Preparation method of high-remanence neodymium-iron-boron magnet

Abstract

The invention discloses a preparation method of a neodymium-iron-boron magnet, and relates to the technical field of rare earth magnetic materials, and the neodymium-iron-boron magnet comprises the following components in percentage by weight: 20-25% of Nd, 3-5% of Bi, 2-3% of Cs, 2-3% of Ho, 0.5-1.5% of Pr, 0.5-1.5% of B, 0.1-1% of Co, 0.1-1% of Al, and the balance of Fe and inevitable impurities. On the basis of the traditional powder metallurgy process, the neodymium-iron-boron magnet is prepared by optimizing the composition and the proportion of the components, so that the consumption of Nd, Pr and heavy rare earth elements can be reduced, the cost is greatly reduced, and the obtained neodymium-iron-boron magnet has excellent magnetic properties such as high residual magnetism and high coercive force; therefore, the application range of the neodymium-iron-boron magnet is widened.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth magnetic materials, and particularly relates to a method for preparing a neodymium iron boron magnet with high remanence. Background Art

[0002] A magnet refers to a material that can generate a magnetic field, which can attract some substances and repel some substances. Magnets are generally divided into permanent magnets and soft magnets. A permanent magnet can maintain its magnetism for a long time, belonging to a hard magnet, not easy to lose magnetism, and not easy to be magnetized. Common hard magnets include neodymium iron boron magnets, samarium cobalt magnets, and alnico magnets, etc. Among them, the neodymium iron boron magnet has a relatively high magnetic volume and coercivity, and is one of the currently strongest permanent magnetic materials, and its maximum magnetic volume far exceeds other types of permanent magnetic materials. The high magnetic performance of the neodymium iron boron magnet enables it to generate a strong magnetic field, and is suitable for application prospects that require high-performance magnets.

[0003] Neodymium iron boron magnets are divided into two types: sintered neodymium iron boron magnets and bonded neodymium iron boron magnets. Sintered neodymium iron boron magnets are made by powder metallurgy process. It is necessary to first pulverize the melted alloy and press it into shape in a magnetic field, and then sinter it in an inert gas or vacuum to achieve densification. Bonded neodymium iron boron magnets are magnets made of rapidly quenched neodymium iron boron magnetic powder and a binder through die pressing or injection molding. Compared with sintered neodymium iron boron magnets, bonded neodymium iron boron magnets are formed in one step and do not require secondary processing, and can be made into complex magnets of various shapes. However, sintered neodymium iron boron magnets have excellent magnetic properties, so they are widely used in fields such as motors, generators, sensors, and magnetic machinery.

[0004] Remanence refers to the magnetization intensity that a magnet still retains after the external magnetic field disappears. The higher the remanence, the stronger the magnetic induction intensity that the magnet can retain, which indicates that the magnet has a stronger magnetic retention ability. The magnitude of remanence is very important for the application of magnetic materials. In a permanent magnet motor, a material with high remanence can provide a stronger magnetic field, thereby improving the efficiency and performance of the motor. In sensors and magnetic storage devices, the magnitude of remanence directly affects the sensitivity and stability of the device.

[0005] Currently, the methods for improving the remanence of sintered neodymium iron boron magnets mainly include the following several:

[0006] (1) Optimize the magnet formula. Add trace elements, adjust the element ratio in the formula, and reduce the content of heavy rare earth elements, while improving the remanence of the neodymium iron boron magnet and reducing the adverse effects on other properties.

[0007] (2) Improve the sintering process. The sintering process is an important factor affecting the remanence of neodymium iron boron magnets. Traditional long-time high-temperature sintering will cause the grains to be too long, damaging the remanence. Adopt a rapid sintering process, through rapid heating and cooling, to refine the grains, thereby enhancing the magnetic properties.

[0008] (3) Surface coating treatment. In practical applications, NdFeB magnets are prone to oxidation and corrosion, resulting in remanence loss. Through surface coating treatment, these losses can be effectively reduced, and the stability and corrosion resistance of NdFeB magnets can be improved.

[0009] (4) Post-treatment process. After the NdFeB magnet is magnetized, appropriate post-treatment processes can improve the remanence, such as heat treatment and annealing.

[0010] (5) Grain boundary diffusion technology. A heavy rare earth film is formed on the surface of the NdFeB magnet, and through vacuum heat treatment, the heavy rare earth enters the magnet interior along the grain boundaries, forming a high coercivity shell layer, thereby improving the coercivity while maintaining a high remanence.

[0011] Based on the considerations of reducing the preparation cost and simplifying the process, by optimizing the composition and ratio of the NdFeB magnet, not only can the remanence of the NdFeB magnet be effectively improved, but also the high coercivity of the NdFeB magnet can be ensured. Summary of the Invention

[0012] The technical problem to be solved by the present invention is to provide a preparation method of NdFeB magnets, which, by optimizing the composition and ratio, enables the NdFeB magnets to have excellent magnetic properties such as high remanence and high coercivity under the condition of reducing the usage amount of heavy rare earth elements.

[0013] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0014] The purpose of the present invention is to provide a preparation method of NdFeB magnets, comprising the following steps:

[0015] (1) Vacuum melting all raw materials and casting them into a mold to obtain a cast sheet;

[0016] (2) Hydrogenating and crushing the cast sheet to obtain coarse magnetic powder;

[0017] (3) Passing the coarse magnetic powder through a jet mill to obtain fine magnetic powder;

[0018] (4) Vacuum pressing and cold isostatic pressing the fine magnetic powder to obtain a green compact;

[0019] (5) Sequentially subjecting the green compact to vacuum sintering and aging treatment to obtain an NdFeB magnet;

[0020] The NdFeB magnet comprises the following components by weight percentage: Nd 20 - 25%, Bi 3 - 5%, Cs 2 - 3%, Ho 2 - 3%, Pr 0.5 - 1.5%, B 0.5 - 1.5%, Co 0.1 - 1%, Al 0.1 - 1%, and the balance is Fe and unavoidable impurities.

[0021] The present invention reduces the usage amounts of Nd and Pr by adding Ho, Bi, and Cs in specific proportions, thereby reducing costs; in addition, the present invention only adds the heavy rare earth element Ho and its content does not exceed 3%, which can not only reduce costs but also solve the problem of a significant reduction in the remanence of NdFeB magnets caused by a large addition amount of heavy rare earth elements.

[0022] Further, the temperature of the vacuum melting is 1400 - 1500 °C. Vacuum melting can not only avoid the reaction of raw materials with oxygen in the air, remove low-boiling impurities and harmful gas elements, thereby improving the purity of NdFeB magnets, but also inhibit the volatilization of rare earth metals, improving the magnetic properties and durability of NdFeB magnets, etc.

[0023] Further, the thickness of the cast sheet is 0.1 - 0.5 mm.

[0024] Further, the hydrogen absorption temperature for hydrogen crushing is 150 - 250 °C, the hydrogen absorption time is 1 - 5 h, the hydrogen absorption pressure is 0.1 - 0.5 MPa, the dehydrogenation temperature is 500 - 600 °C, and the dehydrogenation time is 1 - 5 h. Hydrogen crushing utilizes the intergranular fracture and transgranular fracture generated by the alloy itself during the hydrogen absorption and dehydrogenation processes to cause alloy pulverization, thereby obtaining alloy powder with a certain particle size.

[0025] Further, the rotational speed of the jet mill is 2000 - 3000 rpm. By using the strong collision and shear force of the material in the high-speed air flow, the particles collide and rub against each other, thereby realizing the grinding of the material.

[0026] Further, the particle size of the coarse magnetic powder is 10 - 1000 μm; the particle size of the fine magnetic powder is 2 - 5 μm. In the present invention, the coarse magnetic powder is first obtained by hydrogen crushing, and then the fine magnetic powder is obtained by the jet mill. The particle size of the magnetic powder not only affects the microstructure of NdFeB magnets but also affects the mechanical properties and magnetic properties of NdFeB magnets.

[0027] Further, the magnetic field strength for vacuum pressing is 1.5 - 2 T. During the pressing process, the external magnetic field will affect the microstructure of NdFeB magnets, and thus affect the magnetic properties of NdFeB magnets.

[0028] Further, the pressure for cold isostatic pressing is 150 - 200 MPa, and the time is 20 - 40 s. Cold isostatic pressing can reduce the pores and cracks inside NdFeB magnets, make the structure of NdFeB magnets more dense, and improve its density and mechanical strength.

[0029] Further, the vacuum sintering is carried out by heating to 1000 - 1100 °C at a heating rate of 1 - 5 °C / min and holding for 3 - 5 h. During the vacuum sintering process, the crystal structure of NdFeB magnets becomes more uniform, which is beneficial to improving the magnetic properties and high-temperature resistance of NdFeB magnets.

[0030] Further, the aging treatment is divided into two stages. In the first-stage aging treatment, the temperature is raised to 800 - 900°C at a heating rate of 1 - 5°C / min, held for 3 - 5 h, and then naturally cooled to below 50°C. In the second-stage aging treatment, the temperature is raised to 450 - 550°C at a heating rate of 1 - 5°C / min and held for 3 - 5 h. The purpose of the aging treatment is to improve the magnetic properties and corrosion resistance of the NdFeB magnet.

[0031] The beneficial effects of the present invention are as follows: Based on the traditional powder metallurgy process, the NdFeB magnet is prepared by optimizing the composition and its ratio. This not only reduces the usage of Nd, Pr elements, and heavy rare earth elements, significantly reducing costs, but also the obtained NdFeB magnet has excellent magnetic properties such as high remanence and high coercivity, thus broadening the application range of the NdFeB magnet. Specific Embodiments

[0032] In order to make the technical means, creative features, achieved purposes, and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0033] Example 1

[0034] (1) All raw materials are vacuum melted at 1500°C and cast into a sheet with a thickness of 0.3 mm.

[0035] (2) The sheet is hydrogenated and crushed. The hydrogen absorption temperature is 200°C, the hydrogen absorption time is 3 h, the hydrogen absorption pressure is 0.1 MPa, the dehydrogenation temperature is 500°C, and the dehydrogenation time is 2 h to obtain coarse magnetic powder with a particle size of 100 - 200 μm.

[0036] (3) The coarse magnetic powder is processed by a jet mill at a rotational speed of 2000 rpm to obtain fine magnetic powder with a particle size of 2 - 5 μm.

[0037] (4) The fine magnetic powder is vacuum pressed under a magnetic field strength of 1.5 T and cold isostatically pressed at a pressure of 200 MPa for 40 s to obtain a green compact.

[0038] (5) The green compact is successively subjected to vacuum sintering and aging treatment. The vacuum sintering is carried out by raising the temperature to 1000°C at a heating rate of 5°C / min and holding for 5 h. The aging treatment is divided into two stages. In the first-stage aging treatment, the temperature is raised to 900°C at a heating rate of 2°C / min, held for 3 h, and then naturally cooled to below 50°C. In the second-stage aging treatment, the temperature is raised to 450°C at a heating rate of 5°C / min and held for 5 h to obtain the NdFeB magnet.

[0039] The neodymium-iron-boron magnet prepared in Example 1 comprises the following components by weight percentage: Nd 20%, Bi 5%, Cs 3%, Ho 2%, Pr 1%, B 1%, Co 0.5%, Al 0.35%, with the balance being Fe and inevitable impurities.

[0040] Example 2

[0041] (1) All raw materials are vacuum melted at 1400 °C and cast into a sheet with a thickness of 0.1 mm.

[0042] (2) The sheet is hydrogenated and crushed. The hydrogen absorption temperature is 150 °C, the hydrogen absorption time is 5 h, the hydrogen absorption pressure is 0.2 MPa, the dehydrogenation temperature is 600 °C, and the dehydrogenation time is 2 h to obtain coarse magnetic powder with a particle size of 100 - 200 μm.

[0043] (3) The coarse magnetic powder is passed through a jet mill with a rotational speed of 3000 rpm to obtain fine magnetic powder with a particle size of 2 - 5 μm.

[0044] (4) The fine magnetic powder is vacuum pressed under a magnetic field strength of 2 T and cold isostatically pressed at a pressure of 150 MPa for 40 s to obtain a green compact.

[0045] (5) The green compact is successively subjected to vacuum sintering and aging treatment. The vacuum sintering is carried out by heating at a rate of 2 °C / min to 1050 °C and holding for 3 h; the aging treatment is divided into two stages. The first-stage aging treatment is carried out by heating at a rate of 3 °C / min to 800 °C and holding for 5 h, and then naturally cooling to below 50 °C; the second-stage aging treatment is carried out by heating at a rate of 2 °C / min to 500 °C and holding for 4 h to obtain the neodymium-iron-boron magnet.

[0046] The neodymium-iron-boron magnet prepared in Example 2 comprises the following components by weight percentage: Nd 22%, Bi 5%, Cs 2%, Ho 3%, Pr 1.5%, B 1.5%, Co 1%, Al 0.5%, with the balance being Fe and inevitable impurities.

[0047] Example 3

[0048] (1) All raw materials are vacuum melted at 1450 °C and cast into a sheet with a thickness of 0.5 mm.

[0049] (2) The sheet is hydrogenated and crushed. The hydrogen absorption temperature is 250 °C, the hydrogen absorption time is 3 h, the hydrogen absorption pressure is 0.5 MPa, the dehydrogenation temperature is 550 °C, and the dehydrogenation time is 3 h to obtain coarse magnetic powder with a particle size of 100 - 200 μm.

[0050] (3) The coarse magnetic powder is passed through a jet mill with a rotational speed of 2500 rpm to obtain fine magnetic powder with a particle size of 2 - 5 μm.

[0051] (4) Vacuum press the fine magnetic powder under a magnetic field strength of 1.8 T, and perform cold isostatic pressing at a pressure of 180 MPa for 30 s to obtain a green compact.

[0052] (5) Subject the green compact to vacuum sintering and aging treatment successively. The vacuum sintering is carried out by heating at a heating rate of 3 °C / min to 1100 °C and holding for 3 h; the aging treatment is divided into two stages. The first-stage aging treatment is carried out by heating at a heating rate of 5 °C / min to 850 °C and holding for 4 h, and then naturally cooling to below 50 °C; the second-stage aging treatment is carried out by heating at a heating rate of 3 °C / min to 550 °C and holding for 3 h to obtain a neodymium-iron-boron magnet.

[0053] The neodymium-iron-boron magnet prepared in Example 3 comprises the following components by weight percentage: Nd 25%, Bi 3%, Cs 3%, Ho 2.5%, Pr 0.5%, B 0.5%, Co 0.5%, Al 0.5%, and the balance is Fe and inevitable impurities.

[0054] Example 4

[0055] (1) Vacuum melt all raw materials at 1400 °C, cast and form to obtain a cast sheet with a thickness of 0.3 mm.

[0056] (2) Subject the cast sheet to hydrogen crushing. The hydrogen absorption temperature is 220 °C, the hydrogen absorption time is 3 h, the hydrogen absorption pressure is 0.2 MPa, the dehydrogenation temperature is 500 °C, and the dehydrogenation time is 2 h to obtain coarse magnetic powder with a particle size of 100 - 200 μm.

[0057] (3) Pass the coarse magnetic powder through a jet mill with a rotational speed of 2000 rpm to obtain fine magnetic powder with a particle size of 2 - 5 μm.

[0058] (4) Vacuum press the fine magnetic powder under a magnetic field strength of 2 T, and perform cold isostatic pressing at a pressure of 160 MPa for 30 s to obtain a green compact.

[0059] (5) Subject the green compact to vacuum sintering and aging treatment successively. The vacuum sintering is carried out by heating at a heating rate of 2 °C / min to 1050 °C and holding for 4 h; the aging treatment is divided into two stages. The first-stage aging treatment is carried out by heating at a heating rate of 4 °C / min to 800 °C and holding for 5 h, and then naturally cooling to below 50 °C; the second-stage aging treatment is carried out by heating at a heating rate of 2 °C / min to 450 °C and holding for 4 h to obtain a neodymium-iron-boron magnet.

[0060] The neodymium-iron-boron magnet prepared in Example 4 comprises the following components by weight percentage: Nd 23%, Bi 4%, Cs 3%, Ho 3%, Pr 1%, B 1.5%, Co 0.8%, Al 0.4%, and the balance is Fe and inevitable impurities.

[0061] Example 5

[0062] (1) All raw materials were vacuum melted at 1450 °C and cast into a sheet with a thickness of 0.4 mm.

[0063] (2) The sheet was hydrogenated and dehydrogenated. The hydrogen absorption temperature was 180 °C, the hydrogen absorption time was 4 h, the hydrogen absorption pressure was 0.3 MPa, the dehydrogenation temperature was 600 °C, and the dehydrogenation time was 2 h, obtaining coarse magnetic powder with a particle size of 100 - 200 μm.

[0064] (3) The coarse magnetic powder was ground by a jet mill at a rotational speed of 3000 rpm, obtaining fine magnetic powder with a particle size of 2 - 5 μm.

[0065] (4) The fine magnetic powder was vacuum pressed under a magnetic field strength of 1.6 T and cold isostatically pressed at a pressure of 200 MPa for 25 s to obtain a green compact.

[0066] (5) The green compact was subjected to vacuum sintering and aging treatment successively. The vacuum sintering was carried out by heating at a rate of 3 °C / min to 1050 °C and holding for 5 h; the aging treatment was divided into two stages. The first-stage aging treatment was carried out by heating at a rate of 2 °C / min to 900 °C and holding for 4 h, and then naturally cooling to below 50 °C; the second-stage aging treatment was carried out by heating at a rate of 4 °C / min to 500 °C and holding for 3 h, obtaining a NdFeB magnet.

[0067] The NdFeB magnet prepared in Example 5 comprises the following components by weight percentage: Nd 25%, Bi 5%, Cs 3%, Ho 2%, Pr 0.5%, B 1.5%, Co 0.5%, Al 0.5%, and the balance is Fe and inevitable impurities.

[0068] Comparative Example 1

[0069] The difference between Comparative Example 1 and Example 1 is only that the addition amount of Cs is increased to 4%.

[0070] (1) All raw materials were vacuum melted at 1500 °C and cast into a sheet with a thickness of 0.3 mm.

[0071] (2) The sheet was hydrogenated and dehydrogenated. The hydrogen absorption temperature was 200 °C, the hydrogen absorption time was 3 h, the hydrogen absorption pressure was 0.1 MPa, the dehydrogenation temperature was 500 °C, and the dehydrogenation time was 2 h, obtaining coarse magnetic powder with a particle size of 100 - 200 μm.

[0072] (3) The coarse magnetic powder was ground by a jet mill at a rotational speed of 2000 rpm, obtaining fine magnetic powder with a particle size of 2 - 5 μm.

[0073] (4) The fine magnetic powder was vacuum pressed under a magnetic field strength of 1.5 T and cold isostatically pressed at a pressure of 200 MPa for 40 s to obtain a green compact.

[0074] (5) The green compact is successively subjected to vacuum sintering and aging treatment. The vacuum sintering is carried out by heating at a heating rate of 5 °C / min to 1000 °C and holding for 5 h; the aging treatment is divided into two stages. The first-stage aging treatment is carried out by heating at a heating rate of 2 °C / min to 900 °C and holding for 3 h, and then naturally cooling to below 50 °C; the second-stage aging treatment is carried out by heating at a heating rate of 5 °C / min to 450 °C and holding for 5 h to obtain the NdFeB magnet.

[0075] The NdFeB magnet prepared in Comparative Example 1 comprises the following components by weight percentage: Nd 20%, Bi 5%, Cs 4%, Ho 2%, Pr 1%, B 1%, Co 0.5%, Al 0.35%, and the balance is Fe and inevitable impurities.

[0076] Comparative Example 2

[0077] The difference between Comparative Example 2 and Example 1 is only that the addition amount of Bi is increased to 6%.

[0078] (1) All raw materials are vacuum melted at 1500 °C, cast and formed to obtain a cast sheet with a thickness of 0.3 mm.

[0079] (2) The cast sheet is subjected to hydrogen crushing. The hydrogen absorption temperature is 200 °C, the hydrogen absorption time is 3 h, the hydrogen absorption pressure is 0.1 MPa, the dehydrogenation temperature is 500 °C, and the dehydrogenation time is 2 h to obtain coarse magnetic powder with a particle size of 100 - 200 μm.

[0080] (3) The coarse magnetic powder is passed through a jet mill with a rotational speed of 2000 rpm to obtain fine magnetic powder with a particle size of 2 - 5 μm.

[0081] (4) The fine magnetic powder is vacuum pressed under a magnetic field strength of 1.5 T and cold isostatically pressed at a pressure of 200 MPa for 40 s to obtain a green compact.

[0082] (5) The green compact is successively subjected to vacuum sintering and aging treatment. The vacuum sintering is carried out by heating at a heating rate of 5 °C / min to 1000 °C and holding for 5 h; the aging treatment is divided into two stages. The first-stage aging treatment is carried out by heating at a heating rate of 2 °C / min to 900 °C and holding for 3 h, and then naturally cooling to below 50 °C; the second-stage aging treatment is carried out by heating at a heating rate of 5 °C / min to 450 °C and holding for 5 h to obtain the NdFeB magnet.

[0083] The NdFeB magnet prepared in Comparative Example 2 comprises the following components by weight percentage: Nd 20%, Bi 6%, Cs 3%, Ho 2%, Pr 1%, B 1%, Co 0.5%, Al 0.35%, and the balance is Fe and inevitable impurities.

[0084] Comparative Example 3

[0085] The difference between Comparative Example 3 and Example 1 is only that the addition amount of Cs is reduced to 1%.

[0086] (1) All raw materials were vacuum melted at 1500 °C and cast into a sheet with a thickness of 0.3 mm.

[0087] (2) The sheet was hydrogenated and crushed, the hydrogen absorption temperature was 200 °C, the hydrogen absorption time was 3 h, the hydrogen absorption pressure was 0.1 MPa, the dehydrogenation temperature was 500 °C, and the dehydrogenation time was 2 h to obtain coarse magnetic powder with a particle size of 100 - 200 μm.

[0088] (3) The coarse magnetic powder was passed through a jet mill with a rotation speed of 2000 rpm to obtain fine magnetic powder with a particle size of 2 - 5 μm.

[0089] (4) The fine magnetic powder was vacuum pressed under a magnetic field strength of 1.5 T and cold isostatically pressed at a pressure of 200 MPa for 40 s to obtain a green compact.

[0090] (5) The green compact was successively subjected to vacuum sintering and aging treatment. The vacuum sintering was carried out by heating to 1000 °C at a heating rate of 5 °C / min and holding for 5 h; the aging treatment was divided into two stages. The first-stage aging treatment was carried out by heating to 900 °C at a heating rate of 2 °C / min and holding for 3 h, and then naturally cooling to below 50 °C; the second-stage aging treatment was carried out by heating to 450 °C at a heating rate of 5 °C / min and holding for 5 h to obtain a NdFeB magnet.

[0091] The NdFeB magnet prepared in Comparative Example 3 comprises the following components by weight percentage: Nd 20%, Bi 5%, Cs 1%, Ho 2%, Pr 1%, B 1%, Co 0.5%, Al 0.35%, and the balance is Fe and inevitable impurities.

[0092] Comparative Example 4

[0093] The difference between Comparative Example 4 and Example 1 is only that the addition amount of Bi is reduced to 2%.

[0094] (1) All raw materials were vacuum melted at 1500 °C and cast into a sheet with a thickness of 0.3 mm.

[0095] (2) The sheet was hydrogenated and crushed, the hydrogen absorption temperature was 200 °C, the hydrogen absorption time was 3 h, the hydrogen absorption pressure was 0.1 MPa, the dehydrogenation temperature was 500 °C, and the dehydrogenation time was 2 h to obtain coarse magnetic powder with a particle size of 100 - 200 μm.

[0096] (3) The coarse magnetic powder was passed through a jet mill with a rotation speed of 2000 rpm to obtain fine magnetic powder with a particle size of 2 - 5 μm.

[0097] (4) Vacuum press the fine magnetic powder under a magnetic field strength of 1.5 T, and cold isostatic press it at a pressure of 200 MPa for 40 s to obtain a green compact.

[0098] (5) Subject the green compact to vacuum sintering and aging treatment in sequence. The vacuum sintering is carried out by heating to 1000 °C at a heating rate of 5 °C / min and holding for 5 h; the aging treatment is divided into two stages. The first-stage aging treatment is carried out by heating to 900 °C at a heating rate of 2 °C / min and holding for 3 h, and then naturally cooling to below 50 °C; the second-stage aging treatment is carried out by heating to 450 °C at a heating rate of 5 °C / min and holding for 5 h to obtain a NdFeB magnet.

[0099] The NdFeB magnet prepared in Comparative Example 4 comprises the following components by weight percentage: Nd 20%, Bi 2%, Cs 3%, Ho 2%, Pr 1%, B 1%, Co 0.5%, Al 0.35%, and the balance is Fe and inevitable impurities.

[0100] Comparative Example 5

[0101] The difference between Comparative Example 5 and Example 1 is only that Cs is not added.

[0102] (1) Vacuum melt all the raw materials at 1500 °C, cast and form to obtain a cast sheet with a thickness of 0.3 mm.

[0103] (2) Subject the cast sheet to hydrogen crushing. The hydrogen absorption temperature is 200 °C, the hydrogen absorption time is 3 h, the hydrogen absorption pressure is 0.1 MPa, the dehydrogenation temperature is 500 °C, and the dehydrogenation time is 2 h to obtain coarse magnetic powder with a particle size of 100 - 200 μm.

[0104] (3) Pass the coarse magnetic powder through a jet mill with a rotation speed of 2000 rpm to obtain fine magnetic powder with a particle size of 2 - 5 μm.

[0105] (4) Vacuum press the fine magnetic powder under a magnetic field strength of 1.5 T, and cold isostatic press it at a pressure of 200 MPa for 40 s to obtain a green compact.

[0106] (5) Subject the green compact to vacuum sintering and aging treatment in sequence. The vacuum sintering is carried out by heating to 1000 °C at a heating rate of 5 °C / min and holding for 5 h; the aging treatment is divided into two stages. The first-stage aging treatment is carried out by heating to 900 °C at a heating rate of 2 °C / min and holding for 3 h, and then naturally cooling to below 50 °C; the second-stage aging treatment is carried out by heating to 450 °C at a heating rate of 5 °C / min and holding for 5 h to obtain a NdFeB magnet.

[0107] The Nd-Fe-B magnet prepared in Comparative Example 5 comprises the following components by weight percentage: 23% of Nd, 5% of Bi, 2% of Ho, 1% of Pr, 1% of B, 0.5% of Co, 0.35% of Al, and the balance is Fe and inevitable impurities.

[0108] Comparative Example 6

[0109] The difference between Comparative Example 6 and Example 1 is only that Bi is not added.

[0110] (1) All raw materials are vacuum melted at 1500 °C and cast into a sheet with a thickness of 0.3 mm.

[0111] (2) The sheet is hydrogenated and cracked. The hydrogen absorption temperature is 200 °C, the hydrogen absorption time is 3 h, the hydrogen absorption pressure is 0.1 MPa, the dehydrogenation temperature is 500 °C, and the dehydrogenation time is 2 h to obtain coarse magnetic powder with a particle size of 100 - 200 μm.

[0112] (3) The coarse magnetic powder is passed through a jet mill with a rotation speed of 2000 rpm to obtain fine magnetic powder with a particle size of 2 - 5 μm.

[0113] (4) The fine magnetic powder is vacuum pressed under a magnetic field strength of 1.5 T and cold isostatically pressed at a pressure of 200 MPa for 40 s to obtain a green compact.

[0114] (5) The green compact is subjected to vacuum sintering and aging treatment in sequence. The vacuum sintering is carried out by heating to 1000 °C at a heating rate of 5 °C / min and holding for 5 h; the aging treatment is divided into two stages. The first-stage aging treatment is carried out by heating to 900 °C at a heating rate of 2 °C / min and holding for 3 h, and then naturally cooling to below 50 °C; the second-stage aging treatment is carried out by heating to 450 °C at a heating rate of 5 °C / min and holding for 5 h to obtain the Nd-Fe-B magnet.

[0115] The Nd-Fe-B magnet prepared in Comparative Example 6 comprises the following components by weight percentage: 25% of Nd, 3% of Cs, 2% of Ho, 1% of Pr, 1% of B, 0.5% of Co, 0.35% of Al, and the balance is Fe and inevitable impurities.

[0116] The remanence and intrinsic coercivity of the Nd-Fe-B magnets prepared in the above examples and comparative examples are tested in accordance with GB / T 3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnetic) Materials", and the test results are shown in Table 1.

[0117] Table 1

[0118]

[0119]

[0120] As can be seen from Table 1, the neodymium iron boron magnet with both high remanence and high coercivity can be prepared by optimizing the composition and its ratio in the present invention.

[0121] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have various changes and improvements, and all these changes and improvements fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a neodymium iron boron magnet, characterized in that: The following steps are involved: (1) All raw materials are vacuum melted and cast to obtain a cast sheet; (2) crushing the cast sheet with hydrogen to obtain coarse magnetic powder; (3) jet milling the coarse magnetic powder to obtain fine magnetic powder; (4) vacuum pressing the fine magnetic powder and cold isostatic pressing to obtain a green body; (5) subjecting the green body to vacuum sintering and aging treatment in sequence to obtain a NdFeB magnet; The NdFeB magnet comprises the following components in weight percentage: Nd 20-25%, Bi 3-5%, Cs 2-3%, Ho 2-3%, Pr 0.5-1.5%, B 0.5-1.5%, Co 0.1-1%, Al 0.1-1%, and the balance is Fe and inevitable impurities.

2. The method for preparing a NdFeB magnet according to claim 1, wherein: The temperature of the vacuum melting is 1400-1500°C.

3. The method for preparing a NdFeB magnet according to claim 1, wherein: The thickness of the casting sheet is 0.1-0.5 mm.

4. The method for preparing a NdFeB magnet according to claim 1, wherein: The hydrogen absorption temperature of the hydrogen crushing is 150-250° C., the hydrogen absorption time is 1-5 hours, the hydrogen absorption pressure is 0.1-0.5 MPa, the dehydrogenation temperature is 500-600° C., and the dehydrogenation time is 1-5 hours.

5. The method for preparing a NdFeB magnet according to claim 1, wherein: The rotation speed of the jet mill is 2000-3000 rpm.

6. The method for preparing a NdFeB magnet according to claim 1, wherein: The particle size of the coarse magnetic powder is 10 to 1000 μm; the particle size of the fine magnetic powder is 2 to 5 μm.

7. The method for preparing a NdFeB magnet according to claim 1, characterized in that: The magnetic field strength of the vacuum pressing is 1.5-2T.

8. The method for preparing a NdFeB magnet according to claim 1, wherein: The cold isostatic pressing pressure is 150-200 MPa, and the time is 20-40 seconds.

9. The method for preparing a NdFeB magnet according to claim 1, wherein: The vacuum sintering is performed by heating the temperature to 1000-1100° C. at a heating rate of 1-5° C. / min and keeping the temperature for 3-5 hours.

10. The method for preparing a NdFeB magnet according to claim 1, characterized in that: The aging treatment is divided into two stages. The first stage of aging treatment is to heat the temperature to 800-900°C at a heating rate of 1-5°C / min and keep it warm for 3-5h, and then naturally cool it to below 50°C; the second stage of aging treatment is to heat the temperature to 450-550°C at a heating rate of 1-5°C / min and keep it warm for 3-5h.

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