Aluminum radiator inner cavity surface protective film and preparation method thereof

Abstract

The invention provides an aluminum radiator inner cavity surface protective film and a preparation method thereof, and belongs to the technical field of metal surface protection. A preparation method of a protective film on the surface of an inner cavity of an aluminum radiator comprises the steps that the aluminum radiator serves as a working electrode, two graphite electrodes serve as counter electrodes, an Ag / AgCl electrode serves as a reference electrode, the working electrode and the counter electrodes are soaked in electrolyte, electrochemical treatment is conducted through cyclic voltammetry, and the protective film on the surface of the inner cavity of the aluminum radiator is obtained. And an aluminum fluoride-aluminum oxide composite film is formed on the surface of the inner cavity of the aluminum radiator. A protective film with high corrosion resistance is generated through a cyclic voltammetry method, and the corrosion rate of aluminum is remarkably reduced.

Description

Technical Field

[0001] This invention belongs to the field of metal surface protection technology, specifically relating to a protective film on the inner surface of an aluminum radiator and its preparation method. Background Technology

[0002] In the circulating cooling system of converter valves in high-voltage direct current transmission projects, the inner cavity of aluminum radiators is prone to corrosion, forming aluminum ions. These aluminum ions scale on the platinum equalizing electrodes, causing a decrease in the electrodes' average voltage capability, which in turn leads to the tripping and shutdown of the converter valve system.

[0003] The alumina that spontaneously forms on the inner surface of aluminum radiators cannot resist oxidation under the harsh environment of multiple coupled physical fields, including high electric field, high magnetic field, high temperature field (approximately 50°C), and high water flow velocity field. Therefore, improving the oxidation resistance of the aluminum surface in the converter valve cooling system can solve the problem of aluminum corrosion.

[0004] To improve the corrosion resistance of the inner cavity of aluminum radiators, some studies have reported the following methods: 1) Adjust the composition of the cooling water to inhibit aluminum dissolution, such as by adding corrosion inhibitors (Chemistry - An Asian Journal, 2025, e00818; New Journal of Chemistry, 2023, 47, 17645; International Journal of Electrochemical Science, 2023, 18, 100050; Materials and Corrosion, 2021, 72, 12, 1899; Materials, 2020, 13, 779). 2) Surface treatment of the inner cavity of aluminum radiators, such as: Chinese patent document CN106567075B discloses a method for surface treatment of the inner cavity of an aluminum radiator in a valve internal cooling system for high voltage DC transmission. The inner cavity of the aluminum radiator is provided with an anti-corrosion film, which is a metal film. This can effectively reduce the contact between aluminum and internal cooling water, reduce the problem of internal corrosion of the radiator, and thus mitigate the destructive impact of scale formation on the valve cooling system on the equalizing electrode, thereby improving the reliability of DC transmission.

[0005] Compared to the above two methods, the method of surface treatment in the inner cavity of aluminum radiators is more effective. However, regarding the technical solution disclosed in CN106567075B, this method still has some obvious problems: (1) The standard electrode potential of the metal film (such as Cu, Ag, Au) is significantly higher than that of the aluminum substrate. Once the film layer has pinholes, scratches or local damage, the exposed aluminum and the covered precious metal will form a corrosion cell in the coolant (electrolyte). Aluminum as the anode will be accelerated to corrode, resulting in pitting and perforation, and its corrosion rate is much higher than that of bare aluminum without coating; (2) This technology is used in the valve internal cooling system of high voltage DC transmission. Covering the inner cavity of the radiator with a continuous conductive metal film may change the local electric field distribution and bring uncertain electrical safety risks; (3) The overall process is complicated and the processing flow is lengthy; (4) The use of highly toxic chemical raw materials, such as cyanide (KCN, AgCN), poses a potential threat to production safety, wastewater treatment and operator health, and the environmental compliance cost is extremely high.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing a protective film on the inner surface of an aluminum radiator in a converter valve circulating cooling system for high voltage direct current transmission projects, which is in response to the shortcomings of the prior art. The method generates a protective film with corrosion resistance through cyclic voltammetry, which significantly reduces the corrosion tendency of aluminum.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing a protective film on the inner surface of an aluminum radiator, comprising: using the aluminum radiator as the working electrode, two graphite electrodes as the counter electrode and an Ag / AgCl electrode as the reference electrode, immersing both the working electrode and the counter electrode in an electrolyte, and performing electrochemical treatment by cyclic voltammetry to form an aluminum fluoride-alumina composite film on the inner surface of the aluminum radiator.

[0009] Optionally, the electrolyte composition includes: 5 g / L to 40 g / L potassium fluoride, 55 g / L to 95 g / L potassium hydrofluoride, 2 g / L to 8 g / L potassium ferricyanide, 0.001 g / L to 0.01 g / L hydrogen fluoride solution, pH 3 to 5, and temperature 35°C to 45°C.

[0010] Optionally, the flow rate of the electrolyte in the inner cavity of the aluminum heat sink is 0.1L / h to 1L / h.

[0011] Optionally, the process parameters of the cyclic voltammetry method include: controlling the potential range relative to the reference electrode to be -0.5V to 0.4V, the scan rate to be 0.05V / s to 0.5V / s, and the number of cycles to be 10.

[0012] This invention utilizes cyclic voltammetry to periodically control the potential, alternately promoting the formation of aluminum fluoride and the deposition of alumina in the same electrolyte. After 10 cycles, these two components do not simply stack up, but rather intertwine and composite in situ at the nanoscale, forming a dense, well-bonded AlF3 / Al2O3 composite film with a gradient composition. Potassium ferricyanide in the electrolyte simultaneously functions as an oxidant, a local pH regulator, and a film structure modifier, providing crucial conditions for achieving one-step in-situ composite formation.

[0013] Optionally, the preparation method further includes: pre-treating the aluminum heat sink, the pre-treatment including: Soak the aluminum radiator in an alkaline solution for several minutes to remove oil stains from the aluminum surface, as well as the natural oxide film and minor scratches. Rinse the aluminum radiator with running deionized water until the pH of the cleaning water is neutral. Immerse the aluminum radiator in acid for a few seconds to neutralize the residual alkali and remove the ash, thus obtaining a new activated surface; Rinse the aluminum radiator again with running deionized water.

[0014] Optionally, the alkaline solution is a sodium hydroxide solution of 10 g / L to 35 g / L, and the soaking time is 2 to 5 minutes.

[0015] Optionally, the acid solution is 0.3 g / L to 0.7 g / L nitric acid, and the soaking time is 12 s to 18 s.

[0016] Optionally, the preparation method further includes: post-processing the aluminum heat sink, the post-processing including: Rinse the aluminum radiator with running deionized water to remove residual electrolyte until the pH of the cleaning water is neutral. Dry the aluminum radiator with clean compressed air.

[0017] The present invention also provides a protective film prepared according to the above-mentioned method for preparing a protective film on the inner surface of an aluminum radiator cavity, wherein the protective film is a composite film of aluminum fluoride and aluminum oxide, and the overall thickness of the protective film is 0.1 μm to 7 μm, wherein the thickness of the aluminum fluoride layer is approximately 0.003 μm to 0.006 μm.

[0018] The composite film of aluminum fluoride and aluminum oxide formed by the present invention is not a physical stacked structure with clear boundaries, but a gradient composite structure formed by aluminum fluoride and aluminum oxide interweaving and chemically bonding at the nanoscale, with extremely strong bonding force.

[0019] The present invention also provides an aluminum heat sink, wherein the above-mentioned protective film is provided on the inner cavity surface.

[0020] The present invention also provides the application of the above-mentioned aluminum heat sink in the circulating cooling system of converter valve in high voltage direct current transmission projects.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method for preparing a protective film on the inner surface of an aluminum radiator based on the above-mentioned technical solution. An aluminum fluoride-alumina composite film is formed on the inner surface of the aluminum radiator using a cyclic voltammetry method to mitigate aluminum corrosion. This method solves a series of technical problems associated with existing technologies, such as the risk of galvanic corrosion, complex processes, and poor environmental performance. Aluminum fluoride exhibits higher chemical and electrochemical stability than alumina, and its molecules are tightly packed (pore size <0.4 nm), effectively isolating corrosive media.

[0022] This invention utilizes electrochemical and chemical methods to further form a dense aluminum fluoride-alumina composite film on the original alumina surface of aluminum materials. This composite film combines the density of alumina with the electrochemical and chemical stability of aluminum fluoride, remaining stable at pH values ​​from 1 to 10, and significantly reducing the corrosion rate of aluminum parts. Attached Figure Description

[0023] 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.

[0024] Figure 1 : Microscopic morphology of the protective film on the inner cavity surface of the aluminum heat sink of the present invention. Detailed Implementation

[0025] To better understand the present invention, the following embodiments further illustrate the content of the invention, but the scope of protection of the present invention is not limited to the following embodiments. Numerous specific details are set forth in the following description to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the present invention can be practiced without one or more of these details.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0027] When a numerical range is disclosed in this invention, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Further, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Moreover, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed in this invention should be understood to include any and all subranges to which they are incorporated.

[0028] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0029] Unless otherwise specified, all raw materials are derived from commercially available products and do not contain any unspecified components other than unavoidable impurities.

[0030] In the following case, the aluminum heat sink measures 20cm long × 20cm wide × 4cm thick, with an inner cavity diameter of 2cm. The graphite electrodes, measuring 25cm long × 25cm wide × 0.5cm thick, are placed on either side of the working electrode. The total electrolyte volume is 20L, and the electrolyte temperature and pH are monitored in real time.

[0031] Example 1 A method for preparing a protective film on the inner surface of an aluminum radiator, comprising: (1) Pre-treatment of aluminum radiators, including: Immerse the aluminum radiator in a 10g / L sodium hydroxide solution for 5 minutes to remove oil stains from the aluminum surface, as well as the natural oxide film and minor scratches. Rinse the aluminum radiator with running deionized water until the pH of the cleaning water is neutral. The aluminum radiator was immersed in 0.7 g / L nitric acid for 15 seconds to neutralize the residual alkali and remove the ash, thus obtaining a new activated surface. Rinse the aluminum radiator again with running deionized water. (2) Electrochemical treatment process, including: Using an aluminum heat sink as the working electrode, two graphite electrodes as the counter electrode, and an Ag / AgCl electrode as the reference electrode, both the working and counter electrodes were immersed in an electrolyte. Electrochemical treatment was performed using cyclic voltammetry to form an aluminum fluoride-alumina composite film on the inner surface of the aluminum heat sink. The electrolyte composition includes: 5 g / L potassium fluoride, 55 g / L potassium hydrofluoride, 8 g / L potassium ferricyanide, 0.01 g / L hydrogen fluoride solution, pH 5, and temperature 45°C; The flow rate of the electrolyte in the inner cavity of the aluminum heat sink is 1 L / h; The process parameters for cyclic voltammetry include: a control potential range of -0.5V to 0.4V relative to the reference electrode, a scan rate of 0.5V / s, and 10 cycles. (3) Post-processing of aluminum radiators, including: Rinse the aluminum radiator with running deionized water to remove residual electrolyte until the pH of the cleaning water is neutral. Dry the aluminum radiator with clean compressed air.

[0032] The protective film prepared according to the above-mentioned method for preparing the protective film on the inner surface of the aluminum radiator cavity is a composite film of aluminum fluoride and aluminum oxide. The overall thickness of the protective film is 0.1 μm, of which the thickness of the aluminum fluoride layer is 0.004 μm.

[0033] Figure 1 The composite film formed by this invention is thin and dense, and is not a simple physical stack, but a gradient composite structure in which aluminum fluoride and aluminum oxide are interwoven and chemically bonded at the nanoscale. The film is thin overall (about 0.1-1 μm), highly dense and defect-free, and can provide excellent barrier function.

[0034] Example 2 A method for preparing a protective film on the inner surface of an aluminum radiator, which differs from Example 1 in that: The aluminum radiator was immersed in a 25g / L sodium hydroxide solution for 4 minutes; The aluminum radiator was immersed in 0.4 g / L nitric acid for 15 seconds; Electrolyte composition: 25 g / L potassium fluoride, 58 g / L potassium hydrofluoride, 6 g / L potassium ferricyanide, 0.004 g / L hydrogen fluoride solution, pH 3, temperature 42°C; The flow rate of the electrolyte in the inner cavity of the aluminum heat sink is 0.9 L / h; Cyclic voltammetry process: scan rate of 0.35 V / s; The composite film thickness on the inner surface of the aluminum radiator is 6μm, of which the aluminum fluoride layer is 0.004μm thick.

[0035] Example 3 A method for preparing a protective film on the inner surface of an aluminum radiator, which differs from Example 1 in that: The aluminum radiator was immersed in a 18g / L sodium hydroxide solution for 2 minutes.

[0036] The aluminum radiator was immersed in 0.5 g / L nitric acid for 15 seconds.

[0037] Electrolyte composition: 40 g / L potassium fluoride, 57 g / L potassium hydrofluoride, 3 g / L potassium ferricyanide, 0.002 g / L hydrogen fluoride solution, pH 4, temperature 37°C.

[0038] The electrolyte flow rate inside the aluminum radiator is 0.7 L / h.

[0039] Cyclic voltammetry process: scan rate of 0.27 V / s.

[0040] The composite film thickness on the inner surface of the aluminum radiator is 3μm, of which the aluminum fluoride layer is 0.005μm thick.

[0041] Example 4 A method for preparing a protective film on the inner surface of an aluminum radiator, which differs from Example 1 in that: The aluminum radiator was immersed in a 29g / L sodium hydroxide solution for 3 minutes; The aluminum radiator was immersed in 0.6 g / L nitric acid for 15 seconds; Electrolyte composition: 28 g / L potassium fluoride, 76 g / L potassium hydrofluoride, 5 g / L potassium ferricyanide, 0.002 g / L hydrogen fluoride solution, pH 3, temperature 42°C; The flow rate of the electrolyte in the inner cavity of the aluminum heat sink is 0.6 L / h; Cyclic voltammetry process: scan rate is 0.33V / s.

[0042] The composite film thickness on the inner surface of the aluminum radiator is 5.3 μm, of which the aluminum fluoride layer thickness is 0.006 μm.

[0043] Example 5 A method for preparing a protective film on the inner surface of an aluminum radiator, which differs from Example 1 in that: The aluminum radiator was soaked in a 13g / L sodium hydroxide solution for 5 minutes; The aluminum radiator was immersed in 0.3 g / L nitric acid for 15 seconds; Electrolyte composition: 8 g / L potassium fluoride, 86 g / L potassium hydrofluoride, 6 g / L potassium ferricyanide, 0.007 g / L hydrogen fluoride solution, pH 4, temperature 37°C; The flow rate of the electrolyte in the inner cavity of the aluminum heat sink is 0.3 L / h; Cyclic voltammetry process: scan rate of 0.4 V / s.

[0044] The thickness of the composite film on the inner surface of the aluminum radiator is 0.9 μm, of which the aluminum fluoride layer is 0.003 μm thick.

[0045] Example 6 A method for preparing a protective film on the inner surface of an aluminum radiator, which differs from Example 1 in that: The aluminum radiator was immersed in a 28g / L sodium hydroxide solution for 5 minutes; The aluminum radiator was immersed in 0.6 g / L nitric acid for 15 seconds; Electrolyte composition: 38 g / L potassium fluoride, 64 g / L potassium hydrofluoride, 5 g / L potassium ferricyanide, 0.007 g / L hydrogen fluoride solution, pH 5, temperature 38°C; The flow rate of the electrolyte in the inner cavity of the aluminum heat sink is 0.8 L / h; Cyclic voltammetry process: scan rate is 0.08V / s.

[0046] The thickness of the composite film on the inner surface of the aluminum radiator is 6μm, of which the thickness of the aluminum fluoride layer is 0.006μm.

[0047] Example 7 A method for preparing a protective film on the inner surface of an aluminum radiator, which differs from Example 1 in that: The aluminum radiator was soaked in a 31g / L sodium hydroxide solution for 5 minutes; The aluminum radiator was immersed in 0.6 g / L nitric acid for 15 seconds; Electrolyte composition: 22 g / L potassium fluoride, 74 g / L potassium hydrofluoride, 4 g / L potassium ferricyanide, 0.003 g / L hydrogen fluoride solution, pH 3.5, temperature 39°C; The flow rate of the electrolyte in the inner cavity of the aluminum heat sink is 0.7 L / h; Cyclic voltammetry process: scan rate of 0.3 V / s; The thickness of the composite film on the inner surface of the aluminum radiator is 3μm, of which the thickness of the aluminum fluoride layer is 0.003μm.

[0048] Example 8 A method for preparing a protective film on the inner surface of an aluminum radiator, which differs from Example 1 in that: The aluminum radiator was immersed in a 23g / L sodium hydroxide solution for 2 minutes; The aluminum radiator was immersed in 0.7 g / L nitric acid for 15 seconds; Electrolyte composition: 38 g / L potassium fluoride, 66 g / L potassium hydrofluoride, 3 g / L potassium ferricyanide, 0.002 g / L hydrogen fluoride solution, pH 3, temperature 36°C; The flow rate of the electrolyte in the inner cavity of the aluminum heat sink is 0.9 L / h; Cyclic voltammetry process: scan rate is 0.09 V / s.

[0049] The thickness of the composite film on the inner surface of the aluminum radiator is 0.1 μm, of which the thickness of the aluminum fluoride layer is 0.003 μm.

[0050] Example 9 A method for preparing a protective film on the inner surface of an aluminum radiator, which differs from Example 1 in that: The aluminum radiator was soaked in a 13g / L sodium hydroxide solution for 5 minutes; The aluminum radiator was immersed in 0.4 g / L nitric acid for 15 seconds; Electrolyte composition: 7 g / L potassium fluoride, 92 g / L potassium hydrofluoride, 8 g / L potassium ferricyanide, 0.001 g / L hydrogen fluoride solution, pH 5, temperature 45°C; The flow rate of the electrolyte in the inner cavity of the aluminum heat sink is 1 L / h; Cyclic voltammetry process: scan rate is 0.05V / s.

[0051] The thickness of the composite film on the inner surface of the aluminum radiator is 0.7μm, of which the thickness of the aluminum fluoride layer is 0.006μm.

[0052] Example 10 A method for preparing a protective film on the inner surface of an aluminum radiator, which differs from Example 1 in that: The aluminum radiator was immersed in a 16g / L sodium hydroxide solution for 3 minutes; The aluminum radiator was immersed in 0.6 g / L nitric acid for 15 seconds; Electrolyte composition: 5 g / L potassium fluoride, 95 g / L potassium hydrofluoride, 2 g / L potassium ferricyanide, 0.001 g / L hydrogen fluoride solution, pH 3, temperature 35°C; The flow rate of the electrolyte in the inner cavity of the aluminum heat sink is 0.1 L / h; Cyclic voltammetry process: scan rate is 0.08V / s.

[0053] The composite film thickness on the inner surface of the aluminum radiator is 5μm, of which the aluminum fluoride layer is 0.004μm thick.

[0054] Comparative Example 1 A method for preparing a protective film on the inner surface of an aluminum radiator, which differs from Example 1 in that step "(2) electrochemical treatment process" is omitted.

[0055] Comparative Example 2 A method for preparing a protective film on the inner surface of an aluminum radiator, differing from Example 1 only in that the electrolyte composition does not contain potassium ferricyanide.

[0056] Next, the content of the evaluation test will be explained.

[0057] Generally, in the same corrosion system, the more positive the corrosion potential, the less likely the material is to lose electrons, the lower the tendency to undergo anodic dissolution, and the less likely corrosion will occur; the more negative the corrosion potential, the greater the tendency to lose electrons, the higher the tendency to undergo anodic dissolution, and the easier corrosion will occur.

[0058] The protective films on the inner cavity surface of the aluminum radiators prepared in Examples 1-10 and Comparative Examples 1-2 were tested as samples.

[0059] The steady-state polarization curve testing conditions were as follows: the test temperature was 50 °C, the electrolyte was deionized water, the reference electrode was a saturated calomel electrode, and the auxiliary electrode was a platinum black electrode. The potential scan rate was 0.1 mV / s, and the potential scan range was open-circuit voltage ± 1.5 V. The corrosion potential and corrosion current density of the sample were measured. The results are shown in Table 1.

[0060] Table 1 Test Results

[0061] Table 1 shows that, compared with Comparative Example 1, in the same corrosion system, Examples 1-10 of the present invention all showed a significant positive shift in corrosion potential and a significant decrease in corrosion current density. This indicates that the aluminum fluoride-alumina composite film formed on the inner surface of the aluminum radiator by the present invention can significantly reduce the corrosion tendency of the aluminum radiator and exhibit significant corrosion resistance.

[0062] Comparative Example 2 changed the electrolyte composition, omitting only potassium ferricyanide. Although the corrosion potential shifted positively and the corrosion current density decreased compared to Comparative Example 1, the change was significantly smaller than that in Example 1. This indicates that potassium ferricyanide is not an optional additive in the specific electrolyte system of the present invention, but a key component that participates in electrochemical reactions and regulates the membrane structure. Without potassium ferricyanide, the composite membrane with the expected effect cannot be formed.

[0063] In summary, this invention forms an aluminum fluoride-alumina composite film on the surface of aluminum parts through a unique cyclic voltammetry process. As an organic whole, this composite film significantly reduces the corrosion tendency of aluminum parts and significantly improves their corrosion resistance.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a protective film on the inner surface of an aluminum radiator, characterized in that: include: Using the aluminum radiator as the working electrode, two graphite electrodes as the counter electrode, and an Ag / AgCl electrode as the reference electrode, the working electrode and the counter electrode are both immersed in the electrolyte, and electrochemical treatment is performed by cyclic voltammetry to form an aluminum fluoride-alumina composite film on the inner surface of the aluminum radiator.

2. The method for preparing a protective film on the inner surface of an aluminum radiator as described in claim 1, characterized in that: The electrolyte composition includes: 5 g / L~40 g / L potassium fluoride, 55 g / L~95 g / L potassium hydrofluoride, 2 g / L~8 g / L potassium ferricyanide, 0.001 g / L~0.01 g / L hydrogen fluoride solution, pH 3~5, and temperature 35°C~45°C.

3. The method for preparing a protective film on the inner surface of an aluminum radiator as described in claim 2, characterized in that: The flow rate of the electrolyte in the inner cavity of the aluminum heat sink is 0.1L / h to 1L / h.

4. The method for preparing a protective film on the inner surface of an aluminum radiator as described in claim 3, characterized in that: The process parameters of the cyclic voltammetry method include: a control potential range of -0.5V to 0.4V relative to the reference electrode, a scan rate of 0.05V / s to 0.5V / s, and 10 cycles.

5. The method for preparing a protective film on the inner surface of an aluminum radiator as described in claim 1, characterized in that: Also includes: The aluminum heat sink undergoes a pretreatment process, which includes: Soak the aluminum radiator in an alkaline solution for several minutes to remove oil stains from the aluminum surface, as well as the natural oxide film and minor scratches. Rinse the aluminum radiator with running deionized water until the pH of the cleaning water is neutral. Immerse the aluminum radiator in acid for a few seconds to neutralize the residual alkali and remove the ash, thus obtaining a new activated surface; Rinse the aluminum radiator again with running deionized water.

6. A method for preparing a protective film on the inner surface of an aluminum radiator as described in claim 5, characterized in that: The alkaline solution is a sodium hydroxide solution with a concentration of 10 g / L to 35 g / L, and the soaking time is 2 to 5 minutes.

7. A method for preparing a protective film on the inner surface of an aluminum radiator as described in claim 5, characterized in that: The acid solution is 0.3 g / L to 0.7 g / L nitric acid, and the soaking time is 12s to 18s.

8. The method for preparing a protective film on the inner surface of an aluminum radiator as described in claim 1, characterized in that: Also includes: The aluminum radiator undergoes post-processing, which includes: Rinse the aluminum radiator with running deionized water to remove residual electrolyte until the pH of the cleaning water is neutral. Dry the aluminum radiator with clean compressed air.

9. The protective film prepared by the method of preparing a protective film on the inner surface of an aluminum radiator according to any one of claims 1 to 8, wherein the protective film is a composite film of aluminum fluoride and aluminum oxide, and the overall thickness of the protective film is 0.1 μm to 7 μm, wherein the thickness of the aluminum fluoride layer is 0.003 μm to 0.006 μm.

10. An aluminum heat sink, characterized in that: Its inner cavity surface is provided with the protective film as described in claim 9.

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