A low-temperature heat treatment method for carbon fiber electroplated nickel products

Abstract

The application discloses a low-temperature heat treatment method for carbon fiber electroplated nickel products, which comprises the following steps: placing the carbon fiber product after the electroplated nickel process into a low-temperature heat treatment environment for heat treatment, and the temperature of the low-temperature heat treatment is 120 DEG C-280 DEG C. Through the low-temperature heat treatment, the plating layer adhesion, corrosion resistance and wear resistance of the carbon fiber electroplated nickel product are simultaneously improved, and the existing electroplating production line does not need to be reformed.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber surface treatment technology, and specifically to a low-temperature heat treatment method for nickel-plated carbon fiber products. Background Technology

[0002] With the rapid development of the new energy vehicle industry, lightweighting, long driving range, high safety, and corrosion resistance have become core research and development directions for new energy vehicles. Compared with traditional fuel vehicles, new energy vehicles are equipped with heavy equipment such as power batteries and electronic control components, resulting in a significant increase in vehicle weight. Vehicle weight directly affects energy consumption, driving range, braking performance, and service life.

[0003] Carbon fiber composites, with their excellent physical and chemical properties such as low density, high specific strength, high modulus, fatigue resistance, and corrosion resistance, are gradually replacing traditional metal materials such as steel and aluminum alloys, and are widely used in components such as body shells, chassis load-bearing parts, battery pack shells, deflectors, and internal structural parts of drive motors in new energy vehicles. However, in actual industrial applications, pure carbon fiber composites suffer from insufficient overall electrical conductivity and electromagnetic shielding performance due to the insulating properties of the matrix resin, and their wear resistance and scratch resistance are also poor, failing to meet the requirements for large-scale applications in high-end equipment such as new energy vehicles and electronic and electrical systems.

[0004] Currently, the industry commonly uses electroplating to improve the above-mentioned problems, that is, electroplating a nickel layer on the surface of carbon fiber, giving it both the lightweight and high-strength properties of carbon fiber and the electrical conductivity, corrosion resistance, and wear resistance of metal. However, existing carbon fiber electroplating technology still has shortcomings such as poor coating adhesion, uneven coating, cumbersome pre- and post-processing, susceptibility of the carbon fiber matrix to corrosion and damage, high production costs, and difficulty in large-scale mass production. Specifically, existing commercially available electroplated carbon fiber products for new energy vehicle motors mainly have the following technical defects: (1) The coating and the carbon fiber substrate are mainly mechanically interlocked, lacking stable chemical bonding or metallurgical bonding. The bonding force is only 4.5 to 5.0 N. The coating is easy to fall off when subjected to external force, resulting in poor product structural stability. (2) The coating is not dense enough and has defects such as micro gaps and micropores. Corrosive media can easily penetrate it. The salt spray test time is only 24 to 36 hours, which cannot meet the requirements for high corrosion resistance. (3) The coating has poor wear resistance. Taking the carbon fiber conductive ring widely used in the drive motor of new energy vehicles as an example, the wear amount is greater than 0.2 mm after 168 hours of use in a water-cooled environment, which is far from meeting the long life design requirements of the motor. (4) The micro gaps and micropores at the interface between the coating and the substrate result in an inherent lack of mechanical bonding, making it difficult to balance the coating bonding strength and density.

[0005] To address the aforementioned shortcomings, existing industry improvement solutions primarily focus on front-end processes such as electroplating solution formulation improvement and electroplating process parameter optimization, lacking effective post-treatment methods. A few solutions attempt to improve coating performance through heat treatment, but these require high temperatures (typically ≥400℃) and must be carried out under an inert gas protective atmosphere. This process is complex, has high operational barriers, and incurs high equipment costs. Furthermore, it necessitates modifications to existing electroplating production lines, making implementation difficult and costly. Therefore, the industry urgently needs to develop a low-cost, easy-to-operate post-treatment optimization solution that requires no modification to the existing electroplating system. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a low-temperature heat treatment method for nickel-plated carbon fiber products. This invention simultaneously improves the adhesion, corrosion resistance, and wear resistance of the nickel-plated carbon fiber coating through low-temperature heat treatment, without requiring high-temperature equipment or inert gas protection, and without needing to modify existing electroplating production lines.

[0007] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution: A low-temperature heat treatment method for nickel-plated carbon fiber products specifically involves placing the nickel-plated carbon fiber products in a low-temperature heat treatment environment for heat treatment, wherein the temperature of the low-temperature heat treatment is 120℃~280℃.

[0008] As a preferred embodiment of the present invention, the low-temperature heat treatment is carried out in an air atmosphere, the heat treatment temperature is 120℃~150℃, and the holding time is 20min~30min.

[0009] Furthermore, the heat treatment temperature is 135°C, and the holding time is 25 minutes.

[0010] Furthermore, after the heat treatment is completed, the temperature is lowered to room temperature by natural cooling in an oven or by static cooling at room temperature.

[0011] As another preferred embodiment of the present invention, the low-temperature heat treatment is carried out under nitrogen protection and adopts a multi-stage gradient temperature control process, which includes the following steps in sequence: First stage: Low-temperature dehydration pre-annealing, at a temperature of 150℃~180℃; Second stage: slow gradient heating, linearly and slowly increasing from the end temperature of the first stage to 240℃~280℃; Third stage: Low-temperature stress homogenization isothermal treatment, with a temperature of 240℃~280℃, and isothermal maintenance for 20min~30min; The fourth stage: low-temperature gradient shaping and cooling, gradually decreasing the temperature gradient from the end of the second stage to 160℃.

[0012] Furthermore, the heating rate of the second low-speed gradient heating is 1℃ / min to 5℃ / min.

[0013] Furthermore, the cooling rate of the fourth stage low-temperature gradient shaping cooling is 1℃ / min to 5℃ / min.

[0014] Furthermore, the purity of nitrogen in the nitrogen protection is ≥99.5%.

[0015] Furthermore, in the method of the present invention, the low-temperature heat treatment is carried out in a hot air circulating oven, an infrared heating box, or a tunnel furnace.

[0016] Preferably, the carbon fiber product is in the form of carbon fiber tow, carbon fiber cloth, or carbon fiber braid.

[0017] The beneficial effects of this invention are as follows: This invention utilizes the thermal effect of low-temperature heat treatment to eliminate micro-gaps and micropores at the interface between the electroplated nickel layer and the carbon fiber substrate, enabling the coating and substrate to achieve microstructural bonding, enhancing mechanical interlocking strength, and significantly improving the coating adhesion, effectively solving the problem of easy coating detachment under external force. Simultaneously, low-temperature heat treatment promotes nickel coating grain refinement, reduces grain boundary defects and micro-pinholes, reduces the penetration channels of corrosive media, increases coating density, and effectively enhances corrosion resistance. Furthermore, by optimizing the microstructure of the nickel coating and reducing internal micro-defects through low-temperature heat treatment, the surface hardness and density of the coating are improved, significantly enhancing wear resistance and greatly extending the service life of the product under friction conditions.

[0018] The heat treatment temperature of this invention is lower than the heat damage temperature of carbon fiber and the significant oxidation temperature of nickel. It can be completed in an air atmosphere and conventional heating equipment, or in a nitrogen-protected and multi-stage gradient temperature control equipment. Neither of these methods requires high-temperature equipment or modification of existing electroplating production lines. The operation is simple, the equipment investment and operating costs are low, and it is suitable for continuous mass production. Attached Figure Description

[0019] Figure 1 The images show a comparison of the surface morphology of the carbon fiber electroplated nickel product before and after heat treatment in Embodiment 1 of the present invention, obtained by scanning electron microscopy. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. 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.

[0021] This invention provides a low-temperature heat treatment method for nickel-plated carbon fiber products. The carbon fiber product, having completed a conventional nickel plating process, is placed in a low-temperature heat treatment environment for heat treatment. The carbon fiber product is a semi-finished product with a pre-deposited nickel plating layer, and its surface should be free of obvious impurities and water stains, requiring no additional cleaning, drying, or modification pretreatment. The low-temperature heat treatment temperature is 120℃ to 280℃. Within this temperature range, micro-gaps and micropores between the plating layer and the substrate can be effectively eliminated, promoting grain refinement and microstructure optimization of the nickel plating layer. Furthermore, the temperature is below the thermal damage temperature of the carbon fiber matrix and the significant oxidation temperature of the nickel plating layer, thus preventing thermal damage to the carbon fiber substrate and avoiding adverse oxidation reactions in the plating layer.

[0022] In a preferred embodiment of the present invention, the low-temperature heat treatment is performed in an air atmosphere. In this embodiment, the heat treatment temperature is 120℃~150℃, and the holding time is 20min~30min. This temperature range is selected based on the following considerations: above 120℃, the microstructure adjustment at the atomic scale of the nickel plating can be effectively activated, while below 150℃, it ensures that no significant oxidation or discoloration occurs on the surface of the nickel plating in an air atmosphere. Therefore, no inert gas protection is required, and the process can be completed in a regular air-circulating oven. For example, when the heat treatment temperature is 135℃ and the holding time is 25min, a better overall performance improvement effect of the plating can be obtained. Under this condition, the micro-gap and micropores at the interface between the plating and the carbon fiber substrate undergo microstructural bonding under thermal action, and the plating density and interfacial bonding strength are effectively improved. After the heat treatment is completed, the temperature can be lowered to room temperature by natural cooling in the oven or static cooling at room temperature. No forced cooling or gradient temperature control is required, making the operation extremely simple. This implementation method is particularly suitable for production scenarios with high requirements for equipment investment and ease of operation. It does not require any modification to the existing electroplating production line, and can be achieved simply by adding a regular hot air circulating oven after the electroplating process.

[0023] In another preferred embodiment of the present invention, the low-temperature heat treatment is performed under nitrogen protection using a multi-stage gradient temperature control process. This embodiment is suitable for large-scale production scenarios with higher requirements for coating performance and the availability of continuous heat treatment equipment (such as multi-temperature zone tunnel furnaces). For example, the nitrogen purity under nitrogen protection is not less than 99.5% to ensure that the nickel plating surface does not oxidize and discolor due to the presence of trace amounts of oxygen during the heat treatment process. The multi-stage gradient temperature control process includes the following four stages: The first stage is low-temperature dehydration pre-annealing, at a temperature of 150℃~180℃, under nitrogen protection. The purpose of this stage is to remove trace amounts of moisture and flux residues remaining inside and on the surface of the plating layer after electroplating. The low-temperature pre-annealing method avoids the sudden vaporization and expansion of moisture inside the plating layer caused by rapid temperature rise, thereby effectively preventing plating defects such as blistering or peeling and improving product yield.

[0024] The second stage involves a slow, gradual temperature increase, linearly rising from the initial temperature of the first stage to 240℃–280℃. This stage aims to slowly release the residual internal stress within the crystal lattice of the electroplated nickel layer. During electroplating, the nickel deposit often exhibits residual stress due to lattice distortion. If the heating rate is too rapid, the sudden release of stress can easily generate microcracks within the plating layer, thereby damaging the strength of the carbon fiber matrix. For example, the heating rate is controlled at 1℃ / min–5℃ / min, preferably 1℃ / min–3℃ / min, to ensure a stable and controllable stress release process.

[0025] The third stage is low-temperature stress homogenization isothermal treatment, with a temperature range of 240℃ to 280℃, held for 20 to 30 minutes. Within this temperature range, the nickel plating grains undergo slight reorganization, and the hydrogen atoms introduced during electroplating gain sufficient energy to escape from the plating lattice, thus eliminating hydrogen embrittlement. Simultaneously, the residual stress at the interface between the plating and the carbon fiber substrate is further homogenized and released, significantly improving the interfacial bonding strength. It should be noted that 240℃ to 280℃ is still below the thermal damage initiation temperature of the carbon fiber matrix and will not cause a detectable decrease in the strength and modulus of the carbon fiber itself.

[0026] The fourth stage is low-temperature gradient cooling, where the temperature gradually decreases from the end of the second stage to 160°C. This stage aims to lock in the stable microstructure of the coating formed after homogenization, preventing rapid cooling and shrinkage caused by direct exposure to room temperature from high temperatures, thus preventing the generation of secondary residual stress. For example, the cooling rate is controlled at 1°C / min to 5°C / min, preferably 1°C / min to 3°C / min. This gradient cooling method ensures a uniform temperature field distribution throughout the entire roll of product, making it particularly suitable for large-scale continuous production. It effectively prevents warping and deformation of the product after winding due to uneven residual stress, ensuring product dimensional stability and consistent coating performance.

[0027] In the above-mentioned multi-stage gradient temperature control implementation method, the four temperature ranges constitute a complete low-temperature heat treatment curve. The temperature and rate parameters of each stage can be appropriately adjusted within the above range according to the specifications, batch size and equipment conditions of the carbon fiber products, so as to achieve simultaneous improvement of coating adhesion, corrosion resistance and wear resistance.

[0028] Both of the above preferred embodiments are specific implementation paths under the low-temperature heat treatment technology concept proposed in this invention. The air-atmosphere 120℃~150℃ short-time heat treatment scheme emphasizes equipment versatility and ease of operation, while the nitrogen-protected multi-stage gradient temperature control scheme emphasizes performance optimization under continuous industrial production conditions. Both share a consistent core inventive concept: both achieve coating microstructure optimization and enhanced interface bonding through low-temperature heat treatment within the range of 120℃~280℃, and neither requires high-temperature equipment or modification of existing electroplating production lines.

[0029] The carbon fiber product forms to which the method of the present invention is applicable include, but are not limited to, carbon fiber tow, carbon fiber cloth or carbon fiber braid, and can also be applied to other carbon fiber woven forms, thus having wide applicability.

[0030] Example 1

[0031] Carbon fiber tow products that have undergone conventional nickel plating are placed evenly on the material rack of a hot air circulating oven without additional cleaning, ensuring adequate spacing between the tows to prevent stacking. The oven temperature is set to 135°C, and the holding time is 25 minutes. The heating program is then started. Once the oven temperature reaches the set value, the holding time begins. The entire holding process is conducted in an air atmosphere, without the need for nitrogen or other inert gases. After the holding period, the heating is turned off, and the oven door is opened (or left closed) to allow natural cooling to room temperature (20–25°C). The resulting product is the nickel-plated carbon fiber product treated according to this invention.

[0032] Depend on Figure 1 The scanning electron microscope (SEM) surface morphology comparison images of Example 1 before and after heat treatment clearly show that the surface porosity of the coating is significantly reduced and the metal agglomerates are significantly reduced after treatment. The density and uniformity of the coating are effectively improved, indicating that the low-temperature heat treatment of the present invention has a significant optimization effect on the microstructure of nickel coating.

[0033] Example 2

[0034] Carbon fiber woven products that have undergone conventional nickel electroplating are evenly placed on the conveyor belt of a multi-temperature zone tunnel furnace. The nitrogen protection system is activated, ensuring a nitrogen purity ≥99.5% and maintaining a nitrogen atmosphere within the furnace. The first pre-annealing temperature is set to 160℃, and the material undergoes dehydration pre-annealing in the first temperature zone. It then enters the second temperature zone, where the temperature linearly increases from 160℃ to 240℃ at a rate controlled at 3℃ / min. Next, it enters the third temperature zone, where it is held at 240℃ for 25 minutes. Finally, it enters the fourth temperature zone, where the temperature gradually decreases from 240℃ to 160℃ at a rate controlled at 3℃ / min. After discharge, the resulting carbon fiber nickel-plated product is obtained according to this invention.

[0035] Performance testing The coating adhesion was tested using a conventional tensile tester to assess the coating peel strength; the corrosion resistance was tested using a neutral salt spray test in accordance with GB / T 10125; and the abrasion resistance was tested using a conductive ring under water-cooled cycling conditions to simulate friction.

[0036] The test results show that the nickel-plated carbon fiber products treated in Example 1 of this invention have a coating adhesion of 6.2–6.8 N, a salt spray test duration of 36–48 h, and a water-cooled conductive ring wear resistance test duration of 328 h. All performance characteristics meet the requirements for conductive rings and other components used in new energy vehicle motors. The nickel-plated carbon fiber products treated in Example 2 of this invention show further improvements in coating adhesion, corrosion resistance, and wear resistance compared to Example 1. Furthermore, the coating uniformity is superior to that of Example 1, and the performance differences between the inner and outer layers of the entire roll are small, making it particularly suitable for large-scale continuous production scenarios.

[0037] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0038] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A low-temperature heat treatment method for nickel-plated carbon fiber products, characterized in that, The carbon fiber products that have completed the nickel plating process are placed in a low-temperature heat treatment environment for heat treatment, and the temperature of the low-temperature heat treatment is 120℃~280℃.

2. The low-temperature heat treatment method for nickel-plated carbon fiber products according to claim 1, characterized in that, The low-temperature heat treatment is carried out in an air atmosphere, with a heat treatment temperature of 120℃~150℃ and a holding time of 20min~30min.

3. The low-temperature heat treatment method for nickel-plated carbon fiber products according to claim 2, characterized in that, The heat treatment temperature is 135℃, and the holding time is 25 minutes.

4. The low-temperature heat treatment method for nickel-plated carbon fiber products according to claim 2, characterized in that, After the heat treatment is completed, the temperature is lowered to room temperature by natural cooling in an oven or by static cooling at room temperature.

5. The low-temperature heat treatment method for nickel-plated carbon fiber products according to claim 1, characterized in that, The low-temperature heat treatment is carried out under nitrogen protection, employing a multi-stage gradient temperature control process, sequentially... Includes the following steps: First stage: Low-temperature dehydration pre-annealing, at a temperature of 150℃~180℃; Second stage: slow gradient heating, linearly and slowly increasing from the end temperature of the first stage to 240℃~280℃; Third stage: Low-temperature stress homogenization isothermal treatment, with a temperature of 240℃~280℃, and isothermal maintenance for 20min~30min; The fourth stage: low-temperature gradient shaping and cooling, gradually decreasing the temperature gradient from the end of the second stage to 160℃.

6. The low-temperature heat treatment method for nickel-plated carbon fiber products according to claim 5, characterized in that, The heating rate of the second low-speed gradient heating is 1℃ / min to 5℃ / min.

7. The low-temperature heat treatment method for nickel-plated carbon fiber products according to claim 5, characterized in that, The cooling rate of the fourth stage low-temperature gradient shaping cooling is 1℃ / min to 5℃ / min.

8. The low-temperature heat treatment method for nickel-plated carbon fiber products according to claim 5, characterized in that, The purity of nitrogen in the nitrogen protection is ≥99.5%.

9. The low-temperature heat treatment method for nickel-plated carbon fiber products according to any one of claims 1 to 8, characterized in that, Low-temperature heat treatment is carried out in a hot air circulating oven, an infrared heating box, or a tunnel furnace.

10. A low-temperature heat treatment method for nickel-plated carbon fiber products according to any one of claims 1 to 8, characterized in that, The carbon fiber products are in the form of carbon fiber tows, carbon fiber cloth, or carbon fiber braids.

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