Rare earth permanent magnet single-piece forming preparation method

Abstract

The invention discloses a preparation method for rare earth permanent magnet single-piece forming, and belongs to the technical field of rare earth permanent magnet preparation. Comprising the following steps that 1, raw material powder is prepared, specifically, rare earth alloy is smelted and then condensed into sheets, then fine powder is obtained through a hydrogen explosion crushing technology, an antioxidant and a grain refiner are added, and the raw material powder is obtained through uniform mixing; 2, single-sheet mold orientation pressing, wherein the single-sheet mold with a nanometer coating is used for conducting two-step pressing on the raw material powder under the pulsed magnetic field; step 3, sintering and post-processing: sintering the material obtained by pressing in the step 2 in stages, and then applying an auxiliary magnetic field for cooling; the invention specifically focuses on an innovative method for preparing a high-performance rare earth permanent magnet by means of a single-piece forming process. The method has remarkable advantages and wide applicability in the aspect of efficient and low-cost production of permanent magnets such as neodymium iron boron and samarium cobalt.

Description

Technical Field

[0001] The invention relates to a preparation method for single-piece rare earth permanent magnets, belonging to the technical field of rare earth permanent magnet preparation. Background Art

[0002] In the traditional preparation process of rare earth permanent magnets, most of them use compression molding or isostatic pressing processes. However, these processes have many defects that are difficult to ignore: (1) Poor consistency of magnet density: When multiple pieces are pressed at the same time, the orientation magnetic field is unevenly distributed, resulting in poor consistency of magnet density. The density deviation of magnets with traditional processes can reach ±0.3%. (2) Low material utilization: After sintering, a large amount of mechanical processing is required, resulting in low material utilization. The material utilization rate of traditional processes is only 60%. (3) Complex shape magnet molding is difficult: For complex shape magnets, traditional molding processes are more difficult and prone to cracks or deformation problems. For example, the yield rate of special-shaped magnets using traditional processes is less than 60%. (4) High process energy consumption: Especially when preparing large-sized magnets, the efficiency is extremely low.

[0003] The Chinese invention patent application with application number CN202411013368.1 discloses a method for preparing high-performance rare earth permanent magnets, which relates to the field of magnet preparation technology and includes the following steps: vacuum melting to prepare RTBX quick-setting sheets as the main body; hydrogen cracking treatment, air flow milling, compression molding, cold isostatic pressing and pre-sintering of the RTBX quick-setting sheets in sequence to obtain a blank with a precursor structure; wherein, auxiliary powder is added during hydrogen cracking or air flow milling, and the auxiliary powder composition is MNPQ, wherein M is Fe or Co, N is B or C, P is any one of Al, Ga, and Cu, and Q is any one of O, N, and H; a TbxPry film layer is attached to the surface of the blank, and grain boundary diffusion heat treatment is performed to obtain a high-performance rare earth permanent magnet; the present invention prepares a matrix of a precursor structure that is conducive to diffusion, and with a special ratio of diffusion sources, the comprehensive performance of the diffused magnet can be improved, thereby obtaining a higher-performance magnet. This application improves performance by grain boundary diffusion, but requires two sintering steps. Summary of the Invention

[0004] (1) Technical issues to be solved

[0005] The technical problem to be solved by the present invention is to solve the problems of low production efficiency, high energy consumption and material loss of existing rare earth permanent magnets.

[0006] (2) Technical solution

[0007] In order to solve the above technical problems, the present invention provides a method for preparing a rare earth permanent magnet by single-piece molding, which adopts single-piece molding and comprises the following steps:

[0008] Step 1: Preparation of raw material powder: The rare earth alloy is smelted and rapidly condensed into thin flakes, which are then crushed by hydrogen explosion technology to obtain fine powder, antioxidants and grain refiners are added, and the raw material powder is fully and evenly mixed;

[0009] Step 2: Monolithic mold oriented pressing: Using a nano-coated monolithic mold, the raw material powder is pressed in two steps under a pulsed magnetic field;

[0010] Step 3: Sintering and post-processing: Sinter the material obtained by pressing in step 2 in sections and then apply an auxiliary magnetic field for cooling;

[0011] Among them, the magnetic properties are improved by vacuum rare earth infiltration treatment after sintering.

[0012] Furthermore, the pulse magnetic field strength is 1.8-2.2T, and the direction is perpendicular to the pressing direction.

[0013] Furthermore, the surface roughness of the inner cavity of the mold is ≤0.05 μm, and the coating is titanium nitride or diamond-like carbon.

[0014] Furthermore, in the step 1, the rare earth alloy is smelted and rapidly condensed into 0.3 mm flakes, and then hydrogen explosion crushing technology is used to obtain fine powder with an average particle size of 4 μm, and its particle size distribution is specifically: D10 = 3.2 μm, D90 = 4.8 μm.

[0015] Furthermore, in the step 1, 0.2-0.3 wt% of zinc stearate is added as an antioxidant and 0.1 wt% of aluminum powder is added as a grain refiner.

[0016] Furthermore, in the step 2, the mold is a cemented carbide mold with a titanium nitride coating, the surface roughness of the mold cavity Ra is less than or equal to 0.05 μm, and the coating thickness is controlled at 5-10 μm.

[0017] Furthermore, in the step 2, during the process of filling the magnetic powder, a pulsed magnetic field with an intensity of 2.0 T is applied, the magnetic field frequency is set to 5 Hz, the duty cycle is 30%, and the direction of the magnetic field is perpendicular to the pressing direction.

[0018] Furthermore, in the step 2, the two-step pressing is first performed at a pressure of 80-100 MPa for pre-pressing, and then at a pressure of 250-280 MPa for final pressing, with a holding time of 20 seconds.

[0019] Furthermore, in step 3, the segmented sintering includes:

[0020] Degreasing stage: In a vacuum environment of 10-2Pa, heat the temperature to 900-950℃ at a rate of 5℃ / min and keep at this temperature for 1.5-2 hours.

[0021] Sintering stage: Then increase the temperature to 1100-1120℃ at a heating rate of 10℃ / min and keep it at that temperature for 2.5-3 hours.

[0022] Furthermore, in the step three, after the sintering is completed, an auxiliary magnetic field is applied for cooling, and an auxiliary magnetic field of 1.0 T is applied, and the film is cooled to room temperature at a cooling rate of 25°C / min. After cooling, surface treatment is performed, and a 3μm thick aluminum coating is deposited by magnetron sputtering, and the coating adhesion is ≥50MPa.

[0023] (3) Beneficial effects

[0024] The above technical solution of the present invention has the following advantages:

[0025] (1) Single-piece molding process: Only one magnet is pressed each time, and the pulsed magnetic field technology is combined to optimize the grain orientation, so that the magnetic energy product (BH) max is increased by 12%-18%.

[0026] (2) Low-loss mold technology: The service life of the nano-coated mold is increased by 4 times. The traditional mold can be used 200 times per mold, while the mold of the present invention can be used up to 1,000 times.

[0027] (3) Magnetic field-assisted cooling: effectively suppresses grain boundary phase segregation and increases the coercivity (Hcj) by 10%-15%. For example, the Hcj of NdFeB magnets is increased from 1100kA / m to 1250kA / m.

[0028] (4) Near-net-shape design: The molding dimension accuracy reaches ±0.03mm, and the subsequent processing volume is reduced by 80%.

[0029] The density deviation of the magnets produced by the process of the present invention is only ±0.05%. The material utilization rate can reach 85%, and the yield rate is improved for magnets with complex shapes. The process of the present invention has the potential to reduce energy consumption by 30% compared to traditional processes. By optimizing the magnetic field orientation, molding pressure, and sintering process, the present invention achieves efficient production of high-density, high-performance rare earth permanent magnets, while effectively reducing energy consumption and material loss. This method has significant advantages and wide applicability in the efficient and low-cost production of permanent magnets such as neodymium iron boron (NdFeB) and samarium cobalt (SmCo).

[0030] In addition to the technical problems solved by the present invention, the technical features of the technical solutions constituted, and the advantages brought about by the technical features of these technical solutions described above, other technical features of the present invention and the advantages brought about by these technical features will be further explained in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 The figure is a schematic diagram of the preparation process flow chart of the present invention. DETAILED DESCRIPTION

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0034] Example 1

[0035] like Figure 1 A method for preparing a rare earth permanent magnet by monolithic molding is shown, which comprises the following steps:

[0036] Step 1: Raw material powder preparation: The rare earth alloy is smelted and condensed into flakes, which are then crushed using hydrogen explosion technology to obtain a fine powder. An antioxidant and a grain refiner are added and uniformly mixed to obtain the raw material powder. Specifically, the rare earth alloy is smelted and rapidly condensed into 0.3mm flakes, which are then crushed using hydrogen explosion technology to obtain a fine powder with an average particle size of 4μm. The particle size distribution is: D10 = 3.2μm, D90 = 4.8μm. 0.2-0.3wt% zinc stearate is added as an antioxidant, and 0.1wt% aluminum powder is added as a grain refiner.

[0037] Step 2: Monolithic mold oriented pressing: Use a monolithic mold with a nano-coating to perform two-step pressing on the raw material powder under a pulsed magnetic field; specifically: the mold uses a cemented carbide mold with a titanium nitride coating, the surface roughness of the mold inner cavity Ra ≤ 0.05μm, and the coating thickness is controlled at 5-10μm; during the filling process of magnetic powder, a pulsed magnetic field with a strength of 2.0T is applied, the magnetic field frequency is set to 5Hz, the duty cycle is 30%, and the magnetic field direction is perpendicular to the pressing direction; the two-step pressing is first pre-pressed at a pressure of 80-100MPa, and then final pressed at a pressure of 250-280MPa, and the holding time is 20 seconds.

[0038] Step 3, sintering and post-processing: the material obtained by pressing in step 2 is sintered in sections and then cooled by applying auxiliary magnetic field; the section sintering includes: (1) degreasing stage: in a vacuum degree of 10 -2 Pa environment, heating to 900-950℃ at a rate of 5℃ / min, and keeping at this temperature for 1.5-2 hours; (2) sintering stage: then heating to 1100-1120℃ at a rate of 10℃ / min, and keeping at this temperature for 2.5-3 hours. Apply auxiliary magnetic field cooling. After sintering is completed, apply auxiliary magnetic field of 1.0T, cool to room temperature at a cooling rate of 25℃ / min, and carry out surface treatment after cooling. Deposit a 3μm thick aluminum coating by magnetron sputtering, with a coating adhesion of ≥50MPa.

[0039] Among them, the magnetic properties are improved by vacuum rare earth infiltration treatment after sintering.

[0040] Test Example 1: Preparation of NdFeB Magnets

[0041] Nd 26.5 Fe 63.2 B 10 The alloy was rapidly solidified into 0.3 mm thin sheets, hydrogen exploded, and sieved to obtain 4 μm powder.

[0042] 0.3% zinc stearate and 0.1% aluminum powder were added and mixed, and then filled into a titanium nitride coating mold with an inner diameter of Φ20 mm.

[0043] A 2.0T pulsed magnetic field was applied, with a pre-press of 80MPa and a final press of 250MPa for molding.

[0044] Vacuum sintering was performed: debinding at 950°C for 1.5 hours, sintering at 1100°C for 3 hours, and then cooling down to room temperature under magnetic field cooling.

[0045] Performance test results are: Br = 1.48T, Hcj = 1250kA / m, (BH)max = 420kJ / m 3 .

[0046] Experimental Example 2: Preparation of Samarium Cobalt Magnets

[0047] Sm2Co 17 The alloy was rapidly solidified into 0.5 mm thin sheets after melting, and then processed to 3.5 μm by air jet grinding after hydrogen explosion.

[0048] 0.2% zinc stearate and 0.1% aluminum powder were added and mixed, and the mixture was filled into a diamond-like carbon (DLC) coating mold with an inner diameter of Φ30 mm.

[0049] A 1.8T pulsed magnetic field was applied, with a pre-press of 100MPa and a final press of 280MPa for molding.

[0050] Vacuum sintering: debinding at 900℃ for 2 hours, sintering at 1120℃ for 2.5 hours, and then cooling to room temperature in a magnetic field.

[0051] Performance test results are: Br = 1.12T, Hcj = 850kA / m, (BH)max = 280kJ / m 3 .

[0052] Experimental Example 3: Preparation of high-temperature magnets

[0053] In Nd2Fe 14 3% heavy rare earth element TbH3 (particle size 2 μm) is added to B alloy.

[0054] After forming according to the process of Example 1, vacuum rare earth infiltration treatment (810° C. insulation for 6 hours) was carried out.

[0055] Performance test results are: Br = 1.45T, Hcj = 1300kA / m, (BH)max = 430kJ / m 3 (High temperature stability at 200°C increased by 40%).

[0056] Technical Effects

[0057] Magnetic properties are significantly improved: Br≥1.45T, (BH)max≥400kJ / m 3 , compared with the traditional process, it is improved by 15%-20%; the coercive force (Hcj) is improved by 8%-15%, for example, the NdFeB magnet is improved from 1100kA / m to 1250kA / m.

[0058] Material utilization and efficiency: Material utilization has increased from 60% to over 85%, and the production efficiency of large-size magnets (>50mm) has increased by 3 times; the single-piece molding cycle has been shortened to 30 minutes, while the traditional multi-piece process requires 120 minutes.

[0059] Energy consumption and cost: Production energy consumption is reduced by 30%, and unit energy consumption is reduced from 800kWh / kg to 560kWh / kg; subsequent processing volume is reduced by 70%, and comprehensive costs are reduced by 25%-30%.

[0060] The experimental comparison data table is as follows:

[0061]

[0062] The present invention significantly improves the preparation efficiency and performance of rare earth permanent magnets by integrating the latest technologies (such as nano-coating molds and vacuum rare earth infiltration) and refined parameter control, and has significant industrialization potential.

[0063] The specific embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

Claims

1. A method for preparing a rare earth permanent magnet by monolithic molding, characterized in that: The single-piece molding process includes the following steps: Step 1: Preparation of raw material powder: The rare earth alloy is smelted and condensed into thin flakes, which are then crushed by hydrogen explosion technology to obtain fine powder, antioxidants and grain refiners are added, and the raw material powder is uniformly mixed; Step 2: Monolithic mold oriented pressing: Using a nano-coated monolithic mold, the raw material powder is pressed in two steps under a pulsed magnetic field; Step 3: Sintering and post-processing: Sinter the material obtained by pressing in step 2 in sections and then apply an auxiliary magnetic field for cooling; Among them, the magnetic properties are improved by vacuum rare earth infiltration treatment after sintering.

2. The method for preparing a rare earth permanent magnet by monolithic molding according to claim 1, characterized in that: The pulse magnetic field strength is 1.8-2.2 T, and its direction is perpendicular to the pressing direction.

3. The method for preparing a rare earth permanent magnet by monolithic molding according to claim 1, characterized in that: The surface roughness of the inner cavity of the mold is ≤0.05 μm, and the coating is titanium nitride or diamond-like carbon.

4. The method for preparing a rare earth permanent magnet by monolithic molding according to any one of claims 1 to 3, characterized in that: In the step 1, the rare earth alloy is smelted and rapidly condensed into 0.3 mm flakes, and then crushed by hydrogen explosion technology to obtain fine powder with an average particle size of 4 μm, and its particle size distribution is specifically: D10 = 3.2 μm, D90 = 4.8 μm.

5. The method for preparing a rare earth permanent magnet by monolithic molding according to claim 4, characterized in that: In the step 1, 0.2-0.3 wt % of zinc stearate is added as an antioxidant and 0.1 wt % of aluminum powder is added as a grain refiner.

6. The method for preparing a rare earth permanent magnet by monolithic molding according to any one of claims 1 to 3, characterized in that: In the step 2, the mold is a hard alloy mold with a titanium nitride coating, the surface roughness of the mold cavity Ra is less than or equal to 0.05 μm, and the coating thickness is controlled at 5-10 μm.

7. The method for preparing a rare earth permanent magnet by monolithic molding according to claim 6, characterized in that: In the step 2, during the process of filling the magnetic powder, a pulsed magnetic field with an intensity of 2.0 T is applied, the magnetic field frequency is set to 5 Hz, the duty cycle is 30%, and the direction of the magnetic field is perpendicular to the pressing direction.

8. The method for preparing a rare earth permanent magnet by monolithic molding according to claim 7, characterized in that: In the step 2, the two-step pressing is first performed at a pressure of 80-100 MPa for pre-pressing, and then at a pressure of 250-280 MPa for final pressing, with a holding time of 20 seconds.

9. The method for preparing a rare earth permanent magnet by monolithic molding according to any one of claims 1 to 3, characterized in that: In the step 3, the segmented sintering includes: Degreasing stage: at a vacuum degree of 10 -2 Pa environment, raise the temperature to 900-950℃ at a rate of 5℃ / min, and keep at this temperature for 1.5-2 hours; Sintering stage: Then increase the temperature to 1100-1120℃ at a heating rate of 10℃ / min and keep it at that temperature for 2.5-3 hours.

10. The method for preparing a rare earth permanent magnet by monolithic molding according to claim 9, characterized in that: In the step three, after sintering is completed, an auxiliary magnetic field is applied for cooling, and an auxiliary magnetic field of 1.0 T is applied to cool to room temperature at a cooling rate of 25°C / min. After cooling, surface treatment is performed to deposit a 3 μm thick aluminum coating by magnetron sputtering, and the coating adhesion is ≥50 MPa.

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