Aluminum alloy plasma micro-arc oxidation nano-reinforced composite ceramic layer and preparation method thereof

Abstract

The invention discloses an aluminum alloy plasma micro-arc oxidation nano-reinforced composite ceramic layer and a preparation method thereof. The method comprises the following steps: pretreating an aluminum alloy sample, and sealing and storing for later use; tetraethoxysilane is added into the basic electrolyte; after tetraethoxysilane is completely hydrolyzed, firstly adding a nano enhancer, then adding nano rare earth oxide powder, and stirring to enable the uniformity of the solution to be consistent; the prepared electrolyte is poured into a micro-arc oxidation electrolytic tank, the standby aluminum alloy sample is placed in the electrolytic tank and connected with the positive electrode of a micro-arc oxidation power source, stainless steel serves as a negative electrode, and micro-arc oxidation treatment is conducted in a constant-voltage mode; and the aluminum alloy sample obtained after micro-arc oxidation treatment is taken out of the electrolytic tank, and cleaning and airing are conducted in sequence. The aluminum alloy is subjected to micro-arc oxidation treatment by adopting the composite electrolyte of the phosphate basic electrolyte, the organic silicon solution and nano strengthening, a formed film layer shows excellent corrosion resistance and high hardness, the binding force between the film layer and a matrix is high, and the density is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum alloy surface treatment, and particularly relates to an aluminum alloy plasma micro-arc oxidation nano-strengthened composite ceramic layer, a preparation method thereof, and an application thereof. Background Art

[0002] Due to its good electrical conductivity, thermal conductivity, and certain plasticity, aluminum alloy has been widely used in industrial fields such as electronics, electric power, and automobiles. However, in some specific usage environments, its surface performance reveals obvious deficiencies. In corrosive environments such as humidity, acid, and alkali, aluminum alloy is prone to corrosion, resulting in shortened service life, damaged appearance, and decreased mechanical properties. At the same time, when facing working conditions of friction and wear, its surface hardness is relatively low, its wear resistance is poor, and defects such as scratches and abrasions are likely to occur, thereby affecting its use effect and reliability.

[0003] Micro-arc oxidation technology is a surface treatment method for in-situ growing ceramic films on the surface of aluminum alloy, which can effectively improve the surface performance of aluminum alloy. However, there are still some problems in the treatment of aluminum alloy by traditional micro-arc oxidation technology. For example, the porosity of the formed micro-arc oxidation film is relatively high, which allows corrosive media to easily penetrate into the interior of the film layer, thereby eroding the aluminum alloy substrate and reducing the long-term protection effect of the film layer on the substrate. Moreover, it is difficult to accurately control the thickness uniformity of the traditional micro-arc oxidation film. In some application scenarios with strict requirements for the film layer thickness, the requirements cannot be met. In addition, the surface roughness of the traditional micro-arc oxidation film is relatively large. In the application of some precision components with high requirements for surface flatness, it may affect the assembly accuracy and operation stability of the components. For example, on the heat sink of an electronic device, the rough surface of the micro-arc oxidation film may affect the heat dissipation efficiency and the fit with other components. In addition to the above disadvantages, the film formation speed of the traditional micro-arc oxidation film is relatively slow. When reaching 60μm, it often requires an hour of forming time, and the production cycle is relatively long. These limitations restrict the further application of aluminum alloy micro-arc oxidation films in high-precision electronic devices, high-grade automotive parts, and some industrial products with strict requirements for surface quality. There is an urgent need to improve and optimize the traditional micro-arc oxidation technology. Summary of the Invention

[0004] To solve at least one of the above-mentioned technical problems in the prior art, the present invention provides an aluminum alloy plasma micro-arc oxidation nano-strengthened composite ceramic layer, its preparation method and application. By using a composite electrolyte of "phosphate-based electrolyte + silicone solution + nano-strengthening" to perform micro-arc oxidation treatment on the aluminum alloy, the porosity and roughness problems of the film layer are fundamentally improved, and a dense layer is formed on the surface of the aluminum alloy, which is tightly combined with the aluminum alloy matrix; during the micro-arc oxidation process, while promoting the formation of a dense protective layer, a surface structure with special functions is constructed, which is closely connected to the aluminum alloy matrix, and the film layer performance gradually transitions from the inside to the outside, showing a uniform and delicate structure at the microscopic level, effectively making up for the deficiencies of traditional processes, greatly improving the surface performance of the aluminum alloy in terms of corrosion resistance, wear resistance, film formation rate, etc., expanding the application range and performance of the aluminum alloy micro-arc oxidation film, and strongly promoting the in-depth application of the aluminum alloy in many industrial fields.

[0005] The first object of the present invention is to provide a preparation method for an aluminum alloy plasma micro-arc oxidation nano-strengthened composite ceramic layer.

[0006] The second object of the present invention is to provide an aluminum alloy plasma micro-arc oxidation nano-strengthened composite ceramic layer.

[0007] The third object of the present invention is to provide an application of an aluminum alloy plasma micro-arc oxidation nano-strengthened composite ceramic layer.

[0008] The first object of the present invention can be achieved by adopting the following technical solutions: A preparation method for an aluminum alloy plasma micro-arc oxidation nano-strengthened composite ceramic layer, the method comprising: Successively grinding, polishing, cleaning, drying and hermetically storing the aluminum alloy sample for standby; Adding tetraethyl orthosilicate to the basic electrolyte; after the tetraethyl orthosilicate is completely hydrolyzed, first adding a nano-strengthening agent, and then adding nano rare earth oxide powder, and stirring until the uniformity of the solution reaches consistency to complete the preparation of the electrolyte; wherein, the basic electrolyte includes a main salt, a compounding agent and deionized water, the main salt is sodium hexametaphosphate, and the compounding agent is sodium hydroxide; the nano-strengthening agent is any one of boron nitride and boron carbide and is mixed with graphene; Pour the prepared electrolyte into the micro-arc oxidation electrolytic cell, place the standby aluminum alloy sample in the electrolytic cell and connect it to the positive electrode of the micro-arc oxidation power supply, use stainless steel as the cathode, and perform micro-arc oxidation treatment for 5 to 60 minutes in the constant voltage mode; during the micro-arc oxidation treatment, synchronously stir the electrolyte to ensure the uniformity of the suspension solution and maintain the stability of the electrolyte temperature; Take out the aluminum alloy sample after micro-arc oxidation treatment from the electrolytic cell, and successively wash and air-dry it.

[0009] Further, the concentration of tetraethyl orthosilicate is greater than 0.02 mol / L and less than or equal to 1 mol / L, the concentration of sodium hexametaphosphate is 20 - 60 g / L, the concentration of sodium hydroxide is 2 - 25 g / L, the addition amount of the nano-strengthening agent is 2 - 10 g / L, and the addition amount of the nano rare earth oxide powder is 2 - 10 g / L.

[0010] Further, the average particle sizes of both the nano-strengthening agent and the nano rare earth oxide powder are 1 - 200 nm.

[0011] Further, the nano rare earth oxide powder is at least one of lanthanum oxide (La 2 O 3 ), cerium oxide (CeO 2 ), neodymium oxide (Nd 2 O 3 ), gadolinium oxide (Gd 2 O 3 ), erbium oxide (Er 2 O 3 ), scandium oxide (Sc 2 O 3 ), yttrium oxide (Y 2 O 3 ), holmium oxide (Ho 2 O 3 ), terbium oxide (Tb 4 O 7 ), samarium oxide (Sm 2 O 3 ), europium oxide (Eu 2 O 3 ), lutetium oxide (Lu 2 O 3 ), ytterbium oxide (Yb 2 O 3 ), praseodymium oxide (Pr 6 O 11 ), and dysprosium oxide (Dy 2 O 3 ).

[0012] Further, the process parameters of the micro-arc oxidation treatment are: the forward voltage is 300 - 700 V, the reverse voltage is -200 - 0 V; the current density is 2 - 10 A / dm², the duty cycle is 5% - 40%, the pulse frequency is 300 - 1500 Hz, and the reaction temperature is 5 - 40 °C.

[0013] Furthermore, the cleaning method includes ultrasonic cleaning and vacuum glow plasma cleaning; wherein the ultrasonic cleaning is carried out at room temperature for 15 - 30 min to remove impurities on the surface of the aluminum alloy sample; the vacuum glow plasma cleaning is carried out in a vacuum furnace at 30 - 50 °C for 15 - 30 min of plasma cleaning to improve the surface quality and adhesion of the aluminum alloy sample.

[0014] Furthermore, a ceramic oxide film coating grows in situ on the surface of the aluminum alloy sample after micro-arc oxidation treatment; the oxide film coating is closely combined with the aluminum alloy sample, and the overall surface is flat and distributed with micro-nano scale pores.

[0015] Furthermore, a multi-component electrolyte system is constructed by synergistically combining tetraethyl orthosilicate with sodium hexametaphosphate and sodium hydroxide to drive the growth process of the micro-arc oxidation film layer; during the micro-arc oxidation treatment, tetraethyl orthosilicate hydrolyzes to produce highly active functional groups of silanol groups; the functional groups of silanol groups, on the one hand, can in situ generate SiO 2 and precisely adhere to the surface of the film layer; on the other hand, it has the potential to undergo specific chemical reactions with the remaining components in the electrolyte, and gradually interweaves to build a composite film layer structure to exhibit a dense microstructure, excellent corrosion resistance, and diverse dimensional characteristics.

[0016] Furthermore, during the micro-arc oxidation treatment, tetraethyl orthosilicate hydrolyzes to produce highly active functional groups of silanol groups; during the film formation process, between the functional groups of silanol groups, sodium hexametaphosphate and the nano-strengthening agent, relying on their inherent chemical driving force, spontaneously construct an in-situ growth type composite network structure; the in-situ growth type composite network structure not only has Si-O-P bonds, but also contains Si-O-B bonds and Si-C bonds; in addition, the nano-strengthening agent is evenly distributed in the oxide film layer to form dispersion strengthening to effectively block the expansion of micro-cracks, thereby improving the density and uniformity of the oxide film layer.

[0017] Furthermore, during the micro-arc oxidation treatment, tetraethyl orthosilicate hydrolyzes to produce highly active functional groups of silanol groups; during the dynamic formation process of the oxide film layer, nano rare earth oxide powders are embedded; during the embedding process, between the functional groups of silanol groups, sodium hexametaphosphate and the rare earth nano-oxide powders, an in-situ growth type composite network structure is spontaneously constructed; the in-situ growth type composite network structure covers Si-O-P bonds and Si-O-rare earth metal bonds, as well as the complexation bonds between sodium hexametaphosphate and the rare earth nano-oxide powders, to deeply fit the chemical bond force inside the material and strongly promote the continuous growth and stable formation of the dense oxide film layer; in addition, nano rare earth oxides can promote the uniform nucleation of the micro-arc oxidation film and can refine the grains in the oxide film layer to improve the density and uniformity of the oxide film layer, as well as the overall strength and durability.

[0018] The second object of the present invention can be achieved by adopting the following technical solutions: An aluminum alloy plasma micro-arc oxidation nano-strengthened composite ceramic layer, which is prepared based on the above preparation method.

[0019] The third object of the present invention can be achieved by adopting the following technical solutions: An application of an aluminum alloy plasma micro-arc oxidation nano-strengthened composite ceramic layer, which is the application of the aluminum alloy plasma micro-arc oxidation nano-strengthened composite ceramic layer prepared based on the above preparation method in the fields of automobile manufacturing, electronic equipment, ocean engineering, and aerospace technology.

[0020] The present invention has the following beneficial effects compared with the prior art: (1) In the design of the electrolyte system of the present invention, tetraethyl orthosilicate (TEOS) is innovatively selected and synergistically combined with sodium hexametaphosphate and sodium hydroxide to construct a multi-component electrolyte system to drive the growth process of the micro-arc oxidation film layer; during the aluminum alloy plasma micro-arc oxidation process, TEOS hydrolyzes to generate highly active functional groups silanol groups (Si-OH); on the one hand, these silanol groups can in-situ generate SiO 2 and precisely adhere to the surface of the film layer; on the other hand, it has the potential to undergo specific chemical reactions with the remaining components in the electrolyte, gradually interweaving and building a composite film layer structure. Compared with the film layer composed of conventional components, this composite structure exhibits a denser microstructure, more excellent corrosion resistance, and more diverse dimensional characteristics, and the comprehensive performance is significantly improved.

[0021] (2) The present invention introduces a nano-strengthening agent (nano-scale boron nitride or boron carbide, graphene mixture) by modifying the electrolyte to participate in the formation of the film layer. During the film formation process, between the silanol groups, sodium hexametaphosphate and the nano-strengthening agent, a very unique in-situ growth type composite network structure is spontaneously constructed by virtue of their inherent chemical driving force. In this structure, the types of chemical bonds are rich and diverse, not only including the classic chemical bond Si-O-P, but also including Si-O-B bonds derived from boron nitride or boron carbide and Si-C bonds from graphene. The nano-strengthening agent is evenly distributed in the film layer to form dispersion strengthening, effectively blocking the expansion of micro-cracks and improving the density and uniformity of the film layer; among them, nano-scale boron nitride BN and boron carbide BC both have high hardness and wear resistance, which can significantly improve the hardness and wear resistance of the micro-arc oxidation film and extend the service life of the film layer; graphene provides lubricating properties for the film layer, improves hardness and wear resistance, and increases the toughness of the film layer.

[0022] (3) By introducing nano rare earth oxide powder into the electrolyte modification, on the one hand, it can be embedded during the dynamic formation process of the oxide film layer. During the embedding process, an in-situ growth type composite network structure is spontaneously constructed among silanol groups (Si-OH), sodium hexametaphosphate, and rare earth nano-oxide powder, covering various chemical bond types such as Si-O-P, Si-O-rare earth metal bonds, and complex bonds between sodium hexametaphosphate and rare earth nano-oxide powder. This unique composite network structure can deeply fit the chemical bond force inside the material, provide key support for the leap of the comprehensive performance of the material, and strongly promote the continuous growth and stable formation of the dense film layer. On the other hand, nano rare earth oxide can promote the uniform nucleation of the micro-arc oxidation film and refine the grains in the film layer to make them smaller and more uniform, thereby improving the density and uniformity of the film layer, as well as the overall strength and durability of the film layer.

[0023] (4) The present invention can accurately control the film layer growth rate and structural characteristics by precisely adjusting the addition amount of tetraethyl orthosilicate, phosphate concentration, nano-strengthening agent, content of nano rare earth oxide powder, and process parameters in the electrolyte. The prepared ceramic oxide film shows a uniform and delicate tissue structure at the microscopic level, realizing the on-demand customization of various film layer characteristics from thin and dense to thick and tough; by adjusting the ratio of tetraethyl orthosilicate and phosphate in the electrolyte, as well as the nano-strengthening agent and nano rare earth powder, combined with the change of process parameters, the chemical composition and phase composition of the film layer can be accurately controlled, realizing the precise allocation of various components from high silicon content to high phosphorus content, and meeting the different application requirements for the film layer performance.

[0024] (5) The present invention can significantly improve the film layer formation rate by optimizing the electrolyte formula and electrical parameters; compared with the traditional electrolyte system, the film formation time can be shortened by about 1 / 3 to 1 / 2, improving the production efficiency.

[0025] (6) The whole treatment process of the present invention is mainly based on physical and chemical reactions, without generating a large amount of harmful by-products and there is no serious environmental pollution problem, which is green and environmentally friendly.

[0026] (7) The present invention is applicable to the treatment of various specifications of aluminum alloy components. Whether it is a small precision aluminum alloy part or a medium-sized aluminum alloy structural part, the mixed electrolyte system can be used for micro-arc oxidation treatment. The treatment process is not strictly restricted by the size and shape of the components, and has good versatility and expandability. Description of the Drawings

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0028] Figure 1 、 2 These are two SEM images of the surface of the ceramic coating in Example 2 of the present invention; Figure 3 This is an SEM image of the cross-section of the ceramic coating in Example 2 of the present invention; Figure 4 This is the Nyquist plot of the AC impedance test of the ceramic coating in Example 2 of the present invention in a 3.5 wt% NaCl solution; Figure 5 、 6 These are two Bode plots of the electrochemical AC impedance test of the ceramic coating in Example 2 of the present invention in a 0.35 wt% NaCl solution; Figure 7 This is the electrochemical Tafel test plot of the ceramic coating in Example 2 of the present invention in a 3.5 wt% NaCl solution; Figure 8 This is an SEM image of the surface of the ceramic coating in Example 3 of the present invention; Figure 9 This is an SEM image of the cross-section of the ceramic coating in Example 3 of the present invention; Figure 10 This is an SEM image of the surface of the ceramic coating in Example 4 of the present invention; Figure 11 This is an SEM image of the cross-section of the ceramic coating in Example 4 of the present invention; Figure 12 This is an SEM image of the surface of the ceramic coating in Example 5 of the present invention; Figure 13 This is an SEM image of the cross-section of the ceramic coating in Example 5 of the present invention; Figure 14 This is an SEM image of the surface of the ceramic coating in Example 6 of the present invention; Figure 15 This is an SEM image of the cross-section of the ceramic coating in Example 6 of the present invention. Detailed implementation manners

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. It should be understood that the specific embodiments described are only used to explain the present application and are not used to limit the present application.

[0030] Embodiment 1: This embodiment provides a method for preparing an aluminum alloy plasma micro-arc oxidation nano-strengthened composite ceramic layer, including the following steps: (1) Pretreat the aluminum alloy specimen.

[0031] Select an aluminum alloy workpiece as the raw material and use wire electrical discharge machining to make a specimen with dimensions of 30*30*3 mm (length × width × thickness).

[0032] Among them, the grade of the aluminum alloy workpiece can be 1000 series aluminum alloy, 2000 series aluminum alloy, 3000 series aluminum alloy, 4000 series aluminum alloy, 5000 series aluminum alloy, 6000 series aluminum alloy, or 7000 series aluminum alloy, etc.; the shape can be square, cylindrical, or small and medium-sized parts with a more complex shape, and its effective area is 5 - 100 cm 2 .

[0033] First, perform mechanical polishing on the specimen: Select alumina waterproof sandpapers with grit sizes of 400#, 600#, 800#, 1000#, 1200#, 1500#, and 2000# to polish the specimen to remove the oxide layer; then select polishing cloths with powers of 2.5 w and 0.5 w in combination with polishing paste to perform mechanical polishing on the polished specimen.

[0034] After mechanical polishing, perform electrochemical polishing on the specimen: Prepare a mixed polishing solution of perchloric acid and absolute ethanol, set the voltage parameter to 20 - 30 V, polish for 10 - 20 s, and immediately wash it with clean water after completion to finish the polishing.

[0035] Then, ultrasonically clean the polished specimen with acetone, absolute ethanol, and deionized water for 15 - 30 min to remove impurities such as oil stains; then perform vacuum glow plasma cleaning: Perform plasma cleaning in a vacuum furnace at 30 - 50 °C under appropriate electrical parameter conditions for 15 - 30 min to further remove contaminants, oxide layers, and other impurities on the specimen surface to improve the surface quality and adhesion of the aluminum alloy specimen; then take it out and put it into a vacuum drying oven, dry it at 50 °C for 40 min, and sample and seal it for future use.

[0036] (2) Optimize the design of the electrolyte composition.

[0037] First, prepare the basic electrolyte: The basic electrolyte includes a main salt, a compounding agent, and deionized water. The main salt is selected as sodium hexametaphosphate with a concentration of 20 - 60 g / L; the compounding agent is selected as sodium hydroxide with a concentration of 5 - 25 g / L. Use an alkali to adjust the pH value of the solution, and the solvent is deionized water. After magnetic stirring for 20 min, the basic electrolyte is obtained and stored in the dark for later use.

[0038] Optimize the design of the electrolyte composition: Add tetraethyl orthosilicate (TEOS) solvent to the basic electrolyte, and its concentration can be in the range of 0.01 - 1 mol / L. After the mixed electrolyte is fully stirred and hydrolyzed in a magnetic stirrer for 4 - 8 hours, the TEOS is completely hydrolyzed. Then, modify the electrolyte: First, add a nano-strengthening agent, and then add nano-rare earth oxide powder, and stir together for 30 min to make the uniformity of the solution consistent, thus completing the preparation of the electrolyte.

[0039] In this embodiment, the amount of tetraethyl orthosilicate solvent is greater than 0.2 mol / L because the developed micro-arc oxidation process system provides reasonable and sufficient silicon ions for micro-arc oxidation treatment and generates enough highly active functional groups of silanol (Si-OH).

[0040] Specifically, the addition amount of the nano-strengthening agent is 2 - 10 g / L; the nano-strengthening agent can be one of boron nitride (BN) or boron carbide (BC), and is mixed with graphene. The addition amount of the nano-rare earth oxide powder is 2 - 10 g / L; the nano-rare earth powder can be lanthanum oxide (La 2 O 3 ), cerium oxide (CeO 2 ), neodymium oxide (Nd 2 O 3 ), gadolinium oxide (Gd 2 O 3 ), erbium oxide (Er 2 O 3 ), scandium oxide (Sc 2 O 3 ), yttrium oxide (Y 2 O 3 ), holmium oxide (Ho 2 O 3 ), terbium oxide (Tb 4 O 7 ), samarium oxide (Sm 2 O 3 ), europium oxide (Eu 2 O 3 ), lutetium oxide (Lu 2 O 3 ), ytterbium oxide (Yb 2 O 3) Praseodymium oxide (Pr 6 O 11 ), dysprosium oxide (Dy 2 O 3 ), or a rare earth powder, or a mixed rare earth powder of two or more kinds.

[0041] Among them, the average particle sizes of the nano-strengthening agent and the nano-rare earth oxide powder are both 1 - 200 nm.

[0042] (3) Micro-arc oxidation treatment to prepare a micro-arc oxidation coating on the surface of the aluminum alloy sample.

[0043] Pour the prepared mixed electrolyte into the electrolytic cell of the micro-arc oxidation equipment, and adjust the electrolyte temperature to 5 - 40 °C. Connect the aluminum alloy sample to the anode and use stainless steel as the cathode. Turn on the power supply and adopt a constant voltage mode: the positive voltage is 300 - 700 V, and the negative voltage is -200 - 0 V; the current density is controlled at 2 - 10 A / dm²; the duty cycle can be adjusted correspondingly, generally set at 5% - 40%; the pulse frequency is generally set at 300 - 1500 Hz.

[0044] Then start the micro-arc oxidation treatment. During the micro-arc oxidation treatment, synchronously stir the mixed electrolyte to ensure the uniformity of the suspension solution, and use a solution temperature control device to monitor the micro-arc oxidation treatment temperature and maintain the stability of the mixed electrolyte temperature. The micro-arc oxidation treatment time is controlled at 5 - 60 min. During the treatment process, it is necessary to monitor various parameters in real time to ensure the stable progress of the micro-arc oxidation process. After the treatment is completed, take out the aluminum alloy workpiece from the electrolytic cell, rinse it with deionized water and anhydrous ethanol in turn, and place it in a blast drying oven to dry to obtain the micro-arc oxidized aluminum alloy finished product.

[0045] In this embodiment, the micro-arc oxidation technology generates a micro-arc discharge phenomenon on the surface of the aluminum alloy by applying a high voltage in a specific electrolyte environment, and then in-situ grows a ceramic oxide film coating. This coating is tightly combined with the substrate, which can significantly improve the hardness, wear resistance, corrosion resistance and high temperature resistance of the aluminum alloy, greatly expanding the application range of the aluminum alloy, making it applicable to many fields with high requirements for the surface performance of materials, such as automobile manufacturing, electronic equipment, ocean engineering, aerospace, etc.

[0046] Example 2: Step 1: Select 1060 aluminum alloy, and the other steps are the same as step (1) of Example 1.

[0047] Step 2: Configure the electrolyte. The concentration of TEOS solvent is 0.25 mol / L, and the concentration of sodium hexametaphosphate is 40 g / L; the concentration of the complexing agent sodium hydroxide is 10 g / L; after mixing, make up the volume to 4 L, and stir with a stirring device for 4 - 6 hours until the solution is completely hydrolyzed. Then add a mixed nano-strengthening agent of 2.5 g / L boron nitride and 2.5 g / L graphene, and stir for 30 minutes to make the electrolyte evenly mixed.

[0048] In this example, nano rare earth oxide powder is not added.

[0049] Step 3: Micro-arc oxidation. The micro-arc oxidation process parameters are set as follows: adopt the constant voltage mode, the forward voltage is 400 V, and the reverse voltage is 0 V; the duty cycle is 10%, the pulse frequency is 800 Hz, the time is 18 min, and the temperature is 25 °C.

[0050] Step 4: After micro-arc oxidation, when the voltage drops to 0 V, remove the sample and ultrasonically clean it with deionized water and anhydrous ethanol in sequence, and then air-dry it.

[0051] The surface morphology of the ceramic coating prepared in this example can be referred to Figure 1 、 2 , it can be seen that there are multiple micro-nano scale holes distributed on the surface, presenting a porous morphology on the surface, the overall surface is flat, and the average hole size is 3.31 microns. Figure 3 is the cross-sectional view of the prepared ceramic coating. Its cross-section is mainly composed of aluminum oxide, silicon dioxide, boron nitride, graphene, and phosphide. There are micro-nano scale holes distributed on the surface, the overall surface is flat, and the coating thickness is about 20 microns. Figure 4 is the AC impedance diagram in 0.35 wt% NaCl solution. The inner layer impedance is about 1.7319×10 7 Ω•cm 2 ; Figures 5 - 7 is the polarization curve diagram in 0.35 wt% NaCl solution, and the corrosion current density is 2.358×10 -9 A / cm 2 ; After a 720-hour salt spray corrosion test, its rating reaches level 9, indicating that the coating has good corrosion resistance. The surface microhardness of the original 1060 aluminum alloy substrate is 30 HV, and the surface microhardness of the prepared micro-arc oxidation film layer is 759 HV, and the hardness is increased by 25.3 times. The addition of boron nitride and graphene synergistically enhances the hardness and wear resistance of the film layer and reduces the friction coefficient to 0.45.

[0052] Example 3: Step 1: Select 6061 aluminum alloy, and the other steps are the same as step (1) of Example 1.

[0053] Step 2: Configure the electrolyte. The concentration of TEOS solvent is 0.25 mol / L, the concentration of sodium hexametaphosphate is 40 g / L; the concentration of the complexing agent sodium hydroxide is 12 g / L; after mixing, make up the volume to 4 L, and stir with a stirring device for 4 - 6 hours until TEOS is completely hydrolyzed. Then add 2.5 g / L of boron carbide and 2.5 g / L of graphene mixed nano-strengthening agent, and finally add 2.5 g / L of mixed powder of nano-ceria and 2.5 g / L of nano-yttrium oxide, and stir for 30 minutes to make the electrolyte evenly mixed.

[0054] Step 3: Micro-arc oxidation. The process parameters of micro-arc oxidation are set as follows: adopt the constant voltage mode, the forward voltage is 400 V, the reverse voltage is -50 V, the duty cycle is 10%, the pulse frequency is 800 Hz, the time is 18 min, and the temperature is 25 °C.

[0055] Step 4: After micro-arc oxidation, wait for the voltage to drop to 0 V, remove the sample and ultrasonically clean it with deionized water and anhydrous ethanol in turn, and then air-dry it.

[0056] The surface morphology of the ceramic coating prepared in this example can be referred to Figure 8 , and it can be seen that there are multiple micro-nano scale holes distributed on the surface, presenting a porous morphology on the surface, the overall surface is flat, and the average hole size is 3.31 microns; Figure 9 is the cross-sectional view of the prepared ceramic coating, and its cross-section is mainly composed of alumina, silica, boron carbide, graphene, phosphide and trace rare earth compounds. There are micro-nano scale holes distributed on the surface, the overall surface is flat, and the coating thickness is about 20 microns. Due to the introduction of cerium oxide and yttrium oxide, the properties such as corrosion resistance and hardness of the film layer have been greatly improved. The inner layer impedance in 3.5 wt% NaCl solution is about 7.6284×10 9 Ω / cm 2 ; the corrosion current density in 3.5 wt% NaCl solution is 8.837×10 -10 A / cm 2 ; after a 720-hour salt spray corrosion test, its rating reaches level 10, indicating that the coating has good corrosion resistance. The surface micro-hardness of the original 6061 aluminum alloy substrate is 100 HV, and the surface micro-hardness of the prepared micro-arc oxidation film layer is 1394 HV, and the hardness is increased by 13.94 times. The film layer reduces the friction coefficient to 0.43.

[0057] Example 4: Step 1: Select 7075 aluminum alloy, and the other steps are the same as step (1) of Example 1.

[0058] Step 2: Configure the electrolyte. The concentration of TEOS solvent is 0.3 mol / L, the concentration of sodium hexametaphosphate is 45 g / L; the concentration of the complexing agent sodium hydroxide is 10 g / L; after mixing, make up the volume to 4 L, and stir with a stirring device for 4 - 6 hours. Then add a mixed nano-strengthening agent of 2.5 g / L boron nitride and 2.5 g / L graphene. Finally, add a mixed powder of 3 g / L lanthanum oxide and 3 g / L ytterbium oxide, and stir for 30 minutes to make the electrolyte evenly mixed.

[0059] Step 3: Micro-arc oxidation. The micro-arc oxidation process parameters are set as follows: adopt the constant voltage mode, the forward voltage is 350 V, the reverse voltage is 0 V, the duty cycle is 10%, the pulse frequency is 1000 Hz, the time is 18 min, and the temperature is 25 °C.

[0060] Step 4: After micro-arc oxidation, wait for the voltage to drop to 0 V, take down the sample and ultrasonically clean it with deionized water and anhydrous ethanol in turn, and then air-dry it.

[0061] The surface morphology of the ceramic coating prepared in this example can be referred to Figure 10 , it can be seen that there are multiple micro-nano scale pores distributed on the surface, presenting a porous morphology on the surface, the overall surface is flat, the average pore size is 5.69 microns. Figure 11 is the cross-sectional view of the prepared ceramic coating, and its cross-section is mainly composed of alumina, silica, boron nitride, graphene, phosphide and trace rare earth compounds. There are micro-nano scale pores distributed on the surface, the overall surface is flat, and the coating thickness is about 15 microns. Due to the introduction of lanthanum oxide and ytterbium oxide, the properties such as toughness and hardness of the film layer are greatly improved. The corrosion current density in 3.5 wt% NaCl solution is 2.152×10 -10 A / cm 2 ; the inner layer impedance in 3.5 wt% NaCl solution is about 1.1525×10 9 Ω / cm 2 ; after a salt spray corrosion test for 720 hours, its rating reaches level 10, indicating that the coating has good corrosion resistance. The surface microhardness of the original 7075 aluminum alloy substrate is 180 HV, and the surface microhardness of the prepared micro-arc oxidation layer is 1670 HV, and the hardness is increased by 9.28 times. The friction coefficient of the film layer is reduced to 0.47.

[0062] Example 5: Step 1: Select 2024 aluminum alloy, and the other steps are the same as step (1) of Example 1.

[0063] Step 2: Configure the electrolyte. The concentration of TEOS solvent is 0.35 mol / L, and the concentration of sodium hexametaphosphate is 20 g / L; the concentration of the complexing agent sodium hydroxide is 15 g / L; after mixing, make up the volume to 4 L, and stir with a stirring device for 4 - 6 hours. Then add 2 g / L of boron carbide and 2 g / L of graphene mixed nano-strengthening agent, and finally add 2 g / L of mixed powder of lanthanum oxide and yttrium oxide, and stir for 30 minutes to make the electrolyte evenly mixed.

[0064] Step 3: Micro-arc oxidation. The process parameters of micro-arc oxidation are set as follows: adopt the constant voltage mode, the forward voltage is 450 V, the reverse voltage is -100 V, the duty cycle is 10%, the pulse frequency is 1000 Hz, the time is 18 min, and the temperature is 25 °C.

[0065] Step 4: After micro-arc oxidation, when the voltage drops to 0 V, remove the sample and ultrasonically clean it with deionized water and anhydrous ethanol in turn, and then air-dry it.

[0066] The surface morphology of the ceramic coating prepared in this example can be referred to Figure 12 , and it can be seen that there are multiple micro-nano scale pores distributed on the surface, presenting a porous morphology on the surface, the overall surface is flat, and the average pore size is 7.79 microns. Figure 13 is the cross-sectional view of the prepared ceramic coating, and its cross-section is mainly composed of alumina, silica, boron carbide, graphene, phosphide and trace rare earth compounds. There are micro-nano scale pores distributed on the surface, the overall surface is flat, and the coating thickness is about 20 microns. Due to the introduction of lanthanum oxide and yttrium oxide, the properties such as the thermal stability and hardness of the film layer have been greatly improved. The corrosion current density in 3.5 wt% NaCl solution is 5.376×10 -10 A / cm 2 ; the inner layer impedance in 3.5 wt% NaCl solution is about 4.3448×10 9 Ω / cm 2 ; after a 720-hour salt spray corrosion test, its rating reaches 10 levels, indicating that the coating has good corrosion resistance. The surface microhardness of the original 2024 aluminum alloy substrate is 120 HV, and the surface microhardness of the prepared micro-arc oxidation layer is 1461 HV, and the hardness is increased by 12.18 times. The film layer reduces the friction coefficient to 0.44.

[0067] Example 6: Step 1: Select 6061 aluminum alloy, and the other steps are the same as step (1) of Example 1.

[0068] Step 2: Configure the electrolyte. The concentration of TEOS solvent is 0.4 mol / L, the concentration of sodium hexametaphosphate is 35 g / L, the concentration of the complexing agent sodium hydroxide is 15 g / L. After mixing, make up the volume to 4 L and stir with a stirring device for 4 - 6 hours. Then add 3 g / L of boron nitride and 3 g / L of graphene composite nano-strengthening agent, and finally add 5 g / L of erbium oxide nano-powder, and stir for 30 minutes to make the electrolyte evenly mixed.

[0069] Step 3: Micro-arc oxidation. The process parameters of micro-arc oxidation are set as follows: adopt the constant voltage mode, the forward voltage is 450 V, the reverse voltage is 0 V, the duty cycle is 10%, the pulse frequency is 1200 Hz, the time is 18 min, and the temperature is 25 °C.

[0070] Step 4: After micro-arc oxidation, wait for the voltage to drop to 0 V, take down the specimen and ultrasonically clean it with deionized water and anhydrous ethanol in turn, and then air dry it.

[0071] The surface morphology of the ceramic coating prepared in this example can be referred to Figure 14 ., it can be seen that there are multiple micro-nano scale pores distributed on the surface, presenting a porous morphology on the surface, the overall surface is flat, the average pore size is 8.84 microns. Figure 15 is the cross-sectional view of the prepared ceramic coating, and its cross-section is mainly composed of aluminum oxide, silicon dioxide, boron nitride, graphene, phosphide and trace rare earth compounds. There are micro-nano scale pores distributed on the surface, the overall surface is flat, and the coating thickness is about 20 microns. Due to the introduction of erbium oxide, the color of the film layer becomes pink, and the anti-wear performance is improved. The corrosion current density in 3.5 wt% NaCl solution is 3.778×10 -9 A / cm 2 ; The inner layer impedance in 3.5 wt% NaCl solution is about 1.6898×10 8 Ω / cm 2 ; After a 720-hour salt spray corrosion test, its rating reaches level 10, indicating that the coating has good corrosion resistance. The surface microhardness of the original 1060 aluminum alloy substrate is 30 HV, and the surface microhardness of the prepared micro-arc oxidation layer is 803 HV, and the hardness is increased by 26.8 times. The film layer reduces the friction coefficient to 0.46.

[0072] The performance of the film layers prepared in the above Examples 2 - 6 can be referred to Table 1.

[0073] Table 1 Statistical table of the film layer performance prepared in Examples 2 - 6

[0074] It can be understood that the specific parameters, values, etc. in the above Examples 2 - 6 are only examples, and can be adjusted and optimized according to specific situations in actual applications.

[0075] It should be noted that although the method operations of the above embodiments are described in a specific order, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. On the contrary, the depicted steps can be changed in the order of execution. Additionally or alternatively, certain steps can be omitted, multiple steps can be combined into one step for execution, and / or one step can be decomposed into multiple steps for execution.

[0076] In summary, the aluminum alloy plasma micro-arc oxidation nano-strengthened composite ceramic layer, preparation method and application provided by the present invention perform micro-arc oxidation treatment on the aluminum alloy by using a composite electrolyte of "phosphate-based electrolyte + silicone solution + nano-strengthening". The formed film layer exhibits excellent characteristics in many aspects. It shows excellent corrosion resistance and high hardness, has a strong bonding force between the film and the substrate, high density, can solve the problem of peeling off at the traditional joint, and has good stability of the film layer, greatly improving the service life of the aluminum alloy. The preparation process of the film layer includes pretreatment of the aluminum alloy substrate, precise preparation and preparation of the composite electrolyte, and strictly controlled micro-arc oxidation process steps. The present invention has broad application prospects in many fields such as aerospace, automobile manufacturing, and electronic equipment, and is expected to become a key driving force for the innovation of aluminum alloy surface treatment technology, promoting the overall improvement of the product quality and performance of related industries.

[0077] The above is only a preferred embodiment of the present invention patent, but the protection scope of the present invention patent is not limited thereto. Any person skilled in the art within the scope disclosed by the present invention patent, according to the technical solution and inventive concept of the present invention patent, makes equivalent substitutions or changes, all belong to the protection scope of the present invention patent.

Claims

1. A method for preparing an aluminum alloy plasma micro-arc oxidation nano-reinforced composite ceramic layer, characterized in that: The method comprises: The aluminum alloy samples are ground, polished, cleaned, dried and sealed for future use; Adding tetraethyl orthosilicate to the basic electrolyte; after the tetraethyl orthosilicate is completely hydrolyzed, first adding a nano-strengthening agent, then adding nano rare earth oxide powder, stirring until the solution is uniform, and then completing the configuration of the electrolyte; wherein the basic electrolyte comprises a main salt, a compounding agent and deionized water, the main salt is sodium hexametaphosphate, and the compounding agent is sodium hydroxide; the nano-strengthening agent is any one of boron nitride and boron carbide and is mixed with graphene; Pour the prepared electrolyte into the micro-arc oxidation electrolytic cell, place the spare aluminum alloy sample in the electrolytic cell and connect it to the positive electrode of the micro-arc oxidation power supply, use stainless steel as the cathode, and perform micro-arc oxidation treatment for 5 to 60 minutes in a constant voltage mode; while performing micro-arc oxidation treatment, stir the electrolyte synchronously to ensure the uniformity of the suspension solution and maintain the stability of the electrolyte temperature; The aluminum alloy sample after micro-arc oxidation treatment was taken out from the electrolytic cell and cleaned and dried in sequence.

2. The preparation method according to claim 1, characterized in that: The concentration of the tetraethyl orthosilicate is greater than 0.02 mol / L and less than or equal to 1 mol / L, the concentration of sodium hexametaphosphate is 20-60 g / L, the concentration of sodium hydroxide is 2-25 g / L, the addition amount of the nano-strengthener is 2-10 g / L, and the addition amount of the nano-rare earth oxide powder is 2-10 g / L.

3. The preparation method according to claim 1, characterized in that: The average particle sizes of the nano-strengthener and the nano-rare earth oxide powder are both 1-200 nm.

4. The preparation method according to any one of claims 1 to 3, characterized in that The nano rare earth oxide powder is at least one of lanthanum oxide, cerium oxide, neodymium oxide, gadolinium oxide, erbium oxide, scandium oxide, yttrium oxide, holmium oxide, terbium oxide, samarium oxide, europium oxide, lutetium oxide, ytterbium oxide, praseodymium oxide and dysprosium oxide.

5. The preparation method according to any one of claims 1 to 3, characterized in that The process parameters of the micro-arc oxidation treatment are: forward voltage is 300~700V, negative voltage is -200~0V; current density is 2~10A / dm², duty cycle is 5%~40%, pulse frequency is 300~1500Hz, and reaction temperature is 5~40°C.

6. The preparation method according to any one of claims 1 to 3, characterized in that The cleaning method includes ultrasonic cleaning and vacuum glow plasma cleaning; wherein the ultrasonic cleaning is performed at room temperature for 15 to 30 minutes to remove impurities on the surface of the aluminum alloy sample; and the vacuum glow plasma cleaning is performed in a vacuum furnace at 30 to 50° C. for 15 to 30 minutes to improve the surface quality and adhesion of the aluminum alloy sample.

7. The preparation method according to any one of claims 1 to 3, characterized in that A ceramic oxide film coating is in-situ grown on the surface of the aluminum alloy sample after the micro-arc oxidation treatment; the oxide film coating is tightly combined with the aluminum alloy sample, and the overall surface is flat and distributed with micro-nano-scale pores.

8. The preparation method according to any one of claims 1 to 3, characterized in that The growth process of the micro-arc oxidation film is driven by the synergistic combination of tetraethyl orthosilicate, sodium hexametaphosphate and sodium hydroxide to construct a multi-electrolyte system; during the micro-arc oxidation treatment, tetraethyl orthosilicate is hydrolyzed to produce highly active functional groups, silanol groups; The functional silanol group, on the one hand, can generate SiO2 in situ and precisely adhere to the surface of the film layer; on the other hand, it has the potential to undergo specific chemical reactions with other components in the electrolyte, and gradually interweave to build a composite film layer architecture to exhibit a dense microstructure, excellent corrosion resistance and multi-dimensional characteristics.

9. The preparation method according to any one of claims 1 to 3, characterized in that During the micro-arc oxidation treatment process, ethyl orthosilicate is hydrolyzed to produce highly active functional group silanol groups; during the film formation process, the functional group silanol groups, sodium hexametaphosphate and the nano-strengthener spontaneously construct an in-situ growth type composite network structure by virtue of their inherent chemical driving force; the in-situ growth type composite network structure contains not only Si-OP bonds, but also Si-OB bonds and Si-C bonds; in addition, the nano-strengthener is uniformly distributed in the oxide film layer to form a diffuse strengthening to effectively block the expansion of micro cracks, thereby improving the density and uniformity of the oxide film layer.

10. The preparation method according to any one of claims 1 to 3, characterized in that: During the micro-arc oxidation treatment process, ethyl orthosilicate is hydrolyzed to produce highly active functional group silanol groups; during the dynamic formation process of the oxide film layer, nano rare earth oxide powder is embedded; during the embedding process, an in-situ growth type composite network structure is spontaneously constructed between the functional group silanol groups, sodium hexametaphosphate and rare earth nano oxide powder; the in-situ growth type composite network structure covers Si-OP bonds and Si-O-rare earth metal bonds, as well as complex bonds between sodium hexametaphosphate and rare earth nano oxide powder, so as to deeply match the chemical bonding force inside the material and strongly promote the continuous growth and stable formation of the dense oxide film layer; in addition, nano rare earth oxide can promote the uniform nucleation of the micro-arc oxidation film and refine the grains in the oxide film layer to improve the density and uniformity of the oxide film layer, as well as the overall strength and durability.

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