Method for improving intrinsic coercivity of thick neodymium-iron-boron permanent magnet material

Abstract

The application discloses a method for improving intrinsic coercivity of thick neodymium-iron-boron permanent magnet material, and relates to the technical field of sintered neodymium-iron-boron magnetic material, and aims at solving the problem that the intrinsic coercivity of thick neodymium-iron-boron permanent magnet material is difficult to improve. The method comprises the following steps: cutting the sintered neodymium-iron-boron blank into multiple thin pieces with the same shape and size of the magnetization orientation surface of the target thick product, and cleaning the thin pieces by pickling; uniformly smearing the heavy rare earth slurry containing magnesium nitride on the two orientation surfaces of each thin piece, closely arranging the thin pieces with minimum gap into a molybdenum box after drying, and putting the thin pieces into a vacuum sintering furnace for tempering I; after air cooling, polishing, cleaning and drying, the thin pieces are stacked along the orientation surfaces to the thickness of the target thick product, and the stacked thin pieces are closely connected after being put into the vacuum sintering furnace for tempering I again; after air cooling, tempering II is carried out, the target thick product is obtained after air cooling, polishing and cleaning; and the method can greatly improve the intrinsic coercivity of the thick product, and the method has low cost and no additional pollution.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sintered neodymium-iron-boron magnetic materials, in particular to a method for improving the intrinsic coercivity of thick neodymium-iron-boron permanent magnet materials. BACKGROUND

[0002] Neodymium-iron-boron materials are widely used in the fields of electrical components, new energy vehicles, wind power generation, etc. With the continuous expansion of the application of neodymium-iron-boron permanent magnet materials in various new energy field consumer products, the performance requirements for rare earth permanent magnet materials are becoming higher and higher.

[0003] At present, in the neodymium-iron-boron material industry, remanence and intrinsic coercivity are the two most important performance indicators of products. The remanence is mainly provided by the neodymium-iron-boron main phase Nd2Fe 14 B, and the intrinsic coercivity is mainly improved by the heavy rare earth phase beside the Nd-rich phase. Generally, the heavy rare earth phase such as Dy2Fe 14 B is generated from the coating of heavy rare earth after sintering and tempering. The Dy element replaces the Nd element in the grain boundary and slowly diffuses to form a Dy2Fe 14 B phase during the tempering process.

[0004] The intrinsic coercivity of thin products with a thickness of less than 4mm is basically the same after sintering and then using heavy rare earth surface coating and tempering. That is, under the same tempering temperature and time and appropriate coating amount, the amount of intrinsic coercivity improvement is proportional to the coating amount. However, for thick neodymium-iron-boron products, as the thickness increases, the intrinsic coercivity improved by coating heavy rare earth becomes less and less obvious. SUMMARY

[0005] The purpose of the present application is to provide a method for improving the intrinsic coercivity of thick neodymium-iron-boron permanent magnet materials, so as to solve the problem of difficult improvement of the intrinsic coercivity of thick neodymium-iron-boron permanent magnet materials.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a method for improving the intrinsic coercivity of thick neodymium-iron-boron permanent magnet materials, comprising the following specific steps:

[0007] S1 cutting the sintered neodymium-iron-boron blank into multiple thin pieces with the same shape and size as the magnetization orientation surface of the target thick product, and pickling and cleaning;

[0008] S2 evenly applying heavy rare earth slurry containing magnesium nitride to the two orientation surfaces of each thin piece, tightly arranging the dried thin pieces with the smallest gap into a molybdenum box, and placing the molybdenum box into a vacuum sintering furnace for tempering I, slowly increasing the temperature to 890-925℃ after keeping at 430-550℃ for a period of time, and keeping at 890-925℃ for a period of time.

[0009] S3 After the sheet tempered in step S2 is air-cooled, it is polished, washed, dried, and stacked along the orientation surface to the target thickness of the product, and then re-tempered in a vacuum sintering furnace, so that the sheets stacked along the orientation surface are closely connected;

[0010] S4 After the sheet tempered in step S3 is air-cooled, it is then tempered in step S4, and then air-cooled after being kept at 400-600℃ for a period of time, polished, and washed to obtain the target thickness product.

[0011] Preferably, the thickness of the target thickness product is n·(the thickness of the thin product-a), n is an integer greater than 1, and a is a positive number less than the thickness of the thin product.

[0012] Preferably, the acid pickling uses 3% by volume of dilute nitric acid.

[0013] Preferably, in step S2, the tempering is kept at 430-550℃ for 2h, and then slowly heated to 890-925℃ for 10-20h.

[0014] Preferably, in step S3, the re-tempering is kept at 430-550℃ for 2h, and then slowly heated to 890-925℃ for 9h.

[0015] Preferably, in step S4, the tempering is kept for 2-7h.

[0016] Preferably, the weight ratio of the components in the heavy rare earth slurry is ethanol: heavy rare earth powder: additive: magnesium nitride = 1: 5.5-6: 3-3.3: 0.01-0.05.

[0017] Preferably, the additive is an adhesion improver and / or a thickening agent.

[0018] Preferably, in step S3, the adjacent single target thickness products are separated by ceramic sheets.

[0019] Preferably, the vacuum degree of the tempering, re-tempering, and tempering is kept at 1.0*10 -3 Pa or below.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] The method for improving the intrinsic coercive force of thick neodymium-iron-boron permanent magnet products adopts the self-bonding mode of thin slices in heat treatment to prepare thick products, and through coating special heavy rare earth slurry in the first tempering, permeation is carried out while bonding is avoided, so that thick products with intrinsic coercive force performance equivalent to that of thin slices are obtained, the problem that the intrinsic coercive force of thick neodymium-iron-boron products cannot be greatly improved is effectively solved, the increase of the intrinsic coercive force of the diffused thick products can reach more than 20%, compared with the existing method for improving the intrinsic coercive force of thick products, the increase can reach more than 60%, in addition, the method can also greatly reduce the cost of thick products, the economic benefit is obviously improved, and there is no excess environmental pollution. DETAILED DESCRIPTION

[0022] The present application understands that the heavy rare earth coating cannot effectively improve the intrinsic coercive force of thick products mainly because the heavy rare earth elements are difficult to enter more than 400 um along the grain boundary, and the rare earth elements cannot diffuse to the inside, so the intrinsic coercive force cannot be effectively improved, therefore, through theoretical research and test, a method for improving the intrinsic coercive force of thick neodymium-iron-boron permanent magnet products is proposed, and good results are obtained, the method comprises the following specific steps:

[0023] S1 cut the sintered neodymium-iron-boron blank into a plurality of thin slices with the same shape and size as the magnetization orientation surface of the target thick product, and clean them with 3% volume fraction of dilute nitric acid; in a more preferred embodiment, the thickness of the target thick product = n·(thin product thickness-a), n is an integer greater than 1, a is a surplus for subsequent acid washing and polishing, a is a positive number less than the thickness of the thin product, the thickness of the target thick product is generally greater than 10 mm, of course, products with a thickness of not more than 10 mm can also be prepared from several thin slices by the method of the present application;

[0024] S2 evenly coat the heavy rare earth slurry containing magnesium nitride on the two orientation surfaces of each thin slice (the function of magnesium nitride is to prevent the thin slices from bonding in the first tempering), optionally, the weight ratio of the components in the heavy rare earth slurry is anhydrous ethanol: heavy rare earth powder: additive: magnesium nitride = 1: 5.5-6: 3-3.3: 0.01-0.05; the additive is an adhesion improver and / or thickener, for example, one or more of phenolic resin, rosin modified alkyd resin, urea-formaldehyde resin; after drying, the thin slices are closely arranged and have the smallest gap to be loaded into a molybdenum box (i.e., the thin slices are closely stacked), so as to reduce the oxygen content as much as possible, and then placed into a vacuum sintering furnace for tempering 1, the vacuum degree needs to be kept at 1.0*10 -3 Pa or below, and then slowly heated to 890-925℃ for a period of time (preferably 10-20h);

[0025] S3 After the sheet of step S2 tempering one is air-cooled, polishing, cleaning, drying, the sheet is stacked along the orientation surface to the target thickness product thickness (adjacent stacked single target thickness product should be separated by ceramic sheet), into the vacuum sintering furnace to retemper one to the stacked sheet is closely connected. More preferably, retemper one is 430-550℃ for 2h, slowly heated to 890-925℃ for 9h; When retempering one, there is no any barrier between the atoms of the two same metal contact surfaces in the vacuum environment, when the two surfaces are in close contact, the atoms on the two surfaces will hold each other to become one, 890-925 low temperature holding can accelerate the exchange of atoms on the surface of the two metals, thereby bonding together;

[0026] S4 After the sheet of step S3 retempering one is air-cooled, then tempering two is handled, 400-600℃ for a period of time (preferably 2-7h), air-cooled and taken out, polished and cleaned to obtain the target thickness product.

[0027] Comparative example:

[0028] The target product size is 70mm*42mm*80mm, the orientation is 80mm thick direction, select 45SH brand neodymium iron boron blank, cut 6 pieces of sample size 70.08mm*42.08mm*80.04mm, clean with 3% volume fraction of dilute nitric acid, coat Dy heavy rare earth of mixed magnesium alloy on the orientation surface, dry Dy weight gain 0.7%, put into molybdenum box to ensure close arrangement and minimum gap. The vacuum degree is kept at 1.0*10 -3 Pa or below during the whole tempering process. After 480℃ for 2h in tempering one, slowly heated to 920℃ for 30h, air-cooled and then tempered two is handled, 490℃ for 5h, then air-cooled rapidly. After polishing and cleaning, the performance is as follows:

[0029]

[0030] Example 1:

[0031] The target product size is 70mm*42mm*80mm, the orientation is 80mm thick direction, select 45SH brand neodymium iron boron blank of the same batch, cut 30 pieces of sample size 70.08mm*42.08mm*16.04mm, the orientation is 16.04mm thick direction, clean with 3% volume fraction of dilute nitric acid, coat Dy heavy rare earth of mixed magnesium alloy on the orientation surface, dry Dy weight gain 0.7%, put into molybdenum box to ensure close arrangement and minimum gap. The vacuum degree is kept at 1.0*10 -3Pa below. In the first tempering, after keeping at 480℃ for 2h, slowly increase the temperature to 920℃ and keep for 20h, after air cooling, send to double side grinding to polish the two orientation surfaces and clean, every 5 pieces of orientation surfaces are stacked together and put into molybdenum box to ensure the close arrangement and minimum gap, after keeping at 480℃ for 9h, slowly air cool. In the second tempering, keep at 490℃ for 5h and then quickly air cool. After polishing and cleaning, the performance is as follows:

[0032]

[0033] Example 2:

[0034] The target product size is 70mm*42mm*80mm, and the orientation is 80mm thick direction. The same batch of Nd-Fe-B blanks of 45SH grade are selected, 48 pieces of sample pieces with a size of 70.08mm*42.08mm*10.04mm are cut, and the orientation is 10.04mm thick direction. After cleaning with 3% volume fraction of dilute nitric acid, Dy heavy rare earth of mixed magnesium alloy is coated on the orientation surface, and after drying, the Dy weight gain is 0.7%. The pieces are put into a molybdenum box to ensure close arrangement and minimum gap. The vacuum degree is kept at 1.0*10 -3 Pa below. In the first tempering, after keeping at 480℃ for 2h, slowly increase the temperature to 920℃ and keep for 20h, after air cooling, send to double side grinding to polish the two orientation surfaces and clean, every 5 pieces of orientation surfaces are stacked together and put into molybdenum box to ensure the close arrangement and minimum gap, after keeping at 480℃ for 9h, slowly air cool. In the second tempering, keep at 490℃ for 5h and then quickly air cool. After polishing and cleaning, the performance is as follows:

[0035]

[0036]

[0037] Example 3:

[0038] The target product size is 70mm*42mm*80mm, and the orientation is 80mm thick direction. The same batch of Nd-Fe-B blanks of 45SH grade are selected, 48 pieces of sample pieces with a size of 70.08mm*42.08mm*10.04mm are cut, and the orientation is 10.04mm thick direction. After cleaning with 3% volume fraction of dilute nitric acid, Dy heavy rare earth of mixed magnesium alloy is coated on the orientation surface, and after drying, the Dy weight gain is 0.7%. The pieces are put into a molybdenum box to ensure close arrangement and minimum gap. The vacuum degree is kept at 1.0*10 -3Pa below. After tempering 1 at 480 DEG C for 2h, slowly increase the temperature to 920 DEG C for 20h, air cooling, then send to double-sided grinding to polish two orientation surfaces and clean, every 10 pieces of orientation surfaces are stacked to ensure the arrangement is compact and the gap is minimum, then do tempering 1 again for 9h, slowly air cooling. Tempering 2 at 490 DEG C for 5h, then fast air cooling. After polishing and cleaning, the performance is as follows:

[0039]

[0040] According to the data of the comparative examples and the examples, it can be seen that the process method of the application can obviously improve the intrinsic coercive force of the thick neodymium-iron-boron product, the remanence decreases a little, the mechanical property decreases slightly, the cost of the thick neodymium-iron-boron permanent magnet product can be greatly reduced, and the economic benefit is obviously improved.

[0041] The above is only the preferred embodiment of the application, but the protection scope of the application is not limited to this, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the application, which should be covered in the protection scope of the application. Therefore, the protection scope of the application should be limited by the protection scope defined by the claims.

[0042] The parts not described in the application are the known technology of the person skilled in the art.

Claims

1. A method of increasing the intrinsic coercivity of thick products of neodymium-iron-boron permanent magnetic material, characterized in that, The method comprises the following specific steps: S1: cutting the sintered neodymium iron boron blank into multiple thin pieces with the same shape and size as the magnetization orientation surface of the target thick product; S2: uniformly applying a heavy rare earth slurry containing magnesium nitride to the two orientation surfaces of each thin piece, drying the thin pieces, and then tightly arranging the thin pieces with the smallest gap in a molybdenum box and placing the thin pieces in a vacuum sintering furnace for tempering I, slowly increasing the temperature to 890-925℃ after keeping the temperature at 430-550℃ for a period of time; S3: after air cooling of the thin pieces after tempering I in step S2, polishing, cleaning, and drying, the thin pieces are stacked along the orientation surfaces to the thickness of the target thick product, and the thin pieces are re-tempered I in a vacuum sintering furnace until the thin pieces are tightly connected along the orientation surfaces; S4: after air cooling of the thin pieces after re-tempering I in step S3, tempering II is performed, and the thin pieces are taken out after air cooling at 400-600℃ for a period of time, polished, and cleaned to obtain the target thick product.

2. The method for improving the intrinsic coercive force of thick products of neodymium-iron-boron permanent magnet material as claimed in claim 1, characterized in that: The thickness of the target thick product is n·(thin product thickness-a), n is an integer greater than 1, and a is a positive number less than the thickness of the thin product, which is used for subsequent pickling and polishing.

3. The method for improving the intrinsic coercive force of thick products of neodymium-iron-boron permanent magnet material as claimed in claim 1, characterized in that: The pickling uses 3% by volume of dilute nitric acid.

4. The method for improving the intrinsic coercive force of thick products of neodymium-iron-boron permanent magnet material as claimed in claim 1, characterized in that: In step S2, tempering I is keeping the temperature at 430-550℃ for 2h, and slowly increasing the temperature to 890-925℃ for 10-20h.

5. The method for improving the intrinsic coercive force of thick products of neodymium-iron-boron permanent magnetic material according to claim 1, characterized in that: In step S3, re-tempering I is keeping the temperature at 430-550℃ for 2h, and slowly increasing the temperature to 890-925℃ for 9h.

6. The method for improving the intrinsic coercive force of thick products of neodymium-iron-boron permanent magnetic material according to claim 1, characterized in that: In step S4, the holding time of tempering II is 2-7h.

7. The method for improving the intrinsic coercive force of thick products of neodymium-iron-boron permanent magnetic material according to claim 1, characterized in that: The weight ratio of the components in the heavy rare earth slurry is anhydrous ethanol: heavy rare earth powder: additive: magnesium nitride = 1: 5.5-6: 3-3.3: 0.01-0.

05.

8. The method for improving the intrinsic coercive force of thick products of neodymium-iron-boron permanent magnetic material according to claim 7, characterized in that: The additive is an adhesion improver and / or a thickening agent.

9. The method for improving the intrinsic coercive force of thick products of neodymium-iron-boron permanent magnetic material according to claim 1, characterized in that: In step S3, the adjacent stacked single target thick products are separated by ceramic sheets.

10. The method for improving the intrinsic coercive force of thick products of neodymium-iron-boron permanent magnetic material according to claim 1, characterized in that: The vacuum degree of the tempering, re-tempering and tempering 2 is kept at 1.0*10 -3 Pa or below.

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