Aluminum alloy hard anodized article and method of making and using same

Abstract

This invention provides an aluminum alloy hard anodized part, its preparation method, and its application, belonging to the field of aluminum alloy surface strengthening technology. The invention involves pretreating an aluminum alloy substrate to obtain a pretreated substrate; using the pretreated substrate as an anode, low-temperature hard anodizing is performed in the presence of a cathode and electrolyte to obtain an oxide substrate; the low-temperature hard anodizing includes sequential pre-oxidation and main oxidation, wherein the distance between the anode and cathode during the pre-oxidation process is greater than the distance between the anode and cathode during the main oxidation process; the electrolyte temperature is maintained at 2-3°C during the low-temperature hard anodizing process using a circulating cooling and flow guiding method; the oxide substrate is then sequentially placed in hot water for pre-sealing and in an acetate solution for post-sealing to obtain the aluminum alloy hard anodized part. The aluminum alloy hard anodized part prepared using the method of this invention exhibits excellent comprehensive wear resistance and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy surface strengthening technology, and in particular to an aluminum alloy hard anodized part, its preparation method and application. Background Technology

[0002] Aluminum alloys, such as AA7075 aluminum alloy, have high specific strength, good corrosion resistance, and low density, and are widely used in ships, mechanical transmissions, marine engineering accessories, and lightweight equipment components. During the long-term service of marine propellers, pump impellers, and similar aluminum alloy components, the material surface is often subjected to erosion, friction, corrosion, and impact from foreign objects, which can easily lead to surface scratches, pitting corrosion, roughening, and premature failure.

[0003] Hard anodizing can generate a thick oxide film on the surface of aluminum alloys, improving surface hardness, wear resistance, and corrosion resistance, and is one of the important methods for strengthening the surface of aluminum alloys. Low-temperature sulfuric acid hard anodizing uses sulfuric acid as an electrolyte and is carried out under low-temperature conditions, followed by a sealing treatment. This process can improve the surface properties of AA7075 aluminum alloy to a certain extent, but the traditional low-temperature sulfuric acid hard anodizing process still has the problem that the overall wear and corrosion resistance of the oxide film needs further improvement. Summary of the Invention

[0004] The purpose of this invention is to provide an aluminum alloy hard anodized part, its preparation method and application. The aluminum alloy hard anodized part prepared by the method of this invention has excellent comprehensive properties of wear resistance and corrosion resistance.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing hard anodized aluminum alloy parts, comprising the following steps: The aluminum alloy substrate is pretreated to obtain a pretreated substrate; The pretreated substrate is used as the anode, and low-temperature hard anodizing is performed in the presence of the cathode and electrolyte to obtain an oxidized substrate. The low-temperature hard anodizing includes pre-oxidation and main oxidation in sequence. During the pre-oxidation process, the distance between the anode and the cathode is greater than the distance between the anode and the cathode during the main oxidation process. During the low-temperature hard anodizing process, the electrolyte temperature is maintained at 2~3℃ using a circulating cooling and flow guiding method. The anodized substrate is sequentially placed in hot water for pre-sealing and in an acetate solution for post-sealing to obtain the aluminum alloy hard anodized part.

[0006] Preferably, the pre-oxidation conditions include: a distance of 10-15 cm between the anode and cathode, a current of 4.5-5.5 A, a voltage of 28-34 V, and a pre-oxidation time of 5-15 min; The conditions for the main oxidation include: a distance of 5-8 cm between the anode and cathode, a current of 4.5-5.5 A, a voltage of 28-34 V, and a main oxidation time of 30-60 min.

[0007] Preferably, the total time for the low-temperature hard anodizing is 40-70 minutes; the low-temperature hard anodizing is performed using direct current. The cathode includes a lead plate or an acid-resistant inert cathode plate; the electrolyte is a sulfuric acid electrolyte, and the circulation flow rate of the electrolyte is 0.5~3.0 L / min.

[0008] Preferably, the pre-sealing conditions include: the temperature of the hot water is 95~100℃, and the pre-sealing time is 3~8 minutes; The post-sealing conditions include: the concentration of the acetate solution is 3~8 g / L, the temperature of the acetate solution is 80~100℃, and the post-sealing time is 3~10 min; the acetate in the acetate solution includes one or more of nickel acetate, cobalt acetate, and aluminum acetate.

[0009] Preferably, the aluminum alloy substrate includes a 2-series aluminum alloy substrate, a 5-series aluminum alloy substrate, a 6-series aluminum alloy substrate, or a 7-series aluminum alloy substrate; the 2-series aluminum alloy substrate includes an AA2024 aluminum alloy substrate or a 2A12 aluminum alloy substrate; the 5-series aluminum alloy substrate includes an AA5052 aluminum alloy substrate, an AA5083 aluminum alloy substrate, or an AA5754 aluminum alloy substrate; the 6-series aluminum alloy substrate includes an AA6061 aluminum alloy substrate, an AA6063 aluminum alloy substrate, or an AA6082 aluminum alloy substrate; and the 7-series aluminum alloy substrate includes an AA7050 aluminum alloy substrate or an AA7075 aluminum alloy substrate.

[0010] Preferably, the pretreatment includes grinding, polishing, cleaning, etching and dust removal in sequence.

[0011] Preferably, the polishing includes mechanical polishing, which includes polishing with sandpaper of 120 grit, 240 grit, 400 grit, 600 grit, 800 grit, 1000 grit and 1500 grit in sequence; The polishing includes polishing with metal polishing paste; The cleaning process includes a first cleaning with an ethanol-water solution and a second cleaning with a sodium carbonate-water solution. The conditions for the first cleaning are: the volume fraction of the ethanol-water solution is 65-70%, the temperature of the ethanol-water solution is 20-30°C, and the cleaning time is 3-10 min. The conditions for the second cleaning are: the concentration of the sodium carbonate-water solution is 40-60 g / L, the temperature of the sodium carbonate-water solution is 50-70°C, and the cleaning time is 8-12 min. The etching agent used in the etching process includes an aqueous solution of sodium hydroxide, the concentration of which is 80-120 g / L, the temperature of which is 20-30°C, and the etching time is 0.5-2 min. The ash removal reagent used includes a mixed acid of phosphoric acid, sulfuric acid and nitric acid, the temperature of the mixed acid is 20~30℃, and the ash removal time is 1~3min.

[0012] The present invention provides an aluminum alloy hard anodized part prepared by the preparation method described above, comprising an aluminum alloy substrate and a sealing oxide layer located on the surface of the aluminum alloy substrate.

[0013] Preferably, the thickness of the sealing oxide layer is 55~75μm, and the microhardness is not less than 280HV.

[0014] This invention provides the application of the aluminum alloy hard anodized parts described above as corrosion-resistant and wear-resistant aluminum alloy components.

[0015] Beneficial Effects: This invention employs multi-step or multi-stage anodizing, utilizing a circulating cooling and flow-guiding method to maintain the low-temperature stability of the electrolyte during the oxidation process. This helps to improve the thickness, hardness, and wear resistance of the aluminum alloy oxide layer. Simultaneously, the sealing treatment is particularly important for improving corrosion resistance; hot water sealing significantly enhances corrosion inhibition, while acetate-based sealing further improves pore passivation and surface integrity. Therefore, this invention introduces staged electrode spacing control, circulating cooling and flow-guiding, and dual sealing processes into the low-temperature hard anodizing process, ultimately obtaining a hard oxide layer with superior overall wear and corrosion resistance. Detailed Implementation

[0016] This invention provides a method for preparing hard anodized aluminum alloy parts, comprising the following steps: The aluminum alloy substrate is pretreated to obtain a pretreated substrate; The pretreated substrate is used as the anode, and low-temperature hard anodizing is performed in the presence of the cathode and electrolyte to obtain an oxidized substrate. The low-temperature hard anodizing includes pre-oxidation and main oxidation in sequence. During the pre-oxidation process, the distance between the anode and the cathode is greater than the distance between the anode and the cathode during the main oxidation process. During the low-temperature hard anodizing process, the electrolyte temperature is maintained at 2~3℃ using a circulating cooling and flow guiding method. The anodized substrate is sequentially placed in hot water for pre-sealing and in an acetate solution for post-sealing to obtain the aluminum alloy hard anodized part.

[0017] This invention involves placing a pretreated aluminum alloy substrate in a low-temperature sulfuric acid electrolyte for staged, distance-controlled hard anodizing. The pre-oxidation stage uses a larger electrode spacing (anode-cathode distance) to reduce edge electric field concentration and form a uniform initial oxide layer. The main oxidation stage uses a smaller electrode spacing to improve film growth efficiency, density, hardness, and thickness. Simultaneously, circulating cooling maintains the electrolyte temperature at 2-3°C to suppress localized heat accumulation. Hot water pre-sealing induces initial hydration and shrinkage of the orifices, followed by acetate post-sealing to improve orifice passivation and surface integrity, thus obtaining a hard anodized layer on the aluminum alloy surface. This invention, through the synergistic effect of "low-temperature electrolysis + staged electrode spacing control + circulating cooling + double sealing," improves the uniformity, microhardness, thickness, wear resistance, and surface density of the hard anodized layer on aluminum alloy parts. It is suitable for surface strengthening of marine propellers, pump impellers, marine engineering accessories, and other corrosion-resistant and wear-resistant aluminum alloy components. The method of this invention is described in detail below.

[0018] In this invention, unless otherwise specified, all raw materials used are commercially available products well known to those skilled in the art or prepared using methods well known to those skilled in the art.

[0019] The present invention pre-treats the aluminum alloy substrate to obtain a pre-treated substrate. In one embodiment of the present invention, the aluminum alloy substrate may include a 2-series aluminum alloy substrate, a 5-series aluminum alloy substrate, a 6-series aluminum alloy substrate, or a 7-series aluminum alloy substrate; the 2-series aluminum alloy substrate may include an AA2024 aluminum alloy substrate or a 2A12 aluminum alloy substrate; the 5-series aluminum alloy substrate may include an AA5052 aluminum alloy substrate, an AA5083 aluminum alloy substrate, or an AA5754 aluminum alloy substrate; the 6-series aluminum alloy substrate may include an AA6061 aluminum alloy substrate, an AA6063 aluminum alloy substrate, or an AA6082 aluminum alloy substrate; the 7-series aluminum alloy substrate may include an AA7050 aluminum alloy substrate or an AA7075 aluminum alloy substrate, with the AA7075 aluminum alloy substrate specifically used in this embodiment; the AA7075 aluminum alloy substrate may specifically be an AA7075-T6 aluminum alloy part (i.e., an aluminum alloy part obtained by T6 heat treatment of AA7075 aluminum alloy), or an aluminum alloy part obtained by solution treatment, quenching, and artificial aging treatment of AA7075 aluminum alloy. In this embodiment of the invention, the AA7075 aluminum alloy substrate is specifically in the shape of a disc, with a diameter of 24 mm and a thickness of 6 mm.

[0020] In one embodiment of the present invention, the pretreatment includes sequentially performing grinding, polishing, cleaning, etching, and dust removal. In one embodiment of the present invention, the grinding includes mechanical grinding, which involves sequentially using 120-grit, 240-grit, 400-grit, 600-grit, 800-grit, 1000-grit, and 1500-grit sandpaper. In one embodiment of the present invention, the polishing includes polishing with metal polishing paste. In one embodiment of the present invention, the cleaning includes sequentially performing a first cleaning with an ethanol-water solution and a second cleaning with a sodium carbonate-water solution; the conditions for the first cleaning include: an ethanol-water solution volume fraction of 65-70%, a temperature of 20-30°C (specifically room temperature), and a cleaning time of 3-10 minutes (specifically 5 minutes); the conditions for the second cleaning include: a sodium carbonate-water solution concentration of 40-60 g / L (specifically 50 g / L), a temperature of 50-70°C (specifically 60°C), and a cleaning time of 8-12 minutes (specifically 10 minutes). In one embodiment of the present invention, a water rinse is preferably included between the second cleaning and etching steps, and the water used can be deionized water. In another embodiment of the present invention, the etching agent used for etching includes an aqueous sodium hydroxide solution with a concentration of 80-120 g / L, specifically 100 g / L; the temperature of the aqueous sodium hydroxide solution is 20-30°C, specifically room temperature; and the etching time is 0.5-2 min, specifically 1 min. In another embodiment of the present invention, a water rinse is preferably included between the etching and descaling steps, and the water used can be deionized water. In yet another embodiment of the present invention, the descaling reagent used for descaling includes a mixed acid of phosphoric acid, sulfuric acid, and nitric acid; the mass fraction of phosphoric acid is 80-85 wt%, the mass fraction of sulfuric acid is 95-98%, and the mass fraction of nitric acid is 60-65%; the volume ratio of phosphoric acid, sulfuric acid, and nitric acid is 740-750:190-200:90-100; the temperature of the mixed acid is 20-30°C, specifically room temperature; and the descaling time is 1-3 min, specifically 2 min. As one embodiment of the present invention, the process of removing ash preferably includes rinsing the obtained ash-removed substrate with water to obtain a pretreated substrate; the water used for rinsing can be deionized water.

[0021] After obtaining the pretreated substrate, the present invention uses the pretreated substrate as the anode and performs low-temperature hard anodizing in the presence of the cathode and electrolyte to obtain an oxidized substrate. In one embodiment of the present invention, the cathode includes a lead plate, a platinum titanium plate, or a graphite plate; the electrolyte is a sulfuric acid electrolyte with a concentration of 60-65 wt%, further preferably 61.5-63.5 wt%; specifically, the sulfuric acid electrolyte can be obtained by mixing sulfuric acid with a mass fraction of 95-98% and water at a volume ratio of 1:1. In one embodiment of the present invention, the low-temperature hard anodizing uses direct current; the total time for the low-temperature hard anodizing is 40-70 min, specifically 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, or 70 min. The low-temperature hard anodizing of the present invention includes sequential pre-oxidation and main oxidation, wherein the distance between the anode and cathode during the pre-oxidation process is greater than the distance between the anode and cathode during the main oxidation process. In one embodiment of the present invention, the pre-oxidation conditions include: the distance between the anode and the cathode is 10-15 cm, specifically 10 cm, 11 cm, 12 cm, 13 cm, 14 cm or 15 cm; the current is 4.5-5.5 A, specifically 4.5 A, 5 A, 5.12 A or 5.5 A; the voltage is 28-34 V, specifically 28 V, 29 V, 30 V, 31 V, 31.5 V, 32 V, 33 V or 34 V; and the pre-oxidation time is 5-15 min, specifically 5 min, 8 min, 10 min, 12 min or 15 min. In one embodiment of the present invention, the conditions for the main oxidation include: the distance between the anode and the cathode is 5-8 cm, specifically 5 cm, 6 cm, 7 cm or 8 cm; the current is 4.5-5.5 A, specifically 4.5 A, 5 A, 5.12 A or 5.5 A; the voltage is 28-34 V, specifically 28 V, 29 V, 30 V, 31 V, 31.5 V, 32 V, 33 V or 34 V; and the main oxidation time is 30-60 min, specifically 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min.

[0022] In the low-temperature hard anodizing process described in this invention, a circulating cooling and flow-directing method is used to maintain the electrolyte temperature at 2-3°C. The circulating flow rate of the electrolyte is 0.5-3.0 L / min, specifically 0.5 L / min, 1.0 L / min, 1.5 L / min, 2.0 L / min, 2.5 L / min, or 3.0 L / min. Maintaining the electrolyte temperature at 2-3°C under these conditions using a circulating cooling and flow-directing method can suppress local overheating, ablation, and film loosening, thus improving film continuity and surface roughness. In contrast, while static cooling methods, such as external ice-water baths or cooling jackets, can maintain the overall electrolyte temperature at 2-3°C, localized heat accumulation and concentration polarization occur in the vicinity of the electrode when energized, resulting in a rougher and looser film.

[0023] After obtaining the oxide substrate, the present invention sequentially places the oxide substrate in hot water for pre-sealing and in an acetate solution for post-sealing to obtain the aluminum alloy hard anodized part. As one embodiment of the present invention, the pre-sealing conditions include: the temperature of the hot water is 95~100℃, specifically 98℃; the pre-sealing time is 3~8 minutes, specifically 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, or 8 minutes. In one embodiment of the present invention, the post-sealing conditions include: the concentration of the acetate solution is 3-8 g / L, specifically 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, or 8 g / L; the temperature of the acetate solution is 80-100℃, specifically 80℃, 85℃, 90℃, 95℃, or 100℃; the post-sealing time is 3-10 min, specifically 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, or 10 min; the acetate in the acetate solution includes one or more of nickel acetate, cobalt acetate, and aluminum acetate. In another embodiment of the present invention, the post-sealing process preferably includes sequential washing and drying, wherein the washing is preferably a water rinse, and the water used for the water rinse can be deionized water; the present invention does not have a specific limitation on the drying process, as long as sufficient drying is achieved.

[0024] This invention achieves a more rational electric field distribution during the initial film formation and main growth stages through staged electrode spacing control, which improves film uniformity and reduces edge ablation tendency. The combination of a smaller electrode spacing main oxidation stage and low-temperature circulating cooling improves oxide layer thickness and microhardness while reducing surface roughness. Furthermore, the dual sealing method of hot water pre-sealing and acetate post-sealing further enhances oxide layer pore integrity and corrosion resistance. This invention is particularly suitable for surface strengthening of AA7075 and similar high-strength aluminum alloys in marine propellers, pump impellers, marine accessories, and other corrosion-resistant and wear-resistant components.

[0025] The present invention provides an aluminum alloy hard anodized part prepared by the preparation method described above, comprising an aluminum alloy substrate and a sealing oxide layer located on the surface of the aluminum alloy substrate.

[0026] In one embodiment of the present invention, the thickness of the sealing oxide layer is 55~75μm, and the microhardness is not less than 280HV.

[0027] This invention provides the application of the aluminum alloy hard anodized parts described above as corrosion-resistant and wear-resistant aluminum alloy components.

[0028] As one embodiment of the present invention, the corrosion-resistant and wear-resistant aluminum alloy parts can be marine accessories such as seawater pump housings, pump impellers, guide vanes, ship propulsion accessories, marine connection brackets or corrosion-resistant and wear-resistant mounting bases, or marine propellers.

[0029] When using low-temperature hard anodizing, processes based on fixed electrode spacing, single-step oxidation, and single-pore sealing are prone to problems such as uneven oxide film formation rate, localized temperature rise leading to porosity, and insufficient pore sealing. This invention divides the low-temperature hard anodizing process into a pre-oxidation stage and a main oxidation stage. The pre-oxidation stage uses a larger electrode spacing (10-15 cm) to reduce localized edge electric field concentration and promote the formation of a more uniform initial oxide layer. The main oxidation stage uses a smaller electrode spacing (5-8 cm) to increase the effective electric field strength and oxide layer growth rate, thus balancing uniformity and growth efficiency. This invention introduces circulating cooling during the low-temperature hard anodizing process, stabilizing the electrolyte temperature at 2-3°C. This suppresses localized overheating, ablation, and film porosity, improves film continuity and surface roughness, and facilitates the acquisition of a more uniform and dense hard oxide layer. This invention employs a dual sealing approach after oxidation: hot water pre-sealing followed by acetate post-sealing. Hot water pre-sealing primarily utilizes hydration to initially shrink the oxide layer pores and improve surface integrity. Acetate post-sealing further enhances pore wall passivation and surface density, thereby improving corrosion resistance while maintaining the hardness of the hard anodized layer. The core of this invention lies not in simply extending the oxidation time, but in achieving a balance between thickness, hardness, roughness, and sealing stability in the aluminum alloy hard anodized layer through staged process control of oxide film nucleation, growth, and post-treatment.

[0030] 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.

[0031] The AA7075 aluminum alloy disc samples used in the following examples are commercially available AA7075-T6 aluminum alloy samples with a diameter of 24 mm and a thickness of 6 mm.

[0032] Example 1 Using AA7075 aluminum alloy discs as substrates, the surface of the substrate was successively polished with 120-mesh, 240-mesh, 400-mesh, 600-mesh, 800-mesh, 1000-mesh, and 1500-mesh sandpaper, followed by polishing with metal polishing paste. Then, it was cleaned with a 70% (v / v) ethanol aqueous solution at room temperature (25°C) for 5 minutes. The substrate cleaned with the ethanol aqueous solution was then placed in a 50 g / L sodium carbonate aqueous solution at 60°C for 10 minutes, followed by rinsing with deionized water. The substrate rinsed with deionized water was then etched in a 100 g / L sodium hydroxide aqueous solution at room temperature for 1 minute, followed by rinsing with deionized water. Finally, the substrate rinsed with deionized water was placed in a mixed acid solution of phosphoric acid, sulfuric acid, and nitric acid in a volume ratio of 750:200:100 at room temperature for 2 minutes to remove ash. The phosphoric acid content was 85%, the sulfuric acid content was 98%, and the nitric acid content was 65%. The substrate was then rinsed with deionized water to obtain the pretreated substrate. A sulfuric acid electrolyte was prepared by mixing 98% sulfuric acid with water at a volume ratio of 1:1. Using the pretreated substrate as the anode and a lead plate as the cathode, low-temperature hard anodizing was performed using a DC power supply to obtain an oxidized substrate. During the low-temperature hard anodizing process, the temperature of the sulfuric acid electrolyte was stabilized at 2-3°C through a circulating cooling system with a flow rate of 1.0 L / min. The low-temperature hard anodizing included sequential pre-oxidation and main oxidation. The pre-oxidation conditions were: a 10 cm anode-cathode distance, a 5.12 A current, a 31.5 V voltage, and a pre-oxidation time of 10 min. The main oxidation conditions were: a 5 cm anode-cathode distance, a 5.12 A current, a 31.5 V voltage, and a main oxidation time of 50 min. The oxide substrate was placed in hot water at 98°C for pre-sealing for 5 minutes, and then placed in a nickel acetate aqueous solution with a concentration of 5 g / L for post-sealing at 90°C for 5 minutes. Finally, it was rinsed with deionized water and dried to obtain AA7075 aluminum alloy hard anodized parts.

[0033] Example 2 The process is basically the same as in Example 1, except that: during the low-temperature hard anodizing process, the circulating cooling flow rate is 1.5 L / min, the distance between the anode and cathode during pre-oxidation is 15 cm, the pre-oxidation time is 8 min, the main oxidation time is 42 min, the pre-sealing time is 6 min, and the post-sealing time is 6 min.

[0034] Example 3 The process is basically the same as in Example 1, except that: during the low-temperature hard anodizing process, the circulating cooling flow rate is 2.0 L / min; during the pre-oxidation, the distance between the anode and the cathode is 12 cm and the pre-oxidation time is 12 min; during the main oxidation, the distance between the anode and the cathode is 6 cm and the main oxidation time is 48 min; and the concentration of the nickel acetate aqueous solution used for post-sealing is 6 g / L nickel acetate.

[0035] Comparative Example 1 The process is basically the same as in Example 1, except that the distance between the anode and the cathode is fixed at 10 cm throughout the entire process of the low-temperature hard anodizing, and the total time of the low-temperature hard anodizing is still 60 min.

[0036] Comparative Example 2 The process is basically the same as in Example 1, except that the low-temperature hard anodizing process does not use a circulating cooling method, but instead uses static cooling (specifically an external ice-water bath) to maintain the temperature of the sulfuric acid electrolyte at 2~3°C.

[0037] Comparative Example 3 The process is basically the same as in Example 1, except that the post-sealing step is omitted. Instead, after pre-sealing, the parts are rinsed with deionized water and dried to obtain AA7075 aluminum alloy hard anodized parts.

[0038] Test Example 1 The hard anodized parts prepared in the examples and comparative examples were evaluated using micro-Vickers hardness, cross-sectional film thickness, surface roughness, wear weight loss, and corrosion resistance. The micro-Vickers hardness test load was 200 gf, and the holding time was 15 s. Cross-sectional film thickness was measured using a cross-sectional microscope. Surface roughness was characterized using Ra, specifically measured with a surface roughness meter. The cutoff length was 0.8 mm, the evaluation length was 4.0 mm, and five different locations were tested for each sample, with the average value taken. Wear weight loss was characterized by relative weight loss under the same wear conditions, specifically using the Taber wear test. The grinding wheel was CS-10, the load was 500 g, the rotation speed was 60 rpm, and the wear revolutions were 1000 revs. The wear weight loss was expressed as the difference in mass before and after the test. Corrosion resistance was characterized by the time from a neutral salt spray test to the appearance of obvious pitting corrosion. The conditions for the neutral salt spray test were: 5 wt%... NaCl solution, pH 6.5–7.2, chamber temperature 35±2℃, continuous spraying, and the time to obvious pitting corrosion was used as the corrosion resistance evaluation index; obvious pitting corrosion refers to the time to obvious pitting corrosion within 1 cm. 2At least three visible pitting corrosions were observed within the observation area, with each individual pit having a diameter of at least 0.5 mm, or the total area of ​​pitting corrosion accounting for more than 1% of the observation area. Specific results are shown in Table 1.

[0039] Table 1. Performance test results of hard anodized parts prepared in each embodiment and comparative example.

[0040] As shown in Table 1, the hard anodized part prepared in Example 1 of the present invention has excellent comprehensive performance, with the best balance of microhardness, film thickness, roughness and corrosion resistance; the total time of low-temperature hard anodizing in Example 2 is relatively short, but hard anodized parts with satisfactory performance can still be obtained; in Example 3, a higher circulating cooling flow rate is used, and by optimizing other parameters of low-temperature hard anodizing and the concentration of nickel acetate aqueous solution used for post-sealing, the performance of the obtained hard anodized part is better, between that of Example 1 and Example 2. In Comparative Example 1, the low-temperature hard anodizing process with a fixed electrode spacing resulted in a significant decrease in the performance of the hard anodized parts. Compared to Comparative Example 1, the hard anodized parts prepared in Example 1 showed an increase in microhardness of approximately 12.6%, an increase in film thickness of approximately 25.4%, and a decrease in wear weight loss of approximately 42.0%. The results of Comparative Example 2 indicate that even with staged electrode spacing control, the film layer still exhibits reduced thickness, increased roughness, and increased wear weight loss due to localized heat accumulation in the absence of circulating cooling flow, demonstrating the important role of low-temperature stability control in densifying the hard anodized layer. The results of Comparative Example 3 show that while hot water sealing alone can maintain high hardness, the corrosion resistance is significantly lower than that of Example 1, which uses "hot water pre-sealing + acetate post-sealing," indicating that dual sealing has a positive effect on improving the service stability of the AA7075 aluminum alloy hard anodized layer.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a hard anodized aluminum alloy part, comprising the following steps: The aluminum alloy substrate is pretreated to obtain a pretreated substrate; The pretreated substrate is used as the anode, and low-temperature hard anodizing is performed in the presence of the cathode and electrolyte to obtain an oxidized substrate. The low-temperature hard anodizing includes pre-oxidation and main oxidation in sequence. During the pre-oxidation process, the distance between the anode and the cathode is greater than the distance between the anode and the cathode during the main oxidation process. During the low-temperature hard anodizing process, the electrolyte temperature is maintained at 2~3℃ using a circulating cooling and flow guiding method. The anodized substrate is sequentially placed in hot water for pre-sealing and in an acetate solution for post-sealing to obtain the aluminum alloy hard anodized part.

2. The preparation method according to claim 1, characterized in that, The pre-oxidation conditions include: a distance of 10-15 cm between the anode and cathode, a current of 4.5-5.5 A, a voltage of 28-34 V, and a pre-oxidation time of 5-15 min. The conditions for the main oxidation include: a distance of 5-8 cm between the anode and cathode, a current of 4.5-5.5 A, a voltage of 28-34 V, and a main oxidation time of 30-60 min.

3. The preparation method according to claim 1 or 2, characterized in that, The total time for the low-temperature hard anodizing is 40-70 minutes; the low-temperature hard anodizing is performed using direct current. The cathode includes a lead plate or an acid-resistant inert cathode plate; the electrolyte is a sulfuric acid electrolyte, and the circulation flow rate of the electrolyte is 0.5~3.0 L / min.

4. The preparation method according to claim 1 or 2, characterized in that, The conditions for pre-sealing the hole include: the temperature of the hot water is 95~100℃, and the pre-sealing time is 3~8 minutes; The post-sealing conditions include: the concentration of the acetate solution is 3~8 g / L, the temperature of the acetate solution is 80~100℃, and the post-sealing time is 3~10 min; the acetate in the acetate solution includes one or more of nickel acetate, cobalt acetate, and aluminum acetate.

5. The preparation method according to claim 1, characterized in that, The aluminum alloy substrate includes 2-series aluminum alloy substrates, 5-series aluminum alloy substrates, 6-series aluminum alloy substrates, or 7-series aluminum alloy substrates; the 2-series aluminum alloy substrate includes AA2024 aluminum alloy substrate or 2A12 aluminum alloy substrate; the 5-series aluminum alloy substrate includes AA5052 aluminum alloy substrate, AA5083 aluminum alloy substrate, or AA5754 aluminum alloy substrate; the 6-series aluminum alloy substrate includes AA6061 aluminum alloy substrate, AA6063 aluminum alloy substrate, or AA6082 aluminum alloy substrate; and the 7-series aluminum alloy substrate includes AA7050 aluminum alloy substrate or AA7075 aluminum alloy substrate.

6. The preparation method according to claim 1, characterized in that, The pretreatment includes grinding, polishing, cleaning, etching and dust removal in sequence.

7. The preparation method according to claim 6, characterized in that, The polishing includes mechanical polishing, which involves polishing with sandpaper of 120 grit, 240 grit, 400 grit, 600 grit, 800 grit, 1000 grit and 1500 grit in sequence. The polishing includes polishing with metal polishing paste; The cleaning process includes a first cleaning with an ethanol-water solution and a second cleaning with a sodium carbonate-water solution. The conditions for the first cleaning are: the volume fraction of the ethanol-water solution is 65-70%, the temperature of the ethanol-water solution is 20-30°C, and the cleaning time is 3-10 minutes. The conditions for the second cleaning are: the concentration of the sodium carbonate-water solution is 40-60 g / L, the temperature of the sodium carbonate-water solution is 50-70°C, and the cleaning time is 8-12 minutes. The etching agent used in the etching process includes an aqueous solution of sodium hydroxide, the concentration of which is 80-120 g / L, the temperature of which is 20-30°C, and the etching time is 0.5-2 min. The ash removal reagent used includes a mixed acid of phosphoric acid, sulfuric acid and nitric acid, the temperature of the mixed acid is 20~30℃, and the ash removal time is 1~3min.

8. The aluminum alloy hard anodized part prepared by the preparation method according to any one of claims 1 to 7 includes an aluminum alloy substrate and a sealing oxide layer located on the surface of the aluminum alloy substrate.

9. The aluminum alloy hard anodized part according to claim 8, characterized in that, The thickness of the sealing oxide layer is 55~75μm, and the microhardness is not less than 280HV.

10. The application of the aluminum alloy hard anodized part according to claim 8 or 9 as a corrosion-resistant and wear-resistant aluminum alloy component.

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