Neodymium-iron-boron magnet and preparation method and application thereof

Abstract

The invention discloses a neodymium-iron-boron magnet and a preparation method and application thereof.The neodymium-iron-boron magnet is prepared from at least two main phases, heavy rare earth elements are not added into main phase alloy I, and heavy rare earth elements are added into main phase alloy II. According to the method, a traditional single-phase alloy smelting process is replaced with a multi-main-phase processing technology, so that formation of intergranular phases can be inhibited, and the neodymium-iron-boron magnet shows a low temperature coefficient and a high Curie temperature. Meanwhile, through the modes of powder refining, lubricant adding, hydrogen-containing sintering and the like, a new breakthrough on the temperature resistance of the neodymium iron boron permanent magnet material can be achieved, and research, development and preparation of the neodymium iron boron permanent magnet material with low Co, low heavy rare earth elements and high temperature resistance are achieved; the obtained neodymium-iron-boron permanent magnet material can be widely applied to preparation of humanoid robot motors, high-temperature motors, electric driving systems, medical equipment, electrical equipment, high-temperature sensors, monitoring equipment and the like.

Description

Technical Field

[0001] The invention relates to the technical field of rare earth permanent magnetic materials, and in particular to a neodymium iron boron magnet and a preparation method and application thereof. Background Art

[0002] Nd-Fe-B permanent magnet materials are widely used in high-tech fields such as new energy motors, rail transportation, and humanoid robots due to their excellent magnetic properties. As a key magnetic component, Nd-Fe-B magnets need to provide a continuous and stable magnetic field (magnetic moment effect) under specific working conditions, among which remanence (Br) is crucial to their functional performance. However, in practical applications, the remanence (Br) of Nd-Fe-B magnets is greatly affected by temperature changes, resulting in poor temperature stability. In addition, the Curie temperature (Tc) of Nd-Fe-B magnets is lower than that of Sm-Co magnets, which are also rare earth permanent magnet materials. This shortcoming limits the widespread use of Nd-Fe-B magnets in high-temperature applications such as aerospace, national defense, high-temperature motors, and precision instruments. Despite this, the magnetic energy product of Nd-Fe-B magnets is much higher than that of Sm-Co magnets. With the advancement of technology, the demand for high-performance Nd-Fe-B magnets with better temperature resistance is becoming more urgent. Therefore, improving the magnetic properties and thermal stability of Nd-Fe-B magnets at high temperatures, especially optimizing the remanence temperature coefficient (α), is of great significance for expanding its market prospects in high-temperature applications. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a neodymium iron boron magnet and a preparation method and application thereof.

[0004] The present invention solves the technical problem by adopting the following technical solutions.

[0005] The invention provides a NdFeB magnet. The raw materials for preparing the NdFeB magnet contain at least two main phases, wherein: the main phase alloy I does not contain heavy rare earth elements, and the main phase alloy II contains heavy rare earth elements.

[0006] In some embodiments of the present invention, the main phase alloy I is a NdFeB alloy that does not contain Dy, and the main phase alloy II is a NdFeB alloy that contains Dy and Co.

[0007] In some embodiments of the present invention, the nominal composition of the main phase alloy I is: RE1 x M y Co z Fe bal B t, wherein: RE1 includes one or more of Pr and Nd, M includes one or more of Al, Cu, Zr or Ga, 20wt%≤x≤40wt%, 0.1wt%≤y≤2wt%, 0.1wt%≤z≤0.5wt%, 0.1wt%≤t≤1wt%, and the balance is iron;

[0008] The nominal composition of the main phase alloy II is: RE2 a Dy b Co c M d Fe bal B e , wherein: RE2 includes one or more of Pr, Nd, M includes one or more of Al, Cu, Zr or Ga, 20wt%≤a≤40wt%, 1wt%≤b≤10wt%, 30wt%≤c≤60wt%, 0.1wt%≤d≤2wt%, 0.1wt%≤e≤1wt%, and the balance is iron.

[0009] In some embodiments of the present invention, the mass ratio of main phase alloy I to main phase alloy II is (3:1) to (5:1).

[0010] In some embodiments of the present invention, the coercive force of the NdFeB magnet is 16.1-20.8 kOe.

[0011] The present invention also provides a method for preparing the above-mentioned NdFeB magnet, which comprises: mixing powders of main phase alloy I and main phase alloy II in proportion, forming and pressing them into green compacts through orientation, and then sequentially subjecting the green compacts to high temperature sintering and annealing treatments to obtain NdFeB magnets.

[0012] In some embodiments of the present invention, the preparation of the green body comprises the following steps: subjecting the main phase alloy I and the main phase alloy II to a smelting and stripping treatment to obtain castings of the main phase alloy I and the main phase alloy II, respectively; coarsely crushing the castings of the main phase alloy I and the main phase alloy II, and then hydrogen crushing and air flow pulverizing, mixing them in a mass ratio of (3:1) to (5:1) to obtain a mixed powder, and then orienting and molding the mixed powder and pressing it to obtain a green body;

[0013] Preferably, the hydrogen crushing comprises: placing the castings of the main phase alloy I and the main phase alloy II in a hydrogen crushing furnace, and after the castings are saturated with hydrogen, without performing a dehydrogenation step, directly closing the heating system and cooling the alloy to room temperature by argon gas cooling, so as to obtain hydrogen crushed powder with an average particle size of 7 μm to 12 μm;

[0014] Preferably, the air flow milling comprises: placing the hydrogen-decomposed powder of the main phase alloy I and the main phase alloy II into an air flow mill for crushing to obtain air flow milled powder with an average particle size of 1 μm to 2 μm, more preferably, the classifying wheel speed of the air flow mill is 18000 rpm to 21000 rpm, and the air flow pressure is 0.5 MPa to 0.7 MPa;

[0015] Preferably, the orientation molding and pressing include: adding 0.25wt% to 0.35wt% of a lubricant to the mixed powder and then performing orientation molding and pressing. More preferably, the lubricant includes one or more of tributyl borate and polytetrafluoroethylene, the orientation magnetic field strength is 1.9T to 2.1T, and the pressing pressure is 170MPa to 210MPa.

[0016] In some embodiments of the present invention, high temperature sintering comprises: sintering the green body at high temperature in a hydrogen-containing atmosphere;

[0017] Preferably, the high temperature sintering temperature is 1000°C to 1100°C, the time is 4h to 12h, and the vacuum degree is not less than 5×10 -3 Pa.

[0018] In some embodiments of the present invention, the annealing process is a two-step annealing process;

[0019] Preferably, the first step annealing temperature is 850°C to 950°C, the annealing time is 4h to 8h, and the atmosphere is an inert atmosphere. The second step annealing temperature is 450°C to 600°C, the annealing time is 2h to 4h, and the atmosphere is an inert atmosphere. The NdFeB magnet is obtained by cooling.

[0020] The present invention also provides an application of the above-mentioned NdFeB magnet or the NdFeB magnet prepared by the above-mentioned preparation method in the preparation of humanoid robot motors, high-temperature motors, electric drive systems, medical equipment, electrical equipment, high-temperature sensors and monitoring equipment.

[0021] The present invention has the following beneficial effects:

[0022] The present invention provides a neodymium iron boron magnet and a preparation method and application thereof. The raw materials for preparing the neodymium iron boron magnet provided by the present invention contain at least two main phases, wherein: no heavy rare earth elements are added to the main phase alloy I, and heavy rare earth elements are added to the main phase alloy II. In the present invention, the coercive force of the neodymium iron boron magnet is improved by replacing the neodymium element with heavy rare earth elements. In addition, by mixing main phase particles with different anisotropy fields, the microstructure and magnetic properties of the neodymium iron boron magnet can be improved while the coercive force of the neodymium iron boron magnet is effectively improved. By improving the process, the coercive force is increased while maintaining the thermal stability, remanence and magnetic energy product of the Nd-Fe-B magnet in a high temperature environment without adding a large amount of heavy rare earth elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 The figure is a flow chart of preparing NdFeB magnets in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0026] The following is a detailed description of a neodymium iron boron magnet provided in an embodiment of the present invention and its preparation method and application.

[0027] In a first aspect, an embodiment of the present invention provides a NdFeB magnet, wherein the raw materials for preparing the NdFeB magnet include at least two main phases, wherein: no heavy rare earth elements are added to the main phase alloy I, and heavy rare earth elements are added to the main phase alloy II.

[0028] At present, the demand for high-performance NdFeB magnets with better temperature resistance is very urgent. In order to meet the requirements of high coercivity and low temperature coefficient of NdFeB magnets at high temperatures, the present invention replaces the neodymium element with heavy rare earth elements. In addition, the raw materials for preparing the NdFeB magnets provided by the present invention contain at least two main phases. By mixing the main phase particles with different anisotropy fields, the coercivity of the NdFeB magnets can be effectively improved, and the microstructure and magnetic properties of the NdFeB magnets can also be improved.

[0029] In some embodiments of the present invention, the main phase alloy I is a NdFeB alloy that does not contain Dy, and the main phase alloy II is a NdFeB alloy that contains Dy and Co.

[0030] At present, the main methods to improve the temperature stability of Nd-Fe-B magnets include reducing the remanence temperature coefficient (α) by increasing the coercive force (Hcj) and adding heavy rare earth (HRE) elements, while slightly increasing its Curie temperature (Tc). However, the addition of a large amount of heavy rare earth elements not only significantly increases the production cost, but also may cause the magnetic energy product of the magnet to decrease. In fact, the method of over-reliance on heavy rare earth elements to improve α and Tc has limited benefits in the current application requirements of Nd-Fe-B magnets in high temperature environments. According to relevant research, partial replacement of Fe elements by Co elements can effectively improve the temperature resistance of magnets. When Co completely replaces Fe, the Curie temperature (Tc) can reach 720°C. However, excessive addition of Co elements will also lead to an increase in the cost of magnets, and the substitution of Co will reduce the anisotropic magnetic field of Nd from 7.3T to 5T. In addition, excessive Co addition will also lead to the precipitation of a large amount of Co-rich intergranular phases. When the Co content exceeds 11wt%, the Co-rich intergranular phases (such as Nd(Fe,Co) 2 Phases) will form in the grain boundary region, which contain a large amount of Fe and Co, thereby weakening the magnetic coupling effect of the grain boundary.

[0031] The embodiment of the present invention provides a NdFeB magnet, which uses a dual-main phase processing technology to replace the traditional single-phase alloy smelting process to suppress the formation of intergranular phases. In magnets with high Co content, the dual-main phases suppress the formation of Co-rich intergranular phases, so that the NdFeB magnet exhibits a lower temperature coefficient and a higher Curie temperature, providing a continuous and stable magnetic field for the application of NdFeB magnets at high temperatures.

[0032] In some embodiments of the present invention, the nominal composition of the main phase alloy I is: RE1 x M y Co z Fe bal B t , wherein: RE1 includes one or more of Pr and Nd, M includes one or more of Al, Cu, Zr or Ga, 20wt%≤x≤40wt%, 0.1wt%≤y≤2wt%, 0.1wt%≤z≤0.5wt%, 0.1wt%≤t≤1wt%, and the balance is iron;

[0033] The nominal composition of the main phase alloy II is: RE2 a Dy b Co c M d Fe bal B e, wherein: RE2 includes one or more of Pr, Nd, M includes one or more of Al, Cu, Zr or Ga, 20wt%≤a≤40wt%, 1wt%≤b≤10wt%, 30wt%≤c≤60wt%, 0.1wt%≤d≤2wt%, 0.1wt%≤e≤1wt%, and the balance is iron.

[0034] In some embodiments of the present invention, the mass ratio of main phase alloy I to main phase alloy II is (3:1) to (5:1).

[0035] In some embodiments of the present invention, the coercive force of the NdFeB magnet is 16.1 kOe to 20.8 kOe.

[0036] In a second aspect, an embodiment of the present invention provides a method for preparing the above-mentioned NdFeB magnet, which comprises: mixing powders of main phase alloy I and main phase alloy II in proportion, forming and pressing them into green bodies through orientation molding, and then sequentially subjecting the green bodies to high temperature sintering and annealing treatment to obtain NdFeB magnets.

[0037] In some optional embodiments, the preparation of the green body comprises the following steps: subjecting the main phase alloy I and the main phase alloy II to a smelting and stripping treatment to obtain castings of the main phase alloy I and the main phase alloy II, respectively; coarsely crushing the castings of the main phase alloy I and the main phase alloy II, and then hydrogen crushing and air flow pulverizing, mixing them in a mass ratio of (3:1) to (5:1) to obtain a mixed powder, and then orienting and molding the mixed powder and pressing it to obtain a green body;

[0038] Preferably, the hydrogen crushing comprises: placing the castings of the main phase alloy I and the main phase alloy II in a hydrogen crushing furnace, and after the castings are saturated with hydrogen, without performing a dehydrogenation step, directly closing the heating system and cooling the alloy to room temperature by argon gas cooling, so as to obtain hydrogen crushed powder with an average particle size of 7 μm to 12 μm;

[0039] Preferably, the air flow milling comprises: placing the hydrogen-decomposed powder of the main phase alloy I and the main phase alloy II into an air flow mill for crushing to obtain air flow milled powder with an average particle size of 1 μm to 2 μm, more preferably, the classifying wheel speed of the air flow mill is 18000 rpm to 21000 rpm, and the air flow pressure is 0.5 MPa to 0.7 MPa;

[0040] Preferably, the orientation molding and pressing include: adding 0.25wt% to 0.35wt% of a lubricant to the mixed powder and then performing orientation molding and pressing. More preferably, the lubricant includes one or more of tributyl borate and polytetrafluoroethylene, the orientation magnetic field strength is 1.9T to 2.1T, and the pressing pressure is 170MPa to 210MPa.

[0041] The preparation method of the NdFeB magnet provided by the embodiment of the present invention comprises the following steps: subjecting the main phase alloy I and the main phase alloy II to smelting and stripping treatment to obtain the castings of the main phase alloy I and the main phase alloy II respectively, placing the castings after rough crushing treatment in a hydrogen crushing furnace, and exhausting the air in the furnace by using a vacuum system; introducing a certain amount of high-purity hydrogen at room temperature, and replenishing hydrogen during the hydrogen absorption process; after the castings are saturated with hydrogen, the dehydrogenation step is not performed, and the hydrogen absorbed in the castings is removed in the subsequent high-temperature sintering stage, and the heating system is directly turned off and the alloy is cooled to room temperature by argon gas cooling. After that, the hydrogen powder is sent into the grinding chamber of the air flow mill, and a group of air flow nozzles distributed at a certain angle in space are ejected to drive the hydrogen powder to accelerate, and the high-kinetic energy hydrogen powder violently collides at the intersection of the nozzle direction to realize the powder crushing process. After the powder is mixed after air flow milling, 0.25wt% to 0.35wt% of lubricant is added, which is placed in a powder tank and installed at the feed port of the press. The powder is automatically taken out quantitatively by an electronic scale, and then the powder is loaded into a suitable mold. Orientation molding treatment is carried out under a magnetic field strength of 1.9T to 2.1T, and then isostatic pressing is carried out. The whole process is carried out in a nitrogen-protected glove box to obtain a green body.

[0042] As can be seen from the above, the preparation method of the NdFeB magnet provided by the embodiment of the present invention is to subject the coarsely broken cast sheet to hydrogen crushing and air flow pulverization to obtain a powder with a smaller particle size, and to increase the magnetic properties by refining the magnetic powder, wherein: during hydrogen crushing, after the cast sheet is saturated with hydrogen, the dehydrogenation step is not performed, and it is directly cooled. During air flow pulverization, the speed of the classifying wheel of the air flow mill is increased from 9000rpm of the traditional process to 18000rpm~21000rpm, and the air flow pressure of the air flow mill is maintained at 0.5MPa~0.7MPa. In this state, most of the magnetic powder will remain in the grinding chamber. At this time, the magnetic powder is driven by the nitrogen pressure sprayed from the nozzle into the grinding chamber, and collides with each other, causing crushing. When the powder is small enough, it can pass through the classifying wheel and be collected by the classifying wheel, and a finer magnetic powder can be obtained, which is beneficial to increase the magnetic properties of the NdFeB magnet.

[0043] In some optional embodiments, the high temperature sintering comprises: sintering the green body at a high temperature in a hydrogen-containing atmosphere;

[0044] Preferably, the high temperature sintering temperature is 1000°C to 1100°C, the time is 4h to 12h, and the vacuum degree is not less than 5×10 -3 Pa.

[0045] The preparation method of NdFeB magnet provided by an embodiment of the present invention, high-temperature sintering includes: high-temperature sintering of green billets in a hydrogen-containing atmosphere, the high rotation speed of the classifying wheel in the air flow crushing stage reduces the average particle size of the magnetic powder, increases the surface energy of the magnetic powder, increases the sintering activity, and enhances the magnetic properties, but the increase in the surface area of ​​the powder will lead to insufficient lubricant coating, hindering the alignment of the magnetic powder in the magnetic field formation stage, so the use of lubricants is increased in the green billet preparation process to improve the magnetic properties, but the increase in C content will lead to a decrease in coercive force, and since hydrogen is reducing, the green billets obtained by orientation molding and pressing are subjected to high-temperature sintering in a hydrogen-containing atmosphere, and the dehydrogenation link in the hydrogen crushing stage is moved to the high-temperature sintering stage. The green billets are subjected to high-temperature sintering in a hydrogen-containing atmosphere to release and discharge C elements and H elements together, thereby improving the magnetic properties of the magnet.

[0046] In some optional embodiments, the annealing process is a two-step annealing process;

[0047] Preferably, the first step annealing temperature is 850°C to 950°C, the annealing time is 4h to 8h, the atmosphere is an inert atmosphere, the second step annealing temperature is 450°C to 600°C, the annealing time is 2h to 4h, the atmosphere is an inert atmosphere, and the NdFeB magnet is obtained by cooling. High temperature annealing can improve the microstructure of the magnet and reduce defects, thereby improving the stability and magnetic properties of the NdFeB magnet. It is worth noting that the inert atmosphere for annealing can be an argon atmosphere, a nitrogen atmosphere, etc.

[0048] In some optional embodiments, the method for preparing a neodymium iron boron magnet comprises the following steps:

[0049] Step S1: Preparation of main phase alloy I: Weigh and prepare the ingredients according to the designed main phase alloy I components in proportion, and melt and spin the prepared raw materials to obtain main phase alloy I: RE1 x M y Co z Fe bal B t .

[0050] Step S2 Preparation of main phase alloy II: Weigh and prepare the ingredients according to the designed main phase alloy II components, and melt and spin the prepared raw materials to obtain main phase alloy II: RE2 a Dy b Co c M d Fe bal B e .

[0051] Step S3: crushing and grinding: the main phase alloy I and the main phase alloy II obtained in steps S1 and S2 are roughly crushed, and then hydrogen crushed and air flow pulverized to obtain powders of the main phase alloy I and the main phase alloy II.

[0052] Step S4: powder mixing: the powder of the main phase alloy I and the powder of the main phase alloy II obtained in step S3 are mixed in proportion to obtain a mixed powder.

[0053] Step S5: preparing green compacts: orienting and molding the mixed powder obtained in step S4, and pressing the mixed powder to obtain green compacts.

[0054] Step S6: high temperature sintering: the green body obtained in step S5 is subjected to high temperature sintering to obtain a magnetic matrix.

[0055] Step S7: Annealing treatment: The magnetic matrix obtained in step S6 is subjected to two-step annealing treatment to obtain a NdFeB permanent magnet material.

[0056] As can be seen from the above, the embodiment of the present invention provides a method for preparing NdFeB magnets. Through innovative technical means such as powder refining, lubricant addition and hydrogen-containing sintering, it is possible to achieve new breakthroughs in the temperature resistance of NdFeB permanent magnet materials, and to achieve the research and development and preparation of low-Co, low-heavy rare earth elements and high-temperature-resistant NdFeB permanent magnet materials. In order to obtain temperature resistance and effectively utilize Dy / Co, Dy and Co are added by a double alloy method to prepare NdFeB magnets containing Dy and Co. Compared with the traditional single alloy method, the present invention uses a dual-main phase processing technology instead of the traditional single-phase alloy smelting process to suppress the formation of Co-rich intergranular phases, while making the NdFeB magnet exhibit a lower temperature coefficient, and increasing the Curie temperature from 322°C to 504°C. In the preparation process, the coercivity of the NdFeB magnet is improved by the innovation of technical means such as powder refining, lubricant addition and hydrogen-containing sintering, the magnetic properties are increased by refining the magnetic powder, and the hydrogen and carbon elements are released together by adding lubricants for orientation molding and pressing, and then sintering at high temperature in a hydrogen-containing atmosphere, thereby improving the comprehensive magnetic properties of the magnet. Compared with the traditional process, the preparation method of the NdFeB magnet provided by the present invention increases the magnetic properties (especially the coercivity) while reducing the addition of heavy rare earth elements.

[0057] In the third aspect, an embodiment of the present invention provides an application of the above-mentioned neodymium iron boron magnet in the preparation of humanoid robot motors, high-temperature motors, electric drive systems, medical equipment (such as magnetic resonance imaging systems, high-temperature medical instruments, etc.), electrical equipment (such as air-conditioning compressors, vacuum cleaner motors, etc.), high-temperature sensors and monitoring equipment.

[0058] The present invention will be further described below in conjunction with the embodiments.

[0059] A method for preparing a neodymium iron boron magnet, see Figure 1 , including the following steps:

[0060] Step S1 Preparation of main phase alloy I: Weigh and prepare the ingredients according to the designed main phase alloy I components in proportion, and melt and spin the prepared raw materials to obtain main phase alloy I: RE1 x M y Co z Fe bal B t .

[0061] Step S2 Preparation of main phase alloy II: Weigh and prepare the ingredients according to the designed main phase alloy II components, and melt and spin the prepared raw materials to obtain main phase alloy II: RE2 a Dy b Co c M d Fe bal B e .

[0062] Step S3: crushing and grinding: the main phase alloy I and the main phase alloy II obtained in steps S1 and S2 are roughly crushed, and then subjected to hydrogen crushing and air flow pulverization to obtain powders of the main phase alloy I and the main phase alloy II.

[0063] Step S4: powder mixing: the powder of the main phase alloy I and the powder of the main phase alloy II obtained in step S3 are mixed in proportion to obtain a mixed powder.

[0064] Step S5: preparing green compacts: orienting and molding the mixed powder obtained in step S4, and pressing the mixed powder to obtain green compacts.

[0065] Step S6: high temperature sintering: the green body obtained in step S5 is subjected to high temperature sintering to obtain a magnetic matrix.

[0066] Step S7: Annealing treatment: The magnetic matrix obtained in step S6 is subjected to two-step annealing treatment to obtain a NdFeB permanent magnet material.

[0067] in:

[0068] Step S1: Preparation of main phase alloy I: Weigh and prepare the ingredients according to the designed main phase alloy I components in proportion, and subject the prepared raw materials to smelting and stripping treatment to obtain main phase alloy I. The chemical composition of main phase alloy I is as follows: RE1 x M y Co z Fe bal B t , wherein: RE1 includes one or more of Pr, Nd, M includes one or more of Al, Cu, Zr or Ga, 20wt%≤x≤40wt%, 0.1wt%≤y≤2wt%, 0.1wt%≤z≤0.5wt%, 0.1wt%≤t≤1wt%, and the balance is iron.

[0069] Step S2 Preparation of main phase alloy II: Weigh and prepare the ingredients according to the designed main phase alloy II components in proportion, and melt and spin the prepared raw materials to obtain main phase alloy II. The chemical composition of main phase alloy II is as follows: RE2 a Dy b Co c M d Fe bal B e , wherein: RE2 includes one or more of Pr, Nd, M includes one or more of Al, Cu, Zr or Ga, 20wt%≤a≤40wt%, 1wt%≤b≤10wt%, 30wt%≤c≤60wt%, 0.1wt%≤d≤2wt%, 0.1wt%≤e≤1wt%, and the balance is iron.

[0070] Step S3 crushing and grinding: the main phase alloy I and the main phase alloy II obtained in steps S1 and S2 are roughly crushed and then subjected to hydrogen crushing and air flow pulverization, wherein: the hydrogen crushing process is: the cast pieces after rough crushing are placed in a hydrogen crushing furnace, and the air in the furnace is exhausted by a vacuum system; a certain amount of high-purity hydrogen is introduced at room temperature, and hydrogen is supplemented during the hydrogen absorption process; after the cast pieces are saturated with hydrogen, the dehydrogenation step is not performed, and the heating system is directly closed to cool the alloy to room temperature with argon gas, so as to obtain hydrogen crushed powder with an average particle size of 7μm to 12μm. The air flow pulverization process is: the hydrogen crushed powder after hydrogen crushing is sent to the grinding chamber of the air flow mill, the speed of the air flow mill is set to 18000rpm to 21000rpm, and the air flow pressure is 0.5MPa to 0.7MPa, so as to obtain air flow milled powder with an average particle size of 1μm to 2μm.

[0071] Step S4: powder mixing: the powder of the main phase alloy I and the powder of the main phase alloy II obtained in step S3 are mixed in proportion to obtain a mixed powder.

[0072] Step S5: preparing green compacts: adding 0.25-0.35 wt% of lubricant to the mixed powder obtained in step S4, and then performing orientation molding and pressing to obtain green compacts.

[0073] Step S6: high temperature sintering: the green body obtained in step S5 is subjected to high temperature sintering in a hydrogen atmosphere, and a magnetic matrix is ​​obtained after the high temperature sintering is completed.

[0074] Step S7: Annealing treatment: The magnetic matrix obtained in step S6 is subjected to two-step annealing treatment to obtain a NdFeB permanent magnet material.

[0075] Example 1

[0076] The method for preparing a neodymium iron boron magnet comprises the following steps:

[0077] Step S1 Preparation of main phase alloy I: a certain proportion of Pr, Nd, M metal, Co, Fe, and B are melted and stripped to obtain main phase alloy I: RE1 20 M 0.1 Co 0.1 Fe bal B 0.1 ;

[0078] Step S2 Preparation of main phase alloy II: a certain proportion of Pr, Nd, Dy, Co, M metal, Fe and B are melted and stripped to obtain main phase alloy II: RE2 20 Dy 1 Co 30 M 0.1 Fe bal B 0..1 .

[0079] Step S3 crushing and grinding: the main phase alloy I and the main phase alloy II obtained in steps S1 and S2 are roughly crushed and then subjected to hydrogen crushing and air flow pulverization, wherein: the hydrogen crushing process is: the cast pieces after rough crushing are placed in a hydrogen crushing furnace, and the air in the furnace is exhausted by a vacuum system; a certain amount of high-purity hydrogen is introduced at room temperature, and hydrogen is supplemented during the hydrogen absorption process; after the cast pieces are saturated with hydrogen, the dehydrogenation step is not performed, the heating system is directly closed, and the alloy is cooled to room temperature by argon gas cooling. The air flow pulverization process is: the hydrogen crushed hydrogen powder is sent to the grinding chamber of the air flow mill, the speed of the air flow mill is set to 20000rpm, and the air flow pressure is set to 0.6MPa, and the air flow milled powder with an average particle size of 1μm to 2μm is obtained.

[0080] Step S4: powder mixing: the powders of the main phase alloy I and the main phase alloy II obtained in step S3 are mixed in a mass ratio of 3:1 to obtain a mixed powder.

[0081] Step S5: preparing green compacts: After adding 0.3 wt% of lubricant to the mixed powder obtained in step S4, the mixed powder is placed in a powder tank and installed at the feed port of a press. The powder is automatically quantitatively taken out by an electronic scale, and then the powder is placed in a suitable mold, oriented at a magnetic field strength of 2 T, and then isostatically pressed. The entire process is carried out in a glove box protected by nitrogen to obtain green compacts.

[0082] Step S6: high temperature sintering: the green body obtained in step S5 is sintered in a hydrogen atmosphere at a temperature of 1100°C for 6 hours and a vacuum degree of not less than 5×10 -3 Pa, and obtain the magnetic matrix.

[0083] Step S7: Annealing treatment: The magnetic substrate obtained in step S6 is subjected to two-step annealing treatment. The annealing atmosphere is an argon atmosphere. The first step annealing treatment temperature is 900°C for 6 hours. The second step annealing treatment temperature is 500°C for 2 hours. Finally, the NdFeB magnet is obtained by cooling.

[0084] Example 2

[0085] The method for preparing a neodymium iron boron magnet comprises the following steps:

[0086] Step S1 Preparation of main phase alloy I: a certain proportion of Pr, Nd, M metal, Co, Fe, and B are melted and stripped to obtain main phase alloy I: RE1 22 M 0.2 Co 0.5 Fe bal B 0.5 ;

[0087] Step S2 Preparation of main phase alloy II: a certain proportion of Pr, Nd, Dy, Co, M metal, Fe and B are melted and stripped to obtain main phase alloy II: RE2 25 Dy 5 Co 40 M 0.5 Fe bal B 0.5 .

[0088] Step S3 crushing and grinding: the main phase alloy I and the main phase alloy II obtained in steps S1 and S2 are roughly crushed and then subjected to hydrogen crushing and air flow pulverization, wherein: the hydrogen crushing process is: the cast pieces after rough crushing are placed in a hydrogen crushing furnace, and the air in the furnace is exhausted by a vacuum system; a certain amount of high-purity hydrogen is introduced at room temperature, and hydrogen is supplemented during the hydrogen absorption process; after the cast pieces are saturated with hydrogen, the dehydrogenation step is not performed, the heating system is directly closed, and the alloy is cooled to room temperature by argon gas cooling. The air flow pulverization process is: the hydrogen crushed hydrogen powder is sent to the grinding chamber of the air flow mill, the speed of the air flow mill is set to 20000rpm, and the air flow pressure is set to 0.6MPa, and the air flow milled powder with an average particle size of 1μm to 2μm is obtained.

[0089] Step S4: powder mixing: the powders of the main phase alloy I and the main phase alloy II obtained in step S3 are mixed in a mass ratio of 3:1 to obtain a mixed powder.

[0090] Step S5: preparing green compacts: After adding 0.3 wt% of lubricant to the mixed powder obtained in step S4, the mixed powder is placed in a powder tank and installed at the feed port of a press. The powder is automatically quantitatively taken out by an electronic scale, and then the powder is placed in a suitable mold, oriented at a magnetic field strength of 2 T, and then isostatically pressed. The entire process is carried out in a glove box protected by nitrogen to obtain green compacts.

[0091] Step S6: high temperature sintering: the green body obtained in step S5 is sintered in a hydrogen atmosphere at a temperature of 1100°C for 6 hours and a vacuum degree of not less than 5×10 -3 Pa, and obtain the magnetic matrix.

[0092] Step S7: Annealing treatment: The magnetic substrate obtained in step S6 is subjected to two-step annealing treatment. The annealing atmosphere is an argon atmosphere. The first step annealing treatment temperature is 900°C for 6 hours. The second step annealing treatment temperature is 500°C for 2 hours. Finally, the NdFeB magnet is obtained by cooling.

[0093] Example 3

[0094] The method for preparing a neodymium iron boron magnet comprises the following steps:

[0095] Step S1 Preparation of main phase alloy I: a certain proportion of Pr, Nd, M metal, Co, Fe, and B are melted and stripped to obtain main phase alloy IRE1 30.4 M 0.6 Co 0.4 Fe bal B 0.7 ;

[0096] Step S2 Preparation of main phase alloy II: a certain proportion of Pr, Nd, Dy, Co, M metal, Fe and B are melted and stripped to obtain main phase alloy IIRE2 26.5 Dy 6 Co 45 M 1.4 Fe bal B 0.7 .

[0097] Step S3 crushing and grinding: the main phase alloy I and the main phase alloy II obtained in steps S1 and S2 are roughly crushed and then subjected to hydrogen crushing and air flow pulverization, wherein: the hydrogen crushing process is: the cast pieces after rough crushing are placed in a hydrogen crushing furnace, and the air in the furnace is exhausted by a vacuum system; a certain amount of high-purity hydrogen is introduced at room temperature, and hydrogen is supplemented during the hydrogen absorption process; after the cast pieces are saturated with hydrogen, the dehydrogenation step is not performed, the heating system is directly closed, and the alloy is cooled to room temperature by argon gas cooling. The air flow pulverization process is: the hydrogen crushed hydrogen powder is sent to the grinding chamber of the air flow mill, the speed of the air flow mill is set to 20000rpm, and the air flow pressure is set to 0.6MPa, and the air flow milled powder with an average particle size of 1μm to 2μm is obtained.

[0098] Step S4: powder mixing: the powders of the main phase alloy I and the main phase alloy II obtained in step S3 are mixed in a mass ratio of 4:1 to obtain a mixed powder.

[0099] Step S5: preparing green compacts: After adding 0.3 wt% of lubricant to the mixed powder obtained in step S4, the mixed powder is placed in a powder tank and installed at the feed port of a press. The powder is automatically quantitatively taken out by an electronic scale, and then the powder is placed in a suitable mold, oriented at a magnetic field strength of 2 T, and then isostatically pressed. The entire process is carried out in a glove box protected by nitrogen to obtain green compacts.

[0100] Step S6: high temperature sintering: the green body obtained in step S5 is sintered in a hydrogen atmosphere at a temperature of 1100°C for 6 hours and a vacuum degree of not less than 5×10 -3 Pa, and obtain the magnetic matrix.

[0101] Step S7: Annealing treatment: The magnetic substrate obtained in step S6 is subjected to two-step annealing treatment. The annealing atmosphere is an argon atmosphere. The first step annealing treatment temperature is 900°C for 6 hours. The second step annealing treatment temperature is 500°C for 2 hours. Finally, the NdFeB magnet is obtained by cooling.

[0102] Example 4

[0103] The method for preparing a neodymium iron boron magnet comprises the following steps:

[0104] Step S1 Preparation of main phase alloy I: a certain proportion of Pr, Nd, M metal, Co, Fe, and B are melted and stripped to obtain main phase alloy IRE1 40 M 2 Co 0.5 Fe bal B 1 ;

[0105] Step S2 Preparation of main phase alloy II: a certain proportion of Pr, Nd, Dy, Co, M metal, Fe and B are melted and stripped to obtain main phase alloy IIRE2 40 Dy 10 Co 60 M 2 Fe bal B 1 .

[0106] Step S3 crushing and grinding: the main phase alloy I and the main phase alloy II obtained in steps S1 and S2 are roughly crushed and then subjected to hydrogen crushing and air flow pulverization, wherein: the hydrogen crushing process is: the cast pieces after rough crushing are placed in a hydrogen crushing furnace, and the air in the furnace is exhausted by a vacuum system; a certain amount of high-purity hydrogen is introduced at room temperature, and hydrogen is supplemented during the hydrogen absorption process; after the cast pieces are saturated with hydrogen, the dehydrogenation step is not performed, the heating system is directly closed, and the alloy is cooled to room temperature by argon gas cooling. The air flow pulverization process is: the hydrogen crushed hydrogen powder is sent to the grinding chamber of the air flow mill, the speed of the air flow mill is set to 20000rpm, and the air flow pressure is set to 0.6MPa, and the air flow milled powder with an average particle size of 1μm to 2μm is obtained.

[0107] Step S4: powder mixing: the powders of the main phase alloy I and the main phase alloy II obtained in step S3 are mixed in a mass ratio of 5:1 to obtain a mixed powder.

[0108] Step S5: preparing green compacts: After adding 0.3 wt% of lubricant to the mixed powder obtained in step S4, the mixed powder is placed in a powder tank and installed at the feed port of a press. The powder is automatically quantitatively taken out by an electronic scale, and then the powder is placed in a suitable mold, oriented at a magnetic field strength of 2 T, and then isostatically pressed. The entire process is carried out in a glove box protected by nitrogen to obtain green compacts.

[0109] Step S6: high temperature sintering: the green body obtained in step S5 is sintered in a hydrogen atmosphere at a temperature of 1100°C for 6 hours and a vacuum degree of not less than 5×10 -3 Pa, and obtain the magnetic matrix.

[0110] Step S7: Annealing treatment: The magnetic substrate obtained in step S6 is subjected to two-step annealing treatment. The annealing atmosphere is an argon atmosphere. The first step annealing treatment temperature is 900°C for 6 hours. The second step annealing treatment temperature is 500°C for 2 hours. Finally, the NdFeB magnet is obtained by cooling.

[0111] Comparative Example 1

[0112] The commercially available NdFeB magnets are manufactured by Jiangxi Jinli Permanent Magnet Technology Co., Ltd. and have a model number of 46H.

[0113] Comparative Example 2

[0114] The steps are similar to those in Example 3, except that in step S3, the rotation speed of the jet mill is 9000 rpm.

[0115] Comparative Example 3

[0116] The steps are similar to those in Example 3, except that: a single-phase alloy smelting process is used to prepare a NdFeB magnet, and the same components RE as those in Example 3 are mixed in proportion. 29.6 Dy2 Co 12.4 M 2 Fe bal B 1 As raw material.

[0117] Comparative Example 4

[0118] The steps are similar to those in Example 3, except that in step S6, the high temperature sintering temperature is 970°C, the time is 6 hours, and the vacuum degree is not less than 5x10 -3 Pa.

[0119] Comparative Example 5

[0120] The steps are similar to those in Example 1, except that in step S4, the mass ratio of the powders of the main phase alloy I and the main phase alloy II is 2:1.

[0121] Comparative Example 6

[0122] The steps are similar to those of Example 4, except that in step S4, the mass ratio of the powders of the main phase alloy I and the main phase alloy II is 6:1.

[0123] The following table shows the test results of the NdFeB magnets prepared in the examples and comparative examples.

[0124]

[0125] It can be seen from the above table that the magnetic properties and temperature resistance of the NdFeB magnets prepared by the preparation processes provided in Examples 1 to 4 of the present invention are significantly better than those of the ordinary NdFeB magnets in Comparative Example 1, especially the magnetic properties and temperature resistance of the NdFeB magnet prepared in Example 3 are the best, and its coercive force H cj It can reach 27.25kOe, the remanence Br is 16.24kGs, and the maximum magnetic product energy (BH) max The MGOe is 50.18 and the Curie temperature can reach 504°C, which is significantly optimized compared with the performance of comparative example 1, and can achieve high magnetic properties and high temperature resistance of NdFeB permanent magnet materials.

[0126] In Comparative Example 2, the reduction in the speed of the jet mill will lead to a decrease in the energy of the airflow collision, the particle size of the powder becomes larger, and the powder is unevenly dispersed. For the preparation of NdFeB magnets, powders with larger particle sizes are not easy to be completely sintered during the sintering process, resulting in insufficient bonding between particles, which ultimately affects the magnetic properties. Therefore, the reduction in speed may cause the magnetic properties of NdFeB magnets to decrease, especially the magnetic energy product and coercive force.

[0127] In Comparative Example 3, the NdFeB magnet prepared by using a single alloy will have a large amount of Co-rich intergranular phase (such as Nd(Fe,Co) 2) are formed in the grain boundary region. These phases contain a large amount of Fe and Co, which weakens the magnetic coupling effect of the grain boundary and leads to the reduction of the performance of NdFeB magnets.

[0128] In Comparative Example 4, the sintering temperature is a key factor in phase change and grain growth in NdFeB materials. A lower sintering temperature may cause the grains of NdFeB to fail to grow fully or the connection between the grains is not tight enough, thus affecting its magnetic properties. At the same time, too low a sintering temperature may affect the density and uniformity of the material, resulting in a decrease in magnetic flux density and coercive force, which in turn deteriorates the performance of the final NdFeB magnet.

[0129] It can be seen from Comparative Examples 5 and 6 that a poor mixing ratio will lead to the deterioration of the performance of NdFeB magnets. In Comparative Example 5, the mass ratio of the main phase alloy I and the main phase alloy II is 2:1, and the ratio of the two components is close, which may lead to excessive interaction between certain components during the sintering process, resulting in uneven distribution of certain elements in the alloy or the formation of precipitates, affecting the final magnetic properties, while a higher mixing ratio may lead to uneven grain distribution, thereby affecting the density of the permanent magnetic material and the properties of the grain boundary, resulting in reduced magnetic properties. In Comparative Example 6, the mass ratio of the main phase alloy I and the main phase alloy II is 6:1. The mixed powder under this mixing ratio is not sufficient during the sintering process, and too little Dy element may lead to incomplete phase structure of NdFeB during the sintering process, resulting in poor density of the permanent magnetic material, thereby affecting the performance of magnetic properties.

[0130] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A neodymium iron boron magnet, characterized in that: The raw materials for preparing the NdFeB magnets contain at least two main phases, wherein: the main phase alloy I does not contain heavy rare earth elements, and the main phase alloy II contains heavy rare earth elements.

2. The NdFeB magnet according to claim 1, characterized in that: The main phase alloy I is a NdFeB alloy that does not contain Dy, and the main phase alloy II is a NdFeB alloy that contains Dy and Co.

3. The NdFeB magnet according to claim 2, characterized in that: The nominal composition of the main phase alloy I is: RE1 x M y Co z Fe bal B t , wherein: RE1 includes one or more of Pr and Nd, M includes one or more of Al, Cu, Zr or Ga, 20wt%≤x≤40wt%, 0.1wt%≤y≤2wt%, 0.1wt%≤z≤0.5wt%, 0.1wt%≤t≤1wt%, and the balance is iron; The nominal composition of the main phase alloy II is: RE2 a Dy b Co c M d Fe bal B e , wherein: RE2 includes one or more of Pr, Nd, M includes one or more of Al, Cu, Zr or Ga, 20wt%≤a≤40wt%, 1wt%≤b≤10wt%, 30wt%≤c≤60wt%, 0.1wt%≤d≤2wt%, 0.1wt%≤e≤1wt%, and the balance is iron.

4. The NdFeB magnet according to claim 1, characterized in that: The mass ratio of the main phase alloy I to the main phase alloy II is (3:1) to (5:1).

5. The neodymium iron boron magnet according to any one of claims 1 to 4, characterized in that The coercive force of the NdFeB magnet is 16.1 kOe to 20.8 kOe.

6. A method for preparing a NdFeB magnet according to any one of claims 1 to 5, characterized in that: It includes: The powders of the main phase alloy I and the main phase alloy II are mixed in proportion, oriented, molded and pressed to form a green body, and then the green body is subjected to high temperature sintering and annealing treatment in sequence to obtain a neodymium iron boron magnet.

7. The preparation method according to claim 6, characterized in that: The preparation of the green compact comprises the following steps: subjecting the main phase alloy I and the main phase alloy II to a smelting and stripping treatment to obtain castings of the main phase alloy I and the main phase alloy II respectively, coarsely crushing the castings of the main phase alloy I and the main phase alloy II, performing hydrogen crushing and air flow pulverization, mixing them in a mass ratio of (3:1) to (5:1) to obtain a mixed powder, and then orienting and molding the mixed powder and pressing it to obtain a green compact; Preferably, the hydrogen crushing comprises: placing the castings of the main phase alloy I and the main phase alloy II in a hydrogen crushing furnace, and after the castings are saturated with hydrogen, without performing a dehydrogenation step, directly closing the heating system and cooling the alloy to room temperature by argon gas cooling, so as to obtain hydrogen crushed powder with an average particle size of 7 μm to 12 μm; Preferably, the air flow milling comprises: placing the hydrogen-decomposed powder of the main phase alloy I and the main phase alloy II into an air flow mill for crushing to obtain air flow milled powder with an average particle size of 1 μm to 2 μm, more preferably, the classifying wheel speed of the air flow mill is 18000 rpm to 21000 rpm, and the air flow pressure is 0.5 MPa to 0.7 MPa; Preferably, the orientation molding and pressing include: adding 0.25wt% to 0.35wt% of a lubricant to the mixed powder and then performing orientation molding and pressing. More preferably, the lubricant includes one or more of tributyl borate and polytetrafluoroethylene, the orientation magnetic field strength is 1.9T to 2.1T, and the pressing pressure is 170MPa to 210MPa.

8. The preparation method according to claim 6, characterized in that: The high temperature sintering comprises: sintering the green body at high temperature in a hydrogen-containing atmosphere; Preferably, the high temperature sintering temperature is 1000°C to 1100°C, the time is 4h to 12h, and the vacuum degree is not less than 5×10 -3 Pa.

9. The preparation method according to claim 6, characterized in that: The annealing process is a two-step annealing process; Preferably, the first step annealing temperature is 850°C to 950°C, the annealing time is 4h to 8h, and the atmosphere is an inert atmosphere. The second step annealing temperature is 450°C to 600°C, the annealing time is 2h to 4h, and the atmosphere is an inert atmosphere. The NdFeB magnet is obtained by cooling.

10. Use of the NdFeB magnet according to any one of claims 1 to 5 or the NdFeB magnet prepared by the preparation method according to any one of claims 6 to 9 in preparing humanoid robot motors, high temperature motors, electric drive systems, medical equipment, electrical equipment, high temperature sensors and monitoring equipment.

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