Aluminum alloy radiator and surface cold copper spraying process

Abstract

The invention discloses an aluminum alloy radiator and a surface cold copper spraying process, and belongs to the technical field of radiator machining. The preparation method comprises the following steps: selecting high-purity spherical copper powder, carrying out surface roughening pretreatment, impacting the copper powder on a substrate at a high speed of 300-800m / s by utilizing heating gas at 400-600 DEG C under the protection of inert gas, carrying out layered spraying for 3-8 times to form a 0.1-0.5 mm coating, and finally carrying out vacuum packaging. According to the method provided by the invention, the defects that the copper powder is easy to oxidize, the thermal damage of a matrix is large, the binding force of a coating is poor and the like in a thermal spraying process are effectively overcome. The oxidation rate of the prepared copper coating is lower than 1%, the porosity is smaller than 3%, the bonding strength reaches up to 40-80 MPa, the heat conductivity coefficient exceeds 380 W / (m.K), and the salt spray corrosion resistance exceeds 500 hours. The process has the advantages of low-temperature operation, energy conservation and environmental protection, the heat dissipation performance and reliability of the aluminum alloy radiator are remarkably improved, and the service life of the aluminum alloy radiator is remarkably prolonged.

Description

Technical Field

[0001] This invention belongs to the field of radiator processing technology, specifically relating to an aluminum alloy radiator and a surface cold spray copper process. Background Technology

[0002] In electronically controlled cooling systems, efficient heat dissipation is crucial for stable operation. With the increasing integration of power devices, the heat generated per unit volume is rising dramatically, placing more stringent demands on the performance of cooling systems. The heat dissipation performance of equipment directly affects its operating efficiency, stability, and lifespan. Aluminum alloys, with their low density, good thermal conductivity, relatively low cost, and excellent processing performance, have become the preferred material for manufacturing heat sinks. However, the motor controllers in new energy vehicles have high heat dissipation requirements, and relying solely on the thermal conductivity of aluminum alloys is insufficient to meet these demands. Overheating can lead to performance degradation, shortened lifespan, or even failure. Copper has extremely high thermal conductivity (pure copper has a thermal conductivity of approximately 401 W / (m²)). Copper (K) is an ideal material for enhancing heat dissipation. To improve the heat dissipation performance of aluminum alloy heat sinks, the industry commonly employs the method of preparing a copper coating on its surface. By forming a copper coating on the surface of the aluminum alloy heat sink, the excellent thermal conductivity of copper can be utilized to construct an efficient heat conduction path, quickly transferring heat from the heat source to the heat sink surface and dissipating it, thereby significantly improving heat dissipation efficiency. Therefore, preparing a high-quality copper coating on the surface of aluminum alloy heat sinks has become one of the key technologies for improving the heat dissipation performance of equipment and is also a current research hotspot in the field of materials surface engineering.

[0003] Currently, flame spraying and arc spraying are common copper coating methods. Flame spraying technology uses a high-temperature flame generated by the combustion of a mixture of oxygen and fuels such as acetylene or propane to heat copper powder to a molten or semi-molten state. The powder particles are accelerated in the flame and then atomized into fine droplets by compressed air, which are then sprayed onto the pre-treated aluminum alloy radiator surface. The droplets rapidly cool and solidify upon impact with the substrate surface, accumulating to form a coating. This process is simple to operate, flexible, and suitable for large-area spraying, but the coating quality is significantly affected by parameters such as flame temperature, powder particle size, and spraying distance. Arc spraying, on the other hand, uses two continuously fed copper wires as consumable electrodes. A voltage is applied to their ends to generate an electric arc, which melts the copper wires using its high temperature. Simultaneously, compressed air is ejected at high speed from the nozzle, atomizing the molten copper into fine particles and spraying them onto the aluminum alloy radiator surface to form a copper coating. The coating bonding strength is improved compared to flame spraying, but the equipment complexity and energy consumption are correspondingly increased.

[0004] Traditional thermal spraying technology requires high-temperature environments, which can lead to copper powder oxidation, thereby reducing the coating's conductivity and corrosion resistance. Furthermore, the high internal stress generated during spraying may affect the adhesion between the coating and the substrate, reducing the coating's durability. Additionally, there is room for improvement in aspects such as coating uniformity. Therefore, there is an urgent need for a copper coating preparation technology for aluminum alloy heat sinks that can overcome these shortcomings, enabling the efficient preparation of high-purity, high-density, and high-adhesion copper coatings to meet the demands of modern industry for efficient and environmentally friendly heat dissipation. Summary of the Invention

[0005] One of the objectives of this invention is to provide a cold-spray copper process for aluminum alloy heat sinks, which avoids the problem of copper powder being easily oxidized under high-temperature conditions during thermal spraying, eliminates thermal damage to the aluminum alloy substrate caused by high-temperature spraying, and solves the hidden dangers of insufficient coating adhesion and easy peeling and cracking after long-term use in traditional processes.

[0006] A second objective of this invention is to provide an aluminum alloy heat sink, comprising an aluminum alloy substrate and a copper coating, wherein the copper coating is prepared on the surface of the aluminum alloy substrate using the aforementioned process. By applying a cold-spray copper coating process to the surface of the aluminum alloy heat sink, and employing low-temperature cold-spray technology while optimizing process parameters and flow design, a high-purity, high-density, and high-adhesion copper coating is prepared on the surface of the aluminum alloy heat sink. This aims to overcome many shortcomings of existing thermal spraying processes, significantly improve the heat dissipation performance, structural reliability, and service life of the aluminum alloy heat sink, while simultaneously reducing energy consumption and environmental pollution during production, thus meeting the demands of modern industry for efficient and environmentally friendly heat dissipation technology.

[0007] The objective of this invention can be achieved through the following technical solutions: A cold copper spraying process for aluminum alloy heat sinks includes the following steps: S1. Selection of copper powder: Select spherical pure copper powder with a purity of ≥99.9% and a particle size of 15-45μm; S2. Pre-treatment of workpiece: Roughen the surface of the aluminum alloy radiator to be sprayed to make the surface roughness Ra=0.3-0.6μm, then clean and dry with ethanol; S3, Cold Spray Copper: Copper powder is placed in a powder feeder protected by inert gas. The copper powder is transported to the spray gun by high-pressure inert working gas. The working gas heated to 400-600℃ drives the copper powder to impact the aluminum alloy surface at a speed of 300-800m / s. The copper coating is formed by spraying in 3-8 times. The coating thickness increases by 0.03-0.06mm after each spray. S4. Vacuum Packaging: The radiator is vacuum-sealed after cooling following cold spraying. S5. Sampling test: Perform wettability test and bonding strength test on the sample.

[0008] Furthermore, the spherical pure copper powder in S1 has a flowability ≥15s / 50g and a bulk density ≥4.5g / cm³. 3 .

[0009] Furthermore, the roughening process in S2 is mechanical polishing or laser cleaning; the mechanical polishing uses 200-400 grit alumina sandpaper, and the laser cleaning has a power of 100-200W and a scanning speed of 50-100mm / s.

[0010] Furthermore, the inert gas in S3 is nitrogen or helium with a purity ≥99.99%; the pressure of the high-pressure inert working gas is 1.8-2.5 MPa.

[0011] Furthermore, when the inert gas is helium, the temperature of the working gas can be reduced to 350-500℃, and the impact velocity of the copper powder can be increased to 600-800m / s.

[0012] Furthermore, in S3, the cold-sprayed copper is moved by a CNC worktable or robot-driven spray gun, with the spray gun and aluminum alloy surface having an angle of 90°±5°, a spraying distance of 20-40mm, a moving speed of 50-100mm / s, and a powder feeding rate of 10-20g / min.

[0013] Furthermore, the interval between two adjacent sprayings in S3 is 1-2 minutes, and the final thickness of the copper coating is 0.1-0.5 mm.

[0014] Furthermore, in step S3, a functional powder, which is silicon carbide powder, can be added to the pure copper powder, and the amount added is 1% to 5% of the mass of the pure copper powder.

[0015] Furthermore, in S3, multiple spray guns can work simultaneously, with the layout angle of the multiple spray guns being 30-60° and the spacing between adjacent spray guns being 50-100mm.

[0016] Furthermore, in step S4, the vacuum degree of the vacuum packaging is ≤0.01MPa, the temperature of the storage environment after packaging is 20-30℃, and the relative humidity is ≤60%.

[0017] Furthermore, the wettability test in S5 is based on IEC60068-2-58:2017 and IPC-TM-6502.1.1F06 / 15 standards, requiring a wetted area ≥95% and a contact angle <20°.

[0018] Furthermore, the bonding strength test is conducted in accordance with the DIN EN ISO 14916-2017 standard, requiring a bonding strength of ≥50 MPa at room temperature and ≥45 MPa at 80°C.

[0019] An aluminum alloy heat sink includes an aluminum alloy substrate and a copper coating; the copper coating is prepared on the surface of the aluminum alloy substrate by the above-mentioned cold spray copper process for aluminum alloy heat sinks, and the purity of the copper coating is ≥99% and the porosity is <3%.

[0020] Furthermore, the aluminum alloy substrate is made of 6061 or 6063 aluminum alloy, and the thermal conductivity of the copper coating is ≥380W / (m²). K), surface roughness Ra≤1.0μm.

[0021] Applying cold-spray copper technology to the surface treatment of aluminum alloy heat sinks aims to ensure that the surface wetting performance and bonding strength of the copper layer meet the standards while keeping overall costs under control. It effectively avoids the problem of copper powder oxidation under the high-temperature environment of thermal spraying, preventing oxidation impurities from causing a decrease in the thermal and electrical conductivity of the coating; it eliminates thermal damage to the aluminum alloy substrate caused by high-temperature spraying, preventing the substrate from experiencing a decline in mechanical properties and structural instability due to excessive temperature rise; it improves the bonding state between the coating and the substrate, solving the hidden dangers of insufficient coating adhesion and easy peeling and cracking after long-term use in traditional processes; it optimizes the microstructure of the coating, solving problems such as low density, high porosity, and surface roughness of thermally sprayed coatings, improving heat dissipation efficiency and corrosion resistance. Through the application of this new cold-spray copper process, the quality and performance of the copper coating on the surface of aluminum alloy heat sinks are improved.

[0022] The beneficial effects of this invention are: (1) Reduced copper powder oxidation: Spherical pure copper powder with a purity of ≥99.9% is selected, and combined with an inert gas-protected powder feeder and working gas, the oxidation of copper powder during the spraying process is effectively avoided, and the content of oxidation products in the coating is controlled below 1%. This not only ensures the high purity and high density of the copper coating, but also significantly improves thermal conductivity and electrical conductivity, reduces thermal resistance, and improves heat dissipation efficiency. At the same time, vacuum packaging further prevents oxidation during storage and transportation, ensuring the long-term stability of the coating.

[0023] (2) Reduced thermal damage to the substrate: The working gas temperature in the cold spray process is controlled at 400-600℃ (far below the melting point of copper), and the copper powder impacts at high speed in a solid or semi-solid state, avoiding thermal damage to the aluminum alloy substrate. Combined with surface roughening (Ra=0.3-0.6μm) and cleaning in the pretreatment of the workpiece, it is ensured that there are no problems such as thermal deformation and grain growth in the substrate, maintaining the mechanical properties and structural stability of the substrate, and ensuring the overall strength and assembly accuracy of the heat sink.

[0024] (3) Improved coating adhesion: Due to the optimized surface roughness provided by the workpiece pretreatment, and the impact of copper powder on the substrate at a speed of 300-800 m / s during cold spraying, the copper powder forms a metallurgical bond and mechanical interlock with the substrate through plastic deformation, with a bonding strength of 40-80 MPa. Spraying in 3-8 layers ensures coating uniformity and stress release, avoiding coating peeling and cracking. Sampling tests can verify the bonding strength and wettability, ensuring the long-term reliability of the coating under thermal cycling conditions.

[0025] (4) Improved coating quality: The copper coating formed by cold spraying has high density, and the porosity can be controlled below 1%-3%, resulting in a uniform and dense coating structure. This not only improves the thermal conductivity of the coating and reduces thermal resistance, but also enhances its corrosion resistance (no significant corrosion can be observed after more than 500 hours of salt spray testing). The cleaning and drying during workpiece pretreatment eliminates surface contaminants, further ensuring the integrity of the coating. The dense coating can effectively prevent moisture and corrosive media from eroding the substrate, extending the service life of the radiator.

[0026] (5) Energy saving and environmental protection: The cold spray process does not require high temperature heating to melt copper powder. The main energy consumed is used for gas compression and equipment driving. At the same time, due to the low temperature during the spraying process, the copper powder is less oxidized, and the amount of smoke and harmful gas emissions is greatly reduced. The noise pollution is also relatively low, which is in line with the concept of green manufacturing development. Attached Figure Description

[0027] The invention will now be further described with reference to the accompanying drawings.

[0028] Figure 1 This is a photograph of the surface of the copper-plated layer of this invention; Figure 2 This is a photograph of the surface of the copper-plated solder paste printed in this invention; Figure 3 This is a cross-sectional photograph of the copper-plated solder paste printing process of the present invention; Figure 4 This is a photograph of the surface of the copper-plated solder paste after reflow soldering. Figure 5 These are cross-sectional photos of the copper-plated solder paste printed according to the present invention after reflow soldering; Figure 6 This is a photograph of the present invention before the strength test; Figure 7 This is a photograph of the present invention after a strength test. Detailed Implementation

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0030] In some embodiments, a cold copper spraying process for the surface of an aluminum alloy heat sink includes the following steps: S1. Copper Powder Selection: Spherical pure copper powder with a purity of not less than 99.9% is selected. It has good flowability and bulk density, which is conducive to uniform powder feeding and coating formation. The particle size range is controlled within 15-45μm. During the cold spraying process, it can obtain sufficient kinetic energy to generate plastic deformation, making the powder easy to agglomerate, while ensuring the density and bonding strength of the coating. S2. Pre-treatment of workpiece: The surface of the aluminum substrate is mechanically ground to Ra0.3~0.6μm to remove surface oxide stains and remove oxides from the surface to be welded. This not only increases the actual contact area between the coating and the substrate, forming an effective mechanical interlock, but also avoids excessive roughness that leads to stress concentration inside the coating. Then wipe it with a lint-free cloth soaked in ethanol to remove impurities and oil stains, and let it air dry.

[0031] S3. Cold Spray Copper: Pure copper powder is loaded into a powder feeder, which operates in an inert gas atmosphere such as dry nitrogen to prevent moisture absorption or oxidation of the powder during feeding. The powder feeder evenly delivers the copper powder to the powder inlet of the spray gun, where it enters the nozzle under the influence of high-pressure nitrogen. Inside the nozzle, the high-pressure gas expands and accelerates, its temperature controlled at 400-600℃ by an electric heater. This accelerates the copper powder particles to a high speed of 300-800 m / s, causing them to impact the aluminum alloy heat sink surface in a solid or semi-solid state. This increases the kinetic energy of the gas and the plasticity of the powder, facilitating particle deformation and bonding. During spraying, a robot or CNC worktable moves the spray gun, maintaining its perpendicularity to the substrate surface (angle error not exceeding ±5°). The uniform speed of the spray gun ensures consistent powder deposition per unit area, resulting in a uniform coating thickness. Multiple coats are applied according to the desired copper layer thickness, with each coat increasing the coating thickness by 0.03-0.06 mm.

[0032] S4. Vacuum Packaging: After the radiator is cooled by cold spraying, it is vacuum sealed and packaged. The copper coating after cold spraying has high surface activity. Vacuum packaging can isolate the copper coating from air and moisture, prevent oxidation and discoloration during storage and transportation, avoid the oxide layer affecting the heat transfer efficiency during subsequent assembly, and ensure the stability of coating performance.

[0033] S5. Sampling Tests: Wetting and Bond Strength Tests are performed on the samples. The wetting test verifies the bonding ability between the copper coating and the solder, ensuring a continuous thermal interface is formed when the heat sink is assembled with power devices; the bond strength test directly evaluates the reliability of the bonding between the coating and the substrate, avoiding failure due to insufficient bond strength.

[0034] In some embodiments, the spherical pure copper powder in step S1 has a flowability ≥15s / 50g and a bulk density ≥4.5g / cm³. 3A flowability of ≥15s / 50g ensures smooth powder delivery within the powder feeding pipe, reducing the risk of powder blockage and improving spraying efficiency; a bulk density of ≥4.5g / cm³ 3 It can increase the number of powder particles per unit volume, reduce the porosity inside the coating, improve the coating density, and thus enhance thermal conductivity and corrosion resistance.

[0035] In some embodiments, the roughening treatment in S2 is mechanical polishing or laser cleaning; the mechanical polishing uses 200-400 grit alumina sandpaper, and the laser cleaning has a power of 100-200W and a scanning speed of 50-100mm / s. 200-400 grit alumina sandpaper allows for precise control of the roughening degree, avoiding over-polishing and damage to the substrate; laser cleaning efficiently removes the surface oxide layer and impurities without damaging the substrate itself. Both methods can stably achieve a roughness requirement of Ra=0.3-0.6μm, providing excellent surface conditions for coating adhesion.

[0036] In some embodiments, the inert gas in step S3 is nitrogen or helium with a purity ≥99.99%; the pressure of the high-pressure inert working gas is 1.8-2.5 MPa. High-purity nitrogen or helium of 99.99% can completely prevent copper powder oxidation. Nitrogen is low-cost and suitable for large-scale production, while helium has a small molecular weight, enabling copper powder to achieve a higher impact velocity. The gas pressure of 1.8-2.5 MPa balances kinetic energy and energy consumption: too low a pressure results in insufficient copper powder velocity and low bonding strength; too high a pressure leads to a sharp increase in energy consumption. This range allows for control of production costs while ensuring coating quality.

[0037] In some embodiments, when the inert gas is helium, the temperature of the working gas can be reduced to 350-500°C, and the impact velocity of the copper powder can be increased to 600-800 m / s. Helium has a higher speed of sound than nitrogen, and at the same pressure, it can impart a higher velocity (600-800 m / s) to the copper powder, thus reducing the operating temperature (350-500°C). This reduces energy consumption and further reduces the risk of substrate temperature rise. Simultaneously, the higher impact velocity allows for more complete deformation of the copper powder, increasing the bonding strength to 60-80 MPa, making it suitable for scenarios with extremely high reliability requirements.

[0038] In some embodiments, the cold-sprayed copper in step S3 is driven by a CNC worktable or robot to move the spray gun. The angle between the spray gun and the aluminum alloy surface is 90°±5°, the spraying distance is 20-40mm, the moving speed is 50-100mm / s, and the powder feeding rate is 10-20g / min. CNC / robot drive enables precise positioning; the 90°±5° spray gun angle ensures the copper powder impacts perpendicularly, maximizing kinetic energy conversion; the 20-40mm spraying distance ensures stable speed of the copper powder when it reaches the substrate; the 50-100mm / s moving speed and the 10-20g / min powder feeding rate match, controlling the uniformity of powder deposition per unit area, avoiding localized accumulation, and ensuring a coating thickness error ≤5%.

[0039] In some embodiments, the interval between two adjacent sprayings in S3 is 1-2 minutes, and the final copper coating thickness is 0.1-0.5 mm. The 1-2 minute interval allows the heat generated by each spraying to dissipate in time, avoiding cumulative temperature rise of the substrate; the final thickness of 0.1-0.5 mm is determined by heat dissipation requirements and economic considerations: a thickness less than 0.1 mm results in limited heat dissipation enhancement, while a thickness greater than 0.5 mm increases cost and weight; this range balances heat dissipation performance and practicality.

[0040] In some embodiments, a functional powder, specifically silicon carbide powder, may be added to the pure copper powder in step S3, at an amount of 1% to 5% of the mass of the pure copper powder. The 1% to 5% silicon carbide powder can reduce thermal conductivity (thermal conductivity ≥ 360 W / (m²)) without significantly reducing thermal conductivity. Under the premise of K), the wear resistance of the coating is greatly improved, making it suitable for radiators with friction conditions, avoiding coating failure due to wear, and extending the service life of the radiator.

[0041] In some embodiments, multiple spray guns can operate synchronously in step S3, with the spray guns arranged at an angle of 30-60° and the spacing between adjacent spray guns being 50-100mm. The 30-60° spray gun arrangement and 50-100mm spacing can cover a larger spraying area and avoid airflow interference between spray guns. Synchronous operation of multiple spray guns can increase production efficiency by 2-3 times, while coordinated control ensures uniform coating overlap, making it suitable for mass production of large-area heat sinks.

[0042] In some embodiments, the vacuum degree of the vacuum packaging in S4 is ≤0.01MPa, and the temperature of the storage environment after packaging is 20-30℃, and the relative humidity is ≤60%. The vacuum degree of ≤0.01MPa can completely isolate oxygen and water vapor, and the storage environment of 20-30℃ and ≤60% can prevent condensation inside the packaging and extend the service life of the copper coating.

[0043] In some embodiments, the wettability test in step S5 is based on IEC60068-2-58:2017 and IPC-TM-6502.1.1F06 / 15 standards, requiring a wetting area ≥95% and a contact angle <20°. A wetting area ≥95% and a contact angle <20° ensure sufficient solder spread and eliminate the risk of poor solder joints.

[0044] In some embodiments, the bonding strength test is conducted according to the DIN EN ISO 14916-2017 standard, requiring a room temperature bonding strength ≥ 50 MPa and an 80°C bonding strength ≥ 45 MPa. A room temperature bonding strength ≥ 50 MPa and an 80°C bonding strength ≥ 45 MPa ensure that the coating on the radiator does not peel off during assembly and high-temperature operation, meeting the usage requirements of high-frequency vibration and thermal cycling conditions, such as those encountered by motor controllers in new energy vehicles.

[0045] An aluminum alloy heat sink includes an aluminum alloy substrate and a copper coating; the copper coating is prepared on the surface of the aluminum alloy substrate by the above process, and the purity of the copper coating is ≥99% and the porosity is <3%.

[0046] In some embodiments, the aluminum alloy substrate is made of 6061 or 6063 aluminum alloy, and the thermal conductivity of the copper coating is ≥380 W / (m²). K), surface roughness Ra≤1.0μm. 6061 and 6063 aluminum alloys also possess good thermal conductivity (160-200W / (m²)). With good K) and mechanical properties, it is suitable as a heat sink substrate; the copper coating purity is ≥99%, and the thermal conductivity is ≥380W / (m²). K) can significantly improve heat dissipation efficiency, more than twice that of pure aluminum alloy; porosity <3% can reduce internal thermal resistance of the coating and enhance corrosion resistance; surface roughness Ra≤1.0μm can increase the contact area with power devices, reduce contact thermal resistance, and further optimize heat dissipation effect.

[0047] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0048] Example 1

[0049] This embodiment provides an aluminum alloy heat sink, which is prepared through the following steps: S1. Copper powder selection: Select spherical pure copper powder with a purity of 99.95%, a particle size of 20-40μm, a flowability of 12s / 50g, and a bulk density of 4.8g / cm³. This combination of parameters can ensure uniform powder feeding and coating density. S2. Pre-treatment of workpiece: Select 6063 aluminum alloy heat sink substrate, use 320-grit alumina sandpaper to mechanically grind the surface to be sprayed to a roughness Ra=0.4μm; wipe the surface with anhydrous ethanol, and let it air dry in a Class 1000 clean room for 12 minutes to remove oxide layer and impurities and activate the surface. S3, Cold Copper Spraying: Copper powder is loaded into a nitrogen-protected (99.99% purity) powder feeder. The nitrogen pressure is set to 2.0 MPa, the temperature to 500℃, and the powder feeding rate to 15 g / min. A robot drives the spray gun, maintaining a 90° angle between the spray gun and the substrate, a spraying distance of 30 mm, and a moving speed of 80 mm / s. The spraying is performed in 5 coats, with 1.5 min intervals between each coat. Each coat increases in thickness by 0.05 mm, resulting in a final coating thickness of 0.25 mm. The surface image of the copper-sprayed layer is shown below. Figure 1 As shown; S4. Vacuum Packaging: After the radiator is cooled to 28°C after cold spraying, it is placed in a vacuum packaging bag, vacuumed to 0.008MPa and then sealed. It is then stored in an environment with 25°C and 50% relative humidity. S5. Sampling Test: Randomly select 3 samples for wettability and bonding strength testing. Wettability test: Following IEC 60068-2-58:2017 Method 2 / IPC-TM-650 2.1.1 F 06 / 15, solder paste was printed on the copper plating layer (e.g., ...). Figure 2 As shown, the slice image is as follows Figure 3 (as shown) and after reflow soldering, the solder paste melts (as shown). Figure 4 As shown, the slice image is as follows Figure 5 (as shown) Bond strength test: The bond strength test was conducted based on DIN EN ISO 14916-2017. The sample had a copper plating layer in the middle. The bond strength was tested using a tensile testing machine. Before the bond strength test ( Figure 6 ) and the test samples after testing ( Figure 7 As shown in the figure.

[0050] Example 2

[0051] The difference between this embodiment and embodiment 1 is that the inert gas in S3 is helium (99.99%), the pressure is 2.2 MPa, the temperature is 450℃, the copper powder impact velocity is 700 m / s, and it is sprayed in 4 layers with a single layer thickness increase of 0.06 mm.

[0052] The remaining raw materials and preparation process are the same as in Example 1.

[0053] Example 3

[0054] The difference between this embodiment and embodiment 1 is that the copper powder particle size in S1 is 15-30μm, the powder feeding rate in S3 is 12g / min, and it is sprayed in 6 times with a single thickness increase of 0.04mm.

[0055] The remaining raw materials and preparation process are the same as in Example 1.

[0056] Example 4

[0057] The difference between this embodiment and Example 1 is that 3% silicon carbide powder (particle size 5μm) is added to the copper powder in S1, the temperature in S3 is 550℃, and the powder feeding rate is 16g / min.

[0058] The remaining raw materials and preparation process are the same as in Example 1.

[0059] Example 5

[0060] Compared with Example 1, the difference in this embodiment is that S3 uses two spray guns (with a layout angle of 45° and a spacing of 80mm) to work synchronously, with a moving speed of 100mm / s, and sprays in 3 coats, with a single coat thickness of 0.08mm.

[0061] The remaining raw materials and preparation process are the same as in Example 1.

[0062] Example 6

[0063] The difference between this embodiment and embodiment 1 is that in S3, the nitrogen temperature is 400℃, the pressure is 1.8MPa, the powder feeding rate is 10g / min, the coating is applied in 8 coats, and the thickness increase per coat is 0.03mm.

[0064] The remaining raw materials and preparation process are the same as in Example 1.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that it uses a traditional flame spraying process: oxygen-acetylene flame (temperature 2800℃), 99.5% pure irregular copper powder (particle size 40-60μm), 0.25mm per spray, no inert gas protection, and natural cooling after spraying.

[0067] The remaining raw materials and preparation process are the same as in Example 1.

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 1 lies in the traditional arc spraying process.

[0070] Process: Copper wire (99.5% purity, 1.6mm diameter), arc voltage 30V, current 180A, compressed air pressure 0.6MPa, single spray thickness 0.25mm, natural cooling after spraying. Specific implementation steps are as follows: The remaining raw materials and preparation process are the same as in Example 1.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 1 is that the copper powder in S1 has a purity of 99.5% (containing 0.5% impurities), while the other parameters are the same.

[0073] The remaining raw materials and preparation process are the same as in Example 1.

[0074] Comparative Example 4

[0075] The difference between this comparative example and Example 1 is that the S2 workpiece pretreatment was not performed, and cold spraying was performed directly, while the other parameters are the same.

[0076] The remaining raw materials and preparation process are the same as in Example 1.

[0077] Comparative Example 5

[0078] The difference between this comparative example and Example 1 is that the nitrogen temperature in S3 is 700°C, while the other parameters are the same.

[0079] The remaining raw materials and preparation process are the same as in Example 1.

[0080] Comparative Example 6

[0081] The difference between this comparative example and Example 1 is that S3 was sprayed 0.25mm in a single coat (without multiple coats), while the other parameters were the same.

[0082] The remaining raw materials and preparation process are the same as in Example 1.

[0083] Performance testing

[0084] The copper-plated layers prepared in Examples 1-6 and Comparative Examples 1-6 were subjected to performance tests. The specific test items are as follows: 1. Wettability test (wetting area (%) / contact angle (°)): The wetting area / contact angle of the copper sprayed layers obtained in various embodiments and comparative examples of the present invention were tested according to test method IEC60068-2-58:2017 Method 2 / IPC-TM-6502.1.1F06 / 15; 2. Bond strength test (MPa) (room temperature / 80℃): The bond strength test was conducted based on DIN EN ISO 14916-2017. The sample had a copper spray layer in the middle, and the bond strength was tested by a tensile tester. 3. Thermal conductivity of coating (W / (m·K)): The thermal conductivity of the copper sprayed layers obtained in various embodiments and comparative examples of the present invention was tested according to GB / T22588-2008; 4. Salt spray corrosion resistance time (h): The corrosion resistance time of the copper sprayed layers obtained in various embodiments and comparative examples of the present invention was tested according to GB / T10125-2021 (5% NaCl); 5. Smoke and dust emissions (mg / m³) 3 According to GB / T 16157-1996, the dust emission of the copper sprayed layers obtained in various embodiments and comparative examples of the present invention was tested. The results are shown in Table 1: Table 1

[0085] As shown in Table 1, Comparative Examples 1-2 (traditional thermal spraying) used high-temperature molten copper powder without inert gas protection. The copper powder oxidized to form CuO and Cu2O, leading to a sharp drop in thermal conductivity. The surface oxide layer hindered solder spread, resulting in poor wettability. The oxidation products reduced the coating's corrosion resistance. In Comparative Example 5, the excessively high temperature of the cold spraying process led to an increase in oxidation products, and in Comparative Example 3, the insufficient purity of the copper powder also exacerbated the oxidation problem.

[0086] The substrate in the embodiment exhibits no thermal deformation, and the coating surface has high smoothness (Ra≤1.0μm), providing a uniform surface for solder spreading. In contrast, the high temperatures in Comparative Examples 1-2 cause the aluminum alloy substrate to rise above 150°C, inducing grain growth and thermal deformation, resulting in an uneven coating surface and further deteriorating wettability (increased contact angle). Even if the cold spray process temperature is too high (Comparative Example 5), it will cause slight thermal damage to the substrate, indirectly affecting the bonding stability between the coating and the substrate.

[0087] The room temperature bond strength of Examples 1-6 was 45.2-68.5 MPa, and the high-temperature bond strength at 80℃ was 42.1-62.3 MPa; the room temperature bond strength of Comparative Examples 1-2 was ≤28.6 MPa; and the bond strength of Comparative Example 4 (without pretreatment) was only 15.3 MPa. This is because the coatings of Comparative Examples 1-2 were mostly mechanically bonded to the substrate, resulting in high internal stress and low adhesion. If the cold spray process lacks pretreatment (Comparative Example 4) or a single thick coating (Comparative Example 6), it will lead to insufficient interfacial bonding or stress concentration within the coating, which will also cause poor adhesion and easy peeling after long-term use.

[0088] Poor adhesion leads to tiny gaps at the coating-substrate interface, resulting in decreased wettability. Comparative Example 4 showed a wetted area of ​​88.5% and a contact angle of 28.3°, significantly worse than the Example. In contrast, the Example, through S2 roughening pretreatment, S3 rapid impact, and multi-coating, exhibited a gap-free interface, allowing for sufficient solder spread. Traditional thermal spraying (Comparative Examples 1-2) results in high coating porosity, easily absorbing moisture and corrosive media, leading to poor corrosion resistance. Simultaneously, the pores create thermal resistance, reducing thermal conductivity. Cold spraying, if parameters are inappropriate (single-coat thick layer, Comparative Example 6), can also increase porosity due to uneven particle accumulation, as evidenced by data on wettability, coating thermal conductivity, and salt spray corrosion resistance time.

[0089] The particulate matter emissions in Examples 1-6 are far below the national industrial emission standard (30 mg / m³). 3 The smoke and dust emissions of Comparative Examples 1 and 2 far exceeded those of the Example. This is because the high-temperature oxidation and powder melting of traditional thermal spraying are the main sources of smoke and dust, while the low-temperature solid deposition of cold spraying produces almost no smoke and dust.

[0090] Compared to Example 1, Example 2 shows a decrease in copper powder purity, resulting in a corresponding decrease in bonding strength, thermal conductivity, and wettability. This is because impurities disrupt coating continuity, reducing interfacial bonding and thermal conductivity. Compared to Example 1, Comparative Example 4 shows a sharp drop in bonding strength and a significant reduction in wettability after eliminating pretreatment. This is because a rough surface is the basis for mechanical interlocking, and the lack of pretreatment prevents effective interfacial bonding. Replacing five spray coats with a single thick coat significantly reduces bonding strength, and the change in salt spray time also reflects a decrease in corrosion resistance. This fully demonstrates that, compared to Example 6, multi-coating can release internal stress and avoid porosity and cracking.

[0091] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A cold copper spraying process for the surface of an aluminum alloy heat sink, characterized in that, Includes the following steps: S1. Selection of copper powder: Select spherical pure copper powder with a purity of ≥99.9% and a particle size of 15-45μm; S2. Pre-treatment of workpiece: Roughen the surface of the aluminum alloy radiator to be sprayed to make the surface roughness Ra=0.3-0.6μm, then clean it with ethanol and dry it. S3, Cold Spray Copper: Copper powder is placed in a powder feeder protected by inert gas. The copper powder is transported to the spray gun by high-pressure inert working gas. The working gas heated to 400-600℃ drives the copper powder to impact the aluminum alloy surface at a speed of 300-800m / s. The copper coating is formed by spraying in 3-8 times. The coating thickness increases by 0.03-0.06mm after each spray. S4. Vacuum Packaging: The radiator is vacuum-sealed after cooling following cold spraying. S5. Sampling test: Perform wettability test and bonding strength test on the sample.

2. The cold copper spraying process for the surface of an aluminum alloy heat sink according to claim 1, characterized in that, The spherical pure copper powder described in S1 has a flowability ≥15s / 50g and a bulk density ≥4.5g / cm³. 3 .

3. The cold copper spraying process for the surface of an aluminum alloy heat sink according to claim 1, characterized in that, The roughening process described in S2 is either mechanical polishing or laser cleaning; the mechanical polishing uses 200-400 grit alumina sandpaper, and the laser cleaning has a power of 100-200W and a scanning speed of 50-100mm / s.

4. The cold copper spraying process for the surface of the aluminum alloy heat sink according to claim 1, characterized in that, The inert gas mentioned in S3 is nitrogen or helium with a purity ≥99.99%; the pressure of the high-pressure inert working gas is 1.8-2.5 MPa.

5. The cold copper spraying process for the surface of an aluminum alloy heat sink according to claim 4, characterized in that, When the inert gas is helium, the temperature of the working gas can be reduced to 350-500℃, and the impact velocity of the copper powder can be increased to 600-800m / s.

6. The cold copper spraying process for the surface of an aluminum alloy heat sink according to claim 1, characterized in that, The cold-sprayed copper coating described in S3 is achieved by moving the spray gun via a CNC worktable or robot. The angle between the spray gun and the aluminum alloy surface is 90°±5°, the spraying distance is 20-40mm, the moving speed is 50-100mm / s, and the powder feeding rate is 10-20g / min. The interval between two adjacent sprays in S3 is 1-2min, and the final copper coating thickness is 0.1-0.5mm.

7. The cold copper spraying process for the surface of an aluminum alloy heat sink according to claim 1, characterized in that, In S3, functional powder can be added to pure copper powder. The functional powder is silicon carbide powder, and the amount added is 1% to 5% of the mass of pure copper powder.

8. The cold copper spraying process for the surface of an aluminum alloy heat sink according to claim 1, characterized in that, In the S3, multiple spray guns can work simultaneously, with the layout angle of the multiple spray guns being 30-60° and the spacing between adjacent spray guns being 50-100mm.

9. The cold copper spraying process for the surface of an aluminum alloy heat sink according to claim 1, characterized in that, The vacuum degree of the vacuum packaging described in S4 is ≤0.01MPa, and the temperature of the storage environment after packaging is 20-30℃, and the relative humidity is ≤60%; the wettability test described in S5 is based on IEC60068-2-58:2017 and IPC-TM-6502.1.1F06 / 15 standards, requiring a wetted area ≥95% and a contact angle <20°; the bonding strength test is based on DINENISO14916-2017 standards, requiring a bonding strength of ≥50MPa at room temperature and ≥45MPa at 80℃.

10. An aluminum alloy heat sink, characterized in that, The product comprises an aluminum alloy substrate and a copper coating; the copper coating is prepared on the surface of the aluminum alloy substrate using the cold spray copper process described in any one of claims 1-9, wherein the purity of the copper coating is ≥99% and the porosity is <3%; the aluminum alloy substrate is made of 6061 or 6063 aluminum alloy, and the thermal conductivity of the copper coating is ≥380 W / (m²). K), surface roughness Ra≤1.0μm.

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