A grain boundary diffusion method of a light rare earth-based diffusion source based on protective atmosphere electrospark deposition

Abstract

The present invention discloses a grain boundary diffusion method of a light rare earth diffusion source based on electrospark deposition, which comprises the following steps: First, semi-densification sintering is carried out on magnetic powder to obtain a magnetic material substrate; secondly, with electrospark deposition as the coating means, a light rare earth-based alloy diffusion source is plated on the surface of the magnetic material substrate under the protection of inert gas; finally, densification sintering and tempering treatment are carried out. Electrospark deposition has little influence on the properties of the substrate, can accurately control the coating amount and coating area, and the equipment is simple; at the same time, the protection of inert gas can effectively inhibit the oxidation phenomenon of the light rare earth-based diffusion source during the coating process. The present invention effectively increases the utilization efficiency and diffusion depth of the light rare earth diffusion source, significantly reduces the production cost, and has the effects of preventing the oxidation of the light rare earth diffusion source, effectively improving the coercivity of the magnetic material substrate, enhancing the diffusion efficiency and reducing the cost.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth permanent magnet materials, and particularly to a grain boundary diffusion method of a light rare earth-based diffusion source based on spark deposition in a protective atmosphere. Background Art

[0002] Sintered NdFeB permanent magnet materials have high saturation magnetization intensity and high coercivity, and are indispensable materials in various motors and brakes. In recent years, the popularity of hybrid electric vehicles and electric vehicles has increased year by year, and the market demand for sintered NdFeB permanent magnet materials is also increasing.

[0003] The grain boundary diffusion technology is a commonly used method for improving the coercivity of sintered NdFeB permanent magnet materials at present. Research shows that the demagnetization process of NdFeB magnets originates from the nucleation and growth of reverse magnetic domains at the surface defects and low anisotropy field regions of NdFeB grains. Through grain boundary diffusion, a shell layer with a high anisotropy field will be formed on the surface of hard magnetic grains in the magnet, inhibiting the nucleation of reverse magnetic domains, thereby improving the coercivity of the magnet. Grain boundary diffusion requires a diffusion source coating to be first coated on the surface of the magnet, and the commonly used processes are magnetron sputtering, screen printing, and spraying.

[0004] Due to the increasing price of heavy rare earth elements, light rare earth-based alloy diffusion sources have gradually come into view. Different from heavy rare earth alloy diffusion sources, light rare earth-based alloy diffusion sources have very high chemical activity and are very easy to oxidize during the pulping process. After coating and diffusion with screen printing and spraying processes, the diffusion efficiency and diffusion depth of light rare earth elements are often low; although the coating is not easy to oxidize after coating with the magnetron sputtering process, this process has high costs and low coating efficiency. Therefore, how to effectively inhibit the oxidation of light rare earth-based diffusion sources, improve their diffusion efficiency and diffusion depth, and reduce the usage amount of diffusion sources has become an urgent problem to be solved. Summary of the Invention

[0005] The purpose of the present invention is to provide a grain boundary diffusion method of a light rare earth-based diffusion source based on spark deposition in a protective atmosphere, which has the effects of preventing the oxidation of light rare earth-based diffusion sources, effectively improving the coercivity of the magnetic material matrix, enhancing the diffusion efficiency, and reducing costs.

[0006] The above technical purpose of the present invention is achieved through the following technical solutions: A grain boundary diffusion method of a light rare earth-based diffusion source based on spark deposition in a protective atmosphere, comprising the following steps:

[0007] S1: Orient the sintered NdFeB magnetic powder with an average particle size of 2 - 10 μm under a magnetic field of 1.4 - 2 T, and press it into a green body with a pressure of 10 - 20 Mpa by an isostatic press device;

[0008] S2: Sinter the green body obtained by pressing in S1 at a temperature of 950 - 1010 °C for 1 - 3 h to obtain a semi-densified magnetic material substrate with a density of 6.5 - 7.0 g / cm 3 ³;

[0009] S3: Use a light rare earth-based alloy as the anode electrode and the semi-densified magnetic material substrate as the cathode electrode. Under the protection of an inert gas, deposit a light rare earth-based alloy coating on the magnetic material substrate by electrospark deposition to obtain a semi-densified magnet sample with a light rare earth-based alloy coating;

[0010] S4: Perform densification sintering on the semi-densified magnet sample with a light rare earth-based alloy coating obtained in S3, controlling the sintering temperature to be 1030 - 1090 °C and the sintering duration to be 2 - 5 h;

[0011] S5: Perform tempering treatment on the densified magnet sample with a light rare earth-based alloy coating sintered in S4, controlling the tempering temperature to be 500 - 800 °C and the tempering duration to be 3 - 8 h.

[0012] A further setting of the present invention is that the composition of the light rare earth-based alloy in S3 is LRE-M, where LRE is one or two of the light rare earth metal elements Nd or Pr, and the mass fraction of LRE in the LRE-M light rare earth-based alloy is 85 - 95 wt%; M is one or more of the auxiliary metal elements Cu, Al, Mn, Ga, Co, Fe, and the mass fraction of M in the LRE-M light rare earth-based alloy is 5 - 15 wt%.

[0013] By adopting the above technical solution, the present invention uses the light rare earth metal elements Nd or Pr as the main elements of the diffusion source. Compared with the method of using heavy rare earth elements as the main elements of the diffusion source in the prior art, the price of light rare earth metal elements is cheaper, which is beneficial to reducing the production and processing costs; at the same time, the addition of auxiliary metal elements makes the melting point of the light rare earth diffusion source lower than the diffusion temperature, so that the light rare earth elements can penetrate into the magnet interior faster at high temperature, improving the diffusion efficiency. In addition, the auxiliary metal elements can also optimize the grain boundaries of the magnet, thereby suppressing the nucleation of anti-magnetic domains.

[0014] A further setting of the present invention is that the light rare earth-based alloy in S3 is used as the anode electrode, its electrode diameter is 2 - 10 mm, the electrode rotation speed is 1000 - 2000 r / min, and the electrode moving speed is 1 - 20 mm / s.

[0015] By adopting the above technical solution, if the electrode diameter is too small, the coating time will be too long and the coating efficiency will be low. If the electrode diameter is too large, the density of the coating, the bonding strength between the coating and the substrate will decrease, and the coating is easy to fall off. Therefore, the present invention controls the electrode diameter to be 2 - 10 mm.

[0016] A further setting of the present invention is that the inert protective gas in S3 is nitrogen or argon, and the flow rate of nitrogen or argon is controlled to be 5 - 10 L / min, and the oxygen content in the inert gas atmosphere is controlled to be below 2 ppm.

[0017] By adopting the above technical solution, if the oxygen content is too high, the diffusion source will be oxidized during the film coating process, resulting in a decline in the quality of the coating, and even microcracks may appear. The appearance of microcracks will cause the coating to be easily peeled off; in addition, too high oxygen content will also make the thickness distribution of the coating uneven.

[0018] A further setting of the present invention is that in S3, the deposition voltage of the electrospark deposition is controlled to be 60 - 90 V, the deposition capacitance is 40 - 200 μF, the deposition angle is 70 - 80°, the deposition pressure is 0.2 - 2 N, the deposition frequency is 200 - 450 HZ, and the specific deposition time is 2 - 6 min·cm –2 。

[0019] By adopting the above technical solution, the electrospark deposition technology mainly uses high - density electric energy to coat the metal surface. Through the spark discharge between the electrode material and the metal matrix surface, the electrode material is infiltrated into the metal surface to form a surface alloying coating. The higher the deposition voltage, the faster the film coating speed, but when the voltage is too high, voids and cracks will be generated on the coating; the size of the deposition capacitance directly determines the discharge energy, which in turn affects the quality of the deposition layer. If the capacitance energy is too large, the electrode material will be vaporized and splashed, resulting in cracks in the coating; selecting an appropriate deposition angle can maintain a stable deposition arc, which is beneficial to the deposition process and obtaining the best coating; the deposition pressure will affect the coating quality and the film coating speed; the deposition frequency will affect the coating thickness, and neither too high nor too low is acceptable. If the deposition frequency is too low, the coating thickness will be too thin, so that the performance after diffusion cannot meet the requirements, and if the frequency is too high, the cost will be too high; during deposition, increasing the specific deposition time can increase the thickness of the deposition layer, but if the specific deposition time is too large, the deposition layer thickness will not only decrease but also defects such as porosity and cracks will gradually increase.

[0020] A further setting of the present invention is that the thickness of the light rare - earth - based alloy coating in S3 is controlled to be 20 - 50 μm.

[0021] By adopting the above technical solution, if the coating thickness is too large, the weight of the coating will be large and the cost requirement will be high. And the grain boundary diffusion of the present invention is mainly for cost control to achieve the purpose of cost reduction and efficiency increase. Therefore, the present invention controls the thickness of the light rare - earth - based alloy coating between 20 - 50 μm.

[0022] A further setting of the present invention is that in S3, the light rare - earth - based alloy used as the anode electrode adopts a selective area diffusion coating method to form a light rare - earth - based alloy coating with a predetermined shape on the surface of the semi - dense magnet sample.

[0023] By adopting the above technical solution, the present invention can perform selective area coating on the magnetic material substrate in a selective area diffusion manner, reduce the usage amount of the diffusion source through selective area diffusion, so as to achieve the purpose of cost saving.

[0024] In summary, the present invention has the following beneficial effects:

[0025] The present invention provides a grain boundary diffusion method of a light rare earth-based diffusion source based on electric spark deposition, including the following steps: First, semi-densification sintering is performed on magnetic powder to obtain a magnetic material substrate; secondly, with electric spark deposition as the coating means, a light rare earth-based alloy diffusion source is plated on the surface of the magnetic material substrate under gas protection; finally, densification sintering and tempering treatment are carried out. Electric spark deposition has little influence on the substrate performance, can accurately control the coating amount and coating area, and the equipment is simple; at the same time, gas protection can effectively inhibit the oxidation phenomenon of the light rare earth-based diffusion source during the coating process. The present invention effectively increases the utilization efficiency and diffusion depth of the light rare earth-based diffusion source, significantly reduces the production cost, and has the effects of preventing the oxidation of the light rare earth diffusion source, effectively improving the coercivity of the magnetic material substrate, enhancing the diffusion efficiency and reducing the cost. Description of the Drawings

[0026] Figure 1 is a structural schematic diagram of the present invention.

[0027] Figure 2 is a cross-sectional view of the sample after electric spark deposition coating of the present invention, and the sample has not been diffused.

[0028] Figure 3 is a metallographic photo at a depth of 50 μm from the surface of the magnet after diffusion in Example 1 of the present invention.

[0029] Figure 4 is a metallographic photo at a depth of 50 μm from the surface of the magnet after diffusion in Comparative Example 2 of the present invention.

[0030] Figure 5 is a schematic diagram of the sample after selective area coating by electric spark deposition on a sintered NdFeB magnetic material substrate of the present invention.

[0031] In the figure: 1. Magnetic material substrate; 2. Light rare earth-based alloy coating; 3. Electrode gun; 4. Light rare earth-based alloy electrode; 5. Plasma arc; 6. Protection gas; 7. Coating area; 8. Non-coating area. Detailed Embodiments

[0032] The present invention will be further described below with reference to the drawings.

[0033] A grain boundary diffusion method of a light rare earth-based diffusion source based on electric spark deposition under a protective atmosphere, as Figure 1-2As shown, the grain boundary diffusion device of the present invention includes an electrode gun 3 and a protective gas pipe. The protective gas pipe is used to continuously purge the inert protective gas 6 around the welding site of the electrode gun 3 at a fan-shaped angle. The materials for electrospark deposition include a light rare earth-based alloy electrode 4 and a NdFeB magnetic material substrate 1. The light rare earth-based alloy electrode 4 is melted and welded to the magnetic material substrate 1 by the high-temperature plasma arc 5 generated by the electrode gun 3 to form a light rare earth-based alloy coating 2. The steps are as follows:

[0034] S1: Orient the sintered NdFeB magnetic powder with an average particle size of 2 - 10 μm under a magnetic field of 1.4 - 2 T, and press it into a green compact with a pressure of 10 - 20 Mpa by an isostatic press device;

[0035] S2: Sinter the green compact obtained in S1 at a temperature of 950 - 1010 °C for 1 - 3 h to obtain a semi-densified magnetic material substrate with a density of 6.5 - 7.0 g / cm 3 ³;

[0036] S3: Using the light rare earth-based alloy as the anode electrode and the semi-densified magnetic material substrate as the cathode electrode, under the protection of an inert protective gas, electrospark deposition is used to deposit a light rare earth-based alloy coating on the magnetic material substrate to obtain a semi-densified magnet sample containing a light rare earth-based alloy coating;

[0037] S4: Perform densification sintering on the semi-densified magnet sample containing a light rare earth-based alloy coating obtained in S3, control the sintering temperature to be 1030 - 1090 °C, and the sintering duration to be 2 - 5 h;

[0038] S5: Perform tempering treatment on the densified magnet sample containing a light rare earth-based alloy coating obtained in S4, control the tempering temperature to be 500 - 800 °C, and the tempering duration to be controlled within 3 - 8 h.

[0039] Among them, the composition of the light rare earth-based alloy in S3 is LRE-M, where LRE is one or both of the light rare earth metal elements Nd or Pr, and the mass fraction of LRE in the LRE-M light rare earth-based alloy is 85-95 wt%; M is one or more of the auxiliary metal elements Cu, Al, Mn, Ga, Co, Fe, and the mass fraction of M in the LRE-M light rare earth-based alloy is 5-15 wt%. In the present invention, the light rare earth metal elements Nd or Pr are used as the main elements of the diffusion source. Compared with the method of using heavy rare earth elements as the main elements of the diffusion source in the prior art, the price of light rare earth metal elements is cheaper, which is beneficial to reducing the production and processing costs; at the same time, the addition of auxiliary metal elements makes the melting point of the light rare earth diffusion source lower than the diffusion temperature, so that the light rare earth elements can penetrate into the magnet interior faster at high temperatures, improving the diffusion efficiency. In addition, the auxiliary metal elements can also optimize the grain boundaries of the magnet, thereby suppressing the nucleation of anti-magnetic domains; the light rare earth-based alloy in S3 is used as the anode electrode, its electrode diameter is 2-10 mm, the electrode rotation speed is 1000-2000 r / min, and the electrode moving speed is 1-20 mm / s. If the electrode diameter is too small, the coating time will be too long and the coating efficiency will be low. If the electrode diameter is too large, the density of the coating and the bonding strength between the coating and the substrate will decrease, and the coating is easy to fall off. Therefore, in the present invention, the electrode diameter is controlled at 2-10 mm; the inert protective gas in S3 is nitrogen or argon, and the flow rate of nitrogen or argon is controlled at 5-10 L / min, and the oxygen content in the inert gas atmosphere is controlled below 2 ppm. If the oxygen content is too high, the diffusion source will be oxidized during the coating process, resulting in a decrease in the quality of the coating, and even microcracks will appear. The appearance of microcracks will cause the coating to be easy to fall off; in addition, too high oxygen content will also make the thickness distribution of the coating uneven; in S3, the deposition voltage of the electric spark deposition is controlled at 60-90 V, the deposition capacitance is 40-200 μF, the light rare earth-based alloy as the anode electrode is installed on the electrode gun, and during the deposition process, the deposition angle between the anode electrode and the magnetic material substrate is controlled at 70-80°, and the deposition pressure applied by the anode electrode on the magnetic material substrate is controlled at 0.2 - 2N, the deposition frequency is 200 - 450 HZ, the specific deposition time is 2 - 6 min·cm–2, where the specific deposition time is the ratio of the time used for electro - spark deposition to the deposition area, representing the residence time of the electrode on the substrate. The higher the deposition voltage, the faster the coating speed, but when the voltage is too high, voids and cracks will occur in the coating; the size of the deposition capacitance directly determines the size of the discharge energy, thereby affecting the quality of the deposition layer. If the capacitance energy is too large, the electrode material will be gasified and splashed, resulting in cracks in the coating; selecting an appropriate deposition angle can maintain a stable deposition arc, which is beneficial to the deposition process and obtaining the best coating; the deposition pressure will affect the coating quality and coating speed; the deposition frequency will affect the coating thickness, neither too high nor too low is acceptable. If the deposition frequency is too low, the coating thickness will be too thin, so that the performance after diffusion cannot meet the requirements, and if the frequency is too high, the cost will be too high; during deposition, increasing the specific deposition time can increase the coating thickness; but when the specific deposition time is too large, not only will the coating thickness decrease, but also defects such as porosity and cracks will gradually increase; in S3, the thickness of the light rare - earth - based alloy coating is controlled within 20 - 50 μm. If the coating thickness is too large, the weight of the coating will be large and the cost requirement will be high. And the grain - boundary diffusion of the present invention is mainly to control the cost and achieve the purpose of cost reduction and efficiency improvement. Therefore, the present invention controls the thickness of the light rare - earth - based alloy coating between 20 - 50 μm.

[0040] As Figure 5 shown, in S3, the light rare - earth - based alloy used as the anode electrode adopts a selective - area diffusion coating method to form a coating area 7 and a non - coating area 8 on the magnetic material substrate 1, so as to form a light rare - earth - based alloy coating with a predetermined shape on the surface of the semi - dense magnet sample. The present invention can coat the light rare - earth - based alloy by selective - area diffusion, reducing the usage amount of the diffusion source through selective - area diffusion, thereby achieving the purpose of cost savings. Specific Embodiment 1

[0042] A grain - boundary diffusion method of a light rare - earth - based diffusion source based on electro - spark deposition under a protective atmosphere, comprising the following steps:

[0043] S1: Press the sintered neodymium - iron - boron magnetic powder with an average particle size of 2.8 μm and a grade of N38 under a magnetic field of 2 T at a pressure of 14 Mpa to obtain a green compact;

[0044] S2: Sinter the green compact at 950 °C for 3 h to obtain a semi - dense blank with a density of 6.8 g / cm 3 ;

[0045] S3: The composition is Pr 85 Al 10The light rare earth-based alloy with Cu5 (wt%) is used as the anode electrode, the electrode diameter is 6 mm, the electrode rotation speed is 1200 r / min, the semi-densified blank is used as the cathode electrode, and under the protection of high-purity argon gas with a flow rate of 5 L / min, the anode electrode coats the entire upper surface of the blank, and the coating thickness is 30 μm. During coating, the moving speed of the anode electrode is 10 mm / s, the deposition voltage of the electrospark deposition is 80 V, the deposition angle is 78.8°, the deposition pressure is 1 N, the deposition frequency is 300 HZ, and the specific deposition time is 4 min·cm –2 , and a semi-densified magnet sample with a light rare earth-based alloy coating is obtained. The mass of the sample increases by 1% after coating compared with before coating;

[0046] S4: The sample is subjected to densification sintering at a sintering temperature of 1060 °C for 4 h; then directly subjected to tempering treatment at 620 °C for 5 h.

[0047] Figure 3 It is a surface morphology photo of the sample prepared by the method of Specific Example 1 observed under an electron microscope. The white area in the figure is the grain boundary phase, and the gray area is the Nd2Fe 14 B main phase. It can be observed from the figure that a large number of continuously networked grain boundary phases isolate the Nd2Fe 14 B main phases from each other, which weakens the exchange coupling effect between adjacent main phase grains. This structure is beneficial to the improvement of coercivity.

[0048] Comparative Example 1

[0049] A grain boundary diffusion method of a light rare earth-based diffusion source based on electrospark deposition. The difference between Comparative Example 1 and Specific Example 1 is that during electrospark deposition, the electrode is not protected by high-purity argon gas and is directly exposed to the air.

[0050] Comparative Example 2

[0051] A grain boundary diffusion method of a light rare earth-based diffusion source based on screen printing, including the following steps;

[0052] S1: The sintered neodymium iron boron magnetic powder with an average particle size of 2.8 μm and a grade of N38 is compacted under a magnetic field of 2 T at a pressure of 14 Mpa to obtain a green compact;

[0053] S2: The green compact is sintered at 1060 °C for 5 h to obtain a densified blank with a density of 7.6 g / cm 3 ;

[0054] S3: The light rare earth-based alloy powder with the composition of Pr 85 Al 10 Cu5 (wt%) is mixed with alcohol and PVB in a ratio of 1:1:1 to prepare a slurry, where Pr 85Al 10 The average particle size of the Cu5 alloy powder is 7.6 μm;

[0055] S4: Coat the slurry on the surface of the blank, and then dry it in an oven at 100 °C. The mass of the blank after coating increases by 1% compared with that before coating;

[0056] S5: Perform the optimal diffusion treatment on the sample at 900 °C for 10 h, and then directly perform the tempering treatment at 620 °C for 5 h.

[0057] Figure 4 Figure showing the surface morphology of the sample prepared by the existing technical method of screen printing grain boundary diffusion for Comparative Example 2. The white areas in the figure are the grain boundary phases, and the gray areas are the Nd2Fe 14 B matrix phase, and Figure 3 different, Figure 4 there is a lack of a continuous network-like grain boundary phase between adjacent matrix phase grains in , and the matrix phase grains are directly in contact, which makes the adjacent matrix phase grains form a large grain group. The demagnetization of one matrix phase grain will chain-reactionly drive the demagnetization of adjacent grains, which makes the coercivity of the magnet prepared by the method of Comparative Example 2 lower than that of the magnet prepared by the method of Specific Example 1.

[0058] The effects of the methods of Specific Example 1, Comparative Example 1, and Comparative Example 2 on the performance of the N38 magnet are shown in Table 1 below:

[0059] Table 1: Effects of Specific Example 1, Comparative Example 1, and Comparative Example 2 on the performance of the N38 magnet

[0060]

[0061] As can be seen from Table 1, when comparing Specific Example 1, Comparative Example 1, and Comparative Example 2, the remanence and squareness of the three change less relative to the N38 magnetic material substrate. However, compared with the grain boundary diffusion methods of Comparative Example 1 and Comparative Example 2, the intrinsic coercivity of the sample obtained by the grain boundary diffusion method based on protective atmosphere electro-discharge deposition in Specific Example 1 is increased more. Specific Example 2

[0063] A grain boundary diffusion method of a light rare earth-based diffusion source based on protective atmosphere electro-discharge deposition, comprising the following steps:

[0064] S1: Press the sintered NdFeB magnet powder with a grade of N38 and an average particle size of 2.8 μm under a magnetic field of 2 T at a pressure of 14 Mpa to obtain a green compact;

[0065] S2: Sinter the green compact at 950 °C for 3 h to obtain a semi-dense blank with a density of 6.8 g / cm 3 of;

[0066] S3: Use a light rare earth-based alloy with a composition of Pr 85 Nd 10 Fe 5 (wt%) as the anode electrode. The electrode diameter is 6 mm, the electrode rotation speed is 1200 r / min, and the semi-densified blank is used as the cathode electrode. Under the protection of high-purity argon gas with a flow rate of 5 L / min, the anode electrode coats the entire upper surface of the blank, and the coating thickness is 25 μm. During coating, the moving speed of the anode electrode is 10 mm / s, the deposition voltage of the electric spark deposition is 80 V, the deposition angle is 78.8°, the deposition pressure is 1 N, the deposition frequency is 300 HZ, and the specific deposition time is 4 min·cm –2 , obtaining a semi-densified magnet sample with a light rare earth-based alloy coating. The mass of the sample increases by 0.8% after coating compared to before coating;

[0067] S4: Conduct densification sintering on the sample at a sintering temperature of 1060 °C for 4 h; then directly perform tempering treatment at 620 °C for 5 h.

[0068] The difference between Specific Example 2 and Specific Example 1 is as follows: First, the diffusion source compositions of Example 2 and Example 1 are different. The composition of the diffusion source in Example 1 is Pr 85 Al 10 Cu 5, and the composition of the diffusion source in Example 2 is Pr 85 Nd 10 Fe 5； Secondly, the mass increase after coating is different for the two. In Example 1, the mass increases by 1% after coating compared to before coating, and in Example 2, the mass increases by 0.8% after coating compared to before coating.

[0069] Comparative Example 3

[0070] A grain boundary diffusion method of a light rare earth-based diffusion source based on electric spark deposition. The difference between Comparative Example 3 and Specific Example 2 is that during electric spark deposition, the electrode is not protected by high-purity argon gas and is directly exposed to the air.

[0071] Comparative Example 4

[0072] A grain boundary diffusion method of a light rare earth-based diffusion source based on screen printing, comprising the following steps:

[0073] S1: Compress sintered neodymium iron boron magnetic powder with an average particle size of 2.8 μm and a grade of N38 under a magnetic field of 2 T at a pressure of 14 Mpa to obtain a compacted blank;

[0074] S2: Sinter the compacted blank at 1060 °C for 5 h to obtain a densified blank with a density of 7.6 g / cm 3 ;

[0075] S3: Mix the light rare earth-based alloy powder with a composition of Pr 85 Nd 10 Fe5 (wt%) with alcohol and PVB in a ratio of 1:1:1 to prepare a slurry. Among them, Pr 85 Nd 10 The average particle size of the Fe5 alloy powder is 7.3 μm;

[0076] S4: Coat the slurry on the surface of the blank, and then dry it in an oven at 100 °C. The mass of the blank after coating increases by 1% compared with that before coating;

[0077] S5: Perform the optimal diffusion treatment on the sample at 890 °C for 10 h, and then directly perform the tempering treatment at 620 °C for 5 h.

[0078] Among them, the screen printing grain boundary diffusion method of Comparative Example 4 is the prior art, and one difference between Comparative Example 4 and Specific Example 2 is that its mass increases by 1% after coating compared with that before coating.

[0079] The effects of the methods of Specific Example 2, Comparative Example 3 and Comparative Example 4 on the performance of N38 magnets are shown in Table 2 below:

[0080] Table 2: Effects of Specific Example 2, Comparative Example 3 and Comparative Example 4 on the performance of N38 magnets

[0081]

[0082] As can be seen from Table 2, compared with Comparative Example 4 with a coating weight gain of 1 wt%, Example 2 with a coating weight gain of 0.8 wt% has a higher coercivity, and the remanence and squareness are basically the same; compared with Comparative Example 3 with the same weight gain, Example 2 has a greater improvement in coercivity and the remanence is basically the same. Thus, it can be seen that the electric spark deposition based on a protective atmosphere can improve the use efficiency of the light rare earth diffusion source and reduce the usage amount.

[0083] The above description is only a preferred embodiment of the present invention. Therefore, any equivalent changes or modifications made according to the structures, features and principles described in the scope of the present invention patent application are included in the scope of the present invention patent application.

Claims

1. A grain boundary diffusion method of a light rare earth-based diffusion source based on protective atmosphere electrospark deposition, characterized in that, It includes the following steps: S1: Orient the sintered NdFeB magnetic powder with an average particle size of 2 - 10 μm under a magnetic field of 1.4 - 2 T, and press it into a green compact with a pressure of 10 - 20 Mpa by an isostatic press equipment; S2: Sinter the green compact obtained by pressing in S1 at a temperature of 950 - 1010 °C for 1 - 3 h to obtain a semi-densified magnetic material substrate with a density of 6.5 - 7.0 g / cm 3 ; S3: Use the light rare earth-based alloy as the anode electrode and the semi-densified magnetic material substrate as the cathode electrode. Under the protection of an inert protective gas, deposit a light rare earth-based alloy coating on the magnetic material substrate by electrospark deposition to obtain a semi-densified magnet sample containing a light rare earth-based alloy coating; S4: Perform densification sintering on the semi-densified magnet sample containing a light rare earth-based alloy coating obtained in S3, control the sintering temperature to be 1030 - 1090 °C, and the sintering duration to be 2 - 5 h; S5: Perform tempering treatment on the densified magnet sample containing a light rare earth-based alloy coating sintered in S4, control the tempering temperature to be 500 - 800 °C, and the tempering duration to be controlled within 3 - 8 h.

2. The grain boundary diffusion method of a light rare earth-based diffusion source based on protective atmosphere electrospark deposition according to claim 1, characterized in that: The light rare earth-based alloy in S3 has a composition of LRE-M, where LRE is one or two of the light rare earth metal elements Nd or Pr, and the mass fraction of LRE in the LRE-M light rare earth-based alloy is 85 - 95 wt%; M is one or more of the auxiliary metal elements Cu, Al, Mn, Ga, Co, Fe, and the mass fraction of M in the LRE-M light rare earth-based alloy is 5 - 15 wt%.

3. The grain boundary diffusion method of a light rare earth-based diffusion source based on protective atmosphere electrospark deposition according to claim 1, characterized in that: The light rare earth-based alloy in S3 is used as the anode electrode, its electrode diameter is 2 - 10 mm, the electrode rotation speed is 1000 - 2000 r / min, and the electrode moving speed is 1 - 20 mm / s.

4. A grain boundary diffusion method of a light rare earth-based diffusion source based on protective atmosphere electrospark deposition according to claim 1, characterized in that: The inert protective gas in S3 is nitrogen or argon, and control the flow rate of nitrogen or argon to be 5 - 10 L / min, and control the oxygen content in the inert gas atmosphere to be below 2 ppm.

5. The grain boundary diffusion method of a light rare earth-based diffusion source based on protective atmosphere electrospark deposition according to claim 1, characterized in that: The deposition voltage of S3 controlled by ESD was 60-90 V, the deposition capacitance was 40-200 μF, the deposition angle was 70-80°, the deposition pressure was 0.2-2 N, the deposition frequency was 200-450 Hz, and the specific deposition time was 2-6 min·cm -2 .

6. The grain boundary diffusion method of a light rare earth-based diffusion source based on protective atmosphere electrospark deposition according to claim 1, characterized in that: The thickness of the light rare earth-based alloy coating in S3 is controlled to be 20 - 50 μm.

7. A grain boundary diffusion method of a light rare earth-based diffusion source based on a protective atmosphere electrospark deposition according to claim 1, characterized in that: The light rare earth-based alloy used as the anode electrode in S3 adopts a selective area diffusion coating method to form a light rare earth-based alloy coating with a predetermined shape on the surface of the semi-densified magnet sample.

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