A method for preparing a diffusion source for grain boundary diffusion and a rare earth sintered magnet

Abstract

The invention discloses a diffusion source for grain boundary diffusion and a preparation method of a rare earth sintered magnet. The diffusion source for grain boundary diffusion is composed of alloy A and alloy B; the ratio of alloy A to alloy B is 1-2:2-5; the particle size of alloy A is smaller than that of alloy B; alloy A is (Nd 0.6 Dy 0.4 ) 66 Cu 34 、(Nd 0.6 Dy 0.4)66 Al 10 Cu 24 、(Pr 0.6 Dy 0.4 ) 66 Cu 34 or (Pr 0.6 Dy 0.4 ) 66 Al 10 Cu 24 ; Alloy B is (Nd 0.7 Tb 0.3 ) 80 Al 20 、(Nd0.7Tb 0.3)80 Al 10 Ni 10 、(Pr 0.7 Tb 0.3 ) 80 Al 20 or (Pr 0.7 Tb 0.3 ) 80 Al 10 Ni 10 The present invention utilizes the synergistic effect of the Dy element on the Tb element to obtain the same magnetic properties while reducing the amount of Tb metal used.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth sintered magnets, and in particular to a diffusion source for grain boundary diffusion and a method for preparing a rare earth sintered magnet. Background Art

[0002] Nd-Fe-B materials have excellent hard magnetic properties and are widely used in new energy, intelligent equipment, electronic information, rail transportation and other fields. At present, the magnetic energy product and remanence of magnets are very close to their theoretical values, but the coercive force is still far less than its theoretical value, and its temperature stability is poor, which makes it difficult to meet the requirements of high temperature use. In order to overcome the defects of thermal stability, commercial magnets currently use the grain boundary diffusion method to improve the thermal stability of magnets, mainly using Dy2Fe 14 B and Tb2Fe 14 B higher magnetocrystalline anisotropy field, thereby achieving the purpose of increasing coercive force.

[0003] Considering the role and cost of diffusion sources, various types of diffusion sources have been developed for GBDP, such as oxides, hydrides, fluorides, alloys and pure metals. However, various diffusion sources and diffusion methods still have many problems.

[0004] Patent CN114914077B uses traditional pure Tb, TbHx, TbF3 and other diffusion sources. Due to the high melting point and poor diffusion depth of these materials, they are prone to form a reverse core-shell structure on the magnet surface, which reduces the magnet performance and causes a large amount of waste of diffusion source materials. Using this method, the comprehensive utilization rate of Tb element is less than 50%.

[0005] Patents CN111403167B and CN118366778A use a two-step or multi-step diffusion method, which can solve the problem of Tb element diffusion depth and diffusion uniformity. However, this method requires "one-step coating → one-step heat treatment → two-step coating → two-step heat treatment", which greatly increases the process difficulty and reduces production efficiency.

[0006] Patent CN118231132A uses low melting point alloys to improve the diffusion efficiency and diffusion depth of heavy rare earth elements. However, the introduction of low melting point elements will reduce the content of heavy rare earth in the diffusion source, so that in the subsequent process treatment, the coating amount of the diffusion source needs to be increased to meet the performance requirements of the product. However, increasing the coating amount is likely to cause problems such as poor coating adhesion and surface cracking. It is easy to cause local capillary shrinkage and agglomeration during the heat treatment process.

[0007] The Tb element diffuses in the Dy-containing magnet and forms an obvious Dy-rich Tb double shell on the surface of the main phase grains, which can effectively inhibit the nucleation of the reverse magnetization domain on the grain surface. At the same time, with the increase of Dy elements in the magnet, the coercive force increment of the magnet after Dy / Tb diffusion shows an increasing trend. The above results show that the use of appropriate Dy elements to assist Tb diffusion can solve the above problems, reduce the amount of HRE, inhibit the nucleation of the reverse magnetization domain on the grain surface, and prepare commercial NdFeB magnets with high coercivity and high magnetic energy product. Summary of the invention

[0008] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a diffusion source for grain boundary diffusion and a method for preparing a rare earth sintered magnet, which has low cost and can prepare commercial NdFeB magnets with high coercivity and high magnetic energy product at a relatively low diffusion dosage.

[0009] To achieve the above object, the technical solution adopted by the present invention is: a diffusion source for grain boundary diffusion, which is formed by mixing alloy A and alloy B; the melting point of alloy A is lower than the melting point of alloy B, and the particle size of alloy A is smaller than the particle size of alloy B;

[0010] The alloy A is (Pr / Nd 1-x Dy x ) 66 (M1 1-y M2 y ) 34 Wherein the range of x is 0-1, the range of y is 0-1; the M1-M2 is one or more selected from Fe, Co, Ti, Al, Cu;

[0011] The alloy B is (Pr / Nd 1-a Tba) 80 (M3 1-b M4 b ) 20 , wherein a ranges from 0 to 1, and b ranges from 0 to 1; and M3-M4 is one or more selected from Fe, Co, Bi, Al, Ca, Mg, O, C, N, Cu, Zn, In, Si, S, P, Ti, V, Cr, Mn, Ni, Ga, Ge, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Sb, Hf, Ta or W.

[0012] Furthermore, the mixing ratio of alloy A and alloy B is 1-2:2-5.

[0013] Furthermore, (Nd 0.6 Dy 0.4 ) 66 Cu 34 、(Nd 0.6 Dy 0.4)66Al 10 Cu 24 、(Pr 0.6 Dy 0.4 ) 66 Cu 34 or (Pr 0.6 Dy 0.4 ) 66 Al 10 Cu 24 .

[0014] Furthermore, the alloy B is (Nd 0.7 Tb 0.3 ) 80 Al 20 、(Nd0.7Tb 0.3)80 Al 10 Ni 10 、(Pr 0.7 Tb 0.3 ) 80 Al 20 or (Pr 0.7 Tb 0.3 ) 80 Al 10 Ni 10 .

[0015] Furthermore, the particle size of the alloy A is 1-3 um; the particle size of the alloy B is 4-5 um.

[0016] Furthermore, the melting point of the alloy A is 450-800°C; the melting point of the alloy B is 650-950°C.

[0017] A method for preparing a rare earth sintered magnet comprises the following steps:

[0018] S1) preparing a sintered NdFeB blank for grain boundary diffusion treatment, and processing the sintered NdFeB blank into a substrate for grain boundary diffusion treatment;

[0019] S2) mixing alloy A and alloy B to prepare a slurry to be diffused;

[0020] S3) coating the slurry to be diffused on the surface of the diffusion substrate to obtain a magnetic body to be diffused;

[0021] S4) placing the magnet to be diffused with its coated surface facing each other into a graphite box;

[0022] S5) placing the graphite box containing the magnet to be diffused into a vacuum sintering furnace for two diffusion heat treatments at low temperature and high temperature to obtain a diffused magnet. Placing the graphite box containing the magnet to be diffused into a vacuum sintering furnace for two diffusion heat treatments to obtain a diffused magnet, wherein the diffusion treatment temperature in the first stage is 850-880°C, and the diffusion treatment temperature in the second stage is 900-950°C.

[0023] Furthermore, the preparation method of the diffusion source slurry in step S2 is:

[0024] Put the adhesive into the liquid dispersant and stir to dissolve the adhesive. The weight ratio of the adhesive to the liquid dispersant is 1:9.

[0025] The dissolved colloid is placed in a glove box, and the nitrogen outlet valve and nitrogen inlet valve of the glove box are opened to allow nitrogen to exhaust the air in the glove box to reduce the oxygen content to less than 0.01%.

[0026] Add the diffusion source combination to the colloid in multiple times, stir evenly each time, and extend the stirring time for 5 minutes until the metal powder is completely covered by the colloid to obtain a diffusion source combination slurry. The mass percentage of the diffusion source powder in the slurry is 1%-90%;

[0027] The diffusion source combination slurry is processed twice by a three-roll mill to obtain a refined diffusion source combination slurry.

[0028] Furthermore, the total holding time of the first stage diffusion treatment temperature and the second stage diffusion treatment temperature is 10-16 hours; the tempering temperature is 450-550°C, and the holding time is 4-6 hours.

[0029] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0030] 1. Since the price of Tb metal is much higher than that of Pr and Dy metal, a metal with a melting point difference (Pr / Nd 1-x Dy x ) 66 (M1 1-y M2 y ) 34 Alloy and (Pr / Nd 1-a Tb a ) 80 (M3 1-b M4 b ) 20 The alloy diffusion source combination is fully mixed and coated on the magnet at the same time. By utilizing the synergistic effect of the Dy element on the Tb element, the amount of Tb metal can be reduced while achieving the same magnetic properties, thereby reducing the cost of the diffusion source. In addition, only one coating is required to complete the process, which is simple and has high processing efficiency.

[0031] 2. Due to (Pr / Nd 1-x Dy x ) 66 (M1 1-y M2 y ) 34The melting point of the alloy is lower than (Pr / Nd 1-a Tb a ) 80 (M3 1-b M4 b ) 20 alloy and the alloy has a small particle size. At a lower diffusion treatment temperature, (Pr / Nd 1-x Dy x ) 66 (M1 1-y M2 y ) 34 The alloy will melt first, at (Pr / Nd 1-a Tb a ) 80 (M3 1-b M4 b ) 20 The alloy powder surface is coated, which reduces the direct contact between the Tb-containing diffusion source and the magnet surface, avoids the formation of a thicker reverse core-shell structure layer, and reduces the waste of Tb elements.

[0032] As diffusion proceeds, the (Pr / Nd 1-a Tb a ) 80 (M3 1-b M4 b ) 20 The diffusion channel of the alloy. As (Pr / Nd 1-x Dy x ) 66 (M1 1-y M2 y ) 34 The alloy diffuses into the magnet along the grain boundary, improving the wettability of the grain boundary and establishing the channel of the magnet after expansion. At the same time, since the Dy element tends to enter the main phase, at the first stage diffusion temperature, as the diffusion proceeds, the Dy element will diffuse along the grain surface and diffuse into the magnet. At a higher second stage diffusion treatment temperature, (Pr / Nd 1-a Tb a ) 80 (M3 1-b M4 b ) 20 The alloy will enter the magnet along the grain boundary diffusion source channel constructed by the low melting point diffusion source. Since the grain boundary phase is liquid, (Pr / Nd 1-a Tb a ) 80 (M3 1-b M4 b ) 20The diffusion of the alloy along the liquid-liquid interface can effectively increase the diffusion depth of the Tb element. At the same time, since the Dy element enters the main phase, a diffusion channel for Tb atoms is constructed, thereby improving the effective utilization rate of Tb atoms and achieving better diffusion magnet performance at a lower Tb dosage.

[0033] 3. During the tempering treatment, the Pr, Dy, and Tb atoms diffused to the surface of the main phase grains will replace the Nd atoms in the main phase grains, forming (Nd-Pr-Dy-Tb)2Fe with a higher anisotropic field Ha. 14 B, thereby increasing the coercive force of the magnet; at the same time, due to the Pr2Fe 14 B's Js and Nd2Fe 14 B is close to and higher than Dy2Fe 14 B and Tb2Fe 14 B, therefore, the coercive force is increased without significantly reducing the remanence of the diffused magnet. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The technical solution of the present invention is further described below in conjunction with the accompanying drawings:

[0035] Figure 1 The figure is a schematic diagram of the preparation process of a diffusion source for grain boundary diffusion in one embodiment of the present invention.

[0036] Figure 2 It is a schematic diagram of the process curve of the diffusion heat treatment of the present invention.

[0037] Figure 3 It is a schematic diagram of the process of Dy and Tb entering the magnet during the grain boundary diffusion process according to one embodiment of the present invention. DETAILED DESCRIPTION

[0038] 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.

[0039] The present invention provides a diffusion source for grain boundary diffusion and a method for preparing a rare earth sintered magnet, so as to solve the problem in the prior art that the diffusion source has high cost and commercial NdFeB magnets with high coercive force and high magnetic energy product cannot be prepared at a low diffusion dosage.

[0040] For ease of understanding, the specific process in the embodiment of the present application is described below. A diffusion source for grain boundary diffusion in the embodiment of the present application is formed by mixing alloy A and alloy B, and the melting point of alloy A is lower than the melting point of alloy B; the particle size of alloy A is smaller than the particle size of alloy B.

[0041] Specifically, the material of the alloy A is selected from a low melting point alloy containing Dy, and the low melting point alloy containing Dy is a Nd-Dy-M1-M2 alloy or a Pr-Dy-M1-M2 alloy, and the M1-M2 is selected from one or more of Fe, Co, Ti, Al, and Cu. The general formula of the low melting point alloy can be written as (Pr / Nd 1-x Dy x ) 66 (M1 1-y M2 y ) 34 , where x ranges from 0-1; y ranges from 0-1.

[0042] Among them, Dy-containing low melting point alloys (Nd 0.6 Dy 0.4 ) 66 Cu 34 、(Nd 0.6 Dy 0.4 ) 66 Al 10 Cu 24 , (Pr0.6Dy0.4)66Cu34 or (Pr0.6Dy0.4)66Al10Cu24 are better choices.

[0043] The material of the alloy B is selected from an alloy containing Tb, and the alloy containing Tb is a Nd-Tb-M3-M4 alloy or a Pr-Tb-M3-M4 alloy, and the M3-M4 is selected from one or more of Fe, Co, Bi, Al, Ca, Mg, O, C, N, Cu, Zn, In, Si, S, P, Ti, V, Cr, Mn, Ni, Ga, Ge, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Sb, Hf, Ta or W. The general formula of the alloy containing Tb can be written as (Pr / Nd 1-a Tb a ) 80 (M3 1-b M4 b ) 20 , where a ranges from 0 to 1; b ranges from 0 to 1.

[0044] Among them, the alloy containing Tb (Nd 0.7 Tb 0.3 ) 80 Al 20 、(Nd0.7 Tb 0.3 ) 80 Al 10 Ni 10 、(Pr 0.7 Tb 0.3 ) 80 Al 20 or (Pr 0.7 Tb 0.3 ) 80 Al 10 Ni 10 It is a better choice.

[0045] In summary, since the price of Tb metal is much higher than that of Pr and Dy metal, the use of metals with different melting points (Pr / Nd 1- x Dy x ) 66 (M 11-y M 2y ) 34 Alloy and (Pr / Nd 1-a Tb a ) 80 (M3 1-b M4 b ) 20 The alloy diffusion source combination utilizes the synergistic effect of the Dy element on the Tb element, and can reduce the amount of Tb metal while achieving the same magnetic properties, thereby reducing the cost of the diffusion source.

[0046] In addition, the melting point of alloy A is 450-800℃; the melting point of alloy B is 650-950℃. By adjusting the size of x, y, a, and b, the melting point values ​​of alloy A / B can be easily adjusted. However, no matter how it is adjusted, the melting point of alloy A must be lower than that of alloy B, so that alloy A can be melted first and then a channel for alloy B to enter the magnet can be constructed. At the same time, the particle size of alloy A is 1-3um; the particle size of alloy B is 4-5um, ensuring that the particle size of alloy A is smaller than that of alloy B. The particle size of alloy A is smaller than that of alloy B so that alloy A can cover alloy B more quickly and effectively.

[0047] based on Figure 3 , due to (Pr / Nd 1-x Dy x ) 66 (M1 1-y M2 y ) 34 The melting point of the alloy is lower than (Pr / Nd 1-a Tb a ) 80 (M3 1- b M4 b) 20 alloy and the alloy has a smaller particle size. In this way, at a lower diffusion treatment temperature, (Pr / Nd 1-x Dy x ) 66 (M1 1- y M2 y ) 34 The alloy will melt first, at (Pr / Nd 1-a Tb a ) 80 (M3 1-b M4 b ) 20 The alloy powder surface is coated, which reduces the direct contact between the Tb-containing diffusion source and the magnet surface, avoids the formation of a thicker reverse core-shell structure layer, and reduces the waste of Tb elements.

[0048] Secondly, as the diffusion proceeds, the (Pr / Nd 1-x Dy x ) 66 (M1 1-y M2 y ) 34 The alloy diffuses along the grain boundary phase into the magnet under the action of capillary effect, thus constructing (Pr / Nd 1-a Tb a ) 80 (M3 1-b M4 b ) 20 The diffusion channel of the alloy. As (Pr / Nd 1-x Dy x ) 66 (M1 1-y M2 y ) 34 The alloy diffuses continuously into the magnet along the grain boundary. Since the Dy element tends to enter the main phase, at a lower diffusion temperature, as the diffusion proceeds, the Dy element will diffuse along the grain surface and diffuse into the magnet. At a higher diffusion treatment temperature, (Pr / Nd 1-a Tb a ) 80 (M3 1-b M4 b ) 20 The alloy will enter the magnet along the grain boundary diffusion source channel constructed by the low melting point diffusion source. Since the grain boundary phase is all liquid, (Pr / Nd 1-a Tb a ) 80 (M3 1-b M4 b ) 20The diffusion of the alloy along the liquid-liquid interface can effectively increase the diffusion depth of the Tb element. At the same time, since the Dy element enters the main phase, a diffusion channel for Tb atoms is constructed, thereby improving the effective utilization rate of Tb atoms and achieving better diffusion magnet performance at a lower Tb dosage.

[0049] In addition, during the tempering treatment, the Pr, Dy, and Tb atoms diffused to the surface of the main phase grains will replace the Nd atoms in the main phase grains to form (Nd-Pr-Dy-Tb)2Fe14B with a higher anisotropic field Ha, thereby improving the coercive force of the magnet. At the same time, since the Js of Pr2Fe14B is close to that of Nd2Fe14B, and higher than that of Dy2Fe14B and Tb2Fe14B, the use of the diffusion source combination of the present invention will not significantly reduce the remanence of the diffusion magnet while improving the coercive force.

[0050] At the same time, the preparation method of the present invention only requires coating the magnet once, the preparation process is simple and effective, and the processing efficiency is improved.

[0051] Furthermore, the diffusion source combination is a mixture of alloy A and alloy B in a ratio of 1-2:1-5, wherein the mixing ratio of alloy A and B is more preferably A:B=1:3, 1:2, 1:1.

[0052] In addition, the preparation methods of alloys A and B are both conventional processes, and are obtained through processes such as smelting and spinning, hydrogen cracking, and air flow milling. The speed of the classifying wheel of the air flow mill used for alloy A is 3500-4000, and the speed of the classifying wheel of the air flow mill used for alloy B is 2000-2500.

[0053] The present invention also discloses a method for preparing a rare earth sintered magnet, comprising the following steps:

[0054] 1) preparing a sintered NdFeB blank for grain boundary diffusion treatment, and processing the sintered NdFeB blank into a substrate for grain boundary diffusion treatment;

[0055] Specifically, firstly, a sintered NdFeB blank for grain boundary diffusion treatment is prepared, and the components are composed by mass percentage, including: Pr-Nd: 30.5%, Al: 0.15%, Co: 0.8%, Nb: 0.3%, B: 0.95%, Cu: 0.15%, Ti: 0.2%, Zr: 0.1% and the balance Fe; then the sintered NdFeB blank is processed into a substrate for grain boundary diffusion treatment, and its orientation direction size is similar to the finished product size, the size is in the range of 1mm-6mm, and it is surface treated.

[0056] 2) Using a powder mixer to mix alloy A and alloy B to prepare a slurry to be diffused;

[0057] 3) coating the slurry to be diffused on the surface of the diffusion substrate to obtain the magnet to be diffused;

[0058] 4) Place the magnet to be diffused with its coated surface facing each other into the graphite box;

[0059] 5) Put the graphite box containing the magnet to be diffused into a vacuum sintering furnace for diffusion heat treatment to obtain a diffused magnet.

[0060] Furthermore, the heat treatment process for preparing the sintered NdFeB blank for grain boundary diffusion treatment in step (1) is as follows: solution treatment temperature 1020-1080°C, heat preservation 2-8h; primary tempering temperature 850-950°C, heat preservation 2-5h; secondary tempering temperature 450-550°C, heat preservation 2-5h.

[0061] Furthermore, the surface treatment in step (1) refers to removal of the oxide layer, polishing to a mirror surface, cleaning treatment, etc.

[0062] Furthermore, in step S2, the method for configuring the diffusion source slurry is:

[0063] ① Put the adhesive into the liquid dispersant and stir to dissolve the adhesive. The weight ratio of the adhesive to the liquid dispersant is 1:9.

[0064] ② Put the dissolved colloid into the glove box, open the nitrogen outlet valve of the glove box, open the nitrogen inlet valve, and let the nitrogen exhaust the air in the glove box to make the oxygen content less than 0.01%.

[0065] ③ Add the diffusion source combination to the colloid in multiple times, stir evenly each time, and extend the stirring time for 5 minutes until the metal powder is completely added, so that the metal powder is completely covered by the colloid to obtain a diffusion source combination slurry. The mass percentage of the diffusion source powder in the slurry is 1%-90%.

[0066] ④ Treat the diffusion source combination slurry twice with a three-roll mill to obtain a refined diffusion source combination slurry.

[0067] Wherein, the total amount of the diffusion source in step ③ accounts for 0.1-2% of the mass of the rare earth sintered magnet.

[0068] In addition, the diffusion coating method in step ④ is directly attached to the surface of the magnet by spraying, screen printing, inkjet printing, spin coating, suspended plasma spraying and other processes.

[0069] As a further preferred embodiment of the present application, the diffusion heat treatment process in step (5) is as follows: the temperature of the first stage diffusion heat treatment is 850-880°C, the temperature of the second stage diffusion heat treatment is 900-950°C, and the total insulation time of the first stage diffusion heat treatment temperature and the second stage diffusion heat treatment temperature is 10-16h; the tempering temperature is 450-550°C, and the insulation time is 4-6h.

[0070] The diffusion heat treatment process needs to be adjusted accordingly according to the different proportions of the diffusion source combination. At the same time, the first diffusion treatment temperature and the diffusion heat treatment are continuous treatment curves, and there is no need for secondary heat treatment after cooling.

[0071] like Figure 2 As shown, it is a schematic diagram of the process curve of the diffusion heat treatment in the present invention, wherein the temperature is gradually increased from 350-400°C to 850-880°C, kept warm for 4-8h, and then heated to 910-950°C and kept for 8-12h, thereby realizing the curve change of the temperature of the first stage diffusion heat treatment and the second stage diffusion heat treatment, which is used to adapt the melting point of the DY alloy powder and the TB alloy powder in the present invention.

[0072] The treatment methods of diffusion heat according to different proportions of diffusion source combination are as follows:

[0073] ① When the diffusion source combination ratio is A:B=1:1, the diffusion heat treatment scheme is: the first stage diffusion treatment temperature is 860℃, and the temperature is kept for 8h; the second stage diffusion treatment temperature is 910℃, and the temperature is kept for 8h; the tempering temperature is 500℃, and the temperature is kept for 5h.

[0074] ② When the diffusion source combination ratio is A:B=1:2, the diffusion heat treatment scheme is: the first stage diffusion treatment temperature is 870℃, and the temperature is kept for 6h; the second stage diffusion treatment temperature is 910℃, and the temperature is kept for 10h; the tempering temperature is 500℃, and the temperature is kept for 6h.

[0075] ③ When the diffusion source combination ratio is A:B=1:3, the diffusion heat treatment scheme is: the first stage diffusion treatment temperature is 880℃, and the insulation is 4h; the second stage diffusion treatment temperature is 910℃, and the insulation is 12h; the tempering temperature is 500℃, and the insulation is 6h.

[0076] Several embodiments are listed below for specific description.

[0077] A preparation method of a diffusion source for grain boundary diffusion comprises the following steps:

[0078] 1) Pr, Dy and Cu with a purity of 99.9% by mass are used as raw materials, and the ingredients are prepared according to the atomic percentage of (Pr0.6Dy0.4)66Cu34. Before preparing the ingredients, the oxide layer on the surface of the Pr and Dy needs to be removed by a shot blasting machine.

[0079] 2) Add all raw materials into the quick-setting furnace, flush the furnace chamber with argon, then evacuate to a vacuum degree less than or equal to 3×10-3Pa, and then fill with argon as a protective gas for smelting, and finally pour the molten alloy through the tundish onto a rotating water-cooled copper roller to obtain (Pr0.6Dy0.4)66Cu34 quick-setting sheets. The smelting temperature is 1200℃, and the speed of the water-cooled copper roller is 1.3m / s.

[0080] 3) The obtained (Pr0.6Dy0.4)66Cu34 quick-setting flakes are transferred to a material tank, and then the material tank is placed in a hydrogen cracking furnace for hydrogen cracking to obtain (Pr0.6Dy0.4)66Cu34 hydrogen cracking coarse powder. The hydrogen absorption temperature during the hydrogen cracking process is 300°C, the hydrogen absorption pressure is 0.091Pa, the hydrogen absorption time is 2h, the dehydrogenation temperature is 350°C, and the dehydrogenation time is 1h.

[0081] 4) The obtained (Pr0.6Dy0.4)66Cu34 hydrogen-crushed coarse powder was transferred to a special material tank for air flow mill in the glove box, and then subjected to air flow milling treatment. The air flow mill was performed at a sorting wheel speed of 4500 to finally obtain (Pr0.6Dy0.4)66Cu34 diffusion source powder with a particle size of 3.1um.

[0082] 5) Pr, Tb and Al with a purity of 99.9% by mass are used as raw materials, and the ingredients are prepared according to the atomic percentage of (Pr0.7Tb0.3)80Al20. Before preparing the ingredients, the oxide layer on the surface of the Tb needs to be removed by a shot blasting machine.

[0083] 6) Add all raw materials into the quick-setting furnace, flush the furnace chamber with argon, and then evacuate to a vacuum degree less than or equal to 3×10-3Pa, and then fill with argon as a protective gas for smelting, and finally pour the molten alloy through the tundish onto a rotating water-cooled copper roller to obtain (Pr0.7Tb0.3)80Al20 quick-setting sheets. The smelting temperature is 1200℃, and the speed of the water-cooled copper roller is 1.7m / s.

[0084] 7) The obtained (Pr0.7Tb0.3)80Al20 quick-solidified flakes are transferred to a material tank, and then the material tank is placed in a hydrogen cracking furnace for hydrogen cracking to obtain (Pr0.7Tb0.3)80Al20 hydrogen cracked coarse powder. The hydrogen absorption temperature during the hydrogen cracking process is 300°C, the hydrogen absorption pressure is 0.091Pa, the hydrogen absorption time is 2h, the dehydrogenation temperature is 350°C, and the dehydrogenation time is 1h.

[0085] 8) The obtained (Pr0.7Tb0.3)80Al20 hydrogen-crushed coarse powder was transferred to a special material tank for air flow mill in the glove box, and then subjected to air flow milling treatment. The air flow mill was performed at a sorting wheel speed of 2500 to finally obtain (Pr0.7Tb0.3)80Al20 diffusion source powder with a particle size of 6.3um.

[0086] 9) Using a powder mixer, mix the (Pr0.6Dy0.4)66Cu34 diffusion source powder and the (Pr0.7Tb0.3)80Al20 diffusion source powder evenly in a ratio of A:B=2:1, 1:1, 1:2, 1:3 (Examples 1-4).

[0087] 10) Put the adhesive into the liquid dispersant and stir to dissolve the adhesive. The weight ratio of the adhesive to the liquid dispersant is 1:9.

[0088] 11) Put the dissolved colloid into the glove box, open the nitrogen outlet valve of the glove box, open the nitrogen inlet valve, and let the nitrogen exhaust the air in the glove box to make the oxygen content less than 0.01%.

[0089] 12) Add the evenly mixed diffusion source powder to the colloid in multiple times, stirring evenly each time. After adding completely, extend the stirring time for 5 minutes to allow the metal powder to be completely covered by the colloid to obtain a diffusion source slurry. The mass percentage of the evenly mixed diffusion source powder in the slurry is 75%.

[0090] A method for preparing a rare earth sintered magnet comprises the following steps:

[0091] 1) Prepare sintered NdFeB blank for grain boundary diffusion treatment, the components are composed by mass percentage, including: Pr-Nd: 30.5%, Al: 0.15%, Co: 0.8%, Nb: 0.3%, B: 0.95%, Cu: 0.15%, Ti: 0.2%, Zr: 0.1% and the balance Fe. It is prepared according to the existing rare earth magnet smelting, belt throwing, hydrogen crushing, air flow grinding, orientation pressing, sintering and heat treatment processes.

[0092] 2) The processed sintered magnet is processed into a square magnet of 10mm*10mm*4mm, and the 4mm direction is the magnetic field orientation direction. After the surface of the processed magnet is cleaned, the magnetic properties are tested using the Mianyang Bipolar 264Y permanent magnetic properties automatic measuring instrument. The measuring temperature is 20℃, and the test results are Br: 13.86 kGs, Hcj: 16.32 kOe, (BH)max: 47.63 MGOe, SQ: 97.48%.

[0093] 3) A layer of diffusion source film with mixed diffusion source A:B=2:1, 1:1, 1:2, 1:3 is printed on the surface of the diffusion magnet substrate by screen printing. The diffusion source film with mixed diffusion source A:B=2:1, 1:1, 1:2, 1:3 accounts for 0.9wt.% of the substrate mass.

[0094] 4) Dry the magnet coated with the diffusion source film with the mixed diffusion source A:B=2:1, 1:1, 1:2, 1:3 to obtain the magnet to be diffused. The drying temperature is 120°C and the drying time is 15 minutes.

[0095] 5) Place the coated surfaces of the magnet to be diffused into a graphite box and transfer it to a sintering furnace for diffusion heat treatment to obtain a diffused magnet (Example 1-4). The process conditions of the diffusion heat treatment are as follows:

[0096] ① When the diffusion source combination ratio is A:B=2:1, 1:1, the diffusion heat treatment scheme is: diffusion treatment temperature 1 is 860℃, insulation for 8h; diffusion treatment temperature 2 is 910℃, insulation for 8h; tempering temperature is 500℃, insulation for 5h. (Example 1-2)

[0097] ② When the diffusion source combination ratio is A:B=1:2, the diffusion heat treatment scheme is: diffusion treatment temperature 1 is 870℃, and the temperature is kept for 6h; diffusion treatment temperature 2 is 910℃, and the temperature is kept for 10h; tempering temperature is 500℃, and the temperature is kept for 6h. (Example 3)

[0098] ③ When the diffusion source combination ratio is A:B=1:3, the diffusion heat treatment scheme is: diffusion treatment temperature 1 is 880℃, and the temperature is kept for 4h; diffusion treatment temperature 2 is 910℃, and the temperature is kept for 12h; tempering temperature is 500℃, and the temperature is kept for 6h. (Example 4)

[0099] 6) The diffused magnets were tested for magnetic properties using a 264Y permanent magnet property automatic measuring instrument from Mianyang Bipolar, with the measuring temperature being 20°C.

[0100] 7) A single layer of (Pr0.6Dy0.4)66Cu34 diffusion film was deposited on the diffusion substrate by conventional screen printing as comparative example 1, wherein the (Pr0.6Dy0.4)66Cu34 diffusion source film accounted for 0.9 wt.% of the substrate mass; a single layer of (Pr0.7Tb0.3)80Al20 diffusion film was deposited on the diffusion substrate by conventional screen printing as comparative example 2, wherein the (Pr0.7Tb0.3)80Al20 diffusion source film accounted for 0.9 wt.% of the substrate mass.

[0101] The magnetic properties of the magnets prepared as described above are shown in Table 1.

[0102] Table 1 Magnetic performance evaluation of the examples

[0103] Serial number <![CDATA[B r (kGs)]]> <![CDATA[B r Increment(kGs)]]> <![CDATA[H cj (no)]]> <![CDATA[H cj Increment(kGs)]]> <![CDATA[(BH) max (MGOe)]]> Square degrees (%) Diffusion matrix 13.86 / 16.32 / 47.63 97.48 Example 1 13.59 -0.27 22.58 6.26 44.58 94.12 Example 2 13.64 -0.22 24.95 8.63 45.32 95.23 Example 3 13.71 -0.15 25.89 9.57 46.52 96.32 Example 4 13.73 -0.13 26.12 9.80 45.98 96.31 Comparative Example 1 13.47 -0.39 21.52 5.20 43.58 93.28 Comparative Example 2 13.71 -0.15 24.92 8.60 46.78 95.58

[0104] As can be seen from Table 1, using a pure (Pr0.6Dy0.4)66Cu34 diffusion source (cost of about 1000 yuan / kg), at a weight gain of 0.9wt.%, the coercive force of the magnet increased from 16.32kOe to 21.52kOe; the remanence of the diffused magnet decreased significantly from 13.86kGs to 13.47kGs. Among them, the significant decrease in remanence is due to the fact that the Js of Pr2Fe14B and Dy2Fe14B is lower than that of Nd2Fe14B. Using a pure (Pr0.7Tb0.3)80Al20 diffusion source (cost of about 2050 yuan / kg), at a weight gain of 0.9wt.%, the coercive force of the magnet increased from 16.32kOe to 24.92kOe; the remanence of the diffused magnet decreased from 13.86kGs to 13.71kGs, with a smaller decrease.

[0105] From the above results, it can be seen that the use of diffusion sources containing Tb has the advantages of large coercivity increment and small remanence reduction compared with those containing Tb at the same diffusion source dosage. However, the cost of the (Pr0.7Tb0.3)80Al20 diffusion source is much higher than that of the (Pr0.6Dy0.4)66Cu34 diffusion source. In order to reduce the amount of Tb metal while achieving the same magnetic properties, the cost of the diffusion source is reduced.

[0106] The present invention proposes a diffusion source combination for grain boundary diffusion of RE-Fe-B rare earth sintered magnets, which is a diffusion source combination of two alloys with different melting points, namely, (Pr / Nd1-xDyx)66(M11-yM2y)34 alloy and (Pr / Nd1-aTba)80(M31-bM4b)20 alloy, which are mixed in a certain proportion and utilize the synergistic effect of Dy element on Tb element to reduce the amount of Tb metal while achieving the same magnetic properties, thereby reducing the cost of the diffusion source.

[0107] It can be seen from Examples 1-4 in Table 1 that with the increase of diffusion source B in the mixed powder, the magnet diffused with the mixed diffusion source has a gradually reduced decrease in remanence and a gradually increased increase in coercive force compared to the magnet diffused with the pure (Pr0.6Dy0.4)66Cu34 diffusion source at the same weight increase.

[0108] When the mixing ratio A:B=1:1 (cost is about 1500 yuan / kg), at 0.9 wt.% weight gain, the coercive force of the magnet increases from 16.32kOe to 24.95kOe; the remanence of the diffused magnet decreases from 13.86kGs to 13.64kGs. The performance of the magnet is basically the same as that of the pure (Pr0.7Tb0.3)80Al20 diffusion source after diffusion, but the cost is reduced by 1 / 4. This is due to the coordination of the Dy element on the Tb element, which constructs the diffusion channel of the Tb atoms, improves the effective utilization rate of the Tb atoms, and can achieve better diffused magnet performance at a lower Tb dosage.

[0109] Furthermore, by using diffusion sources with a mixing ratio of A:B=1:2 (cost is about 1735 yuan / kg) and 1:3 (cost is about 1787.5 yuan / kg), at a weight gain of 0.9 wt.%, the coercive force of the magnet increased from 16.32kOe to 25.89kOe and 26.12kOe; the remanence of the diffused magnet decreased from 13.86kGs to 13.71kGs and 13.73kGs. The performance of the magnet after diffusion is significantly better than that of the magnet after diffusion of pure (Pr0.7Tb0.3)80Al20 diffusion source.

[0110] In summary, the preparation method provided by the present invention has a simple process. Through the heat treatment scheme for two alloys mixed in different proportions and two alloys with different melting points, the coordinated cooperation of Dy-containing and Tb-containing diffusion sources with different melting points is achieved, and commercial NdFeB magnets with high coercivity and high magnetic energy product can be prepared at a lower diffusion dosage.

[0111] 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 diffusion source for grain boundary diffusion, characterized in that : It is a mixture of alloy A and alloy B; the melting point of alloy A is lower than the melting point of alloy B; the mixing ratio of alloy A and alloy B is 1~2:2~5; the particle size of alloy A is 1-3um; the particle size of alloy B is 4-5um; The alloy A is (Nd 0.6 Dy 0.4 ) 66 Cu 34 、(Nd 0.6 Dy 0.4)66 Al 10 Cu 24 、(Pr 0.6 Dy 0.4 ) 66 Cu 34 or (Pr 0.6 Dy 0.4 ) 66 Al 10 Cu 24 ; The alloy B is (Nd 0.7 Tb 0.3 ) 80 Al 20 、(Nd0.7Tb 0.3)80 Al 10 Ni 10 、(Pr 0.7 Tb 0.3 ) 80 Al 20 or (Pr 0.7 Tb 0.3 ) 80 Al 10 Ni 10 .

2. The grain boundary diffusion diffusion source according to claim 1, wherein: The melting point of the alloy A is 450-800°C; the melting point of the alloy B is 650-950°C.

3. A method for preparing a rare earth sintered magnet, characterized in that: The steps include: S1) preparing a sintered NdFeB blank for grain boundary diffusion treatment, and processing the sintered NdFeB blank into a substrate for grain boundary diffusion treatment; S2) configuring the diffusion source for grain boundary diffusion according to any one of claims 1 to 2 into a slurry to be diffused; S3) coating the slurry to be diffused on the surface of the diffusion substrate to obtain a magnetic body to be diffused; S4) placing the magnet to be diffused with its coated surface facing each other into a graphite box; S5) placing the graphite box containing the magnet to be diffused into a vacuum sintering furnace for diffusion heat treatment to obtain a diffused magnet, wherein the diffusion treatment temperature in the first stage is 850-880°C, and the diffusion treatment temperature in the second stage is 900-950°C.

4. The method for preparing a rare earth sintered magnet according to claim 3, characterized in that: The preparation method of the diffusion source slurry in step S2 is: ① Put the adhesive into the liquid dispersant and stir to dissolve the adhesive. The weight ratio of the adhesive to the liquid dispersant is 1:9; ② Put the dissolved colloid into the glove box, open the nitrogen outlet valve of the glove box, open the nitrogen inlet valve, and let the nitrogen exhaust the air in the glove box to make the oxygen content less than 0.01%; ③ Add the diffusion source combination to the colloid in multiple times, stir evenly each time, and extend the stirring time for 5 minutes until the metal powder is completely covered by the colloid to obtain a diffusion source combination slurry. The mass percentage of the diffusion source powder in the slurry is 1%-90%; ④ Treat the diffusion source combination slurry twice with a three-roll mill to obtain a refined diffusion source combination slurry.

5. The method for preparing a rare earth sintered magnet according to claim 3, characterized in that: The total holding time of the first stage diffusion heat treatment temperature and the second stage diffusion heat treatment temperature is 10-16h; the tempering temperature is 450-550℃, and the holding time is 4-6h.

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