Multi-layer anodic oxidation process

Abstract

The invention relates to a multi-layer anodic oxidation process which comprises the following steps: carrying out primary anodic oxidation treatment on a workpiece to be oxidized so as to generate a first oxidation film on the surface of the workpiece to be oxidized; carrying out secondary anodic oxidation treatment on the to-be-oxidized workpiece subjected to the primary anodic oxidation treatment so as to generate a second oxidation film on the surface of the first oxidation layer and form a multi-layer oxidation film; and carrying out sealing treatment on the to-be-oxidized workpiece subjected to secondary anodic oxidation treatment so as to block pores in the surface of the multi-layer oxidation film. According to the process, the porosity and the ion adsorption capacity of the oxidation film are optimized layer by layer, deep-layer residues of SOs are reduced, the limitation of a single electrolyte is avoided through the synergistic effect of the electrolyte, sealing treatment is combined with the multiple layers of oxidation films, a double-protection structure of physical blocking and chemical neutralization is formed, the whole-process process chain is complete, and the production efficiency is high. Pollutants are controlled from the source to the terminal.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum alloy surface treatment, and relates to a multilayer anodization process, in particular to a multilayer anodization process for aluminum alloy. BACKGROUND

[0002] In the modern industrial field, aluminum alloy is widely used in key fields such as aerospace, rail transit, electronic equipment, building decoration, etc. due to its lightweight, high strength, easy processing and other excellent characteristics, and becomes the core structural material supporting the development of many industries. However, the surface of aluminum alloy is relatively active in chemical properties, and is prone to oxidation and corrosion in natural environment or service conditions (such as high humidity, salt-containing marine environment, industrial corrosive atmosphere, etc.), which leads to surface failure, performance degradation or even structural damage, seriously restricting its service life and application safety. Therefore, efficient protection treatment of the surface of aluminum alloy is a key link to expand its application boundary and ensure product reliability.

[0003] Anodization treatment is one of the mainstream technologies for protecting the surface of aluminum alloy at present. Its principle is to generate an oxide film (mainly composed of Al2O3) on the surface of aluminum alloy through electrolysis, which is tightly combined with the matrix. The oxide film can effectively isolate the contact between the corrosion medium and the matrix, thereby improving the corrosion resistance, wear resistance and surface decoration of aluminum alloy. Traditional anodization process usually uses sulfuric acid as electrolyte, which will cause SO4²⁻ ions to remain on the surface or in the pores of aluminum alloy. These residual SO4²⁻ ions may have adverse effects on the long-term performance of aluminum alloy, especially in high humidity or corrosive environments, which may cause corrosion or performance degradation of the material. To solve this problem, the existing technology usually uses water washing or chemical cleaning method to remove SO4²⁻ residues, but these methods have limited effect and may introduce other pollutants. Therefore, an anodization process capable of effectively reducing SO4²⁻ residues is needed. SUMMARY

[0004] The present application provides a multilayer anodization process, in particular to a multilayer anodization process for aluminum alloy to solve the problem of SO4²⁻ ion residues on the surface or in the pores of aluminum alloy.

[0005] The present application provides a multilayer anodization process, comprising the following steps: performing primary anodization treatment on a workpiece to be oxidized to generate a first oxide film on the surface of the workpiece to be oxidized; performing secondary anodization treatment on the workpiece to be oxidized after the primary anodization treatment to generate a second oxide film on the surface of the first oxide layer, forming a multilayer oxide film; and performing sealing treatment on the workpiece to be oxidized after the secondary anodization treatment to block the pores on the surface of the multilayer oxide film.

[0006] Further, the workpiece to be oxidized is an aluminum alloy workpiece.

[0007] Further, the primary anodic oxidation treatment is performed in a first electrolyte, the first electrolyte being sulfuric acid, and the concentration of the sulfuric acid being 10-20%.

[0008] Further, in the primary anodic oxidation treatment, the treatment temperature is 15-25℃, the current density is 1.0-2.0 A / dm², and the treatment time is 20-40 min.

[0009] Further, the secondary anodic oxidation treatment is performed in a second electrolyte, the second electrolyte being oxalic acid, and the concentration of the oxalic acid being 3-8%. The oxalic acid layer fills the pores and avoids the unevenness defects of the traditional sulfuric acid oxidation film. In addition, the oxalic acid electrolyte is biodegradable, reducing the environmental risk of sulfuric acid waste liquid.

[0010] Further, in the secondary anodic oxidation treatment, the treatment temperature is 20-30℃, the current density is 0.5-1.5 A / dm², and the treatment time is 10-30 min.

[0011] Further, the primary anodic oxidation treatment further comprises: water washing the workpiece to be oxidized after the primary anodic oxidation treatment to remove the residual sulfuric acid electrolyte on the surface; and / or The secondary anodic oxidation treatment further comprises: water washing the workpiece to be oxidized after the secondary anodic oxidation treatment to remove the residual oxalic acid electrolyte on the surface; Further, the sealing treatment adopts boiling water sealing treatment or nickel salt sealing treatment, and the sealing treatment time is 20-40 min.

[0012] Further, the sealing liquid of the boiling water sealing treatment is boiling water, and the sealing liquid of the nickel salt sealing treatment is Ni(NO3)2, the concentration of the Ni(NO3)2 being 1.0-1.5 g / L, and the pH value being 5.0-6.0.

[0013] Further, it further comprises: water washing and drying the workpiece to be oxidized after the sealing treatment.

[0014] Further, it further comprises: pretreating the workpiece to be oxidized before the primary anodic oxidation treatment.

[0015] Further, the pretreatment comprises: degreasing the workpiece to be oxidized to remove oil stains and impurities on the surface of the workpiece; The degreasing treated workpiece to be oxidized is subjected to alkali washing treatment to remove the surface oxidation layer of the workpiece; and The alkali washed workpiece to be oxidized is subjected to water washing to ensure that there is no residue on the surface.

[0016] Further, in the degreasing treatment, the degreasing agent is an acidic degreasing agent, including any one of sulfuric acid, phosphoric acid, nitric acid or hydrofluoric acid, compounded with a surfactant, the treatment temperature is 60-65 DEG C, and the treatment time is 5-10 min; in the alkali washing treatment, the alkali washing liquid is a NaOH solution, the concentration of the NaOH solution is 50-60 g / L, and the treatment time is 3-5 min.

[0017] The present application has at least the following advantages: 1) the process of the present application optimizes the porosity and ion adsorption capacity of the oxidation film layer by layer, reduces the deep layer residue of SO4²⁻, and the synergistic effect of the electrolyte avoids the limitations of a single electrolyte (such as sulfuric acid residue or low oxalic acid film forming rate); 2) the closed treatment combined with the multi-layer oxidation film forms a double protection structure of "physical barrier + chemical neutralization", and the complete process chain from source to terminal controls the pollutants (such as oil stains and residual ions); 3) the present application reduces water consumption by reducing the cleaning steps (traditional process needs multiple water washing to remove residues), and the closed treatment prolongs the product life and reduces the maintenance cost. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to further clarify the above and other advantages and features of the embodiments of the present application, more particular description of the embodiments of the present application will be presented in reference to the attached drawings. It can be understood that these drawings are only depicting typical embodiments of the present application and therefore should not be considered as limiting its scope. In the drawings, the same or corresponding components will be denoted by the same or similar reference signs for the sake of clarity and intelligibility.

[0019] Figure 1 A schematic diagram of the multi-layer anodic oxidation process of the aluminum alloy frame in some embodiments of the present application is shown. DETAILED DESCRIPTION

[0020] It should be noted that the components in the various drawings can be shown exaggerated for illustration purposes, and are not necessarily to scale.

[0021] In the present application, the embodiments are only intended to illustrate the scheme of the present application, and should not be understood as limiting.

[0022] In the present application, the quantifier "one" does not exclude the scenario of multiple elements, unless specifically indicated.

[0023] It should also be noted that, in the embodiments of the present application, only a part of components or assemblies can be shown for the sake of clarity and simplicity, but those skilled in the art can understand that, under the teaching of the present application, the required components or assemblies can be added according to the specific scene.

[0024] It should also be noted that, within the scope of the present application, the words "same", "equal", "equal to" and the like do not mean that the numerical values of the two are absolutely equal, but allow a certain reasonable error, that is, the words also cover "substantially the same", "substantially equal", "substantially equal to".

[0025] It should also be noted that, in the description of the present application, the orientations or positional relationships indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as limiting the devices or elements indicated to have a specific orientation, to be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first" and "second" are only for descriptive purposes and cannot be understood as explicitly or implicitly indicating relative importance.

[0026] In addition, the embodiments of the present application describe the process steps in a specific order, however, this is only for the convenience of distinguishing the steps, and is not limited to the order of the steps, and in different embodiments of the present application, the order of the steps can be adjusted according to the adjustment of the process.

[0027] In the following examples, deionized water is used for washing.

[0028] Figure 1 A schematic diagram of a multilayer anodizing process flow of an aluminum alloy frame in an embodiment is shown. The aluminum alloy frame enters an alkaline degreasing tank, and the oil stains and other impurities on the surface of the aluminum frame are removed by a degreasing agent. Then, the aluminum frame enters an alkali washing tank, and the surface of the aluminum frame is further cleaned or chemically treated to remove the oxide layer. Then, the aluminum frame enters a water washing tank, and the residual alkaline solution and other substances from the previous steps are washed away by deionized water. After water washing, the aluminum frame first enters a sulfuric acid electrolytic tank, where a first oxide film is generated on the surface of the aluminum frame by using a sulfuric acid electrolyte. Then, the aluminum frame enters an oxalic acid electrolytic tank, where a second oxide film is formed on the basis of the first oxide film by using an oxalic acid electrolyte, so as to form a multilayer oxide film, improve the performance and reduce the residual sulfate. After the two anodizing processes are completed, the aluminum frame enters a closed tank, and a boiling water or nickel salt is used for sealing treatment to seal the pores of the multilayer oxide film, so as to improve the corrosion resistance, wear resistance and other performances.

[0029] Embodiment 1 This embodiment provides a multilayer anodizing process, including the following steps: The aluminum alloy frame was subjected to degreasing, alkaline washing, and water washing in sequence: In the degreasing treatment, the degreasing agent was an acidic degreasing agent, including any one of sulfuric acid, phosphoric acid, nitric acid, or hydrofluoric acid, and a compound surfactant (TN-6525 from Kelion (Wuxi) and BONDERITE 1022R from Henkel), the treatment temperature was 60℃, and the treatment time was 5 min; In the alkaline washing treatment, the alkaline washing solution was a NaOH solution with a concentration of 50 g / L, and the treatment time was 3 min; The aluminum alloy frame was subjected to an anodizing treatment to form a first oxide film on the surface of the aluminum alloy frame: using 15% sulfuric acid electrolyte, temperature 20℃, current density 1.5 A / dm², treatment time 30 min; A second anodizing treatment was performed on the aluminum alloy frame that had undergone a first anodizing treatment to generate a second oxide film on the surface of the first oxide layer, forming a multilayer oxide film: using 5% oxalic acid electrolyte, temperature 25℃, current density 1 A / dm², and treatment time 20 min. The aluminum alloy frame, after secondary anodizing, was subjected to a boiling water sealing treatment for 30 minutes to seal the pores on the surface of the multi-layer oxide film; and The sealed aluminum alloy frame is then washed and dried.

[0030] The workpiece obtained in the above example was inspected, and the following results were obtained: The surface has zero pores; IC test (ion chromatography test) shows SO4²⁻ < 10 ppb.

[0031] Example 2 This embodiment provides a multilayer anodizing process, including the following steps: The aluminum alloy frame was subjected to degreasing, alkaline washing, and water washing in sequence: In the degreasing treatment, the degreasing agent was an acidic degreasing agent, including any one of sulfuric acid, phosphoric acid, nitric acid, or hydrofluoric acid, and a compound surfactant (TN-6525 from Kelion (Wuxi) and BONDERITE 1022R from Henkel), the treatment temperature was 60℃, and the treatment time was 5 min; In the alkaline washing treatment, the alkaline washing solution was a NaOH solution with a concentration of 50 g / L, and the treatment time was 3 min; The aluminum alloy frame was subjected to an anodizing treatment to form a first oxide film on the surface of the aluminum alloy frame: using 20% ​​sulfuric acid electrolyte, temperature 25℃, current density 2 A / dm², treatment time 40 min; A second anodizing treatment was performed on the aluminum alloy frame that had undergone a first anodizing treatment to generate a second oxide film on the surface of the first oxide layer, forming a multilayer oxide film: using 5% oxalic acid electrolyte, temperature 30℃, current density 1.5 A / dm², and treatment time 30 min; The aluminum alloy frame, after secondary anodizing, was subjected to nickel salt sealing treatment for 40 min to seal the pores on the surface of the multilayer oxide film. The sealing solution in the nickel salt sealing treatment was Ni(NO3)2, with a concentration of 0.5 g / L and a pH value of 5. The sealed aluminum alloy frame is then washed and dried.

[0032] The workpiece obtained in the above example was inspected, and the following results were obtained: IC test results showed SO4²⁻ < 10 ppb.

[0033] The process of this invention seals the aluminum alloy frame with multi-layer oxide film to form a dense barrier, which delays the penetration of corrosive media such as Cl⁻ and H₂O, and increases the surface hardness of the multi-layer oxide film to 400-600HV (compared to 250-350HV in the traditional process).

[0034] While some embodiments of the present invention have been described in this application, those skilled in the art will understand that these embodiments are merely illustrative. Numerous variations, alternatives, and improvements will arise in those skilled in the art under the teachings of this invention without departing from its scope. The appended claims are intended to define the scope of the invention and thereby cover methods and structures within the scope of the claims themselves and their equivalents.

Claims

1. A multilayer anodizing process, characterized in that, Includes the following steps: An anodizing treatment is performed on the workpiece to be oxidized to form a first oxide film on the surface of the workpiece; A second anodizing treatment is performed on the workpiece that has undergone a first anodizing treatment to generate a second oxide film on the surface of the first oxide layer, thus forming a multilayer oxide film; as well as The workpiece to be oxidized after secondary anodizing is sealed to block the pores on the surface of the multilayer oxide film.

2. The multilayer anodizing process according to claim 1, characterized in that, The primary anodizing process is carried out in a first electrolyte, which is sulfuric acid with a concentration of 10-20%.

3. The multilayer anodizing process according to claim 1, characterized in that, In the single anodizing process, the processing temperature is 15-25℃, the current density is 1.0-2.0 A / dm², and the processing time is 20-40 min.

4. The multilayer anodizing process according to claim 1, characterized in that, The secondary anodizing treatment is carried out in a second electrolyte, which is oxalic acid with a concentration of 3-8%.

5. The multilayer anodizing process according to claim 1, characterized in that, In the secondary anodizing process, the processing temperature is 20-30℃, the current density is 0.5-1.5 A / dm², and the processing time is 10-30 min.

6. The multilayer anodizing process according to claim 1, characterized in that, The primary anodizing process also includes: The workpiece to be oxidized after a single anodizing treatment is washed with water; and / or The secondary anodizing process further includes: The workpiece to be oxidized after secondary anodizing is washed with water.

7. The multilayer anodizing process according to claim 1, characterized in that, The sealing process is performed using boiling water sealing or nickel salt sealing, and the sealing time is 20-40 minutes.

8. The multilayer anodizing process according to claim 1, characterized in that, Also includes: The workpiece to be oxidized after sealing is washed with water and dried.

9. The multilayer anodizing process according to claim 1, characterized in that, Also includes: Before anodizing, the workpiece to be anodized is pretreated.

10. The multilayer anodizing process according to claim 9, characterized in that, The preprocessing includes: The workpiece to be oxidized is subjected to degreasing treatment; Alkali washing is performed on the degreased workpiece to be oxidized; and The workpiece to be oxidized after alkaline washing is then washed with water.

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