Ce-containing neodymium-iron-boron magnet and preparation method and application thereof

Abstract

The invention relates to a Ce-containing neodymium-iron-boron magnet, and the Ce-containing neodymium-iron-boron magnet comprises thin shell layer crystal grains, reverse shell layer crystal grains and thick shell layer crystal grains, the HRE content of the core part of the reverse shell crystal grain is higher than the HRE content of the shell part; the HRE content of the shell part of the thick-shell crystal grain is higher than the HRE content of the core part of the thick-shell crystal grain; the HRE content of the shell part of the thin-shell crystal grain is higher than the HRE content of the core part, and the thickness of the shell part of the thin-shell crystal grain is less than 2 mu m; in the surface area of the Ce-containing neodymium-iron-boron magnet, the number of the thin shell layer crystal grains is N1, and the total number of the Ce-containing neodymium-iron-boron magnet crystal grains is N; in the near-surface area of the Ce-containing neodymium-iron-boron magnet, the number of the reverse shell crystal grains is N2, the number of the thick shell crystal grains is N3, and the total number of the Ce-containing neodymium-iron-boron magnet crystal grains is N '; wherein N1 / N is more than 70%; according to the Ce-containing neodymium-iron-boron magnet prepared through the method, the residual magnetism is reduced little, the coercive force and the demagnetization curve squareness of the magnetic material are remarkably improved, and the excellent magnet performance is achieved.

Description

Technical Field

[0001] The present invention relates to the field of Ce-containing NdFeB magnets, and in particular to a Ce-containing NdFeB magnet, a preparation method thereof, and uses thereof. Background Art

[0002] Neodymium iron boron (NdFeB) rare earth permanent magnets are the strongest permanent magnets discovered to date. Their superior magnetic properties have led to their widespread application in a growing number of fields, such as medical MRI, computer hard disk drives, audio and mobile phones, wind power generation, and aerospace. With the growing demand for low-carbon and energy-saving technologies, NdFeB rare earth permanent magnets are increasingly being used in automotive motors, energy-saving appliances, and other fields.

[0003] In recent years, the price of PrNd, a key raw material, has fluctuated significantly, making the market more sensitive to price fluctuations. Ce, also a rare earth element, is much more abundant in nature than metallic Nd, and its price is approximately one-tenth that of Nd. Using Ce to replace PrNd in the production of Ce-containing magnets can reduce raw material costs. As the application range of Ce-containing magnets expands, they are increasingly demanding high coercivity and excellent temperature stability.

[0004] In order to improve the coercive force of Ce-containing magnets, the grain boundary diffusion method can be used. One method is to carry out grain boundary diffusion near the melting point of the ReFe2 phase to reduce the influence of the relative diffusion effect of the ReFe2 grain boundary, so as to improve the diffusion efficiency of the heavy rare earth elements in the diffusion source, thereby improving the coercive force of the magnet; another method is to use a double alloy method to prepare the base magnet to eliminate the obstruction of the CeFe2 relative heavy rare earth grain boundary diffusion at the triangular grain boundary of the magnet, to a certain extent improve the diffusion efficiency of the heavy rare earth elements in the magnet, and ultimately improve the coercive force of the magnet. However, both of the above methods carry out grain boundary diffusion at a relatively high diffusion temperature, which easily causes the heavy rare earth elements to be enriched in the main phase grains, resulting in low diffusion efficiency, making it impossible to significantly improve the coercive force of the magnet, and at the same time, the squareness of the magnet deteriorates. Summary of the Invention

[0005] The purpose of the present invention is to provide a Ce-containing NdFeB magnet, a preparation method and use thereof. The Ce-containing NdFeB magnet prepared by the method provided by the present invention has less remanence drop, high coercive force and high demagnetization curve squareness.

[0006] To achieve the above objectives, the present invention provides a Ce-containing NdFeB magnet in a first aspect, wherein the Ce-containing NdFeB magnet comprises thin-shell grains, reverse-shell grains, and thick-shell grains; the HRE content of the core of the reverse-shell grains is higher than the HRE content of the shell; the HRE content of the shell of the thick-shell grains is higher than the HRE content of the core; the thickness of the shell of the reverse-shell grains and the thick-shell grains is respectively greater than 2 μm; the HRE content of the shell of the thin-shell grains is higher than the HRE content of the core, and the thickness of the shell of the thin-shell grains is less than 2 μm;

[0007] The HRE is selected from Dy and / or Tb;

[0008] In the surface area of ​​the Ce-containing NdFeB magnet, the ratio N1 / N of the number N1 of the thin shell grains to the total number N of the Ce-containing NdFeB magnet grains is greater than 70%; in the near-surface area of ​​the Ce-containing NdFeB magnet, the ratio (N2+N3) / N' of the sum of the number N2 of the anti-shell grains and the number N3 of the thick shell grains to the total number N' of the Ce-containing NdFeB magnet grains is less than 5%; wherein, the surface area includes the surface of the Ce-containing NdFeB magnet and the area less than 50 μm away from the surface, and the near-surface area includes the area 50 to 100 μm away from the surface of the Ce-containing NdFeB magnet.

[0009] Optionally, N1 / N is greater than 82%.

[0010] Optionally, in the surface region of the Ce-containing NdFeB magnet, the average grain size of the thin shell grains is less than 5 μm; and the HRE content of the core portion of the thin shell grains is less than 2 wt %.

[0011] Optionally, in the surface region of the Ce-containing NdFeB magnet, the average grain size of the anti-shell grains is 5 to 10 μm; and the thickness of the shell portion of the anti-shell grains is 2 to 4 μm.

[0012] Optionally, in the surface region of the Ce-containing NdFeB magnet, the average grain size of the thick shell grains is 5 to 10 μm; and the thickness of the shell portion of the thick shell grains is 2 to 4 μm.

[0013] Optionally, the Ce-containing NdFeB magnet comprises RL, Ce, M, B, HRE and T, wherein RL is selected from one or more elements of Nd, Pr, La, Y, Ho and Gd, and must include Nd and / or Pr, and M is selected from one or more elements of Al, Cu, Ga, Cr, Ti and Zr; T is Fe and / or Co;

[0014] The Ce-containing NdFeB magnet has an RL content of 19-28wt%, a Ce content of 4-13wt%, an M content of 0.1-2.0wt%, a B content of 0.9-1.0wt%, a HRE content of 0.2-0.8wt%, and the balance of T.

[0015] A second aspect of the present invention provides a method for preparing a Ce-containing NdFeB magnet, wherein the method comprises:

[0016] The Ce-RL1-TBM alloy powder is sequentially subjected to a molding process and a sintering process to obtain a base alloy, wherein the RL1 is selected from one or more elements selected from Nd, Pr, La, Y, Ho, Gd, Dy and Tb, and must include Nd and / or Pr, the M is selected from one or more elements selected from Al, Cu, Ga, Cr, Ti and Zr, and T is Fe and / or Co;

[0017] A film layer containing HRE is attached to the surface of the substrate alloy; the HRE is selected from Dy and / or Tb;

[0018] Performing diffusion treatment and tempering treatment on the base alloy with the HRE-containing film layer attached to the surface to obtain a Ce-containing NdFeB magnet;

[0019] Wherein, the diffusion process includes a first-level diffusion process and a second-level diffusion process;

[0020] The temperature of the first-stage diffusion treatment is 750-890° C., and the holding time is 1.5-4 hours; the temperature of the second-stage diffusion treatment is 900-950° C., and the holding time is 1.5-4.5 hours.

[0021] Optionally, the method further comprises: before the second-stage diffusion treatment, cooling the substrate alloy with the HRE-containing film layer attached to the surface.

[0022] Optionally, the temperature of the first stage diffusion treatment is 810-850°C.

[0023] Optionally, a method of attaching a film layer containing HRE on the surface of the substrate alloy includes attaching a diffusion source containing HRE on the surface of the substrate alloy by vacuum evaporation, magnetron sputtering, slurry coating, dipping, screen printing, roller coating or spraying to form a film layer; the thickness of the film layer is 5 to 30 μm;

[0024] The diffusion source is selected from one or more of metals, alloys or compounds containing HRE.

[0025] Optionally, in the Ce-RL1-TBM alloy powder, the content of Ce is 4-13wt%, the content of RL1 is 19-28wt%, the content of M is 0.1-2.0wt%, the content of B is 0.9-1.0wt%, and the balance is T.

[0026] Optionally, the method also includes: preparing Ce-RL1-TBM alloy sheets using a rapid solidification process, performing hydrogen crushing and fine-crushing treatment on the Ce-RL1-TBM alloy sheets to obtain the Ce-RL1-TBM alloy powder; the D50 particle size of the Ce-RL1-TBM alloy powder is 3 to 5.5 μm.

[0027] Optionally, the molding process is an orientation molding process, and the orientation molding process is performed under the condition that the orientation magnetic induction intensity is 1.5 to 2.0 T;

[0028] The temperature of the sintering treatment is 1010-1050° C., and the holding time is 2-6 hours; the temperature of the tempering treatment is 480-640° C., and the holding time is 1-4 hours.

[0029] The third aspect of the present invention provides a Ce-containing NdFeB magnet prepared by the method described in the second aspect of the present invention.

[0030] Through the above technical solution, the present invention uses a graded diffusion process with different temperatures to diffuse the substrate alloy with a film layer containing HRE attached to the surface. The first stage diffusion treatment is carried out at a temperature of 750-890°C, which can effectively control the rate at which the HRE heavy rare earth elements in the film layer enter the interior of the substrate alloy, so that a large number of uniformly distributed thin shell grains can be formed in the surface area of ​​the substrate alloy (the surface and the area less than 50μm from the surface); then the substrate alloy after the first diffusion treatment is cooled and a second stage diffusion treatment is carried out at a temperature of 900-950°C, which increases the HRE diffusion rate and further forms more uniformly distributed thin shell grains in the magnet surface area, and the shells of the formed thin shell grains are clearer. A large number of thin shell grains uniformly distributed in the magnet surface area can effectively reduce the number of thick shell grains and anti-shell grains in the magnet surface area and near-surface area, and can effectively reduce the content of HRE heavy rare earth elements in the magnet surface area and near-surface area. The graded diffusion process can control the rate at which HRE heavy rare earth elements enter the interior of the base alloy, thereby effectively inhibiting the generation and growth of anti-shell grains, reducing the grain size in the surface area and near-surface area of ​​the magnet, and facilitating the uniform distribution of heavy rare earth elements in the magnet, thereby reducing the content of heavy rare earth elements in the core of the grains. The Ce-containing NdFeB magnet prepared by the present invention has a high proportion of thin-shell grains in the surface area, and a low proportion of anti-shell grains and thick-shell grains in the near-surface area of ​​the magnet. The Ce-containing NdFeB magnet provided by the present invention has a less decrease in remanence, and the coercive force and demagnetization curve squareness of the magnetic material are significantly improved, and has excellent magnet performance.

[0031] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0033] Figure 1 These are SEM images of the base alloy sample after the first-stage diffusion treatment in Example 1 of the present invention, wherein (a) and (b) respectively show the SEM images of the area 0 to 100 μm away from the diffusion surface in two different observation sections of the sample.

[0034] Figure 2 These are SEM images of the Ce-containing NdFeB magnet CT-1 according to Example 1 of the present invention, wherein (a) and (b) respectively show SEM images of the region 0 to 100 μm from the diffusion surface in two different observation sections of the magnet.

[0035] Figure 3This is an SEM image of the Ce-containing NdFeB magnet DCT-1 of Comparative Example 1 of the present invention, wherein (a) and (b) respectively show SEM images of the region 0 to 100 μm from the surface of the diffusion sample in two different observation sections of the magnet.

[0036] Figure 4 This is a SEM image of the substrate alloy used in Example 1 of the present invention.

[0037] Figure 5 Schematic diagram of grain distribution in the surface area of ​​the magnet after diffusion in Comparative Example 1 and Example 1 of the present invention. DETAILED DESCRIPTION

[0038] The following describes the specific embodiments of the present disclosure in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0039] A first aspect of the present disclosure provides a Ce-containing NdFeB magnet, wherein the Ce-containing NdFeB magnet comprises thin-shell grains, inverted-shell grains, and thick-shell grains; the HRE content of the core of the inverted-shell grains is higher than the HRE content of the shell; the HRE content of the shell of the thick-shell grains is higher than the HRE content of the core; the thickness of the shell of the inverted-shell grains and the thick-shell grains is greater than 2 μm; the HRE content of the shell of the thin-shell grains is higher than the HRE content of the core, and the thickness of the shell of the thin-shell grains is less than 2 μm;

[0040] The HRE is selected from Dy and / or Tb;

[0041] In the surface region of the Ce-containing NdFeB magnet, the ratio N1 / N of the number N1 of the thin shell grains to the total number N of the Ce-containing NdFeB magnet grains is greater than 70%;

[0042] In the near-surface region of the Ce-containing NdFeB magnet, the ratio (N2+N3) / N' of the sum of the number N2 of the reverse shell grains and the number N3 of the thick shell grains to the total number N' of the Ce-containing NdFeB magnet grains is less than 5%;

[0043] The surface area includes the surface of the Ce-containing NdFeB magnet and an area below 50 μm from the surface, and the near-surface area is an area 50 to 100 μm from the surface of the Ce-containing NdFeB magnet.

[0044] The thin shell grains in the surface area (surface area and near-surface area) of the Ce-containing NdFeB magnet provided by the present invention are evenly distributed, and the number of thin shell grains in the surface area accounts for a high proportion, the average grain size is small, and the content of heavy rare earth elements in the core of the thin shell grains is low; while in the near-surface area of ​​the magnet, the number of anti-shell grains and thick shell grains accounts for a low proportion, and the grain sizes of the two are effectively suppressed, so that the remanence of the Ce-containing NdFeB magnet provided by the present invention decreases less, has high coercive force and high demagnetization curve squareness, and has excellent magnet performance.

[0045] In the above embodiment, the Ce-containing NdFeB magnet provided by the present disclosure can have a higher proportion of thin-shell grains in the surface area, and a lower proportion of anti-shell grains and thick-shell grains in the central area of ​​the magnet, thereby reducing the residual magnetism of the magnet, further improving the coercive force and the squareness of the demagnetization curve, and making the magnet have better performance.

[0046] In the present disclosure, the N1 / N value of a Ce-containing NdFeB magnet can be represented by the average result of the N1 / N values ​​of multiple cross-sections in the surface area of ​​the magnet, that is, multiple different cross-sections in the surface area of ​​the magnet can be randomly selected to measure the N1 / N value respectively, and the average value of the N1 / N values ​​of the multiple different cross-sections represents the N1 / N value in the surface area of ​​the magnet. Similarly, the (N2+N3) / N' value of a Ce-containing NdFeB magnet can be represented by the average result of the (N2+N3) / N' values ​​of multiple cross-sections in the near-surface area of ​​the magnet, that is, multiple different cross-sections in the near-surface area of ​​the magnet can be randomly selected to measure the (N2+N3) / N' value respectively, and the average value of the (N2+N3) / N' values ​​of the multiple different cross-sections represents the (N2+N3) / N' value in the surface area of ​​the magnet.

[0047] In a specific embodiment, in the surface region of the Ce-containing NdFeB magnet, the average grain size of the thin shell grains is less than 5 μm.

[0048] The surface area of ​​the Ce-containing NdFeB magnet provided by the present disclosure is uniformly distributed with a large number of thin-shell grains, and the average grain size is small, so that the magnet performance is significantly improved.

[0049] In a specific embodiment, in the surface region of the Ce-containing NdFeB magnet, the HRE content in the core of the thin shell grains is less than 2 wt %.

[0050] In the present disclosure, the content of heavy rare earth elements in the core of the thin-shell grains is low, and the heavy rare earth elements are mainly concentrated in the shell of the thin-shell grains, which enables the magnet to have a higher coercive force while ensuring less drop in remanence, and the magnet has a higher squareness of the demagnetization curve.

[0051] In a specific embodiment, in the surface region of the Ce-containing NdFeB magnet, the average grain size of the anti-shell grains is 5 to 10 μm; and the thickness of the shell portion of the anti-shell grains is 2 to 4 μm.

[0052] In a specific embodiment, in the surface region of the Ce-containing NdFeB magnet, the average grain size of the thick shell grains is 5 to 10 μm; and the thickness of the shell portion of the thick shell grains is 2 to 4 μm.

[0053] In the present disclosure, a large number of uniformly distributed thin-shell grains are formed in the surface region of the magnet, so that the number and average grain size of the anti-shell grains and thick-shell grains in the surface region of the magnet can be effectively controlled.

[0054] In a specific embodiment, the Ce-containing NdFeB magnet includes RL, Ce, M, B, HRE and T, wherein the RL is selected from one or more elements of Nd, Pr, La, Y, Ho and Gd, and RL must include Nd and / or Pr, and the M is selected from one or more of Al, Cu, Ga, Cr, Ti and Zr; T is Fe and / or Co.

[0055] In a specific embodiment, the RL content in the Ce-containing NdFeB magnet is 19-28wt%, the Ce content is 4-13wt%, the M content is 0.1-2.0wt%, optionally 0.2-2.0wt%, the B content is 0.9-1.0wt%, the HRE content is 0.2-0.8wt%, and the balance is T.

[0056] A second aspect of the present disclosure provides a method for preparing a Ce-containing NdFeB magnet, wherein the method comprises:

[0057] The Ce-RL1-TBM alloy powder is sequentially subjected to a molding process and a sintering process to obtain a base alloy, wherein the RL1 is selected from one or more elements selected from Nd, Pr, La, Y, Ho, Gd, Dy and Tb, and RL1 must include Nd and / or Pr, the M is selected from one or more elements selected from Al, Cu, Ga, Cr, Ti and Zr, and T is Fe and / or Co;

[0058] Attaching a film layer containing HRE on the surface of the substrate alloy, wherein the HRE is selected from Dy and / or Tb;

[0059] Performing diffusion treatment and tempering treatment on the base alloy with the HRE-containing film layer attached to the surface to obtain a Ce-containing NdFeB magnet;

[0060] Wherein, the diffusion process includes a first-level diffusion process and a second-level diffusion process;

[0061] The temperature of the first-stage diffusion treatment is 750-890° C., and the holding time is 1.5-4 hours; the temperature of the second-stage diffusion treatment is 900-950° C., and the holding time is 1.5-4.5 hours.

[0062] Specifically, the diffusion treatment includes heating the substrate alloy with the HER film layer attached to the surface to the first-stage diffusion treatment temperature under vacuum, cooling it with a protective gas after the first-stage diffusion treatment is completed, and then heating it to the second-stage diffusion treatment temperature under vacuum after cooling to 10-40°C. After the second-stage diffusion treatment is completed, cooling it with a protective gas and cooling it to room temperature. The protective gas can be argon, nitrogen, etc.

[0063] In the present disclosure, the method of attaching a film layer containing HRE on the surface of the substrate alloy includes attaching a diffusion source containing HRE on the surface of the substrate alloy by vacuum evaporation, magnetron sputtering, slurry coating, dipping, screen printing, roller coating, or spraying to form a film layer, wherein the diffusion source is selected from one or more metals, alloys, or compounds containing HRE, and the film layer has a thickness of 5 to 30 μm.

[0064] The inventors of the present disclosure have discovered in their research that, during grain boundary diffusion, at a higher diffusion temperature (900-950°C), it is beneficial to increase the diffusion rate of HRE heavy rare earth elements. However, since the main phase grains in the Ce-containing substrate alloy are more active than the main phase grains in the PrNd substrate alloy, at higher diffusion temperatures, Ce atoms in the main phase grains in the surface region of the substrate alloy are easily replaced by HRE heavy rare earth atoms, making it easy for Dy or Tb to enter the interior of the main phase grains and accumulate in the main phase grains, resulting in the appearance of more anti-shell grains in the surface region (the HRE content in the core of the main phase grains is higher than the HRE content in the shell, and the shell thickness is greater than 2μm). At the same time, thick shell grains (the HRE content in the shell of the main phase grains is higher than the HRE content in the core, and the shell thickness is greater than 2μm) are also likely to appear. Compared with thin shell grains, the shell thickness and average grain size of the anti-shell grains and thick shell grains are larger. The increase of anti-shell grains and thick shell grains in the surface area of ​​the magnet is not conducive to improving the squareness of the demagnetization curve and the coercive force of the magnet. The present invention discloses a method for diffusion-treating a substrate alloy having an HRE-containing film layer attached to its surface by adopting a graded diffusion process. The substrate alloy is subjected to a first-stage diffusion treatment at a temperature of 750-890°C, which can effectively control the rate at which the HRE heavy rare earth elements in the diffusion source enter the interior of the substrate alloy, so that clearer and more uniform thin shell grains can be formed in a surface area less than 50 μm from the magnet surface, effectively reducing the number of anti-shell grains in the near-surface area of ​​the magnet and the content of the HRE heavy rare earth elements entering the surface area of ​​the substrate alloy; the substrate alloy after the first-stage diffusion treatment is then cooled and subjected to a second-stage diffusion treatment at a temperature of 900-950°C, which can further promote the diffusion of the HRE heavy rare earth elements, form more uniformly distributed thin shell grains and a smaller average grain size in the surface area, and at the same time, further effectively inhibit the generation and growth of anti-shell grains, which is beneficial to further optimize the distribution of heavy rare earth elements in the magnet and reduce the content of heavy rare earth elements in the core of the main phase grains. The Ce-containing NdFeB magnet prepared by the present invention has a high proportion of thin-shell grains in the surface area, and a low proportion of anti-shell grains and thick-shell grains in the near-surface area of ​​the magnet, so that the remanence of the Ce-containing NdFeB magnet provided by the present invention decreases less, the coercive force and the squareness of the demagnetization curve of the magnetic material are significantly improved, and the magnet has excellent performance.

[0065] In one specific embodiment, the temperature of the first-stage diffusion treatment is 810-850° C. In the above embodiment, controlling the temperature of the first-stage diffusion treatment within the above range can further effectively control the rate at which the HRE heavy rare earth elements in the diffusion source enter the diffusion surface, further increase the number of thin-shell grains in the surface area of ​​the Ce-containing NdFeB magnet, make the shells of the formed thin-shell grains more uniform, and further reduce the number of anti-shell grains and thick-shell grains in the central area of ​​the magnet.

[0066] In a specific embodiment, the method of attaching the HRE-containing film layer to the surface of the substrate alloy includes attaching the diffusion source containing HRE to the surface of the substrate alloy by vacuum evaporation, magnetron sputtering, slurry coating, dipping, screen printing, roller coating, or spraying to form a film layer, wherein the diffusion source is selected from one or more of the metals, alloys, or compounds containing HRE, and the film layer has a thickness of 5 to 30 μm.

[0067] In a specific embodiment, in the Ce-RL1-TBM alloy powder, the content of Ce is 4-13wt%, the content of RL1 is 19-28wt%, the content of M is 0.1-2.0wt%, the content of B is 0.9-1.0wt%, and the balance is T.

[0068] In a specific embodiment, the method also includes: preparing Ce-RL1-TBM alloy sheets using a rapid solidification process, performing hydrogen crushing and fine-crushing treatment on the Ce-RL1-TBM alloy sheets to obtain the Ce-RL1-TBM alloy powder; the average particle size D50 of the Ce-RL1-TBM alloy powder is 3 to 5.5 μm.

[0069] In the present disclosure, the molding process, the sintering process, the diffusion process and the tempering process may be performed using conventional devices in the art.

[0070] In a preferred embodiment, the fine grinding is carried out in a jet mill, and the grinding pressure of the jet mill is 0.5 to 0.9 MPa.

[0071] In a specific embodiment, the molding process is an orientation molding process, and the orientation molding process is performed under the condition that the orientation magnetic induction intensity is 1.5 to 2.0 T;

[0072] The sintering temperature is 1010-1050°C and the holding time is 2-4 hours;

[0073] The temperature of the tempering treatment is 480-640° C., and the holding time is 1-4 hours.

[0074] The third aspect of the present invention provides a Ce-containing NdFeB magnet prepared by the method described in the second aspect of the present invention.

[0075] The present invention is further illustrated by the following examples, but the present invention is not limited thereto. The raw materials used in the examples can be obtained through commercial channels.

[0076] Example 1

[0077] S1. Prepare Ce-RL1-TBM alloy powders by the following steps:

[0078] Configuration by mass percentage wt% (PrNd) 25.6 Ce 5.6 Fe bal Co 0.3 Al 0.25 Cu 0.15 Ga 0.05 B 0.92 alloy raw materials, casting a quick-setting thin strip with the prepared alloy raw materials by a quick-setting process; wherein, the surface linear speed of the roller in the quick-setting process is 1.0-1.2 m / s, the casting temperature in the quick-setting process is 1480° C., and the thickness of the quick-setting thin strip is 0.1-0.6 mm; performing HD hydrogen explosion treatment on the quick-setting thin strip, dehydrogenating it at 540° C. for 6 hours after saturated hydrogen absorption, and the hydrogen content after dehydrogenation is 1200 ppm to obtain medium powder, and grinding the medium powder by a jet mill at a grinding pressure of 0.6 MPa to obtain a Ce-RL1-TBM alloy powder with an average particle size D50 of 4.5 μm;

[0079] S2. The obtained Ce-RL1-TBM alloy powder is subjected to molding and sintering treatments to obtain a base material alloy; wherein the molding treatment is an orientation molding treatment, and the orientation molding treatment is carried out under N2 gas protection and an orientation magnetic induction intensity of 1.8T; the sintering treatment temperature is 1030°C and the holding time is 1.5h.

[0080] S3. Process the base alloy into a sample with a thickness (orientation direction) of 4mm×9mm in length×9mm in width. Use Tb metal target to magnetron sputter the surface of the processed base alloy sample perpendicular to the magnetization direction, and then perform vacuum diffusion treatment and vacuum tempering treatment to obtain Ce-containing NdFeB magnet 1, recorded as CT-1. Among them, the magnetron sputtering treatment forms a Tb film layer on the surface of the substrate with an average thickness of 8μm; the diffusion treatment includes a first-stage diffusion treatment and a second-stage diffusion treatment, specifically, heating the base alloy containing a Tb film layer on the surface to the first-stage diffusion treatment under vacuum, the first-stage diffusion temperature is 830℃, the holding time is 4h, after the holding is completed, argon gas is introduced to cool to room temperature, and then vacuum heating is started to the second-stage diffusion treatment temperature, the second diffusion treatment temperature is 950℃, the holding time is 1.5h, after the holding is completed, argon gas is filled to cool. The specific tempering treatment process is as follows: the base alloy sample after diffusion treatment is heated to the tempering treatment temperature of 550°C under vacuum, kept at this temperature for 1 hour, filled with argon and cooled to room temperature to obtain Ce-containing NdFeB magnets.

[0081] Among them, the base alloy, the sample after the first stage diffusion treatment and the obtained magnet CT-1 were analyzed by SEM (scanning electron microscope), and the results were as follows: Figure 1 、 Figure 2 and Figure 4The observation surface is a cross section of the substrate or magnet parallel to the orientation direction of the magnet, and the cross section starts from the surface with the HRE film layer attached to it (i.e., the diffusion surface) among the multiple surfaces of the magnet / substrate. Figure 1 and Figure 2 The left side of the figure shows the diffusion surface of the substrate / magnet, Figure 4 , the top of the figure shows the diffusion surface of the substrate. Figure 5 The middle and right figures show schematic diagrams of the grain distribution in the surface area of ​​the base alloy after the first diffusion treatment and the magnet after the second diffusion treatment in Example 1.

[0082] Figure 1 (a) and (b), Figure 2 The 0-50 μm and 50-100 μm double arrows at the top of (a) and (b) respectively indicate the surface area less than 50 μm from the sample surface and the near-surface area 50-100 μm from the sample surface in the cross section. When calculating the distance to the sample surface, the original surface without the HRE film layer attached is used for calculation, and the HRE residual layer remaining on the sample surface after diffusion treatment is not included.

[0083] Depend on Figure 1 、 Figure 4 and Figure 5 It can be seen that after the first diffusion treatment, the grain size of the surface area of ​​the base alloy sample (0-50μm from the surface) is uniform, and almost all of them contain thin shell structure grains with a thickness of 0.5-2.0μm. The average grain size of all grains in the surface area is almost the same as that of the base grains. It can be seen that after the first stage diffusion heat treatment, there is almost no obvious grain growth and very few anti-shell grains; Figure 2 It can be seen that after the two-stage diffusion treatment and tempering treatment, only the surface area of ​​the base alloy has inverted shell grains and thick core-shell grains. The average grain size of all grains increases less than that of the base grains.

[0084] Example 2

[0085] Referring to the preparation method in Example 1, the difference from Example 1 is that in step S3, the temperature of the first stage diffusion treatment is 750° C. and the holding time is 1.5 h, to obtain a Ce-containing NdFeB magnet 2, which is recorded as CT-2.

[0086] Example 3

[0087] Referring to the preparation method in Example 1, the difference from Example 1 is that in step S3, the temperature of the first stage diffusion treatment is 890° C., and the holding time is 1.5 h, to obtain a Ce-containing NdFeB magnet 3, which is recorded as CT-3.

[0088] Example 4

[0089] S1. Prepare Ce-RL1-TBM alloy powders by the following steps:

[0090] In mass percentage wt% (PrNd) 19.5 Ce 11 Fe bal Co 0.3 Al 0.25 Cu 0.15 Ga 0.05 B 0.92 Alloy raw materials are prepared, and the prepared alloy raw materials are cast into a rapid-setting thin strip using a rapid-setting process; wherein, the surface linear speed of the roller in the rapid-setting process is 1 to 1.2 m / s, the casting temperature in the rapid-setting process is 1500° C., and the thickness of the rapid-setting thin strip is 0.1 to 0.6 mm; the rapid-setting thin strip is subjected to HD hydrogen explosion treatment, and after saturated hydrogen absorption, it is dehydrogenated at 540° C. for 6 hours, and the hydrogen content after dehydrogenation is 1200 ppm to obtain medium powder, and the medium powder is ground by a jet mill at a grinding pressure of 0.6 MPa to obtain a Ce-RL1-TBM alloy powder with an average particle size D50 of 4.5 μm;

[0091] S2. The obtained Ce-RL1-TBM alloy powder is subjected to molding and sintering treatments to obtain a base material alloy; wherein the molding treatment is an orientation molding treatment, and the orientation molding treatment is carried out under N2 gas protection and an orientation magnetic induction intensity of 1.8T; the sintering treatment temperature is 1030°C and the holding time is 1.5h.

[0092] S3. Process the base alloy into a sample with a thickness (in the orientation direction) of 4 mm × 9 mm in length × 9 mm in width. Use a slurry containing Dy metal powder to coat the surface of the base alloy, and then perform diffusion treatment and tempering treatment to obtain Ce-containing NdFeB magnet 4, which is recorded as CT-4. The average thickness of the Dy metal powder film formed on the surface of the base alloy is 20 μm, the average particle size of the Dy metal powder in the slurry is 4.5 μm, and the content is 80 wt%. The diffusion treatment includes a first-stage diffusion treatment and a second-stage diffusion treatment. The treatment temperature of the first-stage diffusion treatment is 830°C and the holding time is 4 hours. The treatment temperature of the second-stage diffusion treatment is 950°C and the holding time is 4.5 hours. The temperature of the tempering treatment is 550°C and the holding time is 1 hour.

[0093] Comparative Example 1

[0094] Referring to the preparation method in Example 1, the difference from Example 1 is that in step S3, the diffusion treatment temperature is 950° C. and the holding time is 1.5 h, and a Ce-containing NdFeB magnet is obtained, which is recorded as DCT-1.

[0095] Among them, the obtained magnet DCT-1 was subjected to SEM analysis, and the results were as follows: Figure 3 As shown, Figure 3 The arrows in (a) and (b) indicate the surface area and near-surface area of ​​the sample in the cross section, respectively, ranging from 0 to 50 μm and 50 to 100 μm.

[0096] Figure 5 The left figure shows the grain distribution in the surface area of ​​the magnet after the one-step diffusion treatment of Comparative Example 1. A large number of anti-shell grains (HRE accumulation inside the grains) and thick shell grains appear on the surface.

[0097] Depend on Figure 3 and Figure 5 It can be seen that after diffusion treatment at 950℃ for 1.5h and tempering treatment at 550℃ for 1h, the sample has a large number of anti-shell and thick-shell grains, and the average grain size of the grains is larger than that of the substrate. This shows that using only one-stage diffusion heat treatment is not conducive to inhibiting grain growth.

[0098] Comparative Example 2

[0099] Referring to the preparation method in Example 4, the difference from Example 4 is that in step S3, the diffusion treatment temperature is 950° C. and the holding time is 4.5 h, and a Ce-containing NdFeB magnet is obtained, which is recorded as DCT-2.

[0100] Test Case

[0101] The compositions of the Ce-containing NdFeB magnet samples prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were tested using an ICP composition analyzer. The results are listed in Table 1.

[0102] The microstructures of the base alloy, the base alloy after the first diffusion treatment, and the magnet sample after the second diffusion treatment were analyzed using SEM. The results are as follows: Figures 1 to 3 As shown, the observation surface is the cross section of the substrate or magnet parallel to the orientation direction;

[0103] The number, size, and distribution of grains in the substrate / magnet were tested using the following method and statistically analyzed using IPP (Image-ProPlus) image analysis software: for each substrate / magnet to be tested, five cross-sections as described above were randomly selected, and a 50 μm × 100 μm area with a magnification of 2000 times was randomly selected from each cross-section for observation, including a 50 μm × 50 μm surface area (the area 0 to 50 μm from the surface) and a 50 μm × 50 μm near-surface area (the area 50 to 100 μm from the surface). The heavy rare earth element content in the core and shell of the grains in the surface area of ​​the magnet and the shell thickness were analyzed and listed in Table 2. The types of grains in the surface area and near-surface area of ​​the magnet were also determined.

[0104] Figures 1 to 3The darker (black) contrast of the grain is the core, and the lighter (gray) contrast of the grain periphery is the shell. The shell thickness is the width of the shell between two adjacent grains. Red arrows show examples of inverted shell grains, yellow arrows show examples of thick shell grains, and blue arrows show examples of thin shell grains.

[0105] The number of thin-layer grains N1 in the 50μm×50μm surface region, the total number of magnet grains N in the surface region, the number of anti-shell grains N2 in the 50μm×50μm near-surface region, the number of thick-shell grains N3 in the near-surface region, and the total number of magnet grains N' in the near-surface region were counted in each cross-section. The average value of N1 / N and the average value of (N2+N3) / N' for multiple cross-sections were calculated and used as the N1 / N value and (N2+N3) / N' value of the magnet. The results are listed in Table 2. Incomplete grains in the region are also counted in the number of grains of the corresponding type.

[0106] The statistical results of the average grain size (1) of the surface area of ​​Ce-containing NdFeB magnets and the average grain size (2) of different grains were obtained by using IPP (Image-Pro Plus) image analysis software.

[0107] The magnetic property test results of the Ce-containing NdFeB magnets prepared in Examples 1 to 4 and Comparative Examples 1 to 2 are listed in Table 3.

[0108] Table 1 Composition of Ce-containing NdFeB magnets

[0109]

[0110]

[0111] Note: The average grain size (1) is the average of all grain sizes within the cross-sectional surface area (0 to 50 μm from the surface).

[0112] Table 2 Composition of different grains in Ce-containing NdFeB magnets

[0113]

[0114] Note: The average grain size (2) is the average value of the grain sizes of different main phases in the cross-sectional surface area (0-50 μm from the surface).

[0115] Table 3 Performance data of magnet materials

[0116] Magnet material Remanence Br / kGs <![CDATA[Coercive force H CJ / kOe]]> <![CDATA[H k / H CJ ]]> substrate 13.60 13.90 0.97 CT-1 13.40 20.15 0.96 CT-2 13.38 17.55 0.95 CT-3 13.32 19.23 0.93 CT-4 12.44 16.23 0.96 DCT-1 13.42 19.43 0.89 DCT-2 12.38 15.19 0.91

[0117] As can be seen from Table 3, the present disclosure adopts a graded diffusion process with different temperatures to diffuse the substrate alloy with a film layer containing HRE attached to the surface. The first stage diffusion treatment is carried out at a temperature of 750-890°C, which can effectively control the rate at which the HRE heavy rare earth elements in the film layer enter the interior of the substrate alloy, so that a large number of uniformly distributed thin shell grains can be formed in the surface area of ​​the substrate alloy (the surface of the Ce-containing NdFeB magnet and the cross-sectional area less than 50 μm from the surface); then, the substrate alloy after the first diffusion treatment is cooled and a second stage diffusion treatment is carried out at a temperature of 900-950°C, the HRE diffusion rate is increased, and more uniformly distributed thin shell grains are further formed in the surface area of ​​the magnet, and the shells of the formed thin shell grains are clearer. The large number of thin shell grains uniformly distributed in the surface area of ​​the magnet can effectively reduce the number of thick shell grains and anti-shell grains in the surface area and near-surface area of ​​the magnet, and can effectively reduce the content of HRE heavy rare earth elements in the surface area and near-surface area of ​​the magnet. At the same time, the graded diffusion process can effectively inhibit the generation and growth of anti-shell grains, reduce the grain size in the surface area and near-surface area of ​​the magnet, and is conducive to the uniform distribution of heavy rare earth elements in the magnet, reducing the content of heavy rare earth elements in the core of the grains. The Ce-containing NdFeB magnet prepared by the present invention has a high proportion of thin-shell grains in the surface area, and a low proportion of anti-shell grains and thick-shell grains in the near-surface area of ​​the magnet. The remanence of the Ce-containing NdFeB magnet provided by the present invention decreases less, and the coercive force and demagnetization curve squareness of the magnetic material are significantly improved, and it has excellent magnet performance.

[0118] Comparing Examples 2 and 3 with Example 1, it can be seen that controlling the temperature of the first-stage diffusion treatment within the preferred range of 810-850°C can further effectively control the rate at which the HRE heavy rare earth elements in the diffusion source enter the diffusion surface, further increase the number of thin-shell grains in the surface area of ​​the Ce-containing NdFeB magnet, make the shells of the formed thin-shell grains more uniform, and further reduce the number of anti-shell grains and thick-shell grains in the central area of ​​the magnet, thereby further improving the coercive force and squareness of the prepared magnet.

[0119] Comparing Comparative Example 1 with Example 1 and Comparative Example 2 with Example 4, it can be seen that when the coated substrate alloy is directly diffused at a high temperature of 950°C, Ce atoms in the main phase grains in the surface area of ​​the substrate alloy are easily replaced by HRE heavy rare earth atoms, and it is difficult to effectively control the rate at which Dy or Tb in the film layer enters the interior of the main phase grains, resulting in the heavy rare earth elements being easily enriched in the main phase grains, causing a large number of thick shell grains and anti-shell grains to appear in the surface area and near-surface area of ​​the magnet, and the average grain size of the anti-shell grains is large. As a result, although the coercive force of the magnet prepared in Comparative Example 1 is improved to a certain extent, the squareness of the demagnetization curve is significantly reduced. The coercive force and the squareness of the demagnetization curve of the magnet prepared in Comparative Example 2 are both significantly reduced.

[0120] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0121] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0122] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A Ce-containing NdFeB magnet, wherein: The Ce-containing NdFeB magnet comprises thin-shell grains, reverse-shell grains, and thick-shell grains; the HRE content of the core of the reverse-shell grains is higher than that of the shell; the HRE content of the shell of the thick-shell grains is higher than that of the core; the thickness of the shell of the reverse-shell grains and the thick-shell grains is respectively greater than 2 μm; the HRE content of the shell of the thin-shell grains is higher than that of the core, and the thickness of the shell of the thin-shell grains is less than 2 μm; The HRE is selected from Dy and / or Tb; In the surface region of the Ce-containing NdFeB magnet, the ratio N1 / N of the number N1 of the thin shell grains to the total number N of the Ce-containing NdFeB magnet grains is greater than 70%; In the near-surface region of the Ce-containing NdFeB magnet, the ratio (N2+N3) / N' of the sum of the number N2 of the reverse shell grains and the number N3 of the thick shell grains to the total number N' of the Ce-containing NdFeB magnet grains is less than 5%; The surface area includes the surface of the Ce-containing NdFeB magnet and an area less than 50 μm away from the surface, and the near-surface area includes an area 50 μm to 100 μm away from the surface of the Ce-containing NdFeB magnet.

2. The Ce-containing NdFeB magnet according to claim 1, wherein N1 / N is 82% or more.

3. The Ce-containing NdFeB magnet according to claim 1, wherein In the surface region of the Ce-containing NdFeB magnet, the average grain size of the thin shell grains is less than 5 μm; and the HRE content of the core portion of the thin shell grains is less than 2 wt %.

4. The Ce-containing NdFeB magnet according to claim 1, wherein In the surface region of the Ce-containing NdFeB magnet, the average grain size of the anti-shell grains is 5 to 10 μm; and the thickness of the shell portion of the anti-shell grains is 2 to 4 μm.

5. The Ce-containing NdFeB magnet according to claim 1, wherein In the surface region of the Ce-containing NdFeB magnet, the average grain size of the thick shell grains is 5 to 10 μm; and the thickness of the shell portion of the thick shell grains is 2 to 4 μm.

6. The Ce-containing NdFeB magnet according to claim 1, wherein The Ce-containing NdFeB magnet comprises RL, Ce, M, B, HRE and T, wherein the RL is selected from one or more elements of Nd, Pr, La, Y, Ho and Gd, and must include Nd and / or Pr, the M is selected from one or more elements of Al, Cu, Ga, Cr, Ti and Zr; T is Fe and / or Co; The Ce-containing NdFeB magnet has an RL content of 19-28wt%, a Ce content of 4-13wt%, an M content of 0.1-2.0wt%, a B content of 0.9-1.0wt%, a HRE content of 0.2-0.8wt%, and the balance of T.

7. A method for preparing a Ce-containing NdFeB magnet, wherein: The method includes: The Ce-RL1-TBM alloy powder is sequentially subjected to a molding process and a sintering process to obtain a base alloy, wherein the RL1 is selected from one or more elements selected from Nd, Pr, La, Y, Ho, Gd, Dy and Tb, and must include Nd and / or Pr, the M is selected from one or more elements selected from Al, Cu, Ga, Cr, Ti and Zr, and T is Fe and / or Co; Attaching a film layer containing HRE on the surface of the substrate alloy, wherein the HRE is selected from Dy and / or Tb; Performing diffusion treatment and tempering treatment on the base alloy with the HRE-containing film layer attached to the surface to obtain a Ce-containing NdFeB magnet; Wherein, the diffusion process includes a first-level diffusion process and a second-level diffusion process; The temperature of the first-stage diffusion treatment is 750-890° C., and the holding time is 1.5-4 hours; the temperature of the second-stage diffusion treatment is 900-950° C., and the holding time is 1.5-4.5 hours.

8. The method according to claim 7, wherein: The method further comprises: before the second-stage diffusion treatment, cooling the substrate alloy with the HRE-containing film layer attached to the surface.

9. The method according to claim 7, wherein: The temperature of the first stage diffusion treatment is 810-850°C.

10. The method according to claim 7, wherein: The method of attaching the HRE-containing film layer on the surface of the substrate alloy includes vacuum evaporation, magnetron sputtering, slurry coating, dipping, screen printing, roller coating or spraying to attach the diffusion source containing the HRE to the surface of the substrate alloy to form a film layer; the thickness of the film layer is 5 to 30 μm; The diffusion source is selected from one or more of metals, alloys or compounds containing HRE.

11. The method according to claim 7, wherein: In the Ce-RL1-TBM alloy powder, the content of Ce is 4-13wt%, the content of RL1 is 19-28wt%, the content of M is 0.1-2.0wt%, the content of B is 0.9-1.0wt%, and the balance is T.

12. The method according to claim 7, wherein: The method also includes: preparing Ce-RL1-TBM alloy sheets using a rapid solidification process, performing hydrogen crushing and fine grinding on the Ce-RL1-TBM alloy sheets to obtain the Ce-RL1-TBM alloy powder; the D50 particle size of the Ce-RL1-TBM alloy powder is 3 to 5.5 μm.

13. The method according to claim 7, wherein: The molding process is an orientation molding process, and the orientation molding process is carried out under the condition that the orientation magnetic induction intensity is 1.5 to 2.0 T; The temperature of the sintering treatment is 1010-1050° C., and the holding time is 2-6 hours; the temperature of the tempering treatment is 480-640° C., and the holding time is 1-4 hours.

14. A Ce-containing NdFeB magnet prepared by the method according to any one of claims 7 to 13.

Images