Sintering process of neodymium-yttrium-iron-boron magnet

Abstract

The invention relates to the technical field of permanent magnet materials, and discloses a sintering process of a neodymium-yttrium-iron-boron magnet, the neodymium-yttrium-iron-boron magnet comprises the following raw materials by mass: 28%-32% of neodymium, 1%-2% of yttrium, 0.85%-1% of boron, 0.8%-2% of an auxiliary agent, and the balance Fe and inevitable impurities, the neodymium-yttrium-iron-boron magnet is obtained through smashing, uniform mixing in a mixer, smelting, melt-spinning, powder preparation, compression molding, sintering in a vacuum sintering furnace, tempering and cooling, the magnetic performance is comprehensively improved by optimizing the raw material ratio and process parameters, the microstructure of the magnet can be accurately controlled through sectional sintering and secondary tempering, and the magnetic performance of the magnet is improved. The performance deviation of different batches of magnets in batch production is extremely small, the product percent of pass is improved, grains can be refined and the thermal stability of the magnet can be improved by introducing yttrium, the raw material cost is effectively reduced, the coercivity and high-temperature stability of the neodymium-iron-boron magnet are improved, and the requirements of the fields of new energy, electronic equipment, traffic, electric power and the like are met.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of permanent magnet materials, in particular to a sintering process of a neodymium-yttrium-iron-boron magnet. BACKGROUND

[0002] As the third generation of rare earth permanent magnets, neodymium-iron-boron permanent magnets have the highest magnetic properties, are light in weight, and are widely used in the fields of new energy, electronic devices, transportation, and electric power. Neodymium (Nd) is a key element of light rare earth and is a key raw material of neodymium-iron-boron magnets. The demand for neodymium is increasing rapidly, while the supply is increasing slowly, resulting in a sharp rise in price. Yttrium (Y) is a heavy rare earth element, which is abundant in resources and low in price. The price of yttrium is much lower than that of neodymium. Adding yttrium to neodymium-iron-boron magnets can effectively reduce the cost of raw materials, alleviate the pressure caused by the shortage of neodymium resources, promote the comprehensive balanced utilization of rare earth resources, and improve the corrosion resistance and high-temperature stability by optimizing the composition of the magnet.

[0003] The atomic radius and chemical activity of yttrium are different from those of neodymium. The introduction of yttrium into neodymium-iron-boron magnets also poses new challenges to the preparation process of the magnets. In the sintering process, it will affect the grain growth kinetics, grain boundary phase distribution and formation efficiency of the main phase. Chinese Patent Application No. 201310456582.X discloses a double-main-phase yttrium-containing permanent magnet. Two different main-phase alloys containing and not containing yttrium are used as raw materials. The double-main-phase alloy method is adopted to improve the coercivity by using the magnetic coupling between the grains. The double-main-phase yttrium-containing permanent magnet is prepared. While maintaining good magnetic properties, the relatively abundant yttrium can be used to replace Nd and Pr to a large extent, thereby greatly reducing the production cost of the magnet. However, the sintering temperature is high, and the particle boundaries of the yttrium-containing and non-yttrium-containing powders significantly diffuse, resulting in an increase in the yttrium content at the edges of the non-yttrium-containing particles, which weakens the magnetic crystal anisotropy field of the high-coercivity main-phase grains and reduces the coercivity improvement effect. Chinese Patent Application No. CN103050267A discloses a sintering Nd-Fe-B system magnet manufacturing method based on fine powder heat treatment. Neodymium-iron-boron alloy is used. The coarse powder is crushed and then finely crushed to form fine powder. By increasing the fine powder heat treatment process, the sintering property of the powder is greatly changed. The prepared magnet has improved coercivity and heat resistance. However, the surface energy of the pretreated powder is increased, and local grain coarsening is easily induced during sintering, which reduces the uniformity of the coercivity. SUMMARY

[0004] (I) Technical problems solved In view of the deficiencies of the prior art, the present application provides a sintering process for a neodymium-yttrium-iron-boron magnet, which solves the problem of low coercivity of the magnet.

[0005] (II) Technical solutions In order to achieve the above-mentioned purpose, the present application discloses a sintering process for a neodymium-yttrium-iron-boron magnet, comprising the following steps: S1, each raw material is weighed according to the proportion, and is uniformly mixed in a mixer; S2, the uniformly mixed raw material is smelted, spun, powdered, and press-formed to obtain a green body; S3, the green body is sintered in a vacuum sintering furnace to obtain a rough body; S4, the rough body is tempered and cooled to obtain a neodymium-iron-boron magnet; The raw material in S1 is composed of the following raw materials in mass percentage: 28-32% of neodymium, 1-2% of yttrium, 0.85-1% of boron, 0.8-2% of auxiliary agent, and the rest of Fe and inevitable impurities.

[0006] As a further scheme of the application, the auxiliary agent in S1 is a mixture of aluminum oxide and copper oxide, and the mass ratio of aluminum oxide to copper oxide is 1:(2-3).

[0007] As a further scheme of the application, the mixing time of the raw material in S1 in the mixer is 2-4h, and the mixing is carried out in an argon atmosphere.

[0008] As a further scheme of the application, the smelting in S2 is carried out under vacuum, and the vacuum degree is controlled at 10 -4 ~10 - 5 Pa, the smelting temperature is 1400-1450℃, the holding time is 15-20min, and the heating rate is 8-10℃ / min.

[0009] As a further scheme of the application, the powdering process in S2 includes hydrogen crushing and jet milling.

[0010] As a further scheme of the application, the hydrogen crushing in S2 is carried out in a hydrogen crushing furnace, and in the hydrogen crushing process, the hydrogen pressure is 0.25-0.5MPa, the hydrogen crushing temperature is 400-450℃, and the hydrogen crushing time is 1-2h; after hydrogen crushing, jet milling is carried out, and the jet milling is carried out in a nitrogen atmosphere, and the nitrogen pressure is 0.6-0.8MPa.

[0011] As a further scheme of the application, the average particle size of the powder obtained after the jet milling in S2 is 2.5-3μm.

[0012] As a further scheme of the application, the press forming in S2 is carried out in a mold, the mold pressure is 300-350MPa, and then the pressure is kept at 850-950MPa for 8-10min.

[0013] As a further scheme of the application, the mold is ultrasonically vibrated in a pulse magnetic field before mold pressing, the magnetic field is 1.8-2T, and the ultrasonic vibration frequency is 35-45kHz.

[0014] As a further scheme of the present application: the sintering process in S3 is divided into three stages, and each stage is carried out in an inert gas atmosphere, the first stage is pre-sintering, the pre-sintering temperature is 600-800℃, the holding time is 1-2h, and the heating rate is 1-3℃ / min, in the second stage sintering process, the sintering temperature is 1100-1150℃, the holding time is 2-3h, and the heating rate is 6-8℃ / min; in the third stage sintering process, the sintering temperature is slowly reduced from the holding temperature of the second stage sintering, and the cooling rate is 1-3℃ / min, and the sintering temperature is reduced to 600℃.

[0015] As a further scheme of the present application: the sintering process in S3 is carried out in an inert gas atmosphere, and the inert gas is high-purity argon, and the purity of the high-purity argon is ≥99.9%.

[0016] As a further scheme of the present application: the tempering in S4 is two-stage tempering, and the tempering process is divided into two stages of high-temperature tempering and low-temperature tempering, after sintering, high-temperature tempering treatment is carried out first, the high-temperature tempering temperature is 900-920℃, and the vacuum holding time is 1-3h, and then low-temperature tempering treatment is carried out, the low-temperature tempering is carried out in an argon atmosphere, the low-temperature tempering treatment temperature is 550-580℃, and the holding time is 1-2h.

[0017] As a further scheme of the present application: after the tempering treatment in S4 is completed, it is cooled to room temperature at a cooling rate of 1-3℃ / min.

[0018] (Three) beneficial technical effects Compared with the prior art, the beneficial effects of the present application are: (1) In the present application, the solubility of yttrium in the main phase is improved by step temperature control, and the coercivity of the magnet is improved. The multi-stage step temperature control realizes the balance of "uniform yttrium solid solution" and "grain refinement" by controlling the temperature in stages. The sintering process is divided into three stages. In the pre-sintering stage, the yttrium element is preliminarily diffused in the powder particles by slowly heating and using low temperature environment to reduce the yttrium enrichment on the surface of the particles. Rapid heating to the main sintering temperature, the main phase is quickly formed, and the yttrium pre-diffusion in the pre-sintering stage can avoid the abnormal growth of grains caused by too high local yttrium concentration, and prevent the generation of Y2O3 impurities. Slow cooling reduces thermal stress and promotes the uniform precipitation of yttrium / nickel-rich rare earth phases along the main phase grain boundaries, improves the continuity of the grain boundary phase, and improves the coercivity. The chemical activity of yttrium is higher than that of neodymium, and it is easy to react with residual oxygen and nitrogen to generate hard and brittle impurities during sintering, resulting in the decline of the mechanical properties of the magnet and the attenuation of the coercivity. Inert atmosphere sintering can effectively inhibit the oxidation of yttrium. The tempering treatment can adjust the brittleness of the grain boundary phase, avoid the brittleness of the magnet caused by excessive aggregation of yttrium-rich phase, and improve the coercivity and magnetic stability of the magnet. The segmented sintering and two-stage tempering can precisely control the microstructure of the magnet, ensure that the performance deviation of different batches of magnets in batch production is minimal, and improve the product qualification rate.

[0019] (2) In the present application, the overall improvement of magnetic properties is realized by optimizing the raw material ratio and process parameters. The ratio of neodymium, yttrium and boron in the raw material cooperates synergistically, the introduction of yttrium can refine the grain and improve the thermal stability of the magnet, and the auxiliary agent can effectively purify the grain boundary, improve the grain boundary phase distribution and enhance the magnetic anisotropy. The introduction of yttrium element in the neodymium iron boron magnet effectively reduces the raw material cost, and at the same time improves the coercivity and high temperature stability of the neodymium iron boron magnet, meeting the requirements of new energy, electronic equipment, transportation, power and other fields. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application. EMBODIMENT

[0021] A sintering process of a neodymium yttrium iron boron magnet, comprising the following steps: S1, weigh the following mass percentage of raw materials: neodymium 28%, yttrium 1%, boron 0.85%, auxiliary agent 0.8%, the rest is Fe and unavoidable impurities, wherein the auxiliary agent is composed of aluminum oxide and copper oxide with a mass ratio of 1:2, and is uniformly mixed in a mixer, the mixing time is 2h, and the mixing is carried out in an argon atmosphere; S2, the mixed raw materials are smelted under vacuum condition, the vacuum degree is controlled to 10 -4 Pa, the smelting temperature is 1400 DEG C, the holding time is 15 min, the heating rate is 8 DEG C / min, the tape is thrown, the powder is prepared, the powder preparation process includes hydrogen crushing and jet milling, the hydrogen crushing is carried out in a hydrogen crushing furnace, in the hydrogen crushing process, the hydrogen pressure is 0.25 MPa, the hydrogen crushing temperature is 400 DEG C, the hydrogen crushing time is 1 h, after hydrogen crushing, jet milling is carried out, the jet milling is carried out in a nitrogen atmosphere, the nitrogen pressure is 0. MPa, after jet milling treatment, the average particle size of the obtained powder is 2.5 mu m, the powder is pressed into a shape, before molding, ultrasonic vibration is carried out in a pulse magnetic field, the magnetic field is 1.8 T, the ultrasonic vibration frequency is 35 kHz, the pressing is carried out in a mold, the molding pressure is 300 MPa, and the pressure is kept at 850 MPa for 8 min to obtain a green body; S3, the green body is sintered in a vacuum sintering furnace, the sintering process is divided into three stages, and all the stages are carried out in a high-purity argon atmosphere, the purity of the high-purity argon is greater than or equal to 99.9%, the first stage is pre-sintering, the pre-sintering temperature is 600 DEG C, the holding time is 1 h, and the heating rate is 1 DEG C / min; in the second stage sintering process, the sintering temperature is 1100 DEG C, the holding time is 2 h, and the heating rate is 6 DEG C / min; in the third stage sintering process, the sintering temperature is slowly reduced from the second stage sintering holding temperature, the cooling rate is 1 DEG C / min, and the sintering temperature is reduced to 600 DEG C, to obtain a rough body; S4, the rough body is tempered, the tempering is two-stage tempering, the tempering process is divided into high-temperature tempering and low-temperature tempering two stages, after sintering, high-temperature tempering is carried out first, the high-temperature tempering temperature is 900 DEG C, vacuum holding for 1 h, then low-temperature tempering is carried out, the low-temperature tempering is carried out in an argon atmosphere, the low-temperature tempering temperature is 550 DEG C, the holding time is 1 h, after the tempering treatment is completed, it is cooled to room temperature at a cooling rate of 1 DEG C / min, to obtain a neodymium-iron-boron magnet. Embodiment

[0022] A sintering process of a neodymium-iron-boron magnet, comprising the following steps: S1, the following mass percentage of raw materials is weighed: neodymium 30%, yttrium 1.5%, boron 0.9%, auxiliary agent 1.5%, the rest is Fe and unavoidable impurities, wherein the auxiliary agent is composed of aluminum oxide and copper oxide with a mass ratio of 1:2.5, and is uniformly mixed in a mixer, in the mixing process, the mixing time is 3 h, and the mixing is carried out in an argon atmosphere; S2, the mixed raw materials are smelted under vacuum condition, the vacuum degree is controlled to 10 -5Pa, the temperature of smelting is 1420℃, the holding time is 16min, the heating rate is 9℃ / min, spinning, powdering, the powdering process includes hydrogen crushing and jet milling, the hydrogen crushing is carried out in a hydrogen crushing furnace, in the hydrogen crushing process, the pressure of hydrogen is 0.35MPa, the hydrogen crushing temperature is 420℃, the hydrogen crushing time is 1.5h, after hydrogen crushing, jet milling is carried out, the jet milling is carried out in a nitrogen atmosphere, the pressure of nitrogen is 0.7MPa, after jet milling treatment, the average particle size of the obtained powder is 2.8μm, pressing forming, before molding, ultrasonic vibration is carried out in a pulse magnetic field, the magnetic field is 1.9T, the frequency of ultrasonic vibration is 38kHz, the pressing forming is carried out in a mold, the molding pressure is 320MPa, and then pressure holding is carried out at a pressure of 900MPa for 9min, to obtain a green body; S3, sintering the green body in a vacuum sintering furnace, the sintering process is divided into three stages, and all the stages are carried out in a high-purity argon atmosphere, the purity of the high-purity argon is ≥99.9%, the first stage is pre-sintering, the pre-sintering temperature is 680℃, the holding time is 1.5h, and the heating rate is 2℃ / min, in the second stage sintering process, the sintering temperature is 1120℃, the holding time is 2.5h, and the heating rate is 7℃ / min, in the third stage sintering process, the sintering temperature is slowly reduced from the holding temperature of the second stage sintering, the cooling rate is 2℃ / min, and the temperature is reduced to 600℃, to obtain a rough body; S4, tempering treatment is carried out on the rough body, the tempering is two-stage tempering, the tempering process is divided into two stages of high-temperature tempering and low-temperature tempering, after sintering is completed, high-temperature tempering treatment is carried out first, the high-temperature tempering temperature is 905℃, vacuum holding for 2h, then low-temperature tempering treatment is carried out, the low-temperature tempering is carried out in an argon atmosphere, the low-temperature tempering treatment temperature is 560℃, the holding time is 1.5h, after the tempering treatment is completed, cooling to room temperature at a cooling rate of 2℃ / min, to obtain a neodymium-iron-boron magnet. Embodiment

[0023] A sintering process of a neodymium-iron-boron magnet, comprising the following steps: S1, the following mass percentages of raw materials are weighed: neodymium 30%, yttrium 1.5%, boron 0.9%, auxiliary agent 1.5%, and the rest is Fe and unavoidable impurities, wherein the auxiliary agent is composed of aluminum oxide and copper oxide with a mass ratio of 1:2.5, and is uniformly mixed in a mixer, and the mixing time is 3h in an argon atmosphere; S2, the uniformly mixed raw materials are smelted under vacuum conditions, the vacuum degree is controlled to be 10 -5Pa, the temperature of smelting is 1440℃, the holding time is 18min, the heating rate is 9℃ / min, spinning, powdering, the powdering process includes hydrogen crushing and jet milling, the hydrogen crushing is carried out in a hydrogen crushing furnace, in the hydrogen crushing process, the hydrogen pressure is 0.45MPa, the hydrogen crushing temperature is 440℃, the hydrogen crushing time is 1.5h, after hydrogen crushing, jet milling is carried out, the jet milling is carried out in a nitrogen atmosphere, the nitrogen pressure is 0.7MPa, the average particle size of the powder obtained after jet milling is 2.8μm, pressing, before molding, ultrasonic vibration in a pulse magnetic field, the magnetic field is 1.9T, the ultrasonic vibration frequency is 42kHz, the pressing is carried out in a mold, the molding pressure is 340MPa, and then the pressure is kept at 920MPa for 9min to obtain a green body; S3, sintering the green body in a vacuum sintering furnace, the sintering process is divided into three stages, all in a high-purity argon atmosphere, the purity of high-purity argon is ≥99.9%, the first stage is pre-sintering, the pre-sintering temperature is 750℃, the holding time is 1.5h, and the heating rate is 2℃ / min, in the second stage sintering process, the sintering temperature is 1140℃, the holding time is 2.5h, and the heating rate is 7℃ / min, in the third stage sintering process, the sintering temperature is slowly reduced from the second stage sintering holding temperature, the cooling rate is 2℃ / min, and the sintering temperature is reduced to 600℃ to obtain a rough body; S4, tempering treatment is carried out on the rough body, the tempering is two-stage tempering, the tempering process is divided into high-temperature tempering and low-temperature tempering two stages, after sintering, high-temperature tempering treatment is carried out first, the high-temperature tempering temperature is 915℃, vacuum holding for 2h, then low-temperature tempering treatment is carried out, the low-temperature tempering is carried out in an argon atmosphere, the low-temperature tempering treatment temperature is 570℃, the holding time is 1.5h, after tempering treatment, cooling to room temperature at a cooling rate of 2℃ / min to obtain a neodymium-iron-boron magnet. Embodiment

[0024] A sintering process of a neodymium-iron-boron magnet, comprising the following steps: S1, weighing the following mass percentage of raw materials: neodymium 32%, yttrium 2%, boron 1%, auxiliary agent 2%, the rest is Fe and inevitable impurities, wherein the auxiliary agent is composed of aluminum oxide and copper oxide with a mass ratio of 1:3, and is uniformly mixed in a mixer, the mixing time is 4h, and the mixing is carried out in an argon atmosphere; S2, smelting the uniformly mixed raw materials under vacuum conditions, the vacuum degree is controlled to be 10 -5Pa, the temperature of smelting is 1450℃, the holding time is 20min, the heating rate is 10℃ / min, spinning, powdering, the powdering process includes hydrogen crushing and jet milling, the hydrogen crushing is carried out in a hydrogen crushing furnace, in the hydrogen crushing process, the hydrogen pressure is 0.5MPa, the hydrogen crushing temperature is 450℃, the hydrogen crushing time is 2h, after hydrogen crushing, jet milling is carried out, the jet milling is carried out in a nitrogen atmosphere, the nitrogen pressure is 0.8MPa, after jet milling treatment, the average particle size of the obtained powder is 3μm, pressing forming, before molding, ultrasonic vibration in a pulse magnetic field, the magnetic field is 2T, the ultrasonic vibration frequency is 45kHz, the pressing forming is carried out in a mold, the molding pressure is 350MPa, and then pressure holding is carried out at 950MPa for 10min, to obtain a green body; S3, sintering the green body in a vacuum sintering furnace, the sintering process is divided into three stages, and all are carried out in a high-purity argon atmosphere, the purity of the high-purity argon is ≥99.9%, the first stage is pre-sintering, the pre-sintering temperature is 800℃, the holding time is 2h, and the heating rate is 3℃ / min, in the second stage sintering process, the sintering temperature is 1150℃, the holding time is 3h, and the heating rate is 8℃ / min; in the third stage sintering process, the sintering temperature is slowly reduced from the second stage sintering holding temperature, the cooling rate is 3℃ / min, and the temperature is reduced to 600℃, to obtain a rough body; S4, tempering treatment is carried out on the rough body, the tempering is two-stage tempering, the tempering process is divided into high-temperature tempering and low-temperature tempering two stages, after sintering is completed, high-temperature tempering treatment is carried out first, the high-temperature tempering temperature is 920℃, vacuum holding for 3h, then low-temperature tempering treatment is carried out, the low-temperature tempering is carried out in an argon atmosphere, the low-temperature tempering treatment temperature is 580℃, the holding time is 2h, after the tempering treatment is completed, cooling to room temperature at a cooling rate of 3℃ / min, to obtain a neodymium-iron-boron magnet.

[0025] Comparative Example 1 A sintering process of a neodymium-iron-boron magnet, comprising the following steps: S1, the following mass percentages of raw materials are weighed: neodymium 30%, yttrium 1.5%, boron 0.9%, auxiliary agent 1.5%, and the rest is Fe and unavoidable impurities, wherein the auxiliary agent is composed of aluminum oxide and copper oxide with a mass ratio of 1:2.5, and is uniformly mixed in a mixer, and the mixing time is 3h in an argon atmosphere; S2, the uniformly mixed raw materials are smelted under vacuum conditions, the vacuum degree is controlled to be 10 -5Pa, the temperature of smelting is 1440℃, the holding time is 18min, the heating rate is 9℃ / min, spinning, powdering, the powdering process includes hydrogen crushing and jet milling, the hydrogen crushing is carried out in a hydrogen crushing furnace, in the hydrogen crushing process, the pressure of hydrogen is 0.45MPa, the hydrogen crushing temperature is 440℃, the hydrogen crushing time is 1.5h, after hydrogen crushing, jet milling is carried out, the jet milling is carried out in a nitrogen atmosphere, the pressure of nitrogen is 0.7MPa, the average particle size of the powder obtained after jet milling is 2.8μm, pressing, before molding, ultrasonic vibration in a pulse magnetic field, the magnetic field is 1.9T, the frequency of ultrasonic vibration is 42kHz, the pressing is carried out in a mold, the pressure of molding is 340MPa, and then pressure holding is carried out at 920MPa for 9min, to obtain a green body; S3, sintering the green body in a vacuum sintering furnace, the sintering process is carried out in a high-purity argon atmosphere, the purity of high-purity argon is ≥99.9%, in the sintering process, the sintering temperature is 1140℃, the holding time is 4h, and the heating rate is 7℃ / min, to obtain a rough body; S4, tempering the rough body, the tempering is two-stage tempering, the tempering process includes high-temperature tempering and low-temperature tempering, after sintering, high-temperature tempering is carried out first, the temperature of high-temperature tempering is 915℃, vacuum holding for 2h, then low-temperature tempering is carried out, the low-temperature tempering is carried out in an argon atmosphere, the temperature of low-temperature tempering is 570℃, the holding time is 1.5h, after tempering, cooling to room temperature at a cooling rate of 2℃ / min, to obtain a neodymium-yttrium-iron-boron magnet.

[0026] Comparative Example 2 A sintering process of a neodymium-yttrium-iron-boron magnet, compared with Example 3, only 1.5% of the auxiliary agent used in Example 3 is replaced by an equal amount of yttrium, and the remaining components and preparation method are completely consistent with Example 3.

[0027] Comparative Example 3 A sintering process of a neodymium-yttrium-iron-boron magnet, including the following steps: S1, weighing the following mass percentage of raw materials: neodymium 30%, yttrium 1.5%, boron 0.9%, auxiliary agent 1.5%, and the rest is Fe and inevitable impurities, wherein the auxiliary agent is composed of aluminum oxide and copper oxide with a mass ratio of 1:2.5, and is uniformly mixed in a mixer, and the mixing time is 3h in an argon atmosphere; S2, smelting the uniformly mixed raw materials under vacuum conditions, the vacuum degree is controlled to be 10 -5Pa, the temperature of smelting is 1440 DEG C, the holding time is 18 min, the heating rate is 9 DEG C / min, spinning, powdering, the powdering process includes hydrogen crushing and jet milling, the hydrogen crushing is carried out in a hydrogen crushing furnace, in the hydrogen crushing process, the hydrogen pressure is 0.45 MPa, the hydrogen crushing temperature is 440 DEG C, the hydrogen crushing time is 1.5 h, after hydrogen crushing, jet milling is carried out, the jet milling is carried out in a nitrogen atmosphere, the nitrogen pressure is 0.7 MPa, after jet milling treatment, the average particle size of the obtained powder is 2.8 mu m, pressing forming, before die pressing, ultrasonic vibration in a pulse magnetic field, the magnetic field is 1.9 T, the ultrasonic vibration frequency is 42 kHz, the pressing forming is carried out in a mold, the die pressing forming pressure is 340 MPa, and then pressure holding is carried out under a pressure of 920 MPa for 9 min, to obtain a green body; S3, sintering the green body in a vacuum sintering furnace, the sintering process is divided into three stages, and all are carried out in a high-purity argon atmosphere, the purity of the high-purity argon is greater than or equal to 99.9%, the first stage is pre-sintering, the pre-sintering temperature is 750 DEG C, the holding time is 1.5 h, and the heating rate is 2 DEG C / min, in the second stage sintering process, the sintering temperature is 1140 DEG C, the holding time is 2.5 h, and the heating rate is 7 DEG C / min, in the third stage sintering process, the sintering temperature is slowly reduced from the second stage sintering holding temperature, the cooling rate is 2 DEG C / min, and the sintering temperature is reduced to 600 DEG C, to obtain a neodymium-iron-boron magnet.

[0028] The reagents used in the examples and comparative examples in the present application are all commercially available.

[0029] The neodymium-iron-boron magnets prepared in examples 1-4 and comparative examples 1-3 are taken as samples for performance testing: Magnetic testing: the magnetic properties of the samples are tested according to the standard reference GB / T 3217-2013 "Permanent magnet (hard magnet) material magnetic property test method", the residual magnetism (Br), intrinsic coercive force (Hcj) and maximum magnetic energy product (BH max ) of the test samples are tested, each sample is tested three times, and the average value is taken; The above test results are shown in Table 1: Table 1 Test item Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Br (T) 1.32 1.38 1.41 1.35 1.23 1.26 1.27 Hcj (kOe) 26.4 27.2 27.9 26.8 21.5 22.0 22.3 BH max (MGOe) 38.2 40.1 42.0 39.6 34.1 35.3 36.5 According to the test results in Table 1, it can be seen that the neodymium-iron-boron magnets corresponding to examples 1-4 have excellent magnetic properties, the comprehensive performance of the sample corresponding to example 3 is the best, has higher residual magnetism and intrinsic coercive force, and the maximum magnetic energy product is larger. In comparative example 1, there is no three-stage sintering, single-stage sintering leads to grain coarsening and uneven growth, abnormal growth, the intrinsic coercive force is greatly reduced, and the residual magnetism and magnetic energy product are reduced. In comparative example 2, no auxiliary agent is introduced, the grain boundary lacks strengthening, and the comprehensive performance is reduced. In comparative example 3, there is no tempering to eliminate internal stress and optimize the domain structure, and the intrinsic coercive force is reduced.

[0030] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A sintering process for neodymium-yttrium iron-boron magnets, characterized in that: Includes the following steps: S1. Weigh each raw material according to the proportion, crush the raw materials first, and mix them evenly in the mixer; S2. The uniformly mixed raw materials are melted, spun, powdered, and pressed into shape to obtain a green body; S3. Place the green billet in a vacuum sintering furnace and sinter to obtain a rough billet; S4. Temper and cool the billet to obtain Nd:yttrium iron boron magnets; The raw materials in S1 consist of the following mass percentages: neodymium 28%~32%, yttrium 1%~2%, boron 0.85%~1%, auxiliary agents 0.8%~2%, and the remainder being Fe and unavoidable impurities.

2. The sintering process for a neodymium-yttrium iron-boron magnet according to claim 1, characterized in that: The auxiliary agent in S1 is a mixture of aluminum oxide and copper oxide, wherein the mass ratio of aluminum oxide to copper oxide is 1:(2-3).

3. The sintering process for a neodymium-yttrium iron-boron magnet according to claim 1, characterized in that: In step S1, the raw materials are mixed in a mixer for 2-4 hours in an argon atmosphere.

4. The sintering process for a neodymium-yttrium iron-boron magnet according to claim 1, characterized in that: The melting in S2 is carried out under vacuum conditions, with the vacuum level controlled at 10. -4 ~10 -5 Pa, the melting temperature is 1400-1450℃, the holding time is 15-20min, and the heating rate is 8-10℃ / min.

5. The sintering process for a neodymium-yttrium iron-boron magnet according to claim 1, characterized in that: The powdering process in S2 includes hydrogen crushing and air jet milling.

6. The sintering process for a neodymium-yttrium iron-boron magnet according to claim 1, characterized in that: In step S2, the compression molding is carried out in a mold, with a molding pressure of 300-350 MPa, followed by holding at 850-950 MPa for 8-10 minutes.

7. The sintering process for a neodymium-yttrium iron-boron magnet according to claim 1, characterized in that: The sintering process in S3 is carried out in three stages, all in an inert gas atmosphere. The first stage is pre-sintering, with a pre-sintering temperature of 600-800℃, a holding time of 1-2h, and a heating rate of 1-3℃ / min. In the second stage of sintering, the sintering temperature is 1100-1150℃, the holding time is 2-3h, and the heating rate is 6-8℃ / min. In the third stage of sintering, the sintering temperature is slowly reduced from the holding temperature of the second stage at a cooling rate of 1-3℃ / min, until it drops to 600℃.

8. The sintering process for a neodymium-yttrium iron-boron magnet according to claim 1, characterized in that: The sintering process in S3 is carried out in an inert gas atmosphere, wherein the inert gas is high-purity argon gas with a purity ≥ 99.9%.

9. The sintering process for a neodymium-yttrium iron-boron magnet according to claim 1, characterized in that: The tempering in S4 is a two-stage tempering process, which is divided into two stages: high-temperature tempering and low-temperature tempering. After sintering, high-temperature tempering is performed first at a temperature of 900-920℃ and vacuum holding for 1-3 hours. Then, low-temperature tempering is performed in an argon atmosphere at a temperature of 550-580℃ and a holding time of 1-2 hours.

10. The sintering process for a neodymium-yttrium iron-boron magnet according to claim 1, characterized in that: After the tempering process in step S4 is completed, the temperature is cooled to room temperature at a rate of 1-3℃ / min.