A corrosion-resistant aluminum-based multilayer coating for the surface of a sintered neodymium-iron-boron magnet and a method for producing the same

Abstract

This invention discloses a corrosion-resistant aluminum-based multilayer coating on the surface of a sintered NdFeB magnet and its preparation method, comprising: pretreatment of the magnet; preparation of the aluminum coating: in the presence of an inert gas, after adjusting the pressure of the environment to a first preset value, depositing an aluminum coating on the pretreated sintered NdFeB magnet; preparation of the aluminum-based barrier coating: in the presence of a reactive gas, after adjusting the pressure of the environment to a second preset value, exciting the reactive gas into a high-density plasma, generating an aluminum-based barrier layer on the surface of the sintered NdFeB magnet with the deposited aluminum coating; repeating steps S200 and S300, followed by cooling, to complete the preparation of the corrosion-resistant aluminum-based multilayer coating on the surface of the sintered NdFeB magnet. This invention does not involve reactive sputtering, effectively avoiding the "palladium poisoning" phenomenon during the deposition process, and the prepared multilayer coating has excellent corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of vacuum coating technology, specifically to a corrosion-resistant aluminum-based multilayer coating on the surface of a sintered NdFeB magnet and its preparation method. Background Technology

[0002] Neodymium iron boron (NdFeB) rare-earth permanent magnets possess extremely high magnetic energy product, coercivity, and energy density, leading to their widespread application in modern industry and electronics. This has enabled the miniaturization, weight reduction, and thinning of instruments, electroacoustic motors, and magnetic separation and magnetization equipment. However, NdFeB rare-earth permanent magnets have a multiphase structure and contain highly chemically reactive Nd, making them highly susceptible to corrosion during use. Magnetron sputtering, as a green coating technology, can be applied to the surface treatment of NdFeB rare-earth permanent magnets to improve their corrosion resistance and fundamentally solve the pollution problem caused by the discharge of acidic and alkaline wastewater from electroplating. However, traditional magnetron sputtering technology suffers from low target atom ionization rates, resulting in coatings that often grow with a columnar crystal structure and grain boundaries perpendicular to the surface. These grain boundaries become rapid channels for corrosive liquids, accelerating the failure of the coating's protective performance. Al / Al₂O₃ multilayer coatings can be prepared by alternating deposition of aluminum (Al) coatings and amorphous coatings. The addition of amorphous Al₂O₃ can interrupt the growth of columnar crystals in the Al coating and block the penetrating flow of corrosive liquid, significantly improving the coating's corrosion resistance. However, Al₂O₃ coatings have high insulation properties, and the "target poisoning" phenomenon is particularly severe during deposition, resulting in slow deposition efficiency and making them unsuitable for industrial production. Therefore, there is an urgent need for a corrosion-resistant aluminum-based multilayer coating suitable for the surface protection of NdFeB magnets. Summary of the Invention

[0003] Therefore, embodiments of the present invention provide a corrosion-resistant aluminum-based multilayer coating on the surface of a sintered NdFeB magnet and its preparation method. First, an aluminum coating is deposited on the surface of the NdFeB magnet, and then a nano-amorphous barrier coating is further generated on the surface of the aluminum coating using plasma surface modification technology, thereby forming an aluminum-based multilayer coating. Moreover, the above method does not involve reactive sputtering, effectively avoiding the phenomenon of "palladium poisoning" during the deposition process.

[0004] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0005] In one aspect of this invention, a method for preparing a corrosion-resistant aluminum-based multilayer coating on the surface of a sintered NdFeB magnet is provided, comprising:

[0006] S100. Pretreatment of magnets: The sintered NdFeB magnets are polished, cleaned and dried in sequence to complete the pretreatment of the sintered NdFeB magnets.

[0007] S200, Preparation of aluminum coating: In the presence of inert gas, after adjusting the pressure in the environment to the first preset value, an aluminum coating is deposited on the sintered NdFeB magnet pretreated in step S100.

[0008] S300, Preparation of aluminum-based barrier coating: In the presence of reactive gas, after adjusting the pressure in the environment to the second preset value, the reactive gas is excited into high-density plasma, and an aluminum-based barrier layer is generated on the surface of the sintered NdFeB magnet with aluminum coating deposited in step S200.

[0009] After repeating steps S200 and S300, the magnet is cooled to complete the preparation of a corrosion-resistant aluminum-based multilayer coating on the surface of the sintered NdFeB magnet.

[0010] In a preferred embodiment of the present invention, step S100 further includes plasma cleaning of the sintered NdFeB magnet after drying; and the plasma cleaning specifically includes:

[0011] Vacuum degree not greater than 10 -2 In an environment of Pa, an inert gas is introduced into the environment to adjust the pressure to the third preset value, and the bias power supply is adjusted to the preset parameters to complete the plasma cleaning of the sintered NdFeB magnet.

[0012] In a preferred embodiment of the present invention, the inert gas used in the plasma cleaning process is selected from argon.

[0013] The third preset value is 1-3 Pa;

[0014] The preset parameters of the bias power supply are: voltage value of 500-900V, duty cycle of 40-90%, and plasma cleaning processing time of 5-20min.

[0015] In a preferred embodiment of the present invention, in step S200, the inert gas is selected from argon;

[0016] The first preset value is 0.3-0.8 Pa.

[0017] As a preferred embodiment of the present invention, the aluminum coating is deposited by physical vapor deposition.

[0018] As a preferred embodiment of the present invention, the physical vapor deposition specifically includes: magnetron sputtering of an aluminum target while applying a negative bias voltage to a sintered NdFeB magnet to complete the deposition of an aluminum coating on the surface of the sintered NdFeB magnet.

[0019] As a preferred embodiment of the present invention, the operating parameters of the magnetron sputtering power supply used for magnetron sputtering in the physical vapor deposition process are: current value of 1A-20A, duty cycle of 20%-90%, and frequency of 20kHz-150kHz.

[0020] The operating parameters of the bias power supply used to apply negative bias voltage to sintered NdFeB magnets are: voltage value 0V-300V, duty cycle 20%-90%, and frequency 20kHz-150kHz.

[0021] As a preferred embodiment of the present invention, the deposition time for physical vapor deposition is 10 minutes.

[0022] In a preferred embodiment of the present invention, in step S300, the reaction gas is selected from one or more of oxygen, nitrogen and acetylene, and oxygen and acetylene do not exist simultaneously.

[0023] As a preferred embodiment of the present invention, the reactive gas is excited into a high-density plasma by means of ion source excitation and / or by self-biasing.

[0024] As a preferred embodiment of the present invention, when using an ion source for excitation, the second preset value is 0.4-1 Pa, and the operating parameters of the ion source power supply are: power of 0.2-2 kW, frequency of 20-80 kHz, duty cycle of 20-80%, and excitation time of 2-10 min.

[0025] When using self-biased excitation, the second preset value is 1-3 Pa, and the operating parameters of the bias power supply are: voltage value of 500-900V, duty cycle of 40-90%, and excitation time of 5-20min.

[0026] As a preferred embodiment of the present invention, repeating steps S200 and S300 is recorded as one cycle, and in step S400, the number of cycles is not less than 5.

[0027] In another aspect of the present invention, a corrosion-resistant aluminum-based multilayer coating for the surface of a sintered NdFeB magnet is also provided, which is prepared by the preparation method described above.

[0028] The embodiments of the present invention have the following advantages:

[0029] This invention innovatively achieves the preparation of corrosion-resistant aluminum-based multilayer coatings through plasma surface modification technology. It proposes using an ion source or self-biasing to excite the reactive gas into a high-density plasma, utilizing the high reactivity of the plasma to react with the Al coating to achieve in-situ growth of nanoscale-thickness amorphous compound coatings. This process does not involve reactive sputtering, completely avoiding the slow deposition efficiency caused by "target poisoning" during deposition, thus meeting the requirements of industrial production. Attached Figure Description

[0030] To more clearly illustrate the embodiments of the present invention or the technical solutions in 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 merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0031] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0032] Figure 1 This is a schematic diagram of the structure of a sintered NdFeB magnet with a corrosion-resistant aluminum-based multilayer coating obtained in an embodiment of the present invention.

[0033] Figure 2 Here is an electron microscope image of the aluminum coating obtained in an embodiment of the present invention;

[0034] Figure 3 This is an electron microscope image of the aluminum-based barrier coating obtained in an embodiment of the present invention.

[0035] In the picture:

[0036] 1-Aluminum coating; 2-Aluminum-based barrier coating. Detailed Implementation

[0037] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0038] This invention provides a method for preparing a corrosion-resistant aluminum-based multilayer coating on the surface of a sintered NdFeB magnet, specifically comprising:

[0039] (1) Pretreatment before coating. The sintered NdFeB magnets were successively polished, ultrasonically cleaned with cleaning agent, ultrasonically cleaned with deionized water, and vacuum dried.

[0040] (2) Plasma cleaning. The sintered NdFeB magnet is placed on the workpiece holder in the vacuum chamber. A mechanical pump and a molecular pump are used to evacuate the vacuum to a degree less than or equal to 10. -3 Pa. The argon gas introduced into the vacuum chamber is controlled by a mass flow meter, with a pressure of 1-3 Pa. The bias voltage power supply parameters connected to the workpiece holder are adjusted: voltage 500-900V, duty cycle 40-90%, processing time 5-20 min. This completes the surface cleaning of the sintered NdFeB magnet.

[0041] (3) Al coating deposition. Position the sintered NdFeB magnet directly over the aluminum target. Adjust the argon gas flow into the vacuum chamber using a mass flow meter to achieve a pressure of 0.3-0.8 Pa. Adjust the parameters of the magnetron sputtering power supply connected to the aluminum target: current 1-10 A, duty cycle 40-90%, frequency 10-100 kHz. Simultaneously, adjust the parameters of the bias voltage power supply connected to the workpiece holder: voltage 50-150 V, duty cycle 50-90%, frequency 10-100 kHz. Complete the deposition of an Al coating on the surface of the sintered NdFeB magnet. The processing time is 10-30 min.

[0042] (4) Deposition of nano-amorphous barrier coating (i.e., aluminum-based barrier coating). Turn off the magnetron sputtering power supply and the bias power supply, and stop the argon gas supply. Then, further excite the reaction gas into a high-density plasma by using an ion source or self-bias excitation, and take advantage of the high activity of the plasma to react with the Al coating to generate a nano-sized amorphous compound barrier coating.

[0043] Method 1: Control the flow of reactive gases such as oxygen (O2), nitrogen (N2), or acetylene (C2H2) into the vacuum chamber using a mass flow meter, maintaining a pressure of 1-3 Pa. Adjust the bias voltage power supply parameters connected to the workpiece holder: voltage value 500-900V, duty cycle 40-90%, processing time 5-20 min. Complete the deposition of a nano-amorphous barrier coating on the Al coating surface.

[0044] Method 2: The flow of reactive gases such as oxygen (O2), nitrogen (N2), or acetylene (C2H2) into the vacuum chamber is controlled using a mass flow meter. The pressure is 0.4-1 Pa, and the workpiece holder is connected to ground. The ion source power parameters are adjusted as follows: power 0.2-2 kW, frequency 20-80 kHz, duty cycle 20-80%, and processing time 2-10 min. This completes the deposition of a nano-amorphous barrier coating on the Al coating surface.

[0045] Among them, Method 1 is the specific operation step of using self-biased excitation, and Method 2 is the specific operation step of using plasma excitation.

[0046] (5) Repeated deposition: Repeat steps (3)-(4) above, for a total of 5 times or more.

[0047] (6) Completion: After the magnet has cooled to room temperature, remove the sample.

[0048] The coating structure obtained by the technical solution of the present invention is as follows: Figure 1 As shown, the coating consists of an Al coating and a nano-amorphous barrier coating (i.e., an aluminum-based barrier coating). For the deposition of the aluminum coating, conventional physical vapor deposition (PVD) techniques can be preferentially used to deposit the Al coating on the surface of an NdFeB magnet. Subsequently, a plasma surface modification technique is used to prepare the nano-amorphous barrier coating on the Al coating surface. Specifically, in this invention, reactive gases such as oxygen (O2), nitrogen (N2), or acetylene (C2H2) are introduced into a vacuum chamber. An ion source or self-biasing method is used to excite the reactive gases into a high-density plasma. Utilizing the high reactivity of the plasma, it reacts with the Al coating to generate a nano-sized amorphous compound coating. Repeating the above steps achieves the preparation of a multilayer Al coating / nano-amorphous barrier coating.

[0049] The following specific examples will provide further explanation.

[0050] Example 1

[0051] In this embodiment, a sintered NdFeB magnet with dimensions of 25mm*25mm*3mm and grade N52 was selected. The specific process is as follows:

[0052] (1) Pretreatment before coating. The sintered NdFeB magnets were sequentially polished, ultrasonically cleaned with cleaning agent, ultrasonically cleaned with deionized water, and vacuum dried.

[0053] (2) Plasma cleaning. The sintered NdFeB magnet is placed on the workpiece rack in the vacuum chamber, and a vacuum is evacuated using a mechanical pump and a molecular pump to a vacuum level of 7 × 10⁻⁶. -3 Pa. The argon gas introduced into the vacuum chamber is controlled by a mass flow meter, with a pressure of 1.2 Pa. The bias voltage power supply parameters connected to the workpiece holder are adjusted: voltage value of 900V, duty cycle of 90%, and processing time of 20 min. The surface cleaning of the sintered NdFeB magnet is completed.

[0054] (3) Al coating deposition. The sintered NdFeB magnet was positioned directly over an aluminum target. Argon gas introduced into the vacuum chamber was adjusted using a mass flow meter to achieve a pressure of 0.3 Pa. The magnetron sputtering power supply parameters connected to the aluminum target were adjusted as follows: current 3 A, duty cycle 50%, frequency 100 kHz. Simultaneously, the bias voltage power supply parameters connected to the workpiece holder were adjusted as follows: voltage 75 V, duty cycle 50%, frequency 100 kHz. The Al coating deposition on the surface of the sintered NdFeB magnet was completed within 10 minutes.

[0055] (4) Deposition of nano-amorphous barrier coating. Turn off the magnetron sputtering power supply and bias power supply, and stop the argon gas supply. Control the oxygen (O2) introduced into the vacuum chamber through a mass flow meter, with a pressure of 1 Pa. Adjust the bias voltage power supply parameters connected to the workpiece holder: voltage value of 500V, duty cycle of 70%, and processing time of 5 min. Complete the deposition of nano-amorphous barrier coating on the Al coating surface.

[0056] (5) Repeat deposition: Repeat steps (3)-(4) above, for a total of 10 times.

[0057] (6) Completion: After the magnet has cooled to room temperature, it is removed to obtain a sintered NdFeB magnet A1 with a corrosion-resistant aluminum-based multilayer coating.

[0058] Example 2

[0059] In this embodiment, a sintered NdFeB magnet with dimensions of 25mm*25mm*3mm and grade 45SH was selected. The specific process is as follows:

[0060] (1) Pretreatment before coating. The sintered NdFeB magnets were sequentially polished, ultrasonically cleaned with cleaning agent, ultrasonically cleaned with deionized water, and vacuum dried.

[0061] (2) Plasma cleaning. The sintered NdFeB magnet is placed on the workpiece rack in the vacuum chamber, and a vacuum is evacuated using a mechanical pump and a molecular pump to a vacuum level of 5 × 10⁻⁶. -3 Pa. The argon gas introduced into the vacuum chamber is controlled by a mass flow meter, with a pressure of 1.5 Pa. The bias voltage power supply parameters connected to the workpiece holder are adjusted: voltage value of 800V, duty cycle of 70%, and processing time of 15 min. The surface cleaning of the sintered NdFeB magnet is completed.

[0062] (3) Al coating deposition. The sintered NdFeB magnet was positioned directly over an aluminum target. Argon gas introduced into the vacuum chamber was adjusted using a mass flow meter to achieve a pressure of 0.6 Pa. The magnetron sputtering power supply parameters connected to the aluminum target were adjusted as follows: current 5 A, duty cycle 70%, frequency 100 kHz. Simultaneously, the bias voltage power supply parameters connected to the workpiece holder were adjusted as follows: voltage 100 V, duty cycle 70%, frequency 100 kHz. The Al coating deposition on the surface of the sintered NdFeB magnet was completed, with a processing time of 30 min.

[0063] (4) Deposition of a nano-amorphous barrier coating. Turn off the magnetron sputtering power supply and bias power supply, and stop the argon gas supply. Control the acetylene (C2H2) introduced into the vacuum chamber using a mass flow meter, with a pressure of 1.2 Pa. Adjust the bias voltage power supply parameters connected to the workpiece holder: voltage value of 800V, duty cycle of 60%, and processing time of 10 min. Complete the deposition of the nano-amorphous barrier coating on the Al coating surface.

[0064] (5) Repeated deposition: Repeat steps (3)-(4) above, for a total of 7 times.

[0065] (6) Completion: After the magnet has cooled to room temperature, it is removed to obtain a sintered NdFeB magnet A2 with a corrosion-resistant aluminum-based multilayer coating.

[0066] Example 3

[0067] In this embodiment, a sintered NdFeB magnet with dimensions of 10mm*10mm*8mm and grade 45SH was selected. The specific process is as follows:

[0068] (1) Pretreatment before coating. The sintered NdFeB magnets were successively polished, ultrasonically cleaned with cleaning agent, ultrasonically cleaned with deionized water, and vacuum dried.

[0069] (2) Plasma cleaning. The sintered NdFeB magnet is placed on the workpiece rack in the vacuum chamber. A vacuum is evacuated using a mechanical pump and a molecular pump to a vacuum level of 3 × 10⁻⁶. -3 Pa. The argon gas introduced into the vacuum chamber is controlled by a mass flow meter, with a pressure of 2 Pa. The bias voltage power supply parameters connected to the workpiece holder are adjusted: voltage value of 800V, duty cycle of 40%, and processing time of 10 min. The surface cleaning of the sintered NdFeB magnet is completed.

[0070] (3) Al coating deposition. The sintered NdFeB magnet was positioned directly over an aluminum target. Argon gas introduced into the vacuum chamber was adjusted using a mass flow meter to achieve a pressure of 0.6 Pa. The magnetron sputtering power supply parameters connected to the aluminum target were adjusted as follows: current 7 A, duty cycle 90%, frequency 40 kHz. Simultaneously, the bias voltage power supply parameters connected to the workpiece holder were adjusted as follows: voltage 100 V, duty cycle 90%, frequency 100 kHz. The Al coating deposition on the surface of the sintered NdFeB magnet was completed, with a processing time of 20 min.

[0071] (4) Deposition of a nano-amorphous barrier coating. Turn off the magnetron sputtering power supply and bias power supply, and stop the argon gas supply. Control the nitrogen (N2) gas flow into the vacuum chamber using a mass flow meter, maintaining a pressure of 0.6 Pa. Connect the workpiece holder to ground. Adjust the ion source power parameters: power 1.5 kW, frequency 40 kHz, duty cycle 60%, processing time 5 min. Complete the deposition of the nano-amorphous barrier coating on the Al coating surface.

[0072] (5) Repeated deposition: Repeat steps (3)-(4) above, for a total of 15 times.

[0073] (6) Completion: After the magnet has cooled to room temperature, it is removed to obtain a sintered NdFeB magnet A3 with a corrosion-resistant aluminum-based multilayer coating.

[0074] Comparative Example 1

[0075] The preparation was carried out according to the preparation method of Example 1, except that step (4) was not performed, and a sintered NdFeB magnet D1 with an aluminum coating was obtained.

[0076] Comparative Example 2

[0077] The preparation was carried out according to the preparation method of Example 2, except that step (4) was not performed, and sintered NdFeB magnet D2 with aluminum coating was obtained.

[0078] Comparative Example 3

[0079] The preparation was carried out according to the preparation method of Example 3, except that step (4) was not performed, and sintered NdFeB magnet D3 with aluminum coating was obtained.

[0080] Detection example

[0081] The sintered NdFeB magnet A1 prepared in Example 1 and the sintered NdFeB magnet D1 prepared in Comparative Example 1 were subjected to a neutral salt spray test. It was found that the NdFeB magnet A1 treated by the present invention could withstand neutral salt spray for up to 300 hours, while the sintered NdFeB magnet D1 could withstand neutral salt spray for less than 72 hours.

[0082] The sintered NdFeB magnet A2 prepared in Example 2 and the sintered NdFeB magnet D2 prepared in Comparative Example 2 were subjected to a neutral salt spray test. It was found that the NdFeB magnet A2 treated by the present invention could withstand neutral salt spray for up to 400 hours, while the sintered NdFeB magnet D2 could withstand neutral salt spray for less than 100 hours.

[0083] The sintered NdFeB magnet A3 prepared in Example 3 and the sintered NdFeB magnet D3 prepared in Comparative Example 3 were subjected to a neutral salt spray test. It was found that the NdFeB magnet A3 treated by the present invention could withstand neutral salt spray for up to 350 hours, while the sintered NdFeB magnet D3 could not withstand neutral salt spray for more than 72 hours.

[0084] In summary, the method for preparing aluminum-based multilayer coatings using the technical solution of this invention proposes to excite the reactive gas into a high-density plasma using an ion source or self-biasing, and to utilize the high reactivity of the plasma to react with the Al coating to achieve in-situ growth of amorphous compound coatings with nanoscale thickness. Electron micrographs of the aluminum coatings obtained based on the embodiments of this invention are shown below. Figure 2 As shown, the electron microscope image of the prepared aluminum-based barrier coating is as follows. Figure 3 As shown. (Through) Figure 2 and Figure 3 As can be seen, the obtained aluminum coating has a columnar crystal structure, while the aluminum-based barrier coating structure is densified, which confirms that the technical solution of the present invention can indeed interrupt the continuous growth of columnar crystals, thereby improving the density of the coating.

[0085] Furthermore, the above process does not involve reactive sputtering, completely avoiding the problem of slow deposition efficiency caused by "target poisoning" during deposition, thus meeting the requirements of industrial production. At the same time, the resulting multilayer coating has excellent corrosion resistance.

[0086] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a corrosion-resistant aluminum-based multilayer coating on the surface of a sintered NdFeB magnet, characterized in that, include: S100. Pretreatment of magnets: The sintered NdFeB magnets are polished, cleaned and dried in sequence to complete the pretreatment of the sintered NdFeB magnets. S200, Preparation of aluminum coating: In the presence of inert gas, after adjusting the pressure in the environment to the first preset value, an aluminum coating is deposited on the sintered NdFeB magnet pretreated in step S100. S300, Preparation of aluminum-based barrier coating: In the presence of reactive gas, after adjusting the pressure in the environment to the second preset value, the reactive gas is excited into high-density plasma, and a nano-amorphous aluminum-based barrier coating is generated on the surface of the sintered NdFeB magnet with aluminum coating deposited in step S200. S400, after repeating steps S200 and S300, cool to complete the preparation of the corrosion-resistant aluminum-based multilayer coating on the surface of the sintered NdFeB magnet; In step S300, the reaction gas is selected from one or more of oxygen, nitrogen and acetylene, and oxygen and acetylene do not exist simultaneously; The reactive gas is excited into a high-density plasma by means of ion source excitation and / or self-biased excitation. When using an ion source for excitation, the second preset value is 0.4-1 Pa, and the operating parameters of the ion source power supply are: power of 0.2-2 kW, frequency of 20-80 kHz, duty cycle of 20-80%, and excitation time of 2-10 min. When using self-biased excitation, the second preset value is 1-3 Pa, and the operating parameters of the bias power supply are: voltage value of 500-900V, duty cycle of 40-90%, and excitation time of 5-20min.

2. The preparation method according to claim 1, characterized in that, Step S100 further includes plasma cleaning of the sintered NdFeB magnet after drying; and the plasma cleaning specifically includes: Vacuum degree not greater than 10 -2 In an environment of Pa, an inert gas is introduced into the environment to adjust the pressure to the third preset value, and the bias power supply is adjusted to the preset parameters to complete the plasma cleaning of the sintered NdFeB magnet.

3. The preparation method according to claim 2, characterized in that, During plasma cleaning, the inert gas is selected from argon; The third preset value is 1-3 Pa; The preset parameters of the bias power supply are: voltage value of 500-900V, duty cycle of 40-90%, and plasma cleaning processing time of 5-20min.

4. A preparation method according to any one of claims 1-3, characterized in that, In step S200, the inert gas is selected from argon; The first preset value is 0.3-0.8 Pa.

5. The preparation method according to claim 4, characterized in that, The aluminum coating was deposited using physical vapor deposition.

6. The preparation method according to claim 5, characterized in that, The physical vapor deposition specifically includes: magnetron sputtering of an aluminum target while applying a negative bias voltage to a sintered NdFeB magnet to complete the deposition of an aluminum coating on the surface of the sintered NdFeB magnet.

7. The preparation method according to claim 6, characterized in that, In the physical vapor deposition process, the operating parameters of the magnetron sputtering power supply used for magnetron sputtering are: current value of 1A-20A, duty cycle of 20%-90%, and frequency of 20kHz-150kHz. The operating parameters of the bias power supply used to apply negative bias voltage to sintered NdFeB magnets are: voltage value 0V-300V, duty cycle 20%-90%, and frequency 20kHz-150kHz.

8. The preparation method according to claim 7, characterized in that, The deposition time for physical vapor deposition was 10 minutes.

9. The preparation method according to any one of claims 1-3, characterized in that, Repeating steps S200 and S300 is considered one cycle. In step S400, the number of cycles is not less than 5.

10. A corrosion-resistant aluminum-based multilayer coating on the surface of a sintered NdFeB magnet, characterized in that, It is prepared by any one of the preparation methods described in claims 1-9.

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