrogen conductive nanoparticles; wherein the content of sodium silicate is 8-12 g / L, the content of sodium hydroxide is 6-10 g / L, the content of potassium fluoride is 3-7 g / L, and the content of titanium boron carbon nitrogen conductive nanoparticles is 1.5-4 g / L. Or, the water solution comprises sodium silicate, potassium hydroxide, potassium fluoride and titanium boron carbon nitrogen conductive nanoparticles; wherein the content of sodium silicate is 6-8 g / L, the content of potassium hydroxide is 1-4 g / L, the content of potassium fluoride is 3-5 g / L, and the content of titanium boron carbon nitrogen conductive nanoparticles is 1.5-4 g / L. The titanium boron carbon nitrogen conductive nanoparticles are TiBCN, and comprise the following components in mass percentage: 0.01-0.3% B, 3-7% C, 4-8% N, and the balance of Ti. The particle size of the titanium boron carbon nitrogen conductive nanoparticles is 10-1000 nm.

2. The magnesium alloy surface treatment micro-arc oxidation electrolyte according to claim 1, characterized in that, The titanium boron carbon nitrogen conductive nanoparticles are prepared by the following method: placing Ti powder in a stainless steel tank, filling the interstitial part of the tank with boronizing agent, then sealing the stainless steel tank in an open hearth furnace for heating, the heating temperature is 760-800 ℃, the holding time is 4-6 hours, and after holding, air cooling or furnace cooling treatment is performed to obtain micron-sized TiBCN powder; then, the micron-sized TiBCN powder is prepared into titanium boron carbon nitrogen conductive nanoparticles by mechanical ball milling technology.

3. A method for preparing the electrolyte for micro-arc oxidation surface treatment of magnesium alloys according to claim 1 or 2, characterized in that, The method comprises the following steps: According to the weight ratio, the sodium silicate, sodium hydroxide, potassium fluoride, titanium boron carbon nitrogen conductive nanoparticles and deionized water are mixed to prepare the magnesium alloy surface treatment micro-arc oxidation electrolyte.

4. The method for preparing the electrolyte for micro-arc oxidation surface treatment of magnesium alloy according to claim 3, characterized in that, The mixing is performed by ultrasonic dispersion treatment.

5. Use of the magnesium alloy surface treatment micro-arc oxidation electrolyte according to claim 1 or 2 in the field of micro-arc oxidation film layer preparation.

6. A method for preparing a micro-arc oxidation film layer, characterized in that, The method comprises the following steps: Step (1) magnesium alloy pretreatment; Step (2) using the magnesium alloy surface treatment micro-arc oxidation electrolyte according to claim 1 or 2 to perform micro-arc oxidation reaction on the surface of the magnesium alloy to prepare a micro-arc oxidation film layer on the surface of the magnesium alloy, thereby obtaining a magnesium alloy micro-arc oxidation sheet with high corrosion and wear resistance.

7. The method for preparing the micro-arc oxidation film according to claim 6, characterized in that, Step (1) the pretreatment comprises polishing, cleaning, alkali washing and drying; The cleaning is performed by ultrasonic cleaning with distilled water and alcohol; The alkali solution used for alkali washing is an aqueous solution containing 30-60 g / L sodium phosphate and 40-60 g / L sodium hydroxide, the alkali washing temperature is 55-65 ℃, and the alkali washing time is 5-15 min.

8. The method according to claim 6, wherein the micro-arc oxidation film is formed by using a power supply with a frequency of 50-1000 Hz, a voltage of 300- 600 V, and a current of 1-5 A. In the process of the micro-arc oxidation reaction, a constant voltage mode is adopted, the alternating current is 250-400 V, the pulse frequency is 400-500 Hz, the oxidation time is 3-5 min, the duty cycle is 3%-10%, and the oxidation temperature is 20-42 ℃; Or, the process of micro-arc oxidation reaction using constant current mode, direct current 0.3~0.6A / dm 2 , pulse frequency 400~500Hz, duty cycle 3~10%, oxidation time 3~5min, oxidation temperature 20~42℃.

9. The method for preparing the micro-arc oxidation film according to claim 6, characterized in that, Step (2) the thickness of the micro-arc oxidation film layer is 10-50 μm.

10. The method according to claim 6, wherein the micro-arc oxidation film is prepared by using a power supply with a frequency of 50-1000 Hz, a voltage of 300- 600 V, and a current of 1-10 A. Step (2) after obtaining the magnesium alloy sheet with the high corrosion and wear resistance protective layer, the micro-arc oxidation sheet is cleaned and dried.

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