Conductive micro-arc oxidation coating of magnesium alloy and preparation method and application thereof
By preparing a conductive micro-arc oxidation coating of copper nanowires or silver nanowires on the surface of magnesium alloys and combining it with an interface modifier, the electrical insulation problem of the micro-arc oxidation coating was solved, and the conductivity, corrosion resistance and thermal conductivity were improved, thereby improving the performance and lifespan of the equipment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TAIYUAN UNIVERSITY OF SCIENCE AND TECHNOLOGY
- Filing Date
- 2026-05-11
- Publication Date
- 2026-06-05
AI Technical Summary
The electrical insulation of existing micro-arc oxidation coatings leads to a lack of current path during film formation, resulting in inherent defects such as pores. Furthermore, it easily causes static charge to accumulate on the workpiece surface, resulting in a charging and discharging effect, which affects the service life and reliability of the equipment.
Copper or silver nanowires are used as conductive building blocks. A conductive micro-arc oxidation coating is prepared on the surface of a magnesium alloy using micro-arc oxidation technology. Combined with sodium dodecyl sulfonate as an interface modifier, a three-dimensional conductive network is constructed to avoid the problems of insufficient conductive pathways and high porosity.
It significantly improves the conductivity and density of conductive micro-arc oxidation coatings, reduces density, enhances corrosion resistance and thermal conductivity, and improves the service life and reliability of equipment.
Smart Images
Figure CN122147482A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of corrosion and protection of metal-based materials, specifically relating to a conductive micro-arc oxidation coating of magnesium alloy, its preparation method and application. Background Technology
[0002] Micro-arc oxidation (MAO) is a high-voltage anodic oxidation technology that primarily utilizes an anodic electric field to induce electrolytic breakdown of the metal surface film, generating plasma discharge. This, combined with electrochemical, plasma chemical, and thermochemical processes, leads to the in-situ formation of a ceramic coating on the metal surface. Compared to other coatings, MAO coatings possess advantages such as strong adhesion, high mechanical properties and corrosion resistance, and are less affected by workpiece shape during the preparation process, making them highly anticipated in the protective field. However, their electrical insulation properties are insufficient to meet the evolving protective requirements of metallic materials. This insulation limitation leads to inherent defects such as porosity during film formation due to the lack of current pathways, creating a bottleneck in the coating's protective performance. Furthermore, it easily allows static charges to accumulate on the workpiece surface, causing charge-discharge effects that can damage equipment and severely impact its service life and reliability.
[0003] Introducing conductive elements into micro-arc oxidation coatings is currently an effective way to solve the problem of coating electrical insulation. Commonly used methods for constructing conductive elements include: preparing metal layers with nickel, copper, or other metals as conductive elements on the coating surface through methods such as chemical plating, electroplating, and magnetron sputtering; preparing conductive polymer coatings on the surface of micro-arc oxidation coatings through methods such as spraying and brushing; or forming composite materials by combining conductive elements such as metal oxides with polymer materials and coating them onto the surface of the micro-arc oxidation coating. Although the above methods can improve the conductivity of micro-arc oxidation coatings, they generally suffer from drawbacks such as complex processes, high cost, and poor conductivity. Summary of the Invention
[0004] Therefore, the first objective of this invention is to provide a method for preparing a conductive micro-arc oxidation coating on magnesium alloys to overcome the shortcomings of the prior art. Specifically, using copper nanowires or silver nanowires, or their corresponding derivatives, as conductive building blocks, a conductive micro-arc oxidation coating is directly prepared on the surface of the magnesium alloy by adding the conductive building blocks and an interface modifier to the electrolyte. This method can significantly improve the conductivity of the conductive micro-arc oxidation coating, reduce its density, and avoid the inherent defects of lacking current pathways and creating pores during the film formation process of the conductive micro-arc oxidation coating.
[0005] The second objective of this invention is to provide a conductive micro-arc oxidation coating for magnesium alloys prepared by the above-described method, which has good corrosion resistance, electrical conductivity, and thermal conductivity.
[0006] A third objective of this invention is to provide an application of the conductive micro-arc oxidation coating based on the magnesium alloy obtained above in lightweight conductive components and electronic device housings.
[0007] To achieve the above objective, a method for preparing a conductive micro-arc oxidation coating on a magnesium alloy includes the following steps:
[0008] S1. Pretreatment of the magnesium alloy matrix;
[0009] S2. Prepare the basic electrolyte;
[0010] S3. Add metal wires with dimensions in the micrometer or nanometer range, or corresponding derivatives of the metal wires with dimensions in the micrometer or nanometer range, and an interface modifier to the basic electrolyte to obtain a modified electrolyte; the diameter of the metal wires or the corresponding derivatives of the metal wires is less than 20 μm, the length is less than 500 μm, and the thickness of the corresponding derivatives of the metal wires is 5 to 10 nm.
[0011] S4. The pretreated magnesium alloy substrate is added to a modified electrolyte for micro-arc oxidation treatment to obtain a conductive micro-arc oxidation coating.
[0012] Preferably, in step S1, the magnesium alloy matrix is selected from AZ91 magnesium alloy;
[0013] The specific process for pretreatment of the magnesium alloy matrix is as follows:
[0014] The surface of the magnesium alloy substrate was polished with 800-grit and 1200-grit sandpaper until smooth. The polished magnesium alloy substrate was cleaned with ethanol and dried. The dried magnesium alloy substrate was then used for mounting.
[0015] Preferably, in step S2, the base electrolyte is selected from one or more of silicate electrolyte, phosphate electrolyte, and aluminate electrolyte.
[0016] More preferably, the specific process for preparing the basic electrolyte is as follows: sodium silicate, potassium hydroxide and potassium fluoride solids are added to deionized water to obtain a silicate basic electrolyte, wherein the amount of deionized water is 1L, the amount of sodium silicate is 8-20g, the amount of potassium hydroxide is 3-8g and the amount of potassium fluoride is 2-6g.
[0017] Preferably, in step S3, a metal wire or a corresponding derivative of the metal wire is used as the conductive unit, and sodium dodecyl sulfonate is used as the interface modifier; the metal wire is a copper nanowire or a silver nanowire, and the corresponding derivative of the metal wire is a nanoscale or microscale metal wire modified or coated with a polymer material, ceramic, carbon material, or metal coating, and the shape of the corresponding derivative of the metal wire includes, but is not limited to, linear, spherical, and square.
[0018] More preferably, the specific process of adding metal wires with a size of micrometer or nanometer, or corresponding derivatives of the metal wires with a size of micrometer or nanometer, and an interface modifier to the basic electrolyte in step S3 to obtain the modified electrolyte is as follows: copper nanowires or silver nanowires, or corresponding derivatives of the copper nanowires or silver nanowires, and sodium dodecyl sulfonate are added to the prepared basic electrolyte. After ultrasonic dispersion and continuous stirring for 30 minutes, the modified electrolyte is obtained. The concentration of copper nanowires or silver nanowires or corresponding derivatives of the copper nanowires or silver nanowires is 0.001-100 g / L, the concentration of sodium dodecyl sulfonate is 1-2 g / L, and the ultrasonic power is 100-1400 W.
[0019] Preferably, the specific process of adding the pretreated magnesium alloy substrate to the modified electrolyte for micro-arc oxidation treatment in step S4 to obtain a conductive micro-arc oxidation coating is as follows: the pretreated magnesium alloy substrate is added to the modified electrolyte for micro-arc oxidation treatment, and stirring and water cooling are maintained throughout the preparation process. After the reaction is completed, the surface of the magnesium alloy substrate is washed and dried with ultrapure water or deionized water to obtain a conductive micro-arc oxidation coating with a thickness of 20~58.5μm.
[0020] The micro-arc oxidation process parameters are set as follows: the power supply is a bipolar pulse power supply with a forward current of 0.1-0.2A, a reverse current of 0.1-0.2A, a duty cycle of 20-40%, a frequency of 400-800Hz, a stirring speed of 100-1000r / min, an oxidation time of 10-20min, and a water cooling temperature of 25-60℃.
[0021] Secondly, the present invention provides a conductive micro-arc oxidation coating for a magnesium alloy, which is prepared by the above-mentioned method for preparing a conductive micro-arc oxidation coating for a magnesium alloy.
[0022] Preferably, when the concentration of copper nanowires or silver nanowires, or the corresponding derivatives of said copper nanowires or silver nanowires, is 50 g / L, the concentration of sodium dodecyl sulfonate is 2 g / L, and the oxidation treatment time is 20 min, the thickness of the conductive micro-arc oxidation coating is 58.2 ± 0.2 μm, the volume resistivity is 1.2 Ω·cm, the thermal conductivity is 21.3 W / m / K, the salt spray test time is >1120 h, and the porosity is ≤4%.
[0023] The third aspect of the present invention provides the application of a conductive micro-arc oxidation coating of magnesium alloy as described in the second aspect of the present invention in lightweight conductive components and electronic device housings.
[0024] The beneficial effects of this invention are as follows:
[0025] 1. The copper nanowires or silver nanowires used in this invention, or the corresponding derivative materials of the copper nanowires or silver nanowires mentioned above, exhibit excellent conductivity in solid conductive media due to their abundance of free electrons and have a small volume resistivity, which can significantly improve the conductivity of conductive micro-arc coatings.
[0026] 2. The present invention uses copper nanowires or silver nanowires, or the corresponding derivative materials of the above copper nanowires or silver nanowires, to prepare metal wires with the size limited to the micrometer or nanometer scale. This not only preserves the original excellent conductivity of the metal by constructing a three-dimensional conductive network structure inside the conductive micro-arc oxidation coating, but also significantly reduces the density of the conductive micro-arc oxidation coating by reducing the amount of metal material used.
[0027] 3. The present invention can further modify nanoscale metal wires to obtain corresponding derivatives of nanoscale metal wires, which can further enhance their physicochemical properties such as oxidation resistance, anti-agglomeration and conductivity. By changing the shape of the metal material, the construction of three-dimensional conductive networks becomes simpler.
[0028] 4. This invention uses copper nanowires or silver nanowires, or their corresponding derivatives, as conductive building blocks. These conductive building blocks are added to a modified electrolyte, and a conductive micro-arc oxidation coating is prepared in one step using a micro-arc oxidation process. The conductive building blocks also serve as conductive pathways during film formation, avoiding the defects of high porosity and excessively large pores caused by insufficient conductive pathways in traditional micro-arc oxidation coatings. This significantly enhances the density of the conductive micro-arc oxidation coating, resulting in better protective performance. Attached Figure Description
[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0030] Figure 1 This is a schematic flowchart of a method for preparing a conductive micro-arc oxidation coating on a magnesium alloy according to an embodiment of the present invention. Detailed Implementation
[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0032] like Figure 1 As shown, this invention provides a method for preparing a conductive micro-arc oxidation coating on a magnesium alloy, comprising the following steps:
[0033] S1. Pretreatment of the magnesium alloy matrix.
[0034] S2. Prepare the basic electrolyte.
[0035] S3. Add metal wires with dimensions in the micrometer or nanometer range, or the corresponding derivatives of the aforementioned metal wires with dimensions in the micrometer or nanometer range, and an interface modifier to the base electrolyte to obtain a modified electrolyte; the diameter of the metal wires or the corresponding derivatives of the aforementioned metal wires is less than 20 μm, the length is less than 500 μm, and the thickness of the corresponding derivatives of the metal wires is 5 to 10 nm.
[0036] S4. The pretreated magnesium alloy substrate is added to a modified electrolyte for micro-arc oxidation treatment to obtain a conductive micro-arc oxidation coating.
[0037] First, in step S1, AZ91 magnesium alloy is selected as the magnesium alloy substrate. The specific process for pretreatment of the magnesium alloy substrate is as follows: the surface of the magnesium alloy substrate is polished with 800-grit and 1200-grit sandpaper until smooth. The polished magnesium alloy substrate is cleaned with ethanol and dried. The dried magnesium alloy substrate is then mounted. For example, an AZ91 magnesium alloy sample with dimensions of 16mm × 16mm × 5mm is made. Its surface is polished with 800-grit and 1200-grit sandpaper until smooth. The polished sample is cleaned with ethanol and dried. The dried sample is then mounted to remove oxide scale and impurities from the surface of the AZ91 magnesium alloy and improve its surface activity.
[0038] In step S2, because using metal wires or their corresponding derivatives as conductive elements provides versatility for the electrolyte used in the micro-arc oxidation process, it is applicable to all basic electrolytes capable of forming micro-arc oxidation coatings. All basic electrolytes are selected from silicate electrolytes, phosphate electrolytes, aluminate electrolytes, and one or more of these. Therefore, the selection of basic electrolytes offers better applicability and economy. The specific process for preparing the basic electrolyte is as follows: 8–20 g of sodium silicate, 3–8 g of potassium hydroxide, and 2–6 g of potassium fluoride solid are added to 1 L of deionized water to obtain the silicate basic electrolyte.
[0039] In some embodiments of the present invention, the mass of sodium silicate is any value or a range formed by any two of the following: 8g, 9g, 10g, 11g, 12g, 13g, 14g, 15g, 16g, 17g, 18g, 19g, and 20g; the mass of potassium hydroxide is any value or a range formed by any two of the following: 3g, 4g, 5g, 6g, 7g, and 8g; and the mass of potassium fluoride is any value or a range formed by any two of the following: 2g, 3g, 4g, 5g, and 6g. For example, the preferred mass of sodium silicate is 8g, the preferred mass of potassium hydroxide is 3g, and the preferred mass of potassium fluoride is 2g. This ratio ensures that the conductive micro-arc oxidation coating possesses both good density and thermal conductivity, and can effectively construct a conductive network.
[0040] It should be noted that sodium silicate provides silicate ions, which are the main silicon source for forming conductive micro-arc oxidation coatings, helping to form a dense silicate film. Too low a concentration results in a thin conductive micro-arc oxidation coating with poor corrosion resistance, while too high a concentration increases electrolyte viscosity and affects the dispersion of conductive elements. Potassium hydroxide is used to adjust the pH value, making the electrolyte alkaline, inhibiting the excessive dissolution of magnesium, and maintaining the conductivity of the electrolyte. Insufficient concentration slows down the film formation rate, while excessive concentration may over-corrode the conductive substrate. The fluoride ions in potassium fluoride can inhibit excessive corrosion of magnesium alloys in the electrolyte, stabilize the interface by forming a MgF2 passivation layer, and promote the embedding of nanoscale metal wires, creating conditions for breakdown discharge and improving the uniformity and density of the conductive micro-arc oxidation coating. Too low a concentration will make the conductive micro-arc oxidation coating loose, while too high a concentration will hinder the discharge channel. Deionized water effectively avoids the presence of Cl- in tap water. - Impurity ions interfere with the micro-arc oxidation process and the composition of the conductive micro-arc oxidation coating.
[0041] In step S3, metal wires or their corresponding derivatives are used as conductive building blocks. These metal wires retain the inherent good conductivity of the metal material and can construct a three-dimensional conductive network within the conductive micro-arc oxidation coating, thus imparting excellent conductivity to the coating. Sodium dodecyl sulfonate (SDS) is used as an interface modifier to improve the dispersibility of the conductive reinforcing phase in the electrolyte and its interfacial bonding with the ceramic matrix, preventing particle agglomeration and enhancing the density and conductivity uniformity of the conductive micro-arc oxidation coating. On the one hand, SDS can significantly improve the dispersion of conductive units, such as copper or silver nanowires or their derivatives, in the electrolyte by adsorbing onto the surface of nanoscale metal wires and generating electrostatic repulsion and steric hindrance, thus preventing their aggregation and ensuring the formation of a uniform three-dimensional conductive network in the conductive micro-arc oxidation coating. On the other hand, SDS can reduce the interfacial tension between the electrolyte and the substrate, enhance wettability, and promote the effective embedding of nanoscale metal wires into the conductive micro-arc oxidation coating rather than floating on the surface, thereby greatly improving the bonding force between the conductive reinforcing phase and the ceramic matrix. At the same time, the uniformly dispersed nanoscale metal wires can also fill the pores formed by micro-arc discharge, reducing the inherent defects of the conductive micro-arc oxidation coating and improving its density.
[0042] The metal wires or their derivatives are nanometer- or micrometer-sized, ensuring they are incorporated into the conductive micro-arc oxidation coating during preparation to form a three-dimensional conductive network. Furthermore, the microscopic conductive elements reduce workpiece density while maintaining the conductivity of the micro-arc oxidation coating. The metal wires are copper or silver nanowires, and their derivatives are nanometer- or micrometer-sized metal wires modified or coated with polymers, ceramics, carbon materials, or metal plating. These derivatives can take various shapes, including but not limited to linear, spherical, and square forms. They retain the good conductivity of the metal material, exhibit greater physicochemical stability, and demonstrate better dispersibility in electrolytes.
[0043] Further, the specific process of adding micron- or nano-sized metal wires, or corresponding derivatives of such metal wires, along with an interface modifier, to the base electrolyte to obtain a modified electrolyte is as follows: Copper or silver nanowires, or corresponding derivatives of such copper or silver nanowires, at a concentration of 0.001–100 g / L, and SDS at a concentration of 1–2 g / L are added to the prepared base electrolyte. The mixture is dispersed under ultrasonic treatment at a power of 100–1400 W and continuously stirred for 30 minutes to obtain the modified electrolyte. During micro-arc discharge, the nano-sized metal wires are entrained in the conductive micro-arc oxidation coating, forming a three-dimensional conductive network. This solves the insulation problem of traditional micro-arc oxidation coatings. The presence of nano-sized metal wires can fill the discharge channels, reduce porosity, and increase density. The dispersing effect of SDS can prevent the aggregation of nano-sized metal wires, ensuring their uniform suspension in the electrolyte; its interface bonding enhancement effect can improve the wettability and adhesion between the nano-sized metal wires and the ceramic matrix, preventing the conductive phase from detaching. The electrolyte reduces surface tension, facilitating the expulsion of gases such as oxygen or hydrogen and minimizing discharge defects. Ultrasonic dispersion and stirring ensure that the nanoscale metal wires are fully dispersed in the electrolyte, preventing localized agglomeration that could lead to uneven conductivity in the micro-arc oxidation coating.
[0044] It should be noted that setting the concentration of copper nanowires or silver nanowires, or their corresponding derivatives, between 0.001 and 100 g / L ensures that the lower limit of non-conductive network formation at extremely low concentrations is eliminated, while avoiding the upper limit of electrolyte instability and conductive micro-arc oxidation coating degradation caused by excessively high concentrations. This also provides a wide range of process adjustments for different conductive elements, performance requirements, and application scenarios. When the SDS concentration is below 1 g / L, dispersion is insufficient, leading to a 2-3 order of magnitude increase in volume resistivity and a decrease in binding force; above 2 g / L, it may generate a large amount of foam due to exceeding the critical micelle concentration, interfering with discharge stability and introducing organic residues. Therefore, 1-2 g / L of SDS is a key process window for achieving efficient dispersion of conductive elements, good construction of conductive networks, and improved overall performance of conductive micro-arc oxidation coatings.
[0045] In step S4, the pretreated magnesium alloy substrate is added to a modified electrolyte for micro-arc oxidation treatment to obtain a conductive micro-arc oxidation coating. The specific process is as follows: The pretreated magnesium alloy substrate is added to a modified electrolyte for micro-arc oxidation treatment. Stirring and water cooling are maintained throughout the preparation process. After the reaction is complete, the surface of the magnesium alloy substrate is cleaned and dried with ultrapure water or deionized water to obtain a conductive micro-arc oxidation coating with a thickness of 20~58.5μm. The micro-arc oxidation process parameters are set as follows: a bipolar pulse power supply is used, with a forward current of 0.1~0.2A, a reverse current of 0.1~0.2A, a duty cycle of 20~40%, a frequency of 400~800Hz, a stirring speed of 100~1000r / min, an oxidation treatment time of 10~20min, and a water cooling temperature of 25~60℃.
[0046] In some embodiments of the present invention, the duty cycle is any value or a range formed by any two of the following: 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, and 40%; the oxidation treatment time is any value or a range formed by any two of the following: 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, and 20 min. For example, the duty cycle is preferably 40%, and the oxidation treatment time is preferably 20 min.
[0047] It should be noted that the forward and reverse current settings in the micro-arc oxidation process can control the discharge energy, determining the growth rate and density of the film. Frequency and duty cycle can affect the duration and interval of the discharge, regulating the microstructure and porosity of the conductive micro-arc oxidation coating. The oxidation treatment time is used to control the thickness of the conductive micro-arc oxidation coating; too short a time results in a thin coating with poor protection; too long a time may lead to increased microcracks and damage to the conductive network. Stirring is used to maintain the uniformity of the electrolyte composition; promote gas escape and prevent bubbles from adhering to the magnesium alloy substrate surface, causing abnormal local discharge; and help the nanoscale metal wires continuously contact the magnesium alloy substrate surface, increasing the doping probability. If the oxidation treatment time is too short, the conductive micro-arc oxidation coating will not grow completely, and the amount of conductive reinforcing phase incorporated will be insufficient; if the oxidation treatment time is too long, the already formed three-dimensional conductive network structure may be destroyed. Therefore, there exists an optimal time window within which the best balance between conductivity, density, and corrosion resistance can be achieved. Water cooling is used because micro-arc discharge generates a large amount of heat. Water cooling can maintain the modified electrolyte temperature within a suitable range of 25–60℃, preventing evaporation, compositional changes, or overheating and cracking of the conductive micro-arc oxidation coating. Cleaning the magnesium alloy substrate surface after the reaction is to remove residual modified electrolyte, preventing the alkaline modified electrolyte from crystallizing on the conductive micro-arc oxidation coating surface or continuing to corrode the magnesium alloy substrate; obtaining a clean test surface provides a standardized magnesium alloy substrate surface for subsequent performance testing; and preventing contamination ensures the accuracy of experimental results.
[0048] Furthermore, the present invention provides a conductive micro-arc oxidation coating for magnesium alloy, which is prepared by the above-described method for preparing a conductive micro-arc oxidation coating for magnesium alloy.
[0049] In a preferred embodiment of the present invention, when the concentration of copper nanowires or silver nanowires, or the corresponding derivatives of the above-mentioned copper nanowires or silver nanowires, is 50 g / L, the concentration of sodium dodecyl sulfonate is 2 g / L, and the oxidation treatment time is 20 min, the thickness of the conductive micro-arc oxidation coating is 58.2 ± 0.2 μm, the volume resistivity is 1.2 Ω·cm, the thermal conductivity is 21.3 W / m / K, the salt spray test time is >1120 h, and the porosity is ≤4%.
[0050] Meanwhile, the present invention also provides an application of a conductive micro-arc oxidation coating of magnesium alloy in lightweight conductive components and electronic device housings.
[0051] Next, the present invention will illustrate the significant effect of adding a conductive micro-arc oxidation coating on conductivity through the following embodiments and comparative examples.
[0052] Example 1
[0053] The first step: The AZ91 magnesium alloy is made into a sample with a size of 16mm×16mm×5mm. Its surface is polished with 800-grit and 1200-grit sandpaper until it is smooth. The polished sample is cleaned with ethanol and dried. The dried sample is then mounted.
[0054] The second step involves adding 8g of sodium silicate, 3g of potassium hydroxide, and 2g of potassium fluoride solid to 1L of deionized water to obtain a silicate-based electrolyte.
[0055] The third step involves adding copper nanowires or silver nanowires, or their corresponding derivatives, at a concentration of 50 g / L, and SDS at a concentration of 2 g / L to the prepared basic electrolyte. The electrolyte is then dispersed under ultrasonic treatment at a power of 1200 W and continuously stirred for 30 minutes to obtain the modified electrolyte.
[0056] The fourth step involves adding the pretreated AZ91 magnesium alloy to a modified electrolyte for micro-arc oxidation. Stirring and water cooling are maintained throughout the preparation process. After the reaction is completed, the surface of the AZ91 magnesium alloy is cleaned and dried with ultrapure water or deionized water to obtain a conductive micro-arc oxidation coating.
[0057] The micro-arc oxidation process parameters were set as follows: a bipolar pulse power supply was used, with a forward current of 0.2A, a reverse current of 0.2A, a duty cycle of 40%, a frequency of 500Hz, a stirring speed of 800r / min, an oxidation treatment time of 10min, and a water cooling temperature of 25~60℃.
[0058] Example 2
[0059] The preparation method in this embodiment is the same as that in Example 1, except that the oxidation treatment time in the fourth step is 15 minutes.
[0060] Example 3
[0061] The preparation method in this embodiment is the same as that in Example 1, except that the oxidation treatment time in the fourth step is 20 min.
[0062] Example 4
[0063] The preparation method of this embodiment is the same as that of Example 2, except that in the third step, the concentration of copper nanowires or silver nanowires, or the corresponding derivatives of the above copper nanowires or silver nanowires, is 0.005 g / L.
[0064] Example 5
[0065] The preparation method of this embodiment is the same as that of Example 2, except that in the third step, the concentration of copper nanowires or silver nanowires, or the corresponding derivatives of the copper nanowires or silver nanowires, is 20 g / L.
[0066] Example 6
[0067] The preparation method in this embodiment is the same as that in Example 4, except that the oxidation treatment time in the fourth step is 12 minutes.
[0068] Comparative Example 1
[0069] The difference between this comparative example and Example 1 is that the third step is omitted, and the magnesium alloy matrix that has undergone pretreatment in the first step is directly added to the silicate-based electrolyte in the second step for micro-arc oxidation treatment.
[0070] Comparative Example 2
[0071] The difference between this comparative example and Example 1 is that SDS is not added in the third step.
[0072] Comparative Example 3
[0073] The difference between this comparative example and Example 1 is that copper nanowires or silver nanowires, or their corresponding derivatives, are not added in the third step.
[0074] The thickness of the conductive micro-arc oxidation coatings prepared in Examples 1-6 and Comparative Examples 1-3 was measured using a metallographic microscope; the volume resistivity of the conductive micro-arc oxidation coating surface was measured using a four-probe tester; the thermal conductivity of the conductive micro-arc oxidation coating was determined according to GB / T 46781-2025 standard; a neutral salt spray test was conducted on the conductive micro-arc oxidation coating according to GB / T 10125; and the porosity of the cross-sectional SEM images of the layer was statistically analyzed using Image-J image analysis software. The obtained test data results are shown in Table 1:
[0075] Table 1. Test results of Examples 1-6 and Comparative Examples 1-3
[0076]
[0077] As shown in Table 1, no conductive elements were added in Comparative Example 1, and the resulting coating was a typical micro-arc oxidation ceramic coating. Its main components were magnesium oxide or silicate compounds, which are intrinsically insulating materials. Due to the lack of free electrons or conductive pathways within it, the coating exhibited extremely high volume resistivity, confirming that the micro-arc oxidation coating does not possess conductivity without the addition of copper or silver nanowires, or their corresponding derivatives, in the electrolyte.
[0078] In Examples 1-3, the introduction of copper nanowires or silver nanowires, or their corresponding derivatives, significantly reduced the volume resistivity of the conductive micro-arc oxidation coating to the level of 1 Ω·cm. This indicates that the conductive elements were successfully embedded in the ceramic matrix, forming a continuous three-dimensional conductive network. This three-dimensional conductive network forms electron transport channels through the overlap or contact between nanoscale metal wires, giving the originally insulating micro-arc oxidation ceramic coating excellent conductivity.
[0079] Comparing Example 1 and Comparative Example 2, it is evident that the lack of an interface modifier results in poor dispersion and bonding of the conductive phase, leading to an increase in volume resistivity of more than four orders of magnitude and a decrease in bonding strength. The interface modifier, by reducing surface tension and enhancing electrostatic repulsion or steric hindrance effects, effectively inhibits the aggregation of nanoscale metal wires, ensuring their uniform dispersion in the electrolyte. Simultaneously, the modifier molecules can form an adsorption layer on the surface of the nanoscale metal wires, improving their interfacial compatibility with the ceramic matrix and promoting their effective capture and embedding into the conductive micro-arc oxidation coating during discharge. Furthermore, the uniformly distributed conductive phase contributes to the formation of a denser and more continuous three-dimensional conductive network, thereby significantly improving the uniformity and conductivity of the conductive micro-arc oxidation coating. Therefore, the interface modifier plays a crucial role in improving conductivity and the quality of the conductive micro-arc oxidation coating.
[0080] Examples 1-3 all yielded conductive micro-arc oxidation coatings with low volume resistivity, high thermal conductivity, and excellent corrosion resistance within a 10-20 minute oxidation treatment time window, demonstrating the effectiveness of this time range. Within the 10-20 minute oxidation treatment time range of Examples 1-3, the thickness of the conductive micro-arc oxidation coating increased with increasing oxidation treatment time, gradually improving the salt spray resistance time of the coating. Simultaneously, the addition of sufficient nanoscale metal wires in Examples 1-3 ensured a well-constructed three-dimensional conductive network, resulting in almost constant conductivity and good thermal conductivity, exhibiting optimal overall performance. The thermal conductivity slightly decreased in Example 3, possibly due to increased internal stress caused by the thicker conductive micro-arc oxidation coating, leading to microcracks and affecting the stability of thermal conductivity. Therefore, the thermal conductivity of Example 3 decreased slightly.
[0081] With a coating thickness of approximately 32.1 μm, the performance comparison between Example 1 and Example 6 shows that the concentration of conductive elements is the core factor determining the overall performance of the conductive micro-arc oxidation coating. The volume resistivity of Example 1 is only 0.8 Ω·cm, far lower than the 28.2 Ω·cm of Example 6. The thermal conductivity of Example 1 is also significantly better than that of Example 6. Furthermore, Example 1 has a longer salt spray test time and lower porosity. This indicates that a high concentration of conductive elements can effectively construct a continuous three-dimensional conductive network in a shorter oxidation treatment time, simultaneously filling discharge channels and improving the density and corrosion resistance of the conductive micro-arc oxidation coating. In contrast, a low concentration of conductive elements, even with extended treatment time, cannot achieve the same performance level.
[0082] Thermal conductivity tests showed that the thermal conductivity of the micro-arc oxidation coating without conductive elements was only 3.1~3.2 W / m / K, while the thermal conductivity of the conductive micro-arc oxidation coating with conductive elements reached a maximum of 23.2 W / m / K. The thermal conductivity was closely related to the concentration of conductive elements, the oxidation treatment time, and the addition of SDS: higher conductive element concentration resulted in better thermal conductivity; both excessively short and excessively long oxidation treatment times were detrimental to the formation of the thermally conductive network; and the lack of SDS significantly reduced the thermal conductivity to 4.1 W / m / K. Furthermore, the conductive micro-arc oxidation coating with good thermal conductivity also exhibited low porosity and low volume resistivity, indicating that the construction of the three-dimensional conductive network effectively enhanced both electrical conductivity and thermal conductivity.
[0083] The results in Table 1 show that the porosity of the conductive micro-arc oxidation coating was significantly reduced after adding copper nanowires or silver nanowires, or their corresponding derivatives. Specifically, the porosities of Comparative Examples 1 and 3 (without conductive elements) were ≤12% and ≤11%, respectively, while the porosities of the examples with added nanoscale metal wires all decreased to ≤11%, with the optimal porosity reaching ≤3%. This indicates that the nanoscale metal wires effectively filled the discharge channels during micro-arc discharge. The addition of the interface modifier SDS further improved the dispersibility of the nanoscale metal wires, promoted the formation of a three-dimensional conductive network, and significantly improved the density of the micro-arc oxidation coating. The reduction in porosity not only helps improve the corrosion resistance of the micro-arc oxidation coating but also provides a more continuous path for electron transport, thereby synergistically optimizing conductivity and protective performance.
[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for preparing a conductive micro-arc oxidation coating on a magnesium alloy, characterized in that, Includes the following steps: S1. Pretreatment of the magnesium alloy matrix; S2. Prepare the basic electrolyte; S3. Add metal wires with a size of micrometer or nanometer, or corresponding derivatives of the metal wires with a size of micrometer or nanometer, and an interface modifier to the basic electrolyte to obtain a modified electrolyte. The diameter of the metal wire or the corresponding derivative of the metal wire is less than 20 μm, the length is less than 500 μm, and the thickness of the corresponding derivative of the metal wire is 5 to 10 nm. S4. The pretreated magnesium alloy substrate is added to a modified electrolyte for micro-arc oxidation treatment to obtain a conductive micro-arc oxidation coating.
2. The method for preparing a conductive micro-arc oxidation coating on a magnesium alloy according to claim 1, characterized in that, In step S1, the magnesium alloy matrix is selected from AZ91 magnesium alloy; The specific process for pretreatment of the magnesium alloy matrix is as follows: The surface of the magnesium alloy substrate was polished with 800-grit and 1200-grit sandpaper until smooth. The polished magnesium alloy substrate was cleaned with ethanol and dried. The dried magnesium alloy substrate was then used for mounting.
3. The method for preparing a conductive micro-arc oxidation coating on a magnesium alloy according to claim 1, characterized in that, In step S2, the base electrolyte is selected from one or more of silicate electrolyte, phosphate electrolyte, and aluminate electrolyte.
4. The method for preparing a conductive micro-arc oxidation coating on a magnesium alloy according to claim 3, characterized in that, The specific process for preparing the basic electrolyte is as follows: Add sodium silicate, potassium hydroxide and potassium fluoride solids to deionized water to obtain a silicate basic electrolyte, wherein the amount of deionized water is 1L, sodium silicate is 8-20g, potassium hydroxide is 3-8g and potassium fluoride is 2-6g.
5. The method for preparing a conductive micro-arc oxidation coating on a magnesium alloy according to claim 1, characterized in that, In step S3, a metal wire or a corresponding derivative of the metal wire is used as a conductive unit, and sodium dodecyl sulfonate is used as an interface modifier. The metal wire is a copper nanowire or a silver nanowire, and the corresponding derivative of the metal wire is a nanoscale or microscale metal wire modified or coated with a polymer material, ceramic, carbon material, or metal coating. The shape of the corresponding derivative of the metal wire includes, but is not limited to, linear, spherical, and square shapes.
6. The method for preparing a conductive micro-arc oxidation coating on a magnesium alloy according to claim 5, characterized in that, The specific process of adding metal wires with a size of micrometer or nanometer, or corresponding derivatives of such metal wires with a size of micrometer or nanometer, and an interface modifier to the basic electrolyte in step S3 to obtain a modified electrolyte is as follows: copper nanowires or silver nanowires, or corresponding derivatives of such copper nanowires or silver nanowires, and sodium dodecyl sulfonate are added to the prepared basic electrolyte. After ultrasonic dispersion and continuous stirring for 30 minutes, a modified electrolyte is obtained. The concentration of copper nanowires or silver nanowires or corresponding derivatives of such copper nanowires or silver nanowires is 0.001-100 g / L, the concentration of sodium dodecyl sulfonate is 1-2 g / L, and the ultrasonic power is 100-1400 W.
7. The method for preparing a conductive micro-arc oxidation coating on a magnesium alloy according to claim 1, characterized in that, The specific process of adding the pretreated magnesium alloy substrate to the modified electrolyte for micro-arc oxidation treatment in step S4 to obtain a conductive micro-arc oxidation coating is as follows: the pretreated magnesium alloy substrate is added to the modified electrolyte for micro-arc oxidation treatment. Stirring and water cooling are maintained throughout the preparation process. After the reaction is completed, the surface of the magnesium alloy substrate is washed and dried with ultrapure water or deionized water to obtain a conductive micro-arc oxidation coating with a thickness of 20~58.5μm. The micro-arc oxidation process parameters are set as follows: the power supply is a bipolar pulse power supply with a forward current of 0.1-0.2A, a reverse current of 0.1-0.2A, a duty cycle of 20-40%, a frequency of 400-800Hz, a stirring speed of 100-1000r / min, an oxidation time of 10-20min, and a water cooling temperature of 25-60℃.
8. A conductive micro-arc oxidation coating for magnesium alloy, characterized in that, It is prepared by any one of the methods for preparing a conductive micro-arc oxidation coating of magnesium alloy according to claims 1 to 7.
9. The conductive micro-arc oxidation coating for magnesium alloy according to claim 8, characterized in that, When the concentration of copper nanowires or silver nanowires, or the corresponding derivatives of said copper nanowires or silver nanowires, is 50 g / L, the concentration of sodium dodecyl sulfonate is 2 g / L, and the oxidation treatment time is 20 min, the thickness of the conductive micro-arc oxidation coating is 58.2 ± 0.2 μm, the volume resistivity is 1.2 Ω·cm, the thermal conductivity is 21.3 W / m / K, the salt spray test time is >1120 h, and the porosity is ≤4%.
10. The application of a conductive micro-arc oxidation coating of magnesium alloy according to any one of claims 8 or 9 in lightweight conductive components and electronic device housings.