A method for preparing a high-hardness and high-wear-resistant anodized film on an aluminum alloy surface

Abstract

This invention discloses a method for preparing a high-hardness, high-wear-resistant anodized film on an aluminum alloy surface, including anodizing and sealing steps. The anodizing electrolyte contains 53-57 g / L concentrated sulfuric acid, oxalic acid, boric acid, and citric acid (total concentration 280-320 g / L), 2-8 g / L polyacrylic acid, and 20-30 g / L PTFE emulsion; the current density is 2.5-3.5 A / dm², the oxidation voltage is 25-35 V, and the electrolyte temperature is -2℃ to 5℃. The sealing process involves mixing PVDF-TFE particles and PTFE particles in a 1:1-10 ratio, then spraying or impregnating the resulting anodized film and curing it. This invention utilizes the adsorption-anchoring effect of polyacrylic acid and the synergistic effect of PVDF-TFE / PTFE nanopillar sealing to obtain an anodized film with a thickness ≥20 μm, a hardness ≥550 HV, a coefficient of friction ≤0.08, and no cracking. It possesses both high hardness and excellent wear resistance, making it suitable for consumer electronics products such as camera or mobile phone casings.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy surface treatment technology, specifically relating to a method for preparing anodized aluminum alloy films, which is particularly suitable for preparing anodized composite films with both high hardness and high wear resistance, and can be applied to electronic device housings such as camera shells and mobile phone frames that have high requirements for appearance and durability. Background Technology

[0002] Aluminum alloys are widely used in consumer electronics, aerospace, and automotive industries due to their lightweight, high specific strength, excellent thermal and electrical conductivity, and ease of processing and forming. However, the inherent defects of aluminum alloys, such as low surface hardness and poor wear resistance, severely limit their service life and appearance durability under friction conditions. Anodizing is one of the most commonly used techniques to improve the surface properties of aluminum alloys. By forming a porous alumina film on the surface of the aluminum alloy, surface hardness and corrosion resistance can be significantly improved.

[0003] While conventional sulfuric acid anodizing films are inexpensive and have a mature process, their hardness is typically only 200–350 HV, far from meeting the requirements of high wear-resistant applications. To achieve higher hardness, low-temperature hard anodizing is commonly used in industry, which can increase the film hardness to over 350 HV. However, traditional hard anodizing processes still have the following technical drawbacks:

[0004] Firstly, simply increasing the hardness of the oxide film often leads to increased brittleness. Alumina ceramic layers are inherently brittle and are prone to cracking or even peeling when subjected to impact or bending deformation, resulting in protective failure. This problem is particularly prominent in thin-walled aluminum alloy casings (such as mobile phone frames and camera housings)—when dropped or squeezed, the deformation of the casing is directly transmitted to the oxide film, causing cracking.

[0005] Secondly, high-hardness oxide films typically have a high coefficient of friction (approximately 0.4–0.6), leading to severe wear under relative motion or contact friction conditions, which limits their application in sliding components. Although adding solid lubricants such as PTFE to the electrolyte can reduce the coefficient of friction, the co-deposition of PTFE particles in the oxide film mainly relies on physical adsorption and mechanical inclusion, resulting in insufficient bonding strength. Consequently, the lubricating phase is prone to detachment and failure during long-term use.

[0006] Third, while traditional sealing treatments (such as boiling water sealing and nickel salt sealing) can seal the pores of the oxide film to improve corrosion resistance, the sealing layer lacks chemical bonding with the oxide film, resulting in limited interfacial adhesion and failing to impart self-lubricating properties to the film. Although there have been research reports in recent years on post-treatment using fluoropolymer coatings, most of these studies remain at the surface coating level, failing to achieve deep integration between the polymer and the porous structure of the oxide film, thus hindering durability improvement.

[0007] Furthermore, existing hard anodizing processes largely rely on high concentrations of sulfuric acid (typically 150–200 g / L) to maintain sufficient electrolyte conductivity. However, high concentrations of sulfuric acid have a strong chemical dissolution effect on the oxide film, limiting further improvements in film density. Although adding organic acids (such as oxalic acid, citric acid, and tartaric acid) can partially inhibit dissolution and improve film structure, current technologies lack a systematic and synergistic design approach that integrates electrolyte composition control with the construction of post-processing micro / nano structures.

[0008] Chinese patent CN110219031A discloses a sulfuric acid-organic weak acid system with a sulfuric acid concentration of 40–60 g / L and an organic weak acid concentration of 8–20 g / L, but the organic acid concentration in this patent is relatively low. Another Chinese patent CN108707941B discloses a method for anodizing using a sulfuric acid-tartaric acid system, but its film hardness is only about 300 HV (100 HB), and its wear resistance has not been specifically optimized.

[0009] In summary, there is an urgent need in the field for a method to prepare anodized composite films that can significantly improve the flexibility and wear resistance of oxide films while increasing their hardness, and that have a strong interfacial bond between the lubricating phase and the film layer. Summary of the Invention

[0010] The present invention aims to overcome the technical defects of existing aluminum alloy anodized films, such as difficulty in achieving both hardness and toughness, weak bonding of the lubricating phase interface, and insufficient wear resistance, and provides a method for preparing a high-hardness and high-wear-resistant anodized film on the surface of aluminum alloys.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] A method for preparing a high-hardness, high-wear-resistant anodized film on an aluminum alloy surface includes an anodizing step and a sealing step.

[0013] The anodizing conditions are as follows: the electrolyte contains concentrated sulfuric acid, oxalic acid, boric acid, citric acid, polyacrylic acid, and PTFE emulsion; the concentration of the concentrated sulfuric acid is 53–57 g / L; the sum of the concentrations of the oxalic acid, boric acid, and citric acid is 280–320 g / L; the concentration of the polyacrylic acid is 2–8 g / L; the concentration of the PTFE emulsion is 20–30 g / L; and the current density is 2.5–3.5 A / dm³. 2 The oxidation voltage is 25–35V, and the electrolyte temperature during the anodic oxidation is -2℃ to 5℃.

[0014] The sealing treatment conditions are as follows: PVDF-TFE particles and PTFE particles are mixed in a ratio of 1:1 to 10, then sprayed or impregnated with an oxide film, followed by curing.

[0015] The thickness of the anodic oxide film is greater than 20 μm, and the smooth transition of the aluminum alloy in the thickness direction is ≥ 1:25.

[0016] In the anodizing step, the pretreated aluminum alloy workpiece is used as the anode and placed in an electrolyte for constant current anodizing.

[0017] This invention reduces the sulfuric acid concentration to 53–57 g / L, while increasing the combined concentrations of oxalic acid, boric acid, and citric acid to 280–320 g / L. The organic acid anions form an adsorption layer on the oxide film surface, effectively blocking the chemical erosion of the film by SO4²⁻ and H⁺, significantly reducing the dissolution rate of the oxide film during growth. This results in a dense film with few defects, which is the structural basis for the high hardness of the film.

[0018] Insufficient oxalic acid results in a thin membrane, while excessive oxalic acid leads to a porous membrane, reducing hardness and wear resistance. Boric acid, as a buffer, stabilizes the electrolyte pH, promotes membrane growth, and fosters a denser membrane structure; however, excessive boric acid inhibits membrane growth and weakens its protective effect. Citric acid can reduce the corrosive dissolution of the oxide film by sulfuric acid, improve powder formation efficiency, and refine pore size.

[0019] The mass ratio of oxalic acid, boric acid and citric acid in the electrolyte is (2.5-4.7):1:(1-1.3), preferably (3.6-4.5):1:(1.1-1.3). Within this range, the inorganic and organic acids in the electrolyte work synergistically to obtain a dense, thick oxide film with a pore size of 100-250 nm, providing conditions for the formation of nanopillars by the sealing agent in the sealing process.

[0020] The concentration of the boric acid is 30–50 g / L.

[0021] The concentration of the polyacrylic acid in this invention is 2–8 g / L. The concentration of the PTFE emulsion is 20–30 g / L.

[0022] The number-average molecular weight of polyacrylic acid only needs to meet the requirements of this invention. Preferably, it is 2000-5000, and more preferably 3000-3500, which can achieve the purpose of this invention.

[0023] Polyacrylic acid molecules contain a large number of carboxyl groups, which partially ionize into negatively charged carboxylate ions in acidic electrolytes. These ions are then adsorbed onto the positively charged anode surface through electrostatic attraction. This adsorption layer increases the interfacial resistance, stabilizing the oxidation voltage and providing a stronger electric field driving force for film thickening. Simultaneously, it suppresses large, destructive arc discharges, resulting in finer, more uniform discharges and reducing microporous defects in the film. As the anodic oxidation reaction continues, new alumina is continuously generated and accumulated at the polyacrylic acid adsorption sites, encapsulating the already adsorbed polyacrylic acid macromolecular chains within the oxide film, forming a composite structure and enhancing the toughness of the oxide film.

[0024] In addition, through the bridging effect of macromolecular chains, polyacrylic acid can anchor PTFE particles in the electrolyte to the surface of the growing film, promoting the uniform co-deposition of PTFE and further improving the toughness and abrasion resistance of the oxide film.

[0025] As a preferred embodiment, the PTFE emulsion contains at least one group selected from hydroxyl and amino groups. More preferably, the PTFE emulsion contains amino groups, and the content of amino groups is 500-1000 ppm.

[0026] As one specific implementation, PTFE containing amino groups can be pretreated with a silane coupling agent containing amino groups.

[0027] Under acidic conditions, a large number of carboxyl groups in polyacrylic acid react chemically with amino and / or hydroxyl groups to form chemical bonds. Polyacrylic acid and PTFE are co-deposited in the oxide film, which enhances the toughness of the oxide film. In addition, some PTFE is embedded in the pores of the oxide film, further improving the abrasion resistance.

[0028] For the purposes of this invention, the current density described herein is 2.5–3.5 A / dm². 2 The oxidation voltage is 25–35V, and the electrolyte temperature during anodic oxidation is -2℃ to 5℃. Preferably, the current density of the present invention is 2.5–3.0 A / dm³. 2 The oxidation voltage is 25-30V.

[0029] The PVDF-TFE particles and the PTFE particles have a particle size of less than 250 nm, preferably less than 180 nm, and more preferably less than 100 nm. This allows the PVDF-TFE particles and PTFE particles to enter the pores of the oxide film formed during the spraying or impregnation process, further enhancing the friction and flexibility of the oxide film.

[0030] The anodizing time is 2 to 30 minutes.

[0031] The PVDF-TFE particles and PTFE particles are dispersed in an organic solvent to form a uniform suspension, thereby obtaining a sealing solution. The organic solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, and N-methylformamide.

[0032] Preparation method of sealing solution: Mix PVDF-TFE copolymer and PTFE particles at a mass ratio of 1:1 to 10, disperse in an organic solvent, and ultrasonically disperse for 10 to 30 minutes to obtain a uniform suspension with a total solid content of 3 to 8 wt%.

[0033] The sealing process is preferably carried out under vacuum or normal pressure for 5–20 minutes.

[0034] The PVDF-TFE copolymer, wherein the VDF / TFE molar ratio is preferably 70 / 30 to 80 / 20, can achieve better adhesion to the oxide film. Moreover, it contains the same structural units as PTFE, and the two are intercalated, resulting in less PTFE shedding during the friction process.

[0035] The PVDF-TFE particles and the PTFE particles enter the pores of the oxide film to form nanopillars with an aspect ratio >80:1, achieving a strong bond between the sealing agent and the alumina. The thickness of the anodic oxide film is greater than 20 μm.

[0036] High aspect ratio (>80:1) polymer nanopillars penetrate deep into the pores of the oxide film, inducing the PVDF-TFE molecular chains to align along the pore axis through the nano-confinement effect, significantly enhancing the mechanical strength and toughness of the polymer. Simultaneously, PTFE acts as a dispersed lubricating phase, drastically reducing the surface friction coefficient of the film. The anchoring structure of the nanopillars ensures that the polymer layer will not peel off during long-term use, solving the problem of insufficient durability of the lubricating phase in existing technologies.

[0037] The present invention also provides a high-hardness and high-wear-resistant anodized film prepared by the above preparation method, wherein the high-hardness and high-wear-resistant anodized film has a hardness ≥550HV and a friction coefficient ≤0.08.

[0038] The high-hardness and high-wear-resistant anodized film satisfies: n - 1 ≥ 3T, where n is the number of bends and T is the film thickness.

[0039] Furthermore, the high-hardness, high-wear-resistant anodized film is used as a protective film for the casing of cameras or mobile phones.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) Significantly improved hardness. Through the synergistic effect of low sulfuric acid-high organic acid electrolyte system and polyacrylic acid interface regulation, an anodic oxide film with a hardness ≥550HV can be obtained, which is significantly better than conventional sulfuric acid film (200-350HV) and traditional hard oxide film (350-450HV), and also better than the previously reported sulfuric acid-citric acid system (480.8HV) and PTFE composite oxide film (approximately 440HV).

[0042] (2) Significantly improved wear resistance. Co-deposition of PTFE in the electrolyte, combined with PVDF-TFE / PTFE nanopillars for pore sealing, constructs a dual self-lubricating structure. The surface friction coefficient of the film can be as low as ≤0.08, and the wear rate is reduced by more than two orders of magnitude compared with the unmodified hard oxide film, achieving an ultra-low friction level. Moreover, the adhesive properties of PVDF-TFE can prevent PTFE from falling off.

[0043] (3) Significantly improved toughness and bonding strength. The anchoring structure of PVDF-TFE / PTFE nanopillars in the pores of the oxide film solves the bottleneck of weak interfacial bonding between traditional polymer coatings and oxide films. The nanopillars with a high aspect ratio (>80:1) penetrate deep into the pores and form a large-area tight bond with the pore walls, making the polymer layer less prone to peeling off. At the same time, the flexibility of PVDF-TFE gives the film good impact resistance and bending resistance.

[0044] (4) Wide process window and strong applicability. The electrolyte of this invention can operate stably in a wide temperature range of -2 to 5℃, which is more lenient than the strict requirements of traditional hard anodizing for low temperature, and is beneficial to temperature control in industrial production.

[0045] (5) Improved environmental performance. The concentration of sulfuric acid in the electrolyte is significantly reduced (only 1 / 3 to 1 / 4 of that in the traditional process), reducing acid mist emissions and wastewater treatment burden; the sealing treatment uses a nickel-free and chromium-free fluoropolymer system, avoiding heavy metal pollution. Attached Figure Description

[0046] Figure 1 This is a scanning electron microscope image of the cross-section of the anodic oxide film in Embodiment 1 of the present invention. Detailed Implementation

[0047] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0048] I. Pretreatment of Aluminum Alloy Substrate

[0049] This invention is applicable to various anodizable wrought and cast aluminum alloys. As a preferred embodiment, the aluminum alloy is a 5-series, 6-series, or 7-series aluminum alloy, more preferably 6063, 7075, or 5052 aluminum alloy.

[0050] The pretreatment process includes, in sequence: (1) mechanical grinding or polishing to remove surface processing marks and oxide scale; (2) alkaline degreasing, soaking in an alkaline degreasing solution at 60-70°C for 5-10 minutes; (3) hot water washing and cold water washing; (4) acid pickling to polish, soaking in a 30-50 vol% nitric acid solution for 1-3 minutes; and (5) thorough rinsing with deionized water until the surface has a uniform metallic luster.

[0051] As one specific implementation, it is used to manufacture aluminum alloy housings for camera casings or mobile phone frames.

[0052] II. Preparation of Electrolyte

[0053] The preparation method of the electrolyte of the present invention includes the following steps: (1) Measure concentrated sulfuric acid (98% by mass) according to the ratio, slowly add it to a portion of deionized water, and cool it to room temperature; (2) Weigh oxalic acid, boric acid and citric acid according to the ratio, add them to the above dilute sulfuric acid solution, and stir until completely dissolved; (3) Weigh polyacrylic acid, add it to the solution, and stir until uniform; (4) Measure PTFE emulsion (solid content about 60%), slowly add it and stir continuously to ensure that the PTFE particles are uniformly dispersed in the electrolyte. After preparation, dilute to the final volume with deionized water, stir thoroughly and set aside.

[0054] III. Anodizing Treatment

[0055] The pretreated aluminum alloy workpiece is used as the anode, and a graphite plate or stainless steel plate is used as the cathode. The workpiece is immersed in the prepared composite electrolyte and anodized under constant current mode. The process conditions are as follows:

[0056] Current density: 2.5~3.5A / dm².

[0057] Oxidation voltage: In constant current mode, the initial voltage is about 15-20V. As the film thickness increases and the resistance increases, the voltage automatically rises to 25-35V and tends to stabilize.

[0058] Electrolyte temperature: -2 to 5℃.

[0059] Oxidation time: 20-30 min.

[0060] IV. Sealing Treatment

[0061] After anodizing, the workpiece is removed and thoroughly rinsed with deionized water, followed by sealing.

[0062] The sealing solution is prepared as follows: PVDF-TFE copolymer and PTFE particles are mixed at a mass ratio of 1:1 to 10, dispersed in an organic solvent, and ultrasonically dispersed for 10 to 30 minutes to obtain a uniform suspension. The total solids content is preferably 3 to 8 wt%. The particle size of both PVDF-TFE and PTFE particles is controlled below 250 nm.

[0063] Immerse the anodized aluminum alloy workpiece in the above-mentioned sealing solution and maintain it under vacuum or normal pressure for 5–20 minutes. Then remove the workpiece, dry it at 80–120°C for 10–30 minutes to remove the solvent, and then cure it at 150–200°C for 20–60 minutes.

[0064] In the above process, PVDF-TFE and PTFE particles enter the pores of the oxide film and solidify to form a nanopillar structure with an aspect ratio >80:1.

[0065] As an alternative, a spraying method can be used to coat the sealing solution onto the oxide film surface, allowing the solution to naturally penetrate into the pores and then cure.

[0066] Example 1

[0067] Base material: 6063 aluminum alloy sheet, size 50mm×50mm×3mm.

[0068] Pretreatment: (1) Polish the surface with 400#, 800# and 1200# sandpaper in sequence until smooth; (2) Soak in alkaline degreasing solution at 65℃ for 8 minutes; (3) Rinse with deionized water; (4) Soak in 40 vol% nitric acid solution for 2 minutes; (5) Rinse thoroughly with deionized water.

[0069] Electrolyte preparation: Take 5.5g of 98% concentrated sulfuric acid, dilute and cool in about 800mL of deionized water; add 155g of oxalic acid, 60g of boric acid, and 65g of citric acid (total 280g), and stir to dissolve; add polyacrylic acid (PAA, M... n Add 5g of PTFE emulsion (60% solid content) and stir to dissolve; add 25g of PTFE emulsion (equivalent to 15g / L of PTFE solid content) and stir to disperse; bring the volume to 1L with deionized water and continue stirring for 30 minutes until homogeneous.

[0070] Anodizing: Using 6063 aluminum alloy as the anode and a graphite plate as the cathode, oxidation was performed in constant current mode. The current density was 3.0 A / dm², the electrolyte temperature was 0℃, and the oxidation time was 25 min. The initial voltage was approximately 18V, and the termination voltage was approximately 30V. After oxidation, the sample was rinsed with deionized water.

[0071] Sealing treatment: Take 1g each of PVDF-TFE (VDF / TFE=75 / 25mol%) particles and PTFE particles, mix them at a mass ratio of 1:1, disperse them in an NMP solution containing 4wt% total solids, and ultrasonically disperse for 15min. Immerse the anodized aluminum alloy in the sealing treatment solution, and impregnate it at room temperature and normal pressure for 10min. After removal, dry it at 100℃ for 15min, and then cure it at 180℃ for 30min.

[0072] Test method for film thickness: Determine the oxide film thickness according to GB / T8014 standard.

[0073] Test method for oxide film hardness: determined according to GB / T9790 standard.

[0074] Test method for oxide friction coefficient: determined according to GB / T 12967.1 standard.

[0075] The method for testing the flexibility of oxide films involves bending the sample at a specified angle to determine whether cracks appear in the film. The pass / fail criterion is: n - 1 ≥ 3T (no cracking), where n is the number of bends and T is the film thickness - 10.

[0076] Performance testing: film thickness 23μm, microhardness 586HV, coefficient of friction 0.07, no cracking.

[0077] Example 2

[0078] The difference from Example 1 is as follows: the electrolyte contains 198g of oxalic acid, 55g of boric acid, and 67g of citric acid (totaling 320g); PAA concentration is 8g / L; PTFE emulsion concentration is 30g / L; current density is 3.5A / dm²; oxidation voltage is 32V; electrolyte temperature is -2℃; oxidation time is 30min; the mass ratio of PVDF-TFE to PTFE in the sealing solution is 1:5; impregnation time is 20min; curing temperature is 200℃ and time is 40min.

[0079] Performance testing: film thickness 28μm, microhardness 612HV, coefficient of friction 0.05, no cracking.

[0080] Example 3

[0081] The difference from Example 1 is as follows: the electrolyte contains 198g of oxalic acid, 44g of boric acid, and 58g of citric acid (totaling 300g); PAA concentration is 2g / L; PTFE emulsion concentration is 20g / L; current density is 2.5A / dm²; oxidation voltage is 25V; electrolyte temperature is 5℃; oxidation time is 20min; the mass ratio of PVDF-TFE to PTFE in the sealing solution is 1:10; curing temperature is 160℃, and time is 20min.

[0082] Performance testing: film thickness 21μm, microhardness 558HV, coefficient of friction 0.08, no cracking.

[0083] Comparative Example 1

[0084] Electrolyte: 55 g / L sulfuric acid + 180 g / L oxalic acid + 15 g / L boric acid + 85 g / L citric acid + 5 g / L PAA (excluding PTFE emulsion). Anodizing conditions were the same as in Example 1. Sealing treatment: Only boiling water sealing (95°C, 30 min) was used; PVDF-TFE / PTFE sealing was not performed.

[0085] Performance testing: film thickness 22μm, microhardness 592HV, coefficient of friction 0.48, no cracking.

[0086] Comparative Example 2

[0087] Electrolyte: 55 g / L sulfuric acid + 180 g / L oxalic acid + 15 g / L boric acid + 85 g / L citric acid + 25 g / L PTFE emulsion (PAA excluding). Anodizing conditions were the same as in Example 1. Sealing treatment was the same as in Example 1.

[0088] Performance testing: film thickness 16μm, microhardness 425HV, coefficient of friction 0.15, cracking.

[0089] Comparative Example 3

[0090] The electrolyte was the same as in Example 1. The anodizing conditions were the same as in Example 1. Sealing treatment: Only the PTFE particles used in Example 1 were dispersed in NMP solution, impregnated, and then cured.

[0091] Performance testing: film thickness 23μm, microhardness 568HV, coefficient of friction 0.22, after 500m friction test the coefficient of friction increased to 0.38, no cracking.

[0092] Performance Comparison

[0093] The performance test results of Examples 1-3 and Comparative Examples 1-3 are summarized in Table 1.

[0094] Table 1 Performance comparison between the examples and comparative examples

[0095] Example 1 23 586 0.07 0.08 No cracking Example 2 28 612 0.05 0.06 No cracking Example 3 21 558 0.08 0.09 No cracking Comparative Example 1 22 592 0.48 — No cracking Comparative Example 2 16 425 0.15 0.18 cracking Comparative Example 3 23 568 0.22 0.38 No cracking

[0096] Table 1 shows that the hardness of Examples 1-3 all reached above 550 HV, and the coefficient of friction was ≤0.08. Furthermore, the coefficient of friction remained stable after a 500m friction test. Comparative Example 1, although having a hardness comparable to the Examples, had an extremely high coefficient of friction (0.48) and poor wear resistance. Comparative Example 2, due to the absence of PAA in the electrolyte, had insufficient film density, resulting in a significant decrease in hardness (425 HV) and obvious cracking. Comparative Example 3, due to the absence of PVDF-TFE in the sealing treatment, had a relatively acceptable initial coefficient of friction (0.22), but after 500m of friction, a large amount of lubricating phase detached, increasing the coefficient of friction to 0.38, indicating insufficient durability.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a high-hardness, high-wear-resistant anodized film on an aluminum alloy surface, characterized in that: This includes anodizing and sealing processes. The anodizing conditions are as follows: the electrolyte contains concentrated sulfuric acid, oxalic acid, boric acid, citric acid, polyacrylic acid, and PTFE emulsion; the concentration of the concentrated sulfuric acid is 53–57 g / L; the sum of the concentrations of the oxalic acid, boric acid, and citric acid is 280–320 g / L; the concentration of the polyacrylic acid is 2–8 g / L; the concentration of the PTFE emulsion is 20–30 g / L; and the current density is 2.5–3.5 A / dm³. 2 The oxidation voltage is 25~35V, and the electrolyte temperature in the anodic oxidation is -2℃ to 5℃. The sealing treatment conditions are as follows: PVDF-TFE particles and PTFE particles are mixed in a ratio of 1:1 to 10, then sprayed or impregnated with an oxide film, followed by curing. The thickness of the anodic oxide film is greater than 20 μm.

2. The method for preparing a high-hardness, high-wear-resistant anodized film on an aluminum alloy surface according to claim 1, characterized in that: The concentration of the boric acid is 30–50 g / L.

3. The method for preparing a high-hardness, high-wear-resistant anodized film on an aluminum alloy surface according to claim 1, characterized in that: The mass ratio of oxalic acid, boric acid and citric acid in the electrolyte is (2.5-4.7):1:(1-1.3).

4. The method for preparing a high-hardness, high-wear-resistant anodized film on an aluminum alloy surface according to claim 1, characterized in that: The PTFE emulsion contains at least one group selected from hydroxyl and amino groups.

5. The method for preparing a high-hardness, high-wear-resistant anodized film on an aluminum alloy surface according to claim 3, characterized in that: The PTFE emulsion contains amino groups, and the content of amino groups is 500-1000 ppm.

6. The method for preparing a high-hardness, high-wear-resistant anodized film on an aluminum alloy surface according to claim 1, characterized in that: The particle size of the PVDF-TFE particles and the PTFE particles is less than 100 nm.

7. The method for preparing a high-hardness, high-wear-resistant anodized film on an aluminum alloy surface according to claim 1, characterized in that: The anodizing time is 2 to 30 minutes.

8. The method for preparing a high-hardness, high-wear-resistant anodized film on an aluminum alloy surface according to claim 1, characterized in that: After the anodizing step, the PVDF-TFE particles and the PTFE particles enter the pores to form nanopillars with an aspect ratio >80:

1.

9. A high-hardness, high-wear-resistant anodic oxide film prepared by any one of claims 1 to 8, characterized in that: The high-hardness, high-wear-resistant anodized film has a hardness ≥550HV and a friction coefficient ≤0.

08.

10. The high-hardness, high-wear-resistant anodized film according to claim 8, characterized in that: The high-hardness and high-wear-resistant anodized film satisfies: n - 1 ≥ 3T, where n is the number of bends and T is the film thickness.

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