A fly ash reinforced aluminum alloy hard anodization composite coating and a preparation method thereof

Abstract

This invention belongs to the field of surface modification technology, specifically relating to a fly ash-reinforced hard anodized composite coating for aluminum alloys and its preparation method. Fly ash mainly contains quartz and mullite phases, exhibiting a mixed morphology of irregular particles and locally spherical particles; its surface carries a negative charge, which facilitates migration to the anode region during anodizing and enhances its bonding with the oxide film, forming a fly ash-reinforced composite oxide coating, thereby improving the density, hardness, and wear resistance of the oxide film.

Description

Technical Field

[0001] This invention belongs to the field of surface modification technology, specifically relating to a fly ash reinforced aluminum alloy hard anodized composite coating and its preparation method. Background Technology

[0002] Aluminum alloys are widely used in aerospace, transportation equipment, and machinery manufacturing due to their high specific strength and good machinability. However, their surface hardness and wear resistance are relatively insufficient, making them prone to accelerated wear, surface damage, and reduced service life under medium-to-high load friction conditions. To improve the surface properties of aluminum alloys, anodizing, especially hard anodizing, has become a commonly used surface strengthening method.

[0003] Hard anodizing can form a protective layer mainly composed of aluminum oxide on the surface of aluminum alloys, which can significantly improve surface hardness and corrosion resistance. However, the resulting oxide film usually contains both a barrier layer and a porous layer. The porous structure weakens the mechanical integrity and load-bearing capacity of the coating to some extent.

[0004] Therefore, there is a need to propose a hard anodized composite coating that can further improve surface hardness, reduce surface roughness, and improve tribological performance under wide loads. Summary of the Invention

[0005] The purpose of this invention is to provide a fly ash reinforced aluminum alloy hard anodized composite coating and its preparation method. The composite coating obtained by the method provided by this invention has high surface hardness, low surface roughness and superior wide-load friction and wear performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a fly ash reinforced aluminum alloy hard anodized composite coating, comprising the following steps: using an aluminum alloy substrate as an anode, performing hard anodizing in an electrolyte to obtain a composite coating; wherein the electrolyte includes fly ash; The amount of fly ash added to the electrolyte is 80~120g / L.

[0007] Preferably, the electrolyte comprises sulfuric acid and fly ash.

[0008] Preferably, the average particle size of the fly ash is less than 10 μm.

[0009] Preferably, the mass concentration of sulfuric acid in the electrolyte is 15-25%.

[0010] Preferably, the hard anodizing is performed under constant current conditions, with a current density of 10~20 A / dm³. 2 .

[0011] Preferably, the conditions for hard anodizing further include: being carried out under stirring for 30-60 minutes; and the cathode being an inert conductive material. During the hard anodizing process, the voltage is controlled within the range of ±15V, and the temperature of the system is controlled not to exceed 60℃.

[0012] Preferably, the aluminum alloy matrix is ​​AA2017-T4 aluminum alloy.

[0013] Preferably, the aluminum alloy substrate further includes a pretreatment before hard anodizing; the pretreatment includes grinding, degreasing, alkaline washing, brightening, water washing and drying performed in sequence.

[0014] The present invention also provides a fly ash reinforced aluminum alloy hard anodized composite coating prepared by the preparation method described above, wherein the composite coating contains fly ash particles.

[0015] Preferably, the surface roughness of the composite coating is not higher than 4.0 μm, and the surface hardness is not lower than 440 HV; The wear rate of the composite coating under a 10N load condition is no higher than 5.0 × 10⁻⁶. -6 mm 3 / (N·m).

[0016] This invention provides a method for preparing a fly ash reinforced aluminum alloy hard anodizing composite coating. Compared with the prior art, the advantages of this invention include: (1) This invention introduces industrial waste fly ash into the aluminum alloy anodizing system, which reduces the dependence on commercial ceramic reinforcing particles while taking into account both surface strengthening and resource recycling.

[0017] (2) After fly ash particles enter the oxide film, they can fill and reinforce the pores and surface structure of the film, thereby improving the density, surface hardness and load-bearing capacity of the coating.

[0018] (3) Since fly ash particles contain hard phases such as quartz and mullite, the resulting coating exhibits good wear resistance under a wide load condition; under higher loads, a transfer layer can be formed that helps to reduce direct contact wear.

[0019] (4) Compared with the anodized coating without reinforcing particles, the composite coating obtained by the present invention can achieve lower surface roughness and higher surface hardness, and significantly reduce wear rate.

[0020] (5) The process route of the present invention is clear and the process window is well defined. It can be used for the functional treatment of wear-resistant surfaces of aluminum alloys and has good engineering application prospects. Detailed Implementation

[0021] This invention provides a method for preparing a fly ash reinforced aluminum alloy hard anodized composite coating, comprising the following steps: using an aluminum alloy substrate as an anode, performing hard anodizing in an electrolyte to obtain a composite coating; wherein the electrolyte includes fly ash; The amount of fly ash added to the electrolyte is 80~120g / L.

[0022] In this invention, the electrolyte preferably comprises sulfuric acid and fly ash; the mass concentration of sulfuric acid in the electrolyte is preferably 15-25%, specifically 15%, 18%, 20%, 22%, or 25%; the amount of fly ash added to the electrolyte is 80-120 g / L, specifically 80 g / L, 90 g / L, 100 g / L, 110 g / L, or 120 g / L. This invention does not impose any particular limitation on the preparation method of the electrolyte; fly ash is simply added to a sulfuric acid solution, and stirred and / or ultrasonically dispersed to ensure uniform dispersion of the fly ash particles. In this invention, the average particle size of the fly ash is preferably below 10 μm, more preferably 1-10 μm.

[0023] In this invention, the aluminum alloy substrate is preferably AA2017-T4 aluminum alloy; the aluminum alloy substrate preferably undergoes pretreatment before hard anodizing; the pretreatment preferably includes grinding, degreasing, alkaline washing, brightening, water washing, and drying performed sequentially. This invention does not impose any particular limitations on the processes of grinding, degreasing, alkaline washing, brightening, water washing, and drying; processes well-known to those skilled in the art can be used; the above pretreatment yields a clean surface suitable for anodizing.

[0024] In this invention, the hard anodizing is preferably performed under constant current conditions, with a current density preferably of 10~20 A / dm². 2 Specifically, it can be 10A / dm 2 12A / dm 2 14A / dm 2 15A / dm 2 16A / dm 2 18A / dm 2 20A / dm 2In this invention, the conditions for hard anodizing preferably include: being carried out under stirring for 30-60 minutes, specifically 30 minutes, 40 minutes, 50 minutes, or 60 minutes; the cathode is an inert conductive material; the inert conductive material is preferably stainless steel; during the hard anodizing process, the voltage is preferably controlled within ±15V, and the system temperature is controlled not to exceed 60℃. In this invention, the fly ash mainly contains quartz phase and mullite phase, exhibiting a mixed morphology of irregular particles and locally spherical particles; its surface is negatively charged, which is beneficial for migration to the anode region during the anodizing process and for enhancing the bonding with the oxide film; during the anodizing process, the electrolyte is continuously stirred, causing the fly ash particles to migrate to the anode region under the action of the electric field and embed into the pores or surface structure of the growing oxide film, forming a fly ash-reinforced composite oxide coating, thereby improving the density, hardness, and wear resistance of the oxide film.

[0025] In this invention, the hard anodizing process is preferably followed by a post-treatment, which preferably includes washing and drying.

[0026] This invention also provides a fly ash-reinforced aluminum alloy hard anodized composite coating prepared by the preparation method described above, wherein the composite coating contains fly ash particles. In this invention, the surface roughness of the composite coating is preferably not higher than 4.0 μm, and the surface hardness is preferably not lower than 440 HV; the wear rate of the composite coating under a 10N load condition is not higher than 5.0 × 10⁻⁶. -6 mm 3 / (N·m).

[0027] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0028] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0029] Example 1 AA2017-T4 aluminum alloy was selected as the matrix material and processed into a sample of predetermined size. It was then mechanically polished with sandpaper of different grits, followed by ultrasonic degreasing with acetone, alkaline washing with NaOH solution, and brightening with HNO3 solution. Finally, it was rinsed with deionized water and dried to obtain the pretreated aluminum alloy matrix. Prepare a 20wt% sulfuric acid solution, add 100g / L of fly ash (average particle size not exceeding 10μm), and suspend the particles uniformly by magnetic stirring combined with ultrasonic dispersion to obtain the electrolyte. Using a pretreated aluminum alloy substrate as the anode and a stainless steel plate as the cathode, an application was performed at a current density of 15 A / dm². 2 Hard anodizing was performed under the following conditions: voltage fluctuation range was controlled within ±15V, and oxidation time was 60min; during the oxidation process, the electrolyte was continuously stirred and maintained at a low temperature (not exceeding 60℃); after the oxidation was completed, the sample was taken out, washed with deionized water, and dried at a temperature not exceeding 60℃ to obtain a fly ash reinforced anodized composite coating.

[0030] Example 2 A fly ash-reinforced anodic oxidation composite coating was obtained by referring to Example 1, wherein the amount of fly ash added to the electrolyte was 80 g / L and the oxidation time was 60 min.

[0031] Example 3 A fly ash-reinforced anodic oxidation composite coating was obtained by referring to Example 1, wherein the amount of fly ash added to the electrolyte was 120 g / L and the oxidation time was 60 min.

[0032] Comparative Example 1 A fly ash-reinforced anodized composite coating was obtained by referring to Example 1, wherein the amount of fly ash added to the electrolyte was 0 g / L, that is, no fly ash was added.

[0033] Comparative Example 2 A fly ash-reinforced anodized composite coating was obtained by referring to Example 1, wherein the amount of fly ash added to the electrolyte was 50 g / L.

[0034] Comparative Example 3 A fly ash-reinforced anodized composite coating was obtained by referring to Example 1, wherein the amount of fly ash added to the electrolyte was 10 g / L.

[0035] Performance testing The performance of the composite coatings obtained in the examples and comparative examples was tested. The testing standards include: Surface roughness test: Refer to national standard GB / T 10610-2009 "Geometric Specifications for Products (GPS) - Rules and methods for evaluating surface structure using the surface structure profile method" and GB / T 3505-2009; Surface microhardness (HV) test: Refer to the latest national standard GB / T 4340.1-2024 "Metallic materials Vickers hardness test - Part 1: Test method"; Friction coefficient and wear rate testing: The "ball-on-disc" test for metal and ceramic coatings usually refers to the international standard ASTM G99 "Standard needle / ball-on-disc friction and wear test method"; The test results are shown in Table 1.

[0036] Table 1 Performance test results of the composite coatings obtained in the examples and comparative examples

[0037] Table 1 shows the technical effects achieved by the fly ash addition amount (80~120 g / L) specified in this invention, exhibiting a significant "critical effect." Compared to the blank group without fly ash (Comparative Example 1), the surface microhardness of the composite coatings in Examples 1-3 more than doubled (jumping to over 440 HV), and the wear rate decreased significantly by over 60% (down to 2.65~3.15 × 10⁻⁶). -6 mm 3 The mechanical load-bearing capacity and wear resistance are significantly enhanced. Meanwhile, compared with Comparative Examples 2 and 3, it can be seen that when the addition amount is too low (10~50 g / L), fly ash cannot fully exert its electrophoretic deposition and pore-filling effects, leading to a deterioration in coating roughness (Ra > 5.0 μm) and limited hardness improvement. Only by strictly controlling it within the critical range of 80~120 g / L can the surface roughness be successfully suppressed below 4.0 μm, achieving comprehensive optimization of high hardness, high density, and excellent tribological properties.

[0038] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a fly ash reinforced aluminum alloy hard anodized composite coating, characterized in that, Includes the following steps: An aluminum alloy substrate is used as the anode, and hard anodizing is performed in an electrolyte to obtain a composite coating; the electrolyte includes fly ash. The amount of fly ash added to the electrolyte is 80~120g / L.

2. The preparation method according to claim 1, characterized in that, The electrolyte includes sulfuric acid and fly ash.

3. The preparation method according to claim 1 or 2, characterized in that, The average particle size of the fly ash is less than 10 μm.

4. The preparation method according to claim 3, characterized in that, The mass concentration of sulfuric acid in the electrolyte is 15-25%.

5. The preparation method according to claim 1, characterized in that, The hard anodizing is performed under constant current conditions, with a current density of 10~20 A / dm³. 2 .

6. The preparation method according to claim 5, characterized in that, The conditions for hard anodizing also include: being carried out under stirring for 30-60 minutes; and the cathode being an inert conductive material. During the hard anodizing process, the voltage is controlled within the range of ±15V, and the temperature of the system is controlled not to exceed 60℃.

7. The preparation method according to claim 1, characterized in that, The aluminum alloy matrix is ​​AA2017-T4 aluminum alloy.

8. The preparation method according to claim 1 or 7, characterized in that, Before hard anodizing, the aluminum alloy substrate also includes a pretreatment process, which includes polishing, degreasing, alkaline washing, brightening, water washing, and drying in sequence.

9. The fly ash reinforced aluminum alloy hard anodized composite coating prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The composite coating contains fly ash particles.

10. The composite coating according to claim 9, characterized in that, The surface roughness of the composite coating is not higher than 4.0 μm, and the surface hardness is not lower than 440 HV; The wear rate of the composite coating under a 10N load condition is no higher than 5.0 × 10⁻⁶. -6 mm 3 / (N·m).

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