HRE target material, preparation method and method for preparing magnet by using HRE target material

Abstract

The invention discloses an HRE target material, a preparation method and a method for preparing a magnet by using the HRE target material. The preparation method of the HRE target material comprises the following steps: preparing heavy rare earth metal into a high-density HRE metal block through vacuum induction melting or vacuum arc melting; casting the smelted HRE metal block into a shape and a size meeting the requirements of the target material; cooling the HRE metal block, and processing the cooled HRE metal block into a shaving-shaped HRE target material through a lathe and a milling machine; carrying out surface treatment on the HRE target material and drying the HRE target material; and storing the HRE target material in a vacuum environment. The shaving-shaped HRE target material is introduced into an evaporation grain boundary diffusion process, after multiple times of evaporation, although the roughness of the outer surface of the HRE target material is increased, the inner surface of the HRE target material is hardly influenced, the roughness of the outer surface of the target material tends to be stable along with the increase of the number of times of evaporation, the evaporation capacity is also kept stable, the evaporation capacity of a diffusion source is stabilized, and the diffusion efficiency is improved. And the coercive force and the magnetic energy product of the magnet are improved.

Description

Technical Field

[0001] The invention belongs to the field of preparation of sintered magnets, and in particular relates to an HRE target material, a preparation method and a method for preparing a magnet using the HRE target material. Background Art

[0002] NdFeB magnets are widely used in permanent magnet motors due to their high magnetic energy product (BH) max. However, in practical applications, when the motor operating temperature exceeds 150°C, the performance of NdFeB magnets decreases rapidly. In order to effectively improve the magnetic properties of sintered NdFeB magnets, grain boundary diffusion technology has emerged, which can effectively improve the magnetic properties of sintered NdFeB magnets.

[0003] The grain boundary diffusion process has evolved into a variety of innovative applications, including sputtering, electrophoretic deposition, coating, evaporation, etc. Among them, evaporation is divided into two methods: static evaporation and rotary evaporation. Static evaporation requires special tooling to maintain the plating distance when the diffusion source deposition and magnet diffusion are carried out simultaneously, resulting in complex processes, low production efficiency and poor film consistency. Rotary evaporation, on the other hand, places small magnets and heavy rare earth targets in a rotary furnace, and deposits heavy rare earth metals on the surface of the magnet through rotation and high temperature. It has the advantages of low equipment investment and high efficiency, and is more suitable for commercial and large-scale production.

[0004] At present, in the process of rotary evaporation, the heavy rare earth target used is usually spherical or block-shaped. This shape helps all surfaces of the magnet to contact the target during rotation, and is suitable for grain boundary diffusion of small-sized magnets of various shapes. However, with the repeated use of the target, the surface of the spherical or block target gradually becomes rough, and more pits are produced. Since the increase in pits will cause the saturated vapor pressure in the confined space to decrease, the evaporation amount of the target will decrease accordingly, resulting in a decrease in the amount of heavy rare earth elements attached to the surface of the magnet during the evaporation process, which will cause the coercive force of the magnet to gradually decrease, bringing adverse effects to actual production. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide an HRE target material, a preparation method and a method for preparing a magnet using the HRE target material, which can prepare a magnet with high coercive force and magnetic energy product, and good stability and consistency of the magnet.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a HRE target material, comprising the following steps:

[0007] The heavy rare earth metals are made into high-density HRE metal blocks by vacuum induction melting or vacuum arc melting;

[0008] The smelted HRE metal block is molded into a shape and size that meets the target material requirements;

[0009] After cooling, the HRE metal block is processed into shaving-like HRE target material by lathe and milling machine;

[0010] Surface treatment and drying of HRE target;

[0011] The HRE target is stored in a vacuum environment.

[0012] In one embodiment, the surface treatment is: pre-chamfering 0.1 mm, and pickling with 5% nitric acid solution to remove oxides on the surface of the HRE target.

[0013] In one embodiment, the purity of the HRE target material is 99.5%-99.9%, and the thickness is 0.5mm-1mm.

[0014] In one embodiment, the heavy rare earth metal is Tb or Dy.

[0015] A HRE target material prepared using a method for preparing an HRE target material.

[0016] A method for preparing a magnet using the HRE target material comprises the following steps:

[0017] S1) using a heavy rare earth-free NdFeB sintered magnet as a grain boundary diffusion blank;

[0018] S2) cutting the sintered NdFeB blank into magnets of the required size for grain boundary diffusion, and subjecting the magnets to surface treatment for standby use;

[0019] S3) mixing the surface treated magnet with the HRE target;

[0020] S4) putting the prepared mixed material into a vapor deposition furnace and placing it under a vacuum degree of 5×10 -4 Pa~5×10 -3 Pa, the speed is 10-20r / min and the heat treatment is carried out at 670-685℃ for 4-6h;

[0021] S5) screening the evaporated magnet and the diffusion source with a sieve;

[0022] S6) subjecting the magnet with the diffusion source to diffusion heat treatment to obtain a diffusion magnet.

[0023] In one embodiment, the mass ratio of the magnet to the HRE target is 1:2-1:5.

[0024] In one embodiment, the weight percentage composition of the heavy rare earth-free NdFeB sintered magnet is as follows: Pr-Nd: 30%, Co: 0.35%, B: 1.0%, Ga: 0.05%, Al: 0.3%, Cu: 0.1% and the balance Fe.

[0025] In one embodiment, the primary heat treatment temperature in the diffusion heat treatment is 750-950°C, and the temperature is kept for 8-16 hours; the secondary heat treatment temperature is 400-600°C, and the temperature is kept for 1-6 hours. The vacuum degree of the diffusion heat treatment is controlled at 5×10 -3 Pa~5×10 -2 Pa.

[0026] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0027] The present invention introduces a shaving-like HRE target material into an evaporation grain boundary diffusion process. The shaving-like HRE target material has a curled shape and a thickness greater than 0.5 mm. After multiple evaporations, although the roughness of its outer surface increases, the inner surface is almost unaffected. As the number of evaporations increases, the roughness of the outer surface of the shaving-like HRE target material tends to be stable, and the evaporation amount is therefore kept stable, thereby effectively controlling the diffusion accuracy and stabilizing the evaporation amount of the diffusion source, significantly improving the coercive force and magnetic energy product of the NdFeB magnet, ensuring the stability and consistency of the high-performance magnet, and bringing higher benefits and broader application prospects to the grain boundary diffusion process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The technical solution of the present invention is further described below in conjunction with the accompanying drawings:

[0029] Figure 1 FIG. 4 is a flow chart of the preparation of HRE target material in one embodiment of the present invention.

[0030] Figure 2 Schematic diagram of the structure of the HRE target in one embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0032] The present invention provides an HRE target material, a preparation method and a method for preparing a magnet using the HRE target material, so as to solve the problem in the prior art that as the target material is repeatedly used, pits generated on the surface of the target material will cause the saturated vapor pressure in the closed space to decrease, and the evaporation amount of the target material will decrease accordingly, so that the amount of heavy rare earth elements attached to the surface of the magnet during the evaporation process is reduced, thereby causing the coercive force of the magnet to gradually decrease.

[0033] For ease of understanding, the specific process in the embodiments of the present application is described below. Figure 1 A method for preparing a HRE target material in an embodiment of the present application comprises the following steps:

[0034] S10, forming a high-density HRE metal block by vacuum induction melting or vacuum arc melting of the heavy rare earth metal;

[0035] In step S10, the purity of the HRE target material is 99.5%-99.9%, and the thickness is 0.5mm-1mm.

[0036] S11, the smelted HRE metal block is molded into a shape and size that meets the requirements of the target material;

[0037] S12, cooling the HRE metal block and processing it into a shaving-shaped HRE target material through a lathe and a milling machine;

[0038] S13, performing surface treatment on the HRE target and drying;

[0039] In step S13, the surface treatment is: pre-chamfering 0.1 mm, and pickling with 5% nitric acid solution to remove oxides on the surface of the HRE target.

[0040] S14. Storing the HRE target in a vacuum environment to ensure the purity and activity of the HRE target.

[0041] In this embodiment, the heavy rare earth metal is any one or more of Tb or Dy.

[0042] See also Figure 2 The HRE target in this embodiment is shaving-like and has a curled shape, with a thickness greater than 0.5 mm. During the rotary evaporation process, after multiple evaporation, although the roughness of its outer surface increases, the inner surface is almost unaffected. As the number of evaporation increases, the roughness of the outer surface of the HRE target tends to be stable, and the evaporation amount is therefore kept stable. This characteristic makes the increase in the coercive force of the magnet more stable under the same conditions during each evaporation, thereby significantly improving the stability and efficiency of the grain boundary diffusion evaporation process.

[0043] The present invention also discloses a method for preparing a magnet using an HRE target material, comprising the following steps:

[0044] S1) using a heavy rare earth-free NdFeB sintered magnet as a grain boundary diffusion blank, wherein the weight percentage composition of the heavy rare earth-free NdFeB sintered magnet is as follows: Pr-Nd: 30%, Co: 0.35%, B: 1.0%, Ga: 0.05%, Al: 0.3%, Cu: 0.1% and the balance Fe;

[0045] S2) cutting the sintered NdFeB blank into magnets of the required size for grain boundary diffusion, and subjecting the magnets to surface treatment for standby use;

[0046] S3) mixing the surface treated magnet with the HRE target;

[0047] S4) putting the prepared mixed material into a vapor deposition furnace and placing it under a vacuum degree of 5×10 -4 Pa~5×10 -3 Pa, the speed is 10-20r / min and the heat treatment is carried out at 670-685℃ for 4-6h;

[0048] S5) screening the evaporated magnet and the diffusion source with a sieve;

[0049] S6) subjecting the magnet with the diffusion source to diffusion heat treatment to obtain a diffusion magnet.

[0050] In one embodiment, the mass ratio of the magnet to the HRE target is 1:2-1:5.

[0051] In one embodiment, the primary heat treatment temperature in the diffusion heat treatment is 750-950°C, and the temperature is kept for 8-16 hours; the secondary heat treatment temperature is 400-600°C, and the temperature is kept for 1-6 hours. The vacuum degree of the diffusion heat treatment is controlled at 5×10 -3 Pa~5×10 -2 Pa.

[0052] Several embodiments are listed below for illustration.

[0053] Example 1

[0054] 1) A shaving-like Tb target material with a purity of 99.5% and a thickness of 0.5 mm was processed using a lathe and a milling machine, and then cleaned to remove surface oil and oxides, and dried.

[0055] 2) A heavy rare earth-free NdFeB sintered magnet is prepared as a grain boundary diffusion blank, the composition of which is as follows by mass percentage: Pr-Nd 30%, Co 0.35%, B 1.0%, Ga 0.05%, Al 0.3%, Cu 0.1%, and the rest is Fe.

[0056] 3) The NdFeB sintered blank was processed into a square magnet of 6 mm x 6 mm x 0.8 mm, with the 0.8 mm direction being the magnetic field orientation direction. After surface treatment such as grinding and cleaning, the magnetic properties were tested at 21°C using a Mianyang bipolar 264Y permanent magnetic properties automatic measuring instrument, and the results were: Br 14.36 kGs, Hcj 13.06 kOe, (BH) max 47.88 MGOe, SQ 96.24%.

[0057] 4) The processed square magnet is polished, cleaned and dried.

[0058] 5) The treated Tb target material and the square magnet are mixed in a mass ratio of 2:1, the rotation speed of the evaporation furnace is set to 20 r / min, the mixture is placed in the evaporation furnace, and heat treated at 670° C. to 690° C. for 5 hours, and then cooled in an argon environment.

[0059] 6) After the mixed material is cooled to room temperature, it is taken out from the evaporation furnace, and the magnet and the Tb target are separated by a vibrating screen and a sieve to obtain a magnet with a trace amount of Tb element coated on the surface.

[0060] 7) The magnet with Tb element is placed in a vacuum environment for diffusion heat treatment at 900°C for 8 hours, and then tempered at 500°C for 4 hours to obtain a diffused magnet.

[0061] 8) Finally, the magnetic properties of the diffusion magnet were tested using a Mianyang bipolar 264Y permanent magnet property automatic measuring instrument at a measuring temperature of 21°C.

[0062] The magnetic properties test results of Example 1 are shown in Table 1.

[0063]

[0064] By observing the diffused magnets of Examples 1.1-1.4, no uneven diffusion, unevenness, missing edges or corners, etc. were found. However, in Example 1.5, it was found that when the evaporation temperature reached 690°C, a large number of magnets adhered to the sheets. The reason for the adhesion was that the melting point of Tb powder was lowered under high vacuum conditions. At 690°C, the Tb powder evaporated and diffused on the surface of the magnet melted, and the magnets were stacked together. After cooling, it was difficult to separate them. In addition, during the sintering process, the stacked magnets could not control the amount of Tb target material on the bonding surface, so the performance stability could not be guaranteed. Therefore, the evaporation temperature must be controlled below 690°C.

[0065] According to the magnetic properties test results in Table 1, it can be seen that when the shavings-shaped Tb target is used for diffusion, as the evaporation temperature increases, the film thickness gradually increases, the coercive force (Hcj) also increases synchronously, while the remanence (Br) and squareness (SQ) do not decrease dramatically.

[0066] Example 2

[0067] 1) A shaving-shaped Tb target with a purity of 99.5% and a thickness of 0.5 mm and a spherical Tb target with a diameter of 5 mm were processed using a lathe and a milling machine, and then they were cleaned to remove surface oil and oxides, and dried.

[0068] 2) A heavy rare earth-free NdFeB sintered magnet is prepared as a grain boundary diffusion blank, the composition of which is as follows by mass percentage: Pr-Nd 30%, Co 0.35%, B 1.0%, Ga 0.05%, Al 0.3%, Cu 0.1%, and the rest is Fe.

[0069] 3) The NdFeB sintered blank was processed into a square magnet of 6mm x 6mm x 0.8mm, with the 0.8mm direction being the magnetic field orientation direction. After surface treatment such as grinding and cleaning, the magnetic properties were tested at 21°C using a Mianyang bipolar 264Y permanent magnetic properties automatic measuring instrument, and the results were: Br 14.36kGs, Hcj 13.06kOe, (BH) max 47.88MGOe, SQ 96.24%.

[0070] 4) The processed square magnet is polished, cleaned and dried.

[0071] 5) The treated shavings Tb target and the square magnet were mixed in a mass ratio of 2:1, the rotation speed of the evaporation furnace was set to 20 r / min, the mixture was placed in the evaporation furnace, and heat treated at 685° C. for 5 hours, and then cooled in an argon environment.

[0072] 6) The treated spherical Tb target and the square magnet were mixed in a mass ratio of 2:1, the rotation speed of the evaporation furnace was set to 20 r / min, the mixture was placed in the evaporation furnace, and heat treated at 685° C. for 5 hours, and then cooled in an argon environment.

[0073] 7) After the mixed material is cooled to room temperature, it is taken out from the evaporation furnace, and the magnet and the Tb target are separated by a vibrating screen and a sieve to obtain a magnet with a trace amount of Tb element coated on the surface.

[0074] 8) The magnet with Tb element is placed in a vacuum environment for diffusion heat treatment at 900°C for 8 hours, and then tempered at 500°C for 4 hours to obtain a diffused magnet.

[0075] 9) Finally, the magnetic properties of the diffusion magnet were tested using a Mianyang bipolar 264Y permanent magnet property automatic measuring instrument at a measuring temperature of 21°C.

[0076] The magnetic properties test results of Example 2 are shown in Table 2.

[0077]

[0078] By observing the diffused magnets of Examples 2.1-2.3, no uneven diffusion, uneven surface, missing edges or corners, etc. were found. According to the magnetic property test results in Table 1, it can be seen that when the shavings-like Tb target is used for diffusion, the remanence (Br), coercive force (Hcj), magnetic energy product (BH) max and squareness (SQ) change stably with the increase in the number of uses.

[0079] However, in the diffused magnets of Examples 2.4-2.5, spherical Tb targets are used for diffusion. As the number of uses increases, the increment of coercive force (Hcj) gradually decreases; the remanence (Br), magnetic energy product (BH) max and squareness (SQ) gradually weaken.

[0080] In summary, the present invention introduces the shaving-like HRE target material into the evaporation grain boundary diffusion process, effectively controls the diffusion accuracy, stabilizes the evaporation amount of the diffusion source, significantly improves the coercive force and magnetic energy product of the NdFeB magnet, ensures the stability and consistency of the high-performance magnet, and brings higher benefits and broader application prospects to the grain boundary diffusion process.

[0081] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. 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 application.

Claims

1. A method for preparing a HRE target, characterized in that: The steps include: The heavy rare earth metals are made into high-density HRE metal blocks by vacuum induction melting or vacuum arc melting; The smelted HRE metal block is molded into a shape and size that meets the target material requirements; After cooling, the HRE metal block is processed into shaving-like HRE target material by lathe and milling machine; Surface treatment and drying of HRE target; The HRE target was stored in a vacuum environment.

2. The method for preparing the HRE target according to claim 1, characterized in that: The surface treatment is as follows: pre-chamfering 0.1 mm, and pickling with 5% nitric acid solution to remove oxides on the surface of the HRE target.

3. The method for preparing the HRE target according to claim 1, characterized in that: The purity of the HRE target material is 99.5%-99.9%, and the thickness is 0.5mm-1mm.

4. The method for preparing the HRE target according to claim 1, characterized in that: The heavy rare earth metal is Tb or Dy.

5. A HRE target prepared by the method according to any one of claims 1 to 4.

6. A method for preparing a magnet using the HRE target material as claimed in claim 5, characterized in that: The steps include: S1) using a heavy rare earth-free NdFeB sintered magnet as a grain boundary diffusion blank; S2) cutting the sintered NdFeB blank into magnets of the required size for grain boundary diffusion, and subjecting the magnets to surface treatment for standby use; S3) mixing the surface treated magnet with the HRE target; S4) putting the prepared mixed material into a vapor deposition furnace and placing it under a vacuum degree of 5×10 -4 Pa~5×10 -3 Pa, the speed is 10-20r / min and the heat treatment is carried out at 670-685℃ for 4-6h; S5) screening the evaporated magnet and the diffusion source with a sieve; S6) subjecting the magnet with the diffusion source to diffusion heat treatment to obtain a diffusion magnet.

7. The method for preparing a magnet according to claim 6, characterized in that: The mass ratio of the magnet to the HRE target is 1:2-1:

5.

8. The method for preparing a magnet according to claim 6, characterized in that: The weight percentage composition of the heavy rare earth-free NdFeB sintered magnet is as follows: Pr-Nd: 30%, Co: 0.35%, B: 1.0%, Ga: 0.05%, Al: 0.3%, Cu: 0.1% and the balance Fe.

9. The method for preparing a magnet according to claim 6, characterized in that: The primary heat treatment temperature in the diffusion heat treatment is 750-950°C, and the temperature is kept for 8-16 hours; the secondary heat treatment temperature is 400-600°C, and the temperature is kept for 1-6 hours. The vacuum degree of the diffusion heat treatment is controlled at 5×10 -3 Pa~5×10 -2 Pa.

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