A high remanence high coercivity magnet and method of making same

Abstract

The present application discloses a neodymium-iron-boron-based magnet, the neodymium-iron-boron-based magnet comprises R2T 14 B main phase crystal grains and grain boundary phases, the neodymium-iron-boron-based magnet has R2T 14 B main phase crystal grains surface layer has a heavy rare earth shell layer, the neodymium-iron-boron-based magnet comprises the following components: R: 28-32wt%, B: 0.85-0.94wt%, Co: 0.4-2wt%, Cu: 0.1-0.8wt%, Ga: 0.1-0.3wt%, Al: 0.05-0.5wt%, M1: 0.4-1.0wt%, wherein M1 is selected from one or two of elements Ti, Zr, Nb, W, V, Fe: 63-69wt%; wherein, R is a rare earth element, R at least includes PrNd and R H , R H is a heavy rare earth element, R H is selected from one or two of Dy and Tb; wherein, the area of all grain boundary phases in the cross section of the neodymium-iron-boron-based magnet within the region 0.1-100 μm from the surface of the magnet accounts for 5.2-7.5% of the total area of the cross section.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of magnetic materials. More particularly, the present application relates to a high remanence high coercivity magnet and a preparation method thereof. BACKGROUND

[0002] Since the advent of rare earth magnetic materials, due to its good magnetic properties, it is widely used in energy, transportation, machinery, medical household appliances and other industries, and its products also involve many fields of the national economy. As a rare earth magnetic material, neodymium iron boron sintered magnet is one of the most important permanent magnets. Since many applications of neodymium iron boron sintered magnet are in high temperature environment, it is required not only to have high remanence, but also to have high coercivity. Among them, coercivity is the main parameter of permanent magnet material, the higher the coercivity, the stronger the anti-demagnetization ability. In application, not only is it required that the coercivity of neodymium iron boron sintered magnet is higher, but also it is required to ensure that it has good temperature stability, so that it can work at high temperature.

[0003] Common methods for improving the coercivity of neodymium iron boron sintered magnet include replacing Nd with heavy rare earth elements Dy and Tb to improve its coercivity. One of the common methods is to add heavy rare earth elements Dy, Tb, Ho, etc. to the magnet by grain boundary diffusion, that is, to arrange heavy rare earth elements on the surface of the magnet, and to diffuse the heavy rare earth elements into the magnet by using the concentration difference between the surface and the interior of the magnet as the diffusion driving force. The neodymium iron boron magnet prepared by grain boundary diffusion method has excellent comprehensive magnetic properties and consumes a small amount of heavy rare earth. However, the reserves of heavy rare earth Dy and Tb are scarce, and the price is high, and at the same time, the remanence of the magnet will be reduced. Therefore, under the condition of reducing the addition of heavy rare earth, how to obtain a rare earth permanent magnet diffusion alloy with good remanence, coercivity and squareness consistency is a problem to be solved in the field.

[0004] At present, the research direction of the magnet produced by the grain boundary diffusion process is more focused on the diffusion depth of heavy rare earth elements. By improving the diffusion depth, the heavy rare earth elements penetrate into the interior of the magnet, improve the diffusion efficiency, and improve the coercivity of the magnet. However, when the diffusion depth reaches the limit, the difficulty of further improving the diffusion depth is greatly improved, and the effect of improving the diffusion depth on the performance is not ideal. Based on the above problems, the present application aims to explore a new dimension to improve the diffusion effect and solve the problem of limited diffusion performance improvement, so as to obtain a high remanence high coercivity magnet. SUMMARY

[0005] In order to at least solve one or more technical problems as mentioned above, the present application proposes an improved scheme for the prior art in multiple aspects.

[0006] According to one aspect of the present application, the present application provides a Nd-Fe-B based magnet, the Nd-Fe-B based magnet comprising R2T 14 The Nd-Fe-B based magnet has heavy rare earth shell layers in the main phase crystal grains in the region 0.1-100 μm away from the surface of the magnet, and comprises the following components:

[0007] R: 28-32 wt%,

[0008] B: 0.85-0.94 wt%,

[0009] Co: 0.4-2 wt%,

[0010] Cu: 0.1-0.8 wt%,

[0011] Ga: 0.1-0.3 wt%,

[0012] Al: 0.05-0.5 wt%,

[0013] M1: 0.4-1.0 wt%, wherein M1 is selected from one or two of the elements Ti, Zr, Nb, W, and V,

[0014] Fe: 63-69 wt%,

[0015] wherein R is a rare earth element, R at least includes PrNd and R H , R H is a heavy rare earth element, selected from one or two of Dy and Tb;

[0016] wherein the percentage of the area of all grain boundary phases in the cross section of the region 0.1-100 μm away from the surface of the magnet to the total area of the cross section is 5.2-7.5%.

[0017] According to one embodiment of the present application, the content of R is 29-32 wt%, and the distribution of the grain boundary phases in the central part of the magnet satisfies the following condition: the percentage of the area of all grain boundary phases in the cross section of the central part of the magnet to the total area of the cross section is 4.2-6.1%.

[0018] According to one embodiment of the present application, M1 at least contains one of Ti and Zr.

[0019] According to one embodiment of the present application, the composition of the Nd-Fe-B based magnet comprises at least one of the following features:

[0020] b. Cu: 0.1-0.3 wt%,

[0021] c. Ti: 0.15-0.3 wt%,

[0022] d. Co: 0.7-1.5 wt%,

[0023] e. R H : 0.3-2 wt%.

[0024] According to one embodiment of the present application, the grain boundary phase comprises R6T 13 M1 phase, the cross section of the neodymium-iron-boron based magnet within a region 0.1-100 μm from the surface of the magnet, the percentage of the area of all R6T 13 M1 phase in the total area of the cross section is 5.2-6.0%.

[0025] According to one embodiment of the present application, the R6T 13 M1 phase in the center of the magnet satisfies the following condition: the percentage of the area of all R6T 13 M1 phase in the total area of the cross section is 4.2-5.0%.

[0026] According to one embodiment of the present application, the heavy rare earth element content of the heavy rare earth shell layer within a region 0.1-100 μm from the surface of the magnet is 1.0-4.5 at%.

[0027] According to another aspect of the present application, the present application provides a method for preparing a neodymium-iron-boron based magnet, comprising:

[0028] 1) using a rapid solidification process to prepare a rapidly solidified alloy sheet from a predetermined configuration of raw alloy;

[0029] 2) hydrogen-pulverizing the rapidly solidified alloy sheet obtained in step 1) and adding an additive to obtain an alloy powder after air-jet milling, the average particle size D50 of the alloy powder being 2-5 μm;

[0030] 3) pressing the alloy powder obtained in step 2) into a compact under the orientation of a magnetic field, the magnetic field strength being 1.8-2.5 T, to obtain a compact;

[0031] 4) placing the compact obtained in step 3) into a sintering furnace and performing a sintering treatment in a vacuum or an inert atmosphere, to finally obtain a neodymium-iron-boron magnet substrate;

[0032] 5) coating the surface of the magnet substrate obtained in step 4) with a diffusion source containing a heavy rare earth element, and performing a tempering treatment on the neodymium-iron-boron magnet, to obtain a neodymium-iron-boron based magnet;

[0033] The tempering treatment process is a three-stage process: the first stage tempering temperature is 870-970 °C, the holding time is 2-20 h, the second stage tempering temperature is 380-580 °C, the holding time is 1-10 h, and the third stage tempering temperature is 620-670 °C, the holding time is 1-10 h.

[0034] According to one embodiment of the present application, in the step 5), the tempering process comprises: the first tempering temperature is 870-940 DEG C, the holding time is 2-10 h, the second tempering temperature is 420-570 DEG C, the holding time is 1-10 h, and the third tempering temperature is 630-670 DEG C, and the holding time is 1-6 h.

[0035] According to one embodiment of the present application, in the step 5), the tempering process comprises: the second tempering and the third tempering are further followed by a quenching process, the cooling rate is 5-10 DEG C / min, and the cooling temperature is 100-300 DEG C.

[0036] According to one embodiment of the present application, in the step 4), the sintering process comprises: the sintering temperature is 1030-1120 DEG C, and the time is 1-10 h, preferably 6-10 h.

[0037] According to one embodiment of the present application, in the step 5), before the tempering process, the coated magnet substrate is subjected to a diffusion process.

[0038] According to one embodiment of the present application, the diffusion temperature of the diffusion process is 870-940 DEG C, and the time is 4-20 h.

[0039] The technical scheme of the embodiments of the present application controls the lower B content and the higher content of Ti, Zr and other high melting point metal elements in the substrate, reasonably controls the ratio relationship between the high melting point elements and the Ga element, and adjusts the adding proportion of the Cu element, so as to reduce the hindering effect of the M1B compound formed by the higher melting point element on the diffusion of the heavy rare earth, improve the area proportion of the grain boundary phase of the magnet obtained after the diffusion process, and obtain a neodymium-iron-boron system magnet with high remanence and high coercivity. BRIEF DESCRIPTION OF DRAWINGS

[0040] The above and other objects, features and advantages of the exemplary embodiments of the present application will be more apparent from the following detailed description read in conjunction with the accompanying drawings, in which several embodiments of the present application are shown by way of example, and wherein like reference numerals refer to like elements or parts throughout. In the drawings:

[0041] Figure 1 A scanning electron microscope photo of a section of the magnet of Example 1 of the present application, which is 0.1-100 μm away from the surface of the magnet, is shown.

[0042] Figure 2 A scanning electron microscope photo of a section of the magnet of Comparative Example 1 of the present application, which is 0.1-100 μm away from the surface of the magnet, is shown.

[0043] Figure 3A scanning electron microscope photograph of a center portion cross section of the magnet of Example 1 of the present application is shown.

[0044] Figure 4 A scanning electron microscope photograph of a center portion cross section of the magnet of Comparative Example 1 of the present application is shown. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be apparently and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative work fall within the scope of protection of the present application.

[0046] It should be understood that the terms "comprise" and "include" used in the specification and claims of the present application indicate the presence of the described features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0047] It should also be understood that the terms used in the specification of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. As used in the specification and claims of the present application, the singular forms "a", "an" and "the" are intended to include the plural forms, unless the context clearly indicates otherwise. It should be further understood that the term "and / or" used in the specification and claims of the present application means any combination of one or more of the associated listed items and all possible combinations thereof, and includes these combinations.

[0048] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings, and the materials, reagents and equipment used in the embodiments of the present application are all obtained from conventional market channels unless otherwise specified.

[0049] Specifically, the present application provides a neodymium-iron-boron-based magnet, wherein the neodymium-iron-boron-based magnet comprises R2T 14 B main phase grains and a grain boundary phase, the neodymium-iron-boron-based magnet has R2T 14 B main phase grain surface layer has a heavy rare earth shell layer, and the neodymium-iron-boron-based magnet comprises the following components:

[0050] R: 28-32 wt%,

[0051] B: 0.85-0.94 wt%,

[0052] Co: 0.4-2 wt%,

[0053] Cu: 0.1-0.8 wt%,

[0054] Ga: 0.1-0.3wt%,

[0055] Al: 0.05-0.5wt%,

[0056] M1: 0.4-1.0wt%, wherein M1 is selected from one or two of elements Ti, Zr, Nb, W, V,

[0057] Fe: 63-69wt%;

[0058] wherein R is a rare earth element, R at least includes PrNd and R H , R H is a heavy rare earth element, selected from one or two of Dy and Tb;

[0059] The percentage of the area of all grain boundary phases in the cross section within the region 0.1-100 μm away from the surface of the magnet to the total area of the cross section is 5.2-7.5%.

[0060] Illustratively, the percentage of the area of all grain boundary phases in the cross section within the region 0.1-100 μm away from the surface of the magnet to the total area of the cross section can be 5.2%, 5.8%, 6.0%, 6.2%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5% or any value within the range consisting of any of the above values.

[0061] The technical solution of the embodiments of the present application is under the condition of low B addition amount of neodymium-iron-boron magnet raw material system, and the Ga element addition amount in the base material is controlled at a low level. High content of Ti, Zr and other high melting point metal elements are added. The addition of high content of high melting point metal elements is beneficial to refining the grain and improving the intrinsic coercivity of the magnet, but is not conducive to the improvement of the remanence of the magnet. At the same time, in the process of diffusing heavy rare earth, the remanence of the magnet will inevitably further decrease, and the high melting point metal elements hinder the diffusion. However, by reasonably regulating the relationship between the high melting point elements and the Ga element, adjusting the addition proportion of the Cu element, combining the diffusion and tempering process, and precisely adjusting the area proportion of the grain boundary phase, the distribution of the grain boundary phase and the element distribution in the grain boundary phase, a neodymium-iron-boron magnet with high remanence and high coercivity is prepared.

[0062] In some embodiments, the content of R is 29-32wt%. Illustratively, the content of R can be 29.0wt%, 29.5wt%, 30.0wt%, 30.5wt%, 31.0wt%, 31.5wt%, 32.0wt% or any value within the range consisting of any of the above values.

[0063] In some embodiments, the distribution of the grain boundary phase in the center portion of the magnet satisfies the following condition: the percentage of the total area of the grain boundary phase in the cross section of the center portion of the magnet to the total area of the cross section is 4.2-6.1%. Illustratively, the percentage of the total area of the grain boundary phase in the cross section of the center portion of the magnet to the total area of the cross section can be 4.2%, 4.5%, 5.0%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, or any value within a range between any of the foregoing.

[0064] In some embodiments, M1 contains at least one of Ti and Zr.

[0065] In some embodiments, the composition of the Nd-Fe-B based magnet comprises B: 0.85-0.94 wt%. Illustratively, the content of B can be 0.85 wt%, 0.86 wt%, 0.87 wt%, 0.88 wt%, 0.89 wt%, 0.90 wt%, 0.91 wt%, 0.92 wt%, 0.93 wt%, 0.94 wt%, or any value within a range between any of the foregoing.

[0066] In some embodiments, the composition of the Nd-Fe-B based magnet comprises Cu: 0.1-0.3 wt%. Illustratively, the content of Cu can be 0.10 wt%, 0.12 wt%, 0.15 wt%, 0.18 wt%, 0.20 wt%, 0.22 wt%, 0.25 wt%, 0.28 wt%, 0.30 wt%, or any value within a range between any of the foregoing.

[0067] In some embodiments, the composition of the Nd-Fe-B based magnet comprises Ti: 0.15-0.3 wt%. Illustratively, the content of Ti can be 0.15 wt%, 0.18 wt%, 0.20 wt%, 0.22 wt%, 0.25 wt%, 0.28 wt%, 0.30 wt%, or any value within a range between any of the foregoing.

[0068] In some embodiments, the composition of the Nd-Fe-B based magnet comprises Co: 0.7-1.5 wt%. Illustratively, the content of Co can be 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, or any value within a range between any of the foregoing.

[0069] In some embodiments, the composition of the Nd-Fe-B based magnet comprises R H : 0.3-2 wt%, R HR is a heavy rare earth element selected from one or both of Dy and Tb. Illustratively, R H may be 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, or any value within a range defined by any of the foregoing.

[0070] In some embodiments, the atomic ratio of Al / Ga = 1.2-2, and the atomic ratio of Zr / Ga = 1.5-2. Ga is within the above range, which can reasonably improve the intrinsic coercivity of the magnet, while avoiding the cost increase caused by excessive addition.

[0071] In some embodiments, the grain boundary phase includes R6T 13 M1 phase, the R6T 13 M1 phase within a region 0.1-100 μm from the surface of the magnet satisfies the following condition: the area percentage of all R6T 13 M1 phase in the cross section of the magnet within a region 0.1-100 μm from the surface of the magnet is 5.2-6.0%. Illustratively, the area percentage of all R6T 13 M1 phase in the cross section of the magnet within a region 0.1-100 μm from the surface of the magnet can be 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, or any value within a range defined by any of the foregoing.

[0072] The R6T 13 M1 phase is shown as a gray grain boundary phase in a microstructure cross-sectional photograph, wherein the atomic percentage of rare earth element R is 20%-31%, and the R6T 13 M1 phase includes T element, the atomic percentage of T is 60%-75%, and the T element includes Fe and / or Co, and M is selected from one or more of Al, Cu, Ga, Ti, Sn, Zr, and Nb.

[0073] The central portion of the magnet refers to a region having a distance of 500 μm or more from the surface of the magnet.

[0074] In some embodiments, the R6T 13 M1 phase within the central portion of the magnet satisfies the following condition: the area percentage of all R6T 13 M1 phase in the cross section of the magnet within the central portion of the magnet is 4.2-5.0%. Illustratively, the area percentage of all R6T13 The area percentage of the M1 phase in the total cross-sectional area can be 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, or any value within a range defined by any of the above values.

[0075] In some embodiments, R2T 14 The B main phase grain surface layer has a heavy rare earth shell layer, and the content of heavy rare earth elements in the heavy rare earth shell layer in the region 0.1-100 μm away from the surface of the magnet is 1.0-4.5 at%. Illustratively, the content of heavy rare earth elements in the heavy rare earth shell layer in the region 0.1-100 μm away from the surface of the magnet can be 1.0 at%, 1.5 at%, 2.0 at%, 2.5 at%, 3.0 at%, 3.5 at%, 4.0 at%, 4.5 at%, or any value within a range defined by any of the above values.

[0076] The application also provides a preparation method of a neodymium-iron-boron-based magnet, comprising:

[0077] 1) Using a rapid solidification process to make a rapid solidification alloy sheet from a predetermined configuration of raw material alloy;

[0078] 2) After hydrogen pulverization and addition of additives, the rapid solidification alloy sheet obtained in step 1) is subjected to air jet milling to obtain an alloy powder, and the average particle size D50 of the alloy powder is 2-5 μm;

[0079] 3) The alloy powder obtained in step 2) is pressed into a compact under the orientation of a magnetic field with a magnetic field strength of 1.8-2.5 T to obtain a green compact;

[0080] 4) The green compact obtained in step 3) is placed in a sintering furnace for sintering treatment in a vacuum or inert atmosphere to finally obtain a neodymium-iron-boron magnet base material;

[0081] 5) The surface of the magnet base material obtained in step 4) is coated with a diffusion source containing heavy rare earth elements, and the neodymium-iron-boron magnet is subjected to tempering treatment to obtain a neodymium-iron-boron-based magnet;

[0082] The tempering treatment process is a three-stage process: the first-stage tempering temperature is 870-970 °C, the holding time is 2-20 h, the second-stage tempering temperature is 380-580 °C, the holding time is 1-10 h, and the third-stage tempering temperature is 620-670 °C, and the holding time is 1-10 h.

[0083] According to the description of the prior art (CN111312463), when the B content in the base material is less than 0.95 wt%, for example, 0.84-0.94 wt%, high M1 elements are easy to form M1B compounds at the grain boundaries of the triangular region. During the diffusion of heavy rare earth elements, M1B compounds hinder the diffusion of heavy rare earth elements, affecting the diffusion depth.

[0084] After discovering the above problems, the inventors proposed a process to improve the grain boundary phase area ratio of the magnet, i.e., not tempering after sintering, coating heavy rare earth, and then performing a three-stage tempering process, to precisely control the generation of grain boundary phases in the magnet. The lower temperature of the second tempering and the higher temperature of the third tempering make the main phase grain edges participate in the reaction and promote the consistency of the intergranular reaction in the magnet. Finally, by using the above three-stage tempering process, more liquid phase is generated in the surface region (0.1-100 μm) of the magnet, and more uniform R6T 13 M1 phase, and at the same time, due to the participation of part of the main phase in the reaction, the uniformity of the heavy rare earth shell layer of the magnet is also adjusted. A more uniform shell layer helps to improve the demagnetization consistency of the magnet, thereby preparing a magnet with high remanence and high coercivity.

[0085] In some embodiments, in step 1), the composition ratio of the pre-determined configuration of the raw alloy is according to the composition ratio of the neodymium-iron-boron magnet substrate.

[0086] The composition ratio of the neodymium-iron-boron magnet substrate ranges from:

[0087] Re: 28-32 wt%,

[0088] B: 0.85-0.94 wt%,

[0089] Co: 0.4-2 wt%,

[0090] Cu: 0.1-0.8 wt%,

[0091] Ga: 0.1-0.3 wt%,

[0092] Al: 0.05-0.5 wt%,

[0093] M1: 0.4-1.0 wt%, wherein M1 is selected from one or two of the elements Ti, Zr, Nb, W, and V,

[0094] Fe: 63-69 wt%.

[0095] In some embodiments, in step 5), the diffusion source containing heavy rare earth elements includes a heavy rare earth compound or a heavy rare earth alloy. The heavy rare earth compound is preferably a fluoride or hydride of heavy rare earth, and the heavy rare earth alloy is preferably an alloy of heavy rare earth and transition metal (such as Ti, Co, Ni), low-melting-point metal (such as Al, Cu, Ga).

[0096] In some embodiments, in the three-stage tempering process, the first stage tempering temperature is 870-970 °C, and the holding time is 2-20 h. Preferably, the first stage tempering temperature is 870-940 °C, and the holding time is 2-10 h. Illustratively, the first stage tempering temperature is 870 °C, 880 °C, 890 °C, 900 °C, 910 °C, 920 °C, 930 °C, 940 °C, or any value within a range formed by any of the foregoing. Illustratively, the first stage tempering holding time is 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h, 10 h, or any value within a range formed by any of the foregoing.

[0097] In some embodiments, in the three-stage tempering process, the second stage tempering temperature is 380-580 °C, and the holding time is 1-10 h. Preferably, the second stage tempering temperature is 420-570 °C, and the holding time is 2-10 h. Illustratively, the second stage tempering temperature is 420 °C, 430 °C, 440 °C, 450 °C, 460 °C, 485 °C, 500 °C, 515 °C, 535 °C, 550 °C, 570 °C, or any value within a range formed by any of the foregoing. Illustratively, the second stage tempering holding time is 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or any value within a range formed by any of the foregoing.

[0098] In some embodiments, in the three-stage tempering process, the third stage tempering temperature is 620-670 °C, and the holding time is 1-10 h. Preferably, the third stage tempering temperature is 630-670 °C, and the holding time is 1-6 h. Illustratively, the third stage tempering temperature is 630 °C, 635 °C, 640 °C, 645 °C, 650 °C, 655 °C, 660 °C, 665 °C, 670 °C, or any value within a range formed by any of the foregoing. Illustratively, the third stage tempering holding time is 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, or any value within a range formed by any of the foregoing.

[0099] In some embodiments, in the step 5), the tempering process comprises: between the second stage tempering and the third stage tempering, there is a quenching process, the cooling rate is 5-10 ℃ / min, and the cooling temperature is 100-300 ℃. Illustratively, the cooling rate of the quenching process is 5 ℃ / min, 5.5 ℃ / min, 6 ℃ / min, 6.5 ℃ / min, 7 ℃ / min, 7.5 ℃ / min, 8 ℃ / min, 8.5 ℃ / min, 9 ℃ / min, 9.5 ℃ / min, 10 ℃ / min, or any value within the range consisting of any of the aforementioned values. Illustratively, the cooling temperature of the quenching process is 100 ℃, 120 ℃, 150 ℃, 180 ℃, 200 ℃, 220 ℃, 250 ℃, 280 ℃, 300 ℃, or any value within the range consisting of any of the aforementioned values.

[0100] In some embodiments, in the step 4), the process parameters of the sintering process comprise: the sintering temperature is 1030-1120 ℃, and the time is 1-10 h, preferably 6-10 h. Illustratively, the sintering temperature is 1030 ℃, 1040 ℃, 1050 ℃, 1060 ℃, 1070 ℃, 1080 ℃, 1090 ℃, 1100 ℃, 1110 ℃, 1120 ℃, or any value within the range consisting of any of the aforementioned values. Illustratively, the sintering time is 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h, 10 h, or any value within the range consisting of any of the aforementioned values. Specific embodiments

[0102] Embodiment 1

[0103] Magnet base material formula:

[0104]

[0105] 1) The raw alloy prepared according to the above formula is cast into a rapid solidification alloy sheet by a rapid solidification process;

[0106] 2) The rapid solidification alloy sheet obtained in step 1) is subjected to hydrogen decrepitation and micro-pulverization respectively to obtain a raw alloy powder; wherein the hydrogen decrepitation has a hydrogen absorption pressure of 0.3 MPa and a dehydrogenation temperature of 560 ℃; the micro-pulverization is carried out in an air flow mill, and the grinding pressure of the air flow mill is 0.68 MPa; the average particle size D50 of the raw alloy powder is 4 μm;

[0107] 3) The raw alloy powder obtained in step 2) is pressed into a green body under the orientation of a magnetic field, and the magnetic field strength is 1.8 T;

[0108] 4) The green body obtained in step 3) is placed in a sintering furnace for sintering treatment in a vacuum or inert atmosphere to obtain a neodymium-iron-boron magnet base material;

[0109] 5) The surface of the magnet substrate obtained in step 4) is coated with a diffusion source containing heavy rare earth element Tb (the diffusion source is specifically TbH2), and the coated Nd-Fe-B magnet substrate is tempered to obtain a Nd-Fe-B magnet.

[0110] The tempering process described above adopts a three-stage tempering process:

[0111] The first-stage tempering temperature is 890°C, the holding time is 4h; the second-stage tempering temperature is 500°C, the holding time is 8h; and the third-stage tempering temperature is 630°C, the holding time is 5h.

[0112] Example 2

[0113] Magnet substrate formula:

[0114]

[0115] Different from the preparation method of Example 1, in the three-stage tempering process, the first-stage tempering temperature is 870°C, the holding time is 6h, the second-stage tempering temperature is 430°C, the holding time is 9h, and the third-stage tempering temperature is 640°C, the holding time is 5h; and the other steps are the same as those of Example 1.

[0116] Example 3

[0117] Magnet substrate formula:

[0118]

[0119] Different from the preparation method of Example 1,

[0120] Step 5): The surface of the magnet substrate obtained in step 4) is coated with a diffusion source of hydridized dysprosium, and the coated Nd-Fe-B magnet substrate is subjected to diffusion treatment at a diffusion temperature of 880°C for a diffusion time of 6h; and the diffused magnet is subjected to three-stage tempering. The other steps are the same as those of Example 1.

[0121] In the three-stage tempering process, the first-stage tempering temperature is 870°C, the holding time is 2h, the second-stage tempering temperature is 580°C, the holding time is 4h, and the third-stage tempering temperature is 640°C, the holding time is 5h.

[0122] Comparative Example 1

[0123] Different from Example 1 is only the formula of the magnet substrate, and the other steps are the same as those of Example 1.

[0124] Magnet substrate formula:

[0125]

[0126] Comparative Example 2

[0127] The same magnet formulation as in Example 1 was used, except that the preparation steps other than the diffusion treatment / tempering treatment process were the same as in Example 1.

[0128] The only difference is that step 5) uses a conventional diffusion and tempering process, the diffusion temperature is 800℃, the diffusion time is 10h, the tempering temperature is 550℃, and the tempering time is 8h, to obtain a neodymium-iron-boron-based magnet.

[0129] The test methods used in this application are as follows:

[0130] Microstructure testing method:

[0131] The scanning electron microscope test is performed on any 10 or more cross sections of the magnet perpendicular to the diffusion direction, the area of all grain boundary phases in each cross section is counted, the percentage of the area of all grain boundary phases in the total area of the cross section in each cross section is calculated, and then the average value of the percentages of all cross sections is obtained as the percentage of the area of all grain boundary phases in the total area of the cross section of the neodymium-iron-boron-based magnet; the size of the observation area is, for example, 40μm×40μm and 75μm×75μm; the magnification is 2000-5000 times.

[0132] In a similar manner, the percentage of the area of all grain boundary phases in the total area of the cross section in the 0.1-100μm region from the surface of the magnet, the percentage of the area of all R6T 13 M1 phases in the total area of the cross section in the 0.1-100μm region from the surface of the magnet, the percentage of the area of all grain boundary phases in the total area of the cross section in the center part of the magnet, the percentage of the area of all R6T 13 M1 phases in the total area of the cross section in the center part of the magnet, etc. are obtained. As shown in Figures 1-4 , the triangular area marked with o represents R6T 13 M1 phase.

[0133] EDS energy spectrum analysis is used to test the atomic percentage of each element in the grain boundary phase of the neodymium-iron-boron-based magnet, and element data at each depth of the magnet is obtained.

[0134] The sample size is 35.5*26*3.6mm, and the test is performed using a pulse hysteresis loop measuring instrument.

[0135] The magnetic property test data of Example 1 and Comparative Example 1 are as follows:

[0136]

[0137] The microstructure test results of Example 1 and Comparative Example 1 are as follows:

[0138] Example 1:

[0139] According to the experimental data of Example 1, the percentage of the area of all grain boundary phases in the cross section within the region 0.1-100 μm from the surface of the magnet to the total area of the cross section is 6.75%; the percentage of the area of all R6T 13 The percentage of the area of M1 phase to the total area of the cross section is 5.5%.

[0140] The percentage of the area of all grain boundary phases in the cross section at the center of the magnet to the total area of the cross section is 5.4%; the percentage of the area of all R6T 13 The percentage of the area of M1 phase to the total area of the cross section is 4.37%.

[0141] Comparative Example 1:

[0142] According to the experimental data of Comparative Example 1, the percentage of the area of all grain boundary phases in the cross section within the region 0.1-100 μm from the surface of the magnet to the total area of the cross section is 5.1%; the percentage of the area of all R6T 13 The percentage of the area of M1 phase to the total area of the cross section is 5.0%.

[0143] The percentage of the area of all grain boundary phases in the cross section at the center of the magnet to the total area of the cross section is 4.0%; the percentage of the area of all R6T 13 The percentage of the area of M1 phase to the total area of the cross section is 4.1%.

[0144] As described above, the magnet base material formulation of Comparative Example 1 is different from that of Example 1, in which the content of Ga is 0.31 wt%, the content of Zr is 0.1 wt%, and no element Ti is contained; that is, the content of high melting point metal elements (Zr and Ti, etc.) in Comparative Example 1 is much less than that in the present application, and the content of Ga is slightly higher than that in the present application. In the case of such a magnet base material formulation, even if the same three-stage tempering process as that of Example 1 is used, the percentage of the area of all grain boundary phases or all R6T 13 The percentage of the area of M1 phase is obviously less than the corresponding percentage of Example 1, and the percentage of the area of all grain boundary phases or all R6T 13 The percentage of the area of M1 phase is also obviously less than the corresponding percentage of Example 1.

[0145] Correspondingly, the magnetic properties of the magnet of Comparative Example 1 were also significantly reduced. The coercivity of the magnet of Comparative Example 1 was 24.52 kOe, which was significantly lower than the coercivity of 26.49 kOe of the magnet of Example 1. The squareness of the magnet of Comparative Example 1 was 97.9%, which was significantly lower than the squareness of 99.6% of the magnet of Example 1.

[0146] Comparative Example 2 employed the same magnet formulation as Example 1, but step 5) of Comparative Example 2 employed a conventional diffusion and tempering process. In this case, the magnetic properties of the magnet of Comparative Example 2 were also significantly reduced. The coercivity of the magnet of Comparative Example 2 was 21.97 kOe, which was significantly lower than the coercivity of 26.49 kOe of the magnet of Example 1. The squareness of the magnet of Comparative Example 2 was 97.3%, which was significantly lower than the squareness of 99.6% of the magnet of Example 1.

[0147] While several embodiments of the present application have been shown and described herein, it is obvious that many changes and modifications can be made thereto without departing from the spirit and scope of the present application. It is also to be understood that such embodiments are only provided by way of example. Numerous alternatives to the embodiments described herein will be apparent to those skilled in the art. Such alternatives will fall within the scope of the present application. It is intended that the following claims define the scope of the application and that methods equivalent to those shown and described herein can be utilized and that all such equivalents are within the scope of this application. Accordingly, it is therefore intended that the application not be limited to the specifically set forth herein, but rather only by the appended claims.

Claims

1. A neodymium iron boron magnet, characterized in that, The neodymium iron boron magnet contains R2T 14 B-phase main grains and grain boundary phases, R2T in the region of 0.1~100μm from the magnet surface of the neodymium iron boron magnet. 14 The B-phase grains have a heavy rare earth shell on their surface, and the neodymium iron boron magnet comprises the following components: R: 28~32wt%, B: 0.85~0.94wt%, Co: 0.4~2wt%, Cu: 0.1~0.8wt%, Ga: 0.1~0.25wt%, Al: 0.05~0.5wt%, M1: 0.4~1.0 wt%, wherein M1 is selected from one or two of the elements Ti, Zr, Nb, W, and V, and M1 contains at least one of Ti and Zr. Fe: 63~69wt%; Wherein, R represents rare earth elements, and R includes at least PrNd and R. H R H R is a heavy rare earth element. H Selected from one or both of Dy and Tb; Specifically, in the neodymium iron boron magnet, the area of ​​all grain boundary phases within the cross-section of the region 0.1~100μm from the magnet surface accounts for 6.2~7.5% of the total cross-sectional area; and in the cross-section of the magnet at its center, the area of ​​all grain boundary phases accounts for 4.2~6.1% of the total cross-sectional area. The grain boundary phase includes R6T. 13 M1 phase, all R6T within the cross-section of the neodymium iron boron magnet in the region of 0.1~100μm from the magnet surface. 13 The area of ​​phase M1 accounts for 5.2% to 6.0% of the total cross-sectional area; all R6T within the cross-section of the magnet's central part. 13 The area of ​​phase M1 accounts for 4.2% to 5.0% of the total area of ​​the cross section.

2. The neodymium iron boron magnet according to claim 1, characterized in that, The content of R is 29~32wt%.

3. The neodymium iron boron magnet according to claim 1 or 2, characterized in that, The composition of the neodymium iron boron magnet includes at least one of the following characteristics: a.Cu: 0.1~0.3wt%; b. Ti: 0.15~0.3wt%; c. Co: 0.7~1.5wt%; d. R H : 0.3~2wt%。 4. The neodymium iron boron magnet according to claim 1 or 2, characterized in that, The heavy rare earth element content of the heavy rare earth shell in the region 0.1~100μm from the magnet surface is 1.0~4.5at.

5. The neodymium iron boron magnet according to claim 3, characterized in that, The heavy rare earth element content of the heavy rare earth shell in the region 0.1~100μm from the magnet surface is 1.0~4.5at.

6. A method for preparing a neodymium iron boron magnet as described in any one of claims 1-5, characterized in that, include: 1) The pre-configured raw material alloy is processed into rapidly solidified alloy sheets using a rapid solidification process; 2) The rapidly solidified alloy sheet obtained in step 1) is hydrogen-milled, and after adding additives, it is subjected to air jet milling to obtain alloy powder. The average particle size D50 of the alloy powder is 2~5μm. 3) Press the alloy powder obtained in step 2) into a compact under magnetic field orientation with a magnetic field strength of 1.8-2.5T. 4) Place the pressed blank obtained in step 3) into a sintering furnace and sinter it in a vacuum or inert atmosphere to finally obtain the neodymium iron boron magnet substrate; 5) Coat the surface of the magnet substrate obtained in step 4) with a diffusion source containing heavy rare earth elements, and then temper the neodymium iron boron magnet to obtain a neodymium iron boron magnet. The tempering process is a three-stage process: the first stage tempering temperature is 870-970℃, and the holding time is 2-20h; the second stage tempering temperature is 380-580℃, and the holding time is 1-10h; the third stage tempering temperature is 620-670℃, and the holding time is 1-10h.

7. The preparation method according to claim 6, characterized in that, In step 5), the tempering process is as follows: the first tempering temperature is 870~940℃ and the holding time is 2~10h; the second tempering temperature is 420~570℃ and the holding time is 1~10h; and the third tempering temperature is 630~670℃ and the holding time is 1~6h.

8. The preparation method according to claim 7, characterized in that, In step 5), the tempering process includes: a quenching treatment between the second-stage tempering and the third-stage tempering, with a cooling rate of 5~10℃ / min, cooling to 100~300℃.

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