Preparation method of high-performance sintered neodymium-iron-boron permanent magnet based on multi-element collaborative diffusion

Abstract

The invention relates to the technical field of rare earth permanent magnet material preparation, in particular to a high-performance sintered neodymium-iron-boron permanent magnet preparation method based on multi-element collaborative diffusion, which comprises the following steps: S1, weighing raw materials of a composite diffusion source according to percentage; s2, preparing a main alloy material (a diffusion source A) into main alloy powder; s3, preparing a secondary alloy material (a diffusion source B) into powder; s4, the main alloy powder and the auxiliary alloy powder are mixed, and an additive is added; s5, the prepared sintered neodymium-iron-boron blank is machined into a base body, and printing is conducted after treatment; s6, the printed sintered neodymium-iron-boron permanent magnet is put into a vacuum tube furnace to be subjected to grain boundary diffusion heat treatment; the invention solves the problem that the defects exist when pure heavy rare earth metal or alloy thereof is used as a diffusion source.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth permanent magnet materials preparation, and particularly relates to a method for preparing high-performance sintered Nd-Fe-B permanent magnets based on multi-element synergistic diffusion. Background Art

[0002] Rare earth permanent magnet material Nd-Fe-B products are widely used in many fields such as new energy vehicle power, smart phones, wind power generation, etc. At present, the coercivity of the produced sintered Nd-Fe-B is far from reaching its theoretical value of 6368 kA / m; therefore, there is still a large room for improvement in the coercivity of commercial sintered Nd-Fe-B permanent magnets.

[0003] At present, the industrialized grain boundary diffusion technology mainly uses pure heavy rare earth metals or their alloys as diffusion sources, which has problems such as low diffusion efficiency, large magnetic property loss, and high material cost; for example, the diffusion activation energy of Dy is relatively high, resulting in insufficient diffusion depth; for another example, the high cost of Tb (about 15 times that of Nd) limits its large-scale application. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for preparing high-performance sintered Nd-Fe-B permanent magnets based on multi-element synergistic diffusion, so as to solve the problems of the disadvantages of using pure heavy rare earth metals or their alloys as diffusion sources.

[0005] The present invention discloses a method for preparing high-performance sintered Nd-Fe-B permanent magnets based on multi-element synergistic diffusion. The specific steps of this preparation method are as follows:

[0006] S1, Weigh the raw materials of the composite diffusion source according to the percentage.

[0007] S2, Prepare the master alloy powder by melting, hydrogen decrepitation, and jet milling of the master alloy material (diffusion source A).

[0008] S3, Directly obtain the powder of the sub-alloy material (diffusion source B) by hydrogen decrepitation and jet milling.

[0009] S4, Mix the master alloy powder and the sub-alloy powder, and add additives to obtain the diffusion slurry.

[0010] S5, Process the prepared sintered Nd-Fe-B blank into a substrate with a specification of 10 mm × 10 mm × 2 mm. After degreasing, cleaning, and rust prevention treatment, remove the oxide layer on the surface of the original magnet, rinse it with anhydrous ethanol, dry it and place it on a tray, and then use screen printing technology to print the material on the magnet, with the weight gain ratio set at 0.50 wt.%.

[0011] S6, Put the printed sintered Nd-Fe-B permanent magnet into a vacuum tube furnace for grain boundary diffusion heat treatment.

[0012] Specifically, the average particle size of the master alloy powder is 2 - 3 μm, and the laser particle size ≤ 3.5.

[0013] Specifically, the mass ratio of the additive to the diffusing agent is 3 - 5:95 - 97, and the mixing time is not less than 3 hours.

[0014] Specifically, the additive consists of: the dispersant is composed of 0.5 - 2.0 wt% polyvinyl butyral and zinc stearate; the organic solvent is composed of 0.5 - 2.0 wt% absolute ethanol and terpineol, and the second thermoplastic binder is 0.5 - 2.0 wt% epoxy resin E - 12.

[0015] Specifically, the grain boundary diffusion heat treatment is (850 - 890 °C / 24 h to 450 - 500 °C / 5 h).

[0016] The beneficial effects of the present invention are as follows:

[0017] The present invention infiltrates heavy rare earth elements or rare earth alloys into the interior of the magnet in the form of grain boundary diffusion. By strengthening the weak areas on the surface of the hard magnetic phase grains, while effectively improving the coercivity of the magnet, the usage amount of heavy rare earth is greatly reduced, the adverse effects of heavy rare earth on the remanence and magnetic energy product are reduced, and the material cost is significantly reduced. Detailed implementation manners

[0018] In order to clearly understand the technical solution of the present application, a method for preparing a high - performance sintered Nd - Fe - B permanent magnet based on multi - element synergistic diffusion provided by the present application will be described in detail below in combination with specific embodiments.

[0019] The terms used in the following embodiments 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", "the above", "the", and "this" are also intended to include, for example, the expression form of "one or more", unless there is a clear opposite indication in the context. It should also be understood that in the following embodiments of the present application, "at least one", "one or more" refers to one, two, or more than two.

[0020] References to "one embodiment" or "some embodiments" or the like described in this specification mean that specific features, structures, or characteristics described in connection with that embodiment are included in one or more embodiments of the present application. Thus, statements such as "one embodiment", "in some embodiments", "in other some embodiments", "in still other embodiments", etc. that appear in different places in this specification do not necessarily all refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized. The terms "comprising", "including", "having" and their variants all mean "including but not limited to", unless otherwise specifically emphasized.

[0021] Embodiment 1

[0022] This embodiment provides a method for preparing a high-performance sintered NdFeB permanent magnet based on multi-element co-diffusion. The specific steps of this preparation method are as follows.

[0023] Step 1: Weigh the raw materials of the composite diffusion source (composed of the main diffusing agent A and the secondary diffusing agent B) according to the percentage.

[0024] Step 2: Prepare the main alloy material (diffusion source A) into main alloy powder with an average particle size of 2 - 3 μm through melting, hydrogenation crushing, and air flow milling, and the laser particle size ≤ 3.5.

[0025] Step 3: Directly obtain powder from the secondary alloy material (diffusion source B) through hydrogenation crushing and air flow milling, and the particle size range is consistent with that of the main alloy material.

[0026] Step 4: Mix the main alloy powder and the secondary alloy powder, add additives, and the mass ratio of the additives to the diffusing agent is 3 - 5:95 - 97; the mixing time is not less than 3 hours to obtain a diffusion slurry. Among them, the composition of the additives is as follows: the dispersant is composed of 0.5 - 2.0 wt% polyvinyl butyral and zinc stearate; the organic solvent is composed of 0.5 - 2.0 wt% absolute ethanol and terpineol, and the second thermoplastic binder is 0.5 - 2.0 wt% epoxy resin E - 12.

[0027] As shown in Table 1 below,

[0028] It can be seen from the table that the magnetic properties of the products obtained by using the additives in this embodiment are better, and the magnetic properties of the products can be improved without increasing the heavy rare earth content in the diffusing agent.

[0029] Step 5: Process the prepared sintered NdFeB blank into a substrate with the specification of 10mm×10mm×2mm. After degreasing, cleaning and rust prevention treatment, remove the oxide layer on the surface of the original magnet. After rinsing with anhydrous ethanol and drying, stack them on a tray. Then, use screen printing technology to print materials on the magnet, and set the weight gain ratio to 0.50wt.%.

[0030] Step 6: Put the printed sintered NdFeB permanent magnet into a vacuum tube furnace for grain boundary diffusion heat treatment (850 - 890°C / 24h to 450 - 500°C / 5h); among them, gradient cooling can be used to promote the uniform penetration of elements and further optimize the grain distribution.

[0031] In the present invention, the composite diffusing agent obtained by combining heavy rare earths and alloy elements improves the diffusion efficiency of heavy rare earth elements to a certain extent and provides more liquid-phase diffusion channels for heavy rare earth diffusion; through appropriate diffusion heat treatment, the heavy rare earth on the surface of the magnet can penetrate into the interior of the sintered body through the grain boundaries of the sintered body and diffuse from the grain boundaries into the main phase Nd2Fe14B, improving the surface anisotropy field of the grains and simultaneously improving the grain boundary microstructure, thereby increasing the coercivity of the magnet; in addition, the addition of alloy elements also reduces the content of heavy rare earths in the diffusing agent and improves the cost performance of the magnet.

[0032] The base materials of the sintered NdFeB permanent magnets respectively adopt the contents in Example 1, Example 2, Example 3, and Example 4. Diffuse the sintered NdFeB permanent magnets using the base materials of the corresponding examples, and measure them with a permanent magnet property measuring instrument after diffusion. The performance is shown in Table 2 below:

[0033] It can be seen from Table 2 above that when a part of heavy rare earth elements are replaced by light rare earth elements and non-rare earth elements, the performance of the obtained products is not much different from that of the diffusing agent containing more heavy rare earths. By increasing the amount and thickness of the non-magnetic grain boundary layer between grains, the magnetic coupling between grains is better isolated, thereby increasing the coercivity of the magnet.

[0034] In the diffusion process of Example 4, elements such as Co and Al added form nano-precipitation phases, and pin the domain walls through the stress field; the introduction of La / Ce in Example 3 maintains Hcj at 22.77 kOe while reducing costs, balancing performance and economy; the composite diffusing agent can reduce the cost of the diffusing agent while improving the diffusion efficiency.

[0035] Example 2

[0036] The composite diffusion source is composed of main diffusing agent A and auxiliary diffusing agent B. The specific composition of main diffusing agent A and auxiliary diffusing agent B can have the following four implementation methods.

[0037] The first implementation method, the main diffusing agent A is:

[0038] Dy(0.50 - 0.85)Ga(0.05 - 0.20)Gd(0.20 - 0.50)Ho(0.20 - 0.50)PrNd(0.40 - 0.65)Cu(0.05 - 0.10), and co - diffusing agent B is Tb(90 - 100);

[0039] Diffusion source B: is Tb(90 - 100).

[0040] The composition of the main diffusing agent A is by atomic percentage: Dy 0.50 - 0.85 at.%, Ga 0.05 - 0.20 at.%, Gd 0.20 - 0.50 at.%, Ho 0.20 - 0.50 at.%, PrNd 0.40 - 0.65 at.%, Cu 0.05 - 0.10 at.%;

[0041] The co - diffusing agent B is: Tb 95.00 - 97.00 at.%.

[0042] The second implementation mode, the main diffusing agent A is:

[0043] Dy(0.50 - 0.85)Ga(0.15 - 0.30)Gd(0.20 - 0.50)Ho(0.20 - 0.50);

[0044] The co - diffusing agent B is Tb(90 - 100).

[0045] The composition of the main diffusing agent A is by atomic percentage: Dy 0.50 - 0.85 at.%, Ga 0.15 - 0.30 at.%, Gd 0.20 - 0.50 at.%, Ho 0.20 - 0.50 at.%;

[0046] The co - diffusing agent B is: Tb 97.00 - 99.00 at.%.

[0047] The third implementation mode, the main diffusing agent A is:

[0048] Dy(0.50 - 0.85)Ga(0.15 - 0.30)Gd(0.20 - 0.50)Ho(0.20 - 0.50)La(0.05 - 0.15)Ce(1.5 - 4.0);

[0049] The co - diffusing agent B is Tb(90 - 100).

[0050] The composition of the main diffusing agent A is as follows in atomic percentage: Dy 0.50 - 0.85 at.%, Ga 0.15 - 0.30 at.%, Gd 0.20 - 0.50 at.%, Ho 0.20 - 0.50 at.%, La 0.05 - 0.15 at.%, Ce 1.5 - 4.0 at.%.

[0051] The secondary diffusing agent B is: Tb 94.00 - 96.00 at.%.

[0052] The 4th embodiment, the main diffusing agent A is:

[0053] Dy(0.20 - 0.50)Ga(4 - 8)Gd(0.10 - 0.40)Ho(0.20 - 0.50)Al(0.05 - 0.45)Co(8 - 15)PrNd(25 - 40);

[0054] The secondary diffusing agent B is Tb(50 - 60).

[0055] The composition of the main diffusing agent A is as follows in atomic percentage: Dy 0.20 - 0.50 at.%, Ga 4 - 8 at.%, Gd 0.10 - 0.40 at.%, Ho 0.20 - 0.50 at.%, Al 0.05 - 0.45 at.%, Co 8 - 15 at.%, PrNd 25 - 40 at.%;

[0056] The secondary diffusing agent B is: Tb 53.00 - 58.00 at.%.

Claims

1. A method for preparing a high-performance sintered NdFeB permanent magnet based on multi-element synergistic diffusion, characterized in that, The specific steps of this preparation method are as follows. S1. Weigh the raw materials of the composite diffusion source according to the percentage. S2. Prepare the master alloy powder by melting, hydrogen crushing, and jet milling of the master alloy material (diffusion source A). S3. Directly obtain the powder of the secondary alloy material (diffusion source B) by hydrogen crushing and jet milling. S4. Mix the master alloy powder and the secondary alloy powder, and add additives to obtain the diffusion slurry. S5. Process the prepared sintered NdFeB blank into a substrate with a specification of 10 mm × 10 mm × 2 mm. After degreasing, cleaning, and rust prevention treatment, remove the oxide layer on the surface of the original magnet. After rinsing with anhydrous ethanol and drying and coding on the tray, then use screen printing technology to print the material on the magnet, and set the weight gain ratio to 0.50 wt.%. S6. Put the printed sintered NdFeB permanent magnet into a vacuum tube furnace for grain boundary diffusion heat treatment.

2. The method for preparing a high-performance sintered Nd-Fe-B permanent magnet based on multi-element co-diffusion according to claim 1, characterized in that: The average particle size of the master alloy powder is 2 - 3 μm, and the laser particle size ≤ 3.

5.

3. The method for preparing a high-performance sintered Nd-Fe-B permanent magnet based on multi-element co-diffusion according to claim 1, wherein: The mass ratio of the additive to the dispersant is 3 - 5:95 - 97, and the mixing time is not less than 3 hours.

4. The method for preparing a high-performance sintered Nd-Fe-B permanent magnet based on multi-element synergistic diffusion according to claim 1, wherein: The composition of the additive is: the dispersant consists of 0.5 - 2.0 wt% polyvinyl butyral and zinc stearate; the organic solvent consists of 0.5 - 2.0 wt% anhydrous ethanol and terpineol, and the second thermoplastic binder is 0.5 - 2.0 wt% epoxy resin E - 12.

5. The method for preparing a high-performance sintered Nd-Fe-B permanent magnet based on multi-element co-diffusion according to claim 1, wherein: The grain boundary diffusion heat treatment is (850 - 890 °C / 24 h to 450 - 500 °C / 5 h).

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