Light metal colored micro-arc oxidation gradient method

Abstract

The invention belongs to the technical field of light metal surface modification treatment technologies, and particularly relates to a light metal colored micro-arc oxidation gradual change method which comprises the following steps: S1, workpiece pretreatment: polishing the surface of a light metal workpiece to form roughness Ra gradually changing in the length direction; s2, surface cleaning treatment is conducted, specifically, impurities on the surface of the light metal workpiece are removed through ultrasonic waves, and washing and drying treatment are conducted; and S3, oxidation treatment is conducted, specifically, the light metal workpiece is immersed in an electrolyte with the temperature gradually changed, and micro-arc oxidation treatment is conducted through a bipolar pulse power source. According to the method, the roughness Ra gradual change treatment is applied to the surface of the light metal workpiece in the length direction, and the light metal workpiece is subjected to micro-arc oxidation by adopting the bipolar pulse power supply in the electrolyte with the temperature gradually changed, so that the oxidation film with the color gradually changing along with the position is effectively formed, and the attractiveness of the oxidation film layer is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of light metal surface modification treatment, and particularly relates to a method for colored micro-arc oxidation gradient of light metals. Background Art

[0002] Light metal materials are widely used in the fields of aerospace, automotive manufacturing, electronic products, and decoration due to their light weight, high strength, and good corrosion resistance. However, the surface of light metals is prone to oxidation and has a single appearance, making it difficult to meet the dual requirements of functionality and aesthetics for high-end applications. Micro-arc oxidation (MAO), as an advanced surface modification technology, can form a dense, hard, and wear-resistant and corrosion-resistant ceramic oxide film on the surface of light metals. At the same time, by adjusting process parameters, various colors can be formed, enhancing the decorative effect and added value of the materials.

[0003] The existing micro-arc oxidation technology mainly achieves a uniform color coating, making it difficult to achieve a gradient effect of the surface color, which limits its application in the fields of personalization and high-end decoration. At the same time, how to effectively control the continuous change of color to achieve a gradient effect still faces the technical problem of difficult precise matching between the surface structure and process parameters. The traditional control of micro-arc oxidation color mostly relies on single parameter adjustment, making it difficult to balance the stability and continuity of the film layer performance and color effect. Summary of the Invention

[0004] Aiming at the problem that the color of light metal micro-arc oxidation in the prior art is single and it is difficult to achieve a gradient, the present invention proposes a method for colored micro-arc oxidation gradient of light metals. This method effectively realizes the formation of an oxide film with gradually changing color with position by applying a gradually changing surface roughness Ra along the length direction on the surface of the light metal workpiece, and using a bipolar pulse power supply to perform micro-arc oxidation on the light metal workpiece in an electrolyte with a gradually changing temperature, significantly enhancing the aesthetics of the oxide film.

[0005] To achieve the above object, the technical solutions adopted are as follows: The present invention provides a method for colored micro-arc oxidation gradient of light metals, including the following steps: S1. Workpiece pretreatment: Grinding the surface of the light metal workpiece to form a gradually changing surface roughness Ra along the length direction; S2. Surface cleaning treatment: Using ultrasonic waves to remove impurities on the surface of the light metal workpiece, and performing water washing and drying treatments; S3. Oxidation treatment: Immersing the light metal workpiece in an electrolyte with a gradually changing temperature, and performing micro-arc oxidation treatment using a bipolar pulse power supply.

[0006] Further, in step S1, the grinding method is laser etching.

[0007] Further, in step S1, the range of the surface roughness Ra is 0.10 μm to 1.00 μm, and the gradual change rate of the surface roughness Ra is 0.05 μm / mm to 0.2 μm / mm.

[0008] Further, in step S2, the frequency of the ultrasonic wave is 40 kHz to 60 kHz, the time is 5 to 10 min, and the temperature is controlled at 40°C to 60°C.

[0009] Further, in step S2, deionized water rinsing is used for the water washing treatment; the temperature of the drying treatment is 60°C to 80°C, and the drying time is 20 min to 30 min.

[0010] Further, in step S3, the gradual change direction of the electrolyte temperature is the same as that of the surface roughness Ra of the light metal workpiece, and both change from small to large along the length direction of the light metal workpiece.

[0011] Further, in step S3, the temperature range of the electrolyte is 25°C to 50°C, and the temperature gradual change rate is 2°C / m to 5°C / m.

[0012] Further, in step S3, the time of the micro-arc oxidation treatment is 10 min to 30 min.

[0013] Further, in step S3, the anode pulse voltage of the bipolar pulse power supply is 300 V to 500 V, the cathode pulse voltage is 50 V to 150 V, and the pulse frequency is 200 Hz to 1000 Hz.

[0014] Further, the light metal workpiece includes one or more of aluminum, magnesium, titanium or their alloys.

[0015] Adopting the above technical solution, there are at least the following beneficial effects: ① In the present invention, by constructing a gradually changing surface roughness Ra from 0.10 μm to 1.00 μm along the length direction on the surface of the light metal workpiece, different regions have different discharge intensities and plasma action conditions during the micro-arc oxidation process. The number of micro-protrusions on the surface of the rougher region increases, and it is easier to generate high-energy discharge channels, forming an oxide film with a larger thickness and a darker color tone; while in the smoother region, the discharge is uniform, the film layer is thinner, and the color is brighter. This structure control mechanism enables the color of the film layer to gradually change naturally along the surface of the workpiece, with a soft color transition and rich layers; ②In the present invention, by constructing an electrolyte temperature gradient field from 25°C to 50°C and ensuring that it is consistent with the roughness gradient direction (both increasing from small to large along the length direction), the oxidation reaction rate is effectively regulated. In the temperature-rising region, ion migration is more active, the film formation rate is accelerated, and the film color is promoted to change towards warm colors (such as orange, brown, blue-violet); while in the low-temperature region, the reaction rate is slower, forming cold colors (such as silver-white, cyan-blue). The gradient control of temperature not only improves the gradient accuracy of color presentation, but also helps to reduce thermal stress, and improve the denseness and uniformity of the film layer; ③In the present invention, the synergistic continuous gradient of roughness Ra and temperature significantly improves the structural integrity and decorative performance of the film layer. In the present invention, the roughness Ra on the surface of the light metal workpiece gradually transitions from 0.10 μm to 1.00 μm along the length direction, and the electrolyte temperature also slowly rises from 25°C to 50°C synchronously, both showing continuous and smooth gradient changes. This structural setting effectively avoids local stress concentration caused by sudden changes in surface topography or thermal field, and reduces adverse factors such as uneven thermal shock and sudden change in oxidation rate during the micro-arc discharge process.

[0016] Secondly, due to the continuous gradient of roughness Ra and temperature, the oxidation film realizes a gradient deposition process with balanced composition and stable structure on the entire workpiece surface, thus preventing failure phenomena such as micro-cracks, peeling, and delamination caused by sudden changes in the film layer structure. At the same time, the natural transition of the film color from light to deep and from cold to warm gives it a good sense of hierarchy and artistic beauty visually, enhancing the decorative effect and application attractiveness.

[0017] Thirdly, the continuous gradient of roughness Ra and temperature also helps the progressive release and buffer diffusion of film layer stress, improving the overall adhesion firmness, corrosion resistance and long-term stability of the film layer, and is suitable for surface functional treatment of high-end light alloy products (such as aviation, consumer electronics casings, etc.) with high requirements for appearance consistency and structural reliability. Specific embodiments

[0018] In the following, the example solutions of the embodiments of the present invention will be clearly and completely described. Unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meaning understood by those of ordinary skill in the art.

[0019] The present invention provides a method for light metal colored micro-arc oxidation gradient, including the following steps: S1. Workpiece pretreatment: Grind the surface of the light metal workpiece to form a gradually changing roughness Ra along the length direction; S2. Surface cleaning treatment: Use ultrasonic waves to remove impurities on the surface of the light metal workpiece, and perform water washing and drying treatments; S3. Oxidation treatment: Immerse the light metal workpiece in the electrolyte with a gradually changing temperature, and perform micro-arc oxidation treatment using a bipolar pulse power supply.

[0020] In the present invention, by constructing a gradually changing surface roughness Ra along the length direction on the surface of the light metal workpiece, placing the workpiece in the electrolyte with a gradually changing temperature distribution, and performing micro-arc oxidation treatment using a bipolar pulse power supply, a gradual change in the color of the oxide film is achieved. Specifically, the continuous change in the roughness Ra enables the surface topography at different positions to regulate the local discharge intensity and arc duration. In the relatively rough area, due to the existence of more sharp microstructures, it is easier to form a local high electric field, which promotes the discharge to occur first and more violently, resulting in a thicker and darker film layer; while in the relatively smooth area, the discharge is relatively mild, and the film layer is thin and light in color. At the same time, the gradually increasing setting of the electrolyte temperature along the length direction synchronously enhances the oxidation reaction rate. The high-temperature area promotes the formation of plasma channels and active discharge behavior, intensifies the film formation and coloring reaction, and thus realizes the formation of a micro-arc oxidation film layer with a gradually changing color on the surface of the light metal workpiece.

[0021] In some embodiments, in step S1, the grinding method is laser etching.

[0022] In order to achieve a continuously changing roughness Ra along the length direction on the surface of the light metal workpiece, when using the laser etching method in step S1, the difference in etching depth and microstructure topography in different regions can be realized by regulating parameters such as the power density, scanning speed, pulse frequency, or repetition times of the laser beam during the scanning process, so as to construct a continuous change in the surface roughness from small to large. Specifically, arrange the laser scanning path along the length direction of the workpiece, keep the laser at a lower energy density and a higher scanning speed at the starting point of the scan, generating shallower melting pits and finer surface structures, corresponding to a smaller surface roughness Ra; while gradually increasing the laser energy density or slowing down the scanning speed at the end of the scan, making the etching depth gradually increase and the surface melting traces more rough, thus achieving a larger roughness Ra value. By precisely adjusting the gradual change process of the laser process parameters, a light metal workpiece with a gradually changing roughness Ra can be obtained, providing the necessary basic structural conditions for the gradual change in the film layer color during the subsequent micro-arc oxidation process. This method has the advantages of non-contact, high precision, and strong controllability, and is suitable for processing workpieces with complex geometric shapes.

[0023] In some embodiments, in step S1, the range of the roughness Ra is 0.10 μm to 1.00 μm, and the gradual change rate of the roughness Ra is 0.05 μm / mm to 0.2 μm / mm.

[0024] When the surface roughness Ra of the light metal workpiece is controlled within the range of 0.10 μm to 1.00 μm, stable and effective discharge behavior can be achieved during the micro-arc oxidation process, which not only avoids the difficulty of discharge caused by excessive smoothness but also prevents local ablation and film layer defects caused by excessive surface roughness, making the formation of the oxide film more uniform and dense. At the same time, this roughness range has a good responsiveness to the regulation of the film layer color, which helps to achieve a gradual change effect from light to dark.

[0025] When the gradual change rate of the roughness Ra is controlled between 0.05 μm / mm and 0.2 μm / mm, it can ensure a smooth transition of the surface roughness along the length direction of the workpiece, making the color of the oxide film layer present a linear and continuous visual change, avoiding sudden changes, and enhancing the overall decorative beauty and the structural integrity of the film layer. This rate range is also conducive to achieving high repeatability and consistency in process control, and achieving a balance between the gradual change effect and the film layer quality.

[0026] In some embodiments, in step S2, the frequency of the ultrasonic wave is 40 kHz to 60 kHz, the time is 5 to 10 min, and the temperature is controlled at 40°C to 60°C.

[0027] In the present invention, ultrasonic cleaning treatment with a frequency of 40 kHz to 60 kHz, a time of 5 to 10 min, and a temperature controlled at 40°C to 60°C can efficiently remove the oil stains and fine impurities on the surface of the light metal workpiece, significantly improving the surface cleanliness; at the same time, the ultrasonic wave under this parameter range has a mild effect and will not damage the surface of the workpiece, which helps to maintain the preset surface roughness gradient; the appropriate temperature improves the cleaning efficiency and ensures sufficient contact and uniform reaction between the electrolyte and the workpiece surface during the subsequent micro-arc oxidation process, thereby effectively improving the uniformity, density, and adhesion of the oxide film, and ensuring the stability and continuity of the color gradient effect.

[0028] In some embodiments, in step S2, the water washing treatment uses deionized water rinsing; the temperature of the drying treatment is 60°C to 80°C, and the drying time is 20 to 30 min.

[0029] In the present invention, rinsing the light metal workpiece with deionized water can effectively remove the residual ultrasonic cleaning solution and impurities on the surface of the workpiece, avoiding the adverse effects of ion contamination on the subsequent micro-arc oxidation process; the drying treatment is carried out within the temperature range of 60°C to 80°C for 20 min to 30 min to ensure that the surface of the workpiece is completely dry, avoiding local dilution of the electrolyte during the oxidation process caused by water residue, and improving the uniform gradation and density of the oxide film.

[0030] In some embodiments, in step S3, the gradual change direction of the electrolyte temperature is the same as the gradual change direction of the surface roughness Ra of the light metal workpiece, both changing from small to large along the length direction of the light metal workpiece.

[0031] In the present invention, the gradual change direction of the electrolyte temperature is consistent with the gradual change direction of the surface roughness Ra of the light metal workpiece, and both gradually increase from small to large along the length direction of the workpiece, so that the discharge intensity and reaction activity of different parts of the light metal workpiece during the micro-arc oxidation process show a gradient change distribution. The gradually increasing temperature promotes the enhancement of the ionic activity and conductivity of the electrolyte, while the increasing surface roughness affects the local electric field distribution and the formation of discharge channels. The two work together to effectively control the thickness, pore structure and crystal morphology of the oxide film, and then achieve a smooth gradient change in color. In addition, the gradient design avoids the stress concentration of the film layer caused by sudden changes in temperature or roughness, reduces the risk of cracks and peeling, significantly improves the bonding strength and overall stability of the oxide film, and ensures that the micro-arc oxidation film presents a continuous, uniform and seamless transition color change effect.

[0032] In some embodiments, in step S3, the temperature range of the electrolyte is 25°C to 50°C, and the temperature gradient rate is 2°C / m to 5°C / m.

[0033] In the present invention, under the conditions that the electrolyte temperature range is 25°C to 50°C and the temperature gradient rate is controlled at 2°C / m to 5°C / m, micro-arc oxidation treatment can effectively regulate the intensity and rate of the oxidation reaction, causing gradual changes in the micro-plasma discharge characteristics at different positions, so as to generate a continuous transition oxide film layer structure and color effect on the surface of the light metal workpiece. A moderate temperature range is beneficial to maintaining the stability and reaction activity of the electrolyte, avoiding problems such as film layer ablation caused by high temperature or insufficient discharge at low temperature. The linear gradient of temperature helps the oxide film to gradually thicken and the pore size to change from the cold end to the hot end, and induces the generation of different degrees of hues, ensuring a smooth transition of the film layer color and improving the decoration of the film layer.

[0034] Specifically, in the actual production process, the electrolyte is placed in an electrolyte tank with a length of 5 m. A high-temperature module (such as a PID temperature controller) is set at one end of the electrolyte tank, and the temperature of the high-temperature module is set at 50°C; a low-temperature module (such as a PID temperature controller) is set at the other end of the electrolyte tank, and the temperature of the low-temperature module is set at 25°C. Thus, a stable linear gradient from 25°C to 50°C in the electrolyte in the electrolyte tank is achieved, and the temperature gradient rate is 5°C / m.

[0035] In addition, when the light metal workpiece is placed in the electrolyte tank for micro-arc oxidation, it should be noted that the gradual change direction of the electrolyte temperature is the same as the gradual change direction of the surface roughness Ra of the light metal workpiece, and both change from small to large along the length direction of the light metal workpiece.

[0036] In some embodiments, in step S3, the time of the micro-arc oxidation treatment is 10 min to 30 min.

[0037] In the present invention, controlling the time in micro-arc oxidation treatment between 10 min and 30 min helps to form a dense and structurally complete oxide film layer on the surface of light metal workpieces. Oxidation time above 10 min can ensure sufficient plasma discharge, promote continuous generation and densification of the film layer, and improve the bonding strength and corrosion resistance of the film layer; while limiting the time within 30 min can effectively prevent problems such as excessive film thickness, internal stress accumulation, and micro-crack generation caused by long-term discharge, thus avoiding failure problems such as film peeling and powdering. This time interval also adapts to the gradual changes in electrolyte temperature and workpiece surface roughness, enabling sufficient and balanced oxidation reactions in different regions, enhancing the continuity of color gradient and the overall uniformity of the film layer, and being conducive to obtaining excellent decorative effects.

[0038] In some embodiments, in step S3, the anode pulse voltage of the bipolar pulse power supply is 300 V - 500 V, the cathode pulse voltage is 50 V - 150 V, and the pulse frequency is 200 Hz - 1000 Hz.

[0039] In the present invention, during the micro-arc oxidation process, using a bipolar pulse power supply with an anode pulse voltage of 300 V - 500 V, a cathode pulse voltage of 50 V - 150 V, and a pulse frequency of 200 Hz - 1000 Hz can achieve precise control of the discharge behavior and the film layer growth process. Among them, a moderate anode pulse voltage can promote the formation of a stable plasma discharge channel on the workpiece surface, stimulate the oxidation reaction on the surface of the metal substrate, and form a dense film layer; the introduction of the cathode pulse voltage helps to reduce the plasma thermal effect, reduce the film layer stress, and inhibit surface ablation, thereby improving the flatness and adhesion of the film layer; and controlling the pulse frequency within the range of 200 Hz - 1000 Hz can achieve a high-frequency and low-energy pulse superposition method, which is conducive to improving the oxidation efficiency, slowing down the local temperature rise of the electrolyte, and avoiding the generation of film layer defects.

[0040] In some embodiments, the light metal workpiece includes one or more of aluminum, magnesium, titanium, or their alloys. In specific implementations, aluminum, magnesium, titanium, and their alloys are commonly used substrates in the micro-arc oxidation process due to their excellent specific strength, corrosion resistance, and workability.

[0041] The present invention is further described below through examples.

[0042] Example 1. Formation of an oxide film layer with a color gradient from silver-white to dark gray on the surface of an aluminum alloy rod S1. Workpiece pretreatment: Using laser etching, the surface of the aluminum alloy rod is roughened and polished along the length direction, so that the surface roughness Ra of the aluminum alloy rod gradually changes from 0.10 μm at one end to 1.00 μm at the other end, with a gradual change rate of 0.06 μm / mm.

[0043] S2. Surface cleaning treatment: Put the aluminum alloy bar into an ultrasonic cleaning tank with a frequency of 40 kHz and a temperature of 50 °C for 8 minutes, then rinse it with deionized water, and then dry it in a hot air environment at 60 °C for 25 minutes.

[0044] S3. Oxidation treatment: Immerse the aluminum alloy bar horizontally into an electrolyte tank filled with electrolyte with a gradually changing temperature. The electrolyte tank (and the electrolyte in it) gradually increases from 25 °C at one end to 50 °C at the other end, and the temperature change rate is 2.5 °C / m; among them, the components of the electrolyte include 4.0 g / L of sodium phosphate (Na3PO4), 7.0 g / L of sodium silicate (Na2SiO3), 2.0 g / L of boric acid (H3BO3), and 1.5 g / L of sodium acetate (CH3COONa), and the pH value of the electrolyte is 9.5. Use a bipolar pulse power supply (anode voltage 400 V, cathode voltage 100 V, frequency 500 Hz, anode-cathode duty cycle 3:1) for micro-arc oxidation treatment for 20 minutes.

[0045] So far, the formation of an oxide film layer with a gradual change from silver-white to dark gray on the surface of the aluminum alloy bar is completed. The color of this oxide film gradually transitions from silver-white to dark gray, presenting a natural transition gradient effect, with a uniform film layer adhesion and no cracks or peeling.

[0046] Example 2. Formation of an oxide film layer with a gradual change from light gold to maroon on the surface of a magnesium alloy sheet S1. Workpiece pretreatment: Adopt the laser etching method to roughen and polish the surface of the magnesium alloy sheet along the length direction, so that the surface roughness Ra of the magnesium alloy sheet gradually changes from 0.20 μm at one end to 0.95 μm at the other end, and the change rate is 0.10 μm / mm.

[0047] S2. Surface cleaning treatment: Put the magnesium alloy sheet into an ultrasonic cleaning tank with a frequency of 50 kHz and a temperature of 55 °C for 6 minutes, then rinse it with deionized water, and then dry it in a hot air environment at 50 °C for 20 minutes.

[0048] S3. Oxidation treatment: Immerse the magnesium alloy sheet horizontally into an electrolyte tank filled with electrolyte with a gradually changing temperature. The electrolyte tank (and the electrolyte in it) gradually increases from 30 °C at one end to 50 °C at the other end, and the temperature change rate is 3.0 °C / m; among them, the components of the electrolyte include 8.0 g / L of sodium phosphate (Na3PO4), 3.0 g / L of potassium acetate (CH3COOK), 1.0 g / L of manganese acetate (Mn(CH3COO)2), and 1.5 g / L of potassium sodium tartrate (NaKC4H4O6), and the pH value of the electrolyte is 10.0. Use a bipolar pulse power supply (anode voltage 450 V, cathode voltage 80 V, frequency 700 Hz, anode-cathode duty cycle 3:1) for micro-arc oxidation treatment for 25 minutes.

[0049] So far, the formation of an oxide film layer with a gradual change from light gold to dark red on the surface of the magnesium alloy sheet is completed. The color of this oxide film gradually transitions from light gold to dark red, presenting a natural gradient effect without obvious boundaries and with a delicate texture. The compactness of the film layer is good.

[0050] Example 3. Formation of an oxide film layer with a gradual change from blue-violet to dark blue on the surface of a titanium alloy sheet S1. Workpiece pretreatment: Using the laser etching method, the surface of the titanium alloy sheet is roughened and polished along the length direction, so that the surface roughness Ra of the titanium alloy sheet gradually changes from 0.30 μm at one end to 0.80 μm at the other end, and the gradual change rate is 0.18 μm / mm.

[0051] S2. Surface cleaning treatment: The titanium alloy sheet is placed in an ultrasonic cleaning tank with a frequency of 60 kHz and a temperature of 60 °C for 9 min, then rinsed with deionized water, and then dried in a hot air environment at 55 °C for 25 min.

[0052] S3. Oxidation treatment: The titanium alloy sheet is horizontally immersed in an electrolyte tank filled with electrolyte with a gradually changing temperature. The electrolyte tank (and the electrolyte in the tank) gradually increases from 28 °C at one end to 45 °C at the other end, and the temperature gradual change rate is 4.0 °C / m; among them, the composition of the electrolyte includes potassium silicate (K2SiO3) 5 g / L, tartaric acid (C4H6O6) 2.5 g / L, boric acid (H3BO3) 1.5 g / L, and sodium tungstate (Na2WO4) 0.6 g / L, and the pH value of the electrolyte is 8.0. Micro-arc oxidation treatment is carried out for 25 min using a bipolar pulse power supply (anode voltage 500 V, cathode voltage 100 V, frequency 400 Hz, anode-cathode duty cycle 3:1).

[0053] So far, the formation of an oxide film layer with a gradual change from blue-violet to dark blue on the surface of the titanium alloy sheet is completed. The color of this oxide film gradually transitions from blue-violet to dark blue. After the oxidation treatment, the surface color of the titanium alloy sheet has a natural transition without obvious boundaries, and the overall color is harmonious.

[0054] Comparative Example 1. Micro-arc oxidation on the surface of an aluminum alloy rod The difference between Comparative Example 1 and Example 1 is that the surface roughness Ra of the aluminum alloy rod in Comparative Example 1 is uniform, and the temperature of the electrolyte used is also constant, as follows: S1. Workpiece pretreatment: Using the laser etching method, the surface roughness Ra of the aluminum alloy rod is made to be 0.1 μm.

[0055] S2. Surface cleaning treatment: The aluminum alloy rod is placed in an ultrasonic cleaning tank with a frequency of 40 kHz and a temperature of 50 °C for 8 min, then rinsed with deionized water, and then dried in a hot air environment at 60 °C for 25 min.

[0056] S3. Oxidation treatment: Horizontally immerse the aluminum alloy rod into the electrolyte bath filled with electrolyte, and the temperature of the electrolyte is 25 °C; wherein, the components of the electrolyte include 4.0 g / L of sodium phosphate (Na3PO4), 7.0 g / L of sodium silicate (Na2SiO3), 2.0 g / L of boric acid (H3BO3), and 1.5 g / L of sodium acetate (CH3COONa), and the pH value of the electrolyte is 9.5. Use a bipolar pulse power supply (anode voltage 400 V, cathode voltage 100 V, frequency 500 Hz, anode-cathode duty ratio 3:1) for micro-arc oxidation treatment for 20 min.

[0057] On the surface of the aluminum alloy rod in Comparative Example 1, a grayish-white film layer is formed by micro-arc oxidation, and there is no color gradient phenomenon.

[0058] Comparative Example 2. Micro-arc oxidation on the surface of a magnesium alloy sheet S1. Workpiece pretreatment: Adopt laser etching to roughen and polish the surface of the magnesium alloy sheet, so that the surface roughness Ra of the magnesium alloy sheet is 0.20 μm.

[0059] S2. Surface cleaning treatment: Put the magnesium alloy sheet into an ultrasonic cleaning tank with a frequency of 50 kHz and a temperature of 55 °C for 6 min, then rinse with deionized water, and then dry in a hot air environment at 50 °C for 20 min.

[0060] S3. Oxidation treatment: Horizontally immerse the magnesium alloy sheet into the electrolyte bath filled with electrolyte, and the temperature of the electrolyte is 30 °C; wherein, the components of the electrolyte include 8.0 g / L of sodium phosphate (Na3PO4), 3.0 g / L of potassium acetate (CH3COOK), 1.0 g / L of manganese acetate (Mn(CH3COO)2), and 1.5 g / L of potassium sodium tartrate (NaKC4H4O6), and the pH value of the electrolyte is 10.0. Use a bipolar pulse power supply (anode voltage 450 V, cathode voltage 80 V, frequency 700 Hz, anode-cathode duty ratio 3:1) for micro-arc oxidation treatment for 25 min.

[0061] On the surface of the magnesium alloy sheet in Comparative Example 2, a brownish-red film layer is formed by micro-arc oxidation, and there is no color gradient phenomenon.

[0062] Comparative Example 3. Micro-arc oxidation on the surface of a titanium alloy sheet S1. Workpiece pretreatment: Adopt laser etching to roughen and polish the surface of the titanium alloy sheet, so that the surface roughness Ra of the titanium alloy sheet is 0.30 μm.

[0063] S2. Surface cleaning treatment: Put the titanium alloy sheet into an ultrasonic cleaning tank with a frequency of 60 kHz and a temperature of 60 °C for 9 min, then rinse with deionized water, and then dry in a hot air environment at 55 °C for 25 min.

[0064] S3. Oxidation treatment: Horizontally immerse the titanium alloy sheet into the electrolyte tank filled with electrolyte, and the temperature of the electrolyte tank is 28 °C; wherein, the components of the electrolyte include 5 g / L of potassium silicate (K2SiO3), 2.5 g / L of tartaric acid (C4H6O6), 1.5 g / L of boric acid (H3BO3), and 0.6 g / L of sodium tungstate (Na2WO4), and the pH value of the electrolyte is 8.0. Use a bipolar pulse power supply (anode voltage 500 V, cathode voltage 100 V, frequency 400 Hz, anode-cathode duty ratio 3:1) for micro-arc oxidation treatment for 25 min.

[0065] In Comparative Example 3, a dark blue film layer was formed on the surface of the titanium alloy sheet by micro-arc oxidation, and there was no color gradient phenomenon.

[0066] In Examples 1 to 3, using aluminum alloy bars, magnesium alloy sheets, and titanium alloy sheets as substrates respectively, by means of laser etching, the surface roughness of the workpiece along the length direction gradually increases from one end to the other end, forming a surface structure with a linear gradient of Ra value; at the same time, during the oxidation process, horizontally immerse the workpiece into the electrolyte with a linear gradient of temperature, so that the electrolyte temperature gradually changes from low to high along the length direction. After micro-arc oxidation treatment under the above conditions, continuous gradient oxidation film colors were obtained on the surfaces of each workpiece: the aluminum alloy gradually transitions from silver-white to dark gray, the magnesium alloy transitions from light gold to brownish-red, and the titanium alloy transitions from blue-violet to dark blue. The film layer not only has a natural color transition without obvious boundaries, but also performs well in terms of adhesion and denseness, has a strong visual sense of hierarchy, and has excellent decorative properties and consistency.

[0067] In contrast, in Comparative Examples 1 to 3, the linearly gradient roughness Ra and temperature were not used. The surface roughness of the light metal workpieces was a single fixed value, and the electrolyte temperature was also kept constant. Although the oxidation conditions were correspondingly consistent, the colors of the obtained oxidation film layers were all single-toned, namely uniform grayish-white, brownish-red, and dark blue respectively, lacking transition effects and color levels, with a monotonous visual appearance and obvious lack of decorative properties. In addition, the constant roughness results in a uniform distribution of micro-plasma discharge behavior, limited changes in the film layer structure, and lack of spatial control; the constant-temperature electrolyte limits the differential evolution of the oxidation rate and crystal phase structure in different regions, which is not conducive to forming color differences. The experimental results of the above comparative examples fully prove that: without introducing the roughness gradient and temperature gradient schemes in the present invention, it is impossible to obtain an oxidation film layer with a continuously changing color effect.

[0068] It can be seen that the present invention realizes the formation of a natural and continuous gradient oxidation film layer on the surface of light metals by introducing a surface roughness gradient and an electrolyte temperature gradient along the length direction of the workpiece during the micro-arc oxidation process. This technical solution has a simple structure, rich color expression, and is applicable to various light alloy materials such as aluminum, magnesium, and titanium.

[0069] The preferred embodiments for implementing the present invention have been described in detail above. However, it should be understood that the functions of these embodiments are only for illustration and not for limiting the scope, application or structure of the present invention in any way. The protection scope of the present invention is defined by the appended claims and their equivalent means. Those of ordinary skill in the art can make many changes to the foregoing embodiments under the teaching of the present invention, and these changes all fall within the protection scope of the present invention.

Claims

1. A method for gradient micro-arc oxidation of light metal colored, characterized in that, It includes the following steps: S1. Workpiece pretreatment: Grind the surface of the light metal workpiece to form a gradually changing roughness Ra along the length direction; S2. Surface cleaning treatment: Use ultrasonic waves to remove impurities on the surface of the light metal workpiece, and perform water washing and drying treatments; S3. Oxidation treatment: Immerse the light metal workpiece in an electrolyte with a gradually changing temperature, and perform micro-arc oxidation treatment using a bipolar pulse power supply.

2. A method for micro-arc oxidation gradient of light metal color according to claim 1, characterized in that, In step S1, the grinding method is laser etching.

3. A method for micro-arc oxidation gradient of light metal color according to claim 1, characterized in that In step S1, the roughness Ra ranges from 0.10 μm to 1.00 μm, and the gradual change rate of the roughness Ra is 0.05 μm / mm to 0.2 μm / mm.

4. A method for gradient micro-arc oxidation of light metal color, according to claim 1, characterized in that In step S2, the frequency of the ultrasonic waves is 40 kHz to 60 kHz, the time is 5 min to 10 min, and the temperature is controlled at 40°C to 60°C.

5. A light metal colored micro-arc oxidation gradient method according to claim 1, characterized in that, In step S2, the water washing treatment uses deionized water for rinsing; the temperature of the drying treatment is 60°C to 80°C, and the drying time is 20 min to 30 min.

6. A method for gradually changing micro-arc oxidation of light metal color according to claim 1, characterized in that, In step S3, the gradual change direction of the electrolyte temperature is the same as the gradual change direction of the surface roughness Ra of the light metal workpiece, both changing from small to large along the length direction of the light metal workpiece.

7. A method for micro-arc oxidation gradient of light metal color according to claim 1, characterized in that In step S3, the temperature range of the electrolyte is 25°C to 50°C, and the temperature gradual change rate is 2°C / m to 5°C / m.

8. A method for micro-arc oxidation gradient of light metal color according to claim 1, characterized in that, In step S3, the time of the micro-arc oxidation treatment is 10 min to 30 min.

9. A method for gradually changing the micro-arc oxidation of light metal color according to claim 1, characterized in that In step S3, the anode pulse voltage of the bipolar pulse power supply is 300V to 500V, the cathode pulse voltage is 50V to 150V, and the pulse frequency is 200Hz to 1000Hz.

10. A method for gradient micro-arc oxidation of light metal color, according to claim 1, characterized in that, The light metal workpiece includes one or more of aluminum, magnesium, titanium, or their alloys.