Method for simultaneously improving heat resistance and corrosion resistance of neodymium-iron-boron magnet

Abstract

The invention discloses a method for simultaneously improving heat resistance and corrosion resistance of a neodymium-iron-boron magnet. The method comprises the following steps: 1) preparing a raw material A, a raw material B, a raw material C and a raw material D; 2) forming fine powder A with D50 of 0.5-8 [mu] m from the raw material A; forming fine powder B with D50 of 0.5-8 [mu] m from the raw material B; the C raw material is made into nanoscale C fine powder with D50 ranging from 50 nm to 400 nm; 3) mixing the fine powder A, the fine powder B and the nanoscale fine powder C according to a mass ratio of (48-52): (48-52): (0.6-1) to obtain mixed powder; (4) orientation forming and isostatic pressing are conducted on the mixed powder, and a pressed blank is obtained; sintering and tempering the pressed blank to obtain a sintered magnet; (5) the raw material D serves as a target material, magnetron sputtering is conducted on the sintered magnet obtained in the step (4), the coating thickness is 10 micrometers or above, and a coated magnet is obtained; and performing diffusion heat treatment on the coated magnet to obtain the neodymium-iron-boron magnet. According to the method, the heat resistance and the corrosion resistance of the obtained neodymium-iron-boron magnet can be improved at the same time.

Description

Technical Field

[0001] The invention relates to a method for simultaneously improving the heat resistance and corrosion resistance of a neodymium iron boron magnet. Background Art

[0002] Sintered NdFeB magnets are widely used in motors, electronics, medical devices and other fields due to their excellent magnetic properties. In recent years, with the increasing scarcity of rare earth resources, the application of high-abundance rare earth elements (such as Ce, La, etc.) in sintered NdFeB magnets has attracted more and more attention. However, compared with traditional rare earth elements such as Pr and Nd, the addition of high-abundance rare earth elements often reduces the corrosion resistance of magnets. The main reasons are as follows: (1) The electrode potential of high-abundance rare earth elements (such as Ce and La) is quite different from that of elements such as Fe and B. They are prone to form micro-batteries in a humid environment, accelerating the electrochemical corrosion of magnets. (2) The addition of high-abundance rare earth elements will change the composition and structure of the grain boundary phase of the magnet, reduce the stability of the grain boundary phase, and make it more susceptible to corrosion by corrosive media. (3) High-abundance rare earth elements (such as Ce) are easily oxidized at high temperatures to form loose and porous oxides, which provide channels for the penetration of corrosive media and accelerate the corrosion of magnets. Therefore, the corrosion resistance of NdFeB magnets containing high abundance of rare earth elements needs to be considered.

[0003] Furthermore, it's important to consider the changes in magnetic flux density when the magnet operates at elevated temperatures. Irreversible flux loss refers to the phenomenon in which the magnetic flux density of a magnet decreases to a certain level and cannot be restored to its original state when operating at elevated temperatures. The magnitude of this irreversible flux loss can be used to characterize the magnet's thermal stability (i.e., heat resistance). The lower the irreversible flux loss, the better.

[0004] CN107845466A discloses a method for preparing a low-cost sintered NdFeB magnet, which is prepared in the order of NdFeB main phase → Nd-rich phase powder → NdFeB magnet, wherein the NdFeB main phase powder and the Nd-rich phase powder are prepared separately. Simultaneously, by the addition of Ho, the cost of the alloy is reduced, and the Nd-rich phase is more evenly distributed on the main phase grain boundary and its intersection, improving the microstructure of the NdFeB alloy sheet, and effectively improving the corrosion resistance of the sintered NdFeB permanent magnet, reducing weight loss. Simultaneously, Ce replaces the eutectic temperature of the Nd magnet, causing the sintering and tempering temperature to decrease, saving cost. In this method, Ce content is relatively low, and corrosion resistance is improved by the addition of Ho, reducing weight loss, but the specific weight loss situation is not mentioned.

[0005] CN117542599A discloses a corrosion-resistant NdFeB magnet and its preparation method. The preparation method involves forming a powder from a primary alloy and an auxiliary alloy ingot from a casting sheet. The powder is then pressed, isostatically pressed, vacuum sintered, and tempered to obtain the NdFeB magnet. The NdFeB magnet is then chamfered, alkali-washed, pickled, and ultrasonically cleaned to obtain a pretreated NdFeB magnet. The pretreated NdFeB magnet is then coated with a nano-ZrO2 / Zn-Al composite coating via a dip-coating-centrifugation process to prevent direct contact between the magnet surface and external corrosive media, thereby improving its corrosion resistance. This preparation method is relatively complex.

[0006] CN116741521A discloses a method for reducing high-temperature irreversible magnetic flux loss in sintered magnets, including the following steps: S1: cutting the semi-finished NdFeB magnets into black sheet magnets using a magnet wire, boiling them, and chamfering them; S2: testing the magnets for acceptable aging indicators; S3: baking and chamfering the magnets that failed step S2, and repeating steps S2 and S3 until the indicators pass; S4: pickling and electroplating. This method is suitable for addressing the high high-temperature irreversible magnetic flux loss and high scrap rate of NdFeB magnets in conventional processes. Summary of the Invention

[0007] In view of this, an object of the present invention is to provide a method for simultaneously improving the heat resistance and corrosion resistance of NdFeB magnets, wherein the weight loss and irreversible magnetic flux loss of the NdFeB magnets obtained by this method are further reduced.

[0008] The present invention adopts the following technical solutions to achieve the above-mentioned purpose.

[0009] The present invention provides a method for simultaneously improving the heat resistance and corrosion resistance of a neodymium iron boron magnet, comprising the following steps:

[0010] 1) Prepare raw material A, raw material B, raw material C and raw material D; wherein, based on 100 parts by weight of raw material A, the composition of raw material A is: PrNd 28-33wt%, Al 0.1-0.35wt%, Cu 0.1-0.5wt%, B 0.85-1.5wt%, and Fe is the balance; based on 100 parts by weight of raw material B, the composition of raw material B is: PrNd 7.5-12.5wt%, Ce 18-25wt%, Al 0.05-0.25wt%, Cu 0.05-0.35wt%, Ga 0.05-0.35wt%, B 0.8-1.3wt%, and Fe is the balance; based on 100 parts by weight of raw material C, the composition of raw material C is: Pr 35-45wt%, Ni 6-15wt%, Nb 8-15wt%, B 0.9-1.5wt%, Fe is the balance; based on 100 parts by weight of D raw material, the composition of D raw material is: Tb 63-68wt%, Co 18-25wt%, Cu is the balance;

[0011] 2) Raw material A is formed into fine powder A with a D50 of 0.5 to 8 μm; raw material B is formed into fine powder B with a D50 of 0.5 to 8 μm; raw material C is formed into nano-scale fine powder C with a D50 of 50 to 400 nm;

[0012] 3) mixing fine powder A, fine powder B, and nano-grade fine powder C in a mass ratio of 48-52:48-52:0.6-1 to obtain a mixed powder;

[0013] 4) orienting and isostatically pressing the mixed powder to obtain a green compact; sintering and tempering the green compact to obtain a sintered magnet;

[0014] 5) Using the D raw material as a target, the sintered magnet obtained in step 4) is subjected to magnetron sputtering to obtain a coating thickness of 10 μm or more to obtain a coated magnet; and the coated magnet is subjected to diffusion heat treatment to obtain a NdFeB magnet.

[0015] According to the method of the present invention, preferably, in step 2), raw material A, raw material B, and raw material C are smelted respectively to obtain castings A, castings B, and castings C, respectively; and castings A, castings B, and castings C are hydrogen crushed and air flow milled respectively to obtain fine powder A, fine powder B, and nano-grade fine powder C, respectively.

[0016] According to the method of the present invention, preferably:

[0017] In step 2), raw material A, raw material B, and raw material C are melted in a vacuum rapid solidification casting furnace to obtain castings A, B, and C with a thickness of 0.15 to 0.5 mm, respectively; wherein the preparation order of castings A, B, and C is not particular;

[0018] In step 2), the A and B flakes are hydrogen-crushed to obtain coarse powder A and coarse powder B, respectively; the coarse powder A is mixed with an antioxidant and a lubricant, and subjected to air flow milling to obtain fine powder A; the coarse powder B is mixed with an antioxidant and a lubricant, and subjected to air flow milling to obtain fine powder B; wherein, the preparation order of fine powder A and fine powder B is not particular.

[0019] According to the method of the present invention, preferably, the carbon coarse powder is mixed with an antioxidant and a lubricant, and subjected to jet milling to obtain nano-scale carbon fine powder.

[0020] According to the method of the present invention, preferably, the antioxidant is selected from at least one of polyethylene glycol octane, petroleum ether and isooctyl propionate; and the lubricant is selected from at least one of aviation kerosene, isopropyl alcohol and zinc stearate.

[0021] According to the method of the present invention, preferably, in step 2), the A coarse powder is mixed with 0.1wt‰ to 10wt‰ of an antioxidant and 0.1wt‰ to 10wt‰ of a lubricant and then subjected to air flow milling; the B coarse powder is mixed with 0.1wt‰ to 10wt‰ of an antioxidant and 0.1wt‰ to 10wt‰ of a lubricant and then subjected to air flow milling; the C coarse powder is mixed with 0.1wt‰ to 10wt‰ of an antioxidant and 0.1wt‰ to 10wt‰ of a lubricant and then subjected to air flow milling.

[0022] According to the method of the present invention, preferably, in step 3), the mass ratio of fine powder A, fine powder B and nano-grade fine powder C is 49-51:49-51:0.7-0.9.

[0023] According to the method of the present invention, preferably, in step 4), the sintering is vacuum sintering with a vacuum degree of less than 0.1 Pa; the sintering temperature is 950-1150° C. and the time is 0.5-6 h; after the sintering is completed, the temperature is lowered to below 50° C.

[0024] According to the method of the present invention, preferably, in step 4), the tempering treatment is carried out under vacuum conditions, and the vacuum degree is less than or equal to 0.01 Pa; the tempering treatment includes a first tempering treatment and a second tempering treatment; the temperature of the first tempering treatment is 850-1090°C, and the time is 0.5-4h; after the first tempering treatment is completed, the temperature is reduced to below 50°C; the temperature of the second tempering treatment is 450-750°C, and the time is 0.5-4h.

[0025] According to the method of the present invention, preferably, in step 5), the coating thickness is 10-20 μm; the temperature of the diffusion heat treatment is 800-1000° C., and the time is 0.5-3 h.

[0026] The method of the present invention can simultaneously improve the heat resistance and corrosion resistance of the obtained NdFeB magnet containing a high abundance of rare earth elements (Ce), and the weight loss and irreversible magnetic flux loss of the obtained NdFeB magnet are further reduced. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0028] In the present invention, "inert atmosphere" refers to an atmosphere formed by inert gases that does not affect the performance of the magnet, including helium, neon, argon, krypton and xenon.

[0029] The "vacuum" mentioned in the present invention refers to absolute vacuum; the smaller the value, the higher the vacuum.

[0030] The “average particle size D50” mentioned in the present invention refers to the equivalent diameter of the largest particle when the cumulative distribution in the particle size distribution curve is 50%.

[0031] Prior art research has focused on the heat resistance and corrosion resistance of NdFeB magnets separately, but has focused less on simultaneously improving both. In particular, there are few reports on simultaneously improving the heat resistance and corrosion resistance of NdFeB magnets with high cerium contents (above 8 wt%) through optimization of the manufacturing process and components. The method of the present invention is not a conventional option.

[0032] The present invention provides a method for simultaneously improving the heat resistance and corrosion resistance of NdFeB magnets, comprising the following steps: 1) raw material preparation; 2) fine powder formation; 3) mixed powder formation; 4) sintered magnet formation; and 5) coating and diffusion. The fine powder formation step includes a casting sheet formation step. This is described in detail below.

[0033] Raw material preparation steps

[0034] Prepare raw material A, raw material B, raw material C and raw material D, that is, prepare alloy raw material A, alloy raw material B, alloy raw material C and alloy raw material D. This is beneficial to the next step of processing.

[0035] According to one embodiment of the present invention, based on 100 parts by weight of raw material A, the composition of raw material A is: PrNd 28-33wt%, Al 0.1-0.35wt%, Cu 0.1-0.5wt%, B 0.85-1.5wt%, and Fe is the balance. Based on 100 parts by weight of raw material B, the composition of raw material B is: PrNd 7.5-12.5wt%, Ce 18-25wt%, Al 0.05-0.25wt%, Cu 0.05-0.35wt%, Ga 0.05-0.35wt%, B 0.8-1.3wt%, and Fe is the balance. Based on 100 parts by weight of raw material C, the composition of raw material C is: Pr 35-45wt%, Ni 6-15wt%, Nb 8-15wt%, B 0.9-1.5wt%, and Fe is the balance. Based on 100 parts by weight of raw material D, the composition of raw material D is: Tb 63-68wt%, Co 18-25wt%, and Cu as the balance. Raw materials A, B, C and D do not contain Zr, Ho and Gd elements. The present invention has found that such a specific raw material composition is more conducive to improving the heat resistance and corrosion resistance of the resulting NdFeB magnet at the same time. Through the preparation process of the present invention, Ni and Nb act directly on the grain boundary area of the magnet and do not exist in the matrix phase, which basically does not affect the remanence and magnetic energy product of the magnet. The addition of Ni increases the corrosion potential of the grain boundary phase, and Nb forms a Nb alloy dispersed phase to inhibit the expansion of grain boundary corrosion, thereby improving the corrosion resistance of the magnet. Tb enters the grain boundary phase to form a shell structure, which helps to significantly improve the coercive force. Trace amounts of Co elements replace Fe in the matrix to improve the temperature stability of the magnet.

[0036] Based on 100 parts by weight of raw material A, the PrNd content in raw material A may be 28-33wt%, preferably 29-32wt%, more preferably 30-31wt%; the mass ratio of Pr to Nd is 1:3-4, preferably 1:3; the Al content may be 0.1-0.35wt%, preferably 0.15-0.3wt%, more preferably 0.18-0.25wt%, for example, 0.18wt%, 0.19wt%, 0.2wt%, 0.21wt%, 0.22wt%, 0.23wt%, 0.24wt%, 0.25wt%; the Cu content can be 0.1-0.5wt%, preferably 0.15-0.4wt%, more preferably 0.19-0.22wt%, for example 0.19wt%, 0.2wt%, 0.21wt%, 0.22wt%; the B (boron) content can be 0.85-1.5wt%, preferably 0.9-1.3wt%, more preferably 1-1.2wt%; Fe is the balance.

[0037] Based on 100 parts by weight of the B raw material, the PrNd content in the B raw material may be 7.5 to 12.5 wt%, preferably 8.5 to 11.5 wt%, and more preferably 9 to 10 wt%; the mass ratio of Pr to Nd is 1:3 to 4, preferably 1:3; the Ce content may be 18 to 25 wt%, preferably 19 to 24 wt%, and more preferably 20 to 22 wt%, for example, 20 wt%, 21 wt%, 21.5 wt%, and 22 wt%; the Al content may be 0.05 to 0.25 wt%, preferably 0.08 to 0.2 wt%, and more preferably The Cu content can be 0.05-0.35wt%, preferably 0.08-0.25wt%, more preferably 0.1-0.15wt%; the Ga content can be 0.05-0.35wt%, preferably 0.08-0.25wt%, more preferably 0.1-0.15wt%; the B (boron element) content can be 0.8-1.3wt%, preferably 0.9-1.2wt%, more preferably 0.95-1.1wt%, for example, 0.95wt%, 1wt%, 1.1wt%; Fe is the balance.

[0038] Based on 100 parts by weight of the C raw material, the Pr content in the C raw material can be 35-45wt%, preferably 38-43wt%, and more preferably 40-41wt%; the Ni content can be 6-15wt%, preferably 7-12wt%, and more preferably 7.5-10wt%, for example, it can be 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, and 10wt%; the Nb content can be 8-15wt%, preferably 10-14wt%, and more preferably 11-13wt%, for example, it can be 11wt%, 11.5wt%, 12wt%, 12.5wt%, and 13wt%; the B (boron element) content can be 0.9-1.5wt%, preferably 0.95-1.4wt%, and more preferably 1-1.2wt%, for example, it can be 1wt%, 1.1wt%, and 1.2wt%; and Fe is the balance.

[0039] Based on 100 parts by weight of the D raw material, the D raw material may contain 63-68 wt%, preferably 64-67 wt%, and more preferably 65-66 wt%. The Co content may be 18-25 wt%, preferably 19-23 wt%, and more preferably 20-22 wt%. The balance is Cu. When a target formed from the D raw material is used as a magnetron sputtering target to form a coating film, if the target is not within the scope of the present invention, the resulting neodymium ferromagnet will have increased weight loss and irreversible magnetic flux loss.

[0040] Slab Formation Steps

[0041] Raw material A, raw material B, and raw material C are melted respectively to obtain castings A, B, and C. The preparation order of castings A, B, and C is not specific.

[0042] In the present invention, raw materials A, B and C can be smelted in a vacuum rapid solidification casting furnace to obtain castings A, B and C with thicknesses of 0.15 to 0.5 mm, respectively.

[0043] In order to prevent the raw materials of the sintered magnet and the castings made therefrom from being oxidized, the smelting is carried out in a vacuum or inert atmosphere. The vacuum described here is a vacuum degree of less than 10Pa, preferably less than 5Pa, and more preferably less than 1Pa. The smelting process preferably adopts an ingot casting process or a rapid solidification casting process. The ingot casting process is to cool and solidify the raw materials of the sintered magnet after smelting, and to be made into an ingot. The rapid solidification casting is to quickly cool and solidify the raw materials of the sintered magnet after smelting, and to be thrown into alloy sheets (castings). According to one embodiment of the present invention, the smelting process adopts a rapid solidification casting process. Compared with the ingot casting process, the rapid solidification casting process can avoid the appearance of α-Fe that affects the uniformity of the magnetic powder, and can avoid the appearance of agglomerated neodymium-rich phases, which is beneficial to the main phase of the alloy Nd2Fe 14 B. Refinement of grain size. The rapid solidification sheet casting process of the present invention can be carried out in a vacuum rapid solidification sheet casting furnace (such as a vacuum medium frequency rapid solidification induction furnace).

[0044] According to one embodiment of the present invention, raw material A is added to a vacuum rapid solidification casting furnace, evacuated to below 1 Pa, filled with argon gas, and then heated to melt. The molten liquid is poured onto a rotating cooling copper roller to obtain cast sheet A. The thickness of cast sheet A can be 0.15 to 0.5 mm, preferably 0.2 to 0.4 mm, and more preferably 0.25 to 0.3 mm.

[0045] According to one embodiment of the present invention, raw material B is added to a vacuum rapid solidification casting furnace, evacuated to below 1 Pa, filled with argon, and then heated to melt. The molten liquid is poured onto a rotating cooling copper roller to obtain a cast sheet B. The thickness of the cast sheet B can be 0.15 to 0.5 mm, preferably 0.2 to 0.4 mm, and more preferably 0.25 to 0.3 mm.

[0046] According to one embodiment of the present invention, C raw material is added to a vacuum rapid solidification casting furnace, evacuated to below 1 Pa, filled with argon, and then heated to melt. The molten liquid is poured onto a rotating cooling copper roller to obtain a C cast sheet. The thickness of the C cast sheet can be 0.15 to 0.5 mm, preferably 0.2 to 0.4 mm, and more preferably 0.25 to 0.3 mm.

[0047] Fine powder formation step

[0048] Cast slabs A, B, and C are subjected to hydrogen crushing and jet milling to obtain fine powders A and B with a D50 of 0.5 to 8 μm, and nano-grade fine powder C with a D50 of 50 to 400 nm, respectively. This helps improve both the heat resistance and corrosion resistance of the resulting NdFeB magnets.

[0049] According to one embodiment of the present invention, the A flakes are hydrogen-crushed to obtain A coarse powder; the A coarse powder is mixed with an antioxidant and a lubricant and subjected to airflow milling to obtain A fine powder. The D50 of the A fine powder is 0.5 to 8 μm, preferably 1 to 6 μm, more preferably 2 to 5.5 μm, and even more preferably 3.3 to 4.5 μm, for example, 3.3 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, and 4.5 μm. The amount of the antioxidant is 0.1 wt‰ to 10 wt‰ of the mass of the A coarse powder, preferably 0.2 wt‰ to 2 wt‰, and more preferably 0.3 wt‰ to 0.6 wt‰. The amount of the lubricant is 0.1 wt‰ to 10 wt‰ of the mass of the A coarse powder, preferably 0.2 wt‰ to 2 wt‰, and more preferably 0.3 wt‰ to 0.6 wt‰. The antioxidant is selected from at least one of polyethylene glycol octane, petroleum ether and isooctyl propionate, preferably isooctyl propionate. The lubricant is selected from at least one of aviation kerosene, isopropyl alcohol and zinc stearate, preferably aviation kerosene.

[0050] The B flakes are hydrogen-crushed to obtain B coarse powder; the B coarse powder is mixed with an antioxidant and a lubricant and jet-milled to obtain B fine powder. The D50 of the B fine powder is 0.5-8 μm, preferably 1-6 μm, more preferably 2-5.5 μm, and even more preferably 3.3-4.5 μm, for example, 3.3 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, and 4.5 μm. The amount of the antioxidant is 0.1 wt‰ to 10 wt‰ of the mass of the B coarse powder, preferably 0.2 wt‰ to 2 wt‰, and more preferably 0.3 wt‰ to 0.6 wt‰. The amount of the lubricant is 0.1 wt‰ to 10 wt‰ of the mass of the B coarse powder, preferably 0.2 wt‰ to 2 wt‰, and more preferably 0.3 wt‰ to 0.6 wt‰. The antioxidant is selected from at least one of polyethylene glycol octane, petroleum ether, and isooctyl propionate, and isooctyl propionate is preferred. The lubricant is selected from at least one of aviation kerosene, isopropyl alcohol and zinc stearate, and is preferably aviation kerosene.

[0051] Among them, the preparation of A fine powder and B fine powder is not in any particular order.

[0052] According to one embodiment of the present invention, a C cast sheet is hydrogen-crushed to obtain a C coarse powder; the C coarse powder is mixed with an antioxidant and a lubricant and subjected to air flow milling to obtain a nano-scale C fine powder. The D50 of the nano-scale C fine powder is 50 to 400 nm, preferably 100 to 400 nm, more preferably 150 to 300 nm, and even more preferably 200 to 250 nm. The amount of the antioxidant used is 0.1 wt‰ to 10 wt‰ of the mass of the C coarse powder, preferably 0.2 wt‰ to 2 wt‰, and more preferably 0.3 wt‰ to 0.6 wt‰. The amount of the lubricant used is 0.1 wt‰ to 10 wt‰ of the mass of the C coarse powder, preferably 0.2 wt‰ to 2 wt‰, and more preferably 0.3 wt‰ to 0.6 wt‰.

[0053] The antioxidant is selected from at least one of polyethylene glycol octane, petroleum ether and isooctyl propionate, preferably isooctyl propionate. The lubricant is selected from at least one of aviation kerosene, isopropyl alcohol and zinc stearate, preferably aviation kerosene.

[0054] In the present invention, the coarse powders, the antioxidant and the lubricant can be mixed in a mixer, and the mixing time can be 0.5 to 3 hours, preferably 1 to 2.5 hours, and more preferably 1 to 1.5 hours.

[0055] In the present invention, hydrogen crushing and airflow milling can adopt those known in the art. The hydrogen crushing process may include the following steps: first, hydrogen is absorbed into the slab, the slab reacts with hydrogen to induce volume expansion of the slab crystal lattice, thereby crushing the slab, and then heating to dehydrogenate, thereby obtaining a coarse alloy powder. According to a preferred embodiment of the present invention, the hydrogen crushing process of the present invention is preferably carried out in a hydrogen crushing furnace. The airflow milling process utilizes an airflow to accelerate the mixture and then cause collision and crushing. The airflow can be a nitrogen flow, preferably a high-purity nitrogen flow.

[0056] Mixed powder formation steps

[0057] Fine powder A, fine powder B, and nano-grade fine powder C are mixed in a mass ratio of 48-52:48-52:0.6-1 to obtain a mixed powder. This helps to improve the heat resistance and corrosion resistance of the resulting NdFeB magnet, and reduces irreversible magnetic flux loss and weight loss.

[0058] In the present invention, the mass ratio of fine powder A, fine powder B and nano-grade fine powder C may be 48-52:48-52:0.6-1, preferably 49-51:49-51:0.7-0.9, and more preferably 50-51:50-51:0.8-0.9.

[0059] In the present invention, mixing can be performed in a mixer, and the mixing time can be 0.5 to 2.5 hours, preferably 1 to 2 hours, and more preferably 1 to 1.5 hours.

[0060] Sintered magnet formation steps

[0061] The mixed powder is oriented and molded and isostatically pressed to obtain a green compact, which is then sintered and tempered to obtain a sintered magnet. This is beneficial for obtaining a NdFeB magnet with stable performance.

[0062] In the present invention, orientation molding, isostatic pressing, sintering, and tempering can all be performed using conventional methods in the art. During orientation molding, the oxygen content can be controlled within a range of 0.1 to 100 ppm, preferably 0.1 to 10 ppm. The magnetic field strength during orientation molding can be 1 to 3 T, preferably 1.5 to 2 T. Isostatic pressing is preferably cold isostatic pressing. During sintering and tempering, the oxygen content can be controlled within a range of 0.1 to 50 ppm, preferably 0.1 to 5 ppm.

[0063] The sintering is performed under vacuum, with a vacuum degree of less than 0.1 Pa, preferably less than or equal to 0.01 Pa, and more preferably less than or equal to 0.001 Pa. The sintering temperature is 950-1150°C, preferably 980-1100°C, and more preferably 1050-1080°C. The sintering time can be 0.5-6 hours, preferably 1-5 hours, and more preferably 2-4 hours. After sintering, the temperature is lowered to below 50°C, for example, to room temperature. An inert gas can be introduced during the cooling process.

[0064] The tempering treatment is carried out under vacuum conditions with a vacuum degree of less than or equal to 0.01 Pa, preferably less than or equal to 0.001 Pa. The tempering treatment includes a first tempering treatment and a second tempering treatment. The temperature of the first tempering treatment can be 850-1090°C, preferably 900-1050°C, and more preferably 900-950°C. The duration of the first tempering treatment can be 0.5-4 hours, preferably 1-3 hours, and more preferably 1-1.5 hours. After the first tempering treatment is completed, the temperature is lowered to below 50°C, for example, to room temperature. An inert gas may be introduced during the cooling process. The temperature of the second tempering treatment can be 450-750°C, preferably 500-650°C, and more preferably 550-600°C. The duration of the second tempering treatment can be 0.5-4 hours, preferably 1-3 hours, and more preferably 2-3 hours. After the second tempering treatment is completed, the temperature can be naturally lowered to room temperature. An inert gas may be introduced during the cooling process.

[0065] Coating and diffusion steps

[0066] Using raw material D as a target, the resulting sintered magnet is subjected to magnetron sputtering to a coating thickness of at least 10 μm, thereby obtaining a coated magnet. The coated magnet is then subjected to diffusion heat treatment to obtain an NdFeB magnet. This improves both the heat resistance and corrosion resistance of the resulting NdFeB magnet.

[0067] Specifically, a target material formed from raw material D is used as a target material. Magnetron sputtering can adopt techniques known in the art. Magnetron sputtering is performed on two opposite surfaces of the sintered magnet perpendicular to the orientation direction to form a coating on the two surfaces of the sintered magnet. The coating thickness is preferably 10 to 20 μm, more preferably 10 to 15 μm. The temperature of the diffusion heat treatment can be 800 to 1000°C, preferably 850 to 980°C, more preferably 900 to 950°C. The time of the diffusion heat treatment can be 0.5 to 15 hours, preferably 1 to 10 hours, more preferably 3 to 9 hours.

[0068] According to a specific embodiment of the present invention, the present invention provides a method for simultaneously improving the heat resistance and corrosion resistance of NdFeB magnets, comprising the following steps:

[0069] 1) Prepare raw material A, raw material B, raw material C and raw material D; wherein, based on 100 parts by weight of raw material A, the composition of raw material A is: PrNd 28-33wt%, Al 0.1-0.35wt%, Cu 0.1-0.5wt%, B 0.85-1.5wt%, and Fe is the balance; based on 100 parts by weight of raw material B, the composition of raw material B is: PrNd 7.5-12.5wt%, Ce 18-25wt%, Al 0.05-0.25%, Cu 0.05-0.35wt%, Ga 0.05-0.35wt%, B0.8-1.3wt%, and Fe is the balance; based on 100 parts by weight of raw material C, the composition of raw material C is: Pr 35-45wt%, Ni 6-15wt%, Nb 8-15wt%, B 0.9-1.5wt%, Fe is the balance; based on 100 parts by weight of D raw material, the composition of D raw material is: Tb 63-68wt%, Co 18-25wt%, and Cu is the balance;

[0070] 2) respectively smelting raw material A, raw material B, and raw material C to obtain slab A, slab B, and slab C, respectively;

[0071] The A, B and C castings are subjected to hydrogen crushing and jet milling respectively to obtain A fine powder, B fine powder with a D50 of 0.5 to 8 μm, and C nano-grade fine powder with a D50 of 50 to 400 nm.

[0072] 3) mixing fine powder A, fine powder B, and nano-grade fine powder C in a mass ratio of 48-52:48-52:0.6-1 to obtain a mixed powder;

[0073] 4) orienting the mixed powder and isostatically pressing the mixed powder to obtain a green compact; vacuum sintering the green compact at 950-1150° C. for 0.5-6 hours, cooling the green compact and performing a first tempering treatment at 850-1090° C. for 0.5-4 hours, and cooling the green compact and performing a second tempering treatment at 450-750° C. for 0.5-4 hours to obtain a sintered magnet;

[0074] 5) Using the D raw material as a target material, magnetron sputtering is performed on two opposite surfaces of the sintered magnet obtained in step 5) perpendicular to the orientation direction, and the coating thickness is 10 to 20 μm, respectively, to obtain a coated magnet; and the coated magnet is subjected to diffusion heat treatment at 800 to 1000° C. for 0.5 to 15 hours to obtain a NdFeB magnet.

[0075] Example 1

[0076] 1) Prepare raw materials A, B, C, and D.

[0077] The composition of raw material A is: PrNd 30wt%, Al 0.2wt%, Cu 0.2wt%, B 1.0wt%, and Fe 68.6wt%. The mass ratio of Pr to Nd is 1:3.

[0078] The composition of the B raw material is: PrNd 9wt%, Ce 21wt%, Al 0.1wt%, Cu 0.1wt%, Ga 0.1wt%, B 1.0wt%, and Fe 68.7wt%. The mass ratio of Pr to Nd is 1:3.

[0079] The composition of the C raw material is: Pr 40wt%, Ni 8wt%, Nb 12wt%, B 1.1wt%, and Fe 38.9wt%.

[0080] The composition of the D raw material is: Tb 65wt%, Co 20wt%, and Cu 15wt%.

[0081] 2) Add the prepared raw material A into a vacuum rapid solidification casting furnace, evacuate to 1 Pa, fill with argon, and then heat to melt. Pour the molten liquid onto a rotating cooling copper roller to obtain a cast sheet A with a thickness of about 0.25 mm.

[0082] The prepared B raw material is added into a vacuum rapid solidification casting furnace, evacuated to 1 Pa, filled with argon, and then heated to melt. The molten liquid is poured onto a rotating cooling copper roller to obtain a B casting sheet with a thickness of about 0.25 mm.

[0083] The prepared C raw material is added into a vacuum rapid solidification casting furnace, evacuated to 1 Pa, filled with argon, and then heated to melt. The molten liquid is poured onto a rotating cooling copper roller to obtain a C casting sheet with a thickness of about 0.25 mm.

[0084] The preparation of A casting, B casting and C casting can be done in any order.

[0085] The A flakes were hydrogen crushed to obtain A coarse powder; the A coarse powder was mixed with an antioxidant (the antioxidant was isooctyl propionate, the amount was 0.5wt‰ of the mass of the A coarse powder) and a lubricant (the lubricant was aviation kerosene, the amount was 0.5wt‰ of the mass of the A coarse powder) for 1 hour, and then the A fine powder with an average particle size D50 of 3.5μm was obtained by jet milling.

[0086] The B flakes were hydrogen crushed to obtain B coarse powder, which was mixed with an antioxidant (the antioxidant was isooctyl propionate, with an amount of 0.5 wt‰ of the mass of the B coarse powder) and a lubricant (the lubricant was aviation kerosene, with an amount of 0.5 wt‰ of the mass of the B coarse powder) for 1 h, and then the B fine powder with an average particle size D50 of 3.5 μm was obtained by air jet milling.

[0087] The C flakes were hydrogen crushed to obtain C coarse powder; the C coarse powder was mixed with an antioxidant (the antioxidant was isooctyl propionate, the amount was 0.5wt‰ of the mass of the C coarse powder) and a lubricant (the lubricant was aviation kerosene, the amount was 0.5wt‰ of the mass of the C coarse powder) for 1 hour, and then the mixture was jet milled to obtain nano-scale C fine powder with an average particle size D50 of 200 nm.

[0088] The preparation order of A fine powder and B fine powder can be any order.

[0089] 3) Fine powder A, fine powder B, and nano-grade fine powder C were mixed in a mixer at a mass ratio of 50:50:0.8 for 1.5 hours to obtain a mixed powder.

[0090] 4) The mixed powder is oriented and isostatically pressed in a 2T magnetic field to produce a green compact. The green compact is vacuum sintered at 1080°C for 3 hours, cooled to room temperature in an argon atmosphere, then heated to 900°C and subjected to a first tempering treatment at 900°C for 1.5 hours. The temperature is then cooled to room temperature in an argon atmosphere, then heated to 550°C and subjected to a second tempering treatment at 550°C for 2 hours to produce a sintered magnet.

[0091] 5) Using the target made from raw material D as the target, magnetron sputtering was performed on two opposite surfaces of the obtained sintered magnet perpendicular to the orientation direction, with the coating thickness being 10 μm respectively, to obtain a coated magnet; the coated magnet was subjected to diffusion heat treatment at 920° C. for 5 h to obtain a NdFeB magnet.

[0092] Comparative Example 1

[0093] 1) Prepare raw materials A, B, C, and D.

[0094] The composition of raw material A is: PrNd 30wt%, Al 0.2wt%, Cu 0.2wt%, B 1.0wt%, and Fe 68.6wt%. The mass ratio of Pr to Nd is 1:3.

[0095] The raw material composition of B is: PrNd 9wt%, Ce 21wt%, Al 0.1wt%, Cu 0.1wt%, Ga 0.1wt%, B 1.0wt%, and Fe 68.7wt%. The mass ratio of Pr to Nd is 1:3.

[0096] The composition of C raw materials is: Pr 40wt%, Ni 8wt%, Nb 12wt%, B 1.1wt%, and Fe38.9wt%.

[0097] The composition of D raw materials is: Tb 60wt%, Co 15wt%, Cu 25wt%.

[0098] 2) Add the prepared raw material A into a vacuum rapid solidification casting furnace, evacuate to 1 Pa, fill with argon, and then heat to melt. Pour the molten liquid onto a rotating cooling copper roller to obtain a cast sheet A with a thickness of about 0.25 mm.

[0099] The prepared B raw material is added into a vacuum rapid solidification casting furnace, evacuated to 1 Pa, filled with argon, and then heated to melt. The molten liquid is poured onto a rotating cooling copper roller to obtain a B casting sheet with a thickness of about 0.25 mm.

[0100] The prepared C raw material is added into a vacuum rapid solidification casting furnace, evacuated to 1 Pa, filled with argon, and then heated to melt. The molten liquid is poured onto a rotating cooling copper roller to obtain a C casting sheet with a thickness of about 0.25 mm.

[0101] The preparation of A casting, B casting and C casting can be done in any order.

[0102] The A flakes were hydrogen crushed to obtain A coarse powder; the A coarse powder was mixed with an antioxidant (the antioxidant was isooctyl propionate, the amount was 0.5wt‰ of the mass of the A coarse powder) and a lubricant (the lubricant was aviation kerosene, the amount was 0.5wt‰ of the mass of the A coarse powder) for 1 hour, and then the A fine powder with an average particle size D50 of 3.5μm was obtained by jet milling.

[0103] The B flakes were hydrogen crushed to obtain B coarse powder, which was mixed with an antioxidant (the antioxidant was isooctyl propionate, with an amount of 0.5 wt‰ of the mass of the B coarse powder) and a lubricant (the lubricant was aviation kerosene, with an amount of 0.5 wt‰ of the mass of the B coarse powder) for 1 h, and then the B fine powder with an average particle size D50 of 3.5 μm was obtained by air jet milling.

[0104] The C flakes were hydrogen crushed to obtain C coarse powder; the C coarse powder was mixed with an antioxidant (the antioxidant was isooctyl propionate, the amount was 0.5wt‰ of the mass of the C coarse powder) and a lubricant (the lubricant was aviation kerosene, the amount was 0.5wt‰ of the mass of the C coarse powder) for 1 hour, and then the mixture was jet milled to obtain nano-scale C fine powder with an average particle size D50 of 200 nm.

[0105] The preparation order of A fine powder and B fine powder can be any order.

[0106] 3) Fine powder A, fine powder B, and nano-grade fine powder C were mixed in a mixer at a mass ratio of 50:50:0.8 for 1.5 hours to obtain a mixed powder.

[0107] 4) The mixed powder is oriented and isostatically pressed in a 2T magnetic field to produce a green compact. The green compact is vacuum sintered at 1080°C for 3 hours, cooled to room temperature in an argon atmosphere, then heated to 900°C and subjected to a first tempering treatment at 900°C for 1.5 hours. The mixture is then cooled to room temperature in an argon atmosphere, then heated to 550°C and subjected to a second tempering treatment at 550°C for 2 hours to produce a sintered magnet.

[0108] 5) Using the target made from raw material D as the target, magnetron sputtering was performed on two opposite surfaces of the obtained sintered magnet perpendicular to the orientation direction, with the coating thickness being 8 μm respectively, to obtain a coated magnet; the coated magnet was subjected to diffusion heat treatment at 920° C. for 5 h to obtain a NdFeB magnet.

[0109] Comparative Example 2

[0110] Except for the following differences, the rest is the same as Example 1:

[0111] Only sintered magnets are obtained, and raw material D is not used as a target for magnetron sputtering, that is, step 5 is omitted.

[0112] Experimental example

[0113] The NdFeB magnets obtained in Example 1 and Comparative Example 1, and the sintered magnets obtained in Comparative Example 2 were tested respectively.

[0114] (1) Use a wire-cut electric discharge machine to cut the sample to be tested into a cubic sample with a size of 12 mm × 12 mm × 8 mm. Perform a weight loss experiment for 96 hours using a high-temperature and high-pressure steam test apparatus at 120.0°C, a relative humidity of 100% RH, and an absolute vapor pressure of 0.2 MPa to measure the weight loss data of the sample.

[0115] (2) Use a wire-cut electric discharge machine to cut the test sample into a cylindrical test sample with a size of φ10×7mm, perform saturation magnetization, and place it in a constant temperature box at 80℃ for two hours. Use a fluxmeter to measure the magnetic flux density before and after insulation, and calculate the irreversible magnetic flux loss under the current test conditions.

[0116] Table 1

[0117] serial number <![CDATA[Weight loss (mg / cm 2 )]]> Irreversible flux loss (%) Example 1 5.1 4.1 Comparative Example 1 5.7 5.9 Comparative Example 2 6.9 10.7

[0118] As can be seen from the table, the method of the present invention can reduce weight loss and irreversible magnetic flux loss at the same time, indicating that the method of the present invention can simultaneously improve the heat resistance and corrosion resistance of the obtained NdFeB magnet.

[0119] The present invention is not limited to the above-mentioned embodiments. Any modification, improvement, or substitution that can be conceived by those skilled in the art without departing from the essential content of the present invention shall fall within the scope of the present invention.

Claims

1. A method for simultaneously improving the heat resistance and corrosion resistance of NdFeB magnets, characterized in that: The following steps are involved: 1) Prepare raw material A, raw material B, raw material C and raw material D; wherein, based on 100 parts by weight of raw material A, the composition of raw material A is: PrNd 28-33wt%, Al 0.1-0.35wt%, Cu 0.1-0.5wt%, B 0.85-1.5wt%, and Fe is the balance; based on 100 parts by weight of raw material B, the composition of raw material B is: PrNd 7.5-12.5wt%, Ce 18-25wt%, Al 0.05-0.25wt%, Cu 0.05-0.35wt%, Ga 0.05-0.35wt%, B 0.8-1.3wt%, and Fe is the balance; based on 100 parts by weight of raw material C, the composition of raw material C is: Pr 35-45wt%, Ni 6-15wt%, Nb 8-15wt%, B 0.9-1.5wt%, Fe is the balance; based on 100 parts by weight of D raw material, the composition of D raw material is: Tb 63-68wt%, Co 18-25wt%, Cu is the balance; 2) Raw material A is formed into fine powder A with a D50 of 0.5 to 8 μm; raw material B is formed into fine powder B with a D50 of 0.5 to 8 μm; raw material C is formed into nano-scale fine powder C with a D50 of 50 to 400 nm; 3) mixing fine powder A, fine powder B, and nano-grade fine powder C in a mass ratio of 48-52:48-52:0.6-1 to obtain a mixed powder; 4) orienting and isostatically pressing the mixed powder to obtain a green compact; sintering and tempering the green compact to obtain a sintered magnet; 5) Using the D raw material as a target, the sintered magnet obtained in step 4) is subjected to magnetron sputtering to obtain a coating thickness of 10 μm or more to obtain a coated magnet; and the coated magnet is subjected to diffusion heat treatment to obtain a NdFeB magnet.

2. The method according to claim 1, characterized in that In step 2), raw material A, raw material B, and raw material C are smelted to obtain slab A, slab B, and slab C, respectively; slab A, slab B, and slab C are hydrogen crushed and jet milled to obtain fine powder A, fine powder B, and nano-grade fine powder C, respectively.

3. The method according to claim 2, wherein: In step 2), raw material A, raw material B, and raw material C are melted in a vacuum rapid solidification casting furnace to obtain castings A, B, and C with a thickness of 0.15 to 0.5 mm, respectively; wherein the preparation order of castings A, B, and C is not particular; In step 2), the A and B flakes are hydrogen-crushed to obtain coarse powder A and coarse powder B, respectively; the coarse powder A is mixed with an antioxidant and a lubricant, and subjected to air flow milling to obtain fine powder A; the coarse powder B is mixed with an antioxidant and a lubricant, and subjected to air flow milling to obtain fine powder B; wherein, the preparation order of fine powder A and fine powder B is not particular.

4. The method according to claim 3, characterized in that The C coarse powder is mixed with an antioxidant and a lubricant, and subjected to air flow milling to obtain nano-scale C fine powder.

5. The method according to claim 4, characterized in that The antioxidant is selected from at least one of polyethylene glycol octane, petroleum ether and isooctyl propionate; and the lubricant is selected from at least one of aviation kerosene, isopropyl alcohol and zinc stearate.

6. The method according to claim 5, characterized in that In step 2), the A coarse powder is mixed with 0.1 wt‰ to 10 wt‰ of an antioxidant and 0.1 wt‰ to 10 wt‰ of a lubricant and then subjected to air flow milling; the B coarse powder is mixed with 0.1 wt‰ to 10 wt‰ of an antioxidant and 0.1 wt‰ to 10 wt‰ of a lubricant and then subjected to air flow milling; the C coarse powder is mixed with 0.1 wt‰ to 10 wt‰ of an antioxidant and 0.1 wt‰ to 10 wt‰ of a lubricant and then subjected to air flow milling.

7. The method according to claim 1, characterized in that In step 3), the mass ratio of fine powder A, fine powder B and nano-grade fine powder C is 49-51:49-51:0.7-0.

9.

8. The method according to claim 1, characterized in that In step 4), the sintering is vacuum sintering with a vacuum degree of less than 0.1 Pa; the sintering temperature is 950-1150° C. and the time is 0.5-6 hours; after the sintering is completed, the temperature is lowered to below 50° C.

9. The method according to claim 1, characterized in that In step 4), the tempering treatment is carried out under vacuum conditions with a vacuum degree of less than or equal to 0.01 Pa; the tempering treatment includes a first tempering treatment and a second tempering treatment; the temperature of the first tempering treatment is 850-1090° C. and the time is 0.5-4 hours; after the first tempering treatment is completed, the temperature is lowered to below 50° C.; the temperature of the second tempering treatment is 450-750° C. and the time is 0.5-4 hours.

10. The method according to claim 1, characterized in that In step 5), the coating thickness is 10-20 μm; the temperature of the diffusion heat treatment is 800-1000° C., and the time is 0.5-3 h.