High-orientation-degree sintered neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention discloses a high-orientation-degree sintered neodymium-iron-boron magnet and a preparation method thereof, and belongs to the technical field of rare earth permanent magnet materials. The preparation method provided by the invention is divided into multiple times of profiling and multiple times of orientation, the densities of the first two times of profiling in the profiling process are low, and orientation is carried out in a magnetic field after pressing is completed, so that the situation that magnetic powder orientation is not uniform after traditional profiling orientation is completed can be avoided. Before formal orientation, pre-orientation can be carried out in an alternating-current oscillation magnetic field larger than 1 T, powder agglomeration can be reduced, magnetic powder is made to deflect in the orientation direction, and therefore orientation is more sufficient and even. The preparation method provided by the invention has low requirements on the characteristics of the magnetic powder, and a very high orientation degree can still be obtained under the condition that the magnetic powder is not added with a lubricant. Compared with a traditional technological process, the method has the advantages that the higher orientation degree can be obtained, and the residual magnetism of the sintered neodymium-iron-boron magnet is greatly improved. According to the invention, the production process is optimized, and the magnet performance is improved.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet materials technology, and specifically relates to a highly oriented sintered NdFeB magnet and its preparation method. Background Technology

[0002] Neodymium iron boron (Nd2Fe) 14 B) Since its independent discovery in 1984 by Sumitomo Special Metals of Japan and General Motors of the United States, permanent magnets have been known for their ultra-high magnetic energy product (( BH ) max ), high remanence ( B r ) and high coercivity ( H cj Neodymium iron boron (NdFeB) has rapidly become the core of modern permanent magnet materials. Its performance far surpasses that of traditional magnets (such as ferrite, AlNiCo, and SmCo), playing an irreplaceable role in fields such as new energy, electronic information, and medical equipment. However, with the continuous improvement of application demands, NdFeB research faces challenges such as breaking through theoretical limits, resource sustainability, and high-temperature stability, driving continuous innovation in materials science and preparation technologies.

[0003] Current methods for improving the remanence of sintered NdFeB magnets mainly include: increasing the volume fraction of the main phase, increasing the orientation degree of the main phase grains along the c-axis, increasing the relative density of the magnet, and reducing magnet oxidation. Several studies have been conducted to improve the orientation degree of sintered NdFeB magnets. For example, patent application CN115602439A, entitled "A Method for Improving the Remanence of NdFeB Magnetism," discloses a molding process that divides the molding orientation into three stages, with a single molding density of 3-3.3 g / cm³. 3 The density of the secondary molding is 3.5-3.8 g / cm³. 3 The density of the three-stage molding process is 4-4.5 g / cm³. 3 While this invention method can improve the orientation degree, the initial orientation forming density is relatively high, which is not conducive to obtaining a higher orientation degree. For example, the invention patent application with publication number CN102225465B entitled "An Orientation Method for Sintered NdFeB Powder" discloses an alternating current being passed through during the pressing orientation process to form an alternating oscillating magnetic field. During the orientation process, the NdFeB powder vibrates in the mold cavity, which greatly eliminates the agglomeration of NdFeB powder and improves the orientation degree of the magnet. However, its forming process is a one-time pressing and orientation process, which causes the magnetic powder to deflect along the non-orientation direction, resulting in a limited improvement in the orientation degree. Summary of the Invention

[0004] The purpose of this invention is to provide a high-orientation sintered NdFeB magnet and its preparation method, which can solve the problems of low powder flowability or powder agglomeration in the traditional pressing and orientation process, resulting in low orientation degree, as well as uneven magnetic powder orientation during the orientation process, thereby optimizing the production process and improving production efficiency.

[0005] The objective of this invention is achieved through the following technical solution: A method for preparing a highly oriented sintered NdFeB magnet includes the following steps: In a protective gas environment, neodymium iron boron powder is placed in a mold for the first pressing. After pressing, it is pre-oriented under an alternating oscillating magnetic field to obtain a preliminary billet. The preliminary billet is pressed a second time, and after pressing, it is oriented a second time and then demagnetized to obtain a secondary pressed billet. The secondary pressed billet is pressed a third time, and after pressing, it is oriented a third time and then demagnetized to obtain a rough billet. The density of the preliminary billet, the secondary pressed billet, and the rough billet increases sequentially. The rough blank can be subjected to cold isostatic treatment to obtain a green blank. The green (rough) blank is then subjected to sintering and tempering treatment to obtain a high-orientation sintered NdFeB magnet.

[0006] Preferably, the particle size of the NdFeB powder is 2-10 μm, and a certain proportion of lubricant may be added to the NdFeB magnetic powder.

[0007] Furthermore, the mold is made of a non-magnetic material, the inner wall surface of the mold is smooth, and the roughness can reach 0.8-1.6μm.

[0008] Furthermore, the protective gas is an inert gas, and the oxygen content in the protective gas environment is less than 500 ppm.

[0009] Furthermore, the density of the initial billet is 1.8-2.5 g / cm³. 3 The strength of the alternating oscillating magnetic field is ≥1 T; the density of the secondary pressed billet is 2.5-3.5 g / cm³. 3 The magnetic field strength for the second orientation is ≥1.8T; the density for the third pressing is ≥3.5 g / cm³. 3 The magnetic field strength of the third orientation is ≥2T.

[0010] Furthermore, the pressure of the cold isostatic pressing is ≥100 MPa.

[0011] Furthermore, the sintering temperature is 980-1100℃, and the time is ≥1 h.

[0012] Furthermore, the tempering process includes two tempering stages: the first tempering stage is at a temperature of 800-950℃ for 2-8 hours, and the second tempering stage is at a temperature of 400-600℃ for 2-8 hours.

[0013] The present invention also provides a highly oriented sintered NdFeB magnet, which is prepared by the preparation method described above.

[0014] Compared with the prior art, the beneficial effects of the present invention are: The preparation method provided by this invention involves multiple pressing and multiple orientation processes. During the pressing process, the first two pressing operations have low density, and orientation is performed in a magnetic field after pressing, avoiding the uneven magnetic powder orientation after traditional pressing and orientation. Before formal orientation, pre-orientation can be performed in an AC oscillating magnetic field greater than 1 T, reducing powder agglomeration and causing the magnetic powder to deflect along the orientation direction, resulting in more complete and uniform orientation. The preparation method of this invention does not have high requirements for magnetic powder properties and can still achieve a high degree of orientation even without the addition of lubricant. Compared with traditional processes, this invention can achieve a higher degree of orientation and significantly improve the remanence of sintered NdFeB magnets. This invention optimizes the production process and improves magnet performance. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the magnetic field forming orientation of the sintered NdFeB magnet provided by the present invention.

[0016] Figure 2 The XRD patterns are of the sintered NdFeB magnets prepared in Examples 1-6.

[0017] Figure 3 The XRD patterns are for the sintered NdFeB magnets prepared in Comparative Examples 1-3. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0019] Furthermore, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the art, and therefore will not be described in detail. All raw materials and reagents used in this invention are commercially available products.

[0020] Example 1 A method for preparing highly oriented sintered NdFeB magnets, referenced Figure 1 This includes the following steps: D of NdFeB powder 50 The material, with a thickness of 4.8 μm and without added lubricant, was pressed in an argon atmosphere with an oxygen content of 100 ppm using a smooth-walled 304 stainless steel mold. The density of the first pressing was 2.2 g / cm³. 3Then, along with the mold, it undergoes pre-orientation under a 1.5 T AC oscillating magnetic field; followed by a second pressing, with a pressing density of 3.0 g / cm³. 3 After pressing, the material is oriented under a 1.8 T pulsed magnetic field along with the mold, and then demagnetized; it is then pressed a third time, with a pressing density of 3.9 g / cm³. 3 After pressing, the material is oriented under a 2 T pulsed magnetic field along with the mold. After pressing and orientation, it is demolded and subjected to cold isostatic pressing at 160 MPa to obtain NdFeB green blanks. The green blanks are sintered at 1075℃ for 3 h, then tempered at 890℃ for 2.5 h and 490℃ for 6 h to obtain the target product.

[0021] Example 2 A method for preparing a highly oriented sintered NdFeB magnet includes the following steps: D of NdFeB powder 50 The material, with a thickness of 4.8 μm and without added lubricant, was pressed in an argon atmosphere with an oxygen content of 100 ppm using a smooth-walled 304 stainless steel mold. The density of the first pressing was 2.2 g / cm³. 3 Then, along with the mold, it undergoes pre-orientation under a 2T AC oscillating magnetic field; followed by a second pressing, with a pressing density of 3.0 g / cm³. 3 After pressing, the material was oriented under a 2.5 T pulsed magnetic field along with the mold, and then demagnetized; it was then pressed a third time, with a pressing density of 3.9 g / cm³. 3 After pressing, the material is oriented under a 2.5 T pulsed magnetic field along with the mold. After pressing and orientation, it is demolded and subjected to cold isostatic pressing at 160 MPa to obtain NdFeB green blanks. The green blanks are sintered at 1075℃ for 3 h, then tempered at 890℃ for 2.5 h and 490℃ for 6 h to obtain the target product.

[0022] Example 3 A method for preparing a highly oriented sintered NdFeB magnet includes the following steps: D of NdFeB powder 50 The material, with a thickness of 4.8 μm and without added lubricant, was pressed in an argon atmosphere with an oxygen content of 100 ppm using a smooth-walled 304 stainless steel mold. The density of the first pressing was 2.2 g / cm³. 3 Then, along with the mold, it undergoes pre-orientation under a 1.5 T AC oscillating magnetic field; followed by a second pressing, with a pressing density of 2.9 g / cm³. 3 After pressing, the material is oriented under a constant magnetic field of 1.8 T along with the mold, and then demagnetized; it is then pressed a third time to a density of 3.5 g / cm³. 3After pressing, the material is oriented under a constant magnetic field of 2 T along with the mold. After pressing and orientation, it is demolded and subjected to cold isostatic pressing at 160 MPa to obtain NdFeB green blanks. The green blanks are sintered at 1075℃ for 3 h, then tempered at 890℃ for 2.5 h and 490℃ for 6 h to obtain the target product.

[0023] Example 4 A method for preparing a highly oriented sintered NdFeB magnet includes the following steps: D of NdFeB powder 50 The material, with a thickness of 4.8 μm and without added lubricant, was pressed in an argon atmosphere with an oxygen content of 100 ppm using a smooth-walled 304 stainless steel mold. The density of the first pressing was 2.2 g / cm³. 3 Then, along with the mold, it undergoes pre-orientation under a 1.5 T AC oscillating magnetic field; followed by a second pressing, with a pressing density of 3.0 g / cm³. 3 After pressing, the material is oriented under a constant magnetic field of 1.8 T along with the mold, and then demagnetized; it is then pressed a third time, with a pressing density of 3.9 g / cm³. 3 After pressing, the material is oriented under a constant magnetic field of 2 T along with the mold; then it is demolded and subjected to cold isostatic pressing under a pressure of 160 MPa to obtain NdFeB green blanks. The green blanks are sintered at 1075℃ for 3 h, then tempered at 890℃ for 2.5 h, and then tempered at 490℃ for 6 h to obtain the target product.

[0024] Example 5 A method for preparing a highly oriented sintered NdFeB magnet includes the following steps: D of NdFeB powder 50 The particle size was 4.8 μm. 0.1% lubricant by mass was added to the magnetic powder and mixed thoroughly. The mixture was then pressed in an argon atmosphere with an oxygen content of 300 ppm using a smooth-walled 304 stainless steel mold. The density of the first pressing was 2.2 g / cm³. 3 Then, along with the mold, it undergoes pre-orientation under a 1.5 T AC oscillating magnetic field; followed by a second pressing, with a pressing density of 3.0 g / cm³. 3 After pressing, the material was oriented under a constant magnetic field of 1.8 T along with the mold, and then demagnetized; it was then pressed a third time, with a pressing density of 3.9 g / cm³. 3 After pressing, the material is oriented under a constant magnetic field of 2 T along with the mold. After pressing and orientation, it is demolded and subjected to cold isostatic pressing at 160 MPa to obtain NdFeB green blanks. The green blanks are sintered at 1075℃ for 3 h, then tempered at 890℃ for 2.5 h and 490℃ for 6 h to obtain the target product.

[0025] Example 6 A method for preparing a highly oriented sintered NdFeB magnet includes the following steps: D of NdFeB powder 50 The material, with a thickness of 4.8 μm and without added lubricant, was pressed in an argon atmosphere with an oxygen content of 100 ppm using a smooth-walled 304 stainless steel mold. The density of the first pressing was 2.2 g / cm³. 3 Then, along with the mold, it undergoes pre-orientation under a 1.5 T AC oscillating magnetic field; followed by a second pressing, with a pressing density of 3.0 g / cm³. 3 After pressing, the material is oriented under a constant magnetic field of 1.8 T along with the mold, and then demagnetized; it is then pressed a third time, with a pressing density of 3.9 g / cm³. 3 After pressing, the green body is oriented under a 2T constant magnetic field along with the mold; then it is demolded, and the demolded green body is oriented once under a 2T constant magnetic field. Cold isostatic pressing is not performed. The green body is sintered at 1075℃ for 3 h, then tempered at 890℃ for 2.5 h, and then tempered at 490℃ for 6 h to obtain the target product.

[0026] Comparative Example 1 The difference from Example 1 is that the sintered NdFeB magnet prepared in this case underwent only one pressing process during the forming and orientation process, resulting in a pressing density of 3.9 g / cm³. 3 The orientation is performed once under a 2 T constant magnetic field. All other processes are the same as in Example 1.

[0027] Comparative Example 2 The difference from Example 1 is that the sintered NdFeB magnet prepared in this example has a first pressing density of 3.1 g / cm³. 3 The density after the second pressing was 3.5 g / cm³. 3 All other processes are the same as in Example 1.

[0028] Comparative Example 3 The difference from Example 1 is that the sintered NdFeB magnets prepared were pressed into magnetic powder in an environment with an oxygen content greater than 500 ppm.

[0029] The sintered NdFeB magnets prepared in the above embodiments and comparative examples were tested, and the test results are shown in Table 1: Table 1

[0030] Note: The orientation degree in Table 1 was characterized and analyzed using X-ray diffraction (XRD) technology. The peak intensity ratio of the (006) peak to the (105) peak in the XRD pattern was used as the standard for judging the orientation degree. The XRD test results are shown in […]. Figure 2 and Figure 3 .

[0031] The results in Table 1 show that: As can be seen from Examples 1-6, the process steps selected in this invention can obtain sintered NdFeB magnets with high orientation and can significantly improve the remanence of the magnets.

[0032] As can be seen from Example 1 and Comparative Examples 1-2, the present invention, through multiple pressing and orientation processes, with lower density in the first two pressing stages, facilitates the deflection of magnetic powder along the orientation direction, resulting in more complete and uniform orientation. The process steps of the present invention are beneficial for improving the orientation degree and remanence of sintered NdFeB magnets.

[0033] As can be seen from Example 1 and Comparative Example 3, the molding process needs to be carried out in a low-oxygen environment. High oxygen content will cause some magnetic powder to oxidize, which will reduce the performance of the prepared magnet.

[0034] In summary, this invention, through process improvement, can enhance the orientation degree and remanence of sintered NdFeB magnets, and is convenient and easy to implement.

[0035] The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention are within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a highly oriented sintered NdFeB magnet, characterized in that, Includes the following steps: In a protective gas environment, neodymium iron boron powder is placed in a mold for the first pressing. After pressing, it is pre-oriented under an alternating oscillating magnetic field to obtain a preliminary blank. The preliminary blank is pressed a second time, and after pressing, it is oriented a second time and then demagnetized to obtain a secondary pressed blank. The secondary pressed blank is pressed a third time, and after pressing, it is oriented a third time to obtain a rough blank. The density of the preliminary blank, the secondary pressed blank, and the rough blank increases sequentially. The rough blank is sintered and tempered to obtain a high-orientation sintered NdFeB magnet.

2. The method for preparing a high-orientation sintered NdFeB magnet according to claim 1, characterized in that, The particle size of the neodymium iron boron powder is 2-10 μm.

3. The method for preparing a highly oriented sintered NdFeB magnet according to claim 1, characterized in that, The mold is made of non-magnetic material, and the surface roughness of the inner wall of the mold is 0.8-1.6μm.

4. The method for preparing a highly oriented sintered NdFeB magnet according to claim 1, characterized in that, The oxygen content in the protective gas environment is less than 500 ppm.

5. The method for preparing a high-orientation sintered NdFeB magnet according to claim 1, characterized in that, The density of the initial billet is 1.8-2.5 g / cm³. 3 The strength of the alternating oscillating magnetic field is ≥1T; the density of the secondary pressed billet is 2.5-3.5g / cm³. 3 The magnetic field strength for the second orientation is ≥1.8 T; the density for the third pressing is ≥3.5 g / cm³. 3 The magnetic field strength of the third orientation is ≥2 T.

6. The method for preparing a high-orientation sintered NdFeB magnet according to claim 1, characterized in that, Before sintering, the rough blank is subjected to cold isostatic pressing to form a green blank, which is then sintered; the pressure of the cold isostatic pressing is ≥100MPa.

7. The method for preparing a high-orientation sintered NdFeB magnet according to claim 1, characterized in that, The sintering temperature is 980-1100℃, and the time is ≥1 h.

8. The method for preparing a highly oriented sintered NdFeB magnet according to claim 1, characterized in that, The tempering process includes two stages of tempering: the first stage of tempering is at a temperature of 800-950℃ for 2-8 hours, and the second stage of tempering is at a temperature of 400-600℃ for 2-8 hours.

9. The method for preparing a highly oriented sintered NdFeB magnet according to any one of claims 1 to 8, characterized in that, A lubricant is added to the neodymium iron boron magnetic powder.

10. A highly oriented sintered NdFeB magnet, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 9.

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