Method for recovering grain boundary diffusion neodymium-iron-boron magnet

Abstract

The invention provides a method for recovering a grain boundary diffusion neodymium-iron-boron magnet, which comprises the following steps of: (1) demagnetizing a waste grain boundary diffusion neodymium-iron-boron magnet, and then removing a plating layer from the demagnetized magnet; the method for removing the plating layer is sand blasting; (2) carrying out crushing, hydrogen decrepitation and jet milling on the magnet subjected to coating removal treatment to obtain jet milled powder; and (3) mixing rare earth alloy powder with the airflow powder, and then carrying out orientation forming, cold isostatic pressing, sintering and tempering heat treatment to obtain the regenerated neodymium-iron-boron magnet. According to the method provided by the invention, the deplating treatment is carried out in a sand blasting manner, so that the core-shell structure of the grain boundary diffusion neodymium-iron-boron magnet is not damaged, and the rare earth loss is small; by using the rare earth alloy powder, the purposes of strengthening the core-shell structure of the regenerated neodymium-iron-boron magnet, improving the liquid phase fluidity in the sintering process, optimizing the grain boundary and enabling the regenerated neodymium-iron-boron magnet to have excellent magnetic performance are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic materials and relates to a method for recovering magnets, in particular to a method for recovering grain boundary diffused NdFeB magnets. Background Art

[0002] With the expansion of application fields, NdFeB magnets play an increasingly important role in modern industry. At present, more than 90% of NdFeB magnets are prepared by sintering process. However, in the traditional sintering process, a large amount of raw materials are converted into NdFeB waste. The development of environmentally friendly and cost-effective recycling processes is crucial to the NdFeB industry.

[0003] At present, the recycling of NdFeB magnetic materials mainly includes three methods: wet recycling, pyrometallurgical recycling and short-process regeneration recycling. The process of wet recycling is cumbersome and causes serious environmental burden; pyrometallurgical recycling consumes a lot of energy and has high cost. In order to solve the drawbacks of the above recycling methods, it is necessary to introduce an efficient and energy-saving recycling method. There have been relevant studies on the recycling of NdFeB magnets prepared by single main phase or double main phase, but there has been no relevant research on the recycling of NdFeB magnets prepared by grain boundary diffusion.

[0004] The microstructure of grain boundary diffusion magnets has unique advantages. Heavy rare earth elements form a thin epitaxial layer at the boundary of the main phase grains, which can achieve a good magnetic isolation effect. When recycling grain boundary diffusion magnets, the existing technology uses chemical methods or manual grinding to remove the coating on the surface of the magnet, which is easy to destroy the core-shell structure of the grain boundary diffusion magnet and increase the loss of rare earth.

[0005] Therefore, it is necessary to provide a recycling method for grain boundary diffusion magnets. Summary of the invention

[0006] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for recycling grain boundary diffused NdFeB magnets, which method can maintain the core-shell structure of the grain boundary diffused NdFeB magnets without damage and reduce rare earth loss. It can also achieve the purpose of strengthening the core-shell structure of the regenerated NdFeB magnets, improving the liquid phase fluidity during sintering, optimizing the grain boundaries and making the regenerated NdFeB magnets have excellent magnetic properties.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for recovering grain boundary diffused NdFeB magnets, the method comprising the following steps:

[0009] (1) The waste grain boundary diffusion NdFeB magnet is demagnetized, and then the magnet after demagnetization is de-plated;

[0010] The method of de-plating is sandblasting;

[0011] (2) The magnet after de-plating is crushed, hydrogen-crushed and jet-milled to obtain jet-milled powder;

[0012] (3) mixing rare earth alloy powder with the jet mill powder, and then performing orientation molding, cold isostatic pressing, sintering and tempering heat treatment to obtain a regenerated NdFeB magnet;

[0013] The rare earth alloy powder includes rare earth element RE and metal element ME, wherein RE includes any one of Pr, Nd, Tb, Dy or Ho or a combination of at least two thereof, and ME includes any one of Cu, Al or Ga or a combination of at least two thereof.

[0014] The object of recycling of the method provided by the present invention is waste grain boundary diffusion NdFeB magnets, which have a uniform core-shell structure, in which the heavy rare earth elements are evenly dispersed. The present invention uses sandblasting to remove the coating, so that the core-shell structure of the grain boundary diffusion NdFeB magnet is not damaged and the rare earth loss is small; the use of rare earth alloy powder improves the liquid phase fluidity during the sintering process, optimizes the grain boundary phase, strengthens the original weak core-shell structure in the regenerated magnet, and enables the regenerated NdFeB magnet to obtain higher magnetic properties. The method provided by the present invention has simple process, low production cost, and has the advantages of green and low energy consumption, avoiding the waste of rare earth resources.

[0015] In the rare earth alloy powder used in the present invention, RE includes any one of Pr, Nd, Tb, Dy or Ho or a combination of at least two thereof. Typical but non-limiting combinations include a combination of Pr and Nd, a combination of Tb and Dy, a combination of Nd and Ho, a combination of Pr, Nd and Dy, a combination of Tb, Dy and Ho, or

[0016] In the rare earth alloy powder used in the present invention, ME includes any one of Cu, Al or Ga or a combination of at least two of them. Typical but non-limiting combinations include a combination of Cu and Al, a combination of Al and Ga, a combination of Cu and Ga, and a combination of Cu, Al and Ga.

[0017] Preferably, the material of the rare earth alloy powder includes Pr 70 Cu 30 , Pr 70 Al 30 , Pr 70 Al 10 Cu 20 、Nd 70 Cu 30 or Nd 70 Al 30 Any one or a combination of at least two of the following, typical but non-limiting combinations include Pr 70 Cu 30 With Pr 70 Al30 The combination of Pr 70 Al 10 Cu 20 With Nd 70 Cu 30 The combination of Pr 70 Al 30 With Nd 70 Al 30 A combination of, or Pr 70 Cu 30 , Pr 70 Al 30 , Pr 70 Al 10 Cu 20 、Nd 70 Cu 30 With Nd 70 Al 30 combination.

[0018] Preferably, the average particle size of the jet milled powder in step (2) is 3 μm-4 μm, for example, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm or 4 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0019] Preferably, the average particle size of the rare earth alloy powder in step (3) is 2.5 μm-4 μm, for example, it can be 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm or 4 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0020] Exemplarily, the rare earth alloy powder of the present invention is obtained by smelting, hydrogen crushing and air flow milling. The present invention does not impose too many restrictions on the parameters of hydrogen crushing and air flow milling when obtaining the rare earth alloy powder, as long as the rare earth alloy powder with an average particle size of 2.5μm-4μm can be obtained.

[0021] Preferably, taking the total mass percentage of the rare earth alloy powder and the airflow milled powder in step (3) as 100wt%, the mass percentage of the airflow milled powder is ≥95wt%, for example, it can be 95wt%, 96wt%, 97wt%, 98wt% or 99wt%, but is not limited to the listed values, and the remaining values ​​not listed within the numerical range are also applicable, preferably ≥96wt%.

[0022] Preferably, the blasting pressure of the sandblasting in step (1) is 0.4 MPa-0.8 MPa, for example, it can be 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa or 0.8 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0023] Preferably, the blasting distance of the sandblasting in step (1) is 100 mm-300 mm, for example, it can be 100 mm, 150 mm, 200 mm, 250 mm or 300 mm, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0024] Preferably, the blasting angle of the sandblasting in step (1) is 45°-90°, for example, it can be 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85° or 90°, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] Exemplarily, the sandblasting of the present invention uses an abrasive of 120-200 mesh, and the material of the abrasive includes any one of garnet, brown corundum or glass beads or a combination of at least two of them. Typical but non-limiting combinations include a combination of garnet and brown corundum, a combination of garnet and glass beads, a combination of brown corundum and glass beads, or a combination of garnet, brown corundum and glass beads.

[0026] Preferably, the demagnetization treatment in step (1) comprises: evacuating to maintain an absolute pressure of ≤1×10 -2 Pa, heat to 400℃-440℃ at a heating rate not higher than 10℃ / min, keep warm for 1.5h-2.5h, and then air-cool to room temperature in a protective atmosphere.

[0027] As a preferred technical solution of the present invention, during the demagnetization process, the absolute pressure is maintained at ≤1×10 -2 Pa, for example, can be 0.1×10 -2 Pa, 0.3×10 -2 Pa, 0.5×10 -2 Pa, 0.8×10 -2 Pa or 1×10 -2 Pa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, when performing demagnetization treatment, the heating rate of the temperature is not higher than 10°C / min, for example, it can be 1°C / min, 3°C / min, 5°C / min, 6°C / min, 8°C / min or 10°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] As a preferred technical solution of the present invention, the temperature during demagnetization treatment is 400°C-440°C, for example, it can be 400°C, 410°C, 420°C, 430°C or 440°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] As a preferred technical solution of the present invention, the holding time during demagnetization treatment is 1.5h-2.5h, for example, it can be 1.5h, 1.8h, 2h, 2.2h or 2.5h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Exemplarily, the room temperature during the demagnetization treatment in step (1) is 15°C-30°C, for example, it can be 15°C, 18°C, 20°C, 25°C, 28°C or 30°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] Preferably, the gas used for the protective atmosphere includes any one of nitrogen, helium, argon or neon, or a combination of at least two of them. Typical but non-limiting combinations include a combination of nitrogen and helium, a combination of helium and argon, a combination of argon and neon, a combination of nitrogen, helium and argon, or a combination of nitrogen, helium, argon and neon.

[0033] Preferably, the hydrogen crushing in step (2) comprises: absorbing hydrogen for 3h-5h at a temperature of 150°C-300°C and a hydrogen pressure of 0.05MPa-0.1MPa, and after saturation of hydrogen absorption, absorbing hydrogen at an absolute pressure of ≤1×10 -3 Pa, dehydrogenate at a temperature of 500°C-600°C for 4h-6h; sieve after dehydrogenation.

[0034] The temperature of the hydrogen crushing in step (2) of the present invention is 150°C-300°C, for example, 150°C, 180°C, 200°C, 240°C, 250°C, 280°C or 300°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] The hydrogen pressure of the hydrogen crushing in step (2) of the present invention is 0.05MPa-0.1MPa, for example, it can be 0.05MPa, 0.06MPa, 0.07MPa, 0.08MPa, 0.09MPa or 0.1MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] The hydrogen pressure described in the present invention is an absolute pressure.

[0037] The hydrogen absorption time of the hydrogen fragmentation in step (2) of the present invention is 3h-5h, for example, 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] During the hydrogen decomposition in step (2) of the present invention, the absolute pressure of dehydrogenation is ≤1×10 -3 Pa, for example, can be 0.1×10- 3 Pa, 0.3×10 -3 Pa, 0.5×10 -3 Pa, 0.6×10 -3 Pa, 0.8×10 -3 Pa or 1×10 -3 Pa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] During the dehydrogenation in step (2) of the present invention, the dehydrogenation temperature is 500°C-600°C, for example, 500°C, 520°C, 550°C, 560°C, 580°C or 600°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] During the hydrogen decomposition in step (2) of the present invention, the dehydrogenation time is 4h-6h, for example, 4h, 4.5h, 5h, 5.5h or 6h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] Exemplarily, the screening after dehydrogenation in step (2) is performed using a 20-mesh sieve.

[0042] Preferably, the method provided by the present invention further comprises uniformly mixing with an antioxidant and a lubricant after sieving, wherein, calculated by mass percentage, the amount of the antioxidant is 0.08wt%-0.12wt% of the sieved hydrogen powder, and the amount of the lubricant is 0.04wt%-0.05wt% of the sieved hydrogen powder.

[0043] Preferably, the method provided by the present invention also includes uniformly mixing the airflow milled powder with an antioxidant and a lubricant, and calculated by mass percentage, the amount of the antioxidant is 0.18wt%-0.22wt% of the airflow milled powder, and the amount of the lubricant is 0.08wt%-0.12wt% of the airflow milled powder.

[0044] Preferably, the sintering in step (3) is carried out at an absolute pressure of ≤1×10 -3 Pa, for example, 0.1×10 -3 Pa, 0.3×10 -3 Pa, 0.5×10 -3 Pa, 0.6×10 -3 Pa, 0.8×10 -3 Pa or 1×10 -3 Pa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] Preferably, the sintering temperature in step (3) is 1000°C-1070°C, for example, it can be 1000°C, 1010°C, 1030°C, 1050°C, 1060°C or 1070°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0046] Preferably, the sintering time in step (3) is 3h-6h, for example, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0047] Preferably, the tempering heat treatment in step (3) comprises: -3 Pa, the first tempering heat treatment and the second tempering heat treatment are carried out in sequence, for example, 0.1×10 -3 Pa, 0.3×10 -3 Pa, 0.5×10 -3 Pa, 0.6×10 -3 Pa, 0.8×10 -3 Pa or 1×10 -3 Pa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0048] Preferably, the temperature of the primary tempering heat treatment is 820°C-920°C, for example, it can be 820°C, 840°C, 850°C, 860°C, 880°C, 900°C or 920°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] Preferably, the time of the primary tempering heat treatment is 3h-5h, for example, 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0050] Preferably, the temperature of the secondary tempering heat treatment is 420°C-520°C, for example, 420°C, 450°C, 480°C, 500°C or 520°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0051] Preferably, the time of the secondary tempering heat treatment is 4h-6h, for example, 4h, 4.5h, 5h, 5.5h or 6h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] Preferably, after the tempering heat treatment in step (3), the steel is air-cooled to room temperature in an oxygen-free atmosphere.

[0053] The room temperature in which the tempering heat treatment is air-cooled to room temperature in step (3) of the present invention is 15°C-30°C, for example, 15°C, 18°C, 20°C, 24°C, 25°C, 28°C or 30°C, but is not limited to the listed values, and the remaining values ​​within the numerical range not listed are also applicable.

[0054] Preferably, the gas used in the oxygen-free atmosphere includes any one of nitrogen, helium, argon or neon, or a combination of at least two of them. Typical but non-limiting combinations include a combination of nitrogen and helium, a combination of helium and argon, a combination of argon and neon, a combination of nitrogen, helium and argon, or a combination of nitrogen, helium, argon and neon.

[0055] As a preferred technical solution of the method provided by the present invention, the method comprises the following steps:

[0056] (1) The waste grain boundary diffusion NdFeB magnet is demagnetized, and then the magnet after demagnetization is de-plated;

[0057] The demagnetization process includes: vacuuming to maintain an absolute pressure of ≤1×10 -2 Pa, heat to 400-440°C at a heating rate not higher than 10°C / min, keep warm for 1.5h-2.5h, and then air-cool to room temperature in an argon atmosphere;

[0058] The method of de-plating is sandblasting;

[0059] The blasting pressure of the sandblasting is 0.4MPa-0.8MPa, the blasting distance is 100mm-300mm and the blasting angle is 45°-90°;

[0060] (2) The magnet after de-plating is crushed, hydrogen crushed and jet milled to obtain jet milled powder with an average particle size of 3 μm-4 μm;

[0061] The hydrogen crushing comprises: absorbing hydrogen for 3h-5h at a temperature of 150°C-300°C and a hydrogen pressure of 0.05MPa-0.1MPa, and after the hydrogen is saturated, the hydrogen is crushed at an absolute pressure of ≤1×10 -3 Pa, dehydrogenate at 500°C-600°C for 4h-6h; sieve after dehydrogenation;

[0062] (3) Mixing the jet milled powder with the rare earth alloy powder with an average particle size of 2.5 μm-4 μm, and then performing orientation molding, cold isostatic pressing, sintering and tempering heat treatment, and air cooling to room temperature under an argon atmosphere to obtain a regenerated NdFeB magnet; the material of the rare earth alloy powder includes Pr 70 Cu 30 , Pr 70 Al 30 , Pr 70 Al10 Cu 20 、Nd 70 Cu 30 or Nd 70 Al 30 Any one or a combination of at least two of the following; taking the total mass percentage of the rare earth alloy powder and the airflow milled powder in step (3) as 100wt%, the mass percentage of the airflow milled powder is ≥95wt%;

[0063] The sintering is carried out at an absolute pressure of ≤10 -3 Pa, the sintering temperature is 1000℃-1070℃, and the time is 3h-6h;

[0064] The tempering heat treatment includes an absolute pressure of ≤10 -3 Pa; the temperature of the first tempering heat treatment is 820℃-920℃, and the time is 3h-5h; the temperature of the second tempering heat treatment is 420℃-520℃, and the time is 4h-6h.

[0065] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] The object of recycling of the method provided by the present invention is waste grain boundary diffusion NdFeB magnets, which have a uniform core-shell structure, in which the heavy rare earth elements are evenly dispersed. The present invention uses sandblasting to remove the coating, so that the core-shell structure of the grain boundary diffusion NdFeB magnet is not damaged and the rare earth loss is small; the use of rare earth alloy powder improves the liquid phase fluidity during the sintering process, optimizes the grain boundary phase, strengthens the original weak core-shell structure in the regenerated magnet, and enables the regenerated NdFeB magnet to obtain higher magnetic properties. The method provided by the present invention has simple process, low production cost, and has the advantages of green and low energy consumption, avoiding the waste of rare earth resources. DETAILED DESCRIPTION

[0068] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0069] Example 1

[0070] This embodiment provides a method for recycling grain boundary diffused NdFeB magnets, the method comprising the following steps:

[0071] (1) The waste grain boundary 50UH diffused NdFeB magnet is demagnetized, and then the magnet after demagnetization is de-plated;

[0072] The demagnetization process includes: vacuuming to maintain an absolute pressure of ≤1×10 -2 Pa, heated to 420 °C at a heating rate of 5 °C / min, kept at this temperature for 2 h, and then air-cooled to room temperature in an argon atmosphere;

[0073] The method of de-plating is sandblasting;

[0074] The sandblasting used 160-mesh glass bead abrasive, the sandblasting pressure was 0.6 MPa, the sandblasting distance was 200 mm, and the sandblasting angle was 60°.

[0075] (2) The magnet after de-plating treatment is crushed, hydrogen crushed and jet milled to obtain jet milled powder with an average particle size of 3.5 μm;

[0076] The hydrogen crushing comprises: absorbing hydrogen for 4 hours at a temperature of 260°C and a hydrogen pressure of 0.08 MPa, and after the hydrogen is saturated, the hydrogen is crushed at an absolute pressure of ≤1×10 -3 Pa, dehydrogenate for 5h at a temperature of 550°C; after dehydrogenation, pass through a 20-mesh sieve; add 0.1wt% antioxidant (antioxidant 1010) and 0.05wt% lubricant (SDS) to the sieved hydrogen powder, and mix them evenly in a powder mixer;

[0077] 0.2 wt% antioxidant (antioxidant 1010) and 0.1 wt% lubricant (SDS) are added to the jet mill and mixed evenly by a powder mixer;

[0078] (3) Mixing the jet milled powder with the rare earth alloy powder with an average particle size of 3 μm, and then performing orientation molding, cold isostatic pressing, sintering and tempering heat treatment, and air cooling to room temperature under an argon atmosphere to obtain a regenerated NdFeB magnet; the material of the rare earth alloy powder includes Pr 70 Cu 30 ; Taking the total mass percentage of the rare earth alloy powder and the airflow milled powder in step (3) as 100wt%, the mass percentage of the airflow milled powder is 96wt%;

[0079] The sintering is carried out at an absolute pressure of ≤10 -3 Pa, the sintering temperature is 1040°C and the time is 5h; the tempering heat treatment includes an absolute pressure of ≤10 -3 Pa; the temperature of the first tempering heat treatment is 850°C and the time is 4h; the temperature of the second tempering heat treatment is 460°C and the time is 5h.

[0080] Example 2

[0081] This embodiment provides a method for recycling grain boundary diffused NdFeB magnets. 70 Al 30 Except for this, the rest are the same as in Example 1.

[0082] Example 3

[0083] This embodiment provides a method for recycling grain boundary diffused NdFeB magnets. 70 Cu 30 Except for this, the rest are the same as in Example 1.

[0084] Example 4

[0085] This embodiment provides a method for recycling grain boundary diffused NdFeB magnets. 70 Al 10 Cu 20 Except for this, the rest are the same as in Example 1.

[0086] Example 5

[0087] This embodiment provides a method for recycling grain boundary diffused NdFeB magnets. 70 Al 30 Except for this, the rest are the same as in Example 1.

[0088] Example 6

[0089] This embodiment provides a method for recycling grain boundary diffused NdFeB magnets, the method comprising the following steps:

[0090] (1) The waste grain boundary 50UH diffused NdFeB magnet is demagnetized, and then the magnet after demagnetization is de-plated;

[0091] The demagnetization process includes: vacuuming to maintain an absolute pressure of ≤1×10 -2 Pa, heated to 400 °C at a heating rate of 5 °C / min, kept at this temperature for 2.5 h, and then air-cooled to room temperature in an argon atmosphere;

[0092] The method of de-plating is sandblasting;

[0093] The sandblasting used 120-mesh glass beads, the sandblasting pressure was 0.4 MPa, the sandblasting distance was 100 mm, and the sandblasting angle was 45°.

[0094] (2) The magnet after de-plating treatment is crushed, hydrogen crushed and jet milled to obtain jet milled powder with an average particle size of 3 μm;

[0095] The hydrogen crushing comprises: absorbing hydrogen for 3 hours at a temperature of 180°C and a hydrogen pressure of 0.06 MPa, and after the hydrogen is saturated, the hydrogen is crushed at an absolute pressure of ≤1×10 -3 Pa, dehydrogenation at 500°C for 6h; after dehydrogenation, sieve through a 20-mesh sieve; add 0.1wt% antioxidant (antioxidant 1010) and 0.05wt% lubricant (SDS) to the sieved hydrogen powder, and mix them evenly in a powder mixer;

[0096] 0.2 wt% antioxidant (antioxidant 1010) and 0.1 wt% lubricant (SDS) are added to the jet mill and mixed evenly by a powder mixer;

[0097] (3) Mixing the jet milled powder with the rare earth alloy powder with an average particle size of 2.5 μm, and then performing orientation molding, cold isostatic pressing, sintering and tempering heat treatment, and air cooling to room temperature under an argon atmosphere to obtain a regenerated NdFeB magnet; the material of the rare earth alloy powder includes Pr 70 Cu 30 ; Taking the total mass percentage of the rare earth alloy powder and the airflow milled powder in step (3) as 100wt%, the mass percentage of the airflow milled powder is 96wt%;

[0098] The sintering is carried out at an absolute pressure of ≤10 -3 Pa, the sintering temperature is 1050°C and the time is 6h; the tempering heat treatment includes an absolute pressure of ≤10 -3 Pa; the temperature of the first tempering heat treatment is 840°C and the time is 5h; the temperature of the second tempering heat treatment is 450°C and the time is 6h.

[0099] Example 7

[0100] This embodiment provides a method for recycling grain boundary diffused NdFeB magnets, the method comprising the following steps:

[0101] (1) The waste grain boundary 50UH diffused NdFeB magnet is demagnetized, and then the magnet after demagnetization is de-plated;

[0102] The demagnetization process includes: vacuuming to maintain an absolute pressure of ≤1×10 -2 Pa, heated to 440 °C at a heating rate of 5 °C / min, kept at this temperature for 1.5 h, and then air-cooled to room temperature in an argon atmosphere;

[0103] The method of de-plating is sandblasting;

[0104] The sandblasting used 200-mesh glass beads, the sandblasting pressure was 0.8 MPa, the sandblasting distance was 300 mm, and the sandblasting angle was 90°.

[0105] (2) The magnet after de-plating treatment is crushed, hydrogen crushed and jet milled to obtain jet milled powder with an average particle size of 4 μm;

[0106] The hydrogen crushing comprises: absorbing hydrogen for 5 hours at a temperature of 300°C and a hydrogen pressure of 0.1 MPa, and after the hydrogen is saturated, the hydrogen is crushed at an absolute pressure of ≤1×10 -3 Pa, dehydrogenation at 600°C for 4h; after dehydrogenation, sieve through a 20-mesh sieve; add 0.1wt% antioxidant (antioxidant 1010) and 0.05wt% lubricant (SDS) to the sieved hydrogen powder, and mix them evenly in a powder mixer;

[0107] 0.2 wt% antioxidant (antioxidant 1010) and 0.1 wt% lubricant (SDS) are added to the jet mill and mixed evenly by a powder mixer;

[0108] (3) Mixing the jet milled powder with the rare earth alloy powder with an average particle size of 4 μm, and then performing orientation molding, cold isostatic pressing, sintering and tempering heat treatment, and air cooling to room temperature under an argon atmosphere to obtain a regenerated NdFeB magnet; the material of the rare earth alloy powder includes Pr 70 Cu 30 ; Taking the total mass percentage of the rare earth alloy powder and the airflow milled powder in step (3) as 100wt%, the mass percentage of the airflow milled powder is 96wt%;

[0109] The sintering is carried out at an absolute pressure of ≤10 -3 Pa, the sintering temperature is 1070°C and the time is 3h; the tempering heat treatment includes an absolute pressure of ≤10 -3 Pa; the temperature of the first tempering heat treatment is 920°C and the time is 3h; the temperature of the second tempering heat treatment is 520°C and the time is 4h.

[0110] Example 8

[0111] This embodiment provides a method for recovering grain boundary diffused NdFeB magnets, which is the same as that of Embodiment 1 except that the sandblasting pressure is 0.2 MPa.

[0112] Example 9

[0113] This embodiment provides a method for recovering grain boundary diffused NdFeB magnets, which is the same as that of Embodiment 1 except that the sandblasting pressure is 1.0 MPa.

[0114] Example 10

[0115] This embodiment provides a method for recycling grain boundary diffused NdFeB magnets, which is the same as that of Embodiment 1 except that the sandblasting distance is 80 mm.

[0116] Embodiment 11

[0117] This embodiment provides a method for recycling grain boundary diffused NdFeB magnets, which is the same as that of Embodiment 1 except that the sandblasting distance is 350 mm.

[0118] Comparative Example 1

[0119] This comparative example provides a method for recycling grain boundary diffused NdFeB magnets, which is the same as Example 1 except that the quality of waste grain boundary 50UH diffused NdFeB magnets is replaced by waste 52SH dual-main-phase magnets.

[0120] Comparative Example 2

[0121] This comparative example provides a method for recycling grain boundary diffused NdFeB magnets, which is the same as Example 1 except that no rare earth alloy powder is used.

[0122] Comparative Example 3

[0123] This comparative example provides a method for recycling grain boundary diffused NdFeB magnets, the method comprising the following steps:

[0124] (1) The waste grain boundary 50UH diffused NdFeB magnets were demagnetized;

[0125] The demagnetization process includes: vacuuming to maintain an absolute pressure of ≤1×10 -2 Pa, heated to 420 °C at a heating rate of 5 °C / min, kept at this temperature for 2 h, and then air-cooled to room temperature in an argon atmosphere;

[0126] (2) The magnet after demagnetization is crushed, hydrogen crushed and jet milled to obtain jet milled powder with an average particle size of 3.5 μm;

[0127] The hydrogen crushing comprises: absorbing hydrogen for 4 hours at a temperature of 260°C and a hydrogen pressure of 0.08 MPa, and after the hydrogen is saturated, the hydrogen is crushed at an absolute pressure of ≤1×10 -3 Pa, dehydrogenate for 5 hours at a temperature of 550°C; after dehydrogenation, pass through a 20-mesh sieve; add 0.1wt% antioxidant and 0.05wt% lubricant to the sieved hydrogen powder, and mix them evenly in a powder mixer;

[0128] 0.2 wt% antioxidant and 0.1 wt% lubricant are added to the jet mill and mixed evenly by a powder mixer;

[0129] (3) Mixing the jet milled powder with the rare earth alloy powder with an average particle size of 3 μm, and then performing orientation molding, cold isostatic pressing, sintering and tempering heat treatment, and air cooling to room temperature under an argon atmosphere to obtain a regenerated NdFeB magnet; the material of the rare earth alloy powder includes Pr 70 Cu 30 ; Taking the total mass percentage of the rare earth alloy powder and the airflow milled powder in step (3) as 100wt%, the mass percentage of the airflow milled powder is 96wt%;

[0130] The sintering is carried out at an absolute pressure of ≤10 -3 Pa, the sintering temperature is 1040°C and the time is 5h; the tempering heat treatment includes an absolute pressure of ≤10 -3 Pa; the temperature of the first tempering heat treatment is 850°C and the time is 4h; the temperature of the second tempering heat treatment is 460°C and the time is 5h.

[0131] Performance Characterization

[0132] The remanence (Br), coercive force (Hcj), maximum magnetic energy product (BH) and squareness of magnet demagnetization curve (HK / Hcj) of the regenerated NdFeB magnets obtained in the above embodiments and comparative examples were measured. The magnet size during the measurement was 7mm×7mm×4mm, and the test temperature was 22°C. The results are shown in Table 1; the comparative example is the test result of the waste grain boundary 50UH diffused NdFeB magnet.

[0133] Table 1

[0134]

[0135]

[0136] In summary, the object of recovery of the method provided by the present invention is waste grain boundary diffusion NdFeB magnets, which have a uniform core-shell structure, in which the heavy rare earth elements are evenly dispersed. The present invention uses sandblasting to remove the coating, so that the core-shell structure of the grain boundary diffusion NdFeB magnet is not damaged and the rare earth loss is small; the use of rare earth alloy powder improves the liquid phase fluidity during sintering, optimizes the grain boundary phase, strengthens the original weak core-shell structure in the regenerated magnet, and enables the regenerated NdFeB magnet to obtain higher magnetic properties. The method provided by the present invention has simple process, low production cost, and has the advantages of green and low energy consumption, avoiding the waste of rare earth resources.

[0137] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for recovering grain boundary diffused NdFeB magnets, characterized in that: The method comprises the following steps: (1) The waste grain boundary diffusion NdFeB magnet is demagnetized, and then the magnet after demagnetization is de-plated; The method of de-plating is sandblasting; (2) The magnet after de-plating is crushed, hydrogen-crushed and jet-milled to obtain jet-milled powder; (3) mixing rare earth alloy powder with the jet mill powder, and then performing orientation molding, cold isostatic pressing, sintering and tempering heat treatment to obtain a regenerated NdFeB magnet; The rare earth alloy powder includes rare earth element RE and metal element ME, wherein RE includes any one of Pr, Nd, Tb, Dy or Ho or a combination of at least two thereof, and ME includes any one of Cu, Al or Ga or a combination of at least two thereof.

2. The method according to claim 1, characterized in that The material of the rare earth alloy powder includes Pr 70 Cu 30 , Pr 70 Al 30 , Pr 70 Al 10 Cu 20 、Nd 70 Cu 30 or Nd 70 Al 30 Any one or a combination of at least two of the following.

3. The method according to claim 1, characterized in that The average particle size of the jet milled powder in step (2) is 3 μm-4 μm; Preferably, the average particle size of the rare earth alloy powder in step (3) is 2.5 μm-4 μm; Preferably, taking the total mass percentage of the rare earth alloy powder and the airflow milled powder in step (3) as 100wt%, the mass percentage of the airflow milled powder is ≥95wt%.

4. The method according to claim 1, characterized in that: The blasting pressure of the blasting in step (1) is 0.4MPa-0.8MPa; Preferably, the blasting distance of the blasting in step (1) is 100 mm-300 mm; Preferably, the blasting angle of the sandblasting in step (1) is 45°-90°.

5. The method according to claim 1, characterized in that The demagnetization treatment in step (1) includes: vacuuming to maintain an absolute pressure of ≤1×10 -2 Pa, heat to 400-440°C at a heating rate not higher than 10°C / min, keep warm for 1.5h-2.5h, and then cool to room temperature in a protective atmosphere; Preferably, the gas used for the protective atmosphere includes any one of nitrogen, helium, argon or neon, or a combination of at least two of them.

6. The method according to claim 1, characterized in that The hydrogen crushing in step (2) comprises: absorbing hydrogen for 3 h to 5 h at a temperature of 150 ° C to 300 ° C and a hydrogen pressure of 0.05 MPa to 0.1 MPa, and after the hydrogen is saturated, the hydrogen is crushed at an absolute pressure of ≤1×10 -3 Pa, dehydrogenate at a temperature of 500°C-600°C for 4h-6h; sieve after dehydrogenation.

7. The method according to claim 1, characterized in that The sintering in step (3) is carried out at an absolute pressure of ≤1×10 -3 Pa conditions; Preferably, the sintering temperature in step (3) is 1000° C.-1070° C.; Preferably, the sintering time in step (3) is 3h-6h.

8. The method according to claim 1, characterized in that The tempering heat treatment in step (3) includes heating at an absolute pressure of ≤1×10 -3 The first tempering heat treatment and the second tempering heat treatment were carried out successively under the conditions of Pa; Preferably, the temperature of the primary tempering heat treatment is 820°C-920°C; Preferably, the time of the primary tempering heat treatment is 3h-5h; Preferably, the temperature of the secondary tempering heat treatment is 420°C-520°C; Preferably, the secondary tempering heat treatment time is 4h-6h.

9. The method according to claim 8, characterized in that After the tempering heat treatment in step (3), the product is cooled to room temperature in an oxygen-free atmosphere; Preferably, the gas used in the oxygen-free atmosphere includes any one of nitrogen, helium, argon or neon, or a combination of at least two of them.

10. The method according to claim 1, characterized in that The method comprises the following steps: (1) The waste grain boundary diffusion NdFeB magnet is demagnetized, and then the magnet after demagnetization is de-plated; The demagnetization process includes: vacuuming to maintain an absolute pressure of ≤1×10 -2 Pa, heat to 400-440°C at a heating rate not higher than 10°C / min, keep warm for 1.5h-2.5h, and then air-cool to room temperature in an argon atmosphere; The method of de-plating is sandblasting; The blasting pressure of the sandblasting is 0.4MPa-0.8MPa, the blasting distance is 100mm-300mm and the blasting angle is 45°-90°; (2) The magnet after de-plating is crushed, hydrogen crushed and jet milled to obtain jet milled powder with an average particle size of 3 μm-4 μm; The hydrogen crushing comprises: absorbing hydrogen for 3h-5h at a temperature of 150°C-300°C and a hydrogen pressure of 0.05MPa-0.1MPa, and after the hydrogen is saturated, the hydrogen is crushed at an absolute pressure of ≤1×10 -3 Pa, dehydrogenate at 500°C-600°C for 4h-6h; sieve after dehydrogenation; (3) Mixing the jet milled powder with the rare earth alloy powder with an average particle size of 2.5 μm-4 μm, and then performing orientation molding, cold isostatic pressing, sintering and tempering heat treatment, and air cooling to room temperature under an argon atmosphere to obtain a regenerated NdFeB magnet; the material of the rare earth alloy powder includes Pr 70 Cu 30 , Pr 70 Al 30 , Pr 70 Al 10 Cu 20 、Nd 70 Cu 30 or Nd 70 Al 30 Any one or a combination of at least two of the following; taking the total mass percentage of the rare earth alloy powder and the airflow milled powder in step (3) as 100wt%, the mass percentage of the airflow milled powder is ≥95wt%; The sintering is carried out at an absolute pressure of ≤10 -3 Pa, the sintering temperature is 1000℃-1070℃, and the time is 3h-6h; The tempering heat treatment includes an absolute pressure of ≤10 -3 Pa; the temperature of the first tempering heat treatment is 820℃-920℃, and the time is 3h-5h; the temperature of the second tempering heat treatment is 420℃-520℃, and the time is 4h-6h.

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