Black anodic oxidation treatment process for aerospace aluminum alloy fastener

Abstract

The invention belongs to the technical field of aerospace fastener processing, and particularly relates to an aerospace aluminum alloy fastener black anodic oxidation treatment process which sequentially comprises the following steps: S1, pretreatment; s2, anodic oxidation treatment is conducted, specifically, the fastener subjected to pretreatment is placed in an anodic oxidation electrolyte to be subjected to anodic oxidation; s3, dyeing treatment is conducted, specifically, the fastener subjected to anodic oxidation is placed in a black dyeing solution to be dyed; and S4, sealing treatment is conducted, specifically, the dyed fastener is placed in sealing liquid to be sealed. According to the invention, the growth defect of the oxidation film is inhibited from the source through the composite additive system, and the optimized dyeing process is combined, so that the uniformity of the film layer and the sufficient and firm adsorption of the dye are ensured, and the surface color of the final product is uniform and black without any irregular white points.

Description

TECHNICAL FIELD

[0001] The present application relates to an aerospace aluminum alloy fastener black anodic oxidation process, belonging to the field of aerospace fastener processing technology. BACKGROUND

[0002] In the field of aerospace, aluminum alloy fasteners are widely used for structural connection of various aircraft. Due to the long-term exposure of aerospace vehicles to humid, salt spray, fretting friction, space radiation and atomic oxygen corrosion, etc. Extreme harsh environment, high requirements are put forward for the surface performance of fasteners. In order to ensure the service safety and reliability of aerospace vehicles, surface treatment is required for aluminum alloy fasteners, which can improve the corrosion resistance, wear resistance and specific thermal control and anti-reflection function of the material under the premise of as little as possible affecting the mechanical properties of the material. Black anodic oxidation process is a key surface technology to meet the above requirements. After the process, a dense oxide film is generated on the surface of the fastener, which can effectively isolate the substrate from the contact with the corrosive medium in the corrosive environment, greatly improving the corrosion resistance; through surface hardening, the wear resistance is significantly improved, which can resist scratches and wear caused by installation and removal and fretting friction, thereby ensuring the thread integrity and avoiding torque changes or connection loosening caused by wear; In the space environment, its dark surface can maximize the absorption of visible light to avoid reflected light interference with optical instruments and sensitive equipment, ensuring observation and measurement accuracy; at the same time, the oxide film also has good resistance to atomic oxygen, ultraviolet radiation and micro-meteoroid erosion, which helps to prolong the service life of on-orbit components.

[0003] However, this technology has long been plagued by a technical problem that has not been effectively solved in actual mass production: after black anodic oxidation treatment, irregularly distributed white spots (referred to as "white spots") often appear on the surface of aluminum alloy fasteners. This defect not only affects the appearance of the product, but also may potentially damage the continuity and density of the oxide film, thereby adversely affecting corrosion resistance, wear resistance and anti-reflection functions, ultimately threatening the safety and reliability of the fastener in use. The existence of this problem directly leads to a decrease in product pass rate and an increase in production cost, seriously restricting the realization of standardization, serialization and batch production of aerospace fasteners.

[0004] Therefore, it is urgent to develop a process method that can effectively eliminate or reduce this defect to improve the consistency and reliability of product quality and meet the urgent needs of the aerospace field for high-performance fasteners. SUMMARY

[0005] The present application aims at the above-mentioned defects of the prior art, and provides an aerospace aluminum alloy fastener black anodic oxidation treatment process, which can effectively inhibit film layer growth defects, ensure dyeing uniformity, and finally obtain an oxidation film with no white spots, uniform black color, excellent corrosion resistance and wear resistance, and significantly improve product qualification rate and reliability by optimizing the formula and process parameters of each link of the system, especially the anodic oxidation electrolyte.

[0006] The technical solution of the present application to solve the above technical problems is as follows: An aerospace aluminum alloy fastener black anodic oxidation treatment process, comprising the following steps in sequence: S1, pretreatment: oil removal, alkali etching and lightening treatment are performed on the aluminum alloy fastener; S2, anodic oxidation treatment: the fastener pretreated in step S1 is placed in an anodic oxidation electrolyte for anodic oxidation; S3, dyeing treatment: the fastener after anodic oxidation in step S2 is placed in a black dyeing solution for dyeing; S4, sealing treatment: the fastener after dyeing in step S3 is placed in a sealing solution for sealing; The anodic oxidation electrolyte comprises the following components: sulfuric acid 150-200 g / L, aluminum sulfate 1-3 g / L, 2-mercaptobenzimidazole 0.1-0.2 g / L, polyaspartic acid sodium 0.5-1 g / L, sulfosalicylic acid 10-15 g / L, sodium gluconate 5-10 g / L, polyether modified polysiloxane 0.1-0.3 g / L, sodium toluene-4-sulfonate 0.1-0.3 g / L, and the rest is deionized water.

[0007] Further, in step S1, the oil removal is soaked in acetone for 5-10 min, the alkali etching is performed in a NaOH solution with a concentration of 5-10 g / L, and the immersion is performed at room temperature for 60-80 s; the lightening is performed in a nitric acid solution with a concentration of 450-500 g / L, and the immersion is performed at room temperature for 1-3 min.

[0008] The pretreatment can better remove natural oxidation film and pollutants such as oil stains by precisely controlling the alkali etching concentration and time, and can avoid microcosmic unevenness caused by over-etching; the nitric acid lightening can remove the remaining dust after alkali etching, and obtain a clean and activated surface.

[0009] Further, in step S2, the process conditions of the anodic oxidation treatment are as follows: electrolyte temperature 15-20℃, step-by-step voltage rising method, target voltage 15-20 V, oxidation at the target voltage for 30-40 min; the electrolyte is continuously air stirred during the anodic oxidation process.

[0010] Further, in step S2, the stepwise voltage boosting method comprises: firstly, uniformly increasing the voltage from 0 V to 10 V within 5-8 min, keeping at 10 V for 3 min, and then increasing to the target voltage within 3-5 min.

[0011] Further, in step S3, the black dyeing solution comprises the following components: 8-15 g / L of 1:2 type metal complex black dye, 1-3 g / L of citric acid, 2-4 g / L of sodium dihydrogen citrate, 0.3-0.5 g / L of fatty alcohol polyoxyethylene ether phosphate, 1-2 g / L of N-lauroylsarcosine sodium, and the rest is deionized water.

[0012] Further, in step S3, the dyeing conditions are as follows: temperature 50-60 DEG C, time 20-30 min, and pH value 4.5-5.5.

[0013] Further, in step S4, the sealing solution comprises the following components: 0.5-0.8 g / L of nickel acetate, 0.2-0.5 g / L of titanyl sulfate, 3-6 g / L of boric acid, 1-2 g / L of ammonium citrate, and the rest is deionized water.

[0014] Further, in step S4, the sealing conditions are as follows: temperature 70-80 DEG C, time 15-20 min, and pH value 5.5-6.5.

[0015] Further, in step S1, after the alkali etching and lightening, water washing is performed for 0.5-3 min; and before the anodic oxidation treatment of step S2, drying is performed.

[0016] Compared with the prior art, the present application has the following beneficial effects: The present application can inhibit the growth defects of the oxide film from the source by the composite additive system, and can ensure the uniformity of the film layer and the sufficient and firm adsorption of the dye by the optimized dyeing process, so that the final product has uniform and black color and no irregular white spots.

[0017] The black anodic oxide film obtained by the present application is dense, has high hardness and good adhesion, has excellent neutral salt spray corrosion resistance, wear resistance, stable low solar absorption ratio and low infrared emissivity, and fully meets the use requirements in extreme environments of aerospace.

[0018] The present application adopts a nickel-titanium collaborative sealing system, reduces the amount of traditional nickel salt under the premise of ensuring the sealing effect, has good synergy in each process, has high production repeatability, greatly improves the one-time inspection qualified rate of the product, and is suitable for standardized and batch production. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Figure 1 is a local surface morphology diagram of the aluminum alloy fastener of embodiment 1 of the present application; Figure 2 This is a partial surface morphology diagram of the aluminum alloy fastener in Embodiment 2 of the present invention; Figure 3 This is a partial surface morphology diagram of the aluminum alloy fastener in Embodiment 3 of the present invention; Figure 4 This is the surface water film state of the aluminum alloy fastener of Comparative Example 1 of the present invention after pretreatment cleaning; Figure 5 This is a photograph of the aluminum alloy fastener of Comparative Example 2 of the present invention during the pretreatment and cleaning process; Figure 6 This is a surface morphology diagram of the aluminum alloy fastener of Comparative Example 2 of the present invention after pretreatment and cleaning. Figure 7 This is a surface morphology diagram of the aluminum alloy fastener of Embodiment 1 of the present invention after pretreatment and cleaning. Figure 8 This is a partial surface morphology diagram of the aluminum alloy fastener of Comparative Example 3 of the present invention; Figure 9 This is a partial surface morphology diagram of the aluminum alloy fastener in Comparative Example 4 of the present invention; Figure 10 Metallographic image of the film thickness at the center of the aluminum alloy fastener in Comparative Example 5 of this invention; Figure 11 Metallographic image of the film thickness at the edge of the aluminum alloy fastener in Comparative Example 5 of this invention; Figure 12 This is a partial surface morphology diagram of the aluminum alloy fastener of Comparative Example 6 of the present invention; Figure 13 This is a partial surface morphology diagram of the aluminum alloy fastener of Comparative Example 7 of the present invention; Figure 14 This is a partial surface morphology diagram of the aluminum alloy fastener of Comparative Example 8 of the present invention; Figure 15 This is a partial surface morphology diagram of the aluminum alloy fastener of Comparative Example 9 of the present invention; Figure 16 This is a partial surface morphology diagram of the aluminum alloy fastener of Comparative Example 10 of the present invention; Figure 17 This is a partial surface morphology diagram of the aluminum alloy fastener of Comparative Example 11 of the present invention; Figure 18 This is a partial surface morphology diagram of the aluminum alloy fastener of Comparative Example 12 of the present invention; Figure 19 This is a partial surface morphology image of the aluminum alloy fastener of Comparative Example 14 of the present invention after 5 hours of neutral salt spray testing. Figure 20 This is a partial surface morphology image of the aluminum alloy fastener of Embodiment 2 of the present invention after 96 hours of neutral salt spray testing. DETAILED DESCRIPTION

[0020] The principles and features of the present application are described below in conjunction with the accompanying drawings, in which the examples are used to explain the present application and are not intended to limit the scope of the present application.

[0021] It should be particularly noted that the parts processed in the embodiments and comparative examples of the present application are specific part numbers in the field of aerospace. The specific three-dimensional shape, size and internal structure of the parts are not the technical points of the present application. The protection scope of the present application lies in the surface treatment process itself, which is suitable for various types of aerospace aluminum alloy fasteners (such as bolts, nuts, washers, clamps, etc.) that need to be subjected to high-performance black anodizing. In order to clearly show the process effect, only the local morphology photos of the key surfaces of the parts after being treated by different processes or the local state photos after testing are shown in the drawings. This display method is sufficient to prove the technical effects of the present application and does not affect the understanding and implementation of the present application by those skilled in the art.

[0022] Example 1 (1) Pretreatment: a. The aluminum alloy fastener was placed in acetone for 10 min to remove oil; b. Immersed in a 10 g / L NaOH solution at room temperature for 80 s; c. Washed with flowing water at room temperature for 1 min; d. Lightened in a 500 g / L nitric acid solution for 3 min; e. After rinsing with deionized water for 1 min, dried and ready for anodizing treatment; The part photo after completing the pretreatment cleaning in this example is shown in Figure 7 .

[0023] (2) Anodizing treatment: The electrolyte used for anodizing treatment was prepared according to the formulation shown in Table 1 below: Table 1 Composition and ratio of electrolyte for Example 1

[0024] a. The aluminum alloy fastener was clamped on a special tooling, the structure of which was not specifically limited, and the tooling was required to be clean and tidy without film layer, and could stably fix the aluminum alloy fastener and the contact point with the part was the inner wall of the product, so as to avoid falling and clamping injury; b. Start the compressed air to continuously stir the electrolyte for 2 min; c. Warm the electrolyte to 20℃; d. Set the target voltage to 20V, and use the step-up voltage method to slowly and uniformly rise from 0V to 10V within 8 min; keep at 10V for 3 min; then rise to the target voltage within 5 min, and oxidize at 20V for 40 min; e. After the anodizing treatment, the parts are taken out and rinsed in flowing cold water; f. The parts are taken off the fixture and immersed in deionized water for 3 min for cleaning before dyeing treatment.

[0025] (3) Dyeing treatment: The dyeing solution used in the dyeing treatment is prepared according to the following formula: Table 2 Component ratio of dyeing solution in Example 1

[0026] a. The parts after anodizing are immediately immersed in the above dyeing solution, the temperature of the dyeing solution is set to 60°C, and the dyeing is performed for 30 min, with the pH maintained at 5.5.

[0027] b. After dyeing, the parts are immediately rinsed in flowing deionized water for 4 min before sealing treatment.

[0028] (4) Sealing treatment: The sealing solution used in the sealing treatment is prepared according to the following formula: Table 3 Component ratio of sealing solution in Example 1

[0029] a. The parts after dyeing are immediately immersed in the above sealing solution, the temperature of the sealing solution is set to 80°C, and the sealing is performed for 20 min, with the pH maintained at 6.5.

[0030] b. After the sealing treatment, the parts are washed with deionized water and dried with hot air.

[0031] The local part of the aluminum alloy product after black anodizing treatment in this example is shown in Figure 1 .

[0032] Example 2 (1) Pretreatment: a. The aluminum alloy fastener is placed in acetone for 7 min to remove oil; b. It is immersed in an 8 g / L NaOH solution at room temperature for 70 s; c. It is washed in flowing water at room temperature for 0.8 min; d. It is lightened in a 475 g / L nitric acid solution for 2 min; e. After rinsing in deionized water for 0.8 min, it is dried and ready for anodizing treatment.

[0033] (2) Anodizing treatment: The electrolyte used in the anodizing treatment is prepared according to the following formula: Table 4 Component ratio of electrolyte in Example 2

[0034] a. The aluminum alloy fastener is clamped on a special tool, the tool should be clean and free of film, and the contact point with the part should be the inner wall of the product to avoid dropping and clamping injury; b. Turn on the compressed air to continuously stir the electrolyte for 1.5 min; c. The electrolyte is heated to 18°C; d. Set the target voltage to 18V, use the step-up method, slowly and uniformly rise from 0V to 10V within 6min; keep at 10V for 3min; then rise to the target voltage within 4min, and oxidize at 18V for 35min; e. After the anodic oxidation treatment is completed, the part is taken out and rinsed in flowing cold water; f. The part is removed from the tool and soaked in deionized water for 2min.

[0035] (3) Dyeing treatment: The dyeing liquid used in the dyeing treatment is prepared according to the following formula: the dyeing liquid is prepared according to the formula shown in Table 5 below: Table 5 Component ratio of dyeing liquid of Example 2

[0036] a. Immediately after anodic oxidation, the part is immersed in the above-mentioned dyeing liquid, the temperature of the dyeing liquid is set to 55°C, the time is 25min, and the pH is kept at 5.0.

[0037] b. After dyeing, immediately rinse the part in flowing deionized water for 3min, and then perform sealing treatment.

[0038] (4) Sealing treatment: The sealing liquid used in the sealing treatment is prepared according to the following formula: Table 6 Component ratio of sealing liquid of Example 2

[0039] a. Immediately after dyeing, the part is immersed in the above-mentioned sealing liquid, the temperature of the sealing liquid is 75°C, the time is 18min, and the pH is kept at 6.0.

[0040] b. After the sealing treatment is completed, the part is washed with deionized water and hot air dried.

[0041] The local part of the aluminum alloy product after black anodic oxidation treatment in this example is shown in Figure 2 .

[0042] Example 3 (1) Pretreatment: a. The aluminum alloy fastener is placed in acetone for 5min to remove oil; b. Immersion in 5 g / L NaOH solution at room temperature for 60 s; c. Water washing at room temperature for 0.5 min; d. Light-out in 450 g / L nitric acid solution for 1 min; e. Deionized water rinsing for 0.5 min, and then drying, waiting for anodic oxidation treatment.

[0043] (2) Anodic oxidation treatment: The electrolyte used for anodic oxidation treatment was prepared according to the following Table 7: Table 7 Component ratio of electrolyte for Example 3

[0044] a. The aluminum alloy fastener was clamped on a special tool, the tool should be clean and tidy without film layer, and the contact point with the part should be the inner wall of the product to avoid falling and clamping injury; b. Start the compressed air to continuously stir the electrolyte, and stir for 1 min; c. The electrolyte was heated to 15°C; d. The target voltage was set to 15V, and the step-up method was used, slowly and uniformly rising from 0V to 10V within 5 min; keeping at 10V for 3 min; then rising to the target voltage within 3 min, and oxidizing at 15V for 30 min; e. After the anodic oxidation treatment was completed, the part was taken out and rinsed in flowing cold water; f. The part was taken off from the tool and soaked and cleaned in deionized water for 1 min.

[0045] (3) Dyeing treatment: The dyeing solution used for dyeing treatment was prepared according to the following Table 8: Table 8 Component ratio of dyeing solution for Example 3

[0046] a. The anodized part was immediately immersed in the above dyeing solution, the dyeing solution temperature was set to 50°C, the time was 20 min, and the pH was kept at 4.5.

[0047] b. After dyeing, the part was immediately cleaned in flowing deionized water for 2 min, and then closed treatment was performed.

[0048] (4) Sealing treatment: The sealing solution used for sealing treatment was prepared according to the following Table 9: Table 9 Component ratio of sealing solution for Example 3

[0049] a. After dyeing, the parts are immediately immersed in the above-mentioned sealing solution, the sealing solution temperature is 70°C, the time is 15 min, and the pH is kept at 5.5.

[0050] b. After the sealing treatment is completed, the parts are washed with deionized water and hot air dried.

[0051] The local surface of the aluminum alloy product after the black anodic oxidation treatment of the present example Figure 3 .

[0052] Comparative Example 1 Compared with Example 1, the anodic oxidation treatment, dyeing treatment and sealing treatment process of the present comparative example remain unchanged, the difference is that in the pretreatment process, the concentration of NaOH used is 3 g / L, and the immersion time is 50 s.

[0053] The surface of the aluminum alloy product after the treatment of the present comparative example is not completely cleaned of oil stains, resulting in that the water film continuity test is unqualified, and the water film is broken after being taken out of the deionized water and gathered into drops on the surface of the product (see Figure 4 ).

[0054] Comparative Example 2 Compared with Example 1, the anodic oxidation treatment, dyeing treatment and sealing treatment process of the present comparative example remain unchanged, the difference is that in the pretreatment process, the concentration of NaOH used is 20 g / L, and the immersion time is 90 s.

[0055] In the pretreatment process of the present comparative example, the surface of the aluminum alloy product reacts violently, a large amount of tiny bubbles and irritating odor are generated (see Figure 5 ).

[0056] The part photograph after the cleaning of the present comparative example is shown in Figure 6 , compared with the part photograph after the cleaning of Example 1 shown in Figure 7 , a large number of tiny corrosion pits appear on the surface of the part of the present comparative example, and the roughness significantly increases.

[0057] Comparative Example 3 Compared with Example 3, the pretreatment, dyeing treatment and sealing treatment process of the present comparative example remain unchanged, the difference is that “2-mercaptobenzimidazole” is not added in the anodic oxidation process of the present comparative example.

[0058] In the film forming process of the present comparative example, selective dissolution occurs in the intermetallic compound enrichment area such as Al2CuMg, due to the existence of local film layer defects, the defect area cannot adsorb dye, so that white spots are formed after dyeing treatment which are difficult to eliminate (see Figure 8 ).

[0059] Comparative Example 4 Compared with Example 1, the pretreatment, staining and blocking processes of this comparative example remained unchanged. The difference was that the content of the component "sodium polyaspartate" was increased from 1 g / L to 2 g / L during the anodizing process.

[0060] The porosity of the comparative oxide film is significantly reduced, making it difficult for dye molecules to enter and fill these excessively small pores. This results in insufficient total adsorption of dye, and the film appears grayish-black (see [reference]). Figure 9 ).

[0061] Comparative Example 5 Compared with Example 3, the pretreatment, dyeing and sealing processes of this comparative example remain unchanged. The difference is that "polyether-modified polysiloxane" was not added during the anodizing process of this comparative example.

[0062] The electrolyte in this comparative example has reduced wettability, making it difficult to penetrate the microporous structure and exacerbating the edge effect. Ultimately, this results in a film thickness at the edge of the same part being greater than that in the center area. Figure 10 This is a metallographic image of the film thickness at the center of the aluminum alloy fastener obtained through comparative processing. Figure 10 As can be seen, the film thickness at the center of the aluminum alloy fastener obtained in this comparative example is approximately 3.3 μm. Figure 11 Metallographic images of the film thickness at the edge of the aluminum alloy fastener obtained through comparative processing are shown below. Figure 11 As can be seen, the film thickness at the edge of the aluminum alloy fastener obtained by this comparative treatment is approximately 8.0 μm.

[0063] Comparative Example 6 Compared with Example 1, the pretreatment, staining and blocking processes of this comparative example remained unchanged. The difference was that "sodium pyromellitic sulfonate" was not added during the anodizing process of this comparative example.

[0064] This comparative example did not include sodium pyromellitic sulfonate. The sulfuric acid enhanced the dissolving effect on the oxide film, resulting in "over-corrosion" of the nanoscale pores, leading to enlarged and uneven pores. During dyeing, the dye easily migrated and accumulated unevenly within the pores, resulting in patches of varying color intensity on the film (see [reference]). Figure 12 ).

[0065] Comparative Example 7 Compared with Example 1, the pretreatment, staining and blocking processes of this comparative example remained unchanged. The difference was that the amount of sodium pyromellitic sulfonate was increased from 0.3 g / L to 2 g / L during the anodizing process of this comparative example.

[0066] The content of "sodium benzene tetra sulfonate" in this comparative example is increased to 2g / L, which excessively inhibits the dissolution of the oxide film, seriously destroys the balance of "formation-dissolution", makes the film layer too thin, and the film hole is extremely small, so that the dye molecules cannot enter the film hole, and almost no dye can be absorbed (see Figure 13 ).

[0067] Comparative Example 8 Compared with Example 2, the pretreatment, dyeing treatment and sealing treatment processes of the comparative example remain unchanged, the difference is that in the anodizing process of the comparative example, the concentration of "sulfosalicylic acid" is changed from 12g / L to 5g / L.

[0068] The content of sulfosalicylic acid in this comparative example is insufficient to complex all aluminum ions in the solution, resulting in partial hydrolysis of aluminum ions to form Al(OH)3 and other insoluble precipitates, which are adsorbed and deposited on the surface of the part, hindering the current conduction and oxidation reaction in the local area, resulting in inconsistent film hole structure and different dye adsorption capacity, resulting in cloud-like patches of different colors after dyeing (see Figure 14 ).

[0069] Comparative Example 9 Compared with Example 2, the pretreatment, dyeing treatment and sealing treatment processes of the comparative example remain unchanged, the difference is that in the anodizing process of the comparative example, the concentration of "sulfosalicylic acid" is changed from 12g / L to 20g / L.

[0070] The concentration of sulfosalicylic acid in this comparative example is too high, resulting in a loose, porous, rough film structure, and poor light reflection after dyeing, resulting in a lack of gloss on the black color, which is in a matte state (see Figure 15 ).

[0071] Comparative Example 10 Compared with Example 2, the pretreatment, dyeing treatment and sealing treatment processes of the comparative example remain unchanged, the difference is that in the anodizing process of the comparative example, the "step-by-step voltage" is changed to "linear voltage", that is, starting from 0V, increasing by 1V every min.

[0072] This comparative example uses linear voltage, compared with the step-by-step voltage of the embodiment of the present application, it cannot provide a "formation-stabilization-regrowth" buffer process for the oxide film, resulting in unstable current density distribution, uneven film layer structure and pore size, and white spots on the film layer after dyeing (see Figure 16 ).

[0073] Comparative Example 11 The pretreatment, anodic oxidation treatment and sealing treatment processes of the comparative example are the same as those of Example 3, except that no "fatty alcohol polyoxyethylene ether phosphate" is added in the dyeing process of the comparative example.

[0074] Due to the absence of "fatty alcohol polyoxyethylene ether phosphate" in the comparative example, the dispersion of the solution becomes poor, and the dye particles aggregate to become large. These large particles cannot easily enter the micropores of the oxidation film, resulting in a decrease in the actual adsorption of the dye. On the other hand, the wetting performance of the solution becomes poor, and the effective dye molecules have fewer opportunities to contact the pores of the oxidation film. The dye adsorbed per unit time does not reach saturation, and the combined result is that the film layer is dark and the blackness is insufficient (see Figure 17 ).

[0075] Comparative Example 12 The pretreatment, anodic oxidation treatment and sealing treatment processes of the comparative example are the same as those of Example 2, except that no "sodium N-lauroyl sarcosinate" is added in the dyeing process of the comparative example.

[0076] Due to the absence of "sodium N-lauroyl sarcosinate" in the comparative example, the dyeing solution lacks a slow-dyeing effect, and the dye is quickly adsorbed at the pore sites. The operation window is extremely narrow, and if the time is slightly longer, the film layer will appear mottled and uneven (see Figure 18 ).

[0077] Comparative Example 13 The pretreatment, anodic oxidation treatment and sealing treatment processes of the comparative example are the same as those of Example 2, except that the concentration of "sodium N-lauroyl sarcosinate" is increased from 1.5 g / L to 3 g / L in the dyeing process of the comparative example.

[0078] During the operation process, it is found that the concentration of "sodium N-lauroyl sarcosinate" is increased to 3 g / L in the comparative example, and a large amount of foam appears in the dyeing solution. The process operability becomes poor, the dyeing time is prolonged, and the production efficiency is reduced.

[0079] Comparative Example 14 The pretreatment, anodic oxidation treatment and dyeing processes of the comparative example are the same as those of Example 2, except that no "titanyl sulfate" is added in the sealing process of the comparative example.

[0080] Neutral salt spray tests are performed on the parts treated in Example 2 and the comparative example, respectively. The specific operation is as follows: the parts are placed in a 5% sodium chloride salt spray chamber at 35°C for 96 h, and the parts are periodically checked for rusting.

[0081] Since the present comparative example does not add "titanium oxysulfate", it cannot cooperate with nickel ions, the blocking effect is greatly reduced, and the corrosion medium can easily penetrate the barrier to attack the aluminum matrix. After the neutral salt spray test is carried out for 5 hours, the part film layer of the present comparative example appears corrosion white spot (see Figure 19 ).

[0082] While the part of example 2 still has a complete part film layer after the neutral salt spray test, and no corrosion occurs (see Figure 20 ).

[0083] In summary, the present application successfully solves the "white spot" problem of aerospace aluminum alloy fasteners by a complete and cooperative process system, especially the innovative anodic oxidation electrolyte formula.

[0084] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A black anodizing process for aerospace aluminum alloy fasteners, characterized in that, The steps are as follows: S1. Pretreatment: Degreasing, alkaline etching and brightening treatment of aluminum alloy fasteners; S2, Anodizing treatment: The fasteners pretreated in step S1 are placed in anodizing electrolyte for anodizing; S3. Dyeing treatment: The fasteners anodized in step S2 are placed in a black dyeing solution for dyeing. S4. Sealing treatment: Place the fasteners dyed in step S3 into a sealing solution for sealing. The anodic oxidation electrolyte comprises the following components: sulfuric acid 150–200 g / L, aluminum sulfate 1–3 g / L, 2-mercaptobenzimidazole 0.1–0.2 g / L, sodium polyaspartate 0.5–1 g / L, sulfosalicylic acid 10–15 g / L, sodium gluconate 5–10 g / L, polyether-modified polysiloxane 0.1–0.3 g / L, sodium pyromellitic sulfonate 0.1–0.3 g / L, and the balance being deionized water.

2. The black anodizing process for aerospace aluminum alloy fasteners according to claim 1, characterized in that, In step S1, the degreasing is carried out by soaking in acetone for 5-10 minutes, the alkaline etching is carried out in a NaOH solution with a concentration of 5-10 g / L and immersion at room temperature for 60-80 seconds, and the brightening is carried out in a nitric acid solution with a concentration of 450-500 g / L and immersion at room temperature for 1-3 minutes.

3. The black anodizing process for aerospace aluminum alloy fasteners according to claim 1, characterized in that, In step S2, the process conditions for the anodizing treatment are as follows: electrolyte temperature 15-20°C, step voltage ramping method, target voltage 15-20 V, oxidation at the target voltage for 30-40 min; continuous air stirring of the electrolyte during the anodizing process.

4. The black anodizing process for aerospace aluminum alloy fasteners according to claim 3, characterized in that, In step S2, the stepped voltage increase method includes: first, increasing the voltage from 0 V to 10 V at a constant rate within 5 to 8 minutes, maintaining it at 10 V for 3 minutes, and then increasing it to the target voltage within 3 to 5 minutes.

5. The black anodizing process for aerospace aluminum alloy fasteners according to claim 1, characterized in that, In step S3, the black dyeing solution contains the following components: 8-15 g / L of 1:2 type metal complex black dye, 1-3 g / L of citric acid, 2-4 g / L of sodium dihydrogen citrate, 0.3-0.5 g / L of fatty alcohol polyoxyethylene ether phosphate, 1-2 g / L of N-lauroyl sarcosinate sodium, and the balance being deionized water.

6. The black anodizing process for aerospace aluminum alloy fasteners according to claim 5, characterized in that, In step S3, the staining conditions are: temperature 50-60℃, time 20-30 min, pH 4.5-5.

5.

7. The black anodizing process for aerospace aluminum alloy fasteners according to claim 1, characterized in that, In step S4, the sealing solution contains the following components: nickel acetate 0.5-0.8 g / L, titanium oxysulfate 0.2-0.5 g / L, boric acid 3-6 g / L, ammonium citrate 1-2 g / L, and the balance is deionized water.

8. The black anodizing process for aerospace aluminum alloy fasteners according to claim 7, characterized in that, In step S4, the sealing conditions are: temperature 70-80℃, time 15-20 min, and pH value 5.5-6.

5.

9. The black anodizing process for aerospace aluminum alloy fasteners according to claim 1 or 2, characterized in that, In step S1, after alkaline etching and brightening, the sample is washed with water for 0.5 to 3 minutes; it is dried before the anodizing treatment in step S2.

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