Anodic oxide film, preparation method thereof and metal workpiece

Abstract

The invention provides an anodic oxide film, a preparation method thereof and a metal workpiece. The preparation method of the anodic oxide film comprises the following steps: carrying out anodic oxidation treatment on an aluminum or aluminum alloy metal matrix to form a porous anodic oxide film on the surface of the metal matrix; and the hole walls of the porous anodic oxide film are corroded through an etchant solution, so that a plurality of microstructures are generated on the hole walls, the white anodic oxide film is obtained, the etchant solution contains at least one of aluminum sulfate and sulfuric acid, and the microstructures comprise at least one of microcracks and micropores. According to the preparation method provided by the invention, the diffuse reflection effect of light is enhanced, so that the white appearance of the anodic oxide film is improved, and the stability and uniformity of the anodic oxide film are also improved. In addition, the method is simple in process, better in environmental protection property and capable of meeting the requirements of modern white anodic oxide film production for high performance and sustainable development.

Description

Technical Field

[0001] The present application relates to the technical field of metal surface treatment, and in particular to an anodized film and a preparation method thereof, and a metal workpiece. Background Art

[0002] At present, the anodic white oxidation technology usually adopts methods such as single electrolysis or filling white pigment. However, these methods all have defects, which limit their application and development in industrial production. First, the traditional single electrolysis method usually uses potassium titanium oxalate and chromic acid for oxidation treatment to form a microcrack oxide film, and the oxide film is made white by diffuse reflection of the microcracks, but the electrolysis system has poor stability, and chromic acid contains heavy metals, which causes environmental pollution and does not meet the safety and environmental protection requirements of industrial production. Secondly, the method of filling white pigments fills white inorganic salts such as barium sulfate and calcium carbonate in the porous layer of the oxide film to make the film layer appear white. However, the particle size of the inorganic salt crystals is usually more than 100nm, while the pore size of the oxide film is less than 20nm, and the pore expansion treatment is required, which will damage the closure of the membrane pores and affect the performance of the membrane layer.

[0003] The existing white anodizing technology has problems such as poor stability, environmental protection, poor product performance and complex process in the production process. In order to solve these problems, it is urgent to develop new technical solutions to improve the stability, environmental protection and operability of the production process. Summary of the invention

[0004] In view of this, in order to solve at least one of the above technical problems, an embodiment of the present application provides a novel method for preparing an anodized film.

[0005] In addition, the embodiments of the present application also provide an anodized film prepared by the aforementioned preparation method and a metal workpiece having the anodized film.

[0006] The present invention provides a method for preparing an anodic oxide film, the method comprising: Anodizing a metal substrate of aluminum or aluminum alloy to form a porous anodized film on the surface of the metal substrate; and The pore walls of the porous anodized film are corroded by a corrosive solution to produce a plurality of microstructures on the pore walls, thereby obtaining the white anodized film, wherein the corrosive solution contains at least one of aluminum sulfate and sulfuric acid, and the microstructures include at least one of microcracks and micropores.

[0007] In some possible embodiments, the concentration of the corrosive solution is 10 g / L to 50 g / L; and / or In the step of corroding the porous anodized film, the corrosion time is 1 min to 30 min, and the corrosion temperature is 35° C. to 80° C.

[0008] In some possible embodiments, the corrosion solution contains additives, and the additives include at least one of organic acids, organic alcohols, and surfactants.

[0009] In some possible embodiments, the concentration of the additive is 10 g / L to 300 g / L.

[0010] In some possible embodiments, the organic alcohol includes at least one of triethanolamine, glycerol, ethylene glycol, polyethylene glycol and vinyl alcohol; The organic acid includes at least one of oxalic acid, citric acid, cystine, lactic acid, tartaric acid, aminoacetic acid and malic acid.

[0011] In some possible embodiments, the voltage applied to the metal substrate is 3V~20V.

[0012] In some possible embodiments, in the step of corroding the porous anodized film, ultrasonic waves are applied to the metal substrate, and the direction of the ultrasonic waves is perpendicular to the depth direction of the pores in the porous anodized film.

[0013] In some possible embodiments, the frequency of the ultrasonic wave is 28kHz~100kHz.

[0014] In some possible embodiments, before the metal substrate is anodized, the metal substrate is chemically polished, and the glossiness of the metal substrate measured at an incident angle of 60° is 40GU-100GU.

[0015] In some possible embodiments, the thickness of the anodized film is 1 μm to 20 μm; The pores in the anodized film have a pore size of 10 nm to 100 nm.

[0016] In some possible embodiments, in the step of subjecting the metal substrate to anodizing treatment, the conditions of the anodizing treatment include at least one of the following features: (1) The temperature of the anodizing treatment is 0°C to 30°C; (2) The voltage of the anodizing treatment is 8V~30V; (3) The electrolyte for the anodizing treatment includes a sulfuric acid solution, and the concentration of the sulfuric acid solution is 20 g / L to 250 g / L.

[0017] The present application also provides an anodized film, which is prepared by the aforementioned anodized film preparation method, the anodized film has a porous structure, the pore walls of the porous structure have a plurality of microstructures, the microstructures include at least one of microcracks and micropores, and the anodized film is white.

[0018] The present application also provides a metal workpiece, which is prepared by the aforementioned method for preparing anodized film, the surface of the metal workpiece has a porous anodized film, the pore walls of the porous anodized film have a plurality of microstructures, the microstructures include at least one of microcracks and micropores, and the surface of the metal workpiece is white.

[0019] Compared with the prior art, the preparation method of the anodized film provided in the embodiment of the present application uses anodizing treatment to form a porous anodized film, and then uses a corrosive solvent as a corrosive medium to corrode the pore wall of the porous anodized film, so that a plurality of microstructures are generated on the pore wall, and the microstructure includes at least one of microcracks and micropores, and the anodized film presents a white effect through the diffuse reflection of light by the microstructure. The preparation method forms a large number of microstructures on the pore wall, and a large number of microstructures are evenly distributed along the longitudinal depth of the oxide film, which enhances the diffuse reflection effect of light and improves the whiteness and color uniformity of the oxide film. Moreover, aluminum sulfate and / or sulfuric acid are selected as the corrosive medium, and the microstructures formed on the pore wall are small in size, which has little effect on the performance of the anodized film, and improves the stability of the performance of the anodized film. In addition, the method is simple in process, has strong process operability, and uses aluminum sulfate and / or sulfuric acid as the corrosive medium, which is more environmentally friendly and can meet the needs of modern white anodized film production for high performance and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A process flow chart of a method for preparing an anodized film provided in one embodiment of the present application.

[0021] Figure 2 FIG. 1 is a schematic diagram of a microstructure formed according to an embodiment of the present application.

[0022] Figure 3 This is a scanning electron microscope photograph of the anodized film provided in Example 1 of the present application.

[0023] Figure 4 This is a scanning electron microscope photograph of the anodized film provided in Example 2 of the present application.

[0024] Figure 5 This is a scanning electron microscope photograph of the anodized film provided in Example 3 of the present application. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0026] See also Figure 1 The present invention provides a method for preparing an anodized film. The method specifically comprises the following steps: Step S1, anodizing a metal substrate of aluminum or aluminum alloy to form a porous anodized film on the surface of the metal substrate.

[0027] Specifically, a metal substrate of aluminum or aluminum alloy is placed in an electrolyte, and an anodizing treatment is performed with the metal substrate as an anode at a constant voltage to form a porous anodized film on the surface of the metal substrate.

[0028] In some embodiments, before the metal substrate is anodized, it can be pretreated by at least one of degreasing (emulsification, saponification), alkali biting (removing oil stains and impurities such as natural oxide film on the surface of aluminum alloy), and black film stripping (neutralization and deashing), so as to effectively remove dirt and natural oxide film on the surface of the metal substrate, eliminate slight defects on the surface of the metal substrate, improve the decorativeness of the surface treatment, and facilitate the smooth progress of the anodizing process.

[0029] In some embodiments, before the metal substrate is anodized, the metal substrate may be chemically polished. The chemical polishing step may specifically include: using an acid solution to dissolve at least part of the metal substrate, and controlling the selective dissolution of the metal substrate surface by the acid solution, so that the microscopic protruding parts of the metal substrate surface are preferentially dissolved compared to the concave parts, thereby achieving the purpose of making the metal substrate surface smooth and bright. The chemical polishing gloss will affect the Lab value of the anodized film on the surface of the metal substrate after subsequent aluminum sulfate corrosion. The surface color after anodization is calibrated with the Lab value, where "L" represents the change in light and dark, "a" represents the change from red to green, "+a" is the red direction, "-a" is the green direction, "+b" is the yellow direction, and "-b" is the blue direction. The gloss (L) of the metal substrate after chemical polishing is measured at an incident angle of 60°, and the gloss can reach 40GU~100GU. The gloss in this range is conducive to further improving the whitening effect of the anodized film.

[0030] In some embodiments, the acid solution may include at least one of phosphoric acid, nitric acid, and sulfuric acid.

[0031] In some embodiments, the temperature of the anodizing treatment can be 0°C to 22°C, which is conducive to adjusting the generation rate and thickness of the oxide film, thereby forming a porous anodized film with uniform thickness and moderate pore size. The temperature of the anodizing treatment can be 0°C, 5°C, 10°C, 15°C, 20°C, 22°C or any value within the numerical range composed of any two of the above values.

[0032] In some embodiments, the voltage of the anodizing treatment can be 8V to 30V, which is conducive to optimizing the formation process of the oxide film, regulating the thickness of the oxide film and the size of the pore size, thereby forming a porous anodized film with uniform thickness, uniform depth and moderate pore size. The voltage of the anodizing treatment can be 8V, 12V, 16V, 20V, 24V, 26V, 30V or any value within the numerical range composed of any two of the above values.

[0033] In some embodiments, the electrolyte for anodizing treatment may include a sulfuric acid solution, and the concentration of the sulfuric acid solution may be 20g / L~250g / L, providing an acidic environment for anodizing; the electrolyte for anodizing treatment may also include an organic acid and / or an organic alcohol, and the concentration of the organic acid may be 1g / L~100g / L, and the concentration of the organic alcohol may be 1g / L~300g / L. The organic acid and the organic alcohol may increase the hardness of the porous anodized film, reduce film peeling, and help improve the mechanical properties of the porous anodized film.

[0034] In some embodiments, the organic acid in the electrolyte for anodizing treatment may include at least one of oxalic acid, citric acid, cystine, lactic acid, tartaric acid, aminoacetic acid, and malic acid.

[0035] In some embodiments, the organic alcohol in the electrolyte of the anodizing treatment may include at least one of triethanolamine, glycerol, ethylene glycol, polyethylene glycol, and vinyl alcohol. In some embodiments, the thickness of the porous anodized film may be 1 μm to 20 μm, and further may be 14 μm to 16 μm. The thickness of the porous anodized film will affect the color of the anodized film product obtained after aluminum sulfate corrosion. For example, as the film thickness increases, the b value of the anodized film increases accordingly. The thickness range of the above-mentioned porous anodized film is conducive to improving the Lab value of the anodized film, and can also optimize the mechanical strength and corrosion resistance of the anodized film, which is conducive to improving the overall performance of the anodized film.

[0036] In some embodiments, the pore size of the porous anodized membrane can be 10nm~100nm, further can be 12nm~20nm, illustratively can be 10nm, 15nm, 20nm, 30nm, 40nm, 50nm, 80nm, 100nm or any value within the numerical range composed of any two of the above values.

[0037] Step S2, using a corrosive solution to corrode the pore walls of the porous anodized film to produce multiple microstructures on the pore walls to obtain a white anodized film, wherein the corrosive solution contains at least one of aluminum sulfate and sulfuric acid, and the microstructure includes at least one of microcracks and micropores.

[0038] In this step, the etching solution corrodes the pore wall of the porous anodized film to form a microstructure. Figure 2 As shown, the corrosion solution contains at least one of aluminum sulfate and sulfuric acid. The corrosion effect of the aluminum sulfate solution on the porous anodized film 20 on the metal substrate 10 mainly comes from Al 3+ Dissociation produces hydrogen ions (H + ), and / or, sulfuric acid ionization produces H + , H + The porous anodic oxide film 20 is dissolved, thereby generating a plurality of microstructures 40 on the pore walls 30 . The diffuse reflection of light by the microstructures 40 makes the anodic oxide film 20 appear white.

[0039] Aluminum sulfate hydrolysis produces H + , the hydrolysis process is as follows: Sulfuric acid ionizes to produce H + , the ionization process is as follows: H + Corrosion (dissolution) of porous anodic oxide film, the corrosion process is as follows: Select aluminum sulfate and / or sulfuric acid as the etching solution, and the dissociation rate (generation of H + ) and dissolved oxide film (forming Al 3+ ) are affected by Al 3+ The concentration inhibition effect controls the corrosion rate of the oxide film to a certain extent, which is conducive to the formation of a large number of uniformly distributed microstructures within the longitudinal depth range of the pore wall, thereby improving the whiteness of the anodic oxide film. At the same time, the corrosion rate of the corrosive solution on the porous anodic oxide film is moderate, which can keep the size of the microstructure within a small size range, ensuring that the physical and chemical properties of the porous anodic oxide film are maintained. In addition, aluminum sulfate and / or sulfuric acid have less impact on the environment than other heavy metal salt corrosive agents (such as chromic acid), which meets the environmental protection requirements of modern industry.

[0040] In the process of etching the hole wall with the etching solution, voltage can be further applied to the metal substrate to change the corrosion ions (H +) longitudinal diffusion process. Specifically, a metal substrate is used as an anode and a voltage is applied to the metal substrate, and the direction of the voltage is parallel to the depth direction of the pores in the porous anodized film. The depth direction of the pores can be extended along the thickness direction of the porous anodized film. Because the metal substrate is externally connected to a voltage, an electric field is formed, which can guide charged particles (such as H + ) moves along the direction of the electric field, producing electromigration. By changing the direction of the electric field, the corrosion ions H + Diffusion direction, so that H + Moving back and forth along the depth direction of the pores in the porous anodized film affects the longitudinal distribution of at least one of the microcracks and micropores in the pores, which is beneficial to further improve the uniformity of the longitudinal distribution of the microstructure and reduce local excessive corrosion, thereby further improving the quality and white effect of the anodized film.

[0041] In some embodiments, the voltage applied to the metal substrate may be 3V to 20V, wherein the applied voltage may be a direct current or an alternating current voltage, and within this voltage range, the H + Directional movement, improve H + The diffusion efficiency in the pores of the porous anodized film is conducive to further improving the uniformity of the longitudinal distribution of the microstructure along the pores, improving the whiteness of the anodized film, and the appropriate voltage is not easy to cause the anodized film to undergo secondary anode, which is easy to control the dissolution rate and effectively enhance the stability of the anodized film. The voltage can further be 5V to 15V, and can be exemplarily 3V, 4V, 5V, 6V, 7V, 8V, 9V, 10V, 11V, 12V, 13V, 14V, 15V, 16V, 17V, 18V, 19V, 20V or any value within the numerical range composed of any two of the above values.

[0042] In the process of etching the hole wall with the etching solution, ultrasonic waves can be further applied to the metal substrate to change the corrosion ions (H + ), specifically, the direction of the ultrasonic wave is perpendicular to the depth direction of the pores in the porous anodized film. The addition of ultrasonic waves can further promote the flow and penetration of the corrosive solution by causing microscopic movement of the corrosive solution through high-frequency vibration, so as to further regulate the lateral size of the microstructure, which is beneficial to further control the distribution state of the microstructure, thereby obtaining a microstructure with a relatively uniform size, and improving the stability and overall quality of the anodized film. In addition, aluminum sulfate with moderate corrosiveness as a corrosive solvent is beneficial to control the lateral size of the microstructure within a smaller range when applying ultrasonic waves to the metal substrate, which is beneficial to further improve the stability of the anodized film.

[0043] In some embodiments, the frequency of the ultrasonic wave can be 28kHz to 100kHz. Within this power range, the uniformity of the lateral microstructure size can be effectively improved, the anodized film is not easily damaged, and the stability of the anodized film is further enhanced. The frequency of the ultrasonic wave can further be 30kHz to 50kHz, and can be 28kHz, 30kHz, 40kHz, 50kHz, 60kHz, 70kHz, 80kHz, 90kHz, 100kHz or any value within the range of any two of the above values.

[0044] It can be understood that ultrasound and voltage can be applied simultaneously or in steps, both of which can effectively optimize the treatment effect.

[0045] In some embodiments, the concentration of the etching solution can be 10 g / L to 50 g / L. The appropriate concentration can balance the rate of generating H⁺ and the rate of dissolving the anodic oxide film to generate Al 3+ The rate of etching is further adjusted to control the size of the microstructure and the uniformity of distribution. The concentration of the etching solution can be further 20 g / L to 35 g / L, and can be 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L, 50 g / L or any value within the numerical range consisting of any two of the above values.

[0046] In some embodiments, the corrosion time can be 1min~30min, further can be 3min~8min, illustratively can be 1min, 3min, 4min, 5min, 6min, 7min, 8min, 10min, 12min, 15min, 18min, 20min, 30min or any value in the numerical range composed of any two of the above values. The corrosion temperature can be 35℃~80℃, illustratively can be 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃ or any value in the numerical range composed of any two of the above values. The above corrosion time and temperature range can effectively control the degree and rate of corrosion, which is conducive to controlling the size and uniformity of the distribution of the microstructure, improving the whiteness and gloss of the anodized film, and optimizing its physical and chemical properties to meet the quality requirements of the product.

[0047] In some embodiments, specific additives can be added to the corrosion solution. The additives can be adsorbed on the surface and pore walls of the porous anodized film to reduce the interfacial tension between the surface and pore walls and the corrosion solution, thereby improving the wettability of the corrosion solution, promoting the uniform diffusion of the corrosion solution, reducing local non-uniform corrosion, thereby improving the uniformity of the corrosion process, and further improving the uniformity of the longitudinal distribution of the microstructure, and also playing a certain protective role on the surface of the porous anodized film; in addition, the additives can also affect H + The transfer of the additive further adjusts the corrosion rate, plays a corrosion inhibition effect, and is beneficial to the production process control. Specifically, the additive may include at least one of an organic acid, an organic alcohol, and a surfactant.

[0048] In some embodiments, the concentration of the additive may be 1 g / L to 300 g / L, which is conducive to improving the corrosion effect. The concentration of the additive may further be 15 g / L to 30 g / L, and may be 1 g / L, 10 g / L, 15 g / L, 20 g / L, 30 g / L, 50 g / L, 100 g / L, 200 g / L, 300 g / L or any value within the range of any two of the above values.

[0049] In some embodiments, the above-mentioned organic alcohol may include at least one of triethanolamine, propylene glycol, ethylene glycol, polyethylene glycol and vinyl alcohol; the above-mentioned organic acid may include at least one of oxalic acid, citric acid, cystine, lactic acid, tartaric acid, aminoacetic acid and malic acid; the above-mentioned surfactant may include at least one of cationic surfactants, non-ionic surfactants and benign surfactants.

[0050] Compared with the prior art, the method for preparing the anodized film provided in the embodiment of the present application has the following beneficial effects: 1. Use aluminum sulfate and / or sulfuric acid as the corrosion solvent to generate corrosion ions H + , the pore walls of the porous anodized film are corroded to produce a uniform microstructure on the pore walls, so that the anodized film appears white. 3+ It will slow down the corrosion, help control the corrosion rate, adjust the size of the microstructure, and maintain the physical and chemical properties of the anodic oxide film. In addition, the corrosion solvent has little impact on the environment and is conducive to sustainable development.

[0051] 2. By adding specific additives, such as organic acids, organic alcohols or surfactants, the additives are adsorbed on the surface and pore walls of the porous anodized film, promoting the uniform diffusion of the corrosion solution and reducing local uneven corrosion, thereby improving the uniformity of the corrosion process and helping to improve the uniformity of the longitudinal distribution of the microstructure.

[0052] 3. By applying voltage during the corrosion process, the corrosion ion H + The longitudinal diffusion process makes H + It moves back and forth along the depth direction of the pores on the pore walls of the porous anodic oxide film, thereby improving the uniformity of the longitudinal distribution of the microstructure and improving the quality of the anodic oxide film.

[0053] 4. By applying ultrasound during the corrosion process, the corrosion ion H + The lateral diffusion process promotes the flow and penetration of the corrosive solution, regulates the lateral size of the microstructure, and obtains a microstructure with a relatively uniform size, thereby further improving the stability and overall quality of the anodized film.

[0054] An embodiment of the present application also provides an anodized film, which is prepared by the aforementioned method for preparing an anodized film. The anodized film has a porous structure, and the pore walls of the porous structure have multiple microstructures, and the microstructures include at least one of microcracks and micropores. The anodized film is white.

[0055] In addition, an embodiment of the present application also provides a metal workpiece, which is prepared by the aforementioned method for preparing anodized film. The surface of the metal workpiece has a porous anodized film, and the pore walls of the porous anodized film have multiple microstructures, and the microstructures include at least one of microcracks and micropores. The surface of the metal workpiece is white.

[0056] The above-mentioned anodized film, its preparation method, and metal workpiece are further described below through specific examples.

[0057] Example 1 Step 1: Pre-treat the aluminum alloy metal substrate by degreasing, alkali biting and stripping the black film, use 200g / L sulfuric acid as the electrolyte, the pre-treated metal substrate is the anode, graphite is the cathode, the oxidation voltage is a constant voltage of 16V, the oxidation temperature is 20°C, and the metal substrate is anodized to form a porous anodized film with a thickness of 16μm on the surface of the metal substrate.

[0058] Step 2: Use a corrosion solution containing 35 g / L aluminum sulfate to corrode the pore walls of the porous anodized film for 7 minutes, generate multiple microstructures on the pore walls, and obtain a white anodized film.

[0059] In Example 1, the Lab value of the prepared anodized film is 89GU, a is -0.33, b is 0.91, and the brightness value (gloss) is 6.4. The anodized film has high gloss and is bright white. In addition, using aluminum sulfate as a corrosion solvent is more environmentally friendly and has less impact on the environment. Figure 3 This is a scanning electron microscope photograph of the anodized film in Example 1, and the anodized film forms a microstructure.

[0060] Example 2 Step 1. Pre-treat the aluminum alloy metal substrate by degreasing, alkali biting and stripping the black film, use 200g / L sulfuric acid as the electrolyte, the pre-treated metal substrate is the anode, graphite is the cathode, the oxidation voltage is a constant voltage of 16V, the oxidation temperature is 20°C, and the metal substrate is anodized to form a porous anodized film with a thickness of 14μm on the surface of the metal substrate.

[0061] Step 2: Use a corrosion solution containing 30 g / L aluminum sulfate and 5 g / L sulfuric acid to corrode the pore walls of the above-mentioned porous anodized film for 4 minutes. At the same time, the corrosion solution also contains 20 g / L propylene glycol additive to produce multiple microstructures on the pore walls to obtain a white anodized film.

[0062] In Example 2, the Lab value of the prepared anodized film has L of 91.03 GU, a of -0.31, b of 0.91, and a brightness value (gloss) of 6.6. The anodized film is white, and the surface gloss reaches 91.03, and the brightness value is as high as 6.6, indicating that the anodized film has a smooth and bright appearance. Figure 4 This is a scanning electron microscope photograph of the anodized film prepared in Example 2, and the anodized film forms a microstructure.

[0063] Example 3 Step 1. Pre-treat the aluminum alloy metal substrate by degreasing, alkali biting and stripping the black film, use 200g / L sulfuric acid as the electrolyte, the pre-treated metal substrate is the anode, graphite is the cathode, the oxidation voltage is a constant voltage of 16V, the oxidation temperature is 20°C, and the metal substrate is anodized to form a porous anodized film with a thickness of 14μm on the surface of the metal substrate.

[0064] Step 2: Use a corrosion solution containing 30g / L aluminum sulfate to corrode the pore walls of the above-mentioned porous anodized film for 4 minutes. The corrosion solution also contains 20g / L propylene glycol additive, and apply 3V AC voltage and 30kHz ultrasound to the metal substrate. The direction of the AC voltage is parallel to the depth direction of the pores in the porous anodized film, and the direction of the ultrasound is perpendicular to the depth direction of the pores in the porous anodized film. Multiple microstructures are generated on the pore walls to obtain a white anodized film.

[0065] In Example 3, the Lab value of the prepared anodized film had L of 91 GU, a of -0.3, b of 0.6, and a brightness value (gloss) of 8.5, and the anodized film was bright white. Figure 5 This is a scanning electron microscope photograph of the anodized film prepared in Example 3. The anodized film forms a uniform microstructure.

[0066] Example 4 Step 1. Pre-treat the aluminum alloy metal substrate by degreasing, alkali biting and stripping the black film, use 200g / L sulfuric acid as the electrolyte, the pre-treated metal substrate is the anode, graphite is the cathode, the oxidation voltage is a constant voltage of 16V, the oxidation temperature is 20°C, and the metal substrate is anodized to form a porous anodized film with a thickness of 14μm on the surface of the metal substrate.

[0067] Step 2: Use a corrosion solution containing 15 g / L sulfuric acid to corrode the pore walls of the porous anodized film for 4 minutes, generate multiple microstructures on the pore walls, and obtain a white anodized film.

[0068] In Example 4, the Lab value of the prepared anodized film had L of 92 GU, a of -0.3, b of 0.98, and a brightness value (gloss) of 8.5, and the anodized film was bright white.

[0069] Example 5 Step 1. Pre-treat the aluminum alloy metal substrate by degreasing, alkali biting and stripping the black film, use 200g / L sulfuric acid as the electrolyte, the pre-treated metal substrate is the anode, graphite is the cathode, the oxidation voltage is a constant voltage of 16V, the oxidation temperature is 20°C, and the metal substrate is anodized to form a porous anodized film with a thickness of 14μm on the surface of the metal substrate.

[0070] Step 2: Use a corrosion solution containing 30g / L aluminum sulfate to corrode the pore walls of the above-mentioned porous anodized film for 4 minutes. At the same time, the corrosion solution also contains 20g / L propylene glycol additive, and apply a DC voltage of 3V to the metal substrate. The direction of the AC voltage is parallel to the depth direction of the pores in the porous anodized film, and multiple microstructures are generated on the pore walls to obtain a white anodized film.

[0071] In Example 5, the Lab value of the prepared anodized film had L of 90.1 GU, a of -0.34, b of 0.67, and a brightness value (gloss) of 7.6, and the anodized film was white.

[0072] Example 6 Step 1: Pre-treat the aluminum alloy metal substrate by degreasing, alkali biting and stripping the black film, use 200g / L sulfuric acid as the electrolyte, the pre-treated metal substrate is the anode, graphite is the cathode, the oxidation voltage is a constant voltage of 16V, the oxidation temperature is 20°C, and the metal substrate is anodized to form a porous anodized film with a thickness of 16μm on the surface of the metal substrate.

[0073] Step 2: Use a corrosion solution containing 30 g / L aluminum sulfate to corrode the pore walls of the above-mentioned porous anodized film for 7 minutes. At the same time, the corrosion solution also contains 30 g / L of propylene glycol additive, and apply 30 kHz ultrasonic waves to the metal substrate. The direction of the ultrasonic waves is perpendicular to the depth direction of the pores in the porous anodized film, and multiple microstructures are generated on the pore walls to obtain a white anodized film.

[0074] In Example 6, the Lab value of the prepared anodized film had L of 90 GU, a of -0.29, b of 0.74, and a brightness value (gloss) of 7, and the anodized film was white.

[0075] Example 7 Step 1. Pre-treat the aluminum alloy metal substrate by degreasing, alkali biting and stripping the black film, use 200g / L sulfuric acid as the electrolyte, the pre-treated metal substrate is the anode, graphite is the cathode, the oxidation voltage is a constant voltage of 16V, the oxidation temperature is 20°C, and the metal substrate is anodized to form a porous anodized film with a thickness of 14μm on the surface of the metal substrate.

[0076] Step 2: Use a corrosion solution containing 35g / L aluminum sulfate to corrode the pore walls of the above-mentioned porous anodized film for 14 minutes, and apply a DC voltage of 16V to the metal substrate. The direction of the AC voltage is parallel to the depth direction of the pores in the porous anodized film, and multiple microstructures are generated on the pore walls to obtain a white anodized film.

[0077] In Example 7, the Lab value of the prepared anodized film has L of 88.64 GU, a of -0.40, b of 0.35, and a brightness value (gloss) of 3.7. The anodized film is white, and the b value is lower than that of Example 1. That is, compared with Example 1, the color of the anodized film of Example 7 is closer to white and the degree of yellowing is lower.

[0078] Example 8 Step 1: Pre-treat the aluminum alloy metal substrate by degreasing, alkali biting and stripping the black film, use 200g / L sulfuric acid as the electrolyte, the pre-treated metal substrate is the anode, graphite is the cathode, the oxidation voltage is a constant voltage of 16V, the oxidation temperature is 20°C, and the metal substrate is anodized to form a porous anodized film with a thickness of 16μm on the surface of the metal substrate.

[0079] Step 2: Use a corrosion solution containing 35g / L aluminum sulfate to corrode the pore walls of the above-mentioned porous anodized film for 11 minutes, and apply 40kHz ultrasonic waves to the metal substrate. The direction of the ultrasonic waves is perpendicular to the depth direction of the pores in the porous anodized film, and multiple microstructures are generated on the pore walls to obtain a white anodized film.

[0080] In Example 8, the Lab value of the prepared anodized film has an L value of 90.22 GU, a of -0.37, b of 0.66, a brightness value (gloss) of 8.6, and the anodized film is white. The L value is higher than that of Example 1, and the b value is lower than that of Example 1. That is, compared with Example 1, the color of the anodized film of Example 8 is closer to white and the yellowing degree is lower.

[0081] Comparative Example 1 Step 1: The aluminum alloy metal substrate is pretreated by degreasing, alkali biting and stripping black film, 40g / L chromic acid is used as the electrolyte, the pretreated metal substrate is the anode, graphite is the cathode, the oxidation voltage is a constant voltage of 16V, the oxidation temperature is 40°C, and the metal substrate is anodized to form a white anodized film on the surface of the metal substrate. The film thickness of the anodized film is 4μm.

[0082] In Comparative Example 1, the Lab value of the prepared anodized film has L of 88 GU, a of -5, b of -1.43, and a brightness value (gloss) of 5.1. Compared with Examples 1-8, the brightness value of the anodized film in Comparative Example 1 is lower, and the color is yellowish white.

[0083] The description of the above embodiments is only used to help understand the method of the present application and its core idea; in addition, for ordinary technicians in this field, various other corresponding changes and deformations can be made according to the technical concept of the present application, and all these changes and deformations should fall within the scope of protection of the claims of the present application.

Claims

1. A method for preparing an anodic oxide film, characterized in that: include: Anodizing a metal substrate of aluminum or aluminum alloy to form a porous anodized film on the surface of the metal substrate; as well as The pore walls of the porous anodized film are corroded by a corrosive solution to produce a plurality of microstructures on the pore walls, thereby obtaining the white anodized film, wherein the corrosive solution contains at least one of aluminum sulfate and sulfuric acid, and the microstructures include at least one of microcracks and micropores.

2. The method for preparing anodized film according to claim 1, characterized in that: The concentration of the corrosive solution is 10 g / L to 50 g / L; and / or In the step of corroding the porous anodized film, the corrosion time is 1 min to 30 min, and the corrosion temperature is 35° C. to 80° C.

3. The method for preparing anodized film according to claim 1, characterized in that: The etching solution contains additives, and the additives include at least one of organic acid, organic alcohol and surfactant.

4. The method for preparing anodized film according to claim 3, characterized in that: The concentration of the additive is 10 g / L to 300 g / L.

5. The method for preparing anodized film according to claim 3, characterized in that: The organic alcohol comprises at least one of triethanolamine, glycerol, ethylene glycol, polyethylene glycol and vinyl alcohol; The organic acid includes at least one of oxalic acid, citric acid, cystine, lactic acid, tartaric acid, aminoacetic acid and malic acid.

6. The method for preparing anodized film according to claim 1, characterized in that: In the step of corroding the porous anodized film, the metal substrate is used as an anode, a voltage is applied to the metal substrate, and the direction of applying the voltage is parallel to the depth direction of the pores in the porous anodized film.

7. The method for preparing an anodic oxide film according to claim 6, characterized in that: The voltage applied to the metal substrate is 3V~20V.

8. The method for preparing anodized film according to claim 1, characterized in that: In the step of corroding the porous anodized film, ultrasonic waves are applied to the metal substrate, and the direction of applying the ultrasonic waves is perpendicular to the depth direction of the pores in the porous anodized film.

9. The method for preparing anodized film according to claim 8, characterized in that: The frequency of the ultrasonic wave is 28kHz~100kHz.

10. The method for preparing anodized film according to claim 1, characterized in that: Before the metal substrate is subjected to anodizing treatment, the metal substrate is subjected to chemical polishing, and the glossiness of the metal substrate after polishing is measured at an incident angle of 60° and is 40 GU-100 GU.

11. The method for preparing anodized film according to claim 1, characterized in that: The thickness of the anodized film is 1 μm to 20 μm; The pores in the anodized film have a pore size of 10 nm to 100 nm.

12. The method for preparing anodized film according to claim 1, characterized in that: In the step of anodizing the metal substrate, the anodizing conditions include at least one of the following features: (1) The temperature of the anodizing treatment is 0°C to 30°C; (2) The voltage of the anodizing treatment is 8V~30V; (3) The electrolyte for the anodizing treatment includes a sulfuric acid solution, and the concentration of the sulfuric acid solution is 20 g / L to 250 g / L.

13. An anodic oxide film, characterized in that: The anodized film is prepared by the preparation method as described in any one of claims 1 to 12, the anodized film has a porous structure, the pore walls of the porous structure have a plurality of microstructures, the microstructures include at least one of microcracks and micropores, and the anodized film is white.

14. A metal workpiece, characterized in that: The metal workpiece is prepared by the preparation method described in any one of claims 1 to 12, the surface of the metal workpiece has a porous anodized film, the pore walls of the porous anodized film have multiple microstructures, the microstructures include at least one of microcracks and micropores, and the surface of the metal workpiece is white.

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