Neodymium-iron-boron quick-setting casting sheet, neodymium-iron-boron magnetic powder and preparation method

Abstract

The invention discloses a neodymium-iron-boron quick-setting casting sheet, neodymium-iron-boron magnetic powder and a preparation method. The neodymium iron boron quick-setting casting piece is provided with a roller attaching surface and a free surface, and the neodymium iron boron quick-setting casting piece is composed of a Re2Fe14B main phase and an intergranular Re-rich phase and does not contain an alpha-Fe phase; the main phase has a columnar crystal morphology along the section in the direction from the roller attaching surface to the free surface, the width of the columnar crystal is 2.5-3.7 microns, dendritic crystals are distributed on the two sides of the columnar crystal, the width of the dendritic crystals is close to the width of the columnar crystal, Re-rich phases are attached to the two sides of the columnar crystal and the two sides of the dendritic crystals, and the Re-rich phases are uniformly distributed along the columnar crystal and the dendritic crystals. The neodymium-iron-boron quick-setting casting piece is beneficial to improving the yield of neodymium-iron-boron magnetic powder and improving the normal distribution of the granularity of the neodymium-iron-boron magnetic powder.

Description

Technical Field

[0001] The invention relates to a NdFeB rapid solidification casting sheet, NdFeB magnetic powder and a preparation method thereof. Background Art

[0002] Neodymium iron boron magnets, as the third generation of rare earth permanent magnet materials, have been widely used in consumer electronics, new energy vehicles, medical equipment, wind power generation and other fields.

[0003] At present, the magnetic energy product of NdFeB magnets is very close to its theoretical value, but the coercive force can only reach about 30% of the theoretical value. The research on coercive force mainly focuses on the subsequent processes of magnets, such as grain boundary modification and grain boundary diffusion of magnets. In recent years, the research on optimizing the rapid solidification casting sheet and ultimately improving the magnetic properties of magnets has gradually attracted the attention of scientific researchers.

[0004] CN102031445A discloses a method for preparing magnetic powder, comprising the following steps: putting raw materials into a rapid solidification furnace, smelting in an inert gas or nitrogen protective atmosphere, pouring the molten liquid onto a copper roller with a roller speed of 2 to 4 m / s, and spinning it into a rapid solidification thin strip with an average thickness of 0.1 to 0.3 mm; then performing hydrogen crushing and air flow milling to obtain magnetic powder with an average surface area particle size of 1.5 to 3 μm. By optimizing the rapid solidification process and adjusting the formula, the surface area average particle size of the air flow milled magnetic powder is reduced, thereby reducing the average grain size of the sintered NdFeB permanent magnet material. The method controls the columnar crystals in the rapid solidification casting to maintain a relatively small size as much as possible by controlling the process parameters.

[0005] CN106992053A discloses a Y-containing rare earth permanent magnet alloy quick-setting sheet, in which Y element is added to the rare earth alloy Re-Fe-B, and the alloy quick-setting sheet throwing technology is adopted to obtain a texture composed of main phase columnar crystals and intercrystalline phases, wherein Y mainly enters the main phase to form a 2:14:1 crystal structure, and forms a Y-poor area in the rare earth-rich phase. The alloy quick-setting sheet can effectively adjust the distribution of rare earth elements in the main phase columnar crystals and intercrystalline phases in the quick-setting sheet by regulating the Y content. In the preparation process of the quick-setting sheet, the proportion of columnar crystals of suitable size in the quick-setting casting sheet is increased by controlling reasonable process parameters. Although secondary crystals also exist in the quick-setting sheet, the size of the secondary crystals is too small, and they will be screened out after screening by the grading wheel during the airflow milling process, and cannot be returned to the silo, which is not conducive to improving the recovery rate of magnetic powder.

[0006] CN108257751A discloses an alloy casting sheet for preparing fine-grained rare earth sintered magnets, wherein the alloy casting sheet has a roller-attached surface and a free surface, and comprises R2Fe 14The grains with B-type compounds as the main phase include non-columnar grains and columnar grains along the temperature gradient section, among which the non-columnar grains with an aspect ratio of 0.3 to 2 account for ≥60% of the area percentage of the grains and ≥75% of the number of grains; the columnar grains with an aspect ratio of ≥3 account for ≤15% of the area percentage of the grains and ≤10% of the number of grains. The non-columnar grains in the alloy casting account for a large proportion, which is not conducive to improving the recovery rate of magnetic powder. Summary of the invention

[0007] An object of the present invention is to provide a NdFeB rapid solidification casting sheet, which is beneficial to improving the recovery rate of NdFeB magnetic powder and improving the normal distribution of the particle size of NdFeB magnetic powder.

[0008] Another object of the present invention is to provide a method for preparing the NdFeB rapid solidification casting sheet as described above.

[0009] Another object of the present invention is to provide a method for preparing NdFeB magnetic powder.

[0010] Another object of the present invention is to provide a neodymium iron boron magnetic powder.

[0011] The present invention adopts the following technical solutions to achieve the above-mentioned purpose.

[0012] On the one hand, the present invention provides a NdFeB quick-solidification casting sheet, which has a roller-attached surface and a free surface, and the NdFeB quick-solidification casting sheet is composed of Re2Fe 14 The B main phase and the intergranular Re-rich phase are composed, and no α-Fe phase is contained; wherein Re is a rare earth element, selected from one or more of La, Ce, Y, Pr, Nd, Gd, Ho, Dy, and Tb, and Nd must be contained;

[0013] In the cross section along the direction from the roller surface to the free surface, the main phase has a columnar crystal morphology. The width of the columnar crystal is 2.5 to 3.7 μm. There are dendrites distributed on both sides of the columnar crystal. The width of the dendrites is close to that of the columnar crystals. Re-rich phases are attached to both sides of the columnar crystals and dendrites, and the Re-rich phases are evenly distributed along the columnar crystals and dendrites.

[0014] According to the NdFeB rapid solidification casting sheet of the present invention, preferably, the NdFeB rapid solidification casting sheet does not have an amorphous region.

[0015] According to the NdFeB rapid solidification casting sheet of the present invention, preferably, the thickness of the NdFeB rapid solidification casting sheet is 240-300 μm.

[0016] On the other hand, the present invention provides a method for preparing the above-mentioned NdFeB rapid solidification casting sheet, comprising the following steps:

[0017] 1) Smelting the raw materials required for the NdFeB rapid solidification casting sheet at 1400-1500°C to obtain an alloy solution;

[0018] 2) Casting the alloy solution at 1360-1480° C. and cooling it through a cooling roller to obtain the NdFeB rapid solidification casting sheet; wherein the casting temperature is lower than the smelting temperature; during the casting process, the linear speed of the cooling roller is controlled to be 1.6-1.9 m / s.

[0019] According to the preparation method of the present invention, preferably, the raw materials required for the NdFeB rapid solidification casting sheet include Re, T and B, Re is selected from one or more of La, Ce, Y, Pr, Nd, Gd, Ho, Dy, Tb, and must contain Nd; T includes Fe.

[0020] According to the preparation method of the present invention, preferably, T further comprises one or more of Cu, Al, Ga, Co, Zr, Ni and Nb.

[0021] According to the preparation method of the present invention, preferably, the linear speed of the cooling roller is controlled to be 1.6-1.8 m / s.

[0022] According to the preparation method of the present invention, preferably, both step 1) and step 2) are carried out under vacuum conditions, and the vacuum degree is less than 1.0×10 -1 Pa.

[0023] In another aspect, the present invention provides a method for preparing NdFeB magnetic powder, comprising the following steps:

[0024] According to the above preparation method, a NdFeB rapid solidification casting sheet is prepared;

[0025] The NdFeB rapid solidification casting sheet is subjected to a coarse crushing process and a fine crushing process to obtain NdFeB magnetic powder.

[0026] In another aspect, the present invention provides a NdFeB magnetic powder prepared by the above preparation method.

[0027] The NdFeB rapid solidification casting sheet of the present invention is beneficial to improving the yield of NdFeB magnetic powder and improving the normal distribution of the particle size of NdFeB magnetic powder. According to the preferred technical scheme of the present invention, the present invention controls the casting temperature and the linear speed of the cooling roller within a specific range, so as to form a NdFeB rapid solidification casting sheet with a microstructural structure in which the width of the dendrites (secondary dendrites) and the columnar crystals (primary columnar crystals) are close, the width of the columnar crystals is 2.5 to 3.7 μm, both sides of the columnar crystals and the dendrites are attached with Re-rich phases, and the Re-rich phases are evenly distributed along the columnar crystals and the dendrites. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a microstructure diagram of the NdFeB rapid solidification casting sheet obtained in Example 1 of the present invention.

[0029] Figure 2This is the microstructure diagram of the NdFeB rapid solidification casting sheet obtained by traditional technology. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0031] The "vacuum degree" mentioned in the present invention refers to absolute vacuum degree; the smaller the value, the higher the vacuum degree. The "inert atmosphere" mentioned in the present invention refers to the environment formed under the protection of inert gas, and the inert gas can be helium, argon or nitrogen.

[0032] The inventors of the present application have found through research that the actual microstructure of the current NdFeB rapid solidification casting sheet is very different from the ideal microstructure, for example, the width of the primary main phase columnar crystals is uneven, there are fine secondary dendrites on both sides of the columnar crystals, the rare earth-rich phase (Re-rich phase) is discontinuously distributed, etc. Such a microstructure will greatly affect the powder production yield of the subsequent process and the physical properties of the NdFeB magnetic powder particles. For example, the coverage rate of the rare earth-rich phase on the main phase powder particles is low, which ultimately reduces the magnetic coupling effect between the main phase grains of the magnet, making it difficult to improve the coercive force.

[0033] <NdFeB rapid solidification casting sheet>

[0034] The NdFeB quick solidification casting sheet provided by the present invention is composed of Re2Fe 14 The main phase B and the intergranular Re-rich phase are composed, and do not contain α-Fe phase. The NdFeB rapid solidification casting sheet has a roller-attached surface and a free surface. The cross section along the roller-attached surface (the surface of the casting sheet in contact with the cooling roller during processing) to the free surface (the surface of the casting sheet opposite to the roller-attached surface) has a columnar crystal morphology, and the width of the columnar crystal is 2.5 to 3.7 μm. Dendrites are distributed on both sides of the columnar crystals, and the width of the dendrites is close to the width of the columnar crystals. Re-rich phases are attached to both sides of the columnar crystals and dendrites, and the Re-rich phases are evenly distributed along the columnar crystals and dendrites. In the preferred technical solution, there is no amorphous region in the NdFeB rapid solidification casting sheet. The NdFeB rapid solidification casting sheet with such a microstructure is conducive to obtaining an increased yield of NdFeB magnetic powder and optimizing the normal distribution of the particle size of NdFeB magnetic powder. This can reduce the amount of heavy rare earth elements used and improve the magnetic properties of the magnet (including remanence and coercive force). So far, there is no report on the NdFeB rapid solidification casting sheet having the microstructure described in the present invention.

[0035] In the present invention, Re is a rare earth element, including light rare earth elements and heavy rare earth elements. Light rare earth elements are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm) and europium (Eu). Heavy rare earth elements are gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu) and yttrium (Y).

[0036] According to one embodiment of the present invention, Re is selected from one or more of La, Ce, Y, Pr, Nd, Gd, Ho, Dy, and Tb, and must contain Nd.

[0037] According to another embodiment of the present invention, Re is at least one element selected from Pr and Nd, and Nd must be contained.

[0038] According to a specific embodiment of the present invention, Re is Nd and Pr.

[0039] In the present invention, B is boron.

[0040] The NdFeB quick solidification casting sheet of the present invention is formed by raw materials such as Re, T and B. T includes Fe. T can also include one or more selected from Cu, Al, Ga, Co, Zr, Ni and Nb. In some embodiments, T is Fe. In other embodiments, T is a combination of Fe and other metal elements, that is, part of Fe is replaced by other metal elements. Other metal elements are selected from one or more of Cu, Al, Ga, Co, Zr, Ni and Nb.

[0041] In the present invention, based on the total weight of the NdFeB rapid solidification casting sheet, the Re content is 29-33wt%, preferably 30-33wt%, more preferably 30-32wt%. The B content is 0.88-1.1wt%, preferably 0.89-1.0wt%, more preferably 0.90-1.0wt%. T is the balance.

[0042] According to a specific embodiment of the present invention, based on the total weight of the NdFeB rapid solidification casting sheet, the Re content is 29-33wt%, the B content is 0.88-1.1wt%, and Fe is the balance.

[0043] According to another specific embodiment of the present invention, based on the total weight of the NdFeB rapid solidification casting sheet, the Re content is 29-33wt%, the B content is 0.88-1.1wt%, T is the balance, and T is a combination of Fe and other metal elements, wherein the content of other metal elements is 0.9-2.1wt%, and other metal elements are selected from one or more of Cu, Al, Ga, Co, Zr, Ni and Nb.

[0044] In the present invention, the thickness of the NdFeB rapid solidification casting sheet is 240-300 μm, preferably 250-290 μm, for example, 250 μm, 260 μm, 270 μm, 280 μm, or 290 μm.

[0045] <Method for preparing NdFeB rapid solidification casting sheet>

[0046] The present invention also provides a method for preparing the NdFeB rapid solidification casting sheet as described above, comprising the following steps: 1) a step of forming an alloy solution; and 2) a step of casting, which is described in detail below.

[0047] Alloy solution formation steps

[0048] The raw materials required for the NdFeB rapid casting sheet are melted at 1400-1500°C to obtain an alloy solution. According to one embodiment of the present invention, the raw materials required for the NdFeB rapid casting sheet are melted at 1400-1500°C and kept at 1400-1500°C for 5-10 minutes to obtain an alloy solution.

[0049] In the present invention, smelting is carried out in a vacuum or inert atmosphere. Smelting is preferably carried out in a vacuum melting furnace (such as a vacuum medium frequency rapid solidification induction furnace). The smelting temperature can be 1400-1500°C, preferably 1420-1480°C, and more preferably 1430-1470°C. The insulation temperature can be 1400-1500°C, preferably 1430-1480°C, and more preferably 1440-1480°C. The insulation time at the insulation temperature can be 5-10 minutes, preferably 5-8 minutes, and more preferably 5-6 minutes. In this way, the raw materials can be completely melted and energy consumption can be saved.

[0050] In the present invention, the insulation temperature may be slightly higher than the smelting temperature by about 10°C.

[0051] According to a specific embodiment of the present invention, the raw materials required for the NdFeB rapid solidification casting sheet are placed in a crucible, and then the crucible is placed in a vacuum melting furnace, and the vacuum melting furnace is evacuated to 1×10 -1 Pa, heat to 1420-1470°C to melt the raw materials, and keep them at 1430-1480°C for 5-10 minutes to obtain an alloy solution.

[0052] Casting steps

[0053] The alloy solution is cast at 1360-1480°C and cooled by a cooling roller to obtain the NdFeB rapid solidification casting sheet. During the casting process, the linear speed of the cooling roller is controlled to be 1.6-1.9 m / s. This is conducive to obtaining a NdFeB rapid solidification casting sheet with a specific microstructure. After a lot of research and experiments, the present invention has found that the NdFeB rapid solidification casting sheet of the present invention can be obtained by controlling the casting temperature and the linear speed of the cooling roller within a specific range. Such a NdFeB rapid solidification casting sheet is conducive to improving the yield of NdFeB magnetic powder and optimizing the normal distribution of the particle size of the NdFeB magnetic powder.

[0054] In the present invention, the casting temperature is lower than the melting temperature. The casting temperature may be 1360 to 1480°C, preferably 1380 to 1460°C, more preferably 1400 to 1440°C, and further preferably 1400 to 1420°C. The linear speed of the cooling roller is controlled to be 1.6 to 1.9 m / s, preferably 1.6 to 1.8 m / s, and more preferably 1.6 to 1.7 m / s. The cooling roller may use circulating water as a coolant. The cooling rollers are those known in the art, and their structure is not particularly limited.

[0055] <NdFeB magnetic powder and preparation method>

[0056] The present invention also provides a method for preparing NdFeB magnetic powder, comprising: (1) preparing NdFeB rapid solidification casting sheets; (2) coarse crushing step; and (3) fine crushing step, which is described in detail below.

[0057] Preparation steps of NdFeB rapid solidification casting sheet

[0058] The NdFeB rapid solidification casting sheet is obtained according to the preparation method as described above, which will not be described in detail here.

[0059] Coarse crushing step

[0060] The NdFeB rapid solidification casting sheet is coarsely crushed to obtain coarse magnetic powder.

[0061] In the present invention, in order to prevent the NdFeB rapid solidification casting sheet and the coarse magnetic powder obtained by crushing the NdFeB rapid solidification casting sheet from being oxidized, the coarse crushing of the present invention is carried out in a vacuum or inert atmosphere. The coarse crushing process is to crush the NdFeB rapid solidification casting sheet into coarse magnetic powder with larger particle size.

[0062] In the coarse crushing process, the NdFeB rapid solidification casting sheet is crushed into coarse magnetic powder by a mechanical crushing process and / or a hydrogen crushing process. The mechanical crushing process is to use a mechanical crushing device to crush the NdFeB rapid solidification casting sheet into coarse magnetic powder. The mechanical crushing device can be selected from a jaw crusher or a hammer crusher. The hydrogen crushing process includes the following steps: firstly, the NdFeB rapid solidification casting sheet absorbs hydrogen, and the volume expansion of the NdFeB rapid solidification casting sheet lattice is caused by the reaction of the NdFeB rapid solidification casting sheet with hydrogen to crush the NdFeB rapid solidification casting sheet, and then heated to dehydrogenate to obtain coarse magnetic powder. The present invention preferably uses a hydrogen crushing process. According to a preferred specific embodiment of the present invention, the hydrogen crushing process of the present invention is preferably carried out in a hydrogen crushing furnace. The hydrogen pressure used during crushing is 0.02-0.2MPa, preferably 0.08-0.15MPa. The vacuum dehydrogenation temperature is 400-800°C, preferably 550-600°C.

[0063] Fine crushing step

[0064] The coarse magnetic powder is finely crushed to obtain NdFeB magnetic powder. The process of forming NdFeB magnetic powder is to grind the coarse magnetic powder into NdFeB magnetic powder.

[0065] In the process of forming NdFeB magnetic powder, the coarse magnetic powder is crushed into NdFeB magnetic powder by ball milling and / or air flow milling. The ball milling process is to crush the coarse magnetic powder into NdFeB magnetic powder by a mechanical ball milling device. The mechanical ball milling device can be selected from rolling ball milling, vibrating ball milling or high-energy ball milling. The air flow milling process is to use air flow to accelerate the coarse magnetic powder and then collide with each other to crush it. The air flow can be a nitrogen flow, preferably a high-purity nitrogen flow. The N2 content in the high-purity nitrogen flow can be above 99.0wt%, preferably above 99.9wt%. The pressure of the air flow can be 0.1-2.0MPa, preferably 0.5-1.0MPa, and more preferably 0.6-0.7MPa.

[0066] The present invention preferably adopts the air flow milling process.

[0067] In the present invention, the normal distribution of the magnetic powder is better, that is, the particle size is more uniform. The yield of the NdFeB magnetic powder is above 96%, preferably above 97%.

[0068] In the present invention, the yield of NdFeB magnetic powder refers to the weight ratio of the NdFeB magnetic powder after airflow milling to the weight ratio of the coarse magnetic powder before airflow milling.

[0069] In the present invention, the obtained NdFeB magnetic powder can be subjected to compression molding and sintering treatment to obtain a NdFeB magnet. The compression molding and sintering treatment can adopt those known in the art. Such NdFeB magnetic powder with a relatively uniform particle size can reduce the amount of heavy rare earth elements used and improve the magnetic properties of the magnet.

[0070] <Test Method>

[0071] Microstructure of NdFeB rapid solidification casting sheet: The obtained NdFeB rapid solidification casting sheet was cut along the roller surface and the free surface to obtain a cross section (i.e. the obtained cross section was parallel to the cooling direction of the alloy solution). Then, a Zeiss Sigma 500 field emission electron microscope was used to observe the cross section.

[0072] Determination of D90 and D10: Determined by laser particle size analyzer.

[0073] Example 1

[0074] Prepare the raw materials according to Nd 30wt%, B 1.0wt%, and the balance Fe. Put the raw materials into a crucible, and then put the crucible into a vacuum melting furnace. Evacuate the vacuum melting furnace to 9.0×10 -3 Pa, heat to 1440°C to melt the raw materials, and keep them at 1450°C for 5 minutes to obtain an alloy solution.

[0075] The linear speed of the cooling roller is adjusted to 1.6m / s, and the casting is started when the alloy solution is cooled to 1420℃. The cooling roller is cooled by circulating water coolant. After the casting is completed, the NdFeB rapid solidification casting sheet is obtained after cooling to room temperature. The thickness of the obtained NdFeB rapid solidification casting sheet is 250-300μm.

[0076] The field emission electron microscope test results of the cross section (the cross section parallel to the cooling direction of the alloy solution, that is, the cross section along the direction from the roller surface to the free surface) of the NdFeB rapid solidification casting sheet obtained in this embodiment are shown in FIG. Figure 1 The NdFeB rapid solidification casting sheet is composed of Re2Fe 14 The B main phase and the intergranular Re-rich phase are composed, and there is no α-Fe phase (the morphology of the α-Fe phase is black fishbone-shaped and is not found in the figure). Figure 1 It can be seen that along the cross section from the roller surface to the free surface, the main phase has a columnar crystal morphology, the width of the columnar crystal is 2.5-3.7 μm, and there are dendrites on both sides of the columnar crystal ( Figure 1 In the figure, secondary dendrites refer to dendrites), the width of the dendrites is close to that of the columnar crystals, Re-rich phases are attached to both sides of the columnar crystals and dendrites, and the Re-rich phases are evenly distributed along the columnar crystals and dendrites. There is no amorphous region in the NdFeB rapid solidification casting sheet.

[0077] Example 2

[0078] Prepare the raw materials according to PrNd 30.5wt%, B 0.91wt%, Co 0.6wt%, Cu 0.15wt%, Ga 0.15wt%, Nb 0.2wt%, and the balance Fe. Put the raw materials into a crucible, and then put the crucible into a vacuum melting furnace. Evacuate the vacuum melting furnace to 9.0×10 -3 Pa, heat until the raw materials are melted, keep warm at 1450℃ for 5min to obtain alloy solution.

[0079] The linear speed of the cooling roller is adjusted to 1.7m / s, and the casting is started when the alloy solution is cooled to 1400℃. The cooling roller is cooled by circulating water coolant. After the casting is completed, the NdFeB rapid solidification casting sheet is obtained after cooling to room temperature. The thickness of the obtained NdFeB rapid solidification casting sheet is 250-300μm.

[0080] The NdFeB rapid solidification casting sheet obtained in this embodiment is composed of Re2Fe 14 The main phase B and the intergranular Re-rich phase are composed, and α-Fe phase is not contained. In the cross section from the roller surface to the free surface, the main phase has a columnar crystal morphology, the width of the columnar crystal is 2.5-3.7 μm, and dendrites are distributed on both sides of the columnar crystals. The width of the dendrites is close to that of the columnar crystals. Re-rich phases are attached to both sides of the columnar crystals and dendrites, and the Re-rich phases are evenly distributed along the columnar crystals and dendrites. There is no amorphous region in the NdFeB rapid solidification casting sheet.

[0081] Example 3 - Preparation of NdFeB Magnetic Powder

[0082] The NdFeB rapid solidification casting sheet obtained in Example 1 is provided.

[0083] The NdFeB rapid solidification casting sheet was hydrogen crushed under the conditions of hydrogen supply pressure of 0.12MPa for 50 minutes and dehydrogenation for 2 hours to obtain coarse magnetic powder.

[0084] The coarse magnetic powder is jet-milled at a classifying wheel speed of 4300 rpm to obtain NdFeB magnetic powder.

[0085] The D90 / D10 of the NdFeB magnetic powder is 5.44. The yield of the NdFeB magnetic powder is 97.0%.

[0086] Example 4 - Preparation of NdFeB Magnetic Powder

[0087] The NdFeB rapid solidification casting sheet obtained in Example 2 is provided.

[0088] The NdFeB rapid solidification casting sheet was hydrogen crushed under the conditions of hydrogen supply pressure of 0.12MPa for 50 minutes and dehydrogenation for 2 hours to obtain coarse magnetic powder.

[0089] The coarse magnetic powder is jet-milled at a classifying wheel speed of 4300 rpm to obtain NdFeB magnetic powder.

[0090] The D90 / D10 of the NdFeB magnetic powder is 5.00. The yield of the NdFeB magnetic powder is 97.7%.

[0091] Table 1

[0092]

[0093] In actual production, the field emission electron microscope test results of the cross section of the NdFeB rapid solidification casting sheet obtained by the traditional process are shown in Figure 2 .and Figure 2 compared to, Figure 1 The growth direction of columnar crystals is more vertical; Figure 1 The width of columnar crystals is more uniform; Figure 1 The width of the secondary dendrite is more uniform and closer to the width of the columnar crystal. The yield of the NdFeB magnetic powder obtained by using such NdFeB rapid solidification casting sheet is about 94%.

[0094] In summary, the present invention controls the casting temperature and cooling rate within a specific range, thereby accurately controlling the microstructure of the obtained NdFeB rapid solidification casting sheet, ultimately improving the yield of the obtained NdFeB magnetic powder and optimizing the normal distribution of the NdFeB magnetic powder, making the particle size more uniform and the D90 / D10 value lower.

[0095] The present invention is not limited to the above-mentioned embodiments. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A NdFeB quick-solidification casting sheet having a roller-attaching surface and a free surface, characterized in that: The NdFeB rapid solidification casting sheet is composed of Re2Fe 14 The B main phase and the intergranular Re-rich phase are composed, and no α-Fe phase is contained; wherein Re is a rare earth element, selected from one or more of La, Ce, Y, Pr, Nd, Gd, Ho, Dy, and Tb, and Nd must be contained; In the cross section along the direction from the roller surface to the free surface, the main phase has a columnar crystal morphology. The width of the columnar crystal is 2.5 to 3.7 μm. There are dendrites distributed on both sides of the columnar crystal. The width of the dendrites is close to that of the columnar crystals. Re-rich phases are attached to both sides of the columnar crystals and dendrites, and the Re-rich phases are evenly distributed along the columnar crystals and dendrites.

2. The NdFeB rapid solidification casting sheet according to claim 1, characterized in that: The NdFeB rapid solidification casting sheet does not have an amorphous region.

3. The NdFeB rapid solidification casting sheet according to claim 1, characterized in that: The thickness of the NdFeB rapid solidification casting sheet is 240-300 μm.

4. A method for preparing the NdFeB rapid solidification casting sheet according to claim 1, characterized in that: The following steps are involved: 1) Smelting the raw materials required for the NdFeB rapid solidification casting sheet at 1400-1500°C to obtain an alloy solution; 2) Casting the alloy solution at 1360-1480° C. and cooling it through a cooling roller to obtain the NdFeB rapid solidification casting sheet; wherein the casting temperature is lower than the smelting temperature; during the casting process, the linear speed of the cooling roller is controlled to be 1.6-1.9 m / s.

5. The preparation method according to claim 4, characterized in that: The raw materials required for NdFeB rapid solidification casting sheets include Re, T and B, Re is selected from one or more of La, Ce, Y, Pr, Nd, Gd, Ho, Dy, Tb, and must contain Nd; T includes Fe.

6. The preparation method according to claim 5, characterized in that: T also includes one or more of Cu, Al, Ga, Co, Zr, Ni and Nb.

7. The preparation method according to claim 4, characterized in that: The linear speed of the cooling roller is controlled to be 1.6-1.8 m / s.

8. The preparation method according to claim 4, characterized in that: Step 1) and step 2) are both carried out under vacuum conditions, with a vacuum degree of less than 1.0×10 -1 Pa.

9. A method for preparing NdFeB magnetic powder, characterized in that: The following steps are involved: A NdFeB rapid solidification casting sheet is prepared according to the preparation method according to any one of claims 4 to 8; The NdFeB rapid solidification casting sheet is subjected to a coarse crushing process and a fine crushing process to obtain NdFeB magnetic powder.

10. A neodymium iron boron magnetic powder, characterized in that: It is prepared by the preparation method described in claim 9.

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