A high coercive force NdFeB strong magnet and its preparation method and cylindrical magnetic block made of the magnet

Abstract

To slow the rate of loss of coercivity in NdFeB magnets, the present application provides a high-coercivity NdFeB magnet, a method for preparing the magnet, and a cylindrical magnetic block made from the magnet. The magnets primarily comprise the following raw materials, by weight: 20-29% praseodymium-neodymium alloy, 0-2% copper, 0-2% zirconium, 0-2% cobalt, 0-2% niobium, 0-2% aluminum, 0-2% gallium, 1-5% dysprosium, and the balance iron. The present application has the advantage of slowing the rate of loss of coercivity in NdFeB magnets.

Description

Technical Field

[0001] The present application relates to the field of preparation of permanent magnetic materials, and more specifically, to a high-coercivity NdFeB strong magnet, a preparation method thereof, and a cylindrical magnetic block made of the magnet. Background Art

[0002] NdFeB magnets are magnet materials primarily composed of NdFeB. They exhibit high remanence, coercivity, and magnetic product energy, and are used in wind power generation, new energy vehicles, variable-frequency home appliances, and energy-saving elevators. However, NdFeB magnets have low Curie temperatures and poor temperature stability. During long-term use, NdFeB magnets typically generate high temperatures in their environments, which can affect the magnets and reduce their magnetic properties. This also reduces their coercivity. Existing methods for increasing the coercivity of magnets primarily involve grain refinement. However, grain refinement in existing production processes requires further equipment upgrades, which is extremely costly.

[0003] In view of the above-mentioned related technologies, the inventors believe that in order to increase the service life of NdFeB strong magnets, it is necessary to reduce the cost while slowing down the rate of loss of their coercive force. Summary of the Invention

[0004] In order to slow down the decay rate of the coercive force of a strong NdFeB magnet, the present application provides a strong NdFeB magnet with high coercive force, a preparation method thereof, and a cylindrical magnetic block made of the magnet.

[0005] In the first aspect, the present application provides a high coercivity NdFeB strong magnet:

[0006] A high-coercivity NdFeB strong magnet mainly comprises the following components in weight percentage: 20-29% of praseodymium-neodymium alloy, 0-2% of copper, 0-2% of zirconium, 0-2% of cobalt, 0-2% of niobium, 0-2% of aluminum, 0-2% of gallium, 1-5% of dysprosium, and the balance of iron.

[0007] By adopting the above technical solution, metallic dysprosium is the main additive to improve the coercive force and thermal stability of NdFeB strong magnets. Coercive force is the most important indicator of the magnet's anti-demagnetization ability. Usually, the magnetism of NdFeB strong magnets is easily reduced during long-term use. By adding metallic dysprosium, the coercive force of NdFeB strong magnets can be improved, the magnetic decline of NdFeB strong magnets can be slowed down, and the service life of NdFeB strong magnets can be extended. At the same time, the addition of metallic dysprosium can also replace part of neodymium. Metallic dysprosium replaces neodymium to generate Dy2Fe 14 B, Dy2Fe 14 The anisotropy field of B is much larger, which significantly increases the coercive force in the magnet; metallic dysprosium also has the effect of reducing the grain size, thereby reducing the surface defects of the grains, reducing the probability of reverse magnetization nucleation, and thus increasing the coercive force of the magnet.

[0008] In a second aspect, the present application provides a method for preparing a high coercivity NdFeB strong magnet, which adopts the following technical solution:

[0009] A method for preparing a high coercive force NdFeB strong magnet mainly comprises the following steps:

[0010] S1: uniformly mixing praseodymium-neodymium alloy, copper, zirconium, cobalt, niobium, aluminum and gallium, smelting, taking out and cooling to obtain a preform;

[0011] S2: pulverizing dysprosium and iron by hydrogenation to prepare hydrogen-crushed dysprosium and hydrogen-crushed iron; hydrogen-crushing the preformed material prepared in step S1 to prepare pulverized material, adding hydrogen-crushed dysprosium and hydrogen-crushed iron during the pulverizing process, and mixing them uniformly to prepare a preformed powder;

[0012] S3: placing the preformed powder obtained in step S2 into a mold, pressing and molding it, and sintering it to prepare a semi-finished product;

[0013] S4: Grind the semi-finished product obtained in step S3 to obtain.

[0014] By adopting the above technical solution, the raw materials of praseodymium-neodymium alloy, copper, zirconium, cobalt, niobium, aluminum and gallium are mixed uniformly and then smelted to prepare a preformed material, and the preformed material is subjected to hydrogen crushing and pulverization. Compared with the original mechanical crushing effect, the hydrogen crushing and pulverization method has the characteristics of more uniform size of the powder produced and good surface activity. Hydrogen-crushed dysprosium and hydrogen-crushed iron are added during the process of hydrogen crushing and pulverizing the preformed material, which can reduce the loss of metallic dysprosium and metallic iron during the smelting process. At the same time, the hydrogen cracking treatment also improves the uniformity of the interface between the metallic dysprosium, metallic iron and the preformed material, inhibits the irregular growth of grains during the sintering process of the preformed powder, and improves the coercive force of the prepared NdFeB strong magnet.

[0015] In step S3, the size of the mold can be adjusted according to actual needs to adjust the size of the product. The finished product specifications in this application include but are not limited to small-sized NdFeB strong magnets with a diameter between 4mm-10mm, and their shapes include but are not limited to cylinders, rectangles, etc.

[0016] Optionally, the preformed powder obtained in step S2 is subjected to a dehydrogenation treatment before being pressed, and the dehydrogenation temperature is 300-400°C.

[0017] By adopting the above technical solution, each raw material in the preformed powder is subjected to hydrogen cracking treatment, and the preformed powder is dehydrogenated at a temperature of 300-400°C. As the temperature rises, the preformed powder gradually undergoes a dehydrogenation reaction to generate dihydrides, which have good stability in the atmospheric environment. At the same time, the dehydrogenation reaction reduces the ability of the preformed powder to form hydrogen bonds with water vapor in the air. Water is one of the reactants that cause electrochemical corrosion of the preformed powder. Therefore, the dehydrogenation reaction can reduce the amount of water vapor adsorbed on the surface of the preformed powder, so that the moisture absorption rate of the preformed powder is significantly reduced, the oxidation rate of the preformed powder is reduced, and the rate of loss of the coercive force of the prepared NdFeB strong magnet is slowed down. When the production specification of the product is a small cylindrical magnet product, since the hydrogen cracking treatment is performed on each raw material and the preformed powder is dehydrogenated, the moisture absorption rate and oxidation rate of the prepared preformed powder are significantly reduced, the rate of loss of the coercive force of the prepared finished product is slowed down, the magnetic properties are more stable, and it is more suitable for the processing of precision equipment.

[0018] Optionally, the pressure when the preformed powder is pressed in step S3 is 4-10 MPa.

[0019] By adopting the above technical solution, the pressure during pressing is adjusted. When the pressure during pressing is too low, the pre-formed powders are not tightly bonded together, and a large number of pores exist in the prepared semi-finished product, which makes it easy for air and moisture to enter the interior of the semi-finished product during subsequent use, causing oxidation of the NdFeB strong magnet and a decrease in magnetic force and coercive force. However, when the pressing pressure is too high, the gaps between the pre-formed powders are too small, and the metallic dysprosium after hydrogen decomposition is not easy to enter between the pre-formed powders, affecting the uniformity of the distribution of metallic dysprosium between the various raw materials and the effect of metallic dysprosium on improving the coercive force of the magnet. By adjusting the pressure during pressing, the uniformity of the combination of the various raw materials inside the prepared magnet is optimized, so that the prepared NdFeB strong magnet has good coercive force and performance.

[0020] Optionally, after the semi-finished product is ground in step S4, the coating agent is mixed with a toluene solution to prepare a coating liquid, and then the semi-finished product is immersed in the coating liquid, and then taken out and dried to prepare a coating layer on the surface of the semi-finished product; the coating agent used is a silane coupling agent; the mass ratio of the semi-finished product and the coating agent used is (4-6):(3-5).

[0021] By adopting the above technical solution, the semi-finished product is immersed in the coating liquid. Since the silane coupling agent can form a covalent bond with the surface of the semi-finished product, a strong silane coupling agent molecular film is formed on the surface of the semi-finished product. At the same time, since the silane coupling agent is hydrophobic, it can prevent moisture from entering the interior of the prepared NdFeB strong magnet, reduce the corrosion effect of moisture on the NdFeB strong magnet, and delay the rate of decline of the coercive force of the NdFeB strong magnet; at the same time, since the silane coupling agent molecular film is relatively dense, it can prevent oxygen from penetrating into the interior of the NdFeB strong magnet, reduce the decrease in coercive force caused by oxidation of the NdFeB strong magnet, and improve the performance of the NdFeB strong magnet.

[0022] Optionally, after the coating layer is generated on the surface of the semi-finished product, a Ni-P electroplating layer is electroplated on the outer surface of the coating layer.

[0023] By adopting the above technical solution, the Ni-P electroplating layer has the characteristics of few pores, uniform thickness, high hardness and good surface finish. At the same time, the bonding strength between the Ni-P electroplating layer and the semi-finished product is also good. The setting of the Ni-P plating layer not only slows down the oxidation corrosion rate of the semi-finished product, but also plays a role in protecting the surface of the semi-finished product, thereby improving the wear resistance of the prepared NdFeB strong magnet during use and reducing the decay rate of the coercive force of the NdFeB strong magnet.

[0024] Optionally, the Ni-P electroplating layer contains 7-10% phosphorus.

[0025] By adopting the above technical solution, the phosphorus content in the Ni-P electroplating layer is controlled. As the phosphorus content increases, the Ni-P electroplating layer gradually changes from a crystalline state to an amorphous state, so that the Ni-P electroplating layer has no grain boundary defects and has high corrosion resistance. At the same time, as the phosphorus content in the Ni-P electroplating layer continues to increase, the anions adsorbed by the cathode in the Ni-P electroplating layer reach a maximum value, and the phosphorus content tends to be stable. The amorphous state of the formed Ni-P alloy no longer changes. By controlling the phosphorus content in the Ni-P electroplating layer, the Ni-P electroplating layer is stabilized and has an anti-corrosion effect on the NdFeB strong magnet.

[0026] Optionally, after the Ni-P electroplating layer is formed on the surface of the semi-finished product, an antioxidant is sprayed on the outside of the Ni-P electroplating layer, and the antioxidant layer is obtained by curing. The preparation method of the antioxidant includes the following steps:

[0027] 1) Mixing 4,4-diphenylmethane bismaleimide and diaminodiphenylmethane, heating to a molten state, and standing at a temperature of 110-120° C. for 10-20 minutes to prepare a pretreated material; the molar ratio of 4,4-diphenylmethane bismaleimide to diaminodiphenylmethane is (3-5):(1-2);

[0028] 2) Add epoxy resin to the pretreated material prepared in step 1), mix well, and let stand at 120-140° C. for 10-20 minutes to obtain the product; the molar ratio of 4,4-diphenylmethane bismaleimide to epoxy resin in step 1) is (1-3):(2-5).

[0029] By adopting the above technical solution, 4,4-diphenylmethane bismaleimide, diaminodiphenylmethane and epoxy resin are used to prepare an antioxidant layer. Since 4,4-diphenylmethane bismaleimide has good electrical insulation and high temperature resistance, but poor toughness, 4,4-diphenylmethane bismaleimide is modified by diaminodiphenylmethane to generate a low molecular weight linear polyamine-imide, which improves the toughness and mechanical properties of 4,4-diphenylmethane bismaleimide. Then, by adding epoxy resin, the The low molecular weight linear polyamine-imide in the pretreated material reacts with the epoxy resin, and the polyamine-imide also undergoes a self-polymerization reaction to generate a product with a cross-linked structure; since the epoxy resin has good water resistance, the cross-linking of 4,4-diphenylmethane bismaleimide and the epoxy resin improves the water resistance of the anti-oxidation layer, so that the anti-oxidation layer can reduce the erosion of oxygen and moisture on the coercive force of the NdFeB strong magnet, slow down the decay rate of the coercive force of the NdFeB strong magnet, and improve the performance of the NdFeB strong magnet.

[0030] Optionally, the epoxy value of the epoxy resin in step 2) is 0.4-0.48.

[0031] By adopting the above technical solution, the epoxy value of the epoxy resin is adjusted. When the epoxy value of the epoxy resin is low, the crosslinking degree of the epoxy resin and the 4,4-diphenylmethane-type bismaleimide modified by diaminodiphenylmethane is low, and the generated interpenetrating network structure is relatively sparse, so that the antioxidant layer is not firmly bonded to the surface of the semi-finished product, and there are pores between the antioxidant layer and the semi-finished product. Oxygen can easily enter the pores to cause oxidative corrosion to the NdFeB strong magnet, thereby reducing the coercive force of the NdFeB strong magnet; when the epoxy value of the epoxy resin is too high, the crosslinking degree is high, the density of the generated antioxidant layer is large, the fluidity of the antioxidant layer is poor, and it is not easy to be evenly dispersed on the surface of the semi-finished product, making it difficult to spray the antioxidant layer onto the surface of the semi-finished product, thereby affecting the performance of the prepared NdFeB strong magnet; by adjusting the epoxy value of the epoxy resin, the prepared antioxidant layer has good coating performance on the semi-finished product, thereby slowing down the decrease in coercive force of the NdFeB strong magnet caused by oxidation.

[0032] In a third aspect, the present application provides a cylindrical magnetic block;

[0033] Optionally, the cylindrical magnetic block is made of a high coercive force neodymium iron boron strong magnet.

[0034] In summary, this application has the following beneficial effects:

[0035] 1. The present application adds metallic dysprosium to the raw materials for preparing NdFeB strong magnets. The metallic dysprosium can increase the coercive force of NdFeB strong magnets, and at the same time can refine the grains of NdFeB strong magnets, reduce the surface defects of the grains, and further improve the coercive force of the prepared NdFeB strong magnets.

[0036] 2. The present application coats the surface of the semi-finished product in the preparation process of the NdFeB strong magnet with an antioxidant layer. The antioxidant layer is prepared by 4,4-diphenylmethane bismaleimide, diaminodiphenylmethane and epoxy resin. The antioxidant layer not only has good waterproof performance, but also has good toughness and stability, reduces the oxidation rate of the NdFeB strong magnet, and enables the NdFeB strong magnet to maintain good coercive force after long-term use. DETAILED DESCRIPTION

[0037] The present application is further described in detail below with reference to the embodiments.

[0038] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0039] Preparation Example

[0040] Preparation Example 1

[0041] The preparation method of the antioxidant in this preparation example includes the following steps:

[0042] 1) 4,4-diphenylmethane bismaleimide and diaminodiphenylmethane are placed in a stirring barrel and mixed evenly, the stirring barrel is heated until the 4,4-diphenylmethane bismaleimide and diaminodiphenylmethane are in a molten state, and the stirring barrel is allowed to stand at 115° C. for 15 minutes to obtain a pretreated material; the molar ratio of the 4,4-diphenylmethane bismaleimide to the diaminodiphenylmethane is 3:2; 2) epoxy resin is added to the pretreated material prepared in step 1), mixed evenly, and allowed to stand at 130° C. for 15 minutes to obtain; the molar ratio of the 4,4-diphenylmethane bismaleimide used in step 1) to the epoxy resin used in step 2) is 1:5; the epoxy value of the epoxy resin used is 0.4.

[0043] Preparation Example 2

[0044] The preparation method of the antioxidant in this preparation example includes the following steps:

[0045] 1) 4,4-diphenylmethane bismaleimide and diaminodiphenylmethane are placed in a stirring barrel and mixed evenly, the stirring barrel is heated until the 4,4-diphenylmethane bismaleimide and diaminodiphenylmethane are in a molten state, and the stirring barrel is allowed to stand at 115° C. for 15 minutes to prepare a pretreated material; the molar ratio of 4,4-diphenylmethane bismaleimide to diaminodiphenylmethane is 5:1;

[0046] 2) Add epoxy resin to the pretreated material prepared in step 1), mix evenly, and let stand at 130° C. for 15 minutes to obtain; the molar ratio of 4,4-diphenylmethane bismaleimide used in step 1) to the epoxy resin used in step 2) is 3:2; the epoxy value of the epoxy resin used is 0.4.

[0047] Preparation Example 3

[0048] The preparation method of the antioxidant in this preparation example includes the following steps:

[0049] 1) 4,4-diphenylmethane bismaleimide and diaminodiphenylmethane are placed in a stirring barrel and mixed evenly, the stirring barrel is heated until the 4,4-diphenylmethane bismaleimide and diaminodiphenylmethane are in a molten state, and the stirring barrel is allowed to stand at 115° C. for 15 minutes to prepare a pretreated material; the molar ratio of 4,4-diphenylmethane bismaleimide to diaminodiphenylmethane is 4:1.5;

[0050] 2) Add epoxy resin to the pretreated material prepared in step 1), mix evenly, and let stand at 130° C. for 15 minutes to obtain; the molar ratio of 4,4-diphenylmethane bismaleimide used in step 1) to the epoxy resin used in step 2) is 2:4; the epoxy value of the epoxy resin used is 0.4.

[0051] Preparation Example 4

[0052] The difference between this preparation example and preparation example 3 is that the epoxy value of the epoxy resin used in step 2) is 0.48, and the rest is the same as that in preparation example 3.

[0053] Preparation Example 5

[0054] The difference between this preparation example and preparation example 3 is that the epoxy value of the epoxy resin used in step 2) is 0.45, and the rest is the same as that in preparation example 3.

[0055] Example

[0056] Example 1

[0057] The high coercive force NdFeB strong magnet of this embodiment comprises the following components in weight percentage: 20% of praseodymium-neodymium alloy, 1% of dysprosium, and the balance of iron;

[0058] The method for preparing a high coercive force NdFeB strong magnet of this embodiment comprises the following steps:

[0059] S1: The praseodymium-neodymium alloy of the above formula is loaded into a high-frequency vacuum melting furnace for melting, the high-frequency vacuum melting furnace is evacuated to 0.1 Pa, the temperature in the high-frequency vacuum melting furnace is controlled to 1500°C, and argon gas is injected into the melting furnace for protection, and the pressure of the argon gas in the furnace is maintained at 0.05 MPa; the melted material is taken out of the high-frequency vacuum melting furnace and cooled to obtain a preformed material:

[0060] S2: The dysprosium and iron in the above-mentioned formula amounts are subjected to hydrogen decomposition treatment to prepare hydrogen-decomposed iron and hydrogen-decomposed dysprosium respectively. The preformed material prepared in step S1 is placed in a hydrogen decomposition furnace for hydrogen explosion. The hydrogen decomposition furnace is evacuated to 0.1 Pa, the temperature of the hydrogen decomposition furnace is controlled to 250°C, hydrogen is introduced into the hydrogen decomposition furnace, and the preformed material is allowed to stand in the hydrogen environment for three hours. The preformed material is then taken out, cooled, and evenly mixed with the hydrogen-decomposed iron and hydrogen-decomposed dysprosium, and then taken out of the furnace to obtain a preformed powder.

[0061] S3: placing the preformed powder obtained in step S2 in a mold, orienting and pressing the preformed powder in a magnetic field with a magnetic field strength of 1.9 T and a pressing pressure of 4 MPa; then pre-sintering the pressed preformed powder in a vacuum at 500° C. for 2 h, and then sintering the preformed powder in a vacuum furnace at 1200° C. for 6 h, taking it out and cooling it to obtain a semi-finished product;

[0062] S4: The semi-finished product obtained in step S3 is placed at 800° C. for 5 hours, and then kept at 500° C. for 5 hours. After cooling, it is cut and polished into a cylinder.

[0063] Example 2

[0064] The method for preparing a high coercive force NdFeB strong magnet in this embodiment differs from that in Example 1 in that the raw materials used in step S1 are composed of the following components in weight percentage: 29% praseodymium-neodymium alloy, 2% copper, 2% zirconium, 2% cobalt, 2% niobium, 2% aluminum, and 2% gallium; the weight percentage of dysprosium used in step S2 is 5%, and the weight percentage of iron used is the balance; the rest is the same as in Example 1.

[0065] Example 3

[0066] The method for preparing the high coercive force NdFeB strong magnet of this embodiment differs from that of Example 1 in that the raw materials used in step S1 are composed of the following components in weight percentage: 25% praseodymium-neodymium alloy, 1% copper, 1% zirconium, 1% cobalt, 1% niobium, 1% aluminum, and 1% gallium; the weight percentage of dysprosium used in step S2 is 3%, and the weight percentage of iron used is the balance; the rest is the same as in Example 1.

[0067] Example 4

[0068] The method for preparing high coercive force NdFeB strong magnets in this embodiment is different from that in Example 3 in that the preformed powder is dehydrogenated before being pressed in step S3, and the temperature during the dehydrogenation treatment is 350°C; the rest is the same as in Example 3.

[0069] Example 5

[0070] The method for preparing the high coercive force NdFeB strong magnet of this embodiment is different from that of Example 4 in that the pressure when the preformed powder is pressed in step S3 is 10 MPa; the rest is the same as that of Example 4.

[0071] Example 6

[0072] The method for preparing the high coercive force NdFeB strong magnet of this embodiment is different from that of Example 4 in that the pressure when the preformed powder is pressed in step S3 is 6 MPa; the rest is the same as that of Example 4.

[0073] Example 7

[0074] The high coercive force NdFeB strong magnet of this embodiment comprises the following components in weight percentage: 25% praseodymium-neodymium alloy, 1% copper, 1% zirconium, 1% cobalt, 1% niobium, 1% aluminum, 1% gallium, 3% dysprosium, and the balance is iron;

[0075] The method for preparing a high coercive force NdFeB strong magnet of this embodiment comprises the following steps:

[0076] S1: The praseodymium-neodymium alloy, copper, zirconium, cobalt, niobium, aluminum, and gallium in the above-mentioned formula are loaded into a high-frequency vacuum melting furnace in order of their melting points for melting. The high-frequency vacuum melting furnace is evacuated to 0.1 Pa, and the temperature in the high-frequency vacuum melting furnace is controlled to be 1500°C. At the same time, argon gas is injected into the melting furnace for protection, and the pressure of the argon gas in the furnace is maintained at 0.05 MPa. The melted material is taken out of the high-frequency vacuum melting furnace and cooled to obtain a preformed material:

[0077] S2: The dysprosium and iron in the above-mentioned formula amounts are subjected to hydrogen decomposition treatment to prepare hydrogen-decomposed iron and hydrogen-decomposed dysprosium respectively. The preformed material prepared in step S1 is placed in a hydrogen decomposition furnace for hydrogen explosion. The hydrogen decomposition furnace is evacuated to 0.1 Pa, the temperature of the hydrogen decomposition furnace is controlled to 250°C, and hydrogen is introduced into the hydrogen decomposition furnace. The preformed material is allowed to stand in the hydrogen environment for three hours, then taken out, cooled, and evenly mixed with the hydrogen-decomposed iron and hydrogen-decomposed dysprosium, and then taken out of the furnace to obtain a preformed powder.

[0078] S3: The preformed powder obtained in step S2 is subjected to a dehydrogenation treatment at a dehydrogenation temperature of 350°C; the dehydrogenated preformed material is then placed in a mold, oriented and pressed in a magnetic field with a magnetic field strength of 1.9T, and a pressing pressure of 6 MPa; the pressed preformed powder is pre-sintered in a vacuum at 500°C for 2 hours, and then sintered in a vacuum furnace at 1200°C for 6 hours, taken out and cooled to obtain a semi-finished product; a stirring barrel is taken, a coating agent and a toluene solution are placed in the stirring barrel, and the mixture is uniformly mixed to prepare a coating liquid, and the semi-finished product is then placed in the coating liquid for immersion, taken out and dried, and a coating layer is formed on the surface of the semi-finished product; the mass ratio of the semi-finished product to the coating agent is 4:5; the coating agent used is γ-aminopropyltriethoxysilane;

[0079] S4: The semi-finished product obtained in step S3 is placed at 800° C. for 5 hours, and then kept at 500° C. for 5 hours. After cooling, it is cut and polished into a cylinder.

[0080] Example 8

[0081] The method for preparing the high coercive force NdFeB strong magnet of this embodiment is different from that of Example 7 in that in step S3, the semi-finished product is placed in the coating liquid for immersion, taken out and dried, and a coating layer is formed on the surface of the semi-finished product; the mass ratio of the semi-finished product and the coating agent used is 6:3; the rest is the same as that of Example 7.

[0082] Example 9

[0083] The method for preparing the high coercive force NdFeB strong magnet of this embodiment is different from that of Example 7 in that in step S3, the semi-finished product is placed in the coating liquid for immersion, taken out and dried, and a coating layer is formed on the surface of the semi-finished product; the mass ratio of the semi-finished product and the coating agent used is 5:4; the rest is the same as that of Example 7.

[0084] Example 10

[0085] The method for preparing the high coercive force NdFeB strong magnet of this embodiment is different from that of Example 9 in that, after the semi-finished product is cut and polished in step S4, a Ni-P electroplating layer is electroplated on the surface of the semi-finished product, and the phosphorus content in the Ni-P electroplating layer is 7%; the rest is the same as that of Example 9.

[0086] Example 11

[0087] The method for preparing the high coercive force NdFeB strong magnet of this embodiment is different from that of Example 9 in that, after the semi-finished product is cut and polished in step S4, a Ni-P electroplating layer is electroplated on the surface of the semi-finished product, and the phosphorus content in the Ni-P electroplating layer is 10%; the rest is the same as that of Example 9.

[0088] Example 12

[0089] The method for preparing the high coercive force NdFeB strong magnet of this embodiment is different from that of Example 9 in that, after the semi-finished product is cut and polished in step S4, a Ni-P electroplating layer is electroplated on the surface of the semi-finished product, and the phosphorus content in the Ni-P electroplating layer is 8%; the rest is the same as that of Example 9.

[0090] Example 13

[0091] The method for preparing the high coercive force NdFeB strong magnet of this embodiment differs from that in Example 12 in that, after the Ni-P electroplating layer is electroplated on the surface of the semi-finished product in step S4, an antioxidant is sprayed on the outside of the Ni-P electroplating layer, and the antioxidant is dried and cured at 160°C to obtain an antioxidant layer; the antioxidant is prepared in Preparation Example 1, and the thickness of the antioxidant layer is 2 mm; the rest is the same as in Example 12.

[0092] Example 14

[0093] The preparation method of the high coercive force NdFeB strong magnet in this embodiment is different from that in Example 13 in that the antioxidant sprayed on the outside of the Ni-P electroplating layer in step S4 is prepared in Preparation Example 2; the rest is the same as in Example 13.

[0094] Example 15

[0095] The preparation method of the high coercive force NdFeB strong magnet in this embodiment is different from that in Example 13 in that the antioxidant sprayed on the outside of the Ni-P electroplating layer in step S4 is prepared in Preparation Example 3; the rest is the same as in Example 13.

[0096] Example 16

[0097] The method for preparing the high coercive force NdFeB strong magnet of this embodiment is different from that in Example 13 in that the antioxidant sprayed on the outside of the Ni-P electroplating layer in step S4 is prepared in Preparation Example 4; the rest is the same as that in Example 13.

[0098] Example 17

[0099] The preparation method of the high coercive force NdFeB strong magnet in this embodiment is different from that in Example 13 in that the anti-oxidation layer sprayed on the outside of the Ni-P electroplating layer in step S4 is prepared in Preparation Example 5; the rest is the same as in Example 13.

[0100] Comparative Example

[0101] Comparative Example 1

[0102] The method for preparing the high coercive force NdFeB strong magnet in this comparative example is different from that in Example 13 in that the antioxidant used in step S4 is epoxy resin, and the rest is the same as that in Example 13.

[0103] Comparative Example 2

[0104] The method for preparing the high coercive force NdFeB strong magnet in this comparative example is different from that in Example 13 in that the method for preparing the antioxidant used in step S4 comprises the following steps: 1) heating 4,4-diphenylmethane bismaleimide to a molten state to prepare a pretreated material;

[0105] 2): Add epoxy resin to the pretreated material prepared in step S1, mix evenly, and let stand at 130°C for 15 minutes to obtain; the molar ratio of 4,4-diphenylmethane bismaleimide to epoxy resin in step 1) is 1:5; the epoxy value of the epoxy resin used is 0.4, and the rest are the same as in Example 13.

[0106] Comparative Example 3

[0107] The method for preparing the high coercive force NdFeB strong magnet in this comparative example is different from that in Example 13 in that the method for preparing the antioxidant used in step S4 comprises the following steps: mixing 4,4-diphenylmethane bismaleimide and diaminodiphenylmethane, heating to a molten state, and standing at a temperature of 115°C for 15 minutes to obtain the obtained product; the molar ratio of 4,4-diphenylmethane bismaleimide to diaminodiphenylmethane is 3:2; and the rest are the same as in Example 13.

[0108] Performance testing

[0109] Detection method

[0110] 1. Take the finished products prepared in Examples 1-17 and Comparative Examples 1-3 and cut them into samples of the same size;

[0111] 2. Samples were taken and the coercivity of the samples prepared in Examples 1-17 and Comparative Examples 1-3 was first tested using the GB / T3217-2013 national magnetic properties test standard method, and the data was recorded to obtain the initial coercivity; the samples were then corroded for 30 consecutive days using the GB6458-86 salt spray test national standard, and then tested again using the GB / T3217-2013 national magnetic properties test standard method, and the data was recorded to obtain the coercivity after 30 days; the test results are shown in Table 1;

[0112] Table 1 Coercive force test results of samples of Examples 1-17 and Comparative Examples 1-3

[0113] Serial number Initial coercive force (KOe) Coercivity after 30 days (KOe) Example 1 17.4 12.9 Example 2 17.5 13.1 Example 3 17.6 13.2 Example 4 17.6 13.7 Example 5 17.6 13.8 Example 6 17.6 14.2 Example 7 17.6 15.2 Example 8 17.6 15.0 Example 9 17.6 15.5 Example 10 17.6 15.8 Example 11 17.6 15.8 Example 12 17.6 16.0 Example 13 17.6 16.2 Example 14 17.6 16.3 Example 15 17.6 16.4 Example 16 17.6 16.2 Example 17 17.6 16.6 Comparative Example 1 17.6 12.3 Comparative Example 2 17.6 13.7 Comparative Example 3 17.6 12.2

[0114] From the analysis of Examples 1-6 and in combination with Table 1, it can be seen that the composition ratio of the magnet raw materials is optimized and adjusted. By dehydrogenating the preformed powder in the raw materials for preparing the magnet, dihydride is generated in the preformed powder through the dehydrogenation treatment, and the combination of the preformed powder and water vapor is reduced, thereby reducing the moisture absorption rate of the preformed powder. At the same time, the pressure during pressing is adjusted to improve the uniformity of the distribution of dysprosium into the preformed powder, so that the prepared NdFeB strong magnet has good density and slows down the rate of decrease of coercive force.

[0115] In combination with Examples 7-12 and Table 1, it can be seen that by mixing the semi-finished product with the coating agent, a hydrophobic molecular film is formed on the surface of the semi-finished product through the coating effect of the coating agent, thereby reducing the weakening of the internal magnetism caused by moisture entering the interior of the semi-finished product and slowing down the rate of loss of coercive force during use; at the same time, by arranging a Ni-P electroplating layer on the surface of the semi-finished product and adjusting the phosphorus content in the Ni-P electroplating layer, the Ni-P electroplating layer forms a stable amorphous structure, which has a more stable anti-corrosion effect on the magnet.

[0116] In combination with Examples 13-17, Comparative Examples 1-3 and Table 1, it can be seen that by providing an antioxidant layer on the outside of the semi-finished product after electroplating, the antioxidant layer can reduce the damage to the magnetic properties of the magnet caused by oxygen and moisture, so that the magnet still has good coercive force after long-term use; at the same time, by adjusting the molar ratio of 4,4-diphenylmethane bismaleimide to diaminodiphenylmethane, the toughness and mechanical properties of the modified 4,4-diphenylmethane bismaleimide are improved; then, by mixing the epoxy resin with the 4,4-diphenylmethane bismaleimide modified with diaminodiphenylmethane, the epoxy value of the epoxy resin is adjusted, so that the prepared antioxidant layer has good mechanical properties, toughness and water resistance, and slows down the rate at which the coercive force of the magnet fades.

[0117] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A high coercive force NdFeB strong magnet, characterized by: The main components include the following weight percentages: praseodymium-neodymium alloy 20-29%, copper 0-2%, zirconium 0-2%, cobalt 0-2%, niobium 0-2%, aluminum 0-2%, gallium 0-2%, dysprosium 1-5%, and the balance is iron; A method for preparing a high coercive force NdFeB strong magnet mainly comprises the following steps: S1: uniformly mixing praseodymium-neodymium alloy, copper, zirconium, cobalt, niobium, aluminum and gallium, smelting, taking out and cooling to obtain a preform; S2: pulverizing dysprosium and iron by hydrogenation to prepare hydrogen-crushed dysprosium and hydrogen-crushed iron; hydrogen-crushing the preformed material prepared in step S1 to prepare pulverized material, adding hydrogen-crushed dysprosium and hydrogen-crushed iron during the pulverizing process, and mixing them uniformly to prepare a preformed powder; S3: placing the preformed powder obtained in step S2 into a mold, pressing and molding it, and sintering it to prepare a semi-finished product; S4: Grinding the semi-finished product obtained in step S3 to obtain; The preformed powder obtained in step S2 is subjected to a dehydrogenation treatment before being pressed; After the semi-finished product is ground in step S4, a coating agent is mixed with a toluene solution to prepare a coating liquid, and the semi-finished product is immersed in the coating liquid, and then taken out and dried to form a coating layer on the surface of the semi-finished product; After the coating layer is formed on the surface of the semi-finished product, a Ni-P electroplating layer is formed on the outer surface of the coating layer; After the Ni-P electroplating layer is electroplated on the surface of the semi-finished product, an antioxidant is sprayed on the outside of the Ni-P electroplating layer and cured to obtain an antioxidant layer. The antioxidant layer is prepared from 4,4-diphenylmethane bismaleimide, diaminodiphenylmethane and epoxy resin.

2. The high coercivity NdFeB strong magnet according to claim 1, characterized in that: The dehydrogenation temperature is 300-400℃.

3. The high coercivity NdFeB strong magnet according to claim 1, characterized in that: The pressure when the preformed powder is pressed in step S3 is 4-10 MPa.

4. The high coercivity NdFeB strong magnet according to claim 1, characterized in that: The coating agent used is a silane coupling agent; the mass ratio of the semi-finished product and the coating agent used is (4-6): (3-5).

5. The high coercive force NdFeB strong magnet according to claim 1, characterized in that: The phosphorus content in the Ni-P electroplating layer is 7-10%.

6. The high coercivity NdFeB strong magnet according to claim 1, characterized in that: The preparation method of the antioxidant comprises the following steps: 1): 4,4-diphenylmethane bismaleimide and diaminodiphenylmethane are mixed, heated to a molten state, and allowed to stand at a temperature of 110-120°C for 10-20 minutes to prepare a pretreated material; the molar ratio of 4,4-diphenylmethane bismaleimide to diaminodiphenylmethane is (3-5): (1-2); 2): Add epoxy resin to the pretreated material prepared in step 1), mix evenly, and let stand at 120-140°C for 10-20 minutes to obtain the product; the molar ratio of 4,4-diphenylmethane bismaleimide to epoxy resin in step 1) is (1-3): (2-5).

7. The high coercivity NdFeB strong magnet according to claim 6, characterized in that: The epoxy value of the epoxy resin in step 2) is 0.4-0.

48.

8. A cylindrical magnetic block, characterized in that: Made of the high coercive force NdFeB strong magnet described in claim 1.