A method for preparing a magnet using recycled grain boundary diffusion neodymium-iron-boron

Abstract

The application provides a method for preparing a magnet by recycling grain boundary diffusion neodymium-iron-boron, and the method comprises the following steps: (1) the waste grain boundary diffusion neodymium-iron-boron magnet is subjected to demagnetization treatment, and then the magnet after the demagnetization treatment is subjected to a plating layer removing treatment; the method for the plating layer removing treatment is sand blasting; (2) the magnet after the plating layer removing treatment is subjected to crushing, hydrogen crushing and airflow milling to obtain airflow milled powder; (3) rare earth alloy powder is mixed with the airflow milled powder, and then orientation forming, cold isostatic pressing, sintering and tempering heat treatment are carried out to obtain a regenerated neodymium-iron-boron magnet. The method provided by the application adopts the sand blasting method to carry out the plating layer removing treatment, so that the core-shell structure of the grain boundary diffusion neodymium-iron-boron magnet is not damaged and the loss of rare earth is small, the use of the rare earth alloy powder achieves the purpose of strengthening the core-shell structure of the regenerated neodymium-iron-boron magnet, improving the liquid phase flowability in the sintering process, optimizing the grain boundary and making the regenerated neodymium-iron-boron magnet have excellent magnetic properties.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of magnetic materials, and relates to a method for recycling magnets, in particular to a method for recycling grain boundary diffusion neodymium-iron-boron magnets. BACKGROUND

[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 a sintering process. However, in the traditional sintering process, a large amount of raw materials is converted into NdFeB waste, and the development of an environmentally friendly and cost-effective recycling process is crucial to the NdFeB industry.

[0003] At present, the recycling of neodymium-iron-boron magnetic materials mainly includes three methods: wet recycling, fire recycling and short process recycling. The wet recycling process is complicated and causes serious environmental burden; the fire recycling has high energy consumption and cost. In order to solve the drawbacks of the above-mentioned recycling methods, it is necessary to introduce an efficient and energy-saving recycling method. There are related researches on the recycling of single main phase or double main phase prepared neodymium-iron-boron magnets, but there is no related research on the recycling of grain boundary diffusion prepared neodymium-iron-boron magnets.

[0004] The microstructure of grain boundary diffusion magnets has unique advantages. The heavy rare earth elements form a thin epitaxial layer at the grain boundary of the main phase, which can achieve good magnetic isolation effect. In the prior art, the chemical method or manual polishing is used to remove the plating layer on the surface of the magnet, which easily damages the core-shell structure of the grain boundary diffusion magnet and easily increases the loss of rare earth elements.

[0005] Therefore, it is necessary to provide a recycling method for grain boundary diffusion magnets. SUMMARY

[0006] In view of the deficiencies in the prior art, the purpose of the present application is to provide a method for recycling grain boundary diffusion neodymium-iron-boron magnets, which can not damage the core-shell structure of the grain boundary diffusion neodymium-iron-boron magnets and has small loss of rare earth elements, and can also achieve the purposes of strengthening the core-shell structure of the regenerated neodymium-iron-boron magnets, improving the liquid flowability in the sintering process, optimizing the grain boundaries and making the regenerated neodymium-iron-boron magnets have excellent magnetic properties.

[0007] To achieve this purpose, the present application adopts the following technical solutions:

[0008] The present application provides a method for recycling grain boundary diffusion neodymium-iron-boron magnets, which comprises the following steps:

[0009] (1) The waste grain boundary diffusion neodymium-iron-boron magnets are subjected to demagnetization treatment, and then the magnets after the demagnetization treatment are subjected to a plating layer removal treatment;

[0010] The method for removing the plating layer is sand blasting.

[0011] (2) The magnet after the stripping treatment is broken, hydrogen-fragmented and airflow-milled to obtain airflow-milled powder;

[0012] (3) The mixed rare earth alloy powder and the airflow-milled powder are mixed, and then orientation forming, cold isostatic pressing, sintering and tempering heat treatment are performed to obtain a regenerated neodymium-iron-boron magnet;

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

[0014] The method provided by the application is used for recycling waste grain boundary diffusion neodymium-iron-boron magnets, which have a uniform core-shell structure and in which heavy rare earth elements are uniformly and dispersedly distributed. The method provided by the application uses sand blasting to perform stripping treatment, so that the core-shell structure of the grain boundary diffusion neodymium-iron-boron magnet is not damaged and the loss of rare earth elements is small. The use of the rare earth alloy powder improves the liquid phase flowability in the sintering process, optimizes the grain boundary phase, strengthens the original weak core-shell structure in the regenerated magnet, and enables the regenerated neodymium-iron-boron magnet to obtain high magnetic performance. The method provided by the application has the advantages of simple process, low production cost, green and low energy consumption, and avoids waste of rare earth resources.

[0015] In the rare earth alloy powder used by the application, RE comprises any one or a combination of at least two of Pr, Nd, Tb, Dy or Ho, and 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 a combination of Pr, Nd, Dy and Ho.

[0016] In the rare earth alloy powder used by the application, ME comprises any one or a combination of at least two of Cu, Al or Ga, and typical but non-limiting combinations include a combination of Cu and Al, a combination of Al and Ga, a combination of Cu and Ga, or a combination of Cu, Al and Ga.

[0017] Preferably, the material of the rare earth alloy powder comprises any one or a combination of at least two of Pr 70 Cu 30 , Pr 70 Al 30 , Pr 70 Al 10 Cu 20 , Nd 70 Cu 30 , or Nd 70 Al 30 , and typical but non-limiting combinations include Pr 70 Cu 30 and Pr70 Al 30 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 airflow 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] For example, 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 hydrogen crushing and air flow milling parameters when obtaining the rare earth alloy powder, as long as 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. 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 blasting in step (1) is 100-300 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 the remaining values in the value range are also applicable.

[0024] Preferably, the blasting angle of the blasting 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 the remaining values in the value range are also applicable.

[0025] For example, the blasting in the present application uses 120-200 mesh abrasives, and the material of the abrasive includes any one or a combination of at least two of garnet, brown corundum or glass beads. A typical but non-limiting combination includes 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) includes: maintaining the absolute pressure ≤1×10 -2 Pa by vacuumizing, heating to 400-440℃ at a heating rate of not higher than 10℃ / min, holding for 1.5-2.5h, and then air cooling to room temperature in a protective atmosphere.

[0027] As a preferred technical solution of the present application, when performing the demagnetization treatment, the absolute pressure is maintained ≤1×10 -2 Pa by vacuumizing, for example, it 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 the remaining values in the value range are also applicable.

[0028] As a preferred technical solution of the present application, when performing the demagnetization treatment, the heating rate of the heating is not higher than 10℃ / min, for example, it can be 1℃ / min, 3℃ / min, 5℃ / min, 6℃ / min, 8℃ / min or 10℃ / min, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0029] As a preferred technical solution of the present application, the temperature during the demagnetization treatment is 400-440℃, for example, it can be 400℃, 410℃, 420℃, 430℃ or 440℃, but is not limited to the listed values, and the remaining values in the value range are also applicable.

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

[0031] For example, the room temperature during the demagnetization treatment in step (1) is 15-30℃, for example, it can be 15℃, 18℃, 20℃, 25℃, 28℃ or 30℃, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0032] Preferably, the gas used in the protective atmosphere includes any one or a combination of at least two of nitrogen, helium, argon or neon, and a typical but non-limiting combination includes 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) includes: hydrogen absorption at a temperature of 150-300℃ and a hydrogen pressure of 0.05-0.1MPa for 3-5h, after saturation of hydrogen absorption, hydrogen desorption at an absolute pressure ≤1×10 -3 Pa and a temperature of 500-600℃ for 4-6h; and sieving after hydrogen desorption.

[0034] The temperature of the hydrogen crushing in step (2) of the present application is 150-300℃, for example, it can be 150℃, 180℃, 200℃, 240℃, 250℃, 280℃ or 300℃, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0035] The hydrogen pressure of the hydrogen crushing in step (2) of the present application is 0.05-0.1MPa, 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 the remaining values in the value range are also applicable.

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

[0037] The hydrogenation time of the hydrogenation in step (2) is 3-5 hours, for example, it can be 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0038] The absolute pressure of the dehydrogenation in the hydrogenation in step (2) is ≤1×10 -3 Pa, for example, it 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 the remaining values in the value range are also applicable.

[0039] The temperature of the dehydrogenation in the hydrogenation in step (2) is 500-600℃, for example, it can be 500℃, 520℃, 550℃, 560℃, 580℃ or 600℃, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0040] The time of the dehydrogenation in the hydrogenation in step (2) is 4-6 hours, for example, it can be 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours, but is not limited to the listed values, and the remaining values in the value range are also applicable.

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

[0042] Preferably, the method provided by the application further comprises uniformly mixing the sieved hydrogenation powder with an antioxidant and a lubricant, wherein the amount of the antioxidant is 0.08wt%-0.12wt% of the sieved hydrogenation powder, and the amount of the lubricant is 0.04wt%-0.05wt% of the sieved hydrogenation powder.

[0043] Preferably, the method provided by the application further comprises uniformly mixing the jet mill powder with an antioxidant and a lubricant, wherein the amount of the antioxidant is 0.18wt%-0.22wt% of the jet mill powder, and the amount of the lubricant is 0.08wt%-0.12wt% of the jet mill powder.

[0044] Preferably, the sintering in step (3) is performed under an absolute pressure of ≤1×10 -3 Pa, for example, it can be 0.1×10 -3 Pa, 0.3×10 -3 Pa, 0.5×10-3 Pa, 0.6 x 10 -3 Pa, 0.8 x 10 -3 Pa, or 1 x 10 -3 Pa, but not limited to the listed values, and the remaining unlisted values within the range are also applicable.

[0045] Preferably, the sintering temperature of 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 not limited to the listed values, and the remaining unlisted values within the range are also applicable.

[0046] Preferably, the sintering time of step (3) is 3h-6h, for example, it can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6h, but not limited to the listed values, and the remaining unlisted values within the range are also applicable.

[0047] Preferably, the tempering heat treatment of step (3) comprises a first tempering heat treatment and a second tempering heat treatment, which are sequentially performed under the condition of absolute pressure ≤ 1 x 10 -3 Pa, for example, it can be 0.1 x 10 -3 Pa, 0.3 x 10 -3 Pa, 0.5 x 10 -3 Pa, 0.6 x 10 -3 Pa, 0.8 x 10 -3 Pa, or 1 x 10 -3 Pa, but not limited to the listed values, and the remaining unlisted values within the range are also applicable.

[0048] Preferably, the temperature of the first 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 not limited to the listed values, and the remaining unlisted values within the range are also applicable.

[0049] Preferably, the time of the first tempering heat treatment is 3h-5h, for example, it can be 3h, 3.5h, 4h, 4.5h, or 5h, but not limited to the listed values, and the remaining unlisted values within the range are also applicable.

[0050] Preferably, the temperature of the second tempering heat treatment is 420°C-520°C, for example, it can be 420°C, 450°C, 480°C, 500°C, or 520°C, but not limited to the listed values, and the remaining unlisted values within the range are also applicable.

[0051] Preferably, the time of the secondary tempering heat treatment is 4h-6h, for example, it can be 4h, 4.5h, 5h, 5.5h or 6h, but is not limited to the listed values, and the remaining values in the value range are also applicable.

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

[0053] The room temperature in the air cooling to room temperature after the tempering heat treatment in step (3) of the present application is 15℃-30℃, for example, it can be 15℃, 18℃, 20℃, 24℃, 25℃, 28℃ or 30℃, but is not limited to the listed values, and the remaining values in the value range are also applicable.

[0054] Preferably, the gas used in the oxygen-free atmosphere includes any one or a combination of at least two of nitrogen, helium, argon or neon, and a typical but non-limiting combination includes 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 application, the method comprises the following steps:

[0056] (1) The waste grain boundary diffusion Nd-Fe-B magnet is subjected to demagnetization treatment, and then the magnet after the demagnetization treatment is subjected to a deplating layer treatment;

[0057] The demagnetization treatment comprises: vacuumizing to keep the absolute pressure ≤1×10 -2 Pa, heating to 400℃-440℃ at a heating rate not higher than 10℃ / min, keeping for 1.5h-2.5h, and then air cooling to room temperature in an argon atmosphere;

[0058] The method of the deplating layer treatment is sand blasting;

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

[0060] (2) The magnet after the deplating layer treatment is subjected to crushing, hydrogen decrepitation and airflow milling to obtain an airflow milled powder with an average particle size of 3μm-4μm;

[0061] The hydrogen decrepitation comprises: hydrogen absorption for 3h-5h under the conditions of a temperature of 150℃-300℃ and a hydrogen pressure of 0.05MPa-0.1MPa, after hydrogen absorption saturation, hydrogen desorption for 4h-6h under the conditions of an absolute pressure ≤1×10 -3 Pa and a temperature of 500℃-600℃; and sieving after hydrogen desorption;

[0062] (3) mixing airflow milling powder with rare earth alloy powder with an average particle size of 2.5-4 μm, and then performing orientation forming, cold isostatic pressing, sintering and tempering heat treatment, air cooling to room temperature in an argon atmosphere to obtain a regenerated neodymium-iron-boron 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; the mass percentage of the airflow milling powder is ≥ 95 wt% based on the total mass percentage of the rare earth alloy powder and the airflow milling powder in step (3) being 100 wt%;

[0063] The sintering is performed under an absolute pressure of ≤ 10 -3 Pa, the sintering temperature is 1000-1070 °C, and the time is 3-6 h;

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

[0065] The numerical ranges described in the present application include not only the point values recited above, but also any point values between the recited values, limited only by the practicality and the consideration of simplicity, the present application does not exhaustively list the specific point values included in the range.

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

[0067] The recycling object of the method provided by the present application is waste grain boundary diffusion neodymium-iron-boron magnet, which has a uniform core-shell structure, and heavy rare earth elements are uniformly and dispersedly distributed therein; the present application uses sandblasting to perform plating removal treatment, so that the core-shell structure of the grain boundary diffusion neodymium-iron-boron magnet is not damaged and the loss of rare earth is small; the use of rare earth alloy powder improves the liquid phase flowability in the sintering process, optimizes the grain boundary phase, strengthens the original weak core-shell structure in the regenerated magnet, so that the regenerated neodymium-iron-boron magnet can obtain higher magnetic properties. The method provided by the present application is simple in process, low in production cost, has the advantages of green and low energy consumption, and avoids 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 preparing a magnet by recycling grain boundary diffused NdFeB, the method comprising the following steps:

[0071] (1) The waste grain boundary 50UH diffused NdFeB magnet is demagnetized, and then the demagnetized magnet 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 removing the coating is sandblasting;

[0074] The sandblasting was performed using 160-mesh glass beads, with a sandblasting pressure of 0.6 MPa, a sandblasting distance of 200 mm, and a sandblasting angle of 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 under an absolute pressure of ≤1×10 -3 Dehydrogenate the mixture under the conditions of Pa and temperature of 550°C for 5 hours; after dehydrogenation, pass through a 20-mesh sieve; add 0.1wt% antioxidant (antioxidant 1010) and 0.05wt% lubricant (SDS) to the sieved hydrogenated powder and mix them evenly in a powder mixer;

[0077] 0.2 wt% of antioxidant (antioxidant 1010) and 0.1 wt% of lubricant (SDS) were added to the jet mill and mixed evenly using 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 -3at a temperature of 1040℃ and for a time of 5h; said tempering heat treatment comprises a first tempering heat treatment and a second tempering heat treatment, which are performed successively under a pressure of ≤10 -3 at a temperature of 850℃ and for a time of 4h, and a second tempering heat treatment at a temperature of 460℃ and for a time of 5h.

[0080] Embodiment 2

[0081] The embodiment provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, wherein, except that the material of a rare earth alloy powder is Pr 70 Al 30 The rest is the same as Embodiment 1.

[0082] Embodiment 3

[0083] The embodiment provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, wherein, except that the material of a rare earth alloy powder is Nd 70 Cu 30 The rest is the same as Embodiment 1.

[0084] Embodiment 4

[0085] The embodiment provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, wherein, except that the material of a rare earth alloy powder is Pr 70 Al 10 Cu 20 The rest is the same as Embodiment 1.

[0086] Embodiment 5

[0087] The embodiment provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, wherein, except that the material of a rare earth alloy powder is Nd 70 Al 30 The rest is the same as Embodiment 1.

[0088] Embodiment 6

[0089] The embodiment provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, and the method comprises the following steps:

[0090] (1) the waste grain boundary 50UH diffusion neodymium-iron-boron magnet is subjected to demagnetization treatment, and then the magnet subjected to the demagnetization treatment is subjected to a plating layer removing treatment;

[0091] The demagnetization treatment comprises: vacuumizing to keep an absolute pressure of ≤1x10 -2 Pa, heating to 400℃ at a heating rate of 5℃ / min, and keeping for 2.5h, and then air cooling to room temperature in an argon atmosphere;

[0092] The method of the desmearing treatment is sand blasting;

[0093] The sand blasting uses 120-point glass bead abrasives, the sand blasting pressure is 0.4 MPa, the sand blasting distance is 100 mm, and the sand blasting angle is 45°.

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

[0095] The hydrogen-fragmentation includes: hydrogen absorption for 3 h under the condition of a temperature of 180 ℃ and a hydrogen pressure of 0.06 MPa, after hydrogen absorption saturation, dehydrogenation for 6 h under the condition of an absolute pressure ≤1×10 -3 Pa and a temperature of 500 ℃; after dehydrogenation, screening through a 20-mesh sieve; adding 0.1 wt% of an antioxidant (antioxidant 1010) and 0.05 wt% of a lubricant (SDS) into the hydrogen-fragmented powder after screening, and uniformly mixing in a powder mixer;

[0096] Adding 0.2 wt% of an antioxidant (antioxidant 1010) and 0.1 wt% of a lubricant (SDS) into the airflow-milled powder, and uniformly mixing through a powder mixer;

[0097] (3) mixing the airflow-milled powder with 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 neodymium-iron-boron 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 100 wt%, the mass percentage of the airflow-milled powder is 96 wt%;

[0098] The sintering is performed under the condition of an absolute pressure ≤10 -3 Pa, the sintering temperature is 1050 ℃, and the time is 6 h; the tempering heat treatment includes first-level tempering heat treatment and second-level tempering heat treatment performed in sequence under the condition of an absolute pressure ≤10 -3 Pa; the temperature of the first-level tempering heat treatment is 840 ℃, and the time is 5 h; the temperature of the second-level tempering heat treatment is 450 ℃, and the time is 6 h.

[0099] Example 7

[0100] The embodiment provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, and the method comprises the following steps:

[0101] (1) an abandoned grain boundary 50UH diffusion neodymium-iron-boron magnet is subjected to demagnetization treatment, and then the magnet after the demagnetization treatment is subjected to desmearing treatment;

[0102] The demagnetization treatment comprises: vacuumizing and keeping the absolute pressure ≤1×10 -2 Pa, and heating to 440℃ at a heating rate of 5℃ / min, keeping for 1.5h, and then air cooling to room temperature in an argon atmosphere;

[0103] The method of the deplating treatment is sand blasting.

[0104] The sand blasting uses 200-mesh glass bead abrasive, the sand blasting pressure is 0.8MPa, the sand blasting distance is 300mm, and the sand blasting angle is 90°.

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

[0106] The hydrogen-fragmentation comprises: hydrogen absorption for 5h under the conditions of a temperature of 300℃ and a hydrogen pressure of 0.1MPa, and after hydrogen absorption saturation, hydrogen desorption for 4h under the conditions of an absolute pressure ≤1×10 -3 Pa and a temperature of 600℃; the hydrogen-fragmented powder after desorption is sieved through a 20-mesh sieve; 0.1wt% of an antioxidant (antioxidant 1010) and 0.05wt% of a lubricant (SDS) are added to the sieved hydrogen-fragmented powder, and the mixture is uniformly mixed in a powder mixer;

[0107] 0.2wt% of an antioxidant (antioxidant 1010) and 0.1wt% of a lubricant (SDS) are added to the airflow-milled powder, and the mixture is uniformly mixed in a powder mixer;

[0108] (3) The airflow-milled powder is mixed with rare earth alloy powder with an average particle size of 4μm, and then orientation molding, cold isostatic pressing, sintering, and tempering heat treatment are performed, and air cooling to room temperature is performed in an argon atmosphere to obtain a regenerated neodymium-iron-boron magnet; the material of the rare earth alloy powder comprises Pr 70 Cu 30 ; based on the total mass percentage of the rare earth alloy powder and the airflow-milled powder in step (3) being 100wt%, the mass percentage of the airflow-milled powder is 96wt%;

[0109] The sintering is performed under the condition of an absolute pressure ≤10 -3 Pa, the sintering temperature is 1070℃, and the time is 3h; the tempering heat treatment comprises first-level tempering heat treatment and second-level tempering heat treatment performed in sequence under the condition of an absolute pressure ≤10 -3 Pa; the temperature of the first-level tempering heat treatment is 920℃, and the time is 3h; the temperature of the second-level tempering heat treatment is 520℃, and the time is 4h.

[0110] Example 8

[0111] The embodiment provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, which is identical to that in the embodiment 1, except that the sand blasting pressure is 0.2 MPa.

[0112] Embodiment 9

[0113] The embodiment provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, which is identical to that in the embodiment 1, except that the sand blasting pressure is 1.0 MPa.

[0114] Embodiment 10

[0115] The embodiment provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, which is identical to that in the embodiment 1, except that the sand blasting distance is 80 mm.

[0116] Embodiment 11

[0117] The embodiment provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, which is identical to that in the embodiment 1, except that the sand blasting distance is 350 mm.

[0118] Comparative Example 1

[0119] The comparative example provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, which is identical to that in the embodiment 1, except that the waste grain boundary 50UH diffusion neodymium-iron-boron magnet is replaced by the waste 52SH double main phase magnet.

[0120] Comparative Example 2

[0121] The comparative example provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, which is identical to that in the embodiment 1, except that the rare earth alloy powder is not used.

[0122] Comparative Example 3

[0123] The comparative example provides a method for preparing a magnet by using recycled grain boundary diffusion neodymium-iron-boron, which comprises the following steps:

[0124] (1) the waste grain boundary 50UH diffusion neodymium-iron-boron magnet is subjected to demagnetization treatment;

[0125] The demagnetization treatment comprises: vacuumizing and keeping the absolute pressure less than or equal to 1x10 -2 Pa, heating to 420 ℃ at a heating rate of 5 ℃ / min, keeping for 2 h, and then air cooling to room temperature in an argon atmosphere;

[0126] (2) the magnet subjected to the demagnetization treatment is subjected to crushing, hydrogen crushing and air flow grinding, so as to obtain air flow grinding powder with an average particle size of 3.5 μm;

[0127] The hydrogen decrepitation includes: hydrogen absorption for 4h under the condition of 260℃ and 0.08MPa hydrogen pressure, after hydrogen absorption saturation, dehydrogenation for 5h under the condition of ≤1×10 -3 Pa absolute pressure and 550℃ temperature; after dehydrogenation, the hydrogen decrepitation powder is sieved through a 20 mesh sieve; 0.1wt% antioxidant and 0.05wt% lubricant are added into the sieved hydrogen decrepitation powder and mixed uniformly in a powder mixer;

[0128] 0.2wt% antioxidant and 0.1wt% lubricant are added into the jet mill powder and mixed uniformly in a powder mixer;

[0129] (3) the jet mill powder is mixed with rare earth alloy powder with an average particle size of 3μm, then orientation forming, cold isostatic pressing, sintering and tempering heat treatment are carried out, and the sintered body is air-cooled to room temperature in argon atmosphere to obtain a regenerated neodymium-iron-boron magnet; the material of the rare earth alloy powder includes Pr 70 Cu 30 ; in terms of 100wt% of the total mass percentage of the jet mill powder and the rare earth alloy powder in step (3), the mass percentage of the jet mill powder is 96wt%;

[0130] The sintering is carried out under the condition of ≤10 -3 Pa absolute pressure, the sintering temperature is 1040℃ and the sintering time is 5h; the tempering heat treatment includes first-stage tempering heat treatment and second-stage tempering heat treatment which are carried out successively under the condition of ≤10 -3 Pa absolute pressure; the temperature of the first-stage tempering heat treatment is 850℃ and the time is 4h; the temperature of the second-stage tempering heat treatment is 460℃ and the time is 5h.

[0131] Performance characterization

[0132] The remanence (Br), coercivity (Hcj), maximum magnetic energy product (BH) and squareness degree of demagnetization curve (HK / Hcj) of the regenerated neodymium-iron-boron magnets obtained after the above examples and comparative examples are measured, the magnet size during the measurement is 7mm×7mm×4mm, and the test temperature is 22℃, and the obtained results are shown in Table 1; the comparative example is the test results of the waste grain boundary 50UH diffusion neodymium-iron-boron magnet.

[0133] Table 1

[0134]

[0135] In summary, the present application provides a method for recycling waste grain boundary diffusion Nd-Fe-B magnets having a uniform core-shell structure, wherein heavy rare earth elements are uniformly distributed and dispersed. The present application uses sand blasting to remove the plating layer, which does not damage the core-shell structure of the grain boundary diffusion Nd-Fe-B magnet and has a small loss of rare earth elements. The use of rare earth alloy powder improves the liquid flowability during sintering, optimizes the grain boundary phase, strengthens the original weak core-shell structure in the regenerated magnet, and enables the regenerated Nd-Fe-B magnet to obtain higher magnetic performance. The method provided by the present application is simple, has low production cost, has the advantages of green and low energy consumption, and avoids waste of rare earth resources.

[0136] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method of making a magnet from recycled grain boundary diffusion neodymium-iron-boron characterized in that, The method comprises the following steps: (1) the waste grain boundary diffusion neodymium-iron-boron magnet is subjected to demagnetization treatment, and then the demagnetized magnet is subjected to a plating layer removal treatment; The demagnetization process comprises: vacuumizing to keep the absolute pressure ≤1×10 -2 Pa, heating to 400-440℃ at a heating rate not higher than 10℃ / min, keeping for 1.5-2.5h, and then air cooling to room temperature in argon atmosphere; the plating layer removal treatment method is sand blasting; the sand blasting pressure is 0.4-0.8 MPa, the sand blasting distance is 100-300 mm, and the sand blasting angle is 45-90°; (2) the magnet subjected to the plating layer removal treatment is subjected to crushing, hydrogen fragmentation and airflow grinding to obtain an airflow ground powder with an average particle size of 3-4 μm; The hydrogen decrepitation includes: hydrogen absorption for 3-5 hours under the conditions of a temperature of 150-300 DEG C and a hydrogen pressure of 0.05-0.1 MPa, and after hydrogen absorption saturation, dehydrogenation for 4-6 hours under the conditions of an absolute pressure of ≤1x10 -3 Pa and a temperature of 500-600 DEG C; and sieving after dehydrogenation. (3) mixing airflow mill powder with rare earth alloy powder with an average particle size of 2.5-4 μm, then performing orientation forming, cold isostatic pressing, sintering and tempering heat treatment, air cooling to room temperature in an argon atmosphere to obtain a regenerated neodymium-iron-boron 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; the mass percentage of the airflow mill powder is ≥ 95 wt% based on the total mass percentage of the rare earth alloy powder and the airflow mill powder in step (3) being 100 wt%. The sintering is carried out at an absolute pressure ≤ 10 -3 Pa, at a temperature of 1000-1070 °C for 3-6 h. The tempering heat treatment includes an absolute pressure of ≤10 -3 Pa conditions, the primary tempering heat treatment and the secondary tempering heat treatment are carried out in sequence; the temperature of the primary tempering heat treatment is 820℃-920℃, and the time is 3h-5h; the temperature of the secondary tempering heat treatment is 420℃-520℃, and the time is 4h-6h.

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