Magnet alloys, bonded magnets, and methods of making the same
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BIZYME INC
- Filing Date
- 2021-05-18
- Publication Date
- 2026-05-29
Smart Images
Figure CN115769317B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to magnetic alloys, bonded magnets, and methods for manufacturing the same. Background Technology
[0002] In recent years, there has been ongoing development of microcrystalline isotropic magnets composed of hard magnetic phases such as Nd-Fe-B and Sm-Fe-N formed by microcrystalline grains with nano- to submicron sizes, or nanocomposite isotropic magnets (hereinafter referred to as "nanocomposite magnets") in which hard magnetic phases such as Nd-Fe-B and Sm-Fe-N and soft magnetic phases such as Fe-B or α-Fe exist within the same metal structure. However, since these isotropic iron-based rare earth magnets formed by grains with nano- to submicron sizes are microcrystalline, it has been found through computer fitting and other methods using micromagnetism that each grain is magnetically coupled not only through static magnetic interaction but also through exchange interaction, thus exhibiting excellent magnetic properties and being put into practical applications as high-performance permanent magnet materials.
[0003] To date, microcrystalline isotropic iron-based rare-earth magnets, utilizing their isotropic properties, are pulverized into particles with an average size of approximately 50μm to 200μm and then mixed with epoxy-based thermosetting resins or nylon-based and polyphenylene sulfide (PPS) thermoplastic resins to form resin-bonded magnets (commonly known as bonded magnets). As net-shaped magnets with high shape freedom, they are mainly used in the electronic components industry, such as spindle motors for optical drives and hard drives, pager motors for mobile phones, and various sensors. However, in recent years, there has been a desire to leverage the high magnetic properties of these microcrystalline isotropic iron-based rare-earth magnets to expand their application in the automotive (electric vehicles, including hybrid vehicles) and white goods sectors, using brushless DC motors with outputs up to 1 horsepower (750W).
[0004] Especially in terms of high performance and high efficiency of small electric motors in the tens to hundreds of watt range, there is a transition from traditional brushed motors using ferrite magnets (iron-based oxide permanent magnets) to brushless DC motors using isotropic rare-earth bonded magnets. For isotropic rare-earth bonded magnets, which were previously limited to spindle motors and vibration motors using microcrystalline isotropic iron-based rare-earth magnet materials, consideration is being given to replacing ferrite magnets with magnetic properties that offer superior corrosion resistance. Specifically, the desired magnetic properties are: a demagnetization rate (fluxloss) of less than -20% (0 to -20%) after 1000 hours of immersion in 80℃ / 5% NaCl (salt water) in the bonded magnet state; and a magnetic flux (Open) of a magnet with a diameter of 10mm × height of 7mm and a permeability (Pc) of 2. Flux is an isotropic rare-earth bonded magnet material with extremely excellent corrosion resistance, exceeding 0.5 mWb (milliwebers).
[0005] To ensure the desired performance, it is crucial to suppress the oxidation of rare earth elements (hereinafter referred to as RE), especially Nd, Pr, Dy, and Tb (formation of RE₂O₃), which are fundamental constituent elements of the magnet material, as well as the oxidation of Fe (formation of Fe₂O₃), another fundamental constituent element, which would otherwise affect the permanent magnet properties of the magnet alloy. 14 The volume ratio of type B tetragonal compounds is reduced.
[0006] In addition, it is also necessary to suppress the surrounding main phase RE2Fe. 14 Oxidation of secondary phases, RE-rich phases, RE-Fe phases, etc. at the grain boundaries of type B compounds makes it impossible to maintain the metal structure composed of the main phase and secondary phases when the secondary phase is oxidized. In the worst case, the magnet itself collapses and cannot maintain its shape as a bonded magnet.
[0007] Therefore, there is a need for highly corrosion-resistant isotropic iron-based rare-earth magnet materials that can replace ferrite magnets (iron-based oxide magnets) in terms of corrosion resistance and are suitable for use in small brushless DC motors in the range of tens to hundreds of watts.
[0008] Nd₂Fe, composed of microcrystalline grains, is expected to possess high magnetic properties. 14 Iron-based rare earth magnets with B-type tetragonal compounds as the main phase have a basic stoichiometric composition of Nd:Fe:B = 11.76:balance:5.88. However, because rare earth elements (RE), represented by Nd, are highly reactive to oxygen, iron oxide-based ferrite magnets are still in use in fields such as electric motors for automobiles that require high corrosion resistance.
[0009] However, in the current pursuit of energy conservation, the emergence of hybrid vehicles and EVs (electric vehicles) has led to unprecedented development in electrification, requiring higher performance and efficiency electric motors. Although there is a strong market demand for the transition from brushed DC motors using ferrite magnets to brushless DC motors using rare earth magnets, iron-based rare earth magnets with excellent corrosion resistance that can replace ferrite magnets in a wide range of applications do not yet exist.
[0010] To improve the corrosion resistance of the aforementioned iron-based rare-earth magnets, there are limitations in the methods of composition. Therefore, to date, iron-based rare-earth magnets have been treated with resin molding and other methods to suppress the oxidation of the magnet body, which is then used in electric motors for automotive fuel pumps or inverters, and water pumps for battery cooling. However, because the gap between the rotor and stator is widened in resin molding, the performance of iron-based rare-earth magnets with high magnetic properties is greatly weakened. Not only can the magnetic moment not be effectively utilized, but the motor body also becomes larger, which is not compatible with the applications of household appliances and electrical equipment that also require miniaturization. Therefore, as an alternative to resin molding, heat-resistant injection-bonded magnets were initially produced by mixing and compounding isotropic iron-based rare-earth magnet powder with thermoplastic resins with excellent heat resistance, such as polyphenylene sulfide (PPS) resin. However, even with these injection-bonded magnets, no isotropic iron-based rare-earth magnet alloy with extremely excellent corrosion resistance has been found that can achieve a demagnetization rate (flux loss) of less than -20% after 1000 hours of immersion in 80℃ / 5% NaCl (salt water) test, and a magnetic flux (open flux) of more than 0.5mWb (milliwebers) for a magnet with a diameter of 10mm × height of 7mm and a permeability (Pc) of 2.
[0011] Patent document 1 discloses RE2Fe 14 An anisotropic sintered magnet with a tetragonal crystal structure as the main phase, the magnet having micron-sized RE2Fe... 14 A metallic microstructure composed of tetragonal B-type grains, through magnetic orientation, allows the magnetic moment to align along RE2Fe. 14 The B tetragonal crystals are aligned along the C-axis, thus exhibiting good magnetic properties. However, since the RE-rich phase is essential in the grain boundary phase, corrosion will develop even in the atmosphere at room temperature without surface treatment. Regardless of the type of rust prevention treatment, a significant deterioration of magnetic properties cannot be avoided in the 80℃ / 5% NaCl (salt water) immersion test, with a demagnetization rate (flux loss) far below -20%.
[0012] Patent document 2 discloses an isotropic permanent magnet having a hard magnetic phase as the main phase, wherein the hard magnetic phase comprises RE2Fe, which is composed of at least 10 atomic percent of rare earth elements (RE), about 0.5 atomic percent to about 10 atomic percent of boron, and the balance of iron. 14 B-type tetragonal crystal structure. Although this magnet has a grain boundary-free metallic structure, it is still a fine-grained metallic structure. Therefore, through exchange coupling between the main phases, it can exhibit the properties of a permanent magnet, although it is superior to the aforementioned RE2Fe-based magnet in terms of corrosion resistance. 14 Anisotropic sintered magnets with a tetragonal crystal structure as the main phase cannot avoid oxidation of the main phase constituent element RE. Even injection-bonded magnets made of PPS resin cannot guarantee extremely excellent corrosion resistance such as a demagnetization rate (flux loss) of less than -20% after 1000 hours of immersion in 80℃ / 5% NaCl (salt water) test, and an open flux of more than 0.5mWb (milliwebers) for a magnet with a diameter of 10mm × height of 7mm and a permeability (Pc) of 2.
[0013] Patent documents 3 and 4 disclose iron-based rare earth isotropic nanocomposite magnets. These iron-based rare earth isotropic nanocomposite magnets have a lower RE content ratio than other iron-based rare earth magnets, thus suppressing the deterioration of magnetic properties caused by RE oxidation. However, the soft magnetic phase α-Fe, existing as a secondary phase, becomes a contributing factor to red rust formation under brine immersion. Even injection-bonded magnets made of PPS resin cannot guarantee extremely excellent corrosion resistance, such as a demagnetization rate (flux loss) of less than -20% after 1000 hours of immersion in 80°C / 5% NaCl (salt water) without an open flux of 0.5 mWb or higher for a magnet with a diameter of 10 mm × height of 7 mm and a permeability (Pc) of 2.
[0014] On the other hand, in the iron-based rare earth isotropic nanocomposite magnet of Patent Document 5, which mainly contains iron-based boride phase as the soft magnetic phase, it is disclosed that by adding Ti, the precipitation and growth of α-Fe phase during the cooling process of alloy melt is suppressed, so that Nd2Fe 14 The precipitation and growth of the boron (B) phase can proceed preferentially. However, since Ti readily combines with boron (B), the TiB2 phase will crystallize and precipitate during the crystallization process. Therefore, compared with the iron-based rare earth magnets described in patent documents 1, 2, 3, and 4, although a finer metallic structure is formed and corrosion resistance tends to improve, the formation of the main phase Nd2Fe... 14The absolute amount of boron required for the B phase is reduced, and it exists in trace amounts alone, like RE and iron, or in the form of Fe-RE alloys. Rust will develop from this point. Therefore, even injection-bonded magnets made of PPS resin cannot guarantee extremely excellent corrosion resistance such as a demagnetization rate (flux loss) of less than -20% after 1000 hours of immersion in 80℃ / 5% NaCl (salt water) test.
[0015] In addition, Patent Document 6 describes the formation of a high-density hydrocarbon polymer film on the surface of iron-based rare earth sintered magnets and bonded magnets formed using iron-based rare earth magnet powder by plasma polymerization, which can achieve excellent relative wear resistance, heat resistance and corrosion resistance. However, in this document, the corrosion resistance test is limited to a constant temperature and humidity test at 85℃×95%RH, and the corrosion resistance under extreme harsh environments such as immersion in 80℃ / 5% NaCl (salt water) is not described.
[0016] Similarly, Patent Document 7 discloses a surface treatment for iron-based rare earth sintered magnets, utilizing a three-layer coating: a Ni-P film formed by chemical plating or a combination of chemical plating and electroplating, a Cu electroplating film, and a Ni electroplating film, to obtain a highly corrosion-resistant magnet. However, this method only utilizes conditions of 120°C, 100% RH, and 1 kgf / cm². 2 PCT tests conducted on samples for 24, 72, 120, and 168 hours under certain conditions showed improvement in rusting. This does not mean that the samples are highly corrosion-resistant iron-based rare earth magnets that can be used in extremely harsh environments such as immersion in 80°C / 5% NaCl (salt water).
[0017] Patent document 8 discloses a method of forming a coating layer by vaporizing CF4, argon, nitrogen or air plasma, treating the surface of Sm-Fe-N magnetic powder which is considered to have better corrosion resistance than Nd-Fe-B alloys, and then making an anisotropic bonded magnet to obtain a magnet with excellent corrosion resistance. However, the corrosion resistance is evaluated by a constant temperature and humidity test of 85°C × 85%RH × 200 hours. This document also fails to obtain a highly corrosion-resistant magnet that can be used in a salt water immersion environment.
[0018] Patent document 9 discloses Sm-Fe-N alloy powder and isotropic bonded magnets using the powder. However, this document also does not contain any description of highly corrosion-resistant magnets that can be used in a salt water immersion environment. None of the methods described in patent documents 1 to 9 disclose a method for manufacturing iron-based rare earth magnets with extremely excellent corrosion resistance that have a demagnetization rate (flux loss) of less than -20% after 1000 hours of immersion in 80°C / 5% NaCl (salt water) and a magnetic flux (open flux) of more than 0.5mWb for a magnet with a diameter of 10mm × height of 7mm and a permeability (Pc) of 2.
[0019] Existing technical documents
[0020] Patent documents
[0021] Patent Document 1: Japanese Patent Application Publication No. 59-046008
[0022] Patent Document 2: Japanese Patent Application Publication No. 60-009852
[0023] Patent Document 3: Japanese Patent Application Publication No. 8-162312
[0024] Patent Document 4: Japanese Patent Application Publication No. 10-53844
[0025] Patent Document 5: Japanese Patent Application Publication No. 2002-175908
[0026] Patent Document 6: Japanese Patent Application Publication No. 1-280303
[0027] Patent Document 7: Japanese Patent Application Publication No. 2001-176709
[0028] Patent Document 8: Japanese Patent Application Publication No. 2020-50904
[0029] Patent Document 9: Japanese Patent Application Publication No. 2002-57017 Summary of the Invention
[0030] The problem that the invention aims to solve
[0031] DC brushless motors for electric fuel pumps, water pumps, and EVs require iron-based rare-earth magnets with excellent corrosion resistance, capable of withstanding even saltwater immersion, depending on the environmental conditions. However, traditional methods ultimately only ensure corrosion resistance by forming a weather-resistant coating on the magnet material surface. Once this coating peels off, or the magnet body is damaged or scratched, the base material (the new surface) is exposed, becoming the starting point for rust. Therefore, to achieve even higher corrosion resistance, methods such as resin molding are used. This leads to a situation where even iron-based rare-earth magnets, which possess superior magnetic properties compared to ferrite magnets, suffer from a significant reduction in magnetic moment, which contributes to the high efficiency of motors, thus failing to achieve the cost-effectiveness of using expensive RE as a raw material. The inventors of this invention once considered replacing a portion of the Fe sites in the isotropic Nd-Fe-B magnet alloy with Cr, which helps improve corrosion resistance, to form an Fe-Cr structure. This would allow the formation of an Nd-(Fe,Cr)-B alloy that does not depend on the surface treatment of the magnet, thereby significantly improving corrosion resistance. However, it was ultimately found that simply adding Cr would significantly reduce the magnetic properties, especially the magnetization, making it difficult to obtain magnet performance suitable for brushless DC motors.
[0032] The present invention was made in view of the above circumstances, and its main objective is to provide a magnetic alloy, a bonded magnet, and a method for manufacturing the same, which have both the corrosion resistance to replace ferrite magnets and the magnetic properties suitable for small brushless DC motors.
[0033] Technical means to solve the problem
[0034] The magnet alloy of this invention is RE2Fe 14 An isotropic iron-based rare-earth boron-based magnetic alloy with a B-type tetragonal compound phase (RE being rare-earth elements) as the main phase, characterized by having a compositional formula T 100－x－y－z－m (B 1－n C n ) x RE y Cr z M m The composition is represented by (T is at least one element selected from Fe, Co, and Ni, and is a transition metal element that must contain Fe; RE is a rare earth element that must contain Nd or Pr; M is one or more metallic elements selected from Al, Si, V, Ti, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb), having compositional ratios x, y, z, m, and n respectively satisfying the following formula:
[0035] 5.6 atomic%≤x≤6.4 atomic%,
[0036] 11.2 atomic%≤y≤12.0 atomic%,
[0037] 2.3 atomic%≤z≤5.4 atomic%,
[0038] 0.0 atomic%≤m≤3.0 atomic%,
[0039] 0.0≤n≤0.5,
[0040] And it must contain Cr.
[0041] In this magnet alloy, RE2Fe is preferably the main phase. 14 The average crystal grain size of type B tetragonal compounds is greater than 20 nm and less than 100 nm, and the standard deviation (σ) is within 50% of the average crystal grain size.
[0042] The magnet alloy preferably has a remanent magnetic flux density B. r For 0.7T or above, intrinsic coercivity H cJ It has a maximum energy product (BH) of over 800 kA / m. max 80kJ / m 3 The above are the characteristics of permanent magnets.
[0043] The magnet alloy can be in the form of a highly corrosion-resistant powder with an average particle size of 20 μm or more and less than 200 μm.
[0044] Furthermore, the above-mentioned objective of the present invention is achieved by molding a bonded magnet obtained by mixing and kneading the above-mentioned powdered magnet alloy with thermoplastic resin or thermosetting resin.
[0045] The bonded magnet is a 10 mm diameter, 7 mm height, and magnetic permeability (Pc) of 2 made of at least one thermoplastic resin selected from polyamide, polyphenylene sulfide (PPS), and polyether ether ketone (PEEK) as the resin used in the mixture. Preferably, the demagnetization rate (flux loss) after immersion in 80 °C / 5% NaCl (salt water) for 1000 hours is less than -20% (0 to -20%), and the magnetic flux (open flux) of the magnet itself is greater than 0.5 mWb.
[0046] The reason for setting the demagnetization rate (flux loss) after immersion in 80℃ / 5% NaCl (salt water) for 1000 hours to be below -20% (0 to -20%) is that if the demagnetization exceeds this limit, then if the immersion test in 80℃ / 5% NaCl (salt water) is continued thereafter, the demagnetization rate will exceed -30% before reaching 2000 hours, and the surface magnetic flux (flux) can only be achieved at or below that of ferrite magnets.
[0047] Furthermore, the reason for setting the magnetic flux (open flux) of the bonded magnet with a diameter of 10 mm, a height of 7 mm, and a permeability (Pc) of 2 after 1000 hours of immersion in 80°C / 5% NaCl (salt water) to be above 0.5 mWb is that when it is below 0.5 mWb, it is impossible to achieve a large difference in surface magnetic flux with oxide-based ferrite sintered magnets and ferrite bonded magnets. It is difficult to replace ferrite magnets by exhibiting magnetic properties higher than those of ferrite magnets, thus hindering the application of this invention in small DC brushless motors in the tens to hundreds of watt range, such as fuel pumps or water pumps for electric applications.
[0048] Furthermore, the above-mentioned objective of the present invention can also be achieved by a method for manufacturing a magnetic alloy, the method comprising: a step of preparing an alloy melt, wherein the alloy melt is composed of formula T 100－x－y－z－m (B 1－n C n ) x RE y Cr z M m (T is at least one element selected from Fe, Co, and Ni, and is a transition metal element that must contain Fe; RE is a rare earth element that must contain Nd or Pr; M is one or more metallic elements selected from Al, Si, V, Ti, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb) represents a composition with compositional ratios x, y, z, m, and n that satisfy the following formula:
[0049] 5.6 atomic%≤x≤6.4 atomic%,
[0050] 11.2 atomic%≤y≤12.0 atomic%,
[0051] 2.3 atomic%≤z≤5.4 atomic%,
[0052] 0.0 atomic%≤m≤3.0 atomic%,
[0053] 0.0 ≤ n ≤ 0.5; and
[0054] In the process of preparing a rapidly solidified alloy, the molten alloy is sprayed at an average outflow rate of 200 g / min to 2000 g / min per orifice at the nozzle tip onto the surface of a rotating roller whose main raw material is any one of copper, copper alloy, Mo, and W, thereby preparing an alloy with an amorphous phase or containing RE2Fe. 14 A rapidly solidified alloy with a B-phase crystalline phase of more than 1% by volume.
[0055] In the manufacturing method of this magnet alloy, it is preferable that the surface roughness of the rotating roller is an arithmetic mean roughness (Ra) of 0.1 μm or more and less than 0.6 μm.
[0056] The preferred method for manufacturing this magnet alloy also includes preparing it by performing heat treatment (flash annealing) to obtain RE2Fe. 14 In the process of making a magnet alloy with a type B tetragonal compound as the main phase, the heat treatment involves raising the aforementioned rapidly solidified alloy to a certain temperature range between the crystallization temperature and 850°C at a heating rate of 10°C / sec or more and less than 200°C / sec, and then immediately subjecting it to rapid cooling after 0.01 seconds or more and less than 7 minutes.
[0057] Furthermore, the above-mentioned objective of the present invention can also be achieved by the following method for manufacturing a bonded magnet, which includes: a step of pulverizing a magnetic alloy obtained by the above-mentioned method for manufacturing a magnetic alloy to an average powder particle size of 100 μm or more and less than 200 μm to obtain magnetic alloy powder; a step of adding a thermosetting resin to the magnetic alloy powder, filling it into a molding die, and forming a compression molded body by pressure molding; and a step of heat-treating the compression molded body at a temperature higher than or equal to the polymerization temperature of the thermosetting resin to obtain a bonded magnet. Alternatively, the above-mentioned objective of the present invention can also be achieved by the following method for manufacturing a bonded magnet, which includes: a step of pulverizing a magnetic alloy obtained by the above-mentioned method for manufacturing a magnetic alloy to an average powder particle size of 20 μm or more and less than 100 μm to obtain magnetic alloy powder; and a step of adding a thermoplastic resin to the magnetic alloy powder and injection molding the resulting injection molding composite.
[0058] The effects of the invention
[0059] According to the present invention, a magnet alloy, a bonded magnet, and a method thereof are provided that have both corrosion resistance that can replace ferrite magnets and magnetic properties suitable for use in small brushless DC motors in the tens to hundreds of watt range for electric fuel pumps or water pumps. Attached Figure Description
[0060] [ Figure 1 (a) is a diagram of the apparatus configuration for a heat treatment furnace used to achieve rapid annealing, and (b) is a schematic diagram of the movement of the molten alloy as it rapidly solidifies inside the furnace core tube.
[0061] [ Figure 2 [Illustration] is a conceptual diagram of the thermal process of rapid annealing implemented according to the present invention.
[0062] [ Figure 3[Image] is the powder X-ray diffraction pattern of the rapidly solidified alloy (rapid quenching, as-spun) obtained in Example 3.
[0063] [ Figure 4 [This is the powder X-ray diffraction pattern of the isotropic iron-based rare earth boron magnet obtained in Example 3.]
[0064] [ Figure 5 [Image] is the powder X-ray diffraction pattern of the rapidly solidified alloy (rapid quenching) obtained in Comparative Example 14.
[0065] [ Figure 6 [This is the powder X-ray diffraction pattern of the isotropic iron-based rare earth boron magnet obtained in Comparative Example 14.]
[0066] [ Figure 7 [This refers to the change in demagnetization rate (flux loss) of Examples 1, 2, 3 and Comparative Example 16 in the 80°C / 5% NaCl (salt water) immersion test.]
[0067] [ Figure 8 [This refers to the change in magnetic flux (open flux) in Examples 1, 2, 3 and Comparative Example 16 during the 80°C / 5% NaCl (salt water) immersion test.
[0068] [ Figure 9 The graph shows the relationship between the amount of Cr added and the demagnetization rate (Flux loss) after 1000 hours in an 80℃ / 5% NaCl (salt water) immersion test.
[0069] [ Figure 10 [Image] is a photograph showing the rust condition during the 80°C / 5% NaCl (salt water) immersion test of Example 2.
[0070] [ Figure 11 [This is a photograph showing the rusting condition of Comparative Example 16 during the 80°C / 5% NaCl (salt water) immersion test.] Detailed Implementation
[0071] One embodiment of the present invention uses an isotropic iron-based rare-earth boron-based magnet alloy that requires the addition of Cr, which can produce RE2Fe 14 Within the alloy composition range of a B-phase-dominant magnetic alloy, Cr replaces a portion of the Fe sites, forming RE2(Fe,Cr) containing Fe-Cr, which exhibits excellent corrosion resistance. 14 Phase B. This magnet alloy forms RE2(Fe,Cr). 14The B phase has a uniform and fine metallic structure with an average crystal grain size of 20 nm or more and less than 100 nm, and a standard deviation of crystal grain size within 50% of the average crystal grain size. This results in a metallic structure that can maximize the use of exchange interactions between the main phase grains.
[0072] The inventors discovered that by achieving the above-mentioned uniform and fine metallic structure, RE2(Fe,Cr) as the main phase... 14 In addition to magnetostatic interactions, the B phase is also bonded through strong exchange interactions. Therefore, even if Cr is added to saturate the magnetization, J... s The squareness (B) of the demagnetization curve is reduced by strong interparticle interactions. r / J s This can also be improved, resulting in the suppression of the residual magnetic flux density B. r The invention was conceived because the material, despite having added Cr, still exhibits magnetic properties suitable for small brushless DC motors ranging from tens to hundreds of watts for electric fuel pumps or water pumps.
[0073] When the Cr content is less than 2.3 atomic%, an isotropic rare-earth injection-bonded magnet with a diameter of 10 mm and a height of 7 mm and a permeability (Pc) of 2, prepared by a known injection molding process for bonded magnets, showed a demagnetization rate (flux loss) exceeding -20% after 1000 hours of immersion in 80°C / 5% NaCl (salt water). Therefore, it cannot be guaranteed that it can replace the magnetic properties of ferrite magnets. Furthermore, when the Cr content is 5.4 atomic% or higher, although a demagnetization rate (flux loss) of less than -20% can be guaranteed after 1000 hours, the initial remanent magnetic flux density B... r At temperatures below 0.7T, it is impossible to maintain the magnetic properties of a magnet at a level that can replace a ferrite magnet after immersion in 80℃ / 5% NaCl (salt water) for 1000 hours.
[0074] In contrast, RE2(Fe,Cr) is prepared with a Cr addition of 2.3 atomic% or more but less than 5.4 atomic% as the main phase. 14Magnet alloys with an average crystal grain size of 20 nm or more and less than 100 nm and a standard deviation (σ) within 50% of the average crystal grain size not only exhibit magnetic properties suitable for small DC brushless motors ranging from tens to hundreds of watts for electric fuel pumps or water pumps, but also, when using isotropic rare earth injection-bonded magnets with a diameter of 10 mm × height of 7 mm and a permeability (Pc) of 2 as samples, after 1000 hours of immersion in 80℃ / 5% NaCl (salt water), the demagnetization rate (flux loss) is less than -20%, and the magnet's own magnetic flux (open flux) is above 0.5 mWb. It can combine the extremely excellent corrosion resistance and magnetic properties that can replace ferrite magnets.
[0075] Patent documents 1, 2, 3, 4, 5, 6, 7, 8, and 9 do not disclose that using an iron-based rare-earth magnet with a diameter of 10 mm × height of 7 mm and a permeability (Pc) of 2 as a sample, as an iron-based rare-earth magnet material that can ensure a demagnetization rate (flux loss) of less than -20% after 1000 hours in an 80℃ / 5% NaCl (salt water) immersion test, and whose magnetic flux (open flux) is greater than 0.5 mWb, provides extremely excellent corrosion resistance.
[0076] The isotropic iron-based rare-earth boron magnet of the present invention, characterized by the addition of Cr, is obtained by achieving RE2Fe 14 Within the alloy composition range of a magnet alloy with B phase as the main phase, a portion of the Fe sites are replaced with Cr to form RE2(Fe,Cr) containing Fe-Cr, which has excellent corrosion resistance. 14 Phase B is formed, and RE2(Fe,Cr) is also formed. 14 The B phase is a uniform, fine metallic microstructure with an average grain size greater than 20 nm and less than 100 nm, and a standard deviation of grain size within 50% of the average grain size, consisting of RE2(Fe,Cr). 14 The grains composed of the B phase are bonded together not only by static magnetic interactions but also by strong exchange interactions. As a result, the remanent magnetic flux density of the Cr-added material is higher than that of the B phase. r The reduction is suppressed, resulting in isotropic iron-based rare-earth boron magnets that combine the magnetic properties of small brushless DC motors in the tens to hundreds of watt range suitable for electric fuel pumps or water pumps, with excellent corrosion resistance.
[0077] Furthermore, the isotropic iron-based rare earth boron magnet of the present invention, characterized by the addition of Cr, can further improve corrosion resistance by replacing a portion of B with C.
[0078] The preferred embodiments of the present invention are described below.
[0079] [Alloy Composition]
[0080] The transition metal T, containing Fe as an essential element, constitutes the remainder of the aforementioned element content. Replacing part of Fe with one or both of Co and Ni, which are also strongly magnetic elements like Fe, can also yield the desired hard magnetic properties. However, when the amount of Fe replacement exceeds 30%, it leads to a significant decrease in magnetic flux density; therefore, the replacement amount is limited to the range of 0% to 30%. Adding Co not only helps to improve magnetization but also reduces the viscosity of the molten metal and stabilizes the flow rate from the nozzle during rapid cooling. Therefore, the Co replacement amount is preferably 0.5% to 30%, and from a cost-effectiveness perspective, a Co replacement amount is more preferably 0.5% to 10%.
[0081] When the B+C composition ratio x is less than 5.6 atomic%, the amorphous formation energy of the alloy is significantly reduced, leading to the precipitation of α-Fe during rapid solidification of the melt, thus impairing the squareness of the demagnetization curve. Furthermore, when the B+C composition ratio x exceeds 6.4 atomic%, it exceeds the formation of RE2Fe. 14 The required B+C concentration for the B phase is such that excess B+C becomes grain boundary composition, which does not contribute to the performance of magnetization and leads to a decrease in magnetic properties. Therefore, the composition ratio x is in the range of 5.6 atomic% to 6.4 atomic% and preferably 5.6 atomic% to 6.2 atomic%, more preferably 5.8 atomic% to 6.2 atomic%.
[0082] By replacing a portion of B with C, RE2Fe 14 The corrosion resistance of the B phase is improved, but when the substitution rate of C relative to B exceeds 50%, it is not preferred because the amorphous formation energy is significantly reduced. The substitution rate is limited to 0% to 50%. From the viewpoint of improving corrosion resistance, 2% to 30% is preferred, and 3% to 15% is more preferred.
[0083] In this invention, when the percentage of rare earth elements y containing Nd or Pr is less than 11.2 atomic%, a grain boundary phase composed of iron and rare earth elements cannot be formed, thus failing to ensure the target permanent magnet properties. When it exceeds 12.0 atomic%, it exceeds the formation of RE2Fe. 14 The required RE concentration for phase B results in the formation of a highly oxygen-rich phase at the main phase grain boundaries, leading to reduced corrosion resistance. Therefore, y is less than 12.0 atomic percent. Furthermore, to stably ensure intrinsic coercivity H... cJ From the perspective of y, it is preferably between 11.4 atomic% and 11.9 atomic% to ensure the highest possible B content. r From the perspective of the angle, it is more preferable to be 11.4 atomic percent or more and 11.8 atomic percent or less.
[0084] In this invention, although Cr is necessary from the perspective of ensuring excellent corrosion resistance, the expected corrosion resistance cannot be guaranteed when the addition amount z is less than 2.3 atomic percent, and when it is greater than 5.4 atomic percent, the residual magnetic flux density B r The amount of Cr added is significantly reduced, and the expected magnetic properties cannot be guaranteed. Therefore, the amount of Cr added, z, is set to be 2.3 atomic% or more and 5.4 atomic% or less. From the viewpoint of corrosion resistance, z is preferably 2.5 atomic% or more and 5.4 atomic% or less, and considering the reduction in magnetic properties, it is more preferably 2.5 atomic% or more and 5.0 atomic% or less.
[0085] In this invention, one or more additional elements M selected from Al, Si, V, Ti, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb may be added. Through this additional element, Hf can be achieved by increasing the amorphous formation energy and achieving uniform and finer metal structure after crystallization heat treatment. cJ The improvement in the squareness of the demagnetization curve and other effects enhance the performance of the permanent magnet. However, when the composition ratio m of these elements M exceeds 3.0 atomic%, it will lead to a decrease in magnetization. Therefore, z is limited to 0 atomic% to 3.0 atomic%, preferably 0 atomic% to 2.0 atomic%, and more preferably 0 atomic% to 1.5 atomic%.
[0086] [Metal Structure]
[0087] The isotropic iron-based rare-earth boron magnet obtained by the present invention is characterized by RE2Fe as the main phase. 14 The average crystal grain size of type B tetragonal compounds is greater than 20 nm and less than 100 nm. When the average crystal grain size is less than 20 nm, it will lead to H cJ The remanent magnetic flux density B above 0.7T, a necessary magnetic property, decreases as the exchange interaction between crystalline particles decreases above 100nm, resulting in a reduced squareness of the demagnetization curve. r Intrinsic coercivity H above 800kA / m cJ 80kJ / m 3 The above refers to the maximum magnetic energy product (BH). max From the viewpoint of improving magnetic properties, the average crystal grain size is preferably 20 nm to 80 nm, and more preferably 20 nm to 70 nm.
[0088] In addition, the above RE2Fe 14 When the standard deviation (σ) of the grains of type B tetragonal compounds exceeds 50% of the grain size, the uniformity of the metallic microstructure is impaired, affecting the structure of RE2(Fe,Cr).14 The exchange interaction between the grains of phase B decreases, thus reducing the remanent magnetic flux density B. r Therefore, σ is set to 50% or less. In order to form a more uniform and fine structure and improve magnetic properties, σ is preferably 40% or less, and more preferably 30% or less.
[0089] [Magnetic properties]
[0090] The isotropic iron-based rare-earth boron magnet obtained by this invention can exhibit a remanent magnetic flux density B of over 0.7T. r Intrinsic coercivity H above 800kA / m cJ 80kJ / m 3 The above refers to the maximum magnetic energy product (BH). max While possessing the performance of permanent magnets, H is suitable for use as an injection-bonded magnet in small brushless DC motors ranging from tens to hundreds of watts for electric fuel or water pumps. cJ Preferably, it is 850 kA / m or higher, and more preferably 900 kA / m or higher.
[0091] In addition, B r Preferably, the amount is 0.72T or more, and more preferably 0.75T or more.
[0092] [Sudden cooling of the molten metal]
[0093] In this invention, raw materials prepared to achieve a predetermined alloy composition are melted, and the molten liquid is sprayed onto the surface of a rotating roller with copper, copper alloys, or Mo and W as the main raw materials at an average discharge rate of 200 g / min or more but less than 2000 g / min per hole at the nozzle tip. This process prepares an amorphous phase or a material containing RE2Fe. 14 The alloy is a rapidly solidified alloy containing at least 1% by volume of the crystalline B phase. When the average liquid discharge rate is below 200 g / min, the product yield is poor. When it is above 2000 g / min, a rapidly solidified molten alloy structure containing coarse α-Fe is formed. Therefore, even if crystallization heat treatment is performed, the desired permanent magnet properties cannot be obtained. Therefore, the liquid discharge rate of each orifice configured at the nozzle tip is limited to 200 g / min and below 2000 g / min. This average liquid discharge rate is preferably 300 g / min to 1500 g / min, more preferably 400 g / min to 1300 g / min.
[0094] In preparing the aforementioned rapidly solidified alloy, the adhesion between the molten alloy and the rotating roller is crucial. This adhesion largely depends on the surface roughness of the roller. Therefore, to ensure molten adhesion and maintain a stable rapid cooling state, the surface roughness of the rotating roller is set to an arithmetic mean roughness (Ra) of 0.1 μm or more and less than 0.6 μm. When Ra is less than 0.1 μm, the molten alloy will slip on the surface of the rotating roller, failing to achieve sufficient cooling; while when Ra is greater than 0.6 μm, there is a risk that the rapidly cooled alloy will adhere to the rotating roller. Ra is preferably 0.1 μm or more and less than 0.55 μm, more preferably 0.15 μm or more and less than 0.5 μm.
[0095] When producing the aforementioned rapidly solidified alloy, preventing oxidation of the molten alloy can suppress the increase in molten viscosity and maintain a stable discharge rate. Therefore, the atmosphere for rapid solidification is preferably oxygen-free or low-oxygen. To achieve such an atmosphere, after evacuating the rapid solidification apparatus to below 20 Pa, preferably below 10 Pa, and more preferably below 1 Pa, an inert gas is introduced into the rapid solidification apparatus to reduce the oxygen concentration to below 500 ppm, preferably below 200 ppm, and more preferably below 100 ppm before rapid solidification is performed. As the inert gas, rare gases such as helium or argon, or nitrogen, can be used. However, since nitrogen reacts more readily with rare earth elements and iron, rare gases such as helium or argon are preferred. From a cost perspective, argon is more preferred.
[0096] In the preparation process of rapidly solidified alloys, the material of the rotating roller used to rapidly cool the alloy melt is preferably a substrate made of copper, or molybdenum, tungsten, or a similar alloy. This is because these substrates have excellent thermal conductivity and durability. Furthermore, the surface of the rotating roller substrate can be plated with chromium, nickel, or a combination thereof to increase the heat resistance and hardness of the roller surface and suppress melting or deterioration of the roller surface during rapid solidification.
[0097] The diameter of the rotating roller is, for example, Φ200mm~Φ20000mm. When the quenching solidification time is a short time of less than 10 seconds, it is not necessary to water cool the rotating roller. However, when the quenching solidification time reaches more than 10 seconds, it is preferable to let cooling water flow into the interior of the rotating roller to suppress the temperature rise of the rotating roller substrate. More preferably, the water cooling capacity of the rotating roller is calculated based on the latent heat of solidification and the liquid discharge rate per unit time and appropriately adjusted to the optimal value.
[0098] [Quick Annealing]
[0099] When the heating rate during crystallization heat treatment is lower than 10℃ / sce, excessive grain growth prevents the formation of a fine metallic structure, leading to H... cJ and B rThe temperature decreases; however, when the heating rate exceeds 200℃ / sce, grain growth cannot keep up, and it is impossible to form RE2Fe with an average grain size of 20nm or more and less than 100nm, which is required to exhibit the characteristics of a permanent magnet. 14 The uniform and fine metallic structure with B-type tetragonal compound as the main phase also leads to a decrease in magnetic properties when the heating rate is less than 10℃ / sce. Therefore, the heating rate can be 10℃ / sce or higher and less than 200℃ / sce, preferably 30℃ / sce or higher and less than 200℃ / sce, and more preferably 40℃ / sce or higher and less than 180℃ / sce.
[0100] In the crystallization heat treatment of the present invention, in order to obtain good permanent magnetic properties, it is preferable to immediately perform quenching after reaching a heat treatment temperature within a certain temperature range above the crystallization temperature and below 850°C. Specifically, the holding time from reaching the above-mentioned heat treatment temperature to quenching is substantially sufficient for 0.01 seconds or more. Holding for more than 7 minutes will damage the uniform and fine metal structure, leading to a decrease in various magnetic properties, and is therefore not preferred. Therefore, the holding time can be 0.01 seconds to 7 minutes, preferably 0.01 seconds to 2 minutes, and more preferably 0.01 seconds to 30 seconds.
[0101] In the crystallization heat treatment of the present invention, the molten alloy powder can be rapidly cooled to below 400°C at a cooling rate of 2°C / sce to 200°C / sce. When the cooling rate is below 2°C / sce, coarsening of the crystalline structure progresses, while when it exceeds 200°C / sce, oxidation of the alloy may occur. More preferably, the cooling rate is 5°C / sce to 200°C / sce, and even more preferably 5°C / sce to 150°C / sce.
[0102] The atmosphere for the aforementioned crystallization heat treatment can be an inert gas atmosphere to prevent oxidation of the alloy from rapid solidification of the molten metal. As an inert gas, rare gases such as helium or argon, or nitrogen, can be used. However, since nitrogen reacts more readily with rare earth elements and iron, rare gases such as helium or argon are preferred. From a cost perspective, argon is more preferable.
[0103] [Crushing and shaping]
[0104] The rapidly solidified alloy obtained through the above process can be coarsely pulverized into thin strips before crystallization heat treatment, for example, by cutting or pulverizing to less than 50 mm. The magnet of the present invention after crystallization heat treatment is further pulverized into an appropriate average powder particle size in the range of 20 μm to 200 μm to produce magnet powder. This magnet powder can then be used to manufacture bonded magnets (commonly known as plastic magnets) composed of various resin-bonded magnets using known processes.
[0105] In preparing the above-mentioned resin-bonded magnet, the magnet powder can be mixed with epoxy resin, polyamide, polyphenylene sulfide (PPS), polyether ether ketone (PEEK), liquid crystal polymer, acrylic resin, polyether, etc., and molded into the desired shape.
[0106] In the resin mixture of the above-mentioned resin-bonded magnets, the magnet powder is mixed and kneaded in a ratio of 50% to 80% by volume in thermoplastic resins such as polyamide, polyphenylene sulfide (PPS), and polyether ether ketone (PEEK), and then a composite for injection molding is prepared. The isotropic rare earth injection-bonded magnet with a diameter of 10 mm × height of 7 mm and a magnetic permeability (Pc) of 2 is obtained by using the composite. It is an isotropic iron-based rare earth injection-bonded magnet with extremely excellent corrosion resistance after 1000 hours of immersion in 80℃ / 5% NaCl (salt water) test, with a demagnetization rate (flux loss) of less than -20% and a magnetic flux (open flux) of more than 0.5 mWb. It should be noted that when the amount of magnetic powder is less than 45% by volume, the desired magnetic properties cannot be obtained; when it is more than 80% by volume, the flowability of the composite is poor and injection molding is not possible. Therefore, the mixing ratio of magnetic powder can be more than 45% by volume and less than 80% by volume, preferably more than 50% by volume and less than 80% by volume, and more preferably more than 50% by volume and less than 75% by volume.
[0107] When the magnetic powder of the present invention is used in injection-molded bonded magnets, it is preferable to pulverize it to an average powder particle size of 100 μm or less, and more preferably, the average powder particle size is 20 μm or more and 100 μm or less. Furthermore, when used in compression-molded bonded magnets, it is preferable to pulverize it to an average powder particle size of 100 μm or more and 200 μm or less, and more preferably, the average powder particle size is 50 μm or more and 150 μm or less. It is even more preferable that the particle size distribution has two peaks, with an average powder particle size of 80 μm or more and 130 μm or less.
[0108] Furthermore, by performing surface treatments such as coupling treatment or chemical conversion treatment (including phosphoric acid treatment and glass coating treatment) on the surface of the magnet powder of the present invention, regardless of the molding method, the formability during the molding process of the resin-bonded magnet, as well as the corrosion resistance and heat resistance of the resulting resin-bonded magnet, can be improved. In addition, when the surface of the molded resin-bonded magnet is subjected to surface treatments such as resin coating, chemical conversion treatment, or gold plating, the corrosion resistance and heat resistance of the resin-bonded magnet can be improved in the same way as the surface treatment of the magnet powder.
[0109] The embodiments of the present invention are described below.
[0110] (Example)
[0111] According to the alloy composition in Table 1, 100g of raw materials, which contain the main elements Nd, Pr, B, Cr and Fe with a purity of 99.5% or higher, as well as additional elements such as C, Co, Ga, Si, Ti and Mo, are added to an alumina melting crucible and placed in the working coil of a vacuum melting furnace. Then, the vacuum in the melting furnace is vented to below 0.02Pa, and argon gas is introduced until atmospheric pressure is reached. The alloy melt is then obtained by high-frequency induction heating. Finally, the alloy melt is injected into a water-cooled copper mold for casting to produce the master alloy.
[0112] Next, the obtained master alloy is cut into appropriate sizes, and 40g is inserted into a transparent quartz nozzle. This nozzle has holes of different diameters (0.7mm to 1.2mm) at its bottom, suitable for the liquid discharge rates listed in Table 1. Then, the nozzle is placed in the working coil of a single-roller quenching device. The vacuum in the vacuum melting furnace is then evacuated to below 0.02Pa, and argon gas is introduced until the quenching atmosphere pressure in Table 1 is reached. The master alloy is remelted by high-frequency induction heating, and then the molten metal is sprayed from the nozzle holes at a spray pressure of 30kPa onto the surface of a pure copper rotating roller with the surface roughness listed in Table 1, rotating at the roller surface speed (Vs) listed in Table 1. This process creates a molten metal quenched solidification alloy. At this point, the distance between the nozzle tip and the rotating roller surface is 0.8mm. Figure 3 The image shows the powder XRD pattern of the rapidly solidified alloy of Example 3, which is a representative example. (From...) Figure 3 It can be confirmed that Nd2Fe is already present in the rapid cooling and solidification state (rapid quenching). 14 The B phase contains some α-Fe.
[0113] The rapidly solidified alloy obtained from the above process is coarsely pulverized to a thickness of several millimeters to produce molten rapidly solidified alloy powder. Then, it is used... Figure 1 (a) shows a crystallization heat treatment furnace (rapid annealing furnace, furnace core tube: made of transparent quartz, outer diameter 15mm × inner diameter 12.5mm × length 1000mm; heating zone: 300mm; cooling zone formed by cooling fan: 500mm), in which coarse powder of rapidly solidified alloy is fed into the raw material hopper, and then heat treatment is carried out at a workpiece cutting speed of 20g / min. Figure 1 The crystallization heat treatment furnace shown in (a) includes a raw material hopper 1, a raw material feeder 2, a core tube 3, a tubular furnace 4, a cooling tower 5, a recovery hopper 6, a vibrator 7, a motor for rotating the core tube 8, a core tube rotation shaft 9, and a support frame 10. The core tube tilt angle 11, the core tube rotation speed, and the core tube vibration frequency are appropriately adjusted together with the heat treatment temperature and heat treatment time listed in Table 2 to achieve the heating rate shown in Table 2. Thus, as... Figure 1(b) shows an enlarged view inside the furnace core tube 3. The rapidly cooled solidified powder 13 passes through the furnace core tube (symbol 3a is a cross-sectional view of the furnace core tube 3 cut along the axial direction, and symbol 3b is a cross-sectional view of the furnace core tube 3 cut in a direction orthogonal to the axial direction) while being subjected to the combined effects of the stirring caused by the rotational motion of the furnace core tube rotating motor 8 and the hopping phenomenon 15 caused by the vibration of the furnace core tube caused by the operation of the vibrator 7. Thus, the rapidly cooled solidified powder 13 is under special heat treatment conditions where it does not undergo a thermal process as a whole, but rather each powder undergoes its own thermal process.
[0114] Powder X-ray diffraction was used to confirm the phase composition of the alloy powder formed by the rapid solidification of the melt after crystallization heat treatment, and Nd2Fe was confirmed. 14 The existence of phase B. Figure 4 The image shows the powder XRD pattern after heat treatment for crystallization, as a representative example, in Example 3. Furthermore, in Figure 4 Nd2Fe was observed in 14 The intensity of the B-phase crystallization peak relative to Figure 3 There is an increasing trend, thus confirming that heat treatment promotes the growth of Nd2Fe. 14 The crystallinity of phase B was confirmed. And it was also confirmed to be different from that before heat treatment. Figure 3 The tissue also contains some α-Fe.
[0115] The isotropic iron-based rare-earth boron magnets obtained by the crystallization heat treatment described in Table 2 were fabricated into magnetic property evaluation samples with a length of approximately 7 mm × a width of approximately 0.9 mm to 2.3 mm × a thickness of 18 μm to 25 μm. These samples were then magnetized along their length using an external pulsed magnetic field of 3.2 MA / m. The magnetic property evaluation samples were then positioned along their length to suppress the influence of the counter-magnetic field. The room-temperature magnetic properties were then measured using a vibrating sample magnetometer (VSM), and the results are shown in Table 3. As can be seen from Table 3, the target magnetic property level B can be obtained according to the alloy composition and preparation method described in the examples. r ≥0.7T, H cJ ≥800kA / m, (BH) max ≥80kJ / m 3 .
[0116] The isotropic iron-based rare-earth boron magnets obtained through crystallization heat treatment, as shown in Table 4, were observed using a transmission electron microscope. Bright-field images confirmed the presence of RE₂Fe₂ as the base material. 14 The microstructure is composed mainly of phase B. Table 4 shows the average grain size and standard deviation σ of the main phase. From Table 4, it can be seen that RE2Fe... 14The average crystal grain size of type B tetragonal compounds is greater than 20 nm and less than 100 nm, and σ is less than 50% of the average crystal grain size. Regarding RE₂Fe as the main phase... 14 The crystal grain size of type B tetragonal compounds was evaluated by binarizing bright-field images taken with a transmission electron microscope to separate the main phase from the grain boundaries, and then by image analysis according to JIS standard (JIS G 0551:2005).
[0117] Next, the heat-treated magnetic powder obtained in Examples 1 to 13 was pulverized into an average particle size of 70 μm using a pin mill. The pulverized magnetic powder and PPS resin were weighed to a specified weight and then mixed uniformly using a universal mixer. The mixture was then kneaded using a twin-screw extruder to produce a composite for injection molding of bonded magnets.
[0118] The aforementioned composite material for injection molding was injection molded using an injection molding machine to produce an isotropic injection-molded bonded magnet. The resulting injection-molded bonded magnet had a diameter of 10 mm × a height of 7 mm and a bulk density of 4.4 g / cm³. 3 (The true density of the magnetic powder is 7.5 g / cm³) 3 Therefore, the magnetic powder filling rate is 58.7% by volume.
[0119] After magnetizing the isotropic injection-molded bonded magnets obtained using the magnetic powders of Examples 1 to 13 along the length direction using an external pulsed magnetic field of 3.2 MA / m, the results of the magnetic properties measured using a BH curve analyzer are shown in Table 5.
[0120] Next, using the isotropic injection-molded bonded magnets obtained from the magnetic powders of Examples 1-13, the rusting condition and the change in magnetic flux of the magnets themselves over time were investigated during an immersion test at 80°C / 5% NaCl (salt water). Table 6 shows the demagnetization rate (flux loss) and magnetic flux (open flux) after 1000 hours. Furthermore, Figure 7 This represents the change in demagnetization rate (flux loss) during the 80℃ / 5% NaCl (salt water) immersion test. Figure 8 This represents the change in open flux during an immersion test at 80℃ / 5% NaCl (salt water). Figure 9 This indicates the relationship between the amount of Cr added and the demagnetization rate (flux loss) in the 80℃ / 5% NaCl (salt water) immersion test. Figure 10 A photograph showing the rust condition during the 80°C / 5% NaCl (salt water) immersion test of Example 2.
[0121] (Comparative Example)
[0122] According to the alloy composition in Table 1, 100g of raw materials, which contain Nd, Pr, B and Fe with a purity of 99.5% or higher, and also include Si, Cr, Nb, Ti and Zr as additional elements, are added to an alumina melting crucible and placed in the working coil of a vacuum melting furnace. Then, the vacuum in the melting furnace is vented to below 0.02 Pa, and argon gas is introduced until atmospheric pressure is reached. The alloy melt is then obtained by high-frequency induction heating. Finally, the alloy melt is injected into a water-cooled copper mold for casting to produce the master alloy.
[0123] Next, the obtained master alloy is cut into appropriate sizes, and 40g is inserted into a transparent quartz nozzle. This nozzle has holes of different diameters (0.7mm to 1.2mm) at its bottom, suitable for the liquid discharge rates listed in Table 1. Then, the nozzle is placed in the working coil of a single-roller quenching device. The vacuum in the vacuum melting furnace is then evacuated to below 0.02Pa, and argon gas is introduced until the quenching atmosphere pressure in Table 1 is reached. The master alloy is remelted by high-frequency induction heating, and then the molten metal is sprayed from the nozzle holes at a spray pressure of 30kPa onto the surface of a pure copper rotating roller with the surface roughness listed in Table 1, rotating at the roller surface speed (Vs) listed in Table 1. This process creates a molten metal quenched solidification alloy. At this point, the distance between the nozzle tip and the rotating roller surface is 0.8mm. Figure 5 The powder XRD pattern of the rapidly solidified alloy, as a representative example (Comparative Example 14), is shown. Figure 5 It can be confirmed that Nd2Fe exists in the rapid cooling and solidification state (rapid quenching). 14 Phase B. It is determined to be Nd₂Fe. 14 A single-phase metallic structure of B.
[0124] The rapidly solidified alloy obtained from the above process is coarsely pulverized to a thickness of a few millimeters to form molten rapidly solidified alloy powder. Then, using a crystallization heat treatment furnace (rapid annealing furnace, core tube: transparent quartz, outer diameter 15mm × inner diameter 12.5mm × length 1000mm; heating zone: 300mm; cooling zone formed by the cooling fan: 500mm), the coarse powder of the rapidly solidified alloy is fed into the raw material hopper, and then heat treatment is carried out at a workpiece cutting speed of 20g / min. The furnace core tube tilt angle, furnace core tube rotation speed, and furnace core tube vibration frequency are appropriately adjusted together with the heat treatment temperature and heat treatment time recorded in Table 2 to achieve the heating rate specified in Table 2.
[0125] Powder X-ray diffraction was used to confirm the phase composition of the alloy powder formed by the rapid solidification of the melt after crystallization heat treatment, and Nd2Fe was confirmed. 14 The existence of phase B. Figure 6 The image shows the powder XRD pattern after heat treatment for crystallization, as a representative example, Comparative Example 14. (From...) Figure 6 Confirmed, it is related to Figure 5Similarly, it is also Nd2Fe after heat treatment. 14 B is single-phase.
[0126] After the isotropic iron-based rare earth boron magnets obtained by the crystallization heat treatment described in Table 2 were made into magnetic property evaluation samples with a length of about 7 mm × a width of about 0.9 mm to 2.3 mm × a thickness of 18 μm to 25 μm, they were magnetized along the length direction using an external pulsed magnetic field of 3.2 MA / m. Then, the magnetic property evaluation samples were set along the length direction to suppress the influence of the counter magnetic field. The room temperature magnetic properties were then measured using a vibrating sample magnetometer (VSM), and the measurement results are shown in Table 3.
[0127] The isotropic iron-based rare-earth boron magnets obtained through crystallization heat treatment, as shown in Table 4, were observed using a transmission electron microscope. Bright-field images confirmed the presence of RE₂Fe₂ as the base material. 14 The microstructure consists of a B phase as the main phase and fine metallic structure. Table 4 shows the average grain size and standard deviation σ of the main phase.
[0128] Next, the heat-treated magnetic powder obtained in Comparative Examples 14-18 was pulverized into an average particle size of 70 μm using a pin mill. The pulverized magnetic powder and PPS resin were weighed to a specified weight and then mixed uniformly using a universal mixer. The mixture was then kneaded using a twin-screw extruder to produce a composite for injection molding of bonded magnets.
[0129] The aforementioned composite material for injection molding was injection molded using an injection molding machine to produce an isotropic injection-molded bonded magnet. The resulting injection-molded bonded magnet had a diameter of 10 mm × a height of 7 mm and a bulk density of 4.4 g / cm³. 3 (The true density of the magnetic powder is 7.5 g / cm³) 3 Therefore, the magnetic powder filling rate is 58.7% by volume.
[0130] After magnetizing the above-mentioned isotropic injection-molded bonded magnets obtained using magnetic powders from Comparative Examples 14 to 18 along the length direction using an external pulsed magnetic field of 3.2 MA / m, the results of the magnetic properties measured using a BH curve analyzer are shown in Table 5.
[0131] Next, using the isotropic injection-molded bonded magnets obtained from the magnetic powders of Comparative Examples 14-18, the rusting condition and the change in magnetic flux of the magnets themselves over time were investigated during an immersion test at 80°C / 5% NaCl (salt water). Table 6 shows the demagnetization rate (flux loss) and magnetic flux (open flux) after 1000 hours. Furthermore, Figure 7 This represents the change in demagnetization rate (flux loss) during the 80℃ / 5% NaCl (salt water) immersion test. Figure 8This represents the change in open flux during an immersion test at 80℃ / 5% NaCl (salt water). Figure 11 A photograph showing the rusting condition of Comparative Example 16 during the 80°C / 5% NaCl (salt water) immersion test.
[0132] [Table 1]
[0133]
[0134] [Table 2]
[0135]
[0136] [Table 3]
[0137]
[0138] [Table 4]
[0139]
[0140] [Table 5]
[0141]
[0142] [Table 6]
[0143]
[0144] Explanation of reference numerals in the attached figures
[0145] 1: Raw material hopper; 2: Raw material feeder; 3: Furnace core tube; 3a: Enlarged view of furnace core tube; 3b: Enlarged cross-sectional view of furnace core tube; 4: Tubular furnace; 5: Cooling tower; 6: Recycling hopper; 7: Vibrator; 8: Electric motor for rotating furnace core tube; 9: Rotating shaft of furnace core tube; 10: Device support; 11: Inclination angle of furnace core tube; 12: Cooling fan; 13: Rapid cooling and solidification of molten alloy powder (workpiece); 14: Movement direction of workpiece; 15: Sinking and floating phenomenon of workpiece; 16: Heating rate; 17: Holding temperature; 18: Cooling rate.
Claims
1. A magnetic alloy, wherein RE2Fe 14 An isotropic iron-based rare-earth boron-based magnetic alloy with a B-type tetragonal compound phase as the main phase, wherein... RE is a rare earth element, and the magnetic alloy is characterized by... With composition T 100－x－y－z－m (B 1－n C n ) x RE y Cr z M m This indicates that, where T is at least one element selected from Fe, Co, and Ni, and is a transition metal element that must contain Fe; RE is a rare earth element that must contain Nd or Pr; and M is one or more metallic elements selected from Al, Si, V, Ti, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb, and has a composition in which the compositional ratios x, y, z, m, and n respectively satisfy the following formula: 5.6 atomic%≤x≤6.4 atomic%, 11.2 atomic%≤y≤12.0 atomic%, 2.3 atomic%≤z≤5.4 atomic%, 0.0 atomic%≤m≤3.0 atomic%, 0.0≤n≤0.5， And Cr must be added. RE2Fe as the main phase 14 The average crystal grain size of type B tetragonal compounds is greater than 20 nm and less than 100 nm, and the standard deviation σ is within 50% of the average crystal grain size.
2. The magnetic alloy according to claim 1, characterized in that, The magnetic alloy has a remanent magnetic flux density B. r For 0.7T or above, intrinsic coercivity H cJ With a maximum magnetic energy product of over 800 kA / m, BH max 80kJ / m 3 The above are the characteristics of permanent magnets.
3. The magnetic alloy according to claim 1 or 2, characterized in that, The magnet alloy is in the form of a highly corrosion-resistant powder with an average particle size of 20 μm or more and less than 200 μm.
4. A bonded magnet, characterized in that, It is obtained by mixing and kneading the powdered magnet alloy of claim 3 with thermoplastic resin or thermosetting resin and then molding it.
5. The bonded magnet according to claim 4, characterized in that, The resin used in the mixture is at least one thermoplastic resin selected from polyamide, polyphenylene sulfide (PPS), and polyether ether ketone (PEEK). The bonded magnet has a diameter of 10 mm, a height of 7 mm, and a magnetic permeability Pc of 2. The demagnetization rate after immersion in 80℃ / 5% NaCl for 1000 hours is 0 to -20%, and the magnetic flux of the magnet itself is above 0.5mWb.
6. A method for manufacturing a magnetic alloy, characterized in that, include: The process of preparing alloy melt, wherein the alloy melt is composed of formula T 100－x－y－z－m (B 1－n C n ) x RE y Cr z M m This indicates that, where T is at least one element selected from Fe, Co, and Ni, and is a transition metal element that must contain Fe; RE is a rare earth element that must contain Nd or Pr; and M is one or more metallic elements selected from Al, Si, V, Ti, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb, and has a composition in which the compositional ratios x, y, z, m, and n respectively satisfy the following formula: 5.6 atomic%≤x≤6.4 atomic%, 11.2 atomic%≤y≤12.0 atomic%, 2.3 atomic%≤z≤5.4 atomic%, 0.0 atomic%≤m≤3.0 atomic%, 0.0≤n≤0.5； The process for preparing a rapidly solidified alloy involves spraying the molten alloy at an average outflow rate of 200 g / min to 2000 g / min per orifice provided at the nozzle tip onto the surface of a rotating roller whose main raw material is any one of copper, copper alloy, Mo, and W. This process produces an alloy with an amorphous phase or containing RE₂Fe. 14 The B-phase crystalline phase is more than 1% by volume in the rapidly solidified alloy; and By performing heat treatment, RE2Fe was prepared. 14 In the process of a magnet alloy with a type B tetragonal compound as the main phase, the heat treatment involves rapidly cooling the alloy to a certain temperature range between the crystallization temperature and 850°C at a heating rate of 10°C / sec or higher and less than 200°C / sec, followed by rapid cooling immediately after 0.01 seconds or more and less than 7 minutes.
7. The method for manufacturing the magnetic alloy according to claim 6, characterized in that, The surface roughness of the rotating roller is an arithmetic mean roughness Ra of ≥0.1μm and <0.6μm.
8. A method for manufacturing a bonded magnet, characterized in that, include: The process of pulverizing the magnetic alloy obtained by the manufacturing method of the magnetic alloy according to claim 6 to an average powder particle size of more than 100 μm and less than 200 μm to obtain magnetic alloy powder. The process of adding thermosetting resin to the magnetic alloy powder, filling it into a molding die, and forming a compression molded body by pressure molding; and The process of obtaining a bonded magnet involves heat-treating the compression molded body at a temperature above the polymerization temperature of the thermosetting resin.
9. A method for manufacturing a bonded magnet, characterized in that, include: The process of pulverizing the magnetic alloy obtained by the manufacturing method of the magnetic alloy according to claim 6 to an average powder particle size of 20 μm or more and less than 100 μm to obtain magnetic alloy powder; and The process involves adding thermoplastic resin to the magnet alloy powder and then performing injection molding on the resulting injection molding composite.