A preparation method for obtaining high-performance sintered NdFeB magnets

Abstract

The present invention relates to a preparation method for obtaining a high-performance sintered NdFeB magnet, wherein the method is to obtain an optimized quick-setting sheet alloy structure by adding an inert gas during vacuum melting and casting, and then subject the quick-setting sheet to hydrogen crushing, airflow grinding, pressing, sintering, and tempering to obtain a high-performance sintered NdFeB magnet. The method can, on the one hand, prevent the quick-setting sheet from oxidation and reduce the oxygen content of the final NdFeB permanent magnet, and on the other hand, refine the grains of the quick-setting sheet, thereby refining the grain size of the NdFeB permanent magnet and improving the coercive force of the NdFeB permanent magnet.

Description

Technical Field

[0001] The invention relates to a preparation method of a sintered NdFeB permanent magnet, in particular to a preparation method of obtaining a high-performance sintered magnet by optimizing the structure of a NdFeB quick-solidification sheet. Background Art

[0002] Since its introduction in 1983, NdFeB has been developed for nearly 40 years. Due to its high magnetic energy product, it is known as the "King of Magnets". However, with the development of science and technology in recent years, the performance requirements of NdFeB permanent magnets have become higher and higher. Not only does NdFeB permanent magnets need to have a high magnetic energy product, but they also need to have a high coercive force. Generally, the coercive force of NdFeB magnets is increased by adding heavy rare earths, but this method will reduce the remanence of the magnets. In addition, the price of heavy rare earths has fluctuated too much in recent years, which has increased production costs and is not conducive to the long-term development of NdFeB permanent magnets. With the introduction of the diffusion process, not only the cost price of producing NdFeB permanent magnets has been controlled, but also the remanence of NdFeB permanent magnets has hardly decreased while the coercive force has been increased. This is a great progress for the NdFeB permanent magnet industry. However, it also brings new problems. Diffusion magnets have certain requirements for thickness, and for most products, the magnetic properties of magnets cannot be improved through diffusion processes. Therefore, it is urgent to find new technologies to improve the magnetic properties of magnets.

[0003] Chinese invention patent CN1060128673A discloses a sintered NdFeB magnet and a preparation method thereof. In this method, during the air flow milling process, the NdFeB powder is ground to a particle size of 0.2-0.5μm and then the sintered NdFeB magnet is prepared. By optimizing the process, the coercive force of the magnet can be significantly improved without affecting other magnetic performance indicators. However, the process stability is high and the magnet is easily oxidized, resulting in unnecessary waste.

[0004] The above patents do not involve research on improving the magnetic properties of NdFeB permanent magnets by adjusting the smelting process of the quick-setting sheets to optimize the microstructure of the quick-setting sheets. Summary of the invention

[0005] The present invention provides a preparation method for obtaining a high-performance sintered NdFeB magnet by optimizing the structure of a quick-setting sheet. The method starts with the preparation process of a NdFeB master alloy and uses a method of blowing inert gas during the smelting and casting process to increase the cooling rate of the quick-setting sheet and reduce the oxygen content of the quick-setting sheet, thereby achieving the purpose of refining columnar crystals, optimizing the structure of the quick-setting sheet of the NdFeB alloy, and preparing for further sintering of NdFeB magnets.

[0006] The present invention is achieved through the following technical solutions:

[0007] A preparation method for obtaining high-performance sintered NdFeB magnets, characterized by comprising the following process steps: 1) preparation of master alloy - 2) hydrogen crushing - 3) steam flow milling - 4) pressing and forming - 5) cold isostatic pressing - 6) stripping - 7) sintering - 8) tempering;

[0008] The preparation of the master alloy includes: batching - melting - casting - crushing. The melting and casting processes are carried out in a vacuum rapid solidification furnace, using a vacuum plus inert gas method, with a vacuum degree of ≤10Pa and an inert gas injection volume of 100-200L / Min.

[0009] Furthermore: the casting is performed using an insulating crucible, the insulating crucible receives the molten liquid in the smelting crucible and then casts it onto a cooling roller; the cooling roller performs rotational motion and axial telescopic motion, and the insulating crucible performs vertical radial motion and horizontal radial motion relative to the cooling roller.

[0010] Further: a water-cooled target is arranged in the material throwing direction of the cooling roller, a water-cooled plate is arranged facing the water-cooled target, and a material receiving mechanism is arranged below the water-cooled target;

[0011] The material receiving mechanism is a vertical material dropping mechanism, and a crushing mechanism is arranged on the material dropping channel;

[0012] The outlet end of the material receiving mechanism is connected to a rotating cooling mechanism. The main body of the rotating cooling mechanism is a rotating cylinder. The rotating cylinder is inclined downward from the feeding end to the discharging end. A spiral stirring paddle is arranged in the rotating cylinder. A water cooling system is arranged in the wall of the rotating cylinder.

[0013] Furthermore: in the hydrogen cracking process, hydrogen is absorbed first and then released, the hydrogen absorption pressure is 0.1-0.35Pa, and the temperature during the hydrogen absorption process is 530-570°C; the end standard of hydrogen release is: there is no change in the vacuum degree in the hydrogen cracking furnace for 20 minutes, which means that hydrogen release is completed.

[0014] Further: the powder after hydrogen crushing is mixed before air flow milling, 3-5‰ of oxidant and 1-3‰ of lubricant are added according to the weight of the material, and then air flow milling is performed, the oxidant is phosphite, and the lubricant is zinc stearate;

[0015] The oxygen content in the jet mill is controlled at 10-20 PPm;

[0016] Air flow grinding particle size SMD: 2.5-3.2μm, D90 / D10≤4.5;

[0017] The fine powder after air jet milling is mixed again.

[0018] Furthermore: During the powder pressing process, the oxygen content is controlled at ≤200 PPm and the compact density is 3.9-4.3 g / cm 3 .

[0019] Furthermore: the cold isostatic pressing pressure is controlled at 160-200 MPa.

[0020] Furthermore: the oxygen content is controlled at 100-300PPm during stripping.

[0021] Furthermore, the sintering temperature is controlled at 1050-1080°C, the heat preservation time is 3-5h, and the product is taken out of the furnace when cooled to ≤70°C.

[0022] Furthermore, the tempering is carried out in two stages, the first stage tempering temperature is 880-920°C, the insulation time is 2-3h, the second stage tempering temperature is 450-520°C, the insulation time is 3-5h; and the product is taken out of the furnace when cooled to ≤70°C.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) by adopting the method of vacuum and inert gas addition to the master alloy during the preparation process, the coercive force of the sintered NdFeB permanent magnet can be improved; (2) by protecting the quick-setting sheet, the oxygen content in the quick-setting sheet is greatly reduced, the smelting burn-off rate is reduced, and the production cost is saved; (3) after dynamic casting and multiple cooling and crushing, a fine alloy structure is obtained; (4) the sintered NdFeB magnet prepared by this method not only has improved remanence of the magnet, but also greatly improves the coercive force of the magnet, reduces the use of heavy rare earth, and is conducive to resource integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the microstructure of the quick-setting sheet of Example 1 of the present invention.

[0025] Figure 2 This is the microstructure of the comparative quick-setting sheet of Example 1 of the present invention.

[0026] Figure 3 This is the microstructure of the quick-setting sheet of Example 2 of the present invention.

[0027] Figure 4 This is the microstructure of the comparative quick-setting sheet of Example 2 of the present invention.

[0028] Figure 5 This is the microstructure of the quick-setting sheet of Example 3 of the present invention.

[0029] Figure 6 This is the microstructure of the comparative quick-setting sheet of Example 3 of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0031] The preparation of sintered NdFeB magnets generally goes through the following steps: 1. Preparation of NdFeB master alloy - 2. Hydrogen crushing of alloy quick-solidification sheets - 3. Steam milling - 4. Powder pressing - 5. Sintering and tempering - 6. Post-processing.

[0032] The present invention proposes the following process in each process procedure:

[0033] 1. Preparation of NdFeB master alloy

[0034] The preparation of NdFeB master alloy includes: raw material preparation - smelting - casting and strip throwing - crushing and cooling.

[0035] 1.1 Raw materials

[0036] The raw materials are prepared according to the proportion of the ingredients required by the NdFeB alloy. The surface of the NdFeB raw materials needs to be cleaned before mixing, without rust and oil stains.

[0037] The raw materials of NdFeB include Fe, rare earth materials and other alloys. Among them, rare earth materials include Nd, PrNd, Pr, Tb, Dy, Gd, Ho, Ce, La, Er, etc., and other alloys include Al, Co, Cu, Ga, Nb, Ti, Zr, B, BFe, etc. For NdFeB alloy, Fe, Nd, PrNd, and B are the main components, and the others are elements that help improve various properties.

[0038] The ingredients are prepared according to the ingredient list, where the allowable error range for raw materials greater than 50Kg is ±0.1kg, the allowable error range for raw materials less than 10Kg is 0.01kg, and the allowable error range for raw materials between 10-50kg is ±0.05Kg.

[0039] 1.2 Melting

[0040] The present invention requires that the smelting and casting of the NdFeB alloy are both carried out in a vacuum furnace with a vacuum degree of ≤10Pa.

[0041] During smelting, the raw materials are placed into the smelting crucible in the order of iron, other alloys, and rare earths.

[0042] The melting and casting temperature is determined according to the NdFeB ternary phase diagram, and the melting temperature range is 1380-1470℃. The heating power is increased in the early stage of melting, and the heating power is gradually increased from 200KW to 500KW, so that the alloy added to the crucible is melted quickly. After the alloy in the crucible is completely melted, the power is reduced by 20-50KW, and the insulation time is about 10 minutes, so that the alloy liquid is fully uniform.

[0043] 1.3 Casting belt

[0044] Casting and throwing strips is an important step in obtaining NdFeB alloy quick-setting sheets. The present invention adopts a method of dynamic casting combined with multi-stage cooling and multi-stage crushing.

[0045] Dynamic casting is to use an insulating crucible as a mobile tundish. In addition to setting up a smelting crucible for melting alloys, the present invention also adds an insulating crucible below the smelting crucible, and a high-frequency heating nozzle is provided at the bottom of the insulating crucible. The functions of the insulating crucible are to maintain a constant temperature of the molten liquid and to serve as a tundish for casting onto a cooling roller. As a tundish, it is dynamically adjustable.

[0046] For the NdFeB alloy rapid solidification sheet formation technology, the best process goal is to quickly cool the alloy to form a thin strip when it is cast on the cooling roller, and as the cooling roller rotates, the thin strip can be thrown out uniformly and continuously. Therefore, the best measure is to maintain dynamic casting between the insulation crucible and the cooling roller, rather than fixed-point casting. The ideal state is that the up and down, left and right, front and back positions of the casting can be adjusted at any time.

[0047] Considering that the cooling roller is a rotating part, it is only suitable for rotational movement and axial telescopic movement. Therefore, the present invention sets the cooling roller into a telescopic sleeve structure, the inner shaft can rotate, and the outer sleeve is sleeved on the inner shaft. Through technical means, the outer sleeve can rotate with the inner shaft. At the same time, the outer sleeve can be relatively telescopic outside the inner shaft, that is, the outer sleeve can move axially, and the outer surface of the outer sleeve is the casting surface. The present invention sets the insulating crucible to be able to move vertically and horizontally relative to the cooling roller. In addition, the axial movement of the cooling roller jacket, the present invention forms a three-dimensional motion mode through the insulating crucible and the cooling roller. When the alloy melt is cast on the surface of the cooling roller, it is rapidly cooled to form a thin strip with the rotation of the cooling roller, and is thrown out under the centrifugal action of the cooling roller. The insulating crucible moves in two dimensions above the cooling roller to adjust the casting angle and casting height with the cooling roller, and the cooling roller itself telescopes to adjust the casting surface. Of course, the cooling roller can also be made into only a rotating part, and the insulating crucible can be controlled by a three-dimensional mechanism to move up and down, left and right, and forward and backward, which can all be achieved.

[0048] 1.4 Crushing and cooling

[0049] Crushing and cooling is also an important step in obtaining NdFeB alloy quick-setting sheets. In order to accelerate cooling, the present invention sets a water-cooled target in the direction of the cooling roller throwing the material. The alloy strip is thrown onto the water-cooled target for secondary cooling and is beaten into quick-setting sheets. A material receiving mechanism is set below the water-cooled target. The material receiving mechanism has a vertical channel for natural material dropping, which can avoid the accumulation of dropped materials.

[0050] In order to further break up the quick-setting sheets and buffer the falling of the materials, a breaking mechanism is provided on the falling channel of the receiving mechanism, so that the quick-setting sheets can be further broken up.

[0051] Furthermore, a rotary cooling mechanism is provided at the outlet end of the receiving mechanism for further cooling. The main body of the rotary cooling mechanism can be a rotary drum, and a water cooling jacket is provided on the periphery of the rotary drum. The rotary drum is tilted downward from the feeding end to the discharging end. The material enters the drum and moves downward in a spiral as the drum rotates, accelerating the slide to avoid material accumulation. In addition, a spiral stirring paddle is provided in the rotary drum, which is further hit and broken during the rotation of the drum, and is broken again.

[0052] The present invention adopts multi-stage cooling and multi-stage crushing, which is an important means to obtain refined alloy structure and improve the coercive force of permanent magnets. The present invention quickly cools the alloy by establishing a three-stage cooling mechanism of cooling roller cooling, water-cooled target cooling, and rotating square tube cooling, and obtains a fine alloy structure by rapid quenching. The present invention obtains quick-setting sheets with a high size qualification rate by establishing a three-stage crushing mechanism of water-cooled target crushing, crushing mechanism crushing, and rotating square tube crushing. By refining the quick-setting sheets, the coercive force of sintered NdFeB permanent magnets can be improved. At the same time, since the cooling roller to the water-cooled target is a centrifugal throwing method, the water-cooled target is a dispersed blanking method, the material collection mechanism is a free blanking method, and the rotating cooling mechanism is a rotating blanking method, it will not cause the accumulation of hot sheets and affect its alloy properties.

[0053] As a top priority, the present invention injects inert gas as partial pressure protection during the vacuum stage of smelting, casting and cooling. After many breakthrough experiments, it was found that during the smelting, casting and cooling process, a very optimized alloy structure can be obtained by adopting the method of adding inert gas partial pressure under vacuum conditions, which is a major breakthrough of the present invention. Usually, in some processes, inert gas is added only as a protective gas, while the inert gas added in the present invention is to enhance the optimized cooling and obtain an optimized structure. After a large number of experiments, it was found that the amount of inert gas blown in was controlled at 100-200L / Min. By blowing argon, helium and other inert gases to protect the quick-setting sheet, the carbon and oxygen content in the quick-setting sheet alloy was greatly reduced, thereby making the structure more refined, reducing the smelting burn-out rate, and increasing the coercive force while increasing the residual magnetism of the magnet.

[0054] 2. Hydrogen Break

[0055] The alloy quick-solidification sheet is placed in a hydrogen crushing furnace for hydrogen crushing. The main functions of hydrogen crushing are: 1. Crushing. Hydrogen enters the alloy ribbon along the main phase and the neodymium-rich phase, causing the alloy ribbon to expand and burst, thereby achieving a state of crushing into coarse powder; 2. Improving the microstructure can promote the rearrangement and combination of the various phases of the powder particles in subsequent processing, and can optimize the distribution of the main phase and the neodymium-rich phase; 3. Enhancing the density of the magnet. The powder particle size after hydrogen crushing is refined and evenly distributed, so that the pressed magnet has a higher density. The increase in density can reduce the pores and defects in the magnet, thereby improving the magnetic properties.

[0056] In hydrogen blasting, the hydrogen absorption time is calculated according to the weight of the material put into the hydrogen blasting furnace. When the weight is less than 600kg, the hydrogen absorption time is 3-5h, and the hydrogen release time is 5-8h. When the weight is between 600-1200kg, the hydrogen absorption time is 4-7h, and the hydrogen release time is 6-10h.

[0057] The hydrogen absorption pressure during hydrogen rupture is 0.1-0.35 Pa. The furnace body is heated during hydrogen absorption, and the heating temperature is generally controlled at 530-570°C.

[0058] The standard for the end of hydrogen release in hydrogen blasting is: when the vacuum degree in the hydrogen blasting furnace does not change for 20 minutes, the hydrogen release is completed. After the hydrogen release is completed, open the furnace body to cool down. When the furnace body temperature drops to 40-60℃, the furnace can be taken out.

[0059] 3. Airflow mill

[0060] The function of the air jet mill is to further refine and homogenize the powder particles and optimize the microstructure. The hydrogen-destroyed powder is first mixed, and 3-5‰ of oxidant and 1-3‰ of lubricant are added according to the weight of the material, and then fully stirred on the powder mixer. Common oxidants are phosphite and common lubricants are zinc stearate.

[0061] In the air jet mill, materials less than 600 kg are ground for 2-3 hours, and materials between 600-1200 kg are ground for 3-5 hours.

[0062] The oxygen content in the air jet mill is controlled at 10-20PPm.

[0063] The particle size of the jet mill SMD is 2.5-3.2μm, D90 / D10≤4.5.

[0064] The ground fine powder is mixed again to reduce component segregation.

[0065] 4. Pressing

[0066] Powder pressing is to press the powder ground by airflow mill into green compacts of certain specifications according to production needs, and further control the oxygen content. The oxygen content of the green compact is controlled at ≤200PPm, and the compact density is controlled at 3.9-4.3g / cm 3 .

[0067] 5. Cold isostatic pressing

[0068] The pressed green body is subjected to cold isostatic pressing, and the isostatic pressing pressure is controlled at 160-200MPa. Cold isostatic pressing can increase the molding density and uniformity, improve the magnetic properties and enhance the mechanical properties.

[0069] 6. Stripping

[0070] Stripping is to strip the isostatically pressed green body in a stripping box. The oxygen content must also be controlled during stripping. The oxygen content in the stripping box is controlled at 100-300PPm.

[0071] 7. Sintering

[0072] The stripped material is sintered at a sintering temperature of 1050-1080°C for 3-5h. When the temperature is cooled to ≤70°C, it is taken out of the furnace and prepared for the tempering process.

[0073] 8. Tempering

[0074] Tempering is divided into primary tempering and secondary tempering. The primary tempering temperature is 880-920℃, the holding time is 2-3h, and the secondary tempering temperature is 450-520℃, the holding time is 3-5h. The temperature is cooled to ≤70℃ and then taken out of the furnace to finally obtain NdFeB permanent magnets.

[0075] The present invention obtains a very fine master alloy structure through the above process, and its coercivity, remanence and magnetic energy product are all improved. In particular, the multi-stage rapid cold quenching and inert gas partial pressure process make the alloy structure unprecedentedly optimized.

[0076] The following are several groups of comparative examples, which can fully demonstrate the beneficial effects of the process of the present invention.

[0077] Example 1 of the present invention

[0078] The raw materials are divided into PrNd 28.8 Dy 0.8 Cu 0.15 Co 1.5 Al 0.1 B 0.9 Ga 0.2 Zr 0.1 Fe 余 (wt.%) formula is 600Kg (the lower right corner subscript of the ingredients in each embodiment represents the mass percentage of the ingredients), the raw materials are put into the vacuum quick-setting furnace melting crucible in the order of Fe, other alloys, and rare earths for melting. When the vacuum degree reaches 10Pa, the power is increased, the melting temperature is 1430℃, and when all the alloys are melted, the power is reduced by 20KW, and the temperature is kept for 10 minutes; then the insulation crucible is used as a middle bag to receive the molten liquid in the melting crucible for dynamic casting, and the thin strip is thrown out with the rotation of the cooling roller, and is discharged from the furnace after multi-stage cooling and crushing.

[0079] During the smelting and casting process, argon gas is blown into the vacuum rapid solidification furnace with a gas pressure of 100L / Min. After the casting is completed, the argon gas blowing is stopped.

[0080] Put the quick-setting sheet into the hydrogen rupture furnace for hydrogen rupture. The hydrogen absorption time is 4 hours and the hydrogen absorption pressure is 0.3Pa. Heat it to 550℃ and prepare to release hydrogen for 5 hours. Within 20 minutes, observe that there is no change in the vacuum degree in the furnace, which means that the hydrogen release is completed. When the furnace body cools down to 40℃, take it out of the furnace.

[0081] Put the hydrogen crushing material into the hydrogen crushing tank and weigh it. Add 3‰ of oxidant and 2‰ of lubricant according to the weight, mix it on the powder mixer for 2.5 hours, and then jet mill. The oxygen content of the jet mill is controlled at 10PPm. By adjusting the rotation speed, the particle size is controlled at 2.8μm, and D90 / D10 is 4.3. The fine powder ground by the jet mill is mixed on the powder mixer again for 2.5 hours to fully mix the powder ground by the jet mill and reduce component segregation.

[0082] The fine powder was pressed into 60×60×30 square blocks. The oxygen content was controlled at 158 ​​ppm during the pressing process. The green compact density was 4.2 g / cm 3 ; Then cold isostatic pressing is carried out with an isostatic pressing pressure of 180MPa; the green body pressed by cold isostatic pressing is placed in a stripping box, and when the oxygen content in the stripping box is controlled at 200PPm, stripping is carried out, and the stripped materials are uniformly placed in a sintering furnace with a sintering temperature of 1060℃, a holding time of 4h, and then cooled to 70℃.

[0083] The fired blank was tempered, the first tempering temperature was 900℃, the holding time was 2h, the second tempering temperature was 500℃, the holding time was 4h, cooled to 70℃, and the magnetic properties were tested using NIM-2000. The magnetic properties test results are shown in Table 1.

[0084] Comparative Example 1

[0085] Take 600 kg of the same formula as Example 1 of the present invention, and put them into the vacuum rapid solidification furnace melting crucible in the order of Fe, other alloys, and rare earth for melting. When the vacuum degree reaches 10 Pa, increase the power and the melting temperature is 1430°C. When all the alloys are melted, reduce the power by 20 KW, keep warm for 10 minutes, and cast. The cooling roller rotates and the belt is swung. After the casting and stripping are completed, turn on the fan to cool for 2 hours, and the temperature is cooled to 40°C before being taken out of the furnace.

[0086] Put the quick-setting sheet into the hydrogen rupture furnace for hydrogen rupture. The hydrogen absorption time is 4 hours and the hydrogen absorption pressure is 0.3Pa. Heat it to 550℃ and prepare to release hydrogen for 5 hours. Within 20 minutes, observe that there is no change in the vacuum degree in the furnace, which means that the hydrogen release is completed. When the furnace body cools down to 40℃, take it out of the furnace.

[0087] Put the hydrogen crushing material into the hydrogen crushing tank and weigh it. Add 3‰ of oxidant and 2‰ of lubricant according to the weight, mix it on the powder mixer for 2.5 hours, prepare the air flow mill, control the oxidation amount of the air flow mill at 10PPm, adjust the speed, control the particle size at 2.8μm, D90 / D10 is 4.3, mix the fine powder ground by the air flow mill on the powder mixer again for 2.5 hours to fully mix the powder from the air flow mill and reduce component segregation.

[0088] The fine powder was pressed into 60×60×30 square blocks. The oxygen content was controlled at 158 ​​ppm during the pressing process. The green compact density was 4.2 g / cm 3 , and then cold isostatic pressing is carried out with an isostatic pressing pressure of 180MPa. The green body pressed by cold isostatic pressing is placed in a stripping box. When the oxygen content in the stripping box is controlled at 200PPm, stripping is carried out. The stripped materials are uniformly placed in a sintering furnace with a sintering temperature of 1060℃ and a holding time of 4h, and then cooled to 70℃.

[0089] The fired blank was tempered, the first tempering temperature was 900℃, the holding time was 2h, the second tempering temperature was 500℃, the holding time was 4h, cooled to 70℃, and the magnetic properties were tested using NIM-2000. The magnetic properties test results are shown in Table 1.

[0090] The main differences between Example 1 of the present invention and Comparative Example 1 are: 1. The present invention adopts a tundish and a cooling roller to cooperate with dynamic casting. During the casting process, argon gas is continuously introduced into the vacuum furnace with an inflation pressure of 100L / Min; 2. After the cooling roller is thrown off the belt, it undergoes multiple cooling and crushing.

[0091] Example 2 of the present invention

[0092] The raw materials are divided into PrNd 18.67 Pr 10.9 B 0.9 Cu 0.1 Co 1.0 Zr 0.17 Ga 0.3 Fe 余 600Kg of the formula of (wt.%) is prepared and put into the crucible of the vacuum rapid solidification furnace in the order of Fe, other alloys and rare earth for melting. When the vacuum degree reaches 10Pa, the power is increased and the melting temperature is 1430℃. When all the alloys are melted, the power is reduced by 20KW and the temperature is kept for 10 minutes for preparation of casting.

[0093] The heat-insulating crucible is used as the tundish for dynamic casting, and the thin strip is thrown out with the rotation of the cooling roller, and then it is discharged from the furnace after multi-stage cooling and crushing. At the beginning of smelting, argon gas is blown into the rapid solidification furnace with a gas pressure of 200L / Min. After the casting is completed, the argon gas is stopped and it is discharged from the furnace after multi-stage cooling and crushing.

[0094] Put the quick-setting sheet into the hydrogen cracking furnace for hydrogen cracking. The hydrogen absorption time is 4 hours and the hydrogen absorption pressure is 0.3Pa. Heat it to 550℃ and prepare to release hydrogen. The hydrogen release time is 5 hours. If the vacuum degree in the furnace does not change within 20 minutes, the hydrogen release is completed. When the furnace body cools down to 40℃, it is taken out of the furnace.

[0095] Put the hydrogen crushing material into the hydrogen crushing tank and weigh it. Add 3‰ of oxidant and 2‰ of lubricant according to the weight, mix it on the powder mixer for 2.5 hours, prepare the air flow mill, control the oxidation amount of the air flow mill at 10PPm, adjust the speed, control the particle size at 2.8μm, D90 / D10 is 4.3, mix the fine powder ground by the air flow mill on the powder mixer again for 2.5 hours to fully mix the powder from the air flow mill and reduce component segregation.

[0096] The powder was pressed into 60×60×30 blocks. The oxygen content was controlled at 158 ​​ppm during the pressing process and the green density was 4.2 g / cm 3 ; Then cold isostatic pressing is carried out with an isostatic pressing pressure of 180MPa. The green body after cold isostatic pressing is placed in a stripping box. When the oxygen content in the stripping box is controlled at 200PPm, stripping is carried out. The stripped materials are uniformly placed in a sintering furnace with a sintering temperature of 1060℃ and a holding time of 4h, and then cooled to 70℃.

[0097] The fired blank was tempered, the first tempering temperature was 900℃, the holding time was 2h, the second tempering temperature was 500℃, the holding time was 4h, cooled to 70℃, and the magnetic properties were tested using NIM-2000. The magnetic properties test results are shown in Table 1.

[0098] Comparative Example 2

[0099] Comparative Example 2: 600 kg of raw materials are prepared with the same formula as Example 2 of the present invention, and are put into a vacuum rapid solidification furnace melting crucible in the order of Fe, other alloys, and rare earths for melting. When the vacuum degree reaches 10 Pa, the power is increased and the melting temperature is 1430°C. After all the alloys are melted, the power is reduced by 20 KW. After keeping warm for 10 minutes, casting is performed. During casting, the cooling roller rotates and the belt is spun. After casting, the fan is turned on to cool for 2 hours. The temperature is cooled to 40°C and then the furnace is opened.

[0100] Put the quick-setting sheet into the hydrogen cracking furnace for hydrogen cracking. The hydrogen absorption time is 4 hours and the hydrogen absorption pressure is 0.3Pa. Heat it to 550℃ and prepare to release hydrogen. The hydrogen release time is 5 hours. If the vacuum degree in the furnace does not change within 20 minutes, the hydrogen release is completed. When the furnace body cools down to 40℃, it is taken out of the furnace.

[0101] Put the hydrogen crushing material into the hydrogen crushing tank and weigh it. Add 3‰ of oxidant and 2‰ of lubricant according to the weight, mix it on the powder mixer for 2.5 hours, prepare the air flow mill, control the oxidation amount of the air flow mill at 10PPm, adjust the speed, control the particle size at 2.8μm, D90 / D10 is 4.3, mix the fine powder ground by the air flow mill on the powder mixer again for 2.5 hours to fully mix the powder from the air flow mill and reduce component segregation.

[0102] The powder was pressed into 60×60×30 blocks. The oxygen content was controlled at 158 ​​ppm during the pressing process and the green density was 4.2 g / cm 3 ; Then cold isostatic pressing is carried out with an isostatic pressing pressure of 180MPa. The green body pressed by cold isostatic pressing is placed in a stripping box. When the oxygen content in the stripping box is controlled at 200PPm, stripping is carried out. The stripped materials are uniformly placed in a sintering furnace with a sintering temperature of 1060℃ and a holding time of 4h, and then cooled to 70℃.

[0103] The fired blank was tempered, the first tempering temperature was 900℃, the holding time was 2h, the second tempering temperature was 500℃, the holding time was 4h, cooled to 70℃, and the magnetic properties were tested using NIM-2000. The magnetic properties test results are shown in Table 1.

[0104] The main difference between Example 2 of the present invention and Comparative Example 2 is that the present invention adopts an insulating crucible as a middle bag and a cooling roller to cooperate with dynamic casting. Argon is blown into the rapid solidification furnace at the beginning of smelting, and the inflation pressure is 200L / Min. After the casting is completed, the argon blowing is stopped, and the furnace is taken out of the furnace after multi-stage cooling and crushing.

[0105] Example 3 of the present invention

[0106] The raw materials are divided into PrNd 30.1 Dy 1.5 B 0.9 Cu 0.15 Co 1.5 Al 0.35 Ga 0.25 Zr 0.17 Fe 余 600Kg of the formula of (wt.%) is prepared and put into the melting crucible of the vacuum rapid solidification furnace in the order of Fe, other alloys and rare earth for melting. When the vacuum degree reaches 10Pa, increase the power and the melting temperature is 1430℃. When all the alloys are melted, reduce 20KW, keep warm for 10 minutes and prepare for casting.

[0107] At the beginning of casting, helium is blown into the rapid setting furnace with an inflation pressure of 200L / Min. After the casting is completed, the helium blowing is stopped and the fan is turned on to cool for 2 hours. When the temperature cools to 40℃, it is taken out of the furnace.

[0108] Put the quick-setting sheet into the hydrogen cracking furnace for hydrogen cracking. The hydrogen absorption time is 4 hours and the hydrogen absorption pressure is 0.3Pa. Heat it to 550℃ and prepare to release hydrogen. The hydrogen release time is 5 hours. If the vacuum degree in the furnace does not change within 20 minutes, the hydrogen release is completed. When the furnace body cools down to 40℃, it is taken out of the furnace.

[0109] Put the hydrogen crushing material into the hydrogen crushing tank and weigh it. Add 3‰ of oxidant and 2‰ of lubricant according to the weight, mix it on the powder mixer for 2.5 hours, prepare the air flow mill, control the oxidation amount of the air flow mill at 10PPm, adjust the speed, control the particle size at 2.8μm, D90 / D10 is 4.3, mix the fine powder ground by the air flow mill on the powder mixer again for 2.5 hours to fully mix the powder from the air flow mill and reduce component segregation.

[0110] The powder was pressed into 60×60×30 blocks. The oxygen content was controlled at 158 ​​ppm during the pressing process and the green density was 4.2 g / cm 3 ; Then cold isostatic pressing is carried out with an isostatic pressing pressure of 180MPa. The green body after cold isostatic pressing is placed in a stripping box. When the oxygen content in the stripping box is controlled at 200PPm, stripping is carried out. The stripped materials are uniformly placed in a sintering furnace with a sintering temperature of 1060℃ and a holding time of 4h, and then cooled to 70℃.

[0111] The fired blank was tempered, the first tempering temperature was 900℃, the holding time was 2h, the second tempering temperature was 500℃, the holding time was 4h, cooled to 70℃, and the magnetic properties were tested using NIM-2000. The magnetic properties test results are shown in Table 1.

[0112] Comparative Example 3

[0113] Comparative Example 3 takes the same formula as Example 3 of the present invention, and puts Fe, other alloys, and rare earths into a vacuum rapid solidification furnace melting crucible in the order of smelting. When the vacuum degree reaches 10Pa, the power is increased, and the melting temperature is 1430°C. After all the alloys are melted, the power is reduced by 20KW, and the mixture is kept warm for 10 minutes and cast. After the casting is completed, the fan is turned on to cool for 2 hours, and the temperature is cooled to 40°C before being taken out of the furnace.

[0114] Put the quick-setting sheet into the hydrogen cracking furnace for hydrogen cracking. The hydrogen absorption time is 4 hours, the hydrogen absorption pressure is 0.3Pa, and it is heated to 550℃. Prepare to release hydrogen. The hydrogen release time is 5 hours. Within the next 20 minutes, if the vacuum degree in the furnace does not change, the hydrogen release is completed. When the furnace body cools down to 40℃, it is taken out of the furnace.

[0115] Put the hydrogen crushing material into the hydrogen crushing tank and weigh it. Add 3‰ of oxidant and 2‰ of lubricant according to the weight, mix it on the powder mixer for 2.5 hours, prepare the air flow mill, control the oxidation amount of the air flow mill at 10PPm, adjust the speed, control the particle size at 2.8μm, D90 / D10 is 4.3, mix the fine powder ground by the air flow mill on the powder mixer again for 2.5 hours to fully mix the powder from the air flow mill and reduce component segregation.

[0116] The powder was pressed into 60×60×30 blocks. The oxygen content was controlled at 158 ​​ppm during the pressing process and the green density was 4.2 g / cm 3 ; Then cold isostatic pressing is carried out, the isostatic pressing pressure is 180MPa, the green body after cold isostatic pressing is placed in a stripping box, and when the oxygen content in the stripping box is controlled at 200PPm, stripping is carried out, and the stripped materials are uniformly placed in a sintering furnace, the sintering temperature is 1060℃, the heat preservation time is 4h, and then cooled to 70℃;

[0117] The fired blank was tempered, the first tempering temperature was 900℃, the holding time was 2h, the second tempering temperature was 500℃, the holding time was 4h, cooled to 70℃, and the magnetic properties were tested using NIM-2000. The magnetic properties test results are shown in Table 1.

[0118] The main difference between Example 3 of the present invention and Comparative Example 3 is that: at the beginning of casting, helium is blown into the rapid setting furnace with an inflation pressure of 200 L / Min, and after the casting is completed, the helium blowing is stopped.

[0119] Table 1: Comparison of magnetic properties of NdFeB permanent magnets

[0120]

[0121] The main difference between the three comparative embodiments is that inert gas is blown in. As can be seen from Table 1, the three inventive examples significantly improve the coercive force compared with the comparative example, but have little effect on the remanence. It can be seen that blowing in a certain amount of inert gas has a significant effect on improving the coercive force of the magnet.

[0122] In addition, blowing inert gas can reduce the oxygen and carbon content of the rare earth permanent magnet, as shown in Table 2.

[0123] Table 2: Comparison of oxygen and carbon content of quick-setting sheets

[0124]

[0125] The reduction of oxygen and carbon content can significantly improve the performance and service life of permanent magnets, as follows:

[0126] 1. Improve magnetic properties: The magnetic properties of rare earth permanent magnets are closely related to their internal microstructure. Reducing the oxygen and carbon content can reduce impurities and defects in the material, thereby improving the magnetic properties of the magnet;

[0127] 2. Enhance corrosion resistance and oxidation resistance: Carbon and oxygen are the main causes of corrosion and oxidation of rare earth permanent magnets. By reducing their content, the reaction between the magnet surface and the environment may be reduced, thereby improving the corrosion resistance and oxidation resistance of the magnet. This is especially important for magnets used in harsh environments such as high temperature and humidity.

[0128] 3. Improve processing performance: Reducing carbon and oxygen content can also improve the processing performance of rare earth permanent magnets. For example, during the sintering process, low oxygen content can reduce defects such as sintering shrinkage and cracking, and improve the yield and consistency of the magnet.

Claims

1. A method for preparing a high-performance sintered NdFeB magnet, characterized in that: The process includes: 1) master alloy preparation - 2) hydrogen crushing - 3) steam milling - 4) pressing - 5) cold isostatic pressing - 6) stripping - 7) sintering - 8) tempering; The preparation of the master alloy includes: batching - smelting - casting and strip throwing - crushing. The smelting and casting process is carried out in a vacuum quick-setting furnace, using a vacuum plus inert gas method, the vacuum degree is ≤10Pa, and the inert gas blowing amount is 100-200L / Min; The casting uses an insulating crucible, which receives the molten liquid in the melting crucible and then casts it onto the cooling roller; the cooling roller performs rotational motion and axial telescopic motion, and the insulating crucible performs vertical radial motion and horizontal radial motion relative to the cooling roller; A water-cooled target is arranged in the material-throwing direction of the cooling roller, a water-cooled plate is arranged facing the water-cooled target, and a material-collecting mechanism is arranged below the water-cooled target; The material receiving mechanism is a vertical material dropping mechanism, and a crushing mechanism is arranged on the material dropping channel; The outlet end of the receiving mechanism is connected to a rotating cooling mechanism, the main body of the rotating cooling mechanism is a rotating cylinder, the rotating cylinder is inclined downward from the feeding end to the discharging end, a spiral stirring paddle is arranged in the rotating cylinder, and a water cooling system is arranged in the wall of the rotating cylinder; The hydrogen-crushed powder is mixed before being jet milled. According to the weight of the material, 3-5‰ of oxidant and 1-3‰ of lubricant are added, and then the powder is jet milled. The oxidant is phosphite and the lubricant is zinc stearate. The oxygen content in the jet mill is controlled at 10-20PPm. The jet mill particle size SMD: 2.5-3.2μm, D90 / D10≤4.5; the fine powder after jet milling is mixed again. During compression molding, the oxygen content is controlled at ≤200PPm and the compact density is 3.9-4.3g / cm 3 ; When stripping, the oxygen content is controlled at 100-300PPm.

2. The preparation method according to claim 1, characterized in that: In the hydrogen cracking process, hydrogen is absorbed first and then released. The hydrogen absorption pressure is 0.1-0.35Pa, and the temperature during the hydrogen absorption process is 530-570℃. The end standard of hydrogen release is: there is no change in the vacuum degree in the hydrogen cracking furnace for 20 minutes, which means that hydrogen release is completed.

3. The preparation method according to claim 1, characterized in that: The cold isostatic pressing pressure is controlled at 160-200 MPa.

4. The preparation method according to claim 1, characterized in that: The sintering temperature is controlled at 1050-1080°C, the heat preservation time is 3-5h, and the product is taken out of the furnace when cooled to ≤70°C.

5. The preparation method according to claim 1, characterized in that: The tempering is carried out in two stages, the first stage tempering temperature is 880-920°C, the heat preservation time is 2-3h, the second stage tempering temperature is 450-520°C, the heat preservation time is 3-5h; and the steel is taken out of the furnace when cooled to ≤70°C.

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