A preparation method for preparing a ceramic glaze composite coating on the surface of an alloy

Abstract

The present invention belongs to the technical field of surface treatment of alloy materials, and particularly relates to a preparation method for preparing a ceramic glaze composite coating on the surface of an alloy, comprising the following steps: S1. performing multi-stage polishing on the alloy until the surface roughness of the alloy reaches the micron level; S2. performing chemical activation treatment on the surface of the polished alloy; S3. placing the activated alloy in an electrolyte to generate a micro-arc oxidation layer through a bipolar pulse power supply; S4. performing oxidation modification on the micro-arc oxidation layer by using a plasma method; S5. coating a low-temperature glaze containing a phosphate active component on the alloy after oxidation modification; S6. performing multi-stage gradient sintering on the alloy coated with the low-temperature glaze, and the temperature t of the multi-stage gradient sintering satisfies: 200°C ≤ t ≤ 750°C. By performing treatments such as oxidation modification, plasma treatment, and multi-stage gradient sintering on the alloy, the denseness, bonding strength, and stability of the glaze layer are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface treatment of alloy materials, and particularly relates to a preparation method for preparing a ceramic glaze composite coating on the surface of an alloy. Background Art

[0002] Light alloy materials such as magnesium alloys, aluminum alloys, and titanium alloys are widely used in the fields of aerospace, automotive manufacturing, consumer electronics, etc. due to their excellent specific strength, thermal conductivity, and processing performance. However, the surfaces of such metal materials are prone to oxidation, have poor corrosion resistance, and limited surface decoration and thermal stability, which restricts their application in harsh service environments. To improve the corrosion resistance, mechanical strength, and aesthetic performance of the alloy surface, researchers have proposed various surface modification methods. Among them, micro-arc oxidation (MAO) technology, as a method of in-situ generating a ceramic coating on the alloy surface, has received extensive attention due to its strong adhesion, good wear resistance, and other advantages.

[0003] However, the traditional micro-arc oxidation process has the following deficiencies: the generated ceramic layer has a single color and poor decoration; the coating porosity is generally high, and it is prone to penetration failure under long-term service or the action of corrosive media; at the same time, when the service temperature exceeds 400 °C, the internal phase structure of the micro-arc oxidation layer changes, causing cracks and resulting in high-temperature failure. In addition, to improve the decoration and functionality of the coating, ceramic glazes or colored layers are often used for compounding. However, traditional glazes need to be sintered at a high temperature of 1200 - 1400 °C, which is much higher than the melting points of magnesium and aluminum alloys, and is prone to cause melting or deformation of the alloy substrate. Summary of the Invention

[0004] In view of the above problems, the present invention proposes a preparation method for preparing a ceramic glaze composite coating on the surface of an alloy. By performing oxidation modification, plasma treatment, and multi-stage gradient sintering on the alloy, the compactness, bonding strength, and stability of the glaze layer are improved.

[0005] To achieve the above object, the technical solution adopted is as follows:

[0006] The present invention provides a preparation method for preparing a ceramic glaze composite coating on the surface of an alloy, including the following steps:

[0007] S1. Perform multi-stage polishing on the alloy until the roughness of the alloy surface reaches the micron level;

[0008] S2. Perform chemical activation treatment on the surface of the polished alloy;

[0009] S3. Place the activated alloy in an electrolyte and generate a micro-arc oxidation layer through a bipolar pulse power supply;

[0010] S4. Perform oxidation modification on the micro-arc oxidation layer by the plasma method;

[0011] S5. Coat a low-temperature glaze containing a phosphate active ingredient on the alloy after oxidation modification;

[0012] S6. Perform gradient sintering on the alloy coated with the low-temperature glaze. The temperature t of the multi-stage gradient sintering satisfies: 200°C ≤ t ≤ 750°C.

[0013] Furthermore, in step S1, the multi-stage polishing is mechanical polishing. After polishing, the surface roughness Ra of the alloy satisfies 0.08 μm ≤ Ra ≤ 0.18 μm.

[0014] Furthermore, in step S2, the chemical activation treatment is alkali washing, water washing, acid washing, and water washing; the time for alkali washing is 3 - 10 min, and the time for acid washing is 10 - 60 s.

[0015] Furthermore, in step S2, the materials used for alkali washing include one or more of NaOH solution, KOH solution, and Na3PO4 solution; the materials used for acid washing include one or more of HNO3 solution, H2SO4 solution, and H3PO4 solution.

[0016] Furthermore, in step S4, oxidation modification is carried out on the micro-arc oxidation layer on the surface of the alloy by the plasma method, and hydroxyl groups are formed on the surface of the micro-arc oxidation layer.

[0017] Furthermore, in step S4, the material used in the plasma method is an Ar / O2 mixed plasma. The gas flow ratio of Ar to O2 is 3:1 - 5:1, the radio frequency power density is 1.5 - 3.0 W / cm 2 , the treatment time is 5 - 15 min, and the vacuum pressure is 3 - 8 Pa.

[0018] Furthermore, in step S5, a low-temperature glaze containing a phosphate active ingredient is coated on the alloy after oxidation modification by inkjet printing and dipping glazing processes; the inkjet printing uses a piezoelectric nozzle for electrostatic spraying. The volume of the ink droplets is 4 - 8 pL, and the resolution is ≥ 300 dpi; the voltage range for electrostatic spraying is 40 - 60 kV, and the atomization pressure is 0.2 - 0.5 MPa; the viscosity range of the glaze slurry for the dipping glazing process is 25 - 50 mPa·s (25°C), and the pulling speed range is 1 - 3 mm / s.

[0019] Furthermore, in step S5, the low-temperature glaze includes one or more of micron SiO2, B2O3, nano ZnO, NaH2PO4, nano ZrO2, and transition metal oxide colorants.

[0020] Further, in step S5, in the low-temperature glaze, the mass ratio of the micron SiO2 is 45-55 wt%, and the particle size Dv50 of the micron SiO2 is 2.5 μm; the mass ratio of the B2O3 is 15-25 wt%; the mass ratio of the nano ZnO is 10-20 wt%, and the particle size Dv50 of the nano ZnO is 50 nm; the mass ratio of the NaH2PO4 is 5-8 wt%; the mass ratio of the nano ZrO2 is 1-2 wt%, and the particle size Dv50 of the nano ZrO2 is 100 nm; the mass ratio of the transition metal oxide colorant is 1-5 wt%, and the color difference ΔE of the transition metal oxide colorant ≤ 2.0.

[0021] Further, in step S6, the multi-stage gradient sintering is three-stage gradient sintering. The first-stage sintering process is: heating from room temperature to 200 °C, with a heating rate of 3-5 °C / min, and holding for 20-40 min; the second-stage sintering process is: heating from 200 °C to 600 °C, with a heating rate of 2-3 °C / min, and holding for 15-30 min; the third-stage sintering process is: heating from 600 °C to 750 °C, with a heating rate of 1-2 °C / min, and holding for 10-20 min.

[0022] Adopting the above technical solution, there are at least the following beneficial effects:

[0023] ① In the present invention, by mechanically polishing the alloy surface, the surface roughness is controlled within the micron range of 0.08-0.18 μm, which helps to improve the structural stability and functional performance of the entire coating system. The micron-level surface can not only promote the uniform distribution of discharges during micro-arc oxidation, generate a denser and more uniform oxide layer, significantly reduce the porosity, and improve the corrosion resistance; at the same time, it provides an ideal active interface for subsequent plasma surface modification, is conducive to the uniform introduction of hydroxyl groups, and enhances the wettability and bonding force of the ceramic glaze. In addition, the flat micron-level surface also improves the spreading property of the glaze during inkjet printing, dip glazing, or electrostatic spraying, avoids defects such as uneven coating thickness, sagging, or peeling, and further improves the decoration and surface aesthetics;

[0024] ②In the present invention, the micro-arc oxidation layer on the alloy surface is oxidatively modified by a plasma method, so that the surface of the micro-arc oxidation layer is enriched with hydroxyl (-OH) groups. This process significantly improves the surface chemical activity and wettability of the micro-arc oxidation layer. As a highly polar functional group, the hydroxyl group can enhance the spreading property and adhesion of the glaze on the surface of the micro-arc oxidation layer, forming a more uniform and dense coating layer, and avoiding defects such as bubbles and cracks caused by uneven coating. At the same time, the hydroxyl group can also undergo a chemical bonding reaction with the phosphate component in the glaze to construct a firm interfacial bonding structure, which has higher peel strength and thermal stability compared to physical adhesion, thereby effectively improving the bonding force between the ceramic glaze layer and the micro-arc oxidation layer. In addition, this oxidation modification treatment uses a low-temperature and low-pressure plasma process, which is suitable for heat-sensitive substrates such as magnesium-aluminum alloys and does not cause thermal deformation of the substrate, ensuring the thermal stability and adaptability of the overall process;

[0025] ③In the present invention, a low-temperature glaze containing a phosphate active ingredient is used to coat the surface of the alloy after oxidation modification. This not only effectively solves the problem of alloy deformation caused by too high firing temperature of traditional high-temperature glazes, but also significantly improves the chemical bonding property and comprehensive performance of the coating. Phosphate components (such as NaH2PO4) can undergo a condensation reaction with the hydroxyl groups on the surface of the micro-arc oxidation layer during the low-temperature sintering process to form a firm chemical bonding interface, greatly enhancing the adhesion between the glaze layer and the bottom layer, and avoiding peeling of the coating caused by thermal cycling or mechanical stress;

[0026] ④In the present invention, the alloy coated with the low-temperature glaze is subjected to multi-stage gradient sintering in the range of 200-750 °C, which can effectively coordinate the thermal stress difference between the glaze and the matrix material during the sintering process, and avoid coating cracking, peeling or alloy matrix deformation caused by drastic temperature difference or too fast heating rate. Gradient sintering promotes the gradual softening, melting and rearrangement of each component in the glaze by slowly heating in stages and appropriately holding the temperature, enabling the glass phase to fully wet and fill the surface micropores, forming a dense, continuous and strongly adhesive ceramic coating. Specific embodiments

[0027] In the following, the technical solutions of the present invention will be clearly and completely described in combination with specific embodiments of the present invention. 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.

[0028] The present invention provides a preparation method for preparing a ceramic glaze composite coating on the surface of an alloy, comprising the following steps:

[0029] S1. Perform multi-stage polishing on the alloy until the roughness of the alloy surface reaches the micron level;

[0030] S2. Perform chemical activation treatment on the surface of the polished alloy;

[0031] S3. Place the activated alloy in an electrolyte to generate a micro-arc oxidation layer through a bipolar pulse power supply;

[0032] S4. Use the plasma method to oxidize and modify the micro-arc oxidation layer;

[0033] S5. Coat the alloy after oxidation modification with a low-temperature glaze containing phosphate active ingredients;

[0034] S6. Perform gradient sintering on the alloy coated with the low-temperature glaze. The temperature t of the multi-stage gradient sintering satisfies: 200°C ≤ t ≤ 750°C.

[0035] In the present invention, by mechanically polishing the surface of the alloy, the surface roughness is controlled within the micron range of 0.08 - 0.18 μm, which helps to improve the structural stability and functional performance of the entire coating system. The micron-level surface not only promotes the uniform distribution of discharges during the micro-arc oxidation process, generates a denser and more uniform oxidation layer, significantly reduces the porosity, and improves the corrosion resistance; at the same time, it provides an ideal active interface for subsequent plasma surface modification, is conducive to the uniform introduction of hydroxyl groups, enhances the wettability and bonding force of the ceramic glaze. In addition, the flat micron-level surface also improves the spreadability of the glaze during inkjet printing, dipping glazing, or electrostatic spraying processes, avoids defects such as uneven coating thickness, sagging, or peeling, and further improves the decorative and surface aesthetics.

[0036] In the present invention, the plasma method is used to oxidize and modify the micro-arc oxidation layer on the alloy surface, so that the surface of the micro-arc oxidation layer is enriched with hydroxyl (-OH) groups. This process significantly improves the chemical activity and wetting performance of the surface of the micro-arc oxidation layer. As a highly polar functional group, the hydroxyl group can enhance the spreadability and adhesion of the glaze on the surface of the micro-arc oxidation layer, form a more uniform and dense coating layer, and avoid defects such as bubbles and cracks caused by uneven coatings. At the same time, the hydroxyl group can also undergo a chemical bonding reaction with the phosphate component in the glaze to construct a firm interfacial bonding structure, which has higher peel strength and thermal stability compared to physical adhesion, thereby effectively improving the bonding force between the ceramic glaze layer and the micro-arc oxidation layer and ensuring the thermal stability and adaptability of the overall process.

[0037] In the present invention, the alloy surface after oxidation modification is coated with a low-temperature glaze containing phosphate active ingredients, which not only effectively solves the problem of alloy deformation caused by too high firing temperature of traditional high-temperature glazes, but also significantly improves the chemical bonding and comprehensive performance of the coating. Phosphate components (such as NaH2PO4) can undergo a condensation reaction with the hydroxyl groups on the surface of the micro-arc oxidation layer during the low-temperature sintering process, forming a firm chemical bonding interface, greatly enhancing the adhesion between the glaze layer and the bottom layer, and avoiding peeling of the coating caused by thermal cycling or mechanical stress.

[0038] In the present invention, the alloy coated with the low-temperature glaze is subjected to multi-stage gradient sintering in the range of 200-750 °C, which can effectively coordinate the thermal stress difference between the glaze and the matrix material during sintering, and avoid the cracking, peeling of the coating or the deformation of the alloy matrix caused by severe temperature difference or too fast heating rate. The gradient sintering promotes the gradual softening, melting and rearrangement of each component in the glaze by slowly heating in stages and appropriately keeping warm, enables the glass phase to fully wet and fill the surface micropores, and forms a dense, continuous and strongly adhesive ceramic coating.

[0039] It should be noted that, in the present invention, the alloy is a magnesium alloy, a titanium alloy, an aluminum alloy or other common alloys.

[0040] In some embodiments, in step S1, the multi-stage polishing is mechanical polishing, and the surface roughness Ra of the alloy after polishing satisfies 0.08 μm ≤ Ra ≤ 0.18 μm.

[0041] Controlling the surface roughness Ra of the alloy between 0.08 μm and 0.18 μm can effectively balance the interfacial bonding force and process adaptability, and improve the quality of the subsequent coating. It not only has an appropriate mechanical biting effect, but also is beneficial to the uniformity of micro-arc oxidation discharge and the uniform introduction of hydroxyl groups in plasma modification, enhances the wettability and adhesion of the glaze, and forms a dense and flat composite coating. When the roughness Ra is greater than 0.18 μm, it is easy to cause uneven discharge and increased pores during the micro-arc oxidation process, reducing the density and stability of the coating; if it is less than 0.08 μm, the surface of the alloy is too smooth, the adhesion decreases, and the efficiency of the modification reaction is affected.

[0042] In some embodiments, in step S2, the chemical activation treatment is alkali washing, water washing, acid washing and water washing; the time of the alkali washing is 3-10 min, and the time of the acid washing is 10-60 s. Specifically, the water washing uses deionized water.

[0043] In some embodiments, in step S2, the materials used for the alkali washing include one or more of NaOH solution, KOH solution and Na3PO4 solution; the materials used for the acid washing include one or more of HNO3 solution, H2SO4 solution and H3PO4 solution.

[0044] Adopting a multi-step chemical activation treatment process of "alkali washing, water washing, acid washing and re-water washing" can remove oil stains, oxides and processing residues on the alloy surface, and at the same time enhance the surface reaction activity, laying a good foundation for the formation of subsequent coatings. Among them, alkali washing uses alkaline solutions such as sodium hydroxide, potassium hydroxide or sodium phosphate to effectively remove organic pollution and weakly bonded layers within 3 - 10 minutes, making the surface initially clean and having a certain roughening effect, which is beneficial to enhancing adhesion. Then, it is thoroughly washed with deionized water to avoid the interference of residual alkaline ions on the subsequent acid washing reaction. The acid washing step is carried out by diluted nitric acid, phosphoric acid or sulfuric acid for a short time (10 - 60 s) to further remove the dense oxide layer, activate the metal surface, and increase its hydrophilicity and reactivity. Finally, it is rinsed again with deionized water to completely remove the residual acid solution and prevent corrosion and impurities from affecting. This staged treatment method can not only effectively improve the surface cleanliness and flatness, but also enhance the surface energy and interfacial bonding activity, providing a clean and highly active substrate for micro-arc oxidation and glaze sintering.

[0045] In some embodiments, in step S4, the micro-arc oxidation layer on the alloy surface is oxidized and modified by the plasma method, and hydroxyl groups are formed on the surface of the micro-arc oxidation layer.

[0046] The micro-arc oxidation layer on the alloy surface is oxidized and modified by the plasma method, so that the surface of the micro-arc oxidation layer is enriched with hydroxyl (-OH) groups. This process significantly improves the chemical activity and wetting performance of the surface of the micro-arc oxidation layer. The hydroxyl groups enhance the spreading property and adhesion of the glaze on the surface of the micro-arc oxidation layer, forming a more uniform and dense coating layer, and avoiding defects such as bubbles and cracks caused by uneven coating. At the same time, the hydroxyl groups can also undergo chemical bonding with the phosphate components in the glaze to construct a strong interfacial bonding structure, which has higher peel strength and thermal stability compared to physical adhesion, thereby effectively improving the bonding force between the ceramic glaze layer and the micro-arc oxidation layer and ensuring the thermal stability and adaptability of the overall process.

[0047] In some embodiments, in step S4, the material used in the plasma method is an Ar / O2 mixed plasma, the gas flow ratio of Ar to O2 is 3:1 - 5:1, and the radio frequency power density is 1.5 - 3.0 W / cm 2 , the treatment time is 5 - 15 minutes, and the vacuum pressure is 3 - 8 Pa.

[0048] The Ar / O2 mixed plasma combines the high-energy physical bombardment ability of argon and the chemical activity of oxygen. When treating the alloy surface, it can achieve physical cleaning and chemical modification simultaneously: As an inert gas, Ar gas can improve the discharge stability and remove impurities through momentum transfer; O2 gas can provide active oxygen species to promote the generation of surface hydroxyl groups and enhance the polarity and hydrophilicity of the oxide layer; The mixed use of Ar and O2 can achieve a surface modification effect with high uniformity, low damage and strong activity.

[0049] By controlling the gas flow ratio of Ar to O2 within the range of 3:1 to 5:1, the balance between discharge stability and oxidation reaction activity can be achieved. An appropriate amount of oxygen ensures the formation of sufficient hydroxyl groups, while the predominance of argon can avoid violent discharge or local peroxidation and protect the surface structure. When the amount of oxygen is too small, the formation of hydroxyl groups on the alloy surface is insufficient, the oxidation modification effect is weak, the surface activity is low, and the adhesion of the subsequent glaze decreases. When the amount of oxygen is too large, the solution causes unstable discharge, prone to local overheating or oxygen corrosion, resulting in ablation of the micro-arc oxidation layer, increased roughness, and even micro-cracks.

[0050] Control the radio frequency power density within the range of 1.5 - 3.0 W / cm 2 to ensure that the plasma concentration is high enough to effectively excite reaction species and achieve uniform surface modification; this power density range is moderate, and a uniform hydroxyl group layer can be formed without damaging the structure of the micro-arc oxidation layer. When the radio frequency power density is too large, it is easy to cause excessive bombardment of the surface, resulting in damage to the microstructure, concentration of thermal stress, and reduction of coating adhesion. When the radio frequency power density is too small, the radio frequency energy is insufficient, the plasma is unstable or the reaction is incomplete, the amount of introduced hydroxyl groups is low, and the surface modification effect is poor.

[0051] Control the treatment time within the range of 5 - 15 min to ensure sufficient and uniform surface reactions and avoid thermal damage caused by long-term exposure of the material to the plasma. When the treatment time is too long, it is easy to cause excessive surface oxidation, coarsening of the structure, and formation of a non-uniform layer, affecting the subsequent bonding performance. When the treatment time is too short, the formation of surface hydroxyl groups is insufficient, the activity is non-uniform, reducing the adhesion and denseness of the coating.

[0052] In some embodiments, in step S5, a low-temperature glaze containing a phosphate active ingredient is coated on the oxidized and modified alloy through an inkjet printing and dipping glaze process; the inkjet printing uses a piezoelectric nozzle for electrostatic spraying, the ink droplet volume is 4 - 8 pL, and the resolution is ≥300 dpi; the voltage range of the electrostatic spraying is 40 - 60 kV, and the atomization pressure is 0.2 - 0.5 MPa; the viscosity range of the glaze slurry for the dipping glaze process is 25 - 50 mPa·s (25 °C), and the pulling speed range is 1 - 3 mm / s.

[0053] In step S5, a low-temperature glaze containing a phosphate active ingredient is uniformly coated on the surface of the alloy after oxidation modification by combining inkjet printing and dipping glazing processes, which has significant advantages in process flexibility and coating uniformity. The inkjet printing uses a piezoelectric nozzle, with the ink droplet volume controlled at 4 - 8 pL, and combined with a high-resolution design of ≥300 dpi, it can achieve precise patterning distribution and micro-control of the glaze, being suitable for complex geometric surfaces and personalized decoration requirements. The dipping glazing process ensures that the glaze forms a uniform and continuous coating on the substrate surface by controlling the glaze slurry viscosity (25 - 50 mPa·s) and the lifting speed (1 - 3 mm / s), avoiding defects such as sagging, accumulation, or bubbles, and improving the coating density and aesthetics. In addition, electrostatic spraying can further enhance the adsorption efficiency of the glaze particles on the substrate surface by controlling the voltage (40 - 60 kV) and the atomization pressure (0.2 - 0.5 MPa), improving the process coverage rate and adhesion strength. The combined application of these multiple coating methods not only improves the process adaptability and controllability but also significantly enhances the uniformity, functionality, and decoration of the ceramic glaze composite coating, providing a reliable guarantee for large-scale and high-consistency preparation.

[0054] In some embodiments, in step S5, the low-temperature glaze includes one or more of micron SiO2, B2O3, nano ZnO, NaH2PO4, nano ZrO2, and transition metal oxide colorants. Specifically, the transition metal oxide colorants include colorants of multiple color systems such as red, blue, and green. Among them, the red colorant is a mixture of Fe2O3, Cr2O3, and CeO2; the blue colorant is a mixture of CoAl2O4 spinel and CoO-micron SiO2 solid solution; the green colorant is a mixture of Cr2O3-CuO complex and V2O5.

[0055] In some embodiments, in step S5, in the low-temperature glaze, the mass fraction of the micron SiO2 is 45 - 55 wt%, further, the particle size Dv50 of the micron SiO2 is 2.5 μm; the mass fraction of the B2O3 is 15 - 25 wt%; the mass fraction of the nano ZnO is 10 - 20 wt%, and the particle size Dv50 of the nano ZnO is 50 nm; the mass fraction of the NaH2PO4 is 5 - 8 wt%; the mass fraction of the nano ZrO2 is 1 - 2 wt%, and the particle size Dv50 of the nano ZrO2 is 100 nm; the mass fraction of the transition metal oxide colorant is 1 - 5 wt%, and the color difference ΔE of the transition metal oxide colorant ≤2.0 (D65 light source).

[0056] In the low-temperature glaze formulation used in step S5, each component is optimized and designed within a specific mass range, having good functional complementarity and system synergy, and capable of achieving a dense and high-performance ceramic glaze composite coating at a relatively low temperature. Specifically, SiO2 (45 - 55 wt%) serves as the main glass-phase precursor, constructing the network skeleton of the coating, providing structural strength and stability, and its Dv50 particle size is 2.5 μm, which helps to achieve the flatness and uniformity of the glaze layer. B2O3 (15 - 25 wt%) acts as a flux, which can significantly reduce the melting temperature of the glaze, enhance its fluidity under low-temperature sintering conditions, and avoid thermal deformation of the substrate. ZnO (10 - 20 wt%) is used to regulate the thermal expansion coefficient, making the thermal matching between the glaze layer and the micro-arc oxidation layer better and reducing the cracking risk caused by thermal stress. NaH2PO4 (5 - 8 wt%) serves as an interfacial reaction promoter, which can chemically react with the hydroxyl groups on the surface of the micro-arc oxidation layer to form stable phosphate bonds, significantly enhancing the chemical bonding force between the glaze and the oxide layer. The colorant (1 - 5 wt%) is composed of transition metal oxides, achieving stable and distinct color expression under the condition of ensuring ΔE ≤ 2.0 (D65 light source), and enhancing the decorative effect. Nano-ZrO2 (1 - 2 wt%) exists in the tetragonal phase, which can significantly enhance the mechanical strength and crack resistance of the coating. The overall formulation achieves a good balance among performance, process, and decorativeness, and is suitable for preparing a ceramic glaze composite coating with high adhesion, high density, and high aesthetics under medium- and low-temperature sintering conditions.

[0057] In some embodiments, in step S6, the multi-stage gradient sintering is three-stage gradient sintering. The first-stage sintering process is: heating from room temperature to 200 °C at a heating rate of 3 - 5 °C / min and holding for 20 - 40 min; the second-stage sintering process is: heating from 200 °C to 600 °C at a heating rate of 2 - 3 °C / min and holding for 15 - 30 min; the third-stage sintering process is: heating from 600 °C to 750 °C at a heating rate of 1 - 2 °C / min and holding for 10 - 20 min.

[0058] Performing multi-stage gradient sintering on the alloy coated with low-temperature glaze within the range of 200~750°C can effectively coordinate the thermal stress difference between the glaze and the matrix material during the sintering process, and avoid coating cracking, peeling or alloy matrix deformation caused by severe temperature difference or too fast heating rate. Gradient sintering promotes the gradual softening, melting and rearrangement of each component in the glaze by slowly heating in stages and appropriately holding the temperature, enabling the glass phase to fully wet and fill the surface micropores, forming a dense, continuous and strongly adhesive ceramic coating. Specifically, in the first stage of the sintering process, it is slowly heated from room temperature to 200°C (heating rate 3~5°C / min) and held for 20~40 min, which can remove the residual solvent and adsorbed water in the glaze and prevent the appearance of bubbles or bulges during subsequent sintering; in the second stage, it continues to be heated to 600°C at a medium rate (heating rate 2~3°C / min) and held at a constant temperature for 15~30 min, making the glaze soften and start to melt and flow, filling the pores of the micro-arc oxidation layer and enhancing the physical bonding with the matrix; in the third stage, it is heated to 750°C at a lower rate (heating rate 1~2°C / min) and held for 10~20 min, enabling the components in the glaze to fully react, rearrange and form a dense and continuous glass phase, while controlling the release of thermal stress and avoiding coating cracking or peeling caused by sudden temperature change. This multi-stage gradient sintering path takes into account the coating denseness, adhesion and thermal matching, and is an important guarantee for constructing a high-performance ceramic glaze composite coating.

[0059] The present invention will be further described below through examples.

[0060] Example 1. Surface coating of AZ31 magnesium alloy (Φ40mm×2mm)

[0061] S1. The AZ31 magnesium alloy is polished with diamond until the surface roughness Ra of the AZ31 magnesium alloy reaches 0.1 μm;

[0062] S2. The polished AZ31 magnesium alloy is immersed in a 50 g / L NaOH solution for 5 min at an immersion temperature of 60°C; the AZ31 magnesium alloy is taken out of the NaOH solution and the residual NaOH solution on the surface of the AZ31 magnesium alloy is completely rinsed off with deionized water; the AZ31 magnesium alloy is immersed in a 10% mass fraction HNO3 solution for 30 s for activation at an immersion temperature of 60°C; the AZ31 magnesium alloy is taken out of the HNO3 solution and the residual HNO3 solution on the surface of the AZ31 magnesium alloy is completely rinsed off with deionized water;

[0063] S3. Place the activated AZ31 magnesium alloy in the electrolyte for micro-arc oxidation. The composition of the electrolyte includes Na2SiO3·9H2O (30 g / L), Na2B4O7 (15 g / L), and KF (10 g / L). The parameters of the bipolar pulse power supply are: positive voltage 400 V, negative voltage 50 V, frequency 500 Hz, duty cycle 20%, and micro-arc oxidation time 15 min.

[0064] The AZ31 magnesium alloy forms a micro-arc oxidation layer. The film thickness of the micro-arc oxidation layer is 22 μm, the porosity is 12%, and the surface hardness HV is 940 kgf / mm 2 , and the water contact angle is 112°;

[0065] S4. Use the plasma method to oxidize and modify the micro-arc oxidation layer on the surface of the AZ31 magnesium alloy. Among them, the gas flow ratio of Ar to O2 is 4:1, the radio frequency power density is 2.0 W / cm², the treatment time is 7 min, and the vacuum pressure is 4 Pa;

[0066] After oxidation modification, the oxygen content of the micro-arc oxidation layer on the surface of the AZ31 magnesium alloy is 28 at.%, the porosity is 4%, and the water contact angle is 35°;

[0067] S5. Coating a low-temperature glaze on the alloy after oxidation modification by inkjet printing and dipping glaze processes; for nano-ZnO inkjet printing, a piezoelectric nozzle is used, the ink droplet volume is 6 pL, and the resolution is 350 dpi;

[0068] The viscosity range of the glaze slurry for the nano-ZnO dipping glaze process is 30 mPa·s (25 °C), and the range of the lifting speed is 2 mm / s; the voltage range of electrostatic spraying is 45 kV, and the atomization pressure is 0.25 MPa;

[0069] The low-temperature glaze includes: micron SiO2 (mass ratio 52%), nano B2O3 (mass ratio 20%), nano ZnO (mass ratio 15%), and NaH2PO4 (mass ratio 8%), transition metal oxide colorant CoAl2O4 (mass ratio 3%, ΔE = 1.0), and CoO-micron SiO2 (mass ratio 2%);

[0070] S6. Perform multi-stage gradient sintering on the AZ31 magnesium alloy coated with the low-temperature glaze. The first-stage sintering process is: heating from room temperature to 200 °C, heating rate 3 °C / min, and holding for 25 min; the second-stage sintering process is: heating from 200 °C to 600 °C, heating rate 2.5 °C / min, and holding for 20 min; the third-stage sintering process is: heating from 600 °C to 750 °C, heating rate 1 °C / min, and holding for 10 min.

[0071] So far, the preparation of the blue ceramic glaze composite coating on the surface of AZ31 magnesium alloy (Φ40mm×2mm) has been completed.

[0072] Example 2. Coating on the surface of TC4 titanium alloy (Φ10mm×50mm)

[0073] S1. Sandblast and polish the TC4 titanium alloy with Al2O3 particles with a particle size less than 0.125mm until the surface roughness Ra of the TC4 titanium alloy reaches 0.15μm.

[0074] S2. Immerse the polished TC4 titanium alloy in a 45g / L NaOH solution for 8 minutes at an immersion temperature of 50°C; take out the TC4 titanium alloy from the NaOH solution and completely rinse off the residual NaOH solution on the surface of the TC4 titanium alloy with deionized water; immerse the TC4 titanium alloy in a 12% mass fraction HNO3 solution for 50 minutes at an immersion temperature of 50°C; take out the TC4 titanium alloy from the HNO3 solution and completely rinse off the residual HNO3 solution on the surface of the TC4 titanium alloy with deionized water.

[0075] S3. Perform micro-arc oxidation on the activated TC4 titanium alloy in the electrolyte. The components of the electrolyte include Na3PO4·12H2O (25g / L), NaOH (10g / L), and Na2MoO4 (4g / L); the parameters of the bipolar pulse power supply are: positive voltage 400V, negative voltage 50V, frequency 500Hz, duty cycle 20%, and micro-arc oxidation time 20 minutes.

[0076] The TC4 titanium alloy forms a micro-arc oxidation layer, and the film thickness of the micro-arc oxidation layer is 15μm, the porosity is 13%, and the surface hardness HV is 850kgf / mm 2 , and the water contact angle is 115°;

[0077] S4. Oxidatively modify the micro-arc oxidation layer on the surface of the TC4 titanium alloy by the plasma method. Among them, the gas flow ratio of Ar to O2 is 3:1, the radio frequency power density is 2.5W / cm², the treatment time is 10 minutes, and the vacuum pressure is 6Pa.

[0078] After oxidative modification, the oxygen content of the micro-arc oxidation layer on the surface of the TC4 titanium alloy is 31at.%, the porosity is 6%, and the water contact angle is 32°.

[0079] S5. Coating the low-temperature glaze on the alloy after oxidative modification by inkjet printing and dipping glaze processes; the piezoelectric nozzle is used for nano-ZnO inkjet printing, the ink droplet volume is 7pL, and the resolution is 380dpi.

[0080] The viscosity range of the glaze slurry for the nano-ZnO dipping glaze process is 45 mPa·s (25 °C), and the pulling speed range is 2.7 mm / s; the voltage range for electrostatic spraying is 56 kV, and the atomization pressure is 0.46 MPa;

[0081] The low-temperature glaze includes: micron SiO2 (mass ratio 50%), nano B2O3 (mass ratio 21%), nano ZnO (mass ratio 17%), and NaH2PO4 (mass ratio 7%), and the transition metal oxide colorant Fe2O3 (mass ratio 5%, ΔE = 1.3);

[0082] S6. Perform multi-stage gradient sintering on the TC4 titanium alloy coated with the low-temperature glaze. The first-stage sintering process is: heat from room temperature to 200 °C, heating rate 4.5 °C / min, and hold for 35 min; the second-stage sintering process is: heat from 200 °C to 600 °C, heating rate 2.3 °C / min, and hold for 25 min; the third-stage sintering process is: heat from 600 °C to 750 °C, heating rate 1.8 °C / min, and hold for 12 min.

[0083] Thus, a red ceramic glaze composite coating is prepared on the surface of the AZ31TC4 titanium alloy (Φ40 mm × 2 mm).

[0084] Example 3. Coating on the surface of 6061 aluminum alloy (150 mm × 70 mm × 0.8 mm)

[0085] S1. Perform mechanical polishing on the 6061 aluminum alloy until the surface roughness Ra of the 6061 aluminum alloy reaches 0.15 μm;

[0086] S2. Immerse the polished 6061 aluminum alloy in a 40 g / L NaOH solution for 8 min at an immersion temperature of 45 °C; take out the 6061 aluminum alloy from the NaOH solution and completely rinse off the residual NaOH solution on the surface of the 6061 aluminum alloy with deionized water; immerse the 6061 aluminum alloy in an 8% mass fraction HNO3 solution for 40 s for activation at an immersion temperature of 60 °C; take out the 6061 aluminum alloy from the HNO3 solution and completely rinse off the residual HNO3 solution on the surface of the 6061 aluminum alloy with deionized water;

[0087] S3. Perform micro-arc oxidation on the activated 6061 aluminum alloy in an electrolyte. The components of the electrolyte include Na2SiO3·9H2O (30 g / L), Na2B4O7 (15 g / L), and KF (10 g / L); the parameters of the bipolar pulse power supply are: positive voltage 400 V, negative voltage 50 V, frequency 500 Hz, duty cycle 20%, and micro-arc oxidation time 15 min;

[0088] A micro-arc oxidation layer is formed on 6061 aluminum alloy, and the film thickness of the micro-arc oxidation layer is 15 μm, the porosity is 8%, and the surface hardness HV is 1050 kgf / mm 2 , and the water contact angle is 115°;

[0089] S4. The micro-arc oxidation layer on the surface of 6061 aluminum alloy is oxidized and modified by the plasma method. Among them, the gas flow ratio of Ar to O2 is 5:1, the radio frequency power density is 3.0 W / cm², the treatment time is 13 min, and the vacuum pressure is 7 Pa;

[0090] After oxidation modification, the oxygen content of the micro-arc oxidation layer on the surface of 6061 aluminum alloy is 30 at.%, the porosity is 3%, and the water contact angle is 25°;

[0091] S5. A low-temperature glaze is coated on the oxidized and modified alloy by inkjet printing and dipping glaze process; Piezoelectric nozzles are used for nano-ZnO inkjet printing, the ink droplet volume is 6 pL, and the resolution is 350 dpi;

[0092] The viscosity range of the glaze slurry for the nano-ZnO dipping glaze process is 30 mPa·s (25 °C), and the pulling speed range is 2 mm / s; The voltage range of electrostatic spraying is 45 kV, and the atomization pressure is 0.25 MPa;

[0093] The low-temperature glaze includes: micron SiO2 (mass ratio 50%), nano B2O3 (mass ratio 22%), nano ZnO (mass ratio 15%) and NaH2PO4 (mass ratio 8%), transition metal oxide colorant Cr2O3-CuO complex (mass ratio 3%, ΔE = 1.6) and V2O5 (mass ratio 2%);

[0094] S6. The 6061 aluminum alloy coated with low-temperature glaze is subjected to multi-stage gradient sintering. The first-stage sintering process is: heating from room temperature to 200 °C, heating rate 3 °C / min, and constant temperature treatment for 25 min; The second-stage sintering process is: heating from 200 °C to 600 °C, heating rate 2.5 °C / min, and constant temperature treatment for 20 min; The third-stage sintering process is: heating from 600 °C to 750 °C, heating rate 1 °C / min, and constant temperature treatment for 10 min.

[0095] Thus, the preparation of the ceramic glaze composite coating on the surface of 6061 aluminum alloy (Φ40 mm × 2 mm) is completed.

[0096] It can be seen from Example 1 (AZ31 magnesium alloy), Example 2 (TC4 titanium alloy) and Example 3 (6061 aluminum alloy) that the present invention shows significant advantages in controlling porosity, water contact angle and coating sintering density through the combined process of "plasma oxidation modification and multi-stage gradient sintering".

[0097] First, before plasma treatment, the porosity of the coatings formed on the three alloy substrates after micro-arc oxidation was 12%, 13% and 8% respectively, belonging to the typical porous ceramic structure. Although it has a certain surface roughness and mechanical strength, the pore structure is likely to become the source of coating failure. After the plasma oxidation modification treatment, the porosity of the three materials decreased to 4%, 6% and 3% respectively, indicating that the surface structure has been significantly densified and the number of defects has been greatly reduced, providing an ideal interface for the uniform spreading and high bonding strength of the glaze.

[0098] Secondly, from the perspective of the change in water contact angle, the surface after micro-arc oxidation is highly hydrophobic (contact angle 112° - 115°), which is not conducive to the wetting and adhesion of the subsequent glaze. After the plasma treatment introducing hydroxyl groups, the water contact angle decreased significantly to 35° (AZ31 magnesium alloy), 32° (TC4 titanium alloy) and 25° (6061 aluminum alloy), showing excellent hydrophilicity. This improvement in wettability promotes the rapid spreading and adhesion of the low-temperature glaze on the surface of the metal oxide layer, which is beneficial to the formation of a flat and continuous glaze layer.

[0099] Finally, the three-stage gradient sintering process is customized according to the characteristics of different materials, controlling the heating rate and holding time, and avoiding the thermal stress concentration or interface peeling caused by rapid temperature change. The segmented heating makes the processes of solvent evaporation, glass phase formation and densification sintering more controllable, ensuring the full conversion and rearrangement of the glaze under mild conditions, and thus improving the densification, bonding strength and stability of the glaze layer.

[0100] 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, rather than 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 preparing a ceramic glaze composite coating on an alloy surface, characterized in that: The following steps are involved: S1. Perform multi-stage polishing on the alloy until the roughness of the alloy surface reaches the micron level; S2. chemically activating the surface of the polished alloy; S3. placing the activated alloy in an electrolyte and generating a micro-arc oxidation layer through a bipolar pulse power supply; S4. Oxidative modification of the micro-arc oxidation layer by plasma method; S5. coating a low-temperature glaze containing a phosphate active ingredient on the oxidation-modified alloy; S6. The alloy coated with the low-temperature glaze is subjected to multi-stage gradient sintering, wherein the temperature t of the multi-stage gradient sintering satisfies: 200°C≤t≤750°C; In step S4, the micro-arc oxidation layer on the surface of the alloy is oxidized and modified by a plasma method to form hydroxyl groups on the surface of the micro-arc oxidation layer.

2. The method for preparing a ceramic glaze composite coating on an alloy surface according to claim 1, characterized in that: In step S1, the multi-stage polishing is mechanical polishing, and the surface roughness Ra of the alloy after polishing satisfies 0.08 μm≤Ra≤0.18 μm.

3. The method for preparing a ceramic glaze composite coating on an alloy surface according to claim 1, characterized in that: In step S2, the chemical activation treatment includes alkali washing, water washing, acid washing and water washing; the time of the alkali washing is 3 to 10 minutes, and the time of the acid washing is 10 to 60 seconds.

4. The method for preparing a ceramic glaze composite coating on an alloy surface according to claim 3, characterized in that: In step S2, the material for alkaline washing includes one or more of NaOH solution, KOH solution and Na3PO4 solution; the material for acid washing includes one or more of HNO3 solution, H2SO4 solution and H3PO4 solution.

5. The method for preparing a ceramic glaze composite coating on an alloy surface according to claim 1, characterized in that: In step S4, the material used in the plasma method is Ar / O2 mixed plasma, the gas flow ratio of Ar to O2 is 3:1~5:1, the RF power density is 1.5~3.0W / cm², the processing time is 5~15min, and the vacuum pressure is 3~8Pa.

6. The method for preparing a ceramic glaze composite coating on an alloy surface according to claim 1, characterized in that: In step S5, a low-temperature glaze containing a phosphate active ingredient is coated on the oxidation-modified alloy by inkjet printing and glazing process; The inkjet printing adopts a piezoelectric nozzle for electrostatic spraying, the ink drop volume is 4~8pL, and the resolution is ≥300dpi; the voltage range of electrostatic spraying is 40~60kV, and the atomization pressure is 0.2~0.5MPa; The glaze slurry viscosity of the dipping process is in the range of 25-50 mPa·s, and the pulling speed is in the range of 1-3 mm / s.

7. The method for preparing a ceramic glaze composite coating on an alloy surface according to claim 1, characterized in that: In step S5, the low-temperature glaze includes one or more of micron SiO2, B2O3, nano ZnO, NaH2PO4, nano ZrO2 and transition metal oxide colorants.

8. The method for preparing a ceramic glaze composite coating on an alloy surface according to claim 7, characterized in that: In step S5, in the low temperature glaze, The mass proportion of the micron SiO2 is 45-55wt%, and the particle size Dv50 of the micron SiO2 is 2.5μm; The mass proportion of B2O3 is 15-25wt%; The mass proportion of the nano ZnO is 10-20wt%, and the particle size Dv50 of the nano ZnO is 50nm; The mass proportion of the NaH2PO4 is 5-8wt%; The mass proportion of the nano ZrO2 is 1-2wt%, and the particle size Dv50 of the nano ZrO2 is 100nm; The mass proportion of the transition metal oxide colorant is 1-5wt%, and the color difference ΔE of the transition metal oxide colorant is ≤2.

0.

9. The method for preparing a ceramic glaze composite coating on an alloy surface according to claim 1, characterized in that: In step S6, the multi-stage gradient sintering is a three-stage gradient sintering. The first sintering process is: heating from room temperature to 200℃, heating rate 3~5℃ / min, constant temperature treatment for 20~40min; The second sintering process is: heating from 200℃ to 600℃, heating rate 2~3℃ / min, constant temperature treatment 15~30min; The third sintering process is: heating from 600°C to 750°C, with a heating rate of 1~2°C / min, and constant temperature treatment for 10~20min.