A medium-temperature nickel-free sealing agent for anodic oxide films of aluminum and aluminum alloys and a sealing process

Abstract

The application provides a nickel-free medium-temperature sealing agent for anodic oxidation film of aluminum and aluminum alloy products and a sealing process. After an aluminum or aluminum alloy product is subjected to anodic oxidation and water washing, the product is immersed in a nickel-free sealing liquid for sealing treatment. The nickel-free sealing agent is prepared from the following components: 2g / L-4g / L of magnesium salt, 10g / L-15g / L of calcium salt, 0-2g / L of a surfactant, and the balance of deionized water. The nickel-free medium-temperature sealing liquid has a pH value of 5.5-6.5, a temperature of 75-85 DEG C, and a sealing time of 35-45 min. After sealing, the aluminum or aluminum alloy product is left to stand in an atmospheric environment for more than 3 days. The nickel-free medium-temperature sealing agent does not contain heavy metal ions such as nickel and cobalt, does not contain harmful elements, is environmentally friendly, and does not damage the health of operators.

Description

Technical Field

[0001] This invention belongs to the technical field of metal material surface treatment, specifically relating to a medium-temperature nickel-free sealant and sealing process for aluminum and aluminum alloy anodic oxide films. Background Technology

[0002] Aluminum alloys, due to their excellent electrical and thermal conductivity and high specific strength, are widely used in aerospace, shipbuilding, and 3C industries. However, aluminum has a relatively low equilibrium electrode potential of -1.663V, making it thermodynamically unstable. Although a thin oxide film forms on the surface of aluminum alloys under natural conditions, this film crumbles in harsh environments such as acidic or moderately alkaline conditions, making it susceptible to various forms of corrosion and limiting its practical application. In industrial applications, surface protection treatments are necessary to improve the corrosion resistance of aluminum alloys, and anodizing is one of the most widely used surface treatment technologies. However, during the anodizing process, the formation and dissolution of the anodic oxide film occur simultaneously, resulting in numerous micropores on the surface of the film. These micropores form corrosion channels, accelerating the corrosion of the aluminum alloy. To improve the corrosion resistance, wear resistance, and insulation properties of the anodic oxide film on aluminum and aluminum alloys, these micropores need to be sealed.

[0003] In some technologies, the composition of the sealing agent is quite complex. For example, patent CN 108950645B protects a nickel-free sealing agent for the anodizing of aluminum and aluminum alloys. The raw materials of this sealing agent, calculated per liter, include at least a color-fixing agent, a powder-smearing and dust-inhibiting agent, a complexing agent, a surfactant, and a pH buffer. Another example is patent CN 107604414B, which protects a high-temperature nickel-free sealing agent for the anodizing of aluminum and aluminum alloys. The raw materials of this sealing agent, by volume and mass, include a surfactant, a fading inhibitor, a chelating agent, a pH buffer, and the balance being deionized water; wherein the pH buffer is one or two of ammonium acetate, benzoic acid, and ammonium phthalate.

[0004] In actual production, widely used sealing technologies include boiling water sealing, medium-temperature dichromate sealing, medium-temperature nickel salt sealing, and room-temperature NiF sealing. However, boiling water sealing is greatly affected by water quality, as other ions in the water directly impact the sealing effect. For chromate sealing, Cr6... + Chromium is a toxic, internationally recognized carcinogenic metal, and this process ultimately produces chromium slag, for which there is currently no economical, practical, or environmentally friendly technology. While nickel salt sealing is less environmentally damaging than dichromate sealing, nickel compounds are also toxic, causing pollution and harming human health. Therefore, developing a fluorine-free, chromium-free, nickel-free, and low-energy-consumption sealing technology is of great significance and has substantial social benefits. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a nickel-free sealing agent for aluminum and aluminum alloy anodized films at medium temperature, which aims to solve the environmental pollution caused by nickel-containing, chromium-containing or fluorine-containing sealing agents widely used in the field; wherein the nickel-free sealing agent at medium temperature is composed of magnesium salt, calcium salt, surfactant, pH adjuster and deionized water.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A medium-temperature nickel-free sealant for aluminum and aluminum alloy anodic oxide films, characterized in that it comprises the following raw materials by volume mass: 2 g / L-4 g / L magnesium salt, 10 g / L-15 g / L calcium salt, 0-2 g / L surfactant, pH adjuster, and the balance being deionized water; the pH of the medium-temperature nickel-free sealant is 5.5-6.5.

[0008] Preferably, the magnesium salt and the calcium salt are acetates.

[0009] Preferably, the pH adjuster is diluted glacial acetic acid.

[0010] Preferably, the surfactant is one or both of sulfosalicylic acid and polyethylene glycol.

[0011] Another objective of this invention is to provide a mid-temperature nickel-free sealing process for anodic oxide films of aluminum and aluminum alloys, which can balance environmental protection in all aspects of production, application, and emissions, while reducing process costs and improving corrosion resistance; wherein, the process includes:

[0012] I. Pre-processing

[0013] A. Polishing: Polish the aluminum or aluminum alloy sequentially with 800#, 1000#, 1500#, and 2000# sandpaper to remove the oxide film and impurities from the surface. After polishing, rinse twice with tap water, then twice with deionized water.

[0014] B. Alkali washing: Place the aluminum or aluminum alloy treated in A into an alkaline washing solution containing 10g / L NaOH, 8g / L Na2CO3, and 12g / L Na3PO4, and wash it for 1 minute at room temperature.

[0015] C. Pickling: Place the aluminum or aluminum alloy treated by B into a pickling solution containing 100g / L concentrated H2SO4, 20ml / L H3PO4, 6ml / L HF, and 0.3g / L OP-10, and pickle for 1 minute at room temperature;

[0016] II. Anodizing

[0017] Pretreated aluminum or aluminum alloy is placed in an H2SO4 solution with a concentration of 160 g / L-180 g / L and subjected to constant DC anodizing at 19±1℃ for 35-40 minutes with a current density of 1.5 A / dm³. 2 After anodizing, remove the aluminum or aluminum alloy products and rinse them twice with tap water and twice with deionized water.

[0018] III. Enclosure

[0019] The process parameters for the intermediate-temperature nickel-free sealing agent of aluminum and aluminum alloy anodic oxide films of the present invention are as follows:

[0020] Sealing temperature: 75℃-85℃;

[0021] Sealing time: 35-45 minutes;

[0022] pH value: 5.5-6.5.

[0023] Preferably, the optimal sealing temperature is 80℃; the optimal sealing time is 40min; and the optimal pH value is 6.

[0024] Preferably, the sealed aluminum or aluminum alloy is aged in an atmospheric environment for more than 3 days.

[0025] The beneficial effects of this invention are:

[0026] The magnesium and calcium salts used in the sealant provided by this invention can replace nickel, cobalt, or dichromate salts, and the sealant is fluorine-free, having no adverse impact on the environment. The process formulation is also very simple, involving few additives and resulting in low raw material costs. The corrosion resistance of the anodic oxide film sealed with this sealant is significantly improved. Attached Figure Description

[0027] Figure 1 AC impedance spectra of anodized aluminum alloy products and sealed aluminum alloy products;

[0028] Figure 2 The polarization curves are for anodized aluminum alloy products and sealed aluminum alloy products. Detailed Implementation

[0029] This invention provides a nickel-free sealing agent and sealing process for medium-temperature anodized films of aluminum and aluminum alloys. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0030] I. Anodizing film formation treatment of aluminum or aluminum alloy

[0031] This application uses 6063 aluminum alloy, and the specific process flow is as follows:

[0032] (1) Mechanical polishing: 6063 aluminum alloy is polished with 800#, 1000#, 1500# and 2000# sandpaper in sequence to remove the oxide film and impurities on the surface of the aluminum alloy.

[0033] (2) Rinse twice with running tap water and twice with deionized water.

[0034] (3) Alkaline washing and degreasing: Place aluminum or aluminum alloy in an alkaline washing solution containing 10g / L NaOH, 8g / L Na2CO3 and 12g / L Na3PO4, and wash for 1 minute at room temperature.

[0035] (4) Rinse twice with running tap water and twice with deionized water.

[0036] (5) Pickling head: Aluminum or aluminum alloy is placed in a pickling solution containing 100g / L H2SO4, 20ml / L H3PO4, 6ml / L HF and 0.3g / L OP-10 and pickled for 1 minute at room temperature.

[0037] (6) Rinse twice with running tap water and twice with deionized water.

[0038] (7) Anodizing: The pretreated aluminum or aluminum alloy is placed in a sulfuric acid solution with a concentration of 160 g / L-180 g / L, and anodized under constant DC current at 19±1℃ for 35-40 min with a current density of 1.5 A / dm³. 2 .

[0039] (8) After anodizing, take out the aluminum or aluminum alloy and rinse it twice with tap water and twice with deionized water.

[0040] II. The above-mentioned anodic oxide film is sealed using the sealing agent and sealing process of the present invention.

[0041] Example 1

[0042] After aluminum or aluminum alloy undergoes anodizing film formation in steps (1)-(8) above, the anodized film is immediately sealed as follows:

[0043] 1. Composition of the sealing agent:

[0044] Magnesium acetate 3 g / L, calcium acetate 12 g / L, the remainder is deionized water.

[0045] 2. Sealing process:

[0046] Adjust the pH value to 6 with acetic acid, set the sealing temperature to 80℃, and the sealing time to 40 minutes.

[0047] 3. After sealing, remove the aluminum or aluminum alloy, rinse twice with running tap water, and then rinse twice with deionized water.

[0048] 4. Place the sealed aluminum or aluminum alloy in an atmospheric environment to age for more than 3 days.

[0049] 5. Weight Loss and Dye Spot Tests: Anodized aluminum or aluminum alloys processed using this closed-loop process have a clean surface without any "powder bloom." Dye spot tests show a dyeing grade of 0-1. The weight loss from phosphochromic acid is 23.88 mg / dm³. 2 The weightlessness meets national standards.

[0050] Example 2

[0051] After aluminum or aluminum alloy undergoes anodizing film formation in steps (1)-(8) above, the anodized film is immediately sealed as follows:

[0052] 1. Composition of the sealing agent:

[0053] Magnesium acetate 3 g / L, calcium acetate 12 g / L, sulfosalicylic acid 2 g / L, balance deionized water.

[0054] 2. Sealing process:

[0055] Adjust the pH value to 6 with acetic acid, set the sealing temperature to 80℃, and the sealing time to 40 minutes.

[0056] 3. After sealing, remove the aluminum or aluminum alloy, rinse twice with running tap water, and then rinse twice with deionized water.

[0057] 4. Place the sealed aluminum or aluminum alloy in an atmospheric environment to age for more than 3 days.

[0058] 5. Weight Loss and Dye Spot Tests: Anodized aluminum or aluminum alloys processed using this closed-loop process have a clean surface without any "powder bloom." Dye spot tests show a staining grade of 0-1. The weight loss from phosphochromic acid is 16.74 mg / dm³. 2 The weightlessness meets national standards.

[0059] Example 3

[0060] After aluminum or aluminum alloy undergoes anodizing film formation in steps (1)-(8) above, the anodized film is immediately sealed as follows:

[0061] 1. Composition of the sealing agent:

[0062] Magnesium acetate 3 g / L, calcium acetate 12 g / L, polyethylene glycol 2 g / L, balance deionized water.

[0063] 2. Sealing process:

[0064] Adjust the pH value to 6 with acetic acid, set the sealing temperature to 80℃, and the sealing time to 40 minutes.

[0065] 3. After sealing, remove the aluminum or aluminum alloy, rinse twice with running tap water, and then rinse twice with deionized water.

[0066] 4. Place the sealed aluminum or aluminum alloy in an atmospheric environment to age for more than 3 days.

[0067] 5. Weight Loss and Dye Spot Tests: Anodized aluminum or aluminum alloys processed using this closed-loop process have a clean surface without any "powder bloom." Dye spot tests show a staining grade of 0-1. The weight loss from phosphochromic acid is 17.84 mg / dm³. 2 The weightlessness meets national standards.

[0068] like Figure 1 and Figure 2 As shown, the sample labeled AAO is an unsealed anodized aluminum alloy; the sample labeled Mg-Ca Sealed is an anodized aluminum alloy after sealing according to the embodiment of the present invention; the sample labeled F-Ni Sealed is an anodized aluminum alloy sealed by conventional room temperature nickel salt, with the following specific process parameters: Ni(CH3COO)2·4H2O 4.28g / L, NH4F 1.92g / L, sealing temperature 25℃, sealing agent pH value 6, and sealing time 30min.

[0069] The implementation of the present invention is not limited to the embodiments described above. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

[0070] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

[0071] The above description is only a preferred embodiment of the present invention. For those skilled in the art, there will be changes in the specific implementation and application scope based on the ideas of the present invention. The content of this specification should not be construed as a limitation of the present invention.

Claims

1. A nickel-free, medium-temperature sealing agent for aluminum and aluminum alloy anodic oxide films, characterized in that, It is composed of the following raw materials by volume mass: magnesium acetate 2g / L-4g / L, calcium acetate 10g / L-15g / L, surfactant 0-2g / L, pH adjuster, and the balance being deionized water; the pH of the medium-temperature nickel-free sealing agent is 5.5-6.5; the surfactant is one or both of sulfosalicylic acid and polyethylene glycol.

2. The nickel-free sealing agent for medium-temperature anodized films of aluminum and aluminum alloys according to claim 1, characterized in that, The pH adjuster is diluted glacial acetic acid.

3. The sealing process for aluminum and aluminum alloy anodic oxide films at medium temperature without nickel sealant according to any one of claims 1 or 2, characterized in that, The following technical steps are included: I. Pre-processing A. Grinding: Grind the aluminum or aluminum alloy with 800#, 1000#, 1500#, and 2000# sandpaper in sequence to remove the oxide film and impurities on the surface of the aluminum and aluminum alloy; after grinding, rinse twice with tap water, and then rinse twice with deionized water. B. Alkali washing: Place the aluminum or aluminum alloy treated in A into an alkaline washing solution containing 10 g / L NaOH, 8 g / L Na2CO3, and 12 g / L Na3PO4, and wash for 1 minute at room temperature. C. Pickling: Place the aluminum or aluminum alloy treated by B into a pickling solution containing 100g / L concentrated H2SO4, 20ml / L H3PO4, 6ml / L HF, and 0.3g / L OP-10, and pickle for 1 minute at room temperature; II. Anodizing Pretreated aluminum or aluminum alloy is placed in an H2SO4 solution with a concentration of 160 g / L-180 g / L and subjected to constant DC anodizing at 19±1℃ for 35-40 minutes with a current density of 1.5 A / dm³. 2 After anodizing, remove the aluminum or aluminum alloy and rinse it twice with tap water and twice with deionized water. III. Enclosure The process parameters for the intermediate-temperature nickel-free sealing agent of aluminum and aluminum alloy anodic oxide films of the present invention are as follows: Sealing temperature: 75℃-85℃; Sealing time: 35-45 minutes; pH value: 5.5-6.5; The sealed aluminum or aluminum alloy is aged in an atmospheric environment for more than 3 days.

4. The sealing process for medium-temperature nickel-free sealing agents of aluminum and aluminum alloy anodic oxide films according to claim 3, characterized in that, The optimal sealing temperature is 80℃; the optimal sealing time is 40 min; and the optimal pH value is 6.

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