Diffusion source and grain boundary diffusion process

Abstract

The invention provides a diffusion source and a grain boundary diffusion process, and relates to the technical field of permanent magnet grain boundary diffusion. The diffusion source is prepared by adopting DyF3 and Sn as diffusants and mixing a curing agent and a dispersing agent, and the diffusion source is used for stacking and coating magnetic sheets and then carrying out primary heat treatment at 950-1000 DEG C and secondary heat treatment at 680-700 DEG C to complete grain boundary diffusion. According to the method, the defects in the prior art are overcome, the diffusion source and the grain boundary diffusion process are suitable for industrial application, effective diffusion of DyF3 on the thick magnet is achieved, the corresponding grain boundary diffusion neodymium-iron-boron magnet is provided, and the magnetic performance of the magnet is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of permanent magnet grain boundary diffusion, and in particular to a diffusion source and a grain boundary diffusion process. Background Art

[0002] Sintered NdFeB permanent magnet material, referred to as NdFeB, is an intermetallic compound Nd2Fe 14 B-based high-performance permanent magnetic material, known as the "King of Magnets". It is widely used in consumer electronics, motors and other fields. In industrial production, it is manufactured using powder metallurgy technology combined with oriented molding technology. Thanks to the rapid development of new energy fields such as electric vehicles and wind power generation, the NdFeB industry, as a key material for motors, has maintained a high annual growth rate of 9% in the past decade. It is estimated that the global annual output will exceed 240,000 tons in 2024, and the output value will exceed 120 billion yuan. In most service scenarios, sintered NdFeB will face demagnetization fields of different intensities. Therefore, the greater the intrinsic coercive force (Hcj) that measures its anti-demagnetization ability, the more it can adapt to more stringent use environments. However, under normal circumstances, there is a trade-off between the coercive force of NdFeB magnets and the maximum magnetic energy product (BH) max, which measures their energy conversion efficiency, and both cannot be achieved at the same time.

[0003] The heavy rare earth grain boundary diffusion technology was born at the beginning of this century. It can achieve a substantial increase in the coercive force of magnets without a large loss of the maximum magnetic energy product of the magnet. Compared with the traditional single alloy smelting process, the grain boundary diffusion magnet has a lower cost for preparing NdFeB with the same performance. However, the heavy rare earth fluoride powder (easy to store), the most widely used diffusion source in the industry, drops sharply when processing magnetic sheets with a thickness of more than 5 mm. The coercive force of 20kOe is the entry threshold for NdFeB for motors, and it is difficult to achieve stably without adding heavy rare earths. Therefore, it is very important to improve the technology of grain boundary diffusion of heavy rare earths to achieve a substantial increase in the coercive force of thick magnets and effectively reduce production costs. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a diffusion source and a grain boundary diffusion process, which are suitable for industrial applications, realize the effective diffusion of DyF3 on thick magnets, and provide corresponding grain boundary diffused NdFeB magnets.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented through the following technical solutions: A diffusion source, wherein the mass percentage of each component in the diffusion source is: diffusant x curing agent y dispersant 100-xy, wherein 60≤x≤80, 20≤y≤40; the diffusant is DyF3 and Sn weighed and mixed according to the following atomic percentage content ratio: (100-a)DyF3+ aSn, wherein 5≤a≤10.

[0006] Preferably, the ambient humidity of the diffusant mixture is lower than 20% RH.

[0007] Preferably, the curing agent is one or more combinations of anhydrous ethanol, ethyl ether, petroleum ether, butanol, methyl ether, and dimethyl ether.

[0008] Preferably, the dispersant is any one of polyvinyl butyral or polyvinyl alcohol.

[0009] Preferably, the grain boundary diffusion process is to use the above-mentioned diffusion source for processing, and its specific method includes the following steps: S1. Morphology processing of commercial sintered NdFeB: Slice the commercial sintered NdFeB to prepare cylindrical magnetic sheets; S2, grinding and pickling of magnetic sheets: the magnetic sheets are sandblasted and polished, then pickled and then cleaned with ethanol, and then dried for standby use, so as to obtain pre-treated magnetic sheets for standby use; S3, coating diffusion source: coating the diffusion agent on the bottom plate, and then placing the pre-treated magnetic sheets, and stacking and coating in sequence, stacking three layers of pre-treated magnetic sheets, 3 layers of pre-treated magnetic sheets use 4 layers of diffusion source, and the total mass of the diffusion source accounts for 0.5%-0.8% of the magnet, and the coated magnetic sheets are obtained; S4, curing: after the coating is completed, the coated magnetic sheet is placed in a drying oven for drying to obtain a dry magnetic sheet for use; S5, two-stage heat treatment: the dried magnetic sheet is heated to 950-1000℃, and the first-stage heat treatment is performed for 4-6h, and the vacuum degree is kept below 10 during the whole heating process. -3 Pa, then fill with argon, adjust the temperature to 680-700℃, carry out secondary heat treatment for 3h, and then cool down to below 100℃ at a cooling rate of ≥100℃ / min.

[0010] Preferably, in step S1, the diameter of the magnetic sheet is 10 mm and the thickness is 5-8 mm.

[0011] Preferably, the method of acid washing and then ethanol washing in step S2 is to soak in a dilute nitric acid solution with a volume concentration of 3%-5% for 120s, and then use an ethanol solution for ultrasonic vibration cleaning for 30s.

[0012] Preferably, the coating diffusion in step S3 is completed within 20 minutes after pickling.

[0013] Preferably, in step S4, the drying temperature is 60-90° C., and the drying time is 30-120 min.

[0014] Preferably, the heating rate in step S5 is 8-9° C. / min.

[0015] The present invention provides a diffusion source and a grain boundary diffusion process, which have the following advantages over the prior art: The present invention can effectively solve the problem of DyF3 diffusion efficiency on thick magnets by controlling the element ratio and fine regulation during the preparation process. The coercive force of the substrate is greatly increased and only a small amount of remanence is lost. In addition, the grain boundary diffusion process of the present invention, especially the coating process, is simple and highly compatible with related industries. Compared with the traditional process, the production cost of the grain boundary diffused NdFeB magnet obtained will be greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of a magnetic disk after the slicing process is completed in an embodiment of the present invention; Figure 2 A schematic diagram of coating and spatial stacking of magnetic sheets and diffusion sources in an embodiment of the present invention; Figure 3 Demagnetization curves of Example 2 of the present invention and commercial N45M-based magnets. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Embodiment 1:

[0019] 1. Prepare the diffusing agent by weighing and mixing according to the atomic percentage ratio in Table 1 below (ambient humidity is less than 20% RH) (cost is based on 100% DyF3): Table 1

[0020] 2. Prepare a diffusion source by weighing and mixing according to the mass percentage ratio in Table 2 below, wherein the curing agent is ethanol and the dispersant is polyvinyl butyral (PVB): Table 2

[0021] 3. Grain boundary diffusion process: (1) Cut the commercial N45M grade sintered NdFeB magnets radially into magnetic sheets with a diameter of 10 mm and a thickness of 5-8 mm. Figure 1 As shown; (2) The cut magnetic sheets are sandblasted to remove surface oil and oxides, immersed in a 4% volume concentration dilute nitric acid solution for 120 seconds, ultrasonically cleaned in an ethanol solution for 30 seconds, dried for later use, and the ambient humidity is controlled below 20% RH; (3) Apply the diffusion source to the bottom plate, then place the magnetic sheet, and stack and coat them in sequence to stack three layers of NdFeB magnetic sheets; using spatial stacking can further reduce the use of diffusants, such as Figure 2 As shown in the figure, a three-layer magnet uses four layers of diffusion sources, and the total mass of the diffusion sources accounts for 0.5-0.8% of the magnet; and the diffusion sources are applied within 20 minutes after pickling; (4) After coating, the magnetic sheet is placed in a drying oven and dried at 80°C for 80 minutes.

[0022] (5) Heat up to 980℃ at 8℃ / min and keep at this temperature for 5h. Keep the vacuum degree below 10 during the heating process. -3 Pa; then fill it with 70000Pa of high-purity argon, adjust the temperature to 690℃, carry out secondary heat treatment for 3h, then quickly cool it to below 100℃ at a cooling rate of 100℃ / min, and then cool it naturally to obtain a coated magnet.

[0023] Referring to Table 2, the thick magnets were prepared by the grain boundary diffusion process, and the specific magnetic properties are shown in Table 3 below: Table 3

[0024] Referring to the above grain boundary diffusion process, taking experimental group 2 as the benchmark, the vacuum conditions, heat treatment temperature and thickness of the magnetic sheet were adjusted during the heat treatment, and the magnetic properties under the corresponding conditions were tested. The specific results are shown in Table 4 below: Table 4

[0025] As can be seen from the table above, experimental groups 1 and 2 have better magnetic properties. Different from the common grain boundary diffusion heat treatment process that controls the secondary tempering temperature at about 500°C, the use of DyF3 and Sn to prepare the diffusion agent will seriously corrode Nd2Fe in an inappropriate grain boundary diffusion process. 14 B, precipitation of soft magnetic α-Fe is not conducive to the improvement of coercivity (control group 6).

[0026] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A diffusion source, characterized in that: The mass percentage of each component in the diffusion source is: diffusing agent x curing agent y dispersing agent 100-xy, where 60≤x≤80, 20≤y≤40; The diffusing agent is obtained by weighing and mixing DyF3 and Sn according to the following atomic percentage ratio: (100-a)DyF3+aSn, where 5≤a≤10.

2. The diffusion source according to claim 1, characterized in that: The ambient humidity of the diffusant mixture is lower than 20% RH.

3. The diffusion source according to claim 1, characterized in that: The curing agent is one or more combinations of anhydrous ethanol, ethyl ether, petroleum ether, butanol, methyl ether, and dimethyl ether.

4. The diffusion source according to claim 1, characterized in that: The dispersant is any one of polyvinyl butyral and polyvinyl alcohol.

5. A grain boundary diffusion process, characterized in that: The grain boundary diffusion process is performed using the diffusion source described in any one of claims 1 to 4, and the specific method includes the following steps: S1. Morphological processing of commercial sintered NdFeB: Slice the commercial sintered NdFeB into cylindrical magnetic sheets; S2, grinding and pickling of magnetic sheets: the magnetic sheets are sandblasted and polished, then pickled and cleaned with ethanol, and then dried for use, to obtain pretreated magnetic sheets for use; S3. Applying diffusion source: Apply the diffusion agent on the bottom plate, then place the pre-treated magnetic sheets, and stack and coat them in sequence. Stack three layers of pre-treated magnetic sheets. Use four layers of diffusion source for three layers of pre-treated magnetic sheets, and the total mass of the diffusion source accounts for 0.5%-0.8% of the magnet to obtain coated magnetic sheets. S4, curing: after the coating is completed, the coated magnetic sheet is placed in a drying oven for drying to obtain a dry magnetic sheet for use; S5, two-stage heat treatment: the dried magnetic sheet is heated to 950-1000℃, and the first-stage heat treatment is carried out for 4-6 hours, and the vacuum degree is kept below 10 during the heating process. -3 Pa; then fill with argon, adjust the temperature to 680-700 ° C, perform secondary heat treatment for 3 hours, and then cool to below 100 ° C at a cooling rate of ≥ 100 ° C / min.

6. The process according to claim 5, characterized in that: In step S1, the diameter of the magnetic sheet is 10 mm and the thickness is 5-8 mm.

7. The process according to claim 5, characterized in that: In step S2, the acid washing and ethanol washing method is to soak the substrate in a dilute nitric acid solution with a volume concentration of 3%-5% for 120 seconds, and then use an ethanol solution for ultrasonic vibration washing for 30 seconds.

8. The process according to claim 5, characterized in that: The coating diffusion in step S3 is completed within 20 minutes after pickling.

9. The process according to claim 5, characterized in that: In step S4, the drying temperature is 60-90° C., and the drying time is 30-120 min.

10. The process according to claim 5, characterized in that: The heating rate in step S5 is 8-9°C / min.

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