An anodizing pretreatment agent, its preparation method and application, and an anodizing method for 70 series aluminum alloys.

Abstract

This invention relates to the field of metal surface treatment technology, specifically to an anodizing pretreatment agent, its preparation method and application, and an anodizing method for 70 series aluminum alloys. In the anodizing pretreatment agent provided by this invention, nitric acid and / or sulfuric acid provide the basic acidity for descaling / cleaning the 70 series aluminum alloy, fluorides are used to activate the 70 series aluminum alloy surface and promote oxide removal, and Fe is introduced... 3+ The oxidation-assisted solution promotes the removal of residues on the surface of 7-series aluminum alloys, introduces organic carboxylate complexation to inhibit and reduce the redeposition of dissolved metal ions, thus reducing the formation of black and gray residues, and, in conjunction with a wetting agent, improves the processing uniformity of complex structural parts. The anodizing pretreatment agent provided by this invention offers a wider operating window and a more stable, uniform, and low-defect-rate pretreatment effect for the anodizing pretreatment of 7-series aluminum alloys, improving the consistency of anodized appearance and corrosion resistance, and significantly shortening the pretreatment process for 7-series aluminum alloys. It is also suitable for the pretreatment of complex parts.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, specifically to an anodizing pretreatment agent and its preparation method and application, and an anodizing method for 7-series aluminum alloys. Background Technology

[0002] 7-series aluminum alloys (such as 7075 and 7050) are widely used in aerospace, transportation, and high-end structural components due to their high strength and high specific strength. Anodizing treatment can significantly improve their corrosion resistance and surface stability. However, 7-series aluminum alloys have a high content of alloying elements such as Zn and Cu. If the pretreatment is not done properly, an enriched layer can easily form on the surface, leaving residual black and gray residues and inducing localized pitting corrosion, which in turn leads to uneven oxide film appearance, mottled appearance, and fluctuations in corrosion resistance. Therefore, the pre-anodizing chemical treatment process becomes a key factor affecting the final appearance and performance.

[0003] In existing technologies, acidic descaling / decontamination systems are commonly used before anodizing. Typical processes include nitric acid combined with fluorides to remove oxide scale and residues. Some literature also uses acid pickling methods such as nitric acid-iron salt systems for materials like 7075 to improve subsequent surface conditions. However, for 7-series aluminum alloys, these treatment solutions often suffer from a narrow process window, and the solutions age due to metal ion accumulation during long-term use, further exacerbating fluctuations in appearance quality. Therefore, achieving a stable, uniform surface with a low defect rate in the pre-anodizing treatment of 7-series aluminum alloys, and broadening the pre-anodizing process window, remains a pressing technical challenge. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide an anodizing pretreatment agent, its preparation method and application, and an anodizing method for 70 series aluminum alloys. The anodizing pretreatment agent provided by this invention can provide a wider operating window and a more stable, uniform, and low-defect-rate pretreatment effect for the anodizing pretreatment of 70 series aluminum alloys.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides an anodizing pretreatment agent comprising: an acidic main system of 10-35 vol%, an oxidation co-solvent of 0.5-8 g / L, a fluorinated activator of 0.2-3 g / L, a complexation inhibitor of 0.2-8 g / L, a wetting agent of 0.05-0.5 g / L, and water; wherein the acidic main system comprises nitric acid and / or sulfuric acid; the oxidation co-solvent comprises ferric salts; the fluorinated activator comprises fluorides, the concentration of which is calculated as fluoride ions; and the complexation inhibitor comprises organic carboxylates.

[0006] Preferably, the trivalent ferric salt includes one or more of ferric sulfate, ferric nitrate, and ferric chloride.

[0007] Preferably, the fluoride includes one or more of ammonium hydrofluoride, ammonium fluoride, and sodium fluoride.

[0008] Preferably, the organic carboxylate includes citrate and / or gluconate.

[0009] Preferably, the wetting agent comprises a nonionic surfactant.

[0010] The present invention also provides a method for preparing the anodizing pretreatment agent described in the above technical solution, comprising the following steps: mixing an acidic host system, an oxidation cosolvent, a fluorine-containing activator, a complexation inhibitor, a wetting agent and water to obtain the anodizing pretreatment agent.

[0011] The present invention also provides the application of the anodizing pretreatment agent described in the above technical solution or the anodizing pretreatment agent prepared by the preparation method described in the above technical solution in the anodizing pretreatment of 7-series aluminum alloys.

[0012] The present invention also provides an anodizing method for a 7-series aluminum alloy, comprising the following steps: sequentially subjecting the 7-series aluminum alloy to acidic pretreatment and sulfuric acid anodizing to obtain an anodized 7-series aluminum alloy; wherein the reagent used for acidic pretreatment is the anodizing pretreatment agent described in the above technical solution or the anodizing pretreatment agent prepared by the preparation method described in the above technical solution.

[0013] Preferably, the acidic pretreatment further includes: sequentially degreasing and washing the 7-series aluminum alloy; The process after water washing also includes sequential alkaline etching and water washing.

[0014] Preferably, the acidic pretreatment is performed at a temperature of 15-35°C for 15-90 seconds. The acidic pretreatment is followed by water washing.

[0015] The anodizing pretreatment agent provided by this invention uses nitric acid and / or sulfuric acid as the main acidic system to provide the basic acidity for deashing / decontamination of VII series aluminum alloys. If the concentration of the main acidic system in the anodizing pretreatment agent is too low, the deashing of the VII series aluminum alloy will be incomplete; if the concentration of the main acidic system is too high, the VII series aluminum alloy will be easily over-corroded. This invention uses ferric salt as an oxidation flux, which has both oxidation and fluxing effects. On the one hand, it can promote the transformation of low-valence metal species in the enriched layer and residues on the surface of VII series aluminum; on the other hand, it facilitates the detachment of residues and surface contaminants from the substrate surface and their entry into the solution, thereby reducing the adhesion of black ash residues. If the concentration of the oxidation flux in the anodizing pretreatment agent is too low, black ash residues are likely to remain on the VII series aluminum alloy; if the concentration of the oxidation flux is too high, it may cause excessive reaction on the surface of the VII series aluminum alloy. Excessive reaction mainly refers to Fe...3+ The oxidation-assisted dissolution process promotes the oxidation of some low-valence metal species in the surface residue, making them easier to detach from the substrate surface and enter the solution. This invention uses fluorides as fluorine-containing activators to activate the surface of VII series aluminum alloys and promote oxide removal. If the concentration of the fluorine-containing activator in the anodizing pretreatment agent is too low, the descaling / decontamination treatment of the VII series aluminum alloy will be incomplete; if the concentration of the fluorine-containing activator is too high, the VII series aluminum alloy will be prone to pitting corrosion. This invention uses organic carboxylates as complexation inhibitors to complex the metal ions (mainly Al) dissolved from the surface of VII series aluminum. 3+ Zn 2+ Cu 2+ It may also include a small amount of Mg. 2+ This invention improves the surface wetting uniformity of complex 7-series aluminum alloy components by adding a wetting agent. If the concentration of the wetting agent in the anodizing pretreatment agent is too low, metal ion redeposition will be significant; if the concentration of the wetting agent is too high, the local treatment of complex 7-series aluminum alloy components will be uneven; if the concentration of the wetting agent is too high, it may cause foaming of the anodizing pretreatment agent and residue on the surface of the 7-series aluminum alloy. Compared with conventional nitric acid-fluoride deashing systems, this invention, through the combined effects of nitric acid and / or sulfuric acid, mild fluorine activation, ferric salt oxidation to aid dissolution, organic carboxylic acid complexation inhibition, and wetting agent, and by controlling the concentration of each component, enables deashing, cleaning, and activation treatment of 7-series aluminum alloys before anodizing. It also provides a wider operating window for pre-anodizing treatment, significantly reduces over-corrosion and black ash residue, has a very low defect rate, and improves the stability and uniformity of pre-anodizing treatment, thereby enhancing the consistency of anodized appearance and corrosion resistance, improving batch repeatability, and significantly shortening the pre-anodizing treatment time for 7-series aluminum alloys. It is also suitable for pre-anodizing treatment of complex 7-series aluminum alloy parts. Detailed Implementation

[0016] This invention provides an anodizing pretreatment agent comprising: 10-35% acidic main system, 0.5-8 g / L oxidation co-solvent, 0.2-3 g / L fluorine-containing activator, 0.2-8 g / L complexation inhibitor, 0.05-0.5 g / L wetting agent, and water; wherein the acidic main system comprises nitric acid and / or sulfuric acid; the oxidation co-solvent comprises ferric salt; the fluorine-containing activator comprises fluoride; and the complexation inhibitor comprises organic carboxylate.

[0017] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0018] In this invention, the composition of the anodizing pretreatment agent includes an acidic main system of 10-35 vol%, or 15-30 vol%, specifically 10 vol%, 15 vol%, 20 vol%, 25 vol%, 30 vol%, or 35 vol%. In this invention, the acidic main system includes nitric acid and / or sulfuric acid. In this invention, the function of the acidic main system is to provide the basic acidity for descaling / decontamination of the 7-series aluminum alloy; if the concentration of the acidic main system in the anodizing pretreatment agent is too low, the descaling of the 7-series aluminum alloy will be incomplete; if the concentration of the acidic main system is too high, the 7-series aluminum alloy will be easily over-corroded.

[0019] In this invention, the composition of the anodizing pretreatment agent includes an oxidizing flux of 0.5~8 g / L, which can be 1~7 g / L, specifically 0.5 g / L, 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, or 8 g / L. In this invention, the oxidizing flux includes a ferric salt, which can include one or more of ferric sulfate, ferric nitrate, and ferric chloride. In this invention, the oxidizing flux has both oxidizing and dissolving effects. On the one hand, it can promote the conversion of low-valence metal species in the enriched layer and residues on the surface of VII series aluminum; on the other hand, it facilitates the detachment of residues and surface contaminants from the substrate surface and their entry into the solution, thereby reducing the adhesion of black and gray residues. If the concentration of the oxidizing flux in the anodizing pretreatment agent is too low, black and gray residues are likely to remain on the VII series aluminum alloy; if the concentration of the oxidizing flux is too high, it may cause excessive reaction on the surface of the VII series aluminum alloy.

[0020] In this invention, the anodizing pretreatment agent comprises a fluorinated activator (based on fluoride ion concentration) of 0.2~3 g / L, which can be 0.5~2.5 g / L, specifically 0.2 g / L, 0.5 g / L, 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, or 3 g / L. In this invention, the fluorinated activator comprises fluorides, which may include one or more of ammonium hydrofluoride, ammonium fluoride, and sodium fluoride. In this invention, the function of the fluorinated activator is to activate the surface of the 7-series aluminum alloy and promote oxide removal; if the concentration of the fluorinated activator in the anodizing pretreatment agent is too low, the descaling / decontamination treatment of the 7-series aluminum alloy will be incomplete; if the concentration of the fluorinated activator is too high, the 7-series aluminum alloy will be easily pitted.

[0021] In this invention, the anodizing pretreatment agent comprises a complexation inhibitor at a concentration of 0.2-8 g / L, which can be 1-7 g / L, specifically 0.2 g / L, 0.5 g / L, 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, or 8 g / L. In this invention, the complexation inhibitor comprises an organic carboxylate, which includes citrate and / or gluconate, specifically sodium citrate and / or sodium gluconate. In this invention, the function of the complexation inhibitor is to complex the metal ions dissolved from the surface of VII series aluminum and prevent the redeposition of metal ions to form black ash residue. If the concentration of the complexation inhibitor in the anodizing pretreatment agent is too low, metal ion redeposition will be significant; if the concentration of the complexation inhibitor is too high, it may inhibit the dissolution / removal rate of surface oxides, enriched layers, and black ash residue during the pretreatment process, thereby affecting the deashing, decontamination, and activation efficiency.

[0022] In this invention, the composition of the anodizing pretreatment agent includes a wetting agent at a concentration of 0.05~0.5 g / L, which can be 0.1~0.4 g / L, specifically 0.05 g / L, 0.1 g / L, 0.15 g / L, 0.2 g / L, 0.25 g / L, 0.3 g / L, 0.35 g / L, 0.4 g / L, 0.45 g / L, or 0.5 g / L. In this invention, the wetting agent includes a nonionic surfactant, which can include low-foaming polyethers and / or alkyl glycoside wetting agents, specifically including one or more of polyoxyethylene-polyoxypropylene block copolymers, octyl glycosides, and decyl glycosides. In this invention, the wetting agent is used to improve the surface wetting uniformity of complex 7-series aluminum alloy structural parts. If the concentration of the wetting agent in the anodizing pretreatment agent is too low, the local treatment of the complex 7-series aluminum alloy structural parts will be uneven. If the concentration of the wetting agent is too high, it may cause foaming of the anodizing pretreatment agent and residue of the anodizing pretreatment agent on the surface of the 7-series aluminum alloy.

[0023] The present invention also provides a method for preparing the anodizing pretreatment agent described in the above technical solution, comprising the following steps: mixing an acidic host system, an oxidation cosolvent, a fluorine-containing activator, a complexation inhibitor, a wetting agent and water to obtain the anodizing pretreatment agent.

[0024] In this invention, the mixing process may include: dissolving an oxidation co-solvent, a complexation inhibitor, and a wetting agent in a portion of water, adding them to an acidic main system and mixing, adding a fluorine-containing activator and mixing, and then replenishing the remaining water. In this invention, the volume of the portion of water accounts for 70-85% of the total volume of the anodizing pretreatment agent, and may also be 75-80%.

[0025] This invention also provides the application of the anodizing pretreatment agent described in the above-described technical solutions or the anodizing pretreatment agent prepared by the above-described technical solutions in the anodizing pretreatment of 70 series aluminum alloys. In this invention, the 70 series aluminum alloy may include aluminum alloy 7075, aluminum alloy 7050, aluminum alloy 7475, or aluminum alloy 7A04.

[0026] In the anodizing pretreatment agent provided by this invention, nitric acid and / or sulfuric acid provide the basic acidity for descaling / decontamination of the 7-series aluminum alloy, fluorides are used to activate the surface of the 7-series aluminum alloy and promote oxide removal, and Fe is introduced into the process. 3+ Oxidation-assisted solubilization promotes the removal of residues on the surface of 7-series aluminum alloys, while the introduction of organic carboxylate complexation inhibits the redeposition of dissolved metal ions, reducing the formation of black and gray residues. Furthermore, the use of wetting agents improves the uniformity of treatment for complex structural parts. Compared to conventional nitric acid-fluoride deashing systems, this invention, through the synergistic effects of nitric acid and / or sulfuric acid + mild fluorine activation + ferric salt oxidation-assisted solubilization + organic carboxylate complexation inhibition + wetting agent, and by controlling the concentration of each component, can achieve deashing, decontamination, and activation treatment of 7-series aluminum alloys before anodizing. It provides a wider operating window for pre-anodizing treatment, significantly reduces over-corrosion and black and gray residues, has a very low defect rate, and improves the stability and uniformity of pre-anodizing treatment, thereby enhancing the consistency of anodized appearance and corrosion resistance, improving batch repeatability, and significantly shortening the pre-anodizing treatment process for 7-series aluminum alloys. It is also suitable for the pre-anodizing treatment of complex 7-series aluminum alloy parts.

[0027] The present invention also provides an anodizing method for a 7-series aluminum alloy, comprising the following steps: sequentially subjecting the 7-series aluminum alloy to acidic pretreatment and sulfuric acid anodizing to obtain an anodized 7-series aluminum alloy; wherein the reagent used for acidic pretreatment is the anodizing pretreatment agent described in the above technical solution or the anodizing pretreatment agent prepared by the preparation method described in the above technical solution.

[0028] In this invention, the 7-series aluminum alloys may include aluminum alloy 7075, aluminum alloy 7050, aluminum alloy 7475, or aluminum alloy 7A04.

[0029] In this invention, the acidic pretreatment may further include: sequentially degreasing and rinsing the 7-series aluminum alloy with water (referred to as the first water rinse). In this invention, the degreasing agent may include an alkaline degreasing agent; the alkaline degreasing agent may include one or more of sodium hydroxide, sodium carbonate, phosphate, and surfactant; the phosphate may include trisodium phosphate and / or sodium pyrophosphate; the surfactant may include low-foaming polyether and / or alkyl glycoside wetting agents, specifically including decyl glucoside. In this invention, the degreasing temperature may be 50-65°C, or even 55-60°C; the degreasing time may be 2-5 min, or even 3-4 min. In this invention, the first water rinse may be a running water rinse, and the first water rinse time may be 20-60 s, or even 30-50 s, or further 30-40 s.

[0030] In this invention, the first water wash may be followed by a sequential alkaline etching and water wash (referred to as the second water wash). In this invention, the alkali used for alkaline etching can be an alkali metal hydroxide, specifically including NaOH and / or KOH; the alkali can be used in the form of an alkaline aqueous solution, and the concentration of the alkaline aqueous solution can be 30-50 g / L, or 35-45 g / L, or even 40 g / L; the temperature of the alkaline etching can be 20-35°C, or 25-30°C; the time of the alkaline etching can be 10-60 s, or 20-50 s, or even 30-40 s. In this invention, the second water wash can be 1-2 deionized water washes or running water washes; the time of the running water wash can be 20-60 s, or 30-50 s, or even 30-40 s. For 7-series aluminum alloys with complex surface conditions, original oxide film, or obvious contamination, alkaline etching is beneficial for removing an uneven layer on the surface and improving the consistency of subsequent acid pretreatment. However, for some workpieces with good surface conditions or that are sensitive to size, they can directly enter the acid pretreatment after only degreasing and water washing.

[0031] In this invention, the acidic pretreatment can be performed by immersing the 7-series aluminum alloy in an anodizing pretreatment agent. The temperature of the acidic pretreatment can be 15-35°C, or 20-30°C, or even 25°C; the time of the acidic pretreatment can be 15-90 seconds, or 20-80 seconds, or even 30-70 seconds, specifically 40 seconds, 50 seconds, or 60 seconds; the acidic pretreatment can be carried out under air stirring or circulating stirring conditions. Under the above conditions, the acidic pretreatment of this invention can improve the processing uniformity of large and complex 7-series aluminum alloy parts.

[0032] In this invention, the acidic pretreatment further includes: rinsing the pretreated VII series aluminum alloy with water (referred to as the third water rinse). In this invention, the third water rinse can be 1-2 deionized water rinses or running water rinses; the running water rinse time can be 20-60 seconds, or 30-50 seconds, or even 30-40 seconds.

[0033] In this invention, the conditions for sulfuric acid anodizing may include: a sulfuric acid solution concentration of 150-220 g / L, which may also be 160-210 g / L, further 170-200 g / L, specifically 180 g / L or 190 g / L; a temperature of 12-18°C, which may also be 13-17°C, further 14-16°C, specifically 15°C; a voltage of 12-18V, which may also be 13-17V, further 14-16V, specifically 15V; and a time of 20-40 min, which may also be 25-35 min, further 30 min.

[0034] After anodizing, the present invention may further include washing the anodized aluminum alloy with water (referred to as the fourth water wash) and then drying it. In the present invention, the fourth water wash may be deionized water, and the washing time may be 20-60 seconds, 30-50 seconds, or even 30-40 seconds. In the present invention, the drying temperature may be 50-80°C, or 55-70°C; the drying time may be 0.5-2 hours, or 0.5-1 hour.

[0035] To further illustrate the present invention, the following detailed descriptions, in conjunction with embodiments, describe the anodizing pretreatment agent, its preparation method, and its application, as well as the anodizing method for 7-series aluminum alloys. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1 Composition of the anodizing pretreatment agent: 20 vol% nitric acid, 2.0 g / L ferric nitrate, 1.5 g / L ammonium fluoride, 2.0 g / L sodium citrate, 0.10 g / L decyl glucoside, and the balance being deionized water.

[0037] Preparation of anodizing pretreatment agent: Add deionized water accounting for 80% of the total volume of the anodizing pretreatment agent, then add ferric nitrate, sodium citrate and nonionic surfactant in sequence, stir until dissolved, add nitric acid and mix evenly, add ammonium fluoride and mix evenly, and add the remaining deionized water to the target total volume of the anodizing pretreatment agent to obtain the anodizing pretreatment agent.

[0038] Anodizing of 7075-T6 aluminum alloy: Using a commercially available alkaline degreasing agent (manufacturer: Dongguan Haoquan Chemical Co., Ltd., model HQ-122), aluminum alloy 7075-T6 (dimensions 50mm×100mm×1mm) was degreased at 55℃ for 3 minutes, rinsed with running water for 30 seconds, immersed in a 40g / L NaOH aqueous solution, and alkaline etched at 25℃ for 15 seconds, rinsed with running water for 30 seconds, immersed in an anodizing pretreatment agent, and acidic pretreatment at 25℃ with air stirring for 30 seconds, rinsed with deionized water for 30 seconds, anodized with sulfuric acid, rinsed with deionized water for 30 seconds, and dried at 60℃ for 1 hour to obtain the anodized 7075-T6 aluminum alloy. The conditions for sulfuric acid anodizing were: sulfuric acid solution concentration 180g / L, temperature 18℃, voltage 15V, and time 30 minutes.

[0039] Comparative Example 1 Composition of the anodizing pretreatment agent: 20 vol% nitric acid, 1.5 g / L ammonium hydrofluoride, and the balance deionized water.

[0040] Preparation of anodizing pretreatment agent: Add deionized water accounting for 80% of the total volume of the anodizing pretreatment agent, add nitric acid and mix evenly, add ammonium fluoride and mix evenly, and add the remaining deionized water to the target total volume of the anodizing pretreatment agent to obtain the anodizing pretreatment agent.

[0041] Anodized 7-series aluminum alloys were prepared according to Example 1.

[0042] Comparative Example 2 Composition of the anodizing pretreatment agent: 20 vol% nitric acid, 2.0 g / L ferric nitrate, 1.5 g / L ammonium fluoride, 0.10 g / L low-foaming polyether or alkyl glycoside wetting agent, and the balance being deionized water.

[0043] Preparation of anodizing pretreatment agent: Add 80 vol% deionized water, add ferric nitrate and stir until dissolved, add nitric acid and mix evenly, add ammonium fluoride and mix evenly, add the remaining deionized water to the target total volume of the anodizing pretreatment agent, and obtain the anodizing pretreatment agent.

[0044] Anodized 7-series aluminum alloys were prepared according to Example 1.

[0045] Comparative Example 3 Composition of the anodizing pretreatment agent: 20 vol% nitric acid, 1.5 g / L ammonium fluoride, 2.0 g / L sodium citrate, 0.10 g / L low-foaming polyether or alkyl glycoside wetting agent, and the balance being deionized water.

[0046] Preparation of anodizing pretreatment agent: Add deionized water accounting for 80% of the total volume of the anodizing pretreatment agent, then add ferric nitrate, sodium citrate and nonionic surfactant in sequence, stir until dissolved, add nitric acid and mix evenly, add ammonium fluoride and mix evenly, and add the remaining deionized water to the target total volume of the anodizing pretreatment agent to obtain the anodizing pretreatment agent.

[0047] Anodized 7-series aluminum alloys were prepared according to Example 1.

[0048] Test Example 1 Salt spray resistance test method: Neutral salt spray test shall be conducted in accordance with GB / T 10125, and the changes in film appearance, the appearance of corrosion spots, and the local loss of gloss after the neutral salt spray test shall be used as comparative indicators. The specific exposure time can be determined according to the product application or the company's internal evaluation requirements.

[0049] Test method for surface black and gray residue defect rate: Observe no less than 10 samples in each group, count the number of samples with visible black and gray residue on the sample surface, and take the percentage of samples with black and gray residue to the total number of samples as the surface black and gray residue defect rate; if necessary, combine with optical photographs for auxiliary judgment.

[0050] Method for testing the number of pitting corrosion sites: Select a representative area of ​​1 dm² for each sample. 2 Within a given area, the number of pitting corrosions visible to the naked eye or identifiable under optical magnification was counted. Each group consisted of at least three samples, and the average value was recorded as the number of localized pitting corrosions, expressed as pitting corrosions per dm². 2 .

[0051] Anodizing post-anodization bloom test method: Visually observe the surface of the anodized sample and record whether there are obvious unevenness in light and dark, cloud-like differences, or local light and dark areas on the surface in combination with optical photographs; according to the abnormal area and the proportion of abnormal samples, the degree of bloom is divided into "obvious", "less bloom" and "very little bloom".

[0052] Color difference testing method after anodizing: The CIE L of the sample surface after anodizing is measured using a colorimeter. a b For each sample, select no fewer than 5 test points and take the average value; compare the average value of the samples in the same group with the first sample in the same batch to calculate the overall color difference ΔE. .

[0053] Evaluation method for uniformity of film appearance: Observe no less than 10 samples in each group and make a comprehensive evaluation based on the results of optical photographs and color difference tests. (1) If there are obvious mottled, striped, local light-colored areas or large color differences on the sample surface, and the proportion of abnormal samples is >30%, it is judged as "average appearance uniformity"; (2) If the overall appearance of the sample is relatively uniform, only a few samples have slight mottled or local slight color differences, and the proportion of abnormal samples is 5%~30%, it is judged as "good appearance uniformity"; (3) If the sample surface color is uniform, no obvious mottled, striped or local color differences are seen, and the proportion of abnormal samples is <5%, it is judged as "good appearance uniformity".

[0054] The test results of the anodized VII series aluminum alloys prepared in Example 1 and Comparative Examples 1-2 are shown in Table 1.

[0055] Table 1. Test results of anodized 7-series aluminum alloys prepared in Example 1 and Comparative Examples 1-2

[0056] As shown in Table 1, compared with Comparative Example 1 (traditional nitrate-fluoride deashing system), the present invention, by introducing ferric salt, organic carboxylate and wetting agent, can more effectively remove old oxide residue and inhibit local redeposition, reduce the defect rate of black and gray residue on the surface and the number of local pitting corrosion, alleviate the blooming after old electrode oxidation, improve the color difference and film appearance uniformity after old electrode oxidation, and improve the appearance stability after salt spray.

[0057] By comparing Comparative Example 2 (nitrate-fluoride-Fe) 3+ As can be seen from the system (and Comparative Example 1 and Example 1), only Fe was introduced. 3+ As an oxidizing co-solvent, it can improve residue removal, but due to the lack of complexation inhibition of dissolved metal ions by organic carboxylate salts, it is still easy to cause local blackening due to redeposition.

[0058] By comparing Comparative Example 3 (nitrate-fluoride-organic carboxylate system) with Comparative Example 1 and Example 1, it can be seen that the introduction of organic carboxylate alone can reduce the redeposition of dissolved metal ions, but its ability to remove enriched layers and stubborn black ash residues is worse than that of Example 1.

[0059] 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. An anodizing pretreatment agent, characterized in that, The composition includes: 10-35 vol% acidic main system, 0.5-8 g / L oxidizing co-solvent, 0.2-3 g / L fluorinated activator, 0.2-8 g / L complexation inhibitor, 0.05-0.5 g / L wetting agent, and water; the acidic main system includes nitric acid and / or sulfuric acid; the oxidizing co-solvent includes ferric salts; the fluorinated activator includes fluorides, and the concentration of the fluorinated activator is calculated as fluoride ions; the complexation inhibitor includes organic carboxylates.

2. The anodizing pretreatment agent according to claim 1, characterized in that, The ferric salts include one or more of ferric sulfate, ferric nitrate, and ferric chloride.

3. The anodizing pretreatment agent according to claim 1, characterized in that, The fluoride includes one or more of ammonium hydrofluoride, ammonium fluoride, and sodium fluoride.

4. The anodizing pretreatment agent according to claim 1, characterized in that, The organic carboxylic acid salts include citrate and / or gluconate.

5. The anodizing pretreatment agent according to claim 1, characterized in that, The wetting agent includes a nonionic surfactant.

6. A method for preparing the anodizing pretreatment agent according to any one of claims 1 to 5, characterized in that, The process includes the following steps: mixing an acidic host system, an oxidation co-solvent, a fluorine-containing activator, a complexation inhibitor, a wetting agent, and water to obtain the anodizing pretreatment agent.

7. The application of the anodizing pretreatment agent according to any one of claims 1 to 5 or the anodizing pretreatment agent prepared by the preparation method according to claim 6 in the anodizing pretreatment of 7-series aluminum alloys.

8. A method for anodizing 7-series aluminum alloys, characterized in that, Includes the following steps: The 7-series aluminum alloy was subjected to acid pretreatment and sulfuric acid anodizing in sequence to obtain the anodized 7-series aluminum alloy. The acidic pretreatment reagent is the anodizing pretreatment agent according to any one of claims 1 to 6 or the anodizing pretreatment agent prepared by the preparation method according to claim 7.

9. The anodizing method according to claim 8, characterized in that, The acid pretreatment process also includes: sequentially degreasing and washing the 7-series aluminum alloy with water; The process after water washing also includes sequential alkaline etching and water washing.

10. The anodizing method according to claim 8 or 9, characterized in that, The acidic pretreatment is performed at a temperature of 15~35℃ for a time of 15~90s. The acidic pretreatment is followed by water washing.

Images