Corrosion-resistant neodymium-iron-boron magnet, surface treatment method, permanent magnet motor and application

Abstract

The invention provides a corrosion-resistant neodymium-iron-boron magnet, a surface treatment method, a permanent magnet motor and application, and the surface treatment method comprises the steps: placing the neodymium-iron-boron magnet in a mixed atmosphere of a first atmosphere and a second atmosphere, and carrying out heat treatment under the conditions of 150-200 DEG C and 0.3-5 MPa to obtain the neodymium-iron-boron magnet with a compact oxidation film on the surface, the oxidizing atmosphere comprises that the first atmosphere contains oxygen, and the second atmosphere contains water vapor. The low-temperature and high-pressure heat treatment mode is adopted, the atmosphere containing oxygen and water vapor is controlled, the dense oxidation film with the high ferroferric oxide content is obtained, and the problem that the magnetic property of the magnet is degraded after heat treatment can be effectively solved while the corrosion resistance is improved.

Description

Technical Field

[0001] The invention relates to the technical field of NdFeB magnets, and in particular to a corrosion-resistant NdFeB magnet and a surface treatment method, a permanent magnet motor and uses thereof. Background Art

[0002] The development of NdFeB magnets is very rapid. Due to their excellent comprehensive magnetic properties, they have been widely used in high-tech fields such as computers, network information, aerospace, communications, transportation, and home appliances.

[0003] However, since the magnet contains the active rare earth element Nd, the corrosion resistance of the magnet is very poor. It is very easy to rust and corrode in a hot and humid environment, resulting in a decrease in the magnetic properties of the magnet. Therefore, it is usually used after a corrosion-resistant film such as a metal film or a resin film is formed on the surface of the magnet. For plug-in permanent magnet motors, the magnet is usually fixed by injection molding or glue filling after being inserted into the slot. At the same time, it also plays a certain role in corrosion protection, and the surface protection requirements of the magnet itself are reduced. Among them, the simple anti-corrosion technology of heat treatment in an oxidizing atmosphere to modify the surface of the magnet is sufficient to achieve the above purpose and has attracted people's attention.

[0004] In order to perform surface modification of NdFeB magnets by oxidative heat treatment, CN101819690A discloses that at an oxygen partial pressure of 1×10 2 Pa~1×10 5 Pa, water vapor partial pressure is lower than 1000Pa, and the magnet is subjected to oxidation heat treatment at 300℃~450℃ to obtain a good surface modification film layer to achieve the purpose of corrosion resistance on the magnet surface. With the development of sintered NdFeB magnet technology in recent years, the magnet manufacturing technology with an oxygen content of less than 1000ppm has been established. The surface modification of magnets with very little oxygen content at a heat treatment temperature of more than 300℃ (excluding 300℃) recommended in CN101819690A document can form an oxidizing film layer on the magnet surface as expected to improve the corrosion resistance, but the treatment under such conditions will deteriorate the magnetic properties, affecting its magnetic properties.

[0005] Therefore, an object of the present invention is to provide a method for producing a NdFeB magnet having excellent corrosion resistance and excellent magnetic properties while preventing the surface of the magnet from corroding. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a corrosion-resistant NdFeB magnet and a surface treatment method, a permanent magnet motor and uses, which solve the problem that the magnetic properties of the NdFeB magnet are deteriorated due to the anti-corrosion layer made by the existing heat treatment technology, and can obtain a corrosion-resistant NdFeB magnet with excellent magnetic and corrosion resistance.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a surface treatment method for a NdFeB magnet, the surface treatment method comprising: heat treating the NdFeB magnet in a mixed atmosphere of a first atmosphere and a second atmosphere at 150 to 200°C and 0.3 to 5MPa to obtain a NdFeB magnet having a dense oxide film on its surface; the first atmosphere contains oxygen and carbon dioxide, and the second atmosphere contains water vapor.

[0009] NdFeB magnets contain the active rare earth element Nd, which results in poor corrosion resistance of the magnets. They are very easy to rust and corrode in a hot and humid environment, which results in a decrease in the magnetic properties of the magnets. However, the inventors of the present invention have found that magnets with an oxidation amount of less than 1000ppm are prone to magnetic degradation during surface oxidation treatment, and iron oxides are also prone to generate non-dense oxide films during surface oxidation, which makes it difficult for the formed oxide films to play an anti-corrosion effect. Therefore, the purpose of the present invention is to improve the corrosion resistance of NdFeB magnets while ensuring that the magnetic properties are not degraded, select a low temperature of 150 to 200°C for heat treatment, and match the use of a pressurized condition of 0.3 to 5MPa, so that water vapor, carbon dioxide and oxygen can interact with each other, and react with NdFeB magnets under pressurized low temperature conditions to form a dense oxide film of ferroferric oxide, thereby achieving a corrosion-resistant effect.

[0010] It is worth mentioning that the temperature of heat treatment can be, for example, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C or 200°C, and the pressure of pressurization can be, for example, 0.3MPa, 0.5MPa, 0.8MPa, 1.0MPa, 1.2MPa, 1.5MPa, 2.0MPa, 2.5MPa, 3.0MPa, 3.5MPa, 4.0MPa, 4.5MPa or 5.0MPa.

[0011] In the present invention, the heat treatment adopts pressurization, which can be combined with low-temperature heat treatment conditions to realize the chemical reaction process of oxidation on the surface of the magnet, and at the same time effectively reduce the proportion of ferrous oxide formed due to low-temperature heat treatment, increase the proportion of ferrosoferric oxide, and ensure the corrosion resistance of the magnet; because the atmosphere contains water vapor, the oxidation reaction caused by the hydrogen oxide molecules in the water vapor on the surface of the NdFeB magnet will produce hydrogen by-products, and when the pressure is higher than 5MPa, it will cause the NdFeB magnet to absorb excessive hydrogen, resulting in obvious embrittlement, thereby reducing the magnetic properties. Therefore, the present invention selects a pressurization condition of 0.3-5MPa under low temperature conditions, while ensuring the corrosion resistance and magnetic properties of the NdFeB magnet.

[0012] Regarding the selection of components of the mixed atmosphere, the present invention finds that when only an oxygen-containing atmosphere is used, although the heat treatment pressure is increased after the heat treatment temperature is lowered, and although the surface of the NdFeB magnet can be modified and a surface oxidation reaction occurs, the density and quality of the surface oxide film are poor, and the corrosion resistance of the NdFeB magnet is limited. To this end, the present invention selects to use a first atmosphere of carbon dioxide and oxygen and a second atmosphere containing water vapor for heat treatment, wherein the presence of water vapor can promote the formation of ferroferric oxide and increase the content of ferroferric oxide in the film layer; and carbon dioxide can play the following three roles: A. Promote the adsorption and desorption of oxygen and water vapor on the surface of the NdFeB magnet, increase the surface activity of oxygen and water vapor, and accelerate the oxidation reaction rate of the NdFeB magnet; B. Carbon dioxide can form competitive adsorption with water vapor and oxygen on the surface of the NdFeB magnet, inhibit the excessive reaction of oxygen and the NdFeB magnet, thereby balancing the oxidation reaction process of oxygen and the magnet surface, and controlling the oxide film layer to grow uniformly and finely; C. Carbon dioxide can inhibit the excessive growth of the crystal grain size of the oxide, obtain a dense oxide film layer, and improve the quality of the oxide film layer. That is, the present invention selects a first atmosphere containing oxygen and carbon dioxide and a second atmosphere containing water vapor to combine, which can work synergistically under low temperature and high pressure conditions to form a uniform and dense oxide film layer on the magnet surface, thereby ensuring the corrosion resistance of the magnet surface.

[0013] The mixed atmosphere may be introduced after the first atmosphere and the second atmosphere are mixed, or the first atmosphere and the second atmosphere may be introduced simultaneously, and there is no particular limitation. However, it is preferred to introduce them separately, so that the oxygen in the first atmosphere is preferably in contact with the surface of the magnet, and then mixed with water vapor. The oxygen is in contact with the surface of the magnet in advance, and the surface of the magnet is pre-oxidized first. The oxide formed on the surface of the magnet can increase the surface gap, which increases the contact area of ​​the subsequent chemical modification reaction and facilitates the adsorption of more gases in the mixed atmosphere, ensuring the concentration of the reaction gas in the surface area of ​​the magnet, thereby further optimizing the quality of the surface oxide film.

[0014] Preferably, the volume fraction of oxygen in the first atmosphere is 18-24%, for example, it can be 18%, 18.5%, 19%, 19.5%, 20%, 20.5%, 21%, 21.5%, 22%, 22.5%, 23%, 23.5% or 24%.

[0015] Compared with conventional surface modification treatment atmosphere, the present invention increases the oxygen content, and cooperates with the low temperature and high pressure conditions of heat treatment. The high content of oxygen promotes the rapid completion of oxidation reaction on the magnet surface under low temperature heat treatment conditions, generates an oxide film on the magnet surface, improves production efficiency, and can also effectively avoid magnetic degradation caused by long-term heat treatment.

[0016] Preferably, the volume fraction of carbon dioxide in the first atmosphere is 0.05-1.2%, more preferably, the volume fraction of carbon dioxide in the first atmosphere is 0.06-0.5%, for example, it can be 0.06%, 0.062%, 0.065%, 0.07%, 0.072%, 0.075%, 0.08%, 0.085%, 0.09%, 0.095%, 0.1%, 0.15%, 0.25%, 0.3%, 0.4%, 0.48% or 0.5%, etc.

[0017] When the carbon dioxide content is too low, it is difficult to promote the reaction to form a more uniform oxide film. When the carbon dioxide content is too high, it will lead to a decrease in the oxidation rate, thereby requiring a longer time for oxidation. Long-term heat treatment will lead to magnetic degradation. Therefore, the carbon dioxide content in the present invention needs to be controlled within the above range to ensure the corrosion resistance and magnetic properties of the magnet surface.

[0018] Preferably, the first atmosphere further comprises any one of nitrogen, argon or helium or a combination of at least two of them, wherein typical but non-limiting combinations are a combination of nitrogen and argon, a combination of helium and argon, and a combination of nitrogen and helium.

[0019] Preferably, the flow rate of the first atmosphere is 3 to 10 cm 3 / min, for example, 3cm 3 / min、3.5cm 3 / min、4cm 3 / min、4.2cm 3 / min、4.5cm 3 / min、4.8cm 3 / min、5cm 3 / min、5.6cm 3 / min、6cm 3 / min、7cm 3 / min、7.5cm 3 / min、8cm 3 / min、8.5cm 3 / min、9cm 3 / min or 10cm 3 / min, etc.

[0020] Preferably, the water vapor in the second atmosphere is 2-4 g / (m 3 ×min) of water flow rate, for example, 2g / (m 3 ×min)、2.1g / (m 3 ×min)、2.2g / (m 3 ×min)、2.3g / (m 3×min)、2.5g / (m 3 ×min)、2.8g / (m 3 ×min)、3.0g / (m 3 ×min)、3.2g / (m 3 ×min)、3.5g / (m 3 ×min) or 4.0g / (m 3 ×min) etc.

[0021] In the present invention, a water supply device is additionally provided in addition to the heat treatment, and the content of the water vapor is calculated based on the consumed water flow rate. In the present invention, the flow rate of the water vapor is limited to the above range, which can ensure the formation of an oxide film layer on the surface of the magnet to ensure corrosion resistance, while avoiding a high water vapor content, a large amount of hydrogen is generated as a by-product, and the magnet absorbs the generated hydrogen and becomes embrittled, thereby reducing the magnetic properties.

[0022] Preferably, the heat treatment time is 10 to 80 min, for example, it can be 10 min, 12 min, 13 min, 14 min, 15 min, 20 min, 25 min, 30 min, 40 min, 50 min, 60 min, 70 min or 80 min.

[0023] Preferably, the NdFeB magnet comprises 28wt% to 33wt% of R, 0.8wt% to 1.5wt% of B, 0 to 3wt% of M and the balance of Fe, wherein R is a rare earth element, and the rare earth element R comprises Nd; M is selected from any one or a combination of at least two of Cu, Al, Zr, Nb, Mn, Mg, Si, Cr or Ti, wherein a typical but non-limiting combination is a combination of Cu and Al, a combination of Zr and Ti, a combination of Nb and Mn, a combination of Mn and Al, a combination of Mg and Si, and a combination of Cr and Al.

[0024] The content of rare earth element R in the NdFeB magnet is 28-33wt%, for example, it can be 28wt%, 28.5wt%, 29wt%, 29.2wt%, 29.5wt%, 30wt%, 30.5wt%, 31wt%, 32wt% or 33wt%.

[0025] The content of element B in the NdFeB magnet is 0.8wt% to 1.5wt%, for example, it can be 0.8wt%, 0.85wt%, 0.9wt%, 0.95wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt% or 1.5wt%.

[0026] The content of the element M in the NdFeB magnet may be, for example, 0, 0.5 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 2.8 wt% or 3.0 wt%.

[0027] Preferably, the rare earth element R also includes any one or a combination of at least two of Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb or Lu, wherein typical but non-limiting combinations are a combination of Y and La, a combination of Ce and Eu, a combination of Y and Ce, a combination of Pr and Ho, a combination of Pr and Sm, a combination of Gd and Sm, etc. In addition to Nd, the rare earth element R in the present invention may also be a combination of Nd and any at least one of the above rare earth elements, and is not limited to containing only Nd.

[0028] Preferably, the oxygen content of the NdFeB magnet is below 1000 ppm, for example, it may be 1000 ppm, 950 ppm, 900 ppm, 850 ppm, 800 ppm, 600 ppm or 500 ppm.

[0029] In a second aspect, the present invention provides a corrosion-resistant NdFeB magnet, which is produced by the surface treatment method of the NdFeB magnet described in the first aspect.

[0030] The corrosion-resistant NdFeB magnet provided in the second aspect of the present invention has both excellent corrosion resistance and magnetic properties and has broad application prospects.

[0031] Preferably, the surface of the corrosion-resistant NdFeB magnet contains a dense oxide film.

[0032] Preferably, the dense oxide film comprises ferrosoferric oxide.

[0033] Preferably, the dense oxide film has a thickness of 0.5 to 10 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0034] In a third aspect, the present invention provides a permanent magnet motor, comprising the corrosion-resistant NdFeB magnet described in the second aspect.

[0035] The permanent magnet motor provided in the third aspect of the present invention has excellent magnetic properties and a long service life because it adopts the corrosion-resistant NdFeB magnets described in the second aspect.

[0036] In a fourth aspect, the present invention provides a use of the corrosion-resistant NdFeB magnet according to the second aspect in computers, network information, aerospace, communications, transportation or household appliances.

[0037] The corrosion-resistant NdFeB magnet provided in the second aspect of the present invention can be widely used in various fields because of its guaranteed corrosion resistance and magnetic properties.

[0038] Compared with the prior art, the present invention has at least the following beneficial effects:

[0039] (1) The surface treatment method of NdFeB magnets provided by the present invention adopts low-temperature pressurized heat treatment conditions and cooperates with a specific oxidizing atmosphere, breaking the conventional oxidation process in which the heat treatment temperature needs to be limited to above 300°C to achieve the modification process of the magnet surface;

[0040] (2) The surface treatment method of the NdFeB magnet provided by the present invention can form a dense oxide film layer on the surface of the magnet, thereby improving the corrosion resistance of the magnet. At the same time, the low-temperature heat treatment conditions can avoid the loss of magnetic properties of the magnet during the heat treatment process. Under the preferred conditions, the magnetic property loss rate is within 0.17%;

[0041] (3) The surface treatment method of the NdFeB magnet provided by the present invention can increase the rate of producing an oxide film on the magnet surface by selecting an oxidizing atmosphere containing carbon dioxide, thereby improving the production efficiency and the surface quality of the oxide film, and significantly improving the corrosion resistance; under the preferred condition, the corrosion-resistant NdFeB magnet obtained by treatment has a weight loss of ≤0.21 mg / cm3 under high temperature and high humidity conditions of 120°C, 100% relative humidity, and 2 atm for a test time of 96 h. 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a scanning electron microscope image of the NdFeB magnet containing a dense oxide film obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0044] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0045] It should be understood that, in the description of the present invention, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0046] For the convenience of testing and comparison, the specific embodiments of the present invention all adopt the NdFeB magnets prepared in the following preparation examples for surface treatment, but it does not mean that the present invention is only applicable to the NdFeB magnets. The surface treatment method provided by the present invention can be applied to NdFeB magnets known or improved by technicians in this field, as long as there is a need for surface treatment modification.

[0047] Preparation Example

[0048] Nd is produced by smelting process 30.5 Dy 0.5 Co 1.0 Cu 0.25 Al 0.5 B 0.98 Fe bal (measured in weight percentage, bal in the following table represents the remainder) alloy ingot, the ingot alloy is coarsely crushed, hydrogen crushed, and air flow milled into fine powder according to conventional methods, and the powder D50 is 4.0μm. The fine powder is placed in a magnetic field orientation device for compression, and the orientation magnetic field strength is 1.5T, and pressed into shape. Then the molded body is taken out from the pressing device, placed in a vacuum sintering furnace and sintered at 1075℃ for 3h, and tempered at 600℃ for 5h to obtain a blank magnet. The blank magnet is machined to obtain a NdFeB magnet with a thickness of 0.5mm×5mm in the longitudinal direction×5mm in the transverse direction. The oxygen content of the NdFeB magnet tested by a nitrogen oxygen analyzer is 800ppm.

[0049] Example 1

[0050] This embodiment provides a surface treatment method for a NdFeB magnet, the surface treatment method comprising:

[0051] The NdFeB magnets were respectively introduced into the first atmosphere (20v% oxygen, 0.06v% carbon dioxide and 79.94v% nitrogen, with a flow rate of 3cm 3 / min and the second atmosphere (at 3g / (m 3 ×min) in a mixed atmosphere of water vapor introduced at a water flow rate of ×min) and heat treated at 180°C and 2MPa for 30min, and then cooled in the same atmosphere to obtain a NdFeB magnet with a dense oxide film on the surface.

[0052] The scanning electron microscope spectrum of the NdFeB magnet containing a dense oxide film prepared in this embodiment is as follows: Figure 1 As shown, A represents the NdFeB magnet, and B represents the dense oxide film on the surface of the NdFeB magnet. Figure 1 It can be seen that an oxide film is obviously formed on the surface of the NdFeB magnet, and the thickness of the oxide film can be measured to be about 3.5μm.

[0053] Example 2

[0054] This embodiment provides a surface treatment method for a NdFeB magnet, the surface treatment method comprising:

[0055] The NdFeB magnets were respectively introduced into the first atmosphere (18v% oxygen, 0.10v% carbon dioxide and 81.9v% nitrogen, with a flow rate of 5cm 3 / min and the second atmosphere (at 2g / (m 3 ×min) in a mixed atmosphere of water vapor introduced at a water flow rate of ×min) and heat treated at 200°C and 1MPa for 30min, and then cooled in the same atmosphere to obtain a NdFeB magnet with a dense oxide film on the surface.

[0056] Example 3

[0057] This embodiment provides a surface treatment method for a NdFeB magnet, the surface treatment method comprising:

[0058] The NdFeB magnets were respectively introduced into the first atmosphere (24v% oxygen, 0.50v% carbon dioxide and 75.5v% nitrogen as inert gas, with a flow rate of 8cm 3 / min and the second atmosphere (at 4g / (m 3 ×min) in a mixed atmosphere of water vapor introduced at a water flow rate of ×min) and heat treated at 150°C and 5Mpa for 20min, and then cooled in the same atmosphere to obtain a NdFeB magnet with a dense oxide film on the surface.

[0059] Example 4

[0060] This embodiment provides a surface treatment method for NdFeB magnets. The surface treatment method is the same as that of Embodiment 1 except that the volume fraction of carbon dioxide in the first atmosphere is 0.03v% (the inert gas is adjusted accordingly), and will not be described again.

[0061] Example 5

[0062] This embodiment provides a surface treatment method for NdFeB magnets. The surface treatment method is the same as that of Embodiment 1 except that the volume fraction of carbon dioxide in the first atmosphere is 1.3v% (nitrogen is adjusted accordingly), and will not be described again.

[0063] Example 6

[0064] This embodiment provides a surface treatment method for NdFeB magnets. The surface treatment method is the same as that of Embodiment 1 except that the volume fraction of oxygen in the first atmosphere is 30v% (nitrogen is adjusted accordingly), and will not be described in detail here.

[0065] Example 7

[0066] This embodiment provides a surface treatment method for NdFeB magnets. The surface treatment method includes: 3 Except for the water vapor introduced at a water flow rate of 100 × min), the rest is the same as that in Example 1 and will not be described again.

[0067] Example 8

[0068] This embodiment provides a surface treatment method for a NdFeB magnet. The surface treatment method is the same as that of Embodiment 1 except that the first atmosphere and the second atmosphere are mixed evenly before being introduced together, and thus will not be described in detail.

[0069] Comparative Example 1

[0070] This comparative example provides a surface treatment method for a NdFeB magnet. The surface treatment method is the same as that of Example 1 except that the first atmosphere does not contain carbon dioxide, and thus will not be described in detail.

[0071] Comparative Example 2

[0072] This comparative example provides a surface treatment method for a NdFeB magnet. The surface treatment method is the same as Example 1 except that the heat treatment temperature is 250° C., and will not be described in detail here.

[0073] Comparative Example 3

[0074] This comparative example provides a surface treatment method for a NdFeB magnet, the surface treatment method comprising: performing heat treatment at 400° C. for 15 min in an atmosphere with an oxygen partial pressure of 20000 Pa and a water vapor partial pressure of 600 Pa.

[0075] Comparative Example 4

[0076] This comparative example provides a surface treatment method for a NdFeB magnet. The surface treatment method is the same as Example 1 except that the heat treatment pressure is 0.1 MPa, and the details are not described again.

[0077] Test method: The oxygen content of the magnet is tested by a nitrogen and oxygen analyzer, and the equipment used is ON-330 type, Chongqing Yanrui Instrument Co., Ltd. The magnetic property evaluation method of the magnet is: the magnet is first saturated magnetized by a magnetizer, and then placed in a Helmholtz coil to measure its magnetic flux value in turn: magnetic property loss rate (%) = (AB) / A×100, where A is the magnetic flux value of the magnet without surface heat treatment, and B is the magnetic flux value of the NdFeB magnet with a dense oxide film on the surface obtained by surface heat treatment. Magnet corrosion resistance evaluation method: Under high temperature and high humidity conditions of 120°C, 100% relative humidity, and 2atm pressure, the test time is 96h, and after removing the magnetic powder detached from the surface of the magnet after the test, the weight of the magnet before and after the test is tested.

[0078] The test results of the above embodiments and comparative examples are shown in Table 1.

[0079] Table 1

[0080]

[0081]

[0082] In Table 1, “-” means that there is no relevant data or it is not necessary to measure it.

[0083] From Table 1, we can see the following points:

[0084] (1) It can be seen from Examples 1 to 3 that the surface treatment method of the NdFeB magnet provided by the present invention can effectively avoid the problem of magnetic property degradation of the magnet after heat treatment while ensuring the formation of an oxide film on the surface of the magnet. The magnetic properties are almost not reduced before and after the oxidation heat treatment, and the magnetic property loss rate is within 0.17%. In addition, the corrosion resistance is significantly improved. Under the conditions of high temperature and high humidity of 120°C, 100% relative humidity, and 2atm pressure, the weight loss during the test time of 96h is ≤0.21mg / cm 2 ;

[0085] (2) It can be seen from Example 1 and Examples 4 to 6 that the volume fractions of carbon dioxide and oxygen in the first atmosphere are critical for simultaneously ensuring magnetic properties and corrosion resistance. The volume fractions of carbon dioxide in Examples 4 to 5 are respectively low and high, which lead to insufficient density of the obtained oxide film. The weight loss after the corrosion resistance test is significantly greater than that of Example 1, and the magnetic property loss rate is ≥1.02%. The oxygen content in Example 6 is high, resulting in an excessively fast oxidation rate, and the magnetic property loss rate is as high as 1.55%. This shows that the present invention significantly improves the quality of the oxide film and can effectively avoid the degradation of magnetic properties by controlling the volume fractions of carbon dioxide and oxygen in the first atmosphere within a specific range, so that they cooperate with the second atmosphere.

[0086] (3) Combining Example 1 and Example 7, it can be seen that in Example 1, the second atmosphere is set to have a concentration of 3 g / m 3 The water flow rate of the water vapor is 8g / m 3 As for the water flow rate, both the corrosion resistance and the magnetic properties are excellent in Example 1, while in Example 7, the magnet absorbs more hydrogen, which increases its brittleness and leads to poor corrosion resistance. This shows that the present invention can better guarantee both the magnetic properties and the corrosion resistance by controlling the water vapor flow rate within a specific range.

[0087] (4) It can be seen from Example 1 and Comparative Examples 1 to 4 that in Comparative Example 1, no carbon dioxide is added, which cannot promote the formation of a uniform oxide film and has poor corrosion resistance. In Comparative Examples 2 and 3, after the temperature of the heat treatment is increased, the magnetic property loss rate of the magnet increases significantly. In Comparative Example 4, the corrosion-resistant layer formed after the surface treatment is carried out under low temperature and low pressure conditions has a low thickness and poor corrosion resistance. Due to the serious surface corrosion, the magnetic properties deteriorate significantly. This shows that the present invention can improve the corrosion resistance and effectively ensure that the magnetic properties do not deteriorate by adopting a combination of the first atmosphere and the second atmosphere and performing surface treatment under high pressure and low temperature conditions.

[0088] Application Example 1

[0089] This application example provides a permanent magnet motor, which uses the corrosion-resistant NdFeB magnet prepared in Example 1.

[0090] The permanent magnet motor in this application example has excellent corrosion resistance and long service life.

[0091] The present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A surface treatment method for a neodymium iron boron magnet, characterized in that: The surface treatment method comprises: The NdFeB magnet is heat treated in a mixed atmosphere of the first atmosphere and the second atmosphere at 150-200° C. and 0.3-5 MPa to obtain a NdFeB magnet having a dense oxide film on the surface; The first atmosphere contains oxygen and carbon dioxide, and the second atmosphere contains water vapor.

2. The surface treatment method according to claim 1, characterized in that: The volume fraction of oxygen in the first atmosphere is 18-24%; Preferably, the volume fraction of carbon dioxide in the first atmosphere is 0.05-1.2%, preferably 0.06-0.5%.

3. The surface treatment method according to claim 1 or 2, characterized in that: The first atmosphere also includes any one of nitrogen, argon or helium, or a combination of at least two of them.

4. The surface treatment method according to any one of claims 1 to 3, characterized in that: The flow rate of the first atmosphere is 3-10 cm 3 / min; Preferably, the water vapor in the second atmosphere is 2 to 4 g / (m 3 ×min) of water flow rate is introduced.

5. The surface treatment method according to any one of claims 1 to 4, characterized in that: The heat treatment time is 10 to 80 minutes.

6. The surface treatment method according to any one of claims 1 to 5, characterized in that: The NdFeB magnet comprises 28wt% to 33wt% of R, 0.8wt% to 1.5wt% of B, 0 to 3wt% of M and the balance of Fe, wherein R is a rare earth element, and the rare earth element R comprises Nd; M is selected from any one of Cu, Al, Zr, Nb, Mn, Mg, Si, Cr or Ti, or a combination of at least two thereof; Preferably, the rare earth element R further includes any one or a combination of at least two of Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb or Lu; Preferably, the oxygen content of the NdFeB magnet is below 1000 ppm.

7. A corrosion-resistant NdFeB magnet, characterized in that: The corrosion-resistant NdFeB magnet is obtained by using the surface treatment method for NdFeB magnets according to any one of claims 1 to 6.

8. The corrosion-resistant NdFeB magnet according to claim 7, characterized in that: The surface of the corrosion-resistant NdFeB magnet contains a dense oxide film; Preferably, the components of the dense oxide film include ferrosoferric oxide; Preferably, the thickness of the dense oxide film is 0.5-10 μm.

9. A permanent magnet motor, characterized in that: The permanent magnet motor comprises the corrosion-resistant NdFeB magnet according to claim 7 or 8.

10. Use of the corrosion-resistant NdFeB magnet according to claim 9 in computers, network information, aerospace, communications, transportation or household appliances.

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