Sintered neodymium-iron-boron magnet and preparation method and application thereof

Abstract

The invention discloses a sintered neodymium-iron-boron magnet and a preparation method and application thereof. The magnet comprises main phase crystal particles with RE2Fe14B structures and a grain boundary phase. The grain boundary phase comprises a two-particle grain boundary phase between two main phase crystal particles and a grain boundary triple-phase point composed of more than three main phase crystal particle gaps; the ratio of the number of the main phase crystal particles to the number of grain boundary triphase points is smaller than or equal to 3. According to the sintered neodymium-iron-boron magnet, through proper component design, reasonable control over the (Cu + Ga) / X ratio and control over the thickness of an alloy sheet and the ratio relation between the average width of columnar crystals in the alloy sheet and the granularity of magnetic powder, concentrated distribution of grain boundary three-phase points can be effectively restrained, the grain boundary phase proportion can be increased, grain boundary phase distribution can be optimized, and the performance of the sintered neodymium-iron-boron magnet can be improved. Therefore, both high magnetic performance and high impact toughness are achieved. The sum of the magnetic energy product and the coercive force of the sintered neodymium-iron-boron magnet is larger than or equal to 75, the impact toughness of the sintered neodymium-iron-boron magnet is larger than or equal to 20 kJ / m < 2 >, and the sintered neodymium-iron-boron magnet can be applied to new energy automobile motors, energy-saving

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet preparation, and particularly relates to a sintered neodymium iron boron magnet, a preparation method thereof, and an application thereof. Background Art

[0002] As the third-generation rare earth permanent magnet material, sintered neodymium iron boron is widely used due to its excellent magnetic properties. Especially with the rapid development of new energy vehicles, wind power generation, intelligent consumer electronics, energy-saving motors and other fields in recent years, the penetration rate of sintered neodymium iron boron in related industries has been continuously increasing.

[0003] However, as a typical brittle material, sintered neodymium iron boron has large intrinsic brittleness and poor plastic toughness. Under the production and use conditions of sintered neodymium iron boron, it will inevitably bear a certain impact load, resulting in defects such as edge chipping and cracks, which affect the qualified rate of products and use safety.

[0004] Patent document CN109192425A discloses a method for improving the mechanical properties of a radiation ring magnet by adding RECu alloy toughening powder, but this method will inevitably lead to a decrease in the magnetic properties of the magnet.

[0005] Patent document CN100586612C discloses a method for improving the toughness of a magnet by adding alloy element Q (Q is at least one or more elements including Ti, Al, Ag, Zr), but the method of simply adding elements has a small improvement effect on toughness.

[0006] Patent document CN102568738B discloses a high-Ti formulation system, where the rare earth element is 25%-35%, Ti is 0.49%-0.51%, Co is 0.58-0.62%, and B is 0.77%-1.28%. However, the patent limits the formulation range too small, which has no practical significance in use, and the Ti content is too high, affecting the magnetic properties of the product.

[0007] Therefore, it is an urgent problem to be solved at present to prepare a sintered neodymium iron boron material with both high comprehensive magnetic properties and high impact toughness. Summary of the Invention

[0008] To solve the above problems, the present invention provides a sintered neodymium iron boron magnet with high comprehensive magnetic properties and high impact toughness, a preparation method thereof, and an application thereof.

[0009] The technical solution of the present invention is as follows:

[0010] A sintered neodymium iron boron magnet, the magnet comprising main phase crystal grains with a RE2Fe 14 B structure and a grain boundary phase; the grain boundary phase includes a two-grain grain boundary phase between two main phase crystal grains and a grain boundary triple point formed by the gaps between three or more main phase crystal grains;

[0011] The ratio of the number of main-phase crystal grains to the number of grain-boundary triple points ≤ 3;

[0012] RE is a rare earth element.

[0013] According to an embodiment of the present invention, in the sintered neodymium-iron-boron magnet, the area ratio of the main-phase crystal grains is 95.0% or less.

[0014] According to an embodiment of the present invention, the thickness of the two-grain boundary phase is not particularly limited, and the thickness can be 3 nm or more and 50 nm or less.

[0015] According to an embodiment of the present invention, the chemical elements of the sintered neodymium-iron-boron magnet and their mass percentages are as follows:

[0016] RE: 28% - 31%, Co: 0.3% - 3%, Cu: 0.08% - 0.6%, Ga: 0.08% - 0.6%, Al: 0.001% - 0.6%, B: 0.8 - 1.2%, C: ≤ 0.12%, O: ≤ 0.15%, N: ≤ 0.09%, X: 0.05% - 0.5%, where X includes one or more of Ti, Zr, and Nb; the balance is Fe and other inevitable impurities;

[0017] Among them, the content relationship of Cu, Ga, and X elements is: (Cu + Ga) / X ≥ 2.

[0018] According to an embodiment of the present invention, when X is Ti, the Ti content is 0.05% - 0.45%; when X is Zr, the Zr content is 0.05% - 0.45%; when X is Nb, the Nb content is 0.05% - 0.15%.

[0019] According to an embodiment of the present invention, the RE is at least one of the heavy rare earth element RH and the light rare earth element RL; RH refers to Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; RL refers to La, Ce, Pr, Nd, Pm, Sm, and Eu.

[0020] Preferably, there is no particular limitation on the content of RE, and the RE content can be 28% by mass or more and 31% by mass or less. Preferably, it can be 28.5% by mass or more and 30.5% by mass or less. As the main constituent element of the grain-boundary rare-earth-rich phase, the addition of the RE element will increase the proportion of the grain-boundary phase in the magnet. When intergranular fracture occurs, it will bear more load for the magnet. However, excessive addition of RE will result in too low a proportion of the main phase in the magnet and a reduction in the remanence.

[0021] Preferably, there is no particular limitation on the type of RE, and it is preferably at least RL. Among them, RL is preferably selected from one or more of Nd, Pr, Ce, and La. Preferably, RE is Nd. When RH is included, there is no particular limitation on the type of RH, and it may include at least Dy or Tb as RH. When RH is included, Hcj is liable to increase and Br is liable to decrease.

[0022] According to an embodiment of the present invention, the B element is a main phase crystallization grain forming element of R2Fe 14 There is no particular limitation on its content, and it can be 0.8% by mass or more and 1.2% by mass or less; if the B content is too high, the proportion of the grain boundary phase will be reduced, resulting in a decrease in impact toughness; if the content is too low, the proportion of the main phase crystallization grains in the product will be reduced, and the magnetic energy product will decrease.

[0023] According to an embodiment of the present invention, Co and Al elements form a solid solution in the neodymium iron boron magnet, producing a solid solution strengthening effect, which is beneficial to improving the comprehensive mechanical properties of the magnet. In this embodiment, the Co content can be 0.3% by mass or more and 3% by mass or less, and the Al content can be 0.001% by mass or more and 0.6% by mass or less. Excessive Co and Al elements will cause the magnetic properties of the magnet to decrease, and it is impossible to effectively improve the sum of the magnetic energy product and the coercivity.

[0024] According to an embodiment of the present invention, Cu, Ga, and X are grain boundary enrichment elements. After addition, they are beneficial to improving grain boundary wettability, enhancing the combination of the main phase crystallization grains and the grain boundary phase, and enhancing the impact toughness of the product. At the same time, the grain boundary phase elements are beneficial to hindering the growth of the main phase crystallization grains during the sintering process, and can play the role of reducing the grain size and enhancing the coercivity of the product. However, excessive addition will dilute the proportion of the main phase crystallization grains, resulting in a decrease in the magnetic energy product.

[0025] The inventors found that when (Cu + Ga) / X is less than 2, the proportions of Cu and Ga in the grain boundary decrease sharply, and sufficient grain boundary phase cannot be formed, resulting in a decrease in the impact toughness of the magnet.

[0026] According to an embodiment of the present invention, C, O, and N preferentially react with the rare earth-rich grain boundary phase during the production process. If the content is too high, the bonding strength between the main phase and the grain boundary phase will be reduced, resulting in a decrease in impact toughness. In the R-T-B series permanent magnet of this embodiment, the C content is 1200 ppm or less, the O content is 1500 ppm or less, and the N content is 900 ppm or less. In particular, the C content can be 500 ppm or less, the O content can be 500 ppm or less, and the N content can be 300 ppm or less. By strictly controlling the contents of C, O, and N, the formation of rare earth carbides and / or oxides and / or nitrides at the grain boundary triple point can be inhibited.

[0027] According to an embodiment of the present invention, the sum of the maximum magnetic energy product and the intrinsic coercivity of the sintered neodymium-iron-boron magnet is ≥ 75, i.e., (BH) max (MGOe) + Hcj (kOe) ≥ 75, and its impact toughness is ≥ 20 kJ / m 2 .

[0028] In the present invention, the area ratio of the main-phase crystal grains is 95.0% or less, and the ratio of the number of main-phase crystal grains to the number of grain-boundary triple points ≤ 3. If the area ratio of the main-phase crystal grains is too high and the grain-boundary phase ratio decreases, it will affect the grain-boundary strengthening effect of the grain-boundary phase on the impact toughness, resulting in a decrease in the impact toughness. If the ratio of the number of main-phase crystal grains to the number of grain-boundary triple points is too high, the number of grain-boundary triple points will be too low, and the individual grain-boundary triple points will increase, unable to effectively achieve the dispersion strengthening effect, resulting in a decrease in the impact toughness. Thus, a sintered neodymium-iron-boron magnet with high impact toughness can be obtained, and the sum of its maximum magnetic energy product and intrinsic coercivity is ≥ 75, i.e., (BH) max (MGOe) + Hcj (kOe) ≥ 75, and its impact toughness is ≥ 20 kJ / m 2 .

[0029] The present invention also provides a method for preparing the above-mentioned sintered neodymium-iron-boron magnet, and the method includes:

[0030] (1) Melting process: The raw materials for preparing the magnet are melted, cast, and cooled to form alloy sheets;

[0031] (2) Powder-making process: The alloy sheets in step (1) are subjected to hydrogenation treatment and airflow milling to obtain magnetic powder;

[0032] (3) The magnetic powder in step (2) is subjected to a pressing process, a sintering process, and a grain-boundary diffusion treatment to obtain the sintered neodymium-iron-boron magnet.

[0033] According to an embodiment of the present invention, step (1) is specifically that each component of the magnet is melted in an argon atmosphere, and the melt is cast onto a chill roll to form an alloy sheet.

[0034] Preferably, the thickness of the alloy sheet is 0.2 - 0.3 mm.

[0035] Preferably, the rotation speed of the chill roll is 20 r / min - 40 r / min,

[0036] Preferably, the cooling temperature of the chill roll is 0°C - 10°C, such as 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C, or 10°C. A refrigerator can be used to lower the temperature of the incoming chill roll below the room temperature, which helps to control the average width of the columnar crystals within an ideal range.

[0037] According to an embodiment of the present invention, in step (1), after cooling, the product can also be tempered. The temperature of the tempering treatment is 400 - 600 °C, preferably 500 - 600 °C, and the time of the tempering treatment is 1 - 4 h.

[0038] According to an embodiment of the present invention, in step (2), the specific hydrogenation treatment is as follows: the hydrogen absorption pressure is 100 - 200 kPa, and the hydrogen absorption time is 30 - 180 min; after hydrogen absorption, the temperature is raised to 500 - 600 °C for dehydrogenation treatment, and the dehydrogenation time is 180 - 360 min; after dehydrogenation, argon is filled to more than 30 kPa, then the temperature is raised to 700 - 800 °C, and the heat preservation time is 60 - 180 min; after heat preservation, cooling is carried out. Among them, during the cooling process, when the temperature is above 350 °C, the argon pressure ≥ 20 kPa;

[0039] Preferably, the jet mill grinding means mixing the alloy powder obtained by hydrogenation treatment with a lubricant and performing jet mill grinding treatment to obtain magnetic powder.

[0040] Preferably, the lubricant is selected from organic solvents such as volatile fats or alcohols, for example, zinc stearate. Exemplarily, the addition amount of the lubricant is 0.1 - 1 wt% of the total mass of the preparation raw materials.

[0041] According to an embodiment of the present invention, in the method, in steps (1) and (2), the thickness of the alloy sheet is m, the average width of the columnar crystals in the alloy sheet is n, and the average particle size of the magnetic powder is p. Define s = n / p - m / 100, and s ≤ 0;

[0042] Among them,

[0043] n is 5 - 10 μm;

[0044] m is 200 - 300 μm;

[0045] p is 2 - 5 μm.

[0046] In the present invention, when s > 0, the alloy sheet is excessively broken during the powder making process, the grain boundary phase is peeled off from the main phase crystal grains, and the fine grain boundary phase may be enriched around the columnar crystals, resulting in the rapid growth of the grain boundary triple points and affecting the impact toughness of the magnet.

[0047] According to an embodiment of the present invention, in step (2), the pressing process is specifically: pressing the magnetic powder into a shape under a magnetic field orientation; the orientation magnetic field is 1.5 - 2.5 T.

[0048] According to an embodiment of the present invention, in step (2), the sintering process is specifically as follows: the green compact after the pressing process is subjected to sintering treatment, the sintering temperature is 900-1100 °C, and the sintering time is 3-8 h; after the heat preservation is completed, it is cooled to ≤200 °C, and then primary tempering treatment is carried out at 700-900 °C, and the heat preservation time is 3-7 h; then secondary tempering treatment is carried out at 450-600 °C, and the heat preservation time is 3-7 h.

[0049] According to an embodiment of the present invention, in step (2), before the grain boundary diffusion treatment, the product obtained from the sintering process can also be processed into the required size, and then degreasing and pickling treatments are carried out before the grain boundary diffusion treatment.

[0050] According to an embodiment of the present invention, in step (2), the temperature of the diffusion treatment is 800-950 °C, the time of the diffusion treatment is at least 3 h, and the diffusion source is at least one element among Dy, Tb, Ho, Nd, and Pr.

[0051] The present invention also provides the application of the above-mentioned sintered Nd-Fe-B magnet in the fields of new energy vehicle motors or energy-saving air-conditioning compressors, etc.

[0052] Advantages of the present invention:

[0053] For the sintered Nd-Fe-B magnet of the present invention, through appropriate composition design, by reasonably controlling the ratio of (Cu + Ga) / X, and by controlling the ratio relationship of the thickness of the alloy sheet, the average width of the columnar crystals in the alloy sheet, and the particle size of the magnetic powder, the concentrated distribution of the grain boundary triple points can be effectively inhibited, the grain boundary phase ratio can be increased, and the grain boundary phase distribution can be optimized, thereby achieving both high magnetic properties and high impact toughness. For the sintered Nd-Fe-B magnet of the present invention, the sum of the magnetic energy product and the coercivity is ≥75, and its impact toughness is ≥20 kJ / m 2 , and it can be applied to new energy vehicle motors, energy-saving air-conditioning compressors, etc. Description of the drawings

[0054] Figure 1 It is the scanning electron microscope image of the sintered Nd-Fe-B magnet in Example 1. Detailed implementation manners

[0055] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only for illustrative and explanatory purposes of the present invention, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection of the present invention.

[0056] Unless otherwise specified, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by known methods.

[0057] Next, for RE2Fe14 The calculation method of the area ratio of the B main-phase crystal grains will be described.

[0058] The above area ratio is calculated using the backscattered electron image obtained by SEM (scanning electron microscope). First, the sintered Nd-Fe-B magnet is embedded in epoxy resin and polished flat until the cross-section becomes shiny. The cross-section of the sintered Nd-Fe-B magnet is observed by SEM at a magnification of 1000 times or more and 3000 times or less to obtain a backscattered electron image with a size of 50 μm square. According to the contrast of the backscattered electron image and the point analysis results of EDS, it can be confirmed that the sintered Nd-Fe-B magnet is composed of main-phase crystal grains (main phase) and other parts (grain boundaries), and the area ratio of each phase can be calculated.

[0059] Next, the calculation method of the ratio of the number of RE2Fe 14 B main-phase crystal grains to the number of grain boundary triple points will be described.

[0060] The above area ratio is calculated using the backscattered electron image obtained by SEM (scanning electron microscope). First, the sintered Nd-Fe-B magnet is embedded in epoxy resin and polished flat until the cross-section becomes shiny. The cross-section of the sintered Nd-Fe-B magnet is observed by SEM at a magnification of 1000 times or more and 3000 times or less to obtain a backscattered electron image with a size of 50 μm square. According to the contrast of the backscattered electron image, the number of main-phase crystal grains and the number of grain boundary triple points can be confirmed. Among them, the triple point is defined as: the grain boundary phase with a projection length > 0.5 μm in the direction perpendicular to the side with the longest projection length.

[0061] Next, the calculation method of the average width of columnar crystals in the alloy sheet will be described.

[0062] The average width of the columnar crystals in the above alloy sheet is calculated using the backscattered electron image obtained by SEM (scanning electron microscope). First, the alloy sheet of the sintered Nd-Fe-B magnet is embedded in epoxy resin and polished flat until the cross-section becomes shiny. The cross-section of the sintered Nd-Fe-B magnet is observed by SEM at a magnification of 1000 times or more and 3000 times or less to obtain a backscattered electron image with a size of 50 μm square. According to the contrast of the backscattered electron image, the number and size of the columnar crystals in the alloy sheet can be confirmed, and the average width of the columnar crystals can be calculated.

[0063] Example 1

[0064] The preparation method of the sintered Nd-Fe-B in Example 1 is as follows:

[0065] (1) Melt each magnet component in Table 1 below in an argon atmosphere and cast the melt onto a chill roll to form an alloy sheet. Among them, the rotation speed of the chill roll is 35 r / min, and the cooling temperature of the chill roll is 0 °C. The thickness and average width of the columnar crystals of the alloy sheet are shown in Table 2.

[0066] (2) The above alloy sheets are subjected to hydrogenation treatment. The specific hydrogenation treatment is as follows: the hydrogen absorption pressure is 150 kPa, and the hydrogen absorption time is 60 min; after the hydrogen absorption is completed, the temperature is raised to 600 °C for dehydrogenation treatment, and the dehydrogenation time is 300 min; after the dehydrogenation is completed, argon is filled to more than 30 kPa, and then the temperature is raised to 700 °C, and the holding time is 80 min; after the holding is completed, cooling is carried out. Among them, during the cooling process, when the temperature is above 350 °C, the argon pressure ≥ 20 kPa;

[0067] After the hydrogenation treatment is completed, the alloy powder obtained by the hydrogenation treatment is mixed with 0.5 wt% zinc stearate and ground by a jet mill to obtain magnetic powder. The particle size of the magnetic powder is shown in Table 2 for details.

[0068] (3) The magnetic powder is pressed and formed under a magnetic field orientation; the orientation magnetic field is 2.0 T.

[0069] (4) The green compact after the pressing process is subjected to sintering treatment. The sintering temperature is 1050 °C, and the sintering time is 6 h; after the holding is completed, it is cooled to ≤ 200 °C, and then primary tempering treatment is carried out at 900 °C, and the holding time is 4 h; then secondary tempering treatment is carried out at 500 °C, and the holding time is 4 h;

[0070] (5) The product obtained from the sintering process is processed into the required size, and then degreasing and pickling treatments are carried out, followed by grain boundary diffusion treatment to obtain the sintered NdFeB magnet. Among them, the temperature of the diffusion treatment is 850 °C, the time of the diffusion treatment is at least 3 h, and the diffusion source is Tb element.

[0071] Scanning electron microscope photos of the sintered NdFeB magnet are taken, and the test results are as Figure 1 shown. The ratio of the number of main phase crystal grains to the number of grain boundary triple points and the area ratio of the main phase crystal grains are shown in Table 2 for details.

[0072] Example 2

[0073] The preparation method of the sintered NdFeB in Example 2 is as follows:

[0074] (1) Each magnet component in Table 1 below is melted in an argon atmosphere, and the melt is cast onto a chill roll to make alloy sheets. Among them, the rotation speed of the chill roll is 36 r / min, and the cooling temperature of the chill roll is 5 °C. The alloy sheets are screened by a screening machine to remove uneven parts with a thickness less than 0.23 mm and more than 0.32 mm. The thickness of the alloy sheets and the average width of the columnar crystals are shown in Table 2 for details.

[0075] (2) Subject the above alloy sheet to hydrogenation treatment. The specific hydrogenation treatment is as follows: the hydrogen absorption pressure is 150 kPa, and the hydrogen absorption time is 60 min; after the hydrogen absorption is completed, heat up to 600 °C for dehydrogenation treatment, and the dehydrogenation time is 300 min; after the dehydrogenation is completed, fill with argon to a pressure above 30 kPa, then heat up to 700 °C, and the heat preservation time is 80 min; after the heat preservation is completed, conduct cooling. Among them, during the cooling process, when the temperature is above 350 °C, the argon pressure ≥ 20 kPa;

[0076] After the hydrogenation treatment is completed, mix the alloy powder obtained from the hydrogenation treatment with 0.5 wt% zinc stearate, and conduct grinding treatment with a jet mill to obtain magnetic powder. The particle size of the magnetic powder is shown in Table 2 for details.

[0077] (3) Press and form the magnetic powder under a magnetic field orientation; the orientation magnetic field is 2.0 T.

[0078] (4) Conduct sintering treatment on the green compact after the pressing process. The sintering temperature is 1055 °C, and the sintering time is 6 h; after the heat preservation is completed, cool to ≤ 200 °C, then conduct primary tempering treatment at 900 °C, and the heat preservation time is 4 h; then conduct secondary tempering treatment at 500 °C, and the heat preservation time is 4 h;

[0079] (5) Process the product obtained from the sintering process into the required size, then conduct degreasing and pickling treatments, and then conduct grain boundary diffusion treatment to obtain the sintered NdFeB magnet. Among them, the temperature of the diffusion treatment is 850 °C, the time of the diffusion treatment is at least 3 h, and the diffusion source is at least one element in Tb.

[0080] Take a scanning electron microscope photograph of the sintered NdFeB magnet. The ratio of the number of main phase crystal grains to the number of grain boundary triple points and the area ratio of the main phase crystal grains are shown in Table 2 for details.

[0081] Example 3

[0082] The preparation method of the sintered NdFeB in Example 3 is as follows:

[0083] (1) Melt each magnet component in Table 1 below in an argon atmosphere, and cast the melt onto a chill roll to make an alloy sheet. Among them, the rotation speed of the chill roll is 38 r / min, and the cooling temperature of the chill roll is 0 °C. The alloy sheet is subjected to a tempering heat treatment at 550 °C * 2 h. The thickness of the alloy sheet and the average width of the columnar crystals are shown in Table 2 for details.

[0084] (2) The above alloy sheet is subjected to hydrogenation treatment. The specific hydrogenation treatment is as follows: the hydrogen absorption pressure is 150 kPa, and the hydrogen absorption time is 60 min; after the hydrogen absorption is completed, the temperature is raised to 600 °C for dehydrogenation treatment, and the dehydrogenation time is 300 min; after the dehydrogenation is completed, argon is filled to more than 30 kPa, and then the temperature is raised to 700 °C, and the heat preservation time is 80 min; after the heat preservation is completed, cooling is carried out. Among them, during the cooling process, when the temperature is above 350 °C, the argon pressure ≥ 20 kPa;

[0085] After the hydrogenation treatment is completed, the alloy powder obtained by the hydrogenation treatment is mixed with 0.5 wt% zinc stearate and ground by a jet mill to obtain magnetic powder. The particle size of the magnetic powder is shown in Table 2 for details.

[0086] (3) The magnetic powder is pressed and formed under a magnetic field orientation; the orientation magnetic field is 2.0 T.

[0087] (4) The green compact after the pressing process is subjected to sintering treatment. The sintering temperature is 1060 °C, and the sintering time is 6 h; after the heat preservation is completed, it is cooled to ≤ 200 °C, and then primary tempering treatment is carried out at 900 °C, and the heat preservation time is 4 h; then secondary tempering treatment is carried out at 500 °C, and the heat preservation time is 4 h;

[0088] (5) The product obtained from the sintering process is processed into the required size, and then degreasing and pickling treatments are carried out, followed by grain boundary diffusion treatment to obtain the sintered NdFeB magnet. Among them, the temperature of the diffusion treatment is 850 °C, the time of the diffusion treatment is at least 3 h, and the diffusion source is Tb element.

[0089] The sintered NdFeB magnet is photographed to obtain a scanning electron microscope photo. The ratio of the number of main phase crystal grains to the number of grain boundary triple points and the area ratio of the main phase crystal grains are shown in Table 2 for details.

[0090] Comparative Example 1

[0091] The preparation method of the sintered NdFeB in Comparative Example 1 is as follows:

[0092] (1) Each magnet component in Table 1 below is melted in an argon atmosphere, and the melt is cast onto a chill roll to form an alloy sheet. Among them, the rotation speed of the chill roll is 35 r / min, and the cooling temperature of the chill roll is 0 °C. The thickness of the alloy sheet and the average width of the columnar crystals are shown in Table 2 for details.

[0093] (2) The above alloy sheet is subjected to hydrogenation treatment. The specific hydrogenation treatment is as follows: the hydrogen absorption pressure is 150 kPa, and the hydrogen absorption time is 60 min; after the hydrogen absorption is completed, the temperature is raised to 600 °C for dehydrogenation treatment, and the dehydrogenation time is 300 min; after the dehydrogenation is completed, argon is filled to more than 30 kPa, and then the temperature is raised to 700 °C, and the heat preservation time is 80 min; after the heat preservation is completed, cooling is carried out. Among them, during the cooling process, when the temperature is above 350 °C, the argon pressure ≥ 20 kPa;

[0094] After the hydrogenation treatment, the alloy powder obtained from the hydrogenation treatment is mixed with 0.5 wt% zinc stearate and ground by a jet mill to obtain magnetic powder. The particle size of the magnetic powder is shown in Table 2 for details.

[0095] (3) Press and form the magnetic powder under a magnetic field orientation; the orientation magnetic field is 2.0 T.

[0096] (4) Sinter the green compact after the pressing process. The sintering temperature is 1050 °C and the sintering time is 6 h; after the heat preservation ends, cool it to ≤200 °C, then perform a first-stage tempering treatment at 900 °C with a heat preservation time of 4 h; then perform a second-stage tempering treatment at 500 °C with a heat preservation time of 4 h;

[0097] (5) Process the product obtained from the sintering process into the required size, then perform degreasing and pickling treatments and then perform grain boundary diffusion treatment to obtain the sintered NdFeB magnet. Among them, the temperature of the diffusion treatment is 850 °C, the time of the diffusion treatment is at least 3 h, and the diffusion source is Tb element.

[0098] Take a scanning electron microscope photo of the sample after diffusion. The ratio of the number of main-phase crystal grains to the number of grain boundary triple points and the area ratio of the main-phase crystal grains are shown in Table 2 for details.

[0099] Comparative Example 2

[0100] The preparation method of the sintered NdFeB in Comparative Example 2 is as follows:

[0101] (1) Melt each magnet component in Table 1 below in an argon atmosphere and cast the melt onto a chill roll to make alloy sheets. Among them, the rotation speed of the chill roll is 32 r / min and the cooling temperature of the chill roll is 15 °C. The thickness of the alloy sheet and the average width of the columnar crystals are shown in Table 2 for details.

[0102] (2) Perform hydrogenation treatment on the above alloy sheets. The specific hydrogenation treatment is as follows: the hydrogen absorption pressure is 150 kPa and the hydrogen absorption time is 60 min; after the hydrogen absorption ends, raise the temperature to 600 °C for dehydrogenation treatment with a dehydrogenation time of 300 min; after the dehydrogenation ends, fill with argon to above 30 kPa, then raise the temperature to 700 °C with a heat preservation time of 80 min; after the heat preservation ends, perform cooling. Among them, during the cooling process, when the temperature is above 350 °C, the argon pressure ≥20 kPa;

[0103] After the hydrogenation treatment, the alloy powder obtained from the hydrogenation treatment is mixed with 0.5 wt% zinc stearate and ground by a jet mill to obtain magnetic powder. The particle size of the magnetic powder is shown in Table 2 for details.

[0104] (3) Press and form the magnetic powder under a magnetic field orientation; the orientation magnetic field is 2.0 T.

[0105] (4) Sinter the green compact after the compacting process at a sintering temperature of 1070 °C for 6 h; after the heat preservation ends, cool it to ≤200 °C, then perform a first-stage tempering treatment at 900 °C for 4 h; then perform a second-stage tempering treatment at 500 °C for 4 h;

[0106] (5) Process the product obtained from the sintering process into the required size, then perform degreasing and pickling treatments, and then perform grain boundary diffusion treatment to obtain the sintered NdFeB magnet. Among them, the temperature of the diffusion treatment is 850 °C, the time of the diffusion treatment is at least 3 h, and the diffusion source is the Tb element.

[0107] Take a scanning electron microscope photo of the sample after diffusion. The ratio of the number of main phase crystal grains to the number of grain boundary triple points and the area ratio of the main phase crystal grains are shown in Table 2.

[0108] Comparative Example 3

[0109] The preparation method of the sintered NdFeB in Comparative Example 3 is as follows:

[0110] (1) Melt each magnet component in Table 1 below in an argon atmosphere, and cast the melt onto a chill roll to make alloy sheets. Among them, the rotation speed of the chill roll is 32 r / min, and the cooling temperature of the chill roll is 15 °C. The alloy sheets are passed through a screening machine to remove uneven parts with a thickness less than 0.25 mm and greater than 0.38 mm. The thickness of the alloy sheets and the average width of the columnar crystals are shown in Table 2.

[0111] (2) Perform hydrogenation treatment on the above alloy sheets. The specific hydrogenation treatment is as follows: the hydrogen absorption pressure is 150 kPa, and the hydrogen absorption time is 60 min; after the hydrogen absorption ends, raise the temperature to 600 °C for dehydrogenation treatment, and the dehydrogenation time is 300 min; after the dehydrogenation ends, fill with argon to more than 30 kPa, then raise the temperature to 700 °C, and the heat preservation time is 80 min; after the heat preservation ends, perform cooling. Among them, during the cooling process, when the temperature is above 350 °C, the argon pressure ≥20 kPa;

[0112] After the hydrogenation treatment ends, mix the alloy powder obtained from the hydrogenation treatment with 0.5 wt% zinc stearate, and perform grinding treatment with a jet mill to obtain magnetic powder. The particle size of the magnetic powder is shown in Table 2.

[0113] (3) Press the magnetic powder into shape under a magnetic field orientation; the orientation magnetic field is 2.0 T.

[0114] (4) Sinter the green compact after the compacting process at a sintering temperature of 1085 °C for 6 h; after the heat preservation ends, cool it to ≤200 °C, then perform a first-stage tempering treatment at 900 °C for 4 h; then perform a second-stage tempering treatment at 500 °C for 4 h;

[0115] (5) Process the product obtained from the sintering process into the required size, then perform degreasing and pickling treatments, and then carry out grain boundary diffusion treatment to obtain the sintered NdFeB magnet. Among them, the temperature of the diffusion treatment is 860 °C, the time of the diffusion treatment is at least 3 h, and the diffusion source is Tb element.

[0116] Take a scanning electron microscope photo of the sample after diffusion. The ratio of the number of main phase crystallization grains to the number of grain boundary triple points and the area ratio of the main phase crystallization grains are shown in Table 2.

[0117] Table 1

[0118]

[0119] Table 2

[0120]

[0121] Perform impact toughness tests on the sintered NdFeB magnets prepared in Examples 1-3 and Comparative Examples 1-3 according to the method of single-arm pendulum impact test for metallic materials GB / T 229-2020. The test results are shown in Table 2 above. It can be seen from Table 2 that in Examples 1, 2, and 3, the ratio of (Cu + Ga) / X is greater than 2, and s is less than 0, the area ratio of the main phase particles < 95%, and the ratio of the number of main phase crystallization grains to the number of grain boundary triple points ≤ 3. Therefore, the comprehensive performance of its magnetic energy product and coercivity is relatively high, and at the same time, it has high impact toughness.

[0122] Above, the embodiments of the present invention have been described exemplarily. However, the protection scope of the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A sintered neodymium iron boron magnet, characterized in that, The magnet includes main phase crystallized grains having a RE2Fe 14 B structure and a grain boundary phase; the grain boundary phase includes a two-grain boundary phase between two main phase crystallized grains and a grain boundary triple point formed by the gaps between three or more main phase crystallized grains; The ratio of the number of main-phase crystallization grains to the number of grain-boundary triple points ≤ 3; RE is a rare-earth element.

2. The sintered neodymium iron boron magnet according to claim 1, wherein, In the sintered Nd-Fe-B magnet, the area ratio of the main-phase crystallization grains is 95.0% or less.

3. The sintered neodymium iron boron magnet according to claim 1, characterized in that, The chemical elements and their mass percentages of the sintered Nd-Fe-B magnet are as follows: RE: 28% - 31%, Co: 0.3% - 3%, Cu: 0.08% - 0.6%, Ga: 0.08% - 0.6%, Al: 0.001% - 0.6%, B: 0.8 - 1.2%, C: ≤ 0.12%, O: ≤ 0.15%, N: ≤ 0.09%, X: 0.05% - 0.5%, where X includes one or more of Ti, Zr, and Nb; the balance is Fe and other inevitable impurities; Among them, the content relationship of Cu, Ga, and X elements is: (Cu + Ga) / X ≥ 2.

4. The sintered neodymium iron boron magnet according to claim 3, wherein, The RE is at least one of the heavy rare-earth element RH and the light rare-earth element RL; RH refers to Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; RL refers to La, Ce, Pr, Nd, Pm, Sm, and Eu.

5. The sintered neodymium iron boron magnet according to any one of claims 1-4, characterized in that, The sum of the maximum energy product and the intrinsic coercivity of the sintered NdFeB magnet is ≥ 75, and its impact toughness is ≥ 20 kJ / m 2 .

6. The method for preparing a sintered neodymium iron boron magnet according to any one of claims 1-5, characterized in that, The method includes: (1) Melting process: The raw materials for preparing the magnet are melted, cast, and cooled to form alloy sheets; (2) Powder-making process: The alloy sheets in step (1) are subjected to hydrogenation treatment and air-stream milling to obtain magnetic powder; (3) The magnetic powder in step (2) is subjected to a pressing process, a sintering process, and a grain-boundary diffusion treatment to obtain the sintered Nd-Fe-B magnet.

7. The method according to claim 6, characterized in that, In steps (1) and (2), the thickness of the alloy sheet is m, the average width of columnar crystals in the alloy sheet is n, and the average particle size of the magnetic powder is p. Define s = n / p - m / 100, s ≤ 0; Among them, n is 5 - 10 μm; m is 200 - 300 μm; p is 2 - 5 μm.

8. The method according to claim 6, wherein In step (2), the sintering process is specifically: The green compact after the pressing process is sintered, the sintering temperature is 900 - 1100 °C, and the sintering time is 3 - 8 h; after the heat preservation ends, it is cooled to ≤ 200 °C, and then subjected to a first-stage tempering treatment at 700 - 900 °C, and the heat preservation time is 3 - 7 h; then subjected to a second-stage tempering treatment at 450 - 600 °C, and the heat preservation time is 3 - 7 h.

9. Application of the sintered Nd-Fe-B magnet according to any one of claims 1 - 5 in the field of new energy vehicle motors or energy-saving air-conditioning compressors.

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