Aluminum alloy hard anodizing electrolyte and treatment method

Abstract

The application belongs to the technical field of metal surface treatment, and particularly relates to an aluminum alloy hard anodic oxidation electrolyte and a treatment method. The aluminum alloy hard anodic oxidation electrolyte provided by the application comprises organic phosphonic acid, organic carboxylic acid and organic corrosion inhibitor; the mass concentration of the organic phosphonic acid is 50-100 g / L; the mass concentration of the organic carboxylic acid is 10-30 g / L; and the mass concentration of the organic corrosion inhibitor is 0.5-1.0 g / L. The aluminum alloy hard anodic oxidation electrolyte and the treatment method provided by the application can effectively solve the 'burning loss' phenomenon of the hard anodic oxidation film of high-copper aluminum alloy, improve the compactness and hardness of the oxidation film, and are suitable for high-copper aluminum alloy parts with high wear resistance requirements; and the process is environmentally friendly and non-toxic, does not require high voltage, and significantly reduces energy consumption and wastewater treatment cost.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to an aluminum alloy hard anodizing electrolyte and treatment method. Background Technology

[0002] High-strength aluminum alloys such as 2024, 2A12, and 2219 are widely used as load-bearing structural components in aerospace equipment due to their high specific strength, good mechanical properties, and high fracture toughness. However, their low surface hardness and poor wear resistance affect their service safety. Therefore, anodizing technology, especially hard anodizing, is often used to improve the wear resistance of high-strength aluminum alloy components.

[0003] Currently, sulfuric acid electrolyte systems are commonly used for hard anodizing of aluminum alloys. However, the oxidation voltage (80~120 V) is often high during the anodizing process, and the electrolyte must be kept at a low temperature (-10 ℃~10 ℃), resulting in poor oxidation effects and often causing uneven film thickness and low hardness. Furthermore, aluminum alloys such as 2024, 2A12, and 2219 have high copper content (Cu mass fraction > 3.8%), especially 2219 aluminum alloy with a copper content as high as 5.8~6.8%. Traditional sulfuric acid hard anodizing systems are not well-suited to these alloys, frequently resulting in burn-off and other accidents, severely affecting the quality of the oxide film.

[0004] Some scholars have also improved the hard anodizing process, mainly in two aspects: one is to add oxalic acid, malonic acid, malic acid, etc. to the sulfuric acid electrolyte to form a mixed organic acid electrolyte; the other approach is to change the traditional DC oxidation to AC, AC-DC superposition, and pulse oxidation. However, the existing technology still fails to solve the "burn-off" problem in the hard anodizing process of high copper content aluminum alloys. It generally suffers from poor film uniformity, limited hardness (<350 HV), and even makes it difficult to form a continuous hard oxide film for 2219 aluminum alloy. Moreover, it is difficult to balance the environmental protection and energy consumption of the process. Summary of the Invention

[0005] The purpose of this invention is to provide an electrolyte and treatment method for hard anodizing of aluminum alloys. The electrolyte and treatment method provided by this invention can effectively solve the "burn-off" phenomenon of hard anodized films of high copper content aluminum alloys, improve the density and hardness of the oxide film, and are suitable for high copper content aluminum alloy parts with high wear resistance requirements. Moreover, the process is environmentally friendly and non-toxic, does not require high voltage, and significantly reduces energy consumption and wastewater treatment costs.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides an aluminum alloy hard anodizing electrolyte, comprising an organophosphonic acid, an organic carboxylic acid, and an organic corrosion inhibitor; the organophosphonic acid includes one or more of aminotrimethylenephosphonic acid (ATMP), hydroxyethylidene diphosphonic acid (HEDP), and ethylenediaminetetramethylenephosphonic acid (EDTMP), and the mass concentration of the organophosphonic acid is 50-100 g / L; the organic carboxylic acid includes one or more of tartaric acid, malic acid, and citric acid, and the mass concentration of the organic carboxylic acid is 10-30 g / L; the organic corrosion inhibitor includes one or more of thiourea, benzotriazole, and methylbenzotriazole, and the mass concentration of the organic corrosion inhibitor is 0.5-1.0 g / L.

[0007] This invention provides a method for electrolytic hard anodizing of aluminum alloys, comprising the following steps: (1) The aluminum alloy workpiece is subjected to alkaline etching treatment and then washed with water to obtain the first treated workpiece; (2) The first processed workpiece is placed in the brightening liquid for brightening treatment, and then washed with water to obtain the second processed workpiece; (3) The second processed workpiece is placed in the aluminum alloy hard anodizing electrolyte described in the above technical solution for hard anodizing treatment, and then washed and dried in sequence.

[0008] Preferably, the mass fraction of Cu in the aluminum alloy workpiece is 3.8~6.8%.

[0009] Preferably, the aluminum alloy workpiece includes 2024, 2A12 or 2219.

[0010] Preferably, the alkaline etching treatment is carried out using an alkaline etching solution; the alkaline etching solution comprises the following components at mass concentrations: 60~100 g / L sodium hydroxide and 5~6 g / L sodium sulfide.

[0011] Preferably, the alkaline etching conditions include: a treatment temperature of 50~60℃ and a treatment time of 3~5 min.

[0012] Preferably, the light-emitting liquid is a nitric acid solution, and the volume concentration of HNO3 in the nitric acid solution is 30-50%; the light-emitting treatment time is 30-60 s.

[0013] Preferably, the conditions for the hard anodizing treatment include: a temperature of 0~10℃, hard anodizing treatment using a DC constant voltage method, and an oxidation voltage of 20~30 V.

[0014] Preferably, the hard anodizing treatment includes a first treatment method or a second treatment method; the first treatment method is: increasing the voltage to 20-30 V under 5-10 min conditions, and then maintaining 20-30 V for 30-70 min; the second treatment method is: sequentially increasing the voltage to the first gradient voltage, ..., the nth gradient voltage for treatment, n≥2, the first gradient voltage to the nth gradient voltage are independently 20-30 V, and the first gradient voltage to the nth gradient voltage increase sequentially, and the total time of the second treatment method is ≤90 min.

[0015] Preferably, step (3) prepares a hard anodized film on the surface of the aluminum alloy workpiece; the thickness of the hard anodized film is 20~50 μm, and the hardness of the hard anodized film is ≥400 HV.

[0016] This invention provides an aluminum alloy hard anodizing electrolyte, comprising an organophosphonic acid, an organic carboxylic acid, and an organic corrosion inhibitor; the organophosphonic acid includes one or more of aminotrimethylenephosphonic acid (ATMP), hydroxyethylidene diphosphonic acid (HEDP), and ethylenediaminetetramethylenephosphonic acid (EDTMP), and the mass concentration of the organophosphonic acid is 50-100 g / L; the organic carboxylic acid includes one or more of tartaric acid, malic acid, and citric acid, and the mass concentration of the organic carboxylic acid is 10-30 g / L; the organic corrosion inhibitor includes one or more of thiourea, benzotriazole, and methylbenzotriazole, and the mass concentration of the organic corrosion inhibitor is 0.5-1.0 g / L. This invention constructs a composite electrolyte system of "organophosphonic acid-organic carboxylic acid-organic corrosion inhibitor". By optimizing the specific types and mass concentration ratios of the organicphosphonic acid, organic carboxylic acid, and organic corrosion inhibitor, the synergistic effect of the three is achieved. This controls the dissolution of the film by the electrolyte, inhibits excessive reaction in the copper phase region, and prevents "burn-off", thereby achieving a continuous, dense, and high-hardness hard anodized film on the surface of high-copper-content aluminum alloys (Cu mass fraction 3.8%~6.8%). The organicphosphonic acid (one or more of HEDP, ATMP, and EDTMP) and organic carboxylic acid (one or more of tartaric acid, malic acid, and citric acid) have multi-step ionization characteristics, which can gradually release H+. +In the electrolyte, it forms a buffer system, effectively stabilizing the pH value during the electrolytic treatment of hard anodizing of aluminum alloys, inhibiting drastic changes in acidity at the interface, thereby reducing the oxide film dissolution rate and promoting the densification and growth of the film layer. Furthermore, organophosphonic acids can complex aluminum ions and adsorb them at the film pores, blocking free acid from eroding the film layer, further improving hardness and corrosion resistance. The core function of organic corrosion inhibitors (one of thiourea, benzotriazole, and methylbenzotriazole) is selective adsorption and protection. These inhibitor molecules can preferentially adsorb onto the active sites of the exposed copper-containing phase, thereby effectively inhibiting partial discharge and preventing "burn-out". In this invention, the synergistic effect of organophosphonic acid and organic carboxylic acid ensures sufficient ion mobility, giving the electrolyte high conductivity, while also guaranteeing the electrolyte's buffering capacity and preventing excessive dissolution of the oxide film. The combination of the two can maintain a high film formation rate and film quality of the anodic oxide film at a relatively low oxidation voltage (20~30V). The selective adsorption of the organic corrosion inhibitor can effectively suppress the partial discharge of the copper-containing phase, thereby promoting the dense growth of the oxide film. Ultimately, a uniform thickness and high hardness anodic oxide film is formed on the surface of a high copper-containing aluminum alloy (Cu mass fraction 3.8%~6.8%). At the same time, energy consumption and environmental pollution are significantly reduced.

[0017] This invention provides a method for electrolytic hard anodizing of aluminum alloys, comprising the following steps: (1) subjecting the aluminum alloy workpiece to alkaline etching and then washing it with water to obtain a first treated workpiece; (2) placing the first treated workpiece in a brightening solution for brightening treatment and then washing it with water to obtain a second treated workpiece; (3) placing the second treated workpiece in the aluminum alloy hard anodizing electrolyte described in the above technical solution for hard anodizing treatment, and then washing and drying it sequentially. This invention uses the aluminum alloy hard anodizing electrolyte described in the above technical solution for hard anodizing treatment. By optimizing the specific types and mass concentration ratios of organic phosphonic acid, organic carboxylic acid, and organic corrosion inhibitor, the synergistic effect of the three is achieved, which can effectively suppress the partial discharge of the copper-containing phase and suppress the dissolution of the film layer by the electrolyte, thereby achieving hard anodizing treatment of high copper content (Cu mass fraction 3.8%~6.8%) aluminum alloys at a lower voltage (20~30V) and forming a dense, uniform, and high-hardness anodized film. The aluminum alloy hard anodizing electrolyte provided by this invention is suitable for the hard anodizing process of high copper content (Cu mass fraction 3.8%~6.8%) aluminum alloys. This invention can effectively solve the "burn-off" phenomenon of hard anodized films on high copper content aluminum alloys, improve the density and hardness of the oxide film, and is suitable for high copper content aluminum alloy parts with high wear resistance requirements. Moreover, the process is environmentally friendly and non-toxic, does not require high voltage, and significantly reduces energy consumption and wastewater treatment costs. Attached Figure Description

[0018] The accompanying drawings further illustrate the invention, but the embodiments in the drawings do not constitute any limitation on the invention.

[0019] Figure 1 The cross-sectional morphology and microhardness of the 2024 aluminum alloy hard anodized film obtained in Example 1 are shown at different locations. Figure 2 The cross-sectional morphology of the 2A12 aluminum alloy hard anodized film obtained in Example 2; Figure 3 The cross-sectional morphology and microhardness of the 2219 aluminum alloy hard anodized film obtained in Example 3 are shown. Figure 4 The cross-sectional morphology and microhardness diagram of the 2219 aluminum alloy hard anodized film obtained in Example 4 are shown. Figure 5 The film morphology of the product obtained in Comparative Example 1 ( Figure 5 (Left side of the image) and cross-sectional hardness diagram ( Figure 5 (The right side of the image) Figure 6 This is a macroscopic morphology diagram of the film layer of the product obtained in Comparative Example 2; Figure 7 The macroscopic morphology of the film layer of the product obtained in Comparative Example 3 ( Figure 7 (Left side of the image) and cross-sectional hardness diagram ( Figure 7 (The right side of the image) Figure 8 The microstructure of the film layer of the product obtained in Comparative Example 4 ( Figure 8 (Left side of the image) and cross-sectional hardness diagram ( Figure 8 (The right side of the image) Figure 9 The cross-sectional morphology of the film layer of the product obtained in Comparative Example 5 ( Figure 9 (Left side of the image) and cross-sectional hardness diagram ( Figure 9 (The right side of the image) Figure 10 The cross-sectional morphology of the film layer of the product obtained in Comparative Example 6 ( Figure 10 (Left side of the image) and cross-sectional hardness diagram ( Figure 10 (The right side of the image) Figure 11 The cross-sectional morphology of the film layer of the product obtained in Comparative Example 7 ( Figure 11 (Left side of the image) and cross-sectional hardness diagram ( Figure 11 (The right side of the image) Figure 12 This is a macroscopic morphology diagram of the film layer of the product obtained in Comparative Example 8. Detailed Implementation

[0020] This invention provides an aluminum alloy hard anodizing electrolyte, comprising an organophosphonic acid, an organic carboxylic acid, and an organic corrosion inhibitor; the organophosphonic acid includes one or more of aminotrimethylenephosphonic acid (ATMP), hydroxyethylidene diphosphonic acid (HEDP), and ethylenediaminetetramethylenephosphonic acid (EDTMP), and the mass concentration of the organophosphonic acid is 50-100 g / L; the organic carboxylic acid includes one or more of tartaric acid, malic acid, and citric acid, and the mass concentration of the organic carboxylic acid is 10-30 g / L; the organic corrosion inhibitor includes one or more of thiourea, benzotriazole, and methylbenzotriazole, and the mass concentration of the organic corrosion inhibitor is 0.5-1.0 g / L.

[0021] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art. Unless otherwise specified, the solutions used in this invention are aqueous solutions with water as the solvent; for example, the electrolyte for hard anodizing of aluminum alloys is an aqueous solution. Room temperature in this invention generally refers to a temperature between 15°C and 30°C, and is generally defined as 25°C.

[0022] The aluminum alloy hard anodizing electrolyte provided by this invention includes organophosphonic acid. In this invention, the organophosphonic acid includes one or more of aminotrimethylenephosphonic acid (ATMP), hydroxyethylidene diphosphonic acid (HEDP), and ethylenediaminetetramethylenephosphonic acid (EDTMP). In specific embodiments of this invention, the organophosphonic acid can be ATMP. Alternatively, the organophosphonic acid can be a mixture of ATMP and HEDP. Or, the organophosphonic acid can be HEDP. In this invention, when the organophosphonic acid is a mixture of ATMP and HEDP, the preferred mass ratio of ATMP to HEDP in the mixture is (3~5):(3~5), and in embodiments it can be 1:1 or 5:3. In this invention, the mass concentration of the organophosphonic acid is 50~100 g / L, and in embodiments it can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 g / L. In this invention, when the organophosphonic acid is a mixture of ATMP and HEDP, the mass concentration of ATMP is preferably 30-50 g / L, and the mass concentration of HEDP is preferably 30-50 g / L.

[0023] The aluminum alloy hard anodizing electrolyte provided by this invention comprises an organic carboxylic acid. In this invention, the organic carboxylic acid includes one or more of tartaric acid, malic acid, and citric acid. In specific embodiments of this invention, the organic carboxylic acid can be a mixture of tartaric acid and malic acid. Alternatively, the organic carboxylic acid can be malic acid. Alternatively, the organic carboxylic acid can be citric acid. In this invention, when the organic carboxylic acid is a mixture of tartaric acid and malic acid, the preferred mass ratio of tartaric acid to malic acid in the mixture is (1~2):(1~2), and in some embodiments, it can be 1:1. In this invention, the mass concentration of the organic carboxylic acid is 10~30 g / L, and in some embodiments, it can be 10, 15, 20, 25, or 30 g / L. In some embodiments of this invention, when the organic carboxylic acid is a mixture of tartaric acid and malic acid, the preferred mass concentration of the tartaric acid is 10~15 g / L, and the preferred mass concentration of the malic acid is 10~15 g / L.

[0024] The aluminum alloy hard anodizing electrolyte provided by this invention includes an organic corrosion inhibitor. In this invention, the organic corrosion inhibitor includes one or more of thiourea, benzotriazole, and methylbenzotriazole; in the examples, it can be thiourea, benzotriazole, or methylbenzotriazole. The mass concentration of the organic corrosion inhibitor is 0.5~1.0 g / L; in the examples, it can be 0.5, 0.6, 0.7, 0.8, 0.9, or 1.0 g / L.

[0025] The aluminum alloy hard anodizing electrolyte provided by this invention also includes a solvent. In this invention, the solvent used in the aluminum alloy hard anodizing electrolyte is water, and in the embodiments, it can be deionized water.

[0026] This invention provides a method for preparing the aluminum alloy hard anodizing electrolyte as described above, preferably comprising the following steps: The first portion of water and organophosphonic acid are mixed to obtain an organophosphonic acid solution; the organophosphonic acid solution and an organic carboxylic acid are mixed to obtain a mixed solution; an organic corrosion inhibitor and the second portion of water are mixed to obtain an organic corrosion inhibitor solution; the mixed solution and the organic corrosion inhibitor solution are mixed, then the remaining water is added, and finally, the mixture is allowed to stand for aging to obtain the aluminum alloy hard anodizing electrolyte. The volume of the first portion of water accounts for 1 / 2 of the total water volume. The volume of the second portion of water accounts for 1 / 4 of the total water volume. The preparation of the aluminum alloy hard anodizing electrolyte is preferably carried out in an electrolytic cell, and the above mixing is preferably carried out under stirring conditions. The specific implementation of the stirring method is not particularly required in this invention. The standing aging time is preferably 24~48 hours.

[0027] This invention provides a method for electrolytic hard anodizing of aluminum alloys, comprising the following steps: (1) The aluminum alloy workpiece is subjected to alkaline etching treatment and then washed with water to obtain the first treated workpiece; (2) The first processed workpiece is placed in the brightening liquid for brightening treatment, and then washed with water to obtain the second processed workpiece; (3) The second processed workpiece is placed in the aluminum alloy hard anodizing electrolyte described in the above technical solution for hard anodizing treatment, and then washed and dried in sequence.

[0028] Step (1): In this invention, the aluminum alloy workpiece is subjected to alkaline etching treatment and then washed with water to obtain the first treated workpiece.

[0029] In this invention, the mass fraction of Cu in the aluminum alloy workpiece is preferably 3.8% to 6.8%. In this invention, the aluminum alloy workpiece preferably comprises 2024, 2Al2, or 2219.

[0030] In this invention, the alkaline etching treatment is preferably carried out using an alkaline etching solution. The alkaline etching solution preferably comprises the following components at mass concentrations: 60-100 g / L sodium hydroxide and 5-6 g / L sodium sulfide. In the alkaline etching solution, the mass concentration of sodium hydroxide can be 60, 65, 70, 75, 80, 85, 90, 95, or 100 g / L. The mass concentration of sodium sulfide can be 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, or 6 g / L. The solvent in the alkaline etching solution is water, and in the examples, it can be deionized water. This invention preferably uses a mixture of sodium hydroxide, sodium sulfide, and water to obtain the alkaline etching solution. This invention preferably involves immersing the aluminum alloy workpiece in the alkaline etching solution for the alkaline etching treatment. In this invention, the conditions for the alkaline etching treatment preferably include: a treatment temperature preferably of 50-60°C, and in the examples, it can be 52, 54, 55, 56, 58, or 60°C. The processing time is preferably 3-5 minutes. In this invention, the water washing after alkaline etching preferably includes sequential hot water washing and cold water washing. This invention does not have special requirements for the specific implementation of the hot water washing and cold water washing, wherein the temperature of the hot water washing is higher than the temperature of the cold water washing.

[0031] Step (2): After obtaining the first processed workpiece, the present invention places the first processed workpiece in a brightening solution for brightening treatment, and then washes it with water to obtain the second processed workpiece. In the present invention, the brightening solution is preferably a nitric acid solution. The volume concentration of HNO3 in the nitric acid solution is preferably 30-50%, and in the embodiments it can be 30, 35, 40, 45 or 50%. The brightening treatment time is preferably 30-60 s, and in the embodiments it can be 30, 35, 40, 45, 50, 55 or 60 s. The water washing after the brightening treatment is preferably done with cold water.

[0032] Step (3): After obtaining the second processed workpiece, the present invention places the second processed workpiece in the aluminum alloy hard anodizing electrolyte described in the above technical solution for hard anodizing treatment, and then performs water washing and drying in sequence. In the present invention, the conditions for the hard anodizing treatment preferably include: the temperature is preferably 0~10℃, and in the embodiments it can be 8~10℃ or 5~6℃ or 0~2℃. The present invention preferably uses DC constant voltage method for hard anodizing treatment, and the oxidation voltage is preferably 20~30 V. The oxidation time is preferably 40~90 min.

[0033] In this invention, the hard anodizing treatment preferably includes a first treatment method or a second treatment method. In this invention, the first treatment method is preferably: increasing the voltage to 20-30 V (preferably 25 V or 20 V) under conditions of 5-10 min (5 min or 10 min in the embodiments), and then maintaining it at 20-30 V (preferably 25 V or 20 V) for 30-70 min (preferably 60 min or 45 min). In an embodiment of this invention, the first treatment method can be: applying direct current at 8-10°C, increasing the oxidation voltage to 25 V in 10 min, and then maintaining the voltage for 60 min. Alternatively, the first treatment method can be: applying direct current at 5-6°C, increasing the oxidation voltage to 20 V in 5 min, and then maintaining it for 45 min.

[0034] In this invention, the second processing method is preferably as follows: voltage is sequentially increased to the first gradient voltage, ..., the nth gradient voltage, where n ≥ 2. The first to nth gradient voltages are independently 20-30 V (in the embodiment, 25 V or 30 V), and the first to nth gradient voltages increase sequentially. In this invention, the voltage increase time to the first, ..., and nth gradient voltages is preferably 5-10 min, and in the embodiment, 5 min. In this invention, the processing time under the first gradient voltage condition, ..., and the nth gradient voltage condition is preferably 10-40 min, and in the embodiment, 15 min or 35 min. The total time of the second processing method is ≤ 90 min, and in the embodiment, 50-90 min. The temperature of the second processing is preferably 0-2℃.

[0035] In this embodiment of the invention, the second processing method can be: applying direct current at 0~2℃, first increasing the oxidation voltage to 25 V within 5 min, maintaining the constant voltage for 35 min, and then increasing the oxidation voltage to 30 V within 5 min and maintaining it for 15 min.

[0036] In this invention, the washing after the hard anodizing treatment is preferably performed using deionized water. The drying is preferably performed using cold air.

[0037] In this invention, step (3) involves preparing a hard anodized film on the surface of the aluminum alloy workpiece. The hard anodized film is a uniform and dense hard anodized film. The thickness of the hard anodized film is preferably 20-50 μm, and in the embodiments it can be 36-38 μm, 36-37 μm, 40-41 μm or 37-38 μm. The hardness of the hard anodized film is preferably ≥400 HV, preferably 400-440 HV, and in the embodiments it can be 414-423 HV, 417 HV, 412 HV or 423-430 HV.

[0038] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0039] Example 1: Hard anodizing of 2024 aluminum alloy Prepare 2 L of anodizing electrolyte containing 100 g / L ATMP, 10 g / L tartaric acid, 10 g / L malic acid, and 0.5 g / L thiourea, as follows: S1. Add 1 L of deionized water to the electrolytic cell; S2. Weigh ATMP powder at a concentration of 100 g / L, then slowly add it to the electrolytic cell while stirring until completely dissolved; S3. Weigh out tartaric acid at a rate of 10 g / L, then slowly add it to the electrolytic cell while stirring until homogeneous; S4. Weigh out malic acid at a rate of 10 g / L, then slowly add it to the electrolytic cell while stirring until homogeneous; S5. Weigh out thiourea at a concentration of 0.5 g / L, dissolve it in 500 mL of deionized water, and then slowly add it to the aforementioned solution; S6. Then add water to 2 L; S7. Let stand for 24 hours.

[0040] The anodizing process for 2024 aluminum alloy is as follows: A1. The workpiece is placed in an alkaline etching solution at 60℃ for 5 minutes and then washed with hot water and cold water in sequence. The alkaline etching solution is prepared with 100g / L sodium hydroxide, 6g / L sodium sulfide and deionized water.

[0041] A2. Immediately immerse the workpiece after alkaline etching in a 40% (v / v) nitric acid brightening solution for 30 seconds, and then wash it with water.

[0042] A3. Place the brightened workpiece in an anodizing electrolyte composed of 100 g / L ATMP, 10 g / L tartaric acid, 10 g / L malic acid and 0.5 g / L thiourea. Apply direct current at 8~10℃ and slowly increase the oxidation voltage to 25 V within 10 min. Then, maintain constant voltage for 60 min. After oxidation, thoroughly clean the workpiece with deionized water and dry it with cold air.

[0043] After the above process, an anodized film with a thickness of 36~38 μm can be formed on the surface of 2024 aluminum alloy, and its film thickness and hardness are as follows. Figure 1 As shown. Figure 1 The results show that the hard anodized film on the surface of the 2024 aluminum alloy is uniform and continuous, with no obvious "burn-off" defects. The film hardness at different locations is similar (approximately 414~423 HV), all exceeding 400 HV.

[0044] Example 2: Hard anodizing of 2A12 aluminum alloy Prepare 2 L of a mixed anodic oxidation electrolyte comprising 50 g / L HEDP, 30 g / L ATMP, 10 g / L malic acid, and 0.5 g / L benzotriazole, as follows: S1. Add 1 L of deionized water to the electrolytic cell; S2. Weigh out HEDP powder at a concentration of 50 g / L, then slowly add it to the electrolytic cell while stirring until completely dissolved; S3. Weigh ATMP powder at a concentration of 30 g / L, then slowly add it to the electrolytic cell while stirring until completely dissolved; S4. Weigh out tartaric acid at a rate of 10 g / L, then slowly add it to the electrolytic cell while stirring until homogeneous. S5. Weigh out benzotriazole at a concentration of 0.5 g / L, dissolve it in 500 mL of deionized water, and then slowly add it to the aforementioned solution; S6. Then add water to 2 L; S7. Let stand for 24 hours.

[0045] The anodizing process for 2A12 aluminum alloy is as follows: A1. The workpiece is placed in an alkaline etching solution at 55°C for 4 minutes and then washed with hot water and cold water in sequence. The alkaline etching solution is prepared with 80 g / L sodium hydroxide, 5.5 g / L sodium sulfide and deionized water.

[0046] A2. Immediately immerse the workpiece after alkaline etching in a 50% volume concentration nitric acid brightening solution for 30 seconds, and then wash it with water.

[0047] A3. Place the brightened workpiece in a mixed electrolyte solution consisting of 50 g / L ATMP, 30 g / L HEDP, 10 g / L malic acid and 0.5 g / L benzotriazole. Apply direct current at 5~6℃ and slowly increase the oxidation voltage to 20 V within 5 min, then maintain it for 45 min. After oxidation, thoroughly clean the workpiece with deionized water and dry it with cold air.

[0048] After the above process, an anodized film with a thickness of approximately 36-37 μm can be formed on the surface of 2A12 aluminum alloy, and its cross-sectional morphology is as follows. Figure 2 As shown in the figure, the hard anodized film on the surface of the 2A12 aluminum alloy is uniform and continuous, without obvious "burn-off" defects; the microhardness test results show that the hardness of this oxide film is approximately 417 HV.

[0049] Example 3: Hard Anodizing of 2219 Aluminum Alloy Prepare 2 L of a mixed anodic oxidation electrolyte comprising 50 g / L HEDP, 50 g / L ATMP, 30 g / L citric acid, and 1.0 g / L methylbenzotriazole, as follows: S1. Add 1 L of deionized water to the electrolytic cell; S2. Weigh out HEDP powder at a concentration of 50 g / L, then slowly add it to the electrolytic cell while stirring until completely dissolved; S3. Weigh ATMP powder at a concentration of 50 g / L, then slowly add it to the electrolytic cell while stirring until completely dissolved; S4. Weigh out citric acid at a rate of 30 g / L, then slowly add it to the electrolytic cell while stirring until homogeneous; S5. Weigh out methylbenzotriazole at a concentration of 1.0 g / L, dissolve it in 500 mL of deionized water, and then slowly add it to the aforementioned solution; S6. Then add water to 2 L; S7. Let stand for 24 hours.

[0050] The anodizing process for 2219 aluminum alloy is as follows: A1. The workpiece is placed in an alkaline etching solution at 55℃ for 4 minutes and then washed with hot water and cold water in sequence. The alkaline etching solution is prepared with 100g / L sodium hydroxide, 6g / L sodium sulfide and deionized water.

[0051] A2. Immediately immerse the workpiece after alkaline etching in a 30% (v / v) nitric acid brightening solution for 30 seconds, and then wash it with water.

[0052] A3. Place the brightened workpiece in a mixed electrolyte solution consisting of 50 g / L HEDP, 50 g / L ATMP, 30 g / L citric acid and 1.0 g / L methylbenzotriazole. Apply direct current at 0~2℃, first increase the oxidation voltage to 25V within 5 min, maintain the constant voltage for 35 min, and then slowly increase the voltage to 30V within 5 min and maintain it for 15 min. After oxidation, thoroughly clean the workpiece with deionized water and dry it with cold air.

[0053] After the above process, an anodized film with a thickness of approximately 40-41 μm can be formed on the surface of 2219 aluminum alloy. The film thickness and hardness are as follows: Figure 3 As shown in the figure, the hard anodized film on the surface of the 2219 aluminum alloy is uniform and continuous, without obvious "burn-off" defects, and its microhardness is as high as 412HV.

[0054] Example 4: Hard Anodizing of 2219 Aluminum Alloy Prepare 2 L of anodizing electrolyte containing 100 g / L HEDP, 10 g / L tartaric acid, 10 g / L malic acid, and 0.5 g / L thiourea, as follows: S1. Add 1 L of deionized water to the electrolytic cell; S2. Weigh out HEDP powder at a concentration of 100 g / L, then slowly add it to the electrolytic cell while stirring until completely dissolved; S3. Weigh out tartaric acid at a rate of 10 g / L, then slowly add it to the electrolytic cell while stirring until homogeneous; S4. Weigh out malic acid at a rate of 10 g / L, then slowly add it to the electrolytic cell while stirring until homogeneous; S5. Weigh out thiourea at a concentration of 0.5 g / L, dissolve it in 500 mL of deionized water, and then slowly add it to the aforementioned solution; S6. Then add water to 2 L; S7. Let stand for 24 hours.

[0055] The anodizing process for 2219 aluminum alloy is as follows: A1. The workpiece is placed in an alkaline etching solution at 55℃ for 4 minutes and then washed with hot water and cold water in sequence. The alkaline etching solution is prepared with 100g / L sodium hydroxide, 6g / L sodium sulfide and deionized water.

[0056] A2. Immediately immerse the workpiece after alkaline etching in a 30% (v / v) nitric acid brightening solution for 30 seconds, and then wash it with water.

[0057] A3. Place the brightened workpiece in an anodizing electrolyte composed of 100 g / L HEDP, 10 g / L tartaric acid, 10 g / L malic acid and 0.5 g / L thiourea. Apply direct current at 8~10℃ and slowly increase the oxidation voltage to 25 V within 10 min. Then, maintain the voltage for 60 min. After oxidation, thoroughly clean the workpiece with deionized water and dry it with cold air.

[0058] After the above process, an anodized film with a thickness of 37~38 μm can be formed on the surface of 2219 aluminum alloy. The film thickness and hardness are as follows: Figure 4 As shown. Figure 4 The results show that the hard anodized film on the surface of the 2219 aluminum alloy is uniform and continuous, with no obvious "burn-off" defects. The film hardness at different locations is similar (approximately 423~430 HV), all exceeding 400 HV.

[0059] Comparative Example 1: Compared to Example 4, it does not contain organic carboxylic acids. The method is basically the same as the aluminum alloy hard anodizing electrolyte and treatment method provided in Example 4, except that the aluminum alloy hard anodizing electrolyte provided in Comparative Example 1 includes 2 L of anodizing electrolyte containing 100 g / L HEDP and 0.5 g / L thiourea.

[0060] Omitting organic carboxylic acids, organic phosphonic acids (HEDP) alone are insufficient to maintain a wide-range, high-strength pH buffering capacity. During anodizing, the local pH value at the interface drops sharply, exacerbating the chemical dissolution rate of the oxide film by the electrolyte. This results in poor uniformity and low hardness (approximately 312 HV) of the 2219 aluminum alloy hard anodized film. Figure 5 .

[0061] Comparative Example 2: Compared to Example 4, it does not contain organophosphonic acid HEDP. The aluminum alloy hard anodizing electrolyte and treatment method provided in Example 4 are basically the same, except that the aluminum alloy hard anodizing electrolyte provided in Comparative Example 2 includes 2 L of anodizing electrolyte containing 10 g / L tartaric acid, 10 g / L malic acid and 0.5 g / L thiourea.

[0062] Omitting organophosphonic acid (HEDP) causes the electrolyte to lose its in-situ adsorption protection ability and high ion mobility for the oxide film, resulting in poor and uneven film formation on the 2119 aluminum alloy surface. Figure 6 .

[0063] Comparative Example 3: Compared to Example 4, it does not contain organic corrosion inhibitors (thiourea). The method is basically the same as the aluminum alloy hard anodizing electrolyte and treatment method provided in Example 4, except that the aluminum alloy hard anodizing electrolyte provided in Comparative Example 3 includes 2 L of anodizing electrolyte containing 100 g / L HEDP, 10 g / L tartaric acid, and 10 g / L malic acid.

[0064] Omitting the organic corrosion inhibitor (thiourea) results in the loss of selective adsorption and protection of the copper phase active sites, leading to partial discharge and sample burn-off during the anodizing process. This causes the 2219 aluminum alloy oxide film to have a loose structure, surface burn-off defects, and a decrease in film cross-sectional hardness (approximately 263 HV). Figure 7 .

[0065] Comparative Example 4: Compared with Example 4, the organic carboxylic acid: oxalic acid was changed. The aluminum alloy hard anodizing electrolyte and treatment method provided in Example 4 are basically the same, except that the aluminum alloy hard anodizing electrolyte provided in Example 4 includes 2 L of anodizing electrolyte containing 100 g / L HEDP, 10 g / L oxalic acid, and 0.5 g / L thiourea. After replacing the organic carboxylic acid with oxalic acid, the oxalic acid reacts with the Al dissolved at the anode. 3+ It possesses extremely strong complexing ability; at the bottom of the micropores where the oxide film grows, oxalate ions will combine with Al... 3+ The rapid formation of aluminum oxalate complexes causes cracks in the oxide film of 2219 aluminum alloy and a decrease in hardness (approximately 281 HV), such as... Figure 8 .

[0066] Comparative Example 5: Compared with Example 4, the ratio of organic carboxylic acid to lactic acid was changed. The method is basically the same as the aluminum alloy hard anodizing electrolyte and treatment method provided in Example 4, except that the aluminum alloy hard anodizing electrolyte provided in Comparative Example 5 includes 2 L of anodizing electrolyte containing 100 g / L HEDP, 20 g / L lactic acid and 0.5 g / L thiourea.

[0067] Replacing organic carboxylic acids with lactic acid results in a decrease in electrolyte conductivity due to lactic acid's weak acidity and monoprotic nature, leading to increased oxidation voltage and energy consumption. Furthermore, its single-stage buffering capacity cannot effectively suppress drastic pH fluctuations at the interface, resulting in uneven 2219 aluminum alloy film thickness (approximately 50 μm), a porous structure, and reduced hardness (approximately 148 HV). Figure 9 .

[0068] Comparative Example 6: Compared with Example 4, the content of organophosphonic acid was increased. The aluminum alloy hard anodizing electrolyte and treatment method provided in Example 4 are basically the same, except that the aluminum alloy hard anodizing electrolyte provided in Comparative Example 6 includes 2 L of anodizing electrolyte containing 150 g / L HEDP, 10 g / L tartaric acid, 10 g / L malic acid and 0.5 g / L thiourea.

[0069] When the content of organophosphonic acid is too high, its strong complexing and adsorption effect may excessively inhibit the dissolution process of the oxide film, while increasing the electrolyte viscosity. This leads to hindered growth of the 2219 aluminum alloy film, a decrease in thickness (approximately 20 μm), poor film uniformity, and a decrease in film hardness (approximately 317 HV). Figure 10 .

[0070] Comparative Example 7: Compared with Example 4, the content of organic carboxylic acids was increased by 40 g / L. The method is basically the same as the aluminum alloy hard anodizing electrolyte and treatment method provided in Example 4, except that the aluminum alloy hard anodizing electrolyte provided in Comparative Example 7 includes 2 L of anodizing electrolyte containing 100 g / L HEDP, 40 g / L tartaric acid, 40 g / L malic acid and 0.5 g / L thiourea.

[0071] Excessive organic carboxylic acid content disrupts the dynamic balance between film formation and dissolution, resulting in a loose and uneven film structure on the 2219 aluminum alloy, with the thickest part reaching 70 μm, and a decrease in hardness (approximately 126 HV). Figure 11 .

[0072] Comparative Example 8: Compared with Example 4, the type of organic corrosion inhibitor was changed. The aluminum alloy hard anodizing electrolyte and treatment method provided in Example 4 are basically the same, except that: the aluminum alloy hard anodizing electrolyte provided in Comparative Example 8 includes 2 L of anodizing electrolyte containing 100 g / L HEDP, 10 g / L tartaric acid, 10 g / L malic acid, and 0.5 g / L polyethylene glycol 6000. When polyethylene glycol 6000 is selected, its weak adsorption of copper-containing phases makes it difficult to effectively suppress the local dissolution of copper-containing phases during anodizing. This leads to a sharp increase in local current density, overheating, burn-off, and pitting, resulting in pitting on the surface of the 2219 aluminum alloy and uneven film layer. Figure 12 .

[0073] As can be seen from the above embodiments, the present invention provides a method for hard anodizing of high copper content (Cu mass fraction 3.8%~6.8%) aluminum alloys and a special electrolyte thereof. The aluminum alloy hard anodizing electrolyte provided by the present invention comprises 50~100 g / L organophosphonic acid, 10~30 g / L organic carboxylic acid, and 0.5~1.0 g / L organic corrosion inhibitor. The aluminum alloy hard anodizing electrolytic treatment method provided by the present invention is carried out at a low voltage (20~30V), using a one-step or step-by-step gradual increase, with an oxidation time of 40~90 min. It can prepare a highly dense hard oxide film with a thickness of 20~50 μm and a hardness exceeding 400 HV on the surface of various high copper content aluminum alloys such as 2024, 2A12, and 2219.

[0074] 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. An aluminum alloy hard anodizing electrolyte, characterized in that, The invention comprises organophosphonic acids, organic carboxylic acids, and organic corrosion inhibitors; the organophosphonic acids include one or more of aminotrimethylenephosphonic acid, hydroxyethylidene diphosphonic acid, and ethylenediaminetetramethylenephosphonic acid, and the mass concentration of the organophosphonic acid is 50-100 g / L; the organic carboxylic acids include one or more of tartaric acid, malic acid, and citric acid, and the mass concentration of the organic carboxylic acid is 10-30 g / L; the organic corrosion inhibitors include one or more of thiourea, benzotriazole, and methylbenzotriazole, and the mass concentration of the organic corrosion inhibitors is 0.5-1.0 g / L.

2. A method for electrolytic hard anodizing of aluminum alloys, characterized in that, Includes the following steps: (1) The aluminum alloy workpiece is subjected to alkaline etching treatment and then washed with water to obtain the first treated workpiece; (2) The first processed workpiece is placed in the brightening liquid for brightening treatment, and then washed with water to obtain the second processed workpiece; (3) The second processed workpiece is placed in the aluminum alloy hard anodizing electrolyte of claim 1 for hard anodizing treatment, and then washed and dried in sequence.

3. The method for hard anodizing electrolytic treatment of aluminum alloys according to claim 2, characterized in that, The mass fraction of Cu in the aluminum alloy workpiece is 3.8-6.8%.

4. The method for electrolytic hard anodizing of aluminum alloys according to claim 2 or 3, characterized in that, The aluminum alloy workpiece includes 2024, 2A12 or 2219.

5. The method for electrolytic hard anodizing of aluminum alloys according to claim 2, characterized in that, The alkaline etching treatment is carried out using an alkaline etching solution; the alkaline etching solution comprises the following components at mass concentrations: 60~100 g / L sodium hydroxide and 5~6 g / L sodium sulfide.

6. The method for electrolytic hard anodizing of aluminum alloys according to claim 2 or 5, characterized in that, The conditions for the alkaline etching treatment include: a treatment temperature of 50~60℃ and a treatment time of 3~5 min.

7. The method for hard anodizing electrolytic treatment of aluminum alloys according to claim 2, characterized in that, The light-emitting liquid is a nitric acid solution, and the volume concentration of HNO3 in the nitric acid solution is 30-50%; the light-emitting treatment time is 30-60 s.

8. The method for hard anodizing electrolytic treatment of aluminum alloys according to claim 2, characterized in that, The conditions for the hard anodizing treatment include: a temperature of 0~10℃, hard anodizing treatment using a DC constant voltage method, and an oxidation voltage of 20~30 V.

9. The method for electrolytic hard anodizing of aluminum alloys according to claim 2 or 8, characterized in that, The hard anodizing process includes a first processing method or a second processing method; the first processing method is: increasing the voltage to 20-30 V under 5-10 min conditions, and then maintaining 20-30 V for 30-70 min; the second processing method is: sequentially increasing the voltage to the first gradient voltage, ..., the nth gradient voltage for processing, n≥2, the first gradient voltage to the nth gradient voltage are independently 20-30 V, and the first gradient voltage to the nth gradient voltage increase sequentially, and the total time of the second processing method is ≤90 min.

10. The method for hard anodizing electrolytic treatment of aluminum alloys according to claim 2, characterized in that, Step (3) A hard anodized film is prepared on the surface of the aluminum alloy workpiece; the thickness of the hard anodized film is 20~50 μm, and the hardness of the hard anodized film is ≥400 HV.

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