A method for preparing low-melting-point rare-earth alloys to improve the coercivity and mechanical properties of cerium-containing sintered NdFeB permanent magnets

Abstract

This invention provides a method for preparing low-melting-point rare-earth alloys to improve the coercivity and mechanical properties of cerium-containing sintered NdFeB permanent magnets. The method includes: rotary crushing of low-melting-point rare-earth alloy strips to obtain coarse low-melting-point rare-earth alloy particles; rotary crushing of a matrix alloy casting to obtain coarse matrix alloy particles; mixing the coarse low-melting-point rare-earth alloy particles and the coarse matrix alloy particles, followed by hydrogen crushing and then air jet milling to obtain low-melting-point magnetic powder; orienting and shaping the low-melting-point magnetic powder and then performing isostatic pressing to obtain a billet; sintering and heat-treating the billet to obtain a cerium-containing sintered NdFeB permanent magnet. This invention utilizes melt rapid quenching to prepare low-melting-point rare-earth alloy strips, employs rotary crushing to produce fine coarse particles, and adds these particles during hydrogen crushing to ensure better and more uniform mixing with the matrix alloy, thus meeting the needs of large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of magnetic materials technology, and in particular relates to a method for preparing a low-melting-point rare earth alloy to improve the coercivity and mechanical properties of cerium-containing sintered NdFeB permanent magnets. Background Technology

[0002] In recent years, the rapid development of industries such as new energy vehicles, wind power generation, and industrial robots has led to a continuous increase in the demand for sintered NdFeB permanent magnet materials, resulting in a continuous increase in the consumption of rare earth resources such as praseodymium and neodymium. To fully and rationally utilize high-abundance cerium rare earth resources in the production of rare earth permanent magnet materials, cerium-containing sintered NdFeB magnets have been widely used in the industry. However, because the intrinsic magnetic properties of Re2Fe14B compounds, which contain high-abundance cerium, are relatively low—for example, Ce2Fe14B's saturation magnetization and magnetocrystalline anisotropy field are only 1.18T and 2.40 MA / m, respectively, far lower than Nd2Fe14B compounds' 1.61T and 5.36 MA / m—the addition of high-abundance cerium significantly deteriorates the magnet's coercivity. Furthermore, research has found that cerium is more prone to segregation at the grain boundaries of the magnet, resulting in a significant reduction in the mechanical properties of cerium-containing sintered NdFeB magnets. Therefore, there is an urgent need to provide a method to improve the coercivity and mechanical properties of cerium-containing sintered NdFeB magnets. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a method for preparing cerium-containing sintered NdFeB permanent magnets with improved coercivity and mechanical properties using low-melting-point rare earth alloys. The cerium-containing sintered NdFeB permanent magnets prepared by the method provided by this invention have better coercivity and mechanical properties.

[0004] This invention provides a method for preparing low-melting-point rare-earth alloys to improve the coercivity and mechanical properties of cerium-containing sintered NdFeB permanent magnets, comprising:

[0005] Low-melting-point rare earth alloy strips are subjected to rotary tooth crushing to obtain low-melting-point rare earth alloy coarse particles.

[0006] The matrix alloy casting is subjected to rotary tooth crushing to obtain coarse matrix alloy particles.

[0007] The low-melting-point rare earth alloy coarse particles and the matrix alloy coarse particles are mixed and then subjected to hydrogen crushing, followed by air jet milling to obtain low-melting-point magnetic powder.

[0008] The low-melting-point magnetic powder is oriented and shaped, and then subjected to isostatic pressing to obtain a blank.

[0009] The blank is sintered and heat-treated to obtain a cerium-containing sintered NdFeB permanent magnet.

[0010] The hydrogen crushing is carried out under stirring conditions, and the stirring speed is 20-60 rpm;

[0011] The hydrogen breakup includes:

[0012] The process involves preheating, introducing hydrogen gas to achieve hydrogen saturation, and then performing dehydrogenation.

[0013] The preheating treatment is performed at a temperature of 200–300°C for a time of 30–60 minutes.

[0014] The dehydrogenation treatment is carried out at a temperature of 500–800°C for a time of 300–1200 min.

[0015] Preferably, the composition of the low-melting-point rare earth alloy strip is:

[0016] HR x M y ,

[0017] HR is selected from one or more of Pr, Nd, Tb, and Dy.

[0018] M is selected from one or more of Al, Ga, Cu, Zn, and Sn.

[0019] x is 60–90 wt.%, and y is 10–40 wt.%.

[0020] Preferably, the matrix alloy casting contains Pr, Nd, Ce, Al, Cu, Co, Fe, B and Zr.

[0021] Preferably, the mass content of the low-melting-point rare earth alloy coarse particles in the low-melting-point magnetic powder is 0.1% to 2%.

[0022] Preferably, the low-melting-point magnetic powder has an average particle size of 2–3 μm.

[0023] Preferably, the particle size of the low-melting-point rare earth alloy coarse particles is 0.2 to 0.5 mm.

[0024] Preferably, the particle size of the coarse particles in the matrix alloy is 1 to 5 mm.

[0025] Preferably, the average thickness of the low-melting-point rare earth alloy strip is 0.02 to 0.04 mm.

[0026] Preferably, the magnetic field strength for the orientation forming is 2.0 to 2.5 T;

[0027] The pressure for the isostatic pressing process is 150–220 MPa.

[0028] Preferably, the sintering temperature is 1030–1100°C;

[0029] The heat treatment is tempering, including:

[0030] First-stage tempering and second-stage tempering;

[0031] The temperature for the first-stage tempering is 800–920°C;

[0032] The temperature for the secondary tempering is 460–560°C.

[0033] This invention employs melt rapid quenching to prepare low-melting-point rare-earth alloy strips. The strips are then crushed into fine, coarse particles using a rotary toothed crusher and added during hydrogenation to ensure better and more uniform mixing with the base alloy, meeting the needs of large-scale industrial production. Furthermore, this invention utilizes diffusion of the low-melting-point rare-earth alloy during the dehydrogenation stage, dissolving it and coating the matrix. This more uniform coating results in cerium-containing sintered NdFeB magnets with superior coercivity and mechanical properties. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] This invention provides a method for preparing low-melting-point rare-earth alloys to improve the coercivity and mechanical properties of cerium-containing sintered NdFeB permanent magnets, comprising:

[0036] Low-melting-point rare earth alloy strips are subjected to rotary tooth crushing to obtain low-melting-point rare earth alloy coarse particles.

[0037] The matrix alloy casting is subjected to rotary tooth crushing to obtain coarse matrix alloy particles.

[0038] The low-melting-point rare earth alloy coarse particles and the matrix alloy coarse particles are mixed and then subjected to hydrogen crushing, followed by air jet milling to obtain low-melting-point magnetic powder.

[0039] The low-melting-point magnetic powder is oriented and shaped, and then subjected to isostatic pressing to obtain a blank.

[0040] The blank is sintered and heat-treated to obtain a cerium-containing sintered NdFeB permanent magnet.

[0041] The hydrogen crushing is carried out under stirring conditions, and the stirring speed is 20-60 rpm;

[0042] The hydrogen breakup includes:

[0043] The process involves preheating, introducing hydrogen gas to achieve hydrogen saturation, and then performing dehydrogenation.

[0044] The preheating treatment is performed at a temperature of 200–300°C for a time of 30–60 minutes.

[0045] The dehydrogenation treatment is carried out at a temperature of 500–800°C for a time of 300–1200 min.

[0046] In this invention, the composition of the low rare earth alloy strip is preferably:

[0047] HR x M y ,

[0048] HR is selected from one or more of Pr, Nd, Tb, and Dy.

[0049] M is selected from one or more of Al, Ga, Cu, Zn, and Sn.

[0050] x is 60–90 wt.%, and y is 10–40 wt.%.

[0051] In this invention, x is preferably 70-80 wt.%, more preferably 75 wt.%.

[0052] In this invention, the y is preferably 20-30 wt.%, more preferably 25 wt.%.

[0053] In this invention, the preferred method for preparing the low-melting-point rare earth alloy strip includes:

[0054] After the alloy raw materials are batched, they are rapidly quenched to obtain low-melting-point rare earth alloy strips.

[0055] The present invention does not impose any special restrictions on the alloy raw materials. Any metal materials well known to those skilled in the art can be used to prepare the materials according to the composition of the pre-obtained low-melting-point rare earth alloy strips.

[0056] In this invention, the rapid quenching temperature is preferably 700-1100℃, more preferably 800-1000℃, and most preferably 900℃; the copper roller rotation speed during the rapid quenching process is preferably 15-30m / s, more preferably 20-25m / s; and the average thickness of the low melting point rare earth alloy strip is preferably 0.02-0.04mm, more preferably 0.03mm.

[0057] In this invention, the rotary tooth crushing is preferably carried out under the protection of an inert gas; the particle size of the low melting point rare earth alloy coarse particles is preferably 0.2-0.5 mm, more preferably 0.3-0.4 mm.

[0058] In this invention, the matrix alloy casting contains Pr, Nd, Ce, Al, Cu, Co, Fe, B, and Zr; the mass content of Ce in the matrix alloy casting is preferably 8.5-10, more preferably 9-9.5; the preferred composition of the matrix alloy casting is: PrNd23.5Ce8.5Al0.4Cu0.2Co0.6Fe65.67B0.98Zr0.15 or PrNd21.5Ce10Al0.4Cu0.2Co0.8Fe66.01B0.94Zr0.15.

[0059] In this invention, the preferred method for preparing the matrix alloy casting includes:

[0060] After the alloy raw materials are batched, they are melted and cast to obtain the matrix alloy casting.

[0061] In this invention, the matrix alloy casting is preferably prepared using a rapid solidification process; the melting temperature during the rapid solidification process is preferably 1450–1500℃, more preferably 1480℃; the casting temperature is preferably 1350–1400℃, more preferably 1380℃; the copper roller rotation speed is preferably 1–3 m / s, more preferably 2 m / s; and the average thickness of the matrix alloy casting is preferably 0.2–0.4 mm, more preferably 0.3 mm.

[0062] In this invention, the rotary tooth crushing is preferably carried out under the protection of an inert gas; the particle size of the coarse matrix alloy particles is preferably 1-5 mm, more preferably 2-4 mm, and most preferably 3 mm.

[0063] In this invention, the low-melting-point rare earth alloy strip is relatively thin, and the rotary tooth crusher can break the strip. The broken rare earth alloy particles can coat the main phase grains of the matrix alloy during hydrogen crushing. If it is not broken or the broken particles are large, the uniformity and magnetic properties of the prepared magnet will be poor due to uneven distribution.

[0064] In this invention, the hydrogen crushing is preferably carried out in a hydrogen crushing furnace; the hydrogen crushing is carried out under stirring conditions; the stirring speed is preferably 30-50 rpm, more preferably 40 rpm. In this invention, the preheating temperature is preferably 250°C; the preheating time is preferably 40-50 min, more preferably 45 min; the dehydrogenation treatment temperature is preferably 600-700°C, more preferably 650°C; the dehydrogenation treatment time is preferably 500-1000 min, more preferably 600-800 min.

[0065] In this invention, the air jet mill is preferably carried out in a nitrogen gas flow.

[0066] In this invention, the mass content of the low-melting-point rare earth alloy coarse particles in the low-melting-point magnetic powder is preferably 0.1-2%, more preferably 0.5-1.5%, even more preferably 0.8-1.2%, and most preferably 1%.

[0067] In this invention, the average particle size of the low melting point magnetic powder is preferably 2 to 3 μm, more preferably 2.5 μm.

[0068] In this invention, after obtaining the low-melting-point magnetic powder, it preferably further includes:

[0069] The low-melting-point magnetic powder and lubricant are mixed and then oriented.

[0070] In this invention, the orientation forming is preferably carried out in an inert gas; the magnetic field strength for the orientation forming is preferably 2.0 to 2.5 T, more preferably 2.1 to 2.4 T, and most preferably 2.3 T.

[0071] In this invention, the pressure of the isostatic pressing treatment is preferably 150-220 MPa, more preferably 160-210 MPa, even more preferably 170-200 MPa, and most preferably 180-190 MPa.

[0072] In this invention, the sintering is preferably carried out in a sintering furnace; the sintering temperature is preferably 1030-1100℃, more preferably 1040-1090℃, even more preferably 1050-1080℃, and most preferably 1060-1070℃; the sintering time is preferably 3-5h, more preferably 4h.

[0073] In this invention, the heat treatment is preferably tempering; the tempering method preferably includes:

[0074] First, perform a first-stage tempering process, followed by a second-stage tempering process.

[0075] In this invention, the temperature of the first-stage tempering is preferably 800–920°C, more preferably 850–900°C, and most preferably 860–880°C; the time of the first-stage tempering is preferably 6–10 h, more preferably 7–9 h, and most preferably 8 h; the temperature of the second-stage tempering is preferably 460–560°C, more preferably 480–540°C, and most preferably 500–520°C; and the time of the second-stage tempering is preferably 2–4 h, more preferably 3 h.

[0076] In this invention, the preferred method for preparing the low-melting-point rare earth alloy to improve the coercivity and mechanical properties of cerium-containing sintered NdFeB permanent magnets includes the following steps:

[0077] Step 1) Prepare raw materials according to the composition of the base alloy, and use a rapid solidification process to melt and cast the raw materials to obtain the base alloy casting.

[0078] Step 2) Prepare raw materials according to the low melting point rare earth alloy composition, and use a rapid quenching process to melt and quench the raw materials to obtain low melting point rare earth alloy strips.

[0079] Step 3) The low-melting-point rare earth alloy strips and matrix alloy castings are respectively prepared into coarse particles of low-melting-point rare earth alloy strips with a length of 0.2-0.5 mm and coarse particles of matrix alloy castings with a length of 1-5 mm by rotary tooth crushing under the protection of inert gas.

[0080] Step 4) Mix the coarse particles of low-melting-point rare earth alloy strips and coarse particles of matrix alloy castings in a certain proportion to form total alloy coarse particles, and then place them in a hydrogen crushing furnace. During the hydrogen crushing process, the hydrogen crushing furnace is stirred at 20 rpm to 60 rpm. After preheating at 200 to 300°C for 30 to 60 minutes, hydrogen gas is introduced and the mixture is saturated with hydrogen. Then, it is dehydrogenated at 500 to 800°C for 300 to 1200 minutes to obtain low-melting-point coarse crushed powder composed of low-melting-point rare earth alloy and matrix alloy.

[0081] Step 5) Then the low melting point coarsely crushed powder is ground in a nitrogen air jet mill to obtain low melting point air jet mill magnetic powder;

[0082] Step 6) Weigh the low-melting-point air jet mill magnetic powder, add lubricant and mix evenly, then perform orientation molding in an inert atmosphere, followed by isostatic pressing.

[0083] Step 7) The billet after isostatic pressing is fed into a sintering furnace for high-temperature sintering and tempering heat treatment to obtain cerium-containing sintered NdFeB permanent magnets with high coercivity and high mechanical properties.

[0084] This invention employs melt rapid quenching to prepare low-melting-point rare-earth alloy strips. The strips are crushed into fine, coarse particles using a rotary toothed crusher and added during hydrogenation to ensure better and more uniform mixing with the base alloy, meeting the needs of large-scale industrial production. Furthermore, this invention utilizes diffusion of the low-melting-point rare-earth alloy during the dehydrogenation stage, dissolving it and coating the matrix more uniformly, resulting in cerium-containing sintered NdFeB permanent magnets with high coercivity and high mechanical properties.

[0085] Example 1

[0086] Cerium-containing sintered NdFeB permanent magnets were prepared according to the following method:

[0087] Step 1) Prepare raw materials according to the composition of the matrix alloy, wherein the matrix alloy composition and mass percentage are PrNd23.5Ce8.5Al0.4Cu0.2Co0.6Fe65.67B0.98Zr0.15. Use a rapid solidification process to melt and cast the raw materials to obtain matrix alloy castings; wherein the rapid solidification process is as follows: melting temperature is 1480℃, casting temperature is 1380℃, copper roller speed is 2m / s, and the average thickness of the obtained matrix alloy castings is 0.3mm;

[0088] Step 2) Prepare raw materials according to the composition of low-melting-point rare earth alloy, and use a rapid quenching process to melt and quench the raw materials to obtain low-melting-point rare earth alloy strips; wherein the mass percentage composition of the low-melting-point rare earth alloy is Pr90Cu5Al5; the rapid quenching process is specifically as follows: the rapid quenching temperature is 1100℃, the copper roller speed is 28m / s, and the average thickness of the obtained low-melting-point rare earth alloy strips is 0.02mm.

[0089] Step 3) The low-melting-point rare earth alloy strips and matrix alloy castings are prepared into 0.2 mm low-melting-point rare earth alloy strip coarse particles and 5 mm matrix alloy casting coarse particles respectively by rotary tooth crushing under the protection of inert gas.

[0090] Step 4) The coarse particles of low-melting-point rare earth alloy strips and coarse particles of matrix alloy castings are mixed in a certain proportion to form coarse particles of total alloy and then placed in a hydrogen crushing furnace. The coarse particles of low-melting-point rare earth alloy strips account for 2 wt% of the total coarse particles of alloy. In order to compare the performance of sintered NdFeB magnets, the coarse particles of matrix alloy castings obtained in Step 3) are placed in another hydrogen crushing furnace. The hydrogen crushing process of the hydrogen crushing furnace containing the coarse particles of total alloy is the same as that of the crushing furnace containing the coarse particles of matrix alloy castings. During the hydrogen crushing process, the hydrogen crushing furnace is stirred at 60 rpm. After preheating at 300°C for 30 min, hydrogen is introduced and hydrogen is absorbed to saturation. Then, after dehydrogenation treatment at 800°C for 300 min, low-melting-point coarse crushed powder composed of low-melting-point rare earth alloy and matrix alloy and coarse crushed powder of matrix alloy are obtained in the two hydrogen crushing furnaces, respectively.

[0091] Step 5) Then, the low-melting-point coarse crushed powder and the matrix alloy coarse crushed powder obtained in step 4) are ground in a nitrogen gas flow mill to obtain low-melting-point gas flow mill magnetic powder and matrix alloy gas flow mill magnetic powder, respectively; wherein the average particle size of the low-melting-point gas flow mill magnetic powder and the matrix alloy gas flow mill magnetic powder are both 2μm.

[0092] Step 6) Weigh the low-melting-point air jet mill magnetic powder and the matrix alloy air jet mill magnetic powder separately, add lubricant to each and mix evenly, then perform orientation molding in an inert atmosphere, followed by isostatic pressing; the magnetic field strength for orientation molding is 2.0T, and the isostatic pressing pressure is 150MPa.

[0093] Step 7) Both the low-melting-point air-jet mill magnetic powder blanks and the matrix alloy air-jet mill magnetic powder blanks, after isostatic pressing, are fed into a sintering furnace for high-temperature sintering and tempering heat treatment. The low-melting-point air-jet mill magnetic powder blanks, after sintering, yield cerium-containing sintered NdFeB permanent magnets with high coercivity and high mechanical properties, labeled B1. The matrix alloy air-jet mill magnetic powder blanks, after sintering, yield matrix sintered NdFeB permanent magnets, labeled A1. The high-temperature sintering temperature is 1040℃, and the high-temperature sintering time is 5h. The tempering heat treatment process includes: a first-stage tempering temperature of 900℃ and a first-stage tempering time of 8h, and a second-stage tempering temperature of 460℃ and a second-stage tempering time of 4h.

[0094] The low-melting-point sintered NdFeB permanent magnet B1 and the matrix sintered NdFeB permanent magnet A1 prepared in Example 1 were cut into D10mm*10mm sample columns for magnetic properties (GB / T 3217-2013 Magnetic Test Methods for Permanent Magnet (Hard Magnetic) Materials) and cut into 15mm*6mm*5mm magnets for mechanical properties (GB / T232-2010 Bending Test Methods for Metallic Materials). The test results are as follows:

[0095] Br(kGs) Hcj(kOe) (BH)max(MGOe) Hk / Hci Flexural strength [MPa] A1 12.8 12.7 39.68 96.8 260 B1 12.5 15.85 37.76 97.2 320

[0096] It can be seen that the cerium-containing sintered NdFeB permanent magnet B1 prepared in Example 1 has a coercivity increased by 3.15 kOe and mechanical properties increased by 60 MPa compared with the matrix sintered NdFeB permanent magnet A1 prepared without the addition of low melting point alloy.

[0097] Example 2

[0098] Cerium-containing sintered NdFeB permanent magnets were prepared according to the following method:

[0099] Step 1) Prepare raw materials according to the composition of the matrix alloy, wherein the composition and mass percentage of the matrix alloy are PrNd21.5Ce10Al0.4Cu0.2Co0.8Fe66.01B0.94Zr0.15. Use a rapid solidification process to melt and cast the raw materials to obtain matrix alloy castings; wherein the rapid solidification process is as follows: melting temperature is 1460℃, casting temperature is 1360℃, copper roller speed is 2m / s, and the average thickness of the obtained matrix alloy casting is 0.3mm;

[0100] Step 2) Prepare raw materials according to the composition of low-melting-point rare earth alloy, and use a rapid quenching process to melt and quench the raw materials to obtain low-melting-point rare earth alloy strips; wherein the mass percentage composition of the low-melting-point rare earth alloy is Pr60Cu10Ga25Zn5; the rapid quenching process is specifically a rapid quenching temperature of 700℃, a copper roller speed of 15m / s, and the average thickness of the obtained low-melting-point rare earth alloy strips is 0.04mm.

[0101] Step 3) The low-melting-point rare earth alloy strips and matrix alloy castings are prepared into 0.2 mm low-melting-point rare earth alloy strip coarse particles and 0.5 mm matrix alloy casting coarse particles respectively by rotary tooth crushing under the protection of inert gas.

[0102] Step 4) The coarse particles of low-melting-point rare earth alloy strips and coarse particles of matrix alloy castings are mixed in a certain proportion to form coarse particles of total alloy and then placed in a hydrogen crushing furnace. The coarse particles of low-melting-point rare earth alloy strips account for 0.5 wt% of the total coarse particles of alloy. In order to compare the performance of sintered NdFeB magnets, the coarse particles of matrix alloy castings obtained in Step 3) are placed in another hydrogen crushing furnace. The hydrogen crushing process of the hydrogen crushing furnace containing the total alloy coarse particles and the crushing furnace containing the coarse particles of matrix alloy castings is the same. During the hydrogen crushing process, the hydrogen crushing furnace is stirred at 20 rpm. After preheating at 300°C for 30 min, hydrogen is introduced and hydrogen is absorbed to saturation. Then, after dehydrogenation treatment at 500°C for 1200 min, low-melting-point coarse crushed powder composed of low-melting-point rare earth alloy and matrix alloy and coarse crushed powder of matrix alloy are obtained in the two hydrogen crushing furnaces, respectively.

[0103] Step 5) Then, the low-melting-point coarse crushed powder and the matrix alloy coarse crushed powder obtained in step 4) are ground in a nitrogen gas flow mill to obtain low-melting-point gas flow mill magnetic powder and matrix alloy gas flow mill magnetic powder, respectively; wherein the average particle size of the low-melting-point gas flow mill magnetic powder and the matrix alloy gas flow mill magnetic powder is 3μm.

[0104] Step 6) Weigh the low-melting-point air jet mill magnetic powder and the matrix alloy air jet mill magnetic powder separately, add lubricant to each and mix evenly, then perform orientation molding in an inert atmosphere, followed by isostatic pressing; the magnetic field strength for orientation molding is 2.5T, and the isostatic pressing pressure is 220MPa.

[0105] Step 7) Both the low-melting-point air-jet mill magnetic powder blanks and the matrix alloy air-jet mill magnetic powder blanks, after isostatic pressing, are fed into a sintering furnace for high-temperature sintering and tempering heat treatment. The low-melting-point air-jet mill magnetic powder blanks, after sintering, yield cerium-containing sintered NdFeB permanent magnets with high coercivity and high mechanical properties, labeled B1. The matrix alloy air-jet mill magnetic powder blanks, after sintering, yield matrix sintered NdFeB permanent magnets, labeled A1. The high-temperature sintering temperature is 1037℃, and the high-temperature sintering time is 5h. The tempering heat treatment process includes: a first-stage tempering temperature of 800℃ and a first-stage tempering time of 10h, and a second-stage tempering temperature of 560℃ and a second-stage tempering time of 4h.

[0106] The low-melting-point sintered NdFeB permanent magnet B1 and the matrix sintered NdFeB permanent magnet A1 prepared in Example 2 were cut into D10mm*10mm sample columns for magnetic performance measurement, and magnets cut into 15mm*6mm*5mm samples for mechanical performance measurement. The test methods were the same as in Example 1, and the test results were as follows:

[0107] Br(kGs) Hcj(kOe) (BH)max(MGOe) Hk / Hci Flexural strength [MPa] A1 12.08 12.52 34.86 97.8 180 B1 11.90 16.82 34.02 96.2 350

[0108] It can be seen that the cerium-containing sintered NdFeB permanent magnet B1 prepared in Example 2 has a coercivity increased by 4.3 kOe and mechanical properties increased by 170 MPa compared with the matrix sintered NdFeB permanent magnet A1 prepared without the addition of low melting point alloy.

[0109] Example 3

[0110] Cerium-containing sintered NdFeB permanent magnets were prepared according to the following method:

[0111] Step 1) Prepare raw materials according to the composition of the matrix alloy, wherein the composition and mass percentage of the matrix alloy are PrNd23.5Ce8.5Al0.4Cu0.2Co0.6Fe65.67B0.98Zr0.15. Use a rapid solidification process to melt and cast the raw materials to obtain matrix alloy castings; wherein the rapid solidification process is as follows: melting temperature is 1480℃, casting temperature is 1380℃, copper roller speed is 2m / s, and the average thickness of the obtained matrix alloy castings is 0.3mm;

[0112] Step 2) Prepare raw materials according to the composition of low-melting-point rare earth alloy, and use a rapid quenching process to melt and quench the raw materials to obtain low-melting-point rare earth alloy strips; wherein the mass percentage composition of the low-melting-point rare earth alloy is Pr10Nd70Sn10Al10; the rapid quenching process is specifically a rapid quenching temperature of 700℃, a copper roller speed of 20m / s, and the average thickness of the obtained low-melting-point rare earth alloy strips is 0.03mm.

[0113] Step 3) The low-melting-point rare earth alloy strips and matrix alloy castings are prepared into 0.2 mm low-melting-point rare earth alloy strip coarse particles and 5 mm matrix alloy casting coarse particles respectively by rotary tooth crushing under the protection of inert gas.

[0114] Step 4) The coarse particles of low-melting-point rare earth alloy strips and coarse particles of matrix alloy castings are mixed in a certain proportion to form coarse particles of total alloy and then placed in a hydrogen crushing furnace. The coarse particles of low-melting-point rare earth alloy strips account for 0.1 wt% of the total coarse particles of alloy. In order to compare the performance of sintered NdFeB magnets, the coarse particles of matrix alloy castings obtained in Step 3) are placed in another hydrogen crushing furnace. The hydrogen crushing process of the hydrogen crushing furnace containing the total alloy coarse particles is the same as that of the crushing furnace containing the coarse particles of matrix alloy castings. During the hydrogen crushing process, the hydrogen crushing furnace is stirred at 20 rpm. After preheating at 200°C for 30 min, hydrogen is introduced and hydrogen is absorbed to saturation. Then, after dehydrogenation treatment at 600°C for 1000 min, low-melting-point coarse crushed powder composed of low-melting-point rare earth alloy and matrix alloy and coarse crushed powder of matrix alloy are obtained in the two hydrogen crushing furnaces, respectively.

[0115] Step 5) Then, the low-melting-point coarse crushed powder and the matrix alloy coarse crushed powder obtained in step 4) are ground in a nitrogen gas flow mill to obtain low-melting-point gas flow mill magnetic powder and matrix alloy gas flow mill magnetic powder, respectively; wherein the average particle size of the low-melting-point gas flow mill magnetic powder and the matrix alloy gas flow mill magnetic powder is 2.5 μm.

[0116] Step 6) Weigh the low-melting-point air jet mill magnetic powder and the matrix alloy air jet mill magnetic powder separately, add lubricant to each and mix evenly, then perform orientation molding in an inert atmosphere, followed by isostatic pressing; the magnetic field strength for orientation molding is 2.0T, and the isostatic pressing pressure is 200MPa.

[0117] Step 7) Both the low-melting-point air-jet mill magnetic powder blanks and the matrix alloy air-jet mill magnetic powder blanks, after isostatic pressing, are fed into a sintering furnace for high-temperature sintering and tempering heat treatment. The low-melting-point air-jet mill magnetic powder blanks, after sintering, yield cerium-containing sintered NdFeB permanent magnets with high coercivity and high mechanical properties, labeled B1. The matrix alloy air-jet mill magnetic powder blanks, after sintering, yield matrix sintered NdFeB permanent magnets, labeled A1. The high-temperature sintering temperature is 1040℃, and the high-temperature sintering time is 5h. The tempering heat treatment process includes: a first-stage tempering temperature of 900℃ and a first-stage tempering time of 8h, and a second-stage tempering temperature of 460℃ and a second-stage tempering time of 4h.

[0118] The cerium-containing sintered NdFeB permanent magnet B1 and the matrix sintered NdFeB permanent magnet A1 prepared in Example 3 were cut into D10mm*10mm sample columns for magnetic performance measurement, and magnets cut into 15mm*6mm*5mm samples for mechanical performance measurement. The testing methods were the same as in Example 1, and the test results are as follows:

[0119] Br(kGs) Hcj(kOe) (BH)max(MGOe) Hk / Hci Flexural strength [MPa] A1 12.8 12.7 39.68 96.8 260 B1 12.76 13.05 39.26 97.2 300

[0120] It can be seen that the cerium-containing sintered NdFeB permanent magnet prepared in Example 3, namely B1, has a coercivity increased by 0.35 kOe and mechanical properties increased by 40 MPa compared with the matrix sintered NdFeB permanent magnet A1 prepared without the addition of low-melting-point alloy.

[0121] Example 4

[0122] Cerium-containing sintered NdFeB permanent magnets were prepared according to the following method:

[0123] Step 1) Prepare raw materials according to the composition of the matrix alloy, wherein the composition and mass percentage of the matrix alloy are PrNd21.5Ce10Al0.4Cu0.2Co0.8Fe66.01B0.94Zr0.15. Use a rapid solidification process to melt and cast the raw materials to obtain matrix alloy castings; wherein the rapid solidification process is as follows: melting temperature is 1460℃, casting temperature is 1360℃, copper roller speed is 2m / s, and the average thickness of the obtained matrix alloy casting is 0.3mm;

[0124] Step 2) Prepare raw materials according to the composition of low-melting-point rare earth alloy, and use a rapid quenching process to melt and quench the raw materials to obtain low-melting-point rare earth alloy strips; wherein the mass percentage composition of the low-melting-point rare earth alloy is Pr4.6Nd15.4Tb70Sn3Cu7; the rapid quenching process is specifically a rapid quenching temperature of 900℃, a copper roller speed of 20m / s, and the average thickness of the obtained low-melting-point rare earth alloy strips is 0.03mm;

[0125] Step 3) The low-melting-point rare earth alloy strips and matrix alloy castings are prepared into 0.3 mm low-melting-point rare earth alloy strip coarse particles and 3 mm matrix alloy casting coarse particles respectively by rotary tooth crushing under the protection of inert gas.

[0126] Step 4) The coarse particles of low-melting-point rare earth alloy strips and coarse particles of matrix alloy castings are mixed in a certain proportion to form coarse particles of total alloy and then placed in a hydrogen crushing furnace. The coarse particles of low-melting-point rare earth alloy strips account for 1 wt% of the total coarse particles of alloy. In order to compare the performance of sintered NdFeB magnets, the coarse particles of matrix alloy castings obtained in Step 3) are placed in another hydrogen crushing furnace. The hydrogen crushing process of the hydrogen crushing furnace containing the total alloy coarse particles and the crushing furnace containing the coarse particles of matrix alloy castings is the same. During the hydrogen crushing process, the hydrogen crushing furnace is stirred at 20 rpm. After preheating at 300°C for 30 min, hydrogen is introduced and hydrogen is absorbed to saturation. Then, after dehydrogenation treatment at 600°C for 1200 min, low-melting-point coarse crushed powder composed of low-melting-point rare earth alloy and matrix alloy and coarse crushed powder of matrix alloy are obtained in the two hydrogen crushing furnaces, respectively.

[0127] Step 5) Then, the low-melting-point coarse crushed powder and the matrix alloy coarse crushed powder obtained in step 4) are ground in a nitrogen gas flow mill to obtain low-melting-point gas flow mill magnetic powder and matrix alloy gas flow mill magnetic powder, respectively; wherein the average particle size of the low-melting-point gas flow mill magnetic powder and the matrix alloy gas flow mill magnetic powder are both 2μm.

[0128] Step 6) Weigh the low-melting-point air jet mill magnetic powder and the matrix alloy air jet mill magnetic powder separately, add lubricant to each and mix evenly, then perform orientation molding in an inert atmosphere, followed by isostatic pressing; the magnetic field strength for orientation molding is 2.0T, and the isostatic pressing pressure is 150MPa.

[0129] Step 7) Both the low-melting-point air-jet mill magnetic powder blanks and the matrix alloy air-jet mill magnetic powder blanks, after isostatic pressing, are fed into a sintering furnace for high-temperature sintering and tempering heat treatment. The low-melting-point air-jet mill magnetic powder blanks, after sintering, yield cerium-containing sintered NdFeB permanent magnets with high coercivity and high mechanical properties, labeled B1. The matrix alloy air-jet mill magnetic powder blanks, after sintering, yield matrix sintered NdFeB permanent magnets, labeled A1. The high-temperature sintering temperature is 1040℃, and the high-temperature sintering time is 5h. The tempering heat treatment process includes: a first-stage tempering temperature of 900℃ and a first-stage tempering time of 8h, and a second-stage tempering temperature of 460℃ and a second-stage tempering time of 4h.

[0130] The low-melting-point sintered NdFeB permanent magnet B1 and the matrix sintered NdFeB permanent magnet A1 prepared in Example 4 were cut into D10mm*10mm sample columns for magnetic performance measurement, and magnets cut into 15mm*6mm*5mm samples for mechanical performance measurement. The testing methods were the same as in Example 1, and the test results are as follows:

[0131] Br(kGs) Hcj(kOe) (BH)max(MGOe) Hk / Hci Flexural strength [MPa] A1 12.08 12.52 34.86 97.8 180 B1 11.85 20.69 34.02 96.2 370

[0132] It can be seen that the cerium-containing sintered NdFeB permanent magnet B1 prepared in Example 4 has a coercivity increased by 8.17 kOe and mechanical properties increased by 190 MPa compared with the matrix sintered NdFeB permanent magnet A1 prepared without the addition of low melting point alloy.

[0133] Example 5

[0134] Cerium-containing sintered NdFeB permanent magnets were prepared according to the following method:

[0135] Step 1) Prepare raw materials according to the composition of the matrix alloy, wherein the composition and mass percentage of the matrix alloy are PrNd23.5Ce8.5Al0.4Cu0.2Co0.6Fe65.67B0.98Zr0.15. Use a rapid solidification process to melt and cast the raw materials to obtain matrix alloy castings; wherein the rapid solidification process is as follows: melting temperature is 1480℃, casting temperature is 1380℃, copper roller speed is 2m / s, and the average thickness of the obtained matrix alloy castings is 0.3mm;

[0136] Step 2) Prepare raw materials according to the composition of low-melting-point rare earth alloy, and use a rapid quenching process to melt and quench the raw materials to obtain low-melting-point rare earth alloy strips; wherein the mass percentage composition of the low-melting-point rare earth alloy is Nd30Dy60Cu5Al5; the rapid quenching process is specifically as follows: the rapid quenching temperature is 1000℃, the copper roller speed is 30m / s, and the average thickness of the obtained low-melting-point rare earth alloy strips is 0.02mm.

[0137] Step 3) The low-melting-point rare earth alloy strips and matrix alloy castings are prepared into 0.2 mm low-melting-point rare earth alloy strip coarse particles and 1 mm matrix alloy casting coarse particles respectively by rotary tooth crushing under the protection of inert gas.

[0138] Step 4) The coarse particles of low-melting-point rare earth alloy strips and coarse particles of matrix alloy castings are mixed in a certain proportion to form coarse particles of total alloy and then placed in a hydrogen crushing furnace. The coarse particles of low-melting-point rare earth alloy strips account for 1.5 wt% of the total coarse particles of alloy. In order to compare the performance of sintered NdFeB magnets, the coarse particles of matrix alloy castings obtained in Step 3) are placed in another hydrogen crushing furnace. The hydrogen crushing process of the hydrogen crushing furnace containing the coarse particles of total alloy and the crushing furnace containing the coarse particles of matrix alloy castings is the same. During the hydrogen crushing process, the hydrogen crushing furnace is stirred at 40 rpm. After preheating at 300°C for 30 min, hydrogen is introduced and hydrogen is absorbed to saturation. Then, after dehydrogenation treatment at 500-800°C for 300-1200 min, low-melting-point coarse crushed powder composed of low-melting-point rare earth alloy and matrix alloy and coarse crushed powder of matrix alloy are obtained in the two hydrogen crushing furnaces, respectively.

[0139] Step 5) Then, the low-melting-point coarse crushed powder and the matrix alloy coarse crushed powder obtained in step 4) are ground in a nitrogen gas flow mill to obtain low-melting-point gas flow mill magnetic powder and matrix alloy gas flow mill magnetic powder, respectively; wherein the average particle size of the low-melting-point gas flow mill magnetic powder and the matrix alloy gas flow mill magnetic powder is 2.2 μm.

[0140] Step 6) Weigh the low-melting-point air jet mill magnetic powder and the matrix alloy air jet mill magnetic powder separately, add lubricant to each and mix evenly, then perform orientation molding in an inert atmosphere, followed by isostatic pressing; the magnetic field strength for orientation molding is 2.2T, and the isostatic pressing pressure is 220MPa.

[0141] Step 7) Both the low-melting-point air-jet mill magnetic powder blanks and the matrix alloy air-jet mill magnetic powder blanks, after isostatic pressing, are fed into a sintering furnace for high-temperature sintering and tempering heat treatment. The low-melting-point air-jet mill magnetic powder blanks, after sintering, yield cerium-containing sintered NdFeB permanent magnets with high coercivity and high mechanical properties, labeled B1. The matrix alloy air-jet mill magnetic powder blanks, after sintering, yield matrix sintered NdFeB permanent magnets, labeled A1. The high-temperature sintering temperature is 1042℃, and the high-temperature sintering time is 5h. The tempering heat treatment process includes: a first-stage tempering temperature of 920℃ and a first-stage tempering time of 10h, and a second-stage tempering temperature of 560℃ and a second-stage tempering time of 2h.

[0142] The low-melting-point sintered NdFeB permanent magnet B1 and the matrix sintered NdFeB permanent magnet A1 prepared in Example 5 were cut into D10*10mm sample columns for magnetic performance measurement, and magnets cut into 15*6*5mm samples were used for mechanical performance measurement. The testing methods were the same as in Example 1, and the test results are as follows:

[0143] Br(kGs) Hcj(kOe) (BH)max(MGOe) Hk / Hci Flexural strength [MPa] A1 12.8 12.7 39.68 96.8 260 B1 12.55 16.76 37.66 97.8 360

[0144] It can be seen that the cerium-containing sintered NdFeB permanent magnet B1 prepared in Example 5 has a coercivity increased by 4.06 kOe and mechanical properties increased by 100 MPa compared with the matrix sintered NdFeB permanent magnet A1 prepared without the addition of low melting point alloy.

[0145] In this invention, the mechanical properties of high Ce rare earth permanent magnet materials are significantly improved.

[0146] This invention employs melt rapid quenching to prepare low-melting-point rare-earth alloy strips. The strips are then crushed into fine, coarse particles using a rotary toothed crusher and added during hydrogenation to ensure better and more uniform mixing with the base alloy, meeting the needs of large-scale industrial production. Furthermore, this invention utilizes diffusion of the low-melting-point rare-earth alloy during the dehydrogenation stage, dissolving it and coating the matrix. This more uniform coating results in cerium-containing sintered NdFeB magnets with superior coercivity and mechanical properties.

[0147] While the invention has been described and illustrated with reference to specific embodiments thereof, such description and illustration are not intended to limit the invention. It will be readily understood by those skilled in the art that various changes may be made to suit particular circumstances, materials, compositions, substances, methods, or processes to the objectives, spirit, and scope of this application without departing from the true spirit and scope of the invention as defined by the appended claims. All such modifications are intended to be within the scope of the appended claims. Although the methods disclosed herein have been described with reference to specific operations performed in a particular order, it should be understood that these operations may be combined, subdivided, or reordered to form equivalent methods without departing from the teachings of the invention. Therefore, unless specifically indicated herein, the order and grouping of operations are not a limitation of this application.

Claims

1. A method for preparing a low-melting-point rare earth alloy to improve the coercivity and mechanical properties of cerium-containing sintered NdFeB permanent magnets, comprising: Low-melting-point rare earth alloy strips are subjected to rotary tooth crushing to obtain low-melting-point rare earth alloy coarse particles; the particle size of the low-melting-point rare earth alloy coarse particles is 0.2~0.5mm. The matrix alloy casting is subjected to rotary tooth crushing to obtain coarse matrix alloy particles. The low-melting-point rare earth alloy coarse particles and the matrix alloy coarse particles are mixed and then subjected to hydrogen crushing, followed by air jet milling to obtain low-melting-point magnetic powder; the average particle size of the low-melting-point magnetic powder is 2~3μm. The low-melting-point magnetic powder is oriented and shaped, and then subjected to isostatic pressing to obtain a blank. The blank is sintered and heat-treated to obtain a cerium-containing sintered NdFeB permanent magnet. The hydrogen crushing is carried out under stirring conditions, and the stirring speed is 20~60 rpm; The hydrogen breakup includes: The process involves preheating, introducing hydrogen gas to achieve hydrogen saturation, and then performing dehydrogenation. The preheating treatment is performed at a temperature of 200~300℃ for a time of 30~60 minutes. The dehydrogenation treatment is performed at a temperature of 500~800℃ for a time of 300~1200 min; The composition of the matrix alloy casting is: PrNd23.5Ce8.5Al0.4Cu0.2Co0.6Fe65.67B0.98Zr0.15 or PrNd21.5Ce10Al0.4Cu0.2Co0.8Fe66.01B0.94Zr0.15; The composition of the low-melting-point rare earth alloy strip is as follows: HR x M y , HR is selected from one or more of Pr, Nd, Tb, and Dy. M is selected from one or more of Al, Ga, Cu, Zn, and Sn. x is 60~90 wt.%, y is 10~40 wt.%.

2. The method according to claim 1, characterized in that, The mass content of the low-melting-point rare earth alloy coarse particles in the low-melting-point magnetic powder is 0.1~2%.

3. The method according to claim 1, characterized in that, The particle size of the coarse particles in the matrix alloy is 1~5mm.

4. The method according to claim 1, characterized in that, The average thickness of the low-melting-point rare earth alloy strip is 0.02~0.04 mm.

5. The method according to claim 1, characterized in that, The magnetic field strength for the orientation forming is 2.0~2.5T; The isostatic pressure treatment pressure is 150~220MPa.

6. The method according to claim 1, characterized in that, The sintering temperature is 1030~1100℃; The heat treatment is tempering, including: First-stage tempering and second-stage tempering; The temperature for the first-stage tempering is 800~920℃; The temperature for the secondary tempering is 460~560℃.