A heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet and its preparation method

Abstract

The present invention discloses a heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet and a preparation method thereof. The specific preparation method comprises the following steps: S1, weighing main alloy raw materials and auxiliary alloy raw materials according to a certain proportion; S2, respectively carrying out vacuum melting, hydrogen breaking and air flow grinding treatment on the weighed main alloy raw materials and auxiliary alloy raw materials to prepare main phase magnetic powder and auxiliary phase powder; S3, mixing the main phase magnetic powder and the auxiliary phase powder, and carrying out orientation pressing and forming treatment on the mixed material to obtain a green magnet; S4, carrying out sintering and tempering treatment on the green magnet, and cooling to obtain a NdFeB permanent magnet with a heavy rare earth segregation type structure. By adding aluminum and nickel elements, the present invention can improve the high temperature resistance of the magnet. The addition of an appropriate amount of cobalt element can not only increase the Curie temperature, but also reduce the temperature coefficient, thereby improving the heat resistance of the NdFeB permanent magnet. The addition of Mg nanopowder further improves the magnetic properties and high temperature resistance of the NdFeB permanent magnet.

Description

Technical Field

[0001] The present invention relates to the technical field of neodymium iron boron permanent magnets, and specifically to a preparation method of a heavy rare earth segregation type high temperature resistant and high performance neodymium iron boron permanent magnet. Background Technique

[0002] Neodymium iron boron permanent magnets are tetragonal magnetic materials formed by neodymium, iron, and boron. Neodymium iron boron permanent magnets have extremely high magnetic energy products and coercive forces. At the same time, the advantages of high energy density enable neodymium iron boron permanent magnet materials to be widely used in modern industry and electronic technology;

[0003] The neodymium iron boron permanent magnets in the prior art have strong magnetic properties at room temperature, but as the temperature increases, their magnetic properties will decrease. Therefore, when preparing neodymium iron boron permanent magnets, their high temperature resistance needs to be considered.

[0004] The defects of the existing neodymium iron boron permanent magnets are as follows:

[0005] 1. In the preparation process of the existing neodymium iron boron permanent magnets, little consideration is given to improving the high temperature resistance of neodymium iron boron, resulting in excellent thermal stability of the neodymium iron boron permanent magnets;

[0006] 2. Patent document CN105489368B proposes a preparation method of neodymium iron boron permanent magnets, but the preparation method of neodymium iron boron in this patent document does not consider improving the corrosion resistance and magnetic properties of neodymium iron boron permanent magnets by increasing the density and orientation degree of the magnets;

[0007] 3. In the prior art, the magnetic properties of the neodymium iron boron permanent magnets prepared according to the conventional preparation method of neodymium iron boron permanent magnets are already excellent, so little consideration is given to further improving the magnetic properties of neodymium iron boron permanent magnets;

[0008] 4. Patent document CN104966607B discloses a preparation method of sintered neodymium iron boron permanent magnets. For the magnets in this patent document where heavy rare earth elements are only concentrated on the surface layer of the grains, if the external magnetic field strength is large enough, once the magnetic domain wall breaks through the high anisotropy layer on the surface layer, the magnetic domains in the low anisotropy field region inside the grains will instantaneously magnetize and reverse, and the final coercivity of the magnet is relatively low. Summary of the Invention

[0009] The purpose of the present invention is to provide a heavy rare earth segregation type high temperature resistant and high performance neodymium iron boron permanent magnet and its preparation method to solve the problems raised in the above background technique.

[0010] To achieve the above purpose, the present invention provides the following technical solution: A preparation method of a heavy rare earth segregation type high temperature resistant and high performance neodymium iron boron permanent magnet, including the following steps:

[0011] S1. Weigh the main alloy raw materials and auxiliary alloy raw materials according to a certain ratio;

[0012] S2. Weigh the master alloy raw materials and the auxiliary alloy raw materials respectively, and conduct vacuum melting, hydrogen decrepitation, and air flow grinding treatments to prepare the main phase magnetic powder and the auxiliary phase powder.

[0013] S3. Mix the main phase magnetic powder and the auxiliary phase powder, and conduct orientation pressing and forming treatment on the mixed material to obtain a green magnet.

[0014] S4. Conduct sintering and tempering treatments on the green magnet, and cool it to obtain a NdFeB permanent magnet with a heavy rare earth segregation type structure.

[0015] Among them, in S1, the master alloy raw materials include 32 parts to 36 parts of neodymium powder, 62 parts to 70 parts of iron powder, 4.8 parts to 4.9 parts of boron powder, 0.04 parts to 0.07 parts of copper powder, 0.3 parts to 0.8 parts of aluminum powder, 0.4 parts to 0.7 parts of nickel powder, and 0.6 parts to 0.8 parts of cobalt powder by weight.

[0016] In S3, during the mixing process of the main phase magnetic powder and the auxiliary phase powder, add 0.08wt% to 0.12wt% of Mg nanopowder.

[0017] Preferably, in S1, the auxiliary alloy is an alloy of heavy rare earths, and the raw materials of the auxiliary alloy include 6 parts to 13 parts of gadolinium, 13 parts to 14 parts of terbium, 8 parts to 15 parts of aluminum powder, and 15 parts to 19 parts of copper powder.

[0018] Preferably, in the vacuum melting step of S2, the melting temperature of the melting furnace is 1400°C to 1600°C, and the melting holding time is 25 min to 65 min.

[0019] Preferably, in the hydrogen decrepitation step of S2, feed the melted material into a hydrogen decrepitation furnace, evacuate to a vacuum degree less than or equal to 3.2 Pa, introduce hydrogen, maintain the pressure at 1.6×10 5 Pa to 2×10 5 Pa, the hydrogen decrepitation treatment duration is 3.8 h to 4.5 h, after pumping out the residual hydrogen, raise the temperature of the hydrogen decrepitation furnace to 460°C, and hold for 3.6 h.

[0020] Preferably, in the air flow grinding step of S2, collect the material after hydrogen decrepitation and feed it into an air flow grinder for air flow grinding to obtain the main phase magnetic powder and the auxiliary phase powder with a particle size of 2.6 μm to 3.2 μm.

[0021] Preferably, in the orientation pressing and forming step of S3, the pressing and forming step adopts a combined pressing method of vertical pressing and isostatic pressing for densification, the orientation magnetic field is 2.5 T to 4.2 T, the forming pressure is 15 Mpa to 55 Mpa, the pressure of isostatic pressing is 180 Mpa to 250 Mpa, and the pressure holding time is 30 s to 150 s.

[0022] Preferably, in the sintering step of S4, the green magnet blank is heated in the furnace to 800 °C in a vacuum environment and sintered for 2 h, then the green magnet blank is continuously heated in the furnace to 1150 °C in a vacuum environment and sintered for 3.5 h, and then cooled in the furnace to obtain a sintered body.

[0023] Preferably, in the tempering step of S4, two-stage tempering treatment is adopted;

[0024] First-stage tempering treatment: the tempering temperature is 850 °C to 1200 °C, and the time is 1.5 h to 8 h;

[0025] Second-stage tempering treatment: the tempering temperature is 450 °C to 800 °C, and the time is 1.5 h to 6 h.

[0026] Preferably, a heavy rare earth segregated high-temperature resistant high-performance NdFeB permanent magnet, the NdFeB permanent magnet is divided into a main phase and a secondary phase, the main phase is an alloy containing NdFeB; the secondary phase is an alloy of heavy rare earth, and the main phase grains of the NdFeB permanent magnet have a heavy rare earth element segregation structure, wherein the heavy rare earth elements diffuse into the main phase grains to form a segregation layer and a heavy rare earth surface layer.

[0027] Preferably, the segregation layer is located inside the heavy rare earth surface layer, and the concentration of heavy rare earth elements is higher than that of the heavy rare earth surface layer. The thickness of the segregation layer is 0.2 μm to 3 μm, and the thickness of the heavy rare earth surface layer is 1 μm to 5 μm.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. By adding aluminum and nickel elements, the present invention can improve the high-temperature resistance of the magnet. The addition of cobalt can not only increase the Curie temperature but also reduce the temperature coefficient, thereby improving the heat resistance of the NdFeB permanent magnet. By adding an appropriate amount of cobalt element and adding Mg nanoflakes, the high-temperature resistance of the permanent magnet can be improved while ensuring excellent magnetic properties of the magnet.

[0030] 2. By adding Mg nanoflakes, the present invention can significantly improve the magnetic properties and thermal stability of the NdFeB magnet. This improvement is mainly achieved through the distribution of Mg nanoflakes in the grain boundary region. It improves the wettability of the Nd-rich phase along the main phase particles, improves the microstructure of the grain boundary phase, and refines the main phase grains, thereby improving the magnetic properties of the magnet and the thermal stability of the NdFeB permanent magnet. The addition of an appropriate amount of Mg nanoflakes can make the density of the magnet reach the maximum value and improve the orientation degree of the magnet, thereby contributing to improving the corrosion resistance of the permanent magnet.

[0031] 3. By adding an appropriate amount of aluminum and nickel to the NdFeB permanent magnet, the present invention improves the high-temperature resistance of the permanent magnet. At the same time, the addition of cobalt can also increase the coercivity and magnetic saturation of the NdFeB permanent magnet; the introduction of the auxiliary alloy makes the main phase grains have chemical inhomogeneity, further enhancing the magnetic properties of the magnet.

[0032] 4. By mixing the master alloy and the auxiliary alloy, the heavy rare earth elements diffuse into the master phase grains to form a segregation layer and a heavy rare earth surface layer, so that the master phase grains of the Nd-Fe-B permanent magnet have a heavy rare earth segregation type structure. The magnet with grains of this structure can prevent the reverse magnetization domain from moving into the magnet interior, improving the demagnetization resistance and coercivity of the magnet. Specific Embodiments

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] An embodiment provided by the present invention: A preparation method of a heavy rare earth segregation type high temperature resistant and high performance Nd-Fe-B permanent magnet, comprising the following steps:

[0035] S1. Weigh the master alloy raw materials and the auxiliary alloy raw materials according to a certain ratio;

[0036] S2. Vacuum melt, hydrogenate and air flow grind the weighed master alloy raw materials and auxiliary alloy raw materials respectively to prepare master phase magnetic powder and auxiliary phase powder;

[0037] S3. Mix the master phase magnetic powder and the auxiliary phase powder, and perform orientation pressing and forming treatment on the mixed material to obtain a green magnet;

[0038] S4. Sinter and temper the green magnet, and cool to obtain a Nd-Fe-B permanent magnet with a heavy rare earth segregation type structure;

[0039] Among them, in S1, the master alloy raw materials include 32 parts to 36 parts of neodymium powder, 62 parts to 70 parts of iron powder, 4.8 parts to 4.9 parts of boron powder, 0.04 parts to 0.07 parts of copper powder, 0.3 parts to 0.8 parts of aluminum powder, 0.4 parts to 0.7 parts of nickel powder and 0.6 parts to 0.8 parts of cobalt powder by weight;

[0040] In S3, during the mixing process of the master phase magnetic powder and the auxiliary phase powder, 0.08 wt% to 0.12 wt% of Mg nanopowder is added.

[0041] In S1, the auxiliary alloy is an alloy of heavy rare earths, and the raw materials of the auxiliary alloy include 6 parts to 13 parts of gadolinium, 13 parts to 14 parts of terbium, 8 parts to 15 parts of aluminum powder and 15 parts to 19 parts of copper powder.

[0042] In the vacuum melting step of S2, the melting temperature of the melting furnace is 1400 °C to 1600 °C, and the melting holding time is 25 min to 65 min.

[0043] In the hydrogen decrepitation step of S2, the smelted material is fed into a hydrogen crushing furnace, the vacuum is pumped to a degree of vacuum less than or equal to 3.2 Pa, hydrogen is introduced, and the pressure is maintained at 1.6×10 5 Pa to 2×10 5 Pa. The hydrogen decrepitation treatment duration is 3.8 h to 4.5 h. After the residual hydrogen is extracted, the temperature of the hydrogen crushing furnace is raised to 460 °C and held for 3.6 h.

[0044] In the air jet milling step of S2, the material after hydrogen decrepitation is collected and fed into an air jet mill for air jet milling to obtain main phase magnetic powder with a particle size of 2.6 μm to 3.2 μm and auxiliary phase powder.

[0045] In the orientation pressing and forming step of S3, the pressing and forming step adopts a combined pressing method of vertical pressing and isostatic pressing for densification. The orientation magnetic field is 2.5 T to 4.2 T, the forming pressure is 15 Mpa to 55 Mpa, the pressure of isostatic pressing is 180 Mpa to 250 Mpa, and the pressure holding time is 30 s to 150 s.

[0046] In the sintering step of S4, the green magnet blank is heated in the furnace to 800 °C in a vacuum environment and sintered for 2 h. Then the green magnet blank is continuously heated in the furnace to 1150 °C in a vacuum environment and sintered for 3.5 h, and then cooled in the furnace to obtain a sintered body.

[0047] In the tempering step of S4, two-stage tempering treatment is adopted;

[0048] The first-stage tempering treatment: the tempering temperature is 850 °C to 1200 °C, and the time is 1.5 h to 8 h;

[0049] The second-stage tempering treatment: the tempering temperature is 450 °C to 800 °C, and the time is 1.5 h to 6 h;

[0050] A heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet is prepared according to the above-mentioned preparation method of a heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet. The NdFeB permanent magnet is divided into a main phase and an auxiliary phase. The main phase is an alloy containing NdFeB; the auxiliary phase is an alloy of heavy rare earth. There is a heavy rare earth element segregation structure in the main phase grains of the NdFeB permanent magnet. Among them, the heavy rare earth elements diffuse into the main phase grains to form a segregation layer and a heavy rare earth surface layer. The segregation layer is located inside the heavy rare earth surface layer, and the concentration of heavy rare earth elements is higher than that of the heavy rare earth surface layer. The thickness of the segregation layer is 0.2 μm to 3 μm, and the thickness of the heavy rare earth surface layer is 1 μm to 5 μm.

[0051] Furthermore, in the preparation process of NdFeB permanent magnets, neodymium is one of the main rare earth metal elements of NdFeB permanent magnets and one of the key elements to improve the coercivity and remanence of NdFeB permanent magnets. Iron is one of the main reference elements of NdFeB permanent magnets and one of the most important components of alloy materials. Boron is one of the important components to improve the coercivity and magnetic saturation of NdFeB permanent magnets.

[0052] Nickel can improve the corrosion resistance of the permanent magnet. Aluminum is one of the necessary elements to increase the oxidation resistance and high-temperature resistance of NdFeB permanent magnets. By adding elements such as aluminum and nickel, the high-temperature resistance of the magnet can be improved. Copper is one of the necessary elements to increase the electrical conductivity of NdFeB permanent magnets. Cobalt is one of the important components to increase the coercivity and magnetic saturation of NdFeB permanent magnets. Adding cobalt to NdFeB permanent magnets can significantly improve the temperature resistance. The addition of cobalt can not only increase the Curie temperature but also reduce the temperature coefficient, thereby improving the heat resistance of NdFeB alloys.

[0053] The introduction of the auxiliary alloy makes the main phase grains have chemical inhomogeneity, further enhancing the magnetic properties of the magnet. The NdFeB rare earth permanent magnet has a heavy rare earth element segregation structure in the main phase grains. The concentration of heavy rare earth elements on the surface layer of the main phase grains of the magnet is relatively low, and the concentration of the segregation layer inside is relatively high. The magnet with grains having this structure can prevent the movement of reverse magnetization domains into the magnet interior, improving the demagnetization resistance and coercivity of the magnet.

[0054] By adding Mg nanopowder, the magnetic properties and thermal stability of NdFeB magnets can be significantly improved. This improvement is mainly achieved through the distribution of Mg nanopowder in the grain boundary region. It improves the wettability of the neodymium-rich phase along the main phase particles, improves the microstructure of the grain boundary phase, and refines the main phase grains, thereby improving the magnetic properties of the magnet. The addition of Mg nanopowder also improves the thermal stability of NdFeB permanent magnets. At high temperatures, NdFeB permanent magnets are prone to aging, resulting in a decrease in magnetic properties. However, by adding Mg nanopowder, this trend of property decline can be slowed down to a certain extent. Especially when the temperature does not exceed 100 °C, the remanence, coercivity, and maximum magnetic energy product of NdFeB permanent magnets with the addition of an appropriate amount of Mg nanopowder show a basically the same downward trend with the increase in temperature, indicating that Mg nanopowder has a certain effect on improving thermal stability. Adding Mg nanopowder to NdFeB permanent magnets can change the microstructure of the grain boundary and the magnet density, thereby achieving an improvement in the magnetic properties of the NdFeB permanent magnet.

[0055] The addition of Mg nanopowder in the permanent magnet can increase the corrosion potential of the permanent magnet, reduce the corrosion current density, and increase the charge transfer resistance, thereby improving the corrosion resistance of the permanent magnet. By adding an appropriate amount of Mg nanopowder, the density of the magnet can reach the maximum value, and at the same time, the orientation degree of the magnet can be increased, which all contribute to improving the corrosion resistance.

[0056] In the preparation process of the NdFeB permanent magnet, the component ratios of the main neodymium, iron, and boron are relatively reasonable, and other trace elements and rare earth elements that can promote the magnetic properties and temperature resistance of the magnet are added to ensure that the prepared permanent magnet has excellent properties. At the same time, the forming method is reasonable.

[0057] Example 1:

[0058] An example provided by the present invention: A preparation method of a heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet, comprising the following steps:

[0059] S1. Weigh the main alloy raw materials and auxiliary alloy raw materials according to a certain ratio;

[0060] S2. Vacuum melt, hydrogen break, and air flow grinding treatment are respectively carried out on the weighed main alloy raw materials and auxiliary alloy raw materials to prepare main phase magnetic powder and auxiliary phase powder;

[0061] S3. Mix the main phase magnetic powder and the auxiliary phase powder, and perform orientation pressing on the mixed material to obtain a green magnet;

[0062] S4. Sinter and temper the green magnet, and cool to obtain an NdFeB permanent magnet with a heavy rare earth segregation type structure;

[0063] Among them, in S1, the main alloy raw materials include 33 parts of neodymium powder, 65 parts of iron powder, 4.85 parts of boron powder, 0.05 parts of copper powder, 0.5 parts of aluminum powder, 0.5 parts of nickel powder, and 0.7 parts of cobalt powder by weight;

[0064] In S3, during the mixing process of the main phase magnetic powder and the auxiliary phase powder, 0.1 wt% of Mg nanopowder is added.

[0065] In S1, the auxiliary alloy is an alloy of heavy rare earths, and the raw materials of the auxiliary alloy include 9 parts of gadolinium, 13 parts of terbium, 10 parts of aluminum powder, and 15 parts of copper powder.

[0066] In the vacuum melting step of S2, the melting temperature of the melting furnace is 1500 °C, and the melting holding time is 40 min.

[0067] In the hydrogen break step of S2, the melted material is sent into a hydrogen crushing furnace, evacuated to a vacuum degree less than 3.2 Pa, hydrogen is introduced, and the pressure is maintained at 1.6×10 5 Pa, the hydrogen break treatment duration is 4.5 h, and after the residual hydrogen is extracted, the hydrogen crushing furnace is heated to 460 °C and held for 3.6 h.

[0068] In the air flow grinding step of S2, the material after hydrogen break is collected and sent into an air flow grinder for air flow grinding to obtain main phase magnetic powder and auxiliary phase powder with a particle size of 2.6 μm.

[0069] In the orientation pressing and forming step of S3, the pressing and forming step adopts a combined pressing method of vertical pressing and isostatic pressing for densification. The orientation magnetic field is 3.2 T, the forming pressure is 45 Mpa, the pressure of isostatic pressing is 200 Mpa, and the pressure holding time is 100 s.

[0070] In the sintering step of S4, the green magnet blank is heated in the furnace to 800 °C in a vacuum environment and sintered for 2 h. Then the green magnet blank is continuously heated in the furnace to 1150 °C in a vacuum environment and sintered for 3.5 h, and then cooled in the furnace to obtain a sintered body.

[0071] In the tempering step of S4, the tempering treatment adopts two-stage tempering treatment;

[0072] The first-stage tempering treatment: the tempering temperature is 1000 °C and the time is 4 h;

[0073] The second-stage tempering treatment: the tempering temperature is 600 °C and the time is 4 h;

[0074] A heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet is prepared according to the above preparation method of a heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet. The NdFeB permanent magnet is divided into a main phase and an auxiliary phase. The main phase is an alloy containing NdFeB; the auxiliary phase is an alloy of heavy rare earths. The main phase grains of the NdFeB permanent magnet have a heavy rare earth element segregation structure. Among them, the heavy rare earth elements diffuse into the main phase grains to form a segregation layer and a heavy rare earth surface layer. The segregation layer is located inside the heavy rare earth surface layer, and the concentration of heavy rare earth elements is higher than that of the heavy rare earth surface layer. The thickness of the segregation layer is 0.4 μm, and the thickness of the heavy rare earth surface layer is 1 μm.

[0075] Example Two:

[0076] An example provided by the present invention: A preparation method of a heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet, comprising the following steps:

[0077] S1. Weigh the main alloy raw materials and auxiliary alloy raw materials according to a certain ratio;

[0078] S2. Vacuum melt, hydrogen break and air flow grinding treatment are respectively carried out on the weighed main alloy raw materials and auxiliary alloy raw materials to prepare main phase magnetic powder and auxiliary phase powder;

[0079] S3. Mix the main phase magnetic powder and the auxiliary phase powder, and perform orientation pressing and forming treatment on the mixed material to obtain a green magnet blank;

[0080] S4. Sinter and temper the green magnet blank, and cool to obtain a NdFeB permanent magnet with a heavy rare earth segregation type structure;

[0081] Among them, in S1, the main alloy raw materials include 34 parts by weight of neodymium powder, 67 parts of iron powder, 4.8 parts of boron powder, 0.06 parts of copper powder, 0.4 parts of aluminum powder, 0.6 parts of nickel powder and 0.68 parts of cobalt powder;

[0082] In S3, during the mixing process of the main phase magnetic powder and the auxiliary phase powder, 0.09 wt% of Mg nanopowder is added.

[0083] In S1, the auxiliary alloy is an alloy of heavy rare earths, and the raw materials of the auxiliary alloy include 10 parts of gadolinium, 13 parts of terbium, 12 parts of aluminum powder and 15 parts of copper powder.

[0084] In the vacuum melting step of S2, the melting temperature of the melting furnace is 1500 °C, and the melting holding time is 55 min.

[0085] In the hydrogen breaking step of S2, the melted material is fed into a hydrogen crushing furnace, evacuated to a vacuum degree equal to 3.2 Pa, hydrogen is introduced, and the pressure is maintained at 1.6×10 5 Pa, the hydrogen breaking treatment duration is 4 h, after the residual hydrogen is extracted, the hydrogen crushing furnace is heated to 460 °C and held for 3.6 h.

[0086] In the air flow grinding step of S2, the material after hydrogen breaking is collected and fed into an air flow grinding machine for air flow grinding to obtain the main phase magnetic powder and the auxiliary phase powder with a particle size of 3.2 μm.

[0087] In the orientation pressing and forming step of S3, the pressing and forming step adopts a combined pressing method of vertical pressing and isostatic pressing for densification, the orientation magnetic field is 4 T, the forming pressure is 35 Mpa, the pressure of isostatic pressing is 220 Mpa, and the pressure holding time is 110 s.

[0088] In the sintering step of S4, the green magnet blank is heated in a vacuum environment to 800 °C with the furnace and sintered for 2 h, then the green magnet blank is continuously heated in a vacuum environment to 1150 °C with the furnace and sintered for 3.5 h, and then cooled with the furnace to obtain a sintered body.

[0089] In the tempering step of S4, the tempering treatment adopts two-stage tempering treatment;

[0090] The first-stage tempering treatment: the tempering temperature is 1200 °C and the time is 2 h;

[0091] The second-stage tempering treatment: the tempering temperature is 800 °C and the time is 1.5 h;

[0092] A heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet, which is prepared according to the preparation method of the heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet described above. The NdFeB permanent magnet is divided into a main phase and an auxiliary phase. The main phase is an alloy containing NdFeB; the auxiliary phase is an alloy of heavy rare earths. The main phase grains of the NdFeB permanent magnet have a heavy rare earth element segregation structure. Among them, the heavy rare earth elements diffuse into the main phase grains to form a segregation layer and a heavy rare earth surface layer. The segregation layer is located inside the heavy rare earth surface layer, and the concentration of heavy rare earth elements is higher than that of the heavy rare earth surface layer. The thickness of the segregation layer is 0.3μm, and the thickness of the heavy rare earth surface layer is 1.2μm.

[0093] Example Three:

[0094] An example provided by the present invention: A preparation method of a heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet, comprising the following steps:

[0095] S1. Weigh the main alloy raw materials and auxiliary alloy raw materials according to a certain ratio;

[0096] S2. Vacuum melt, hydrogen break and airflow grind the weighed main alloy raw materials and auxiliary alloy raw materials respectively to prepare main phase magnetic powder and auxiliary phase powder;

[0097] S3. Mix the main phase magnetic powder and the auxiliary phase powder, and perform orientation pressing on the mixed material to obtain a green magnet;

[0098] S4. Sinter and temper the green magnet, and cool to obtain a NdFeB permanent magnet with a heavy rare earth segregation type structure;

[0099] Among them, in S1, the main alloy raw materials include 36 parts of neodymium powder, 70 parts of iron powder, 4.9 parts of boron powder, 0.07 parts of copper powder, 0.8 parts of aluminum powder, 0.7 parts of nickel powder and 0.8 parts of cobalt powder by weight;

[0100] In S3, during the mixing process of the main phase magnetic powder and the auxiliary phase powder, 0.11wt% of Mg nanopowder is added.

[0101] In S1, the auxiliary alloy is an alloy of heavy rare earths, and the raw materials of the auxiliary alloy include 13 parts of gadolinium, 14 parts of terbium, 15 parts of aluminum powder and 15 parts of copper powder.

[0102] In the vacuum melting step of S2, the melting temperature of the melting furnace is 1450°C, and the melting holding time is 35min.

[0103] In the hydrogen break step of S2, the melted material is sent into a hydrogen crushing furnace, evacuated to a vacuum degree less than or equal to 3.2Pa, hydrogen is introduced, and the pressure is maintained at 1.6×10 5 Pa, the hydrogen break treatment duration is 3.8h - 4.5h, and after the residual hydrogen is extracted, the hydrogen crushing furnace is heated to 460°C and held for 3.6h.

[0104] In the air jet milling step of S2, the materials after hydrogen decrepitation are collected and fed into an air jet mill for air jet milling to obtain main phase magnetic powder with a particle size of 2.6 μm and auxiliary phase powder.

[0105] In the orientation pressing and forming step of S3, the pressing and forming step adopts a combined pressing method of vertical pressing and isostatic pressing for densification. The orientation magnetic field is 3.5 T, the forming pressure is 35 Mpa, the pressure of isostatic pressing is 180 Mpa, and the pressure holding time is 150 s.

[0106] In the sintering step of S4, the green magnet blank is heated in the furnace to 800 °C in a vacuum environment and sintered for 2 h. Then, the green magnet blank is continuously heated in the furnace to 1150 °C in a vacuum environment and sintered for 3.5 h, and then cooled in the furnace to obtain a sintered body.

[0107] In the tempering step of S4, two-stage tempering treatment is adopted;

[0108] The first-stage tempering treatment: the tempering temperature is 1000 °C and the time is 6 h;

[0109] The second-stage tempering treatment: the tempering temperature is 500 °C and the time is 6 h;

[0110] A heavy rare earth segregated high-temperature resistant high-performance NdFeB permanent magnet is prepared according to the above preparation method of a heavy rare earth segregated high-temperature resistant high-performance NdFeB permanent magnet. The NdFeB permanent magnet is divided into a main phase and an auxiliary phase. The main phase is an alloy containing NdFeB; the auxiliary phase is an alloy of heavy rare earth. There is a heavy rare earth element segregation structure in the main phase grains of the NdFeB permanent magnet. Among them, the heavy rare earth elements diffuse into the main phase grains to form a segregation layer and a heavy rare earth surface layer. The segregation layer is located inside the heavy rare earth surface layer, and the concentration of heavy rare earth elements is higher than that of the heavy rare earth surface layer. The thickness of the segregation layer is 2 μm, and the thickness of the heavy rare earth surface layer is 4 μm.

[0111] Comparative Example 1:

[0112] The difference between the preparation method of this comparative example and that of Example 1 is that in S3, during the mixing process of the main phase magnetic powder and the auxiliary phase powder, Mg nanoflakes are not added, and the rest are the same as those in Example 1.

[0113] Comparative Example 2:

[0114] This comparative example provides a preparation method of a NdFeB permanent magnet, and the specific steps are as follows:

[0115] S1. Pretreatment

[0116] Weigh each raw material in proportion and conduct vacuum melting to obtain a NdFeB ingot;

[0117] S2. Hydrogen decrepitation

[0118] The neodymium-iron-boron ingot is subjected to hydrogen explosion treatment to obtain neodymium-iron-boron particles;

[0119] S3. Powder making

[0120] The neodymium-iron-boron particles are ground to obtain neodymium-iron-boron powder;

[0121] S4. Molding

[0122] The neodymium-iron-boron powder is pressed into shape under the conditions of an orientation pressing magnetic field of 2 T, isostatic pressing of 250 MPa, and a pressing time of 90 s to obtain a neodymium-iron-boron green body;

[0123] S5. Sintering

[0124] The neodymium-iron-boron green body is subjected to vacuum sintering and secondary tempering treatment. The vacuum sintering includes two stages:

[0125] In the first stage, it is first heated from room temperature to 760 °C, held for 1 h, and the heating rate is 7 °C / min; in the second stage, the temperature is raised to 1020 °C, held for 1.5 h, and the heating rate is 5 °C / min, and then it is naturally cooled to obtain a neodymium-iron-boron permanent magnet.

[0126] Among them, for the neodymium-iron-boron permanent magnet of this comparative example, by weight, the raw materials include the following components:

[0127] Pr-Nd 138 parts, Ho-Fe 20 parts, Ce 40 parts, B 30 parts, Cu 1.2 parts, Al 3 parts, Zr 4 parts, Co 3 parts, Fe 385 parts.

[0128] The neodymium-iron-boron permanent magnet prepared by the preparation method of this comparative example does not have grains with a heavy rare earth segregation type structure.

[0129] The raw material weight parts and the addition mass ratio data of Mg nanoflakes in the above-mentioned examples and comparative examples are as follows in the table:

[0130]

[0131] According to GB / T3217 Magnetic test methods for permanent magnet materials, the magnetic properties of the neodymium-iron-boron permanent magnets obtained in Examples 1-3 and Comparative Examples 1-2 are tested. The test results are shown in the table:

[0132]

[0133] Combined with the above-mentioned examples and comparative examples, and analyzed in combination with the test results:

[0134] By comparing Examples 1-3 with Comparative Examples 1-2, the Nd-Fe-B permanent magnet prepared by the preparation method of the present invention has excellent magnetic properties. The magnet with a heavy rare earth segregation type structure grain can prevent the movement of the reverse magnetization domain into the interior of the magnet, improve the demagnetization resistance and coercivity of the magnet. Adding Mg nanopowder to the Nd-Fe-B permanent magnet can change the microstructure of the grain boundary and the density of the magnet, thereby realizing the improvement of the magnetic properties of the Nd-Fe-B permanent magnet.

[0135] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. A method for preparing a heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet, comprising the following steps: S1. Weigh the main alloy raw materials and auxiliary alloy raw materials according to a certain proportion; S2. Vacuum melt, hydrogen break and airflow grind the weighed main alloy raw materials and auxiliary alloy raw materials respectively to prepare main phase magnetic powder and auxiliary phase powder; S3. Mix the main phase magnetic powder and the auxiliary phase powder, and perform orientation pressing and forming treatment on the mixed material to obtain a green magnet; S4. Sinter and temper the green magnet, and cool to obtain a NdFeB permanent magnet with a heavy rare earth segregation type structure; Among them, In S1, the main alloy raw materials include 32 parts - 36 parts of neodymium powder, 62 parts - 70 parts of iron powder, 4.8 parts - 4.9 parts of boron powder, 0.04 parts - 0.07 parts of copper powder, 0.3 parts - 0.8 parts of aluminum powder, 0.4 parts - 0.7 parts of nickel powder and 0.6 parts - 0.8 parts of cobalt powder by weight; In S3, during the mixing process of the main phase magnetic powder and the auxiliary phase powder, add 0.08wt% - 0.12wt% of Mg nanopowder; In S1, the auxiliary alloy is an alloy of heavy rare earths, and the raw materials of the auxiliary alloy include 6 parts - 13 parts of gadolinium, 13 parts - 14 parts of terbium, 8 parts - 15 parts of aluminum powder and 15 parts - 19 parts of copper powder.

2. The preparation method of a heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet according to claim 1, characterized in that: In the vacuum melting step of S2, the melting temperature of the melting furnace is 1400°C - 1600°C, and the melting holding time is 25min - 65min.

3. The preparation method of a heavy rare earth segregated high temperature resistant high performance NdFeB permanent magnet according to claim 1, characterized in that: In the hydrogen desorption step of S2, the smelted material is fed into a hydrogen crushing furnace, the vacuum is pumped to a vacuum degree less than or equal to 3.2 Pa, hydrogen is introduced, and the pressure is maintained at 1.6×10 5 Pa to 2×10 5 Pa, the hydrogen desorption treatment duration is 3.8 h to 4.5 h, after the residual hydrogen is extracted, the temperature of the hydrogen crushing furnace is raised to 460 °C and held for 3.6 h.

4. The preparation method of a heavy rare earth segregated high temperature resistant high performance NdFeB permanent magnet according to claim 1, characterized in that: In the airflow grinding step of S2, collect the material after hydrogen break and send it into an airflow grinder for airflow grinding to obtain main phase magnetic powder and auxiliary phase powder with a particle size of 2.6μm - 3.2μm.

5. The preparation method of a heavy rare earth segregated type high temperature resistant and high performance NdFeB permanent magnet according to claim 1, characterized in that: In the orientation pressing and forming step of S3, the pressing and forming step adopts a combined pressing method of vertical pressing and isostatic pressing for densification, the orientation magnetic field is 2.5T - 4.2T, the forming pressure is 15Mpa - 55Mpa, the pressure of isostatic pressing is 180Mpa - 250Mpa, and the pressure holding time is 30s - 150s.

6. The preparation method of a heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet according to claim 1, characterized in that: In the sintering step of S4, heat the green magnet in a vacuum environment to 800°C with the furnace, sinter for 2h, continue to heat the green magnet in a vacuum environment to 1150°C with the furnace, sinter for 3.5h, and cool with the furnace to obtain a sintered body.

7. The preparation method of a heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet according to claim 1, characterized in that: In the tempering step of S4, two-stage tempering treatment is adopted; First-stage tempering treatment: the tempering temperature is 850°C - 1200°C, and the time is 1.5h - 8h; Second-stage tempering treatment: the tempering temperature is 450°C - 800°C, and the time is 1.5h - 6h.

8. A heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet, which is prepared by the preparation method of a heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet according to claim 1, and is characterized in that, This NdFeB permanent magnet is divided into a main phase and an auxiliary phase. The main phase is an alloy containing NdFeB; The auxiliary phase is an alloy of heavy rare earths. The main phase grains of this NdFeB permanent magnet have a heavy rare earth element segregation structure, in which the heavy rare earth elements diffuse into the main phase grains to form a segregation layer and a heavy rare earth surface layer.

9. A heavy rare earth segregation type high temperature resistant and high performance NdFeB permanent magnet according to claim 8, characterized in that: The segregation layer is located inside the heavy rare earth surface layer, and the concentration of heavy rare earth elements is higher than that of the heavy rare earth surface layer. The thickness of the segregation layer is 0.2μm - 3μm, and the thickness of the heavy rare earth surface layer is 1μm - 5μm.

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