JP2004281493A - Process for producing permanent magnet material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small or thin permanent magnet having S/V=6 mm-1 or above representing good magnetic characteristics by preventing the magnetic characteristics from deteriorating due to grinding. <P>SOLUTION: In the process for producing the permanent magnet material, a sintered magnet body having an R-Fe-B based composition (R is one kind or more than one kinds being selected from rare earth elements including Y) and ground to have a specific surface area of 6 mm<SP>-1</SP>or above is subjected to surface diffusion heat treatment for 1 min to 10 hours in vacuum or inert gas at a temperature not lower than the fusion starting temperature of an R rich grain boundary phase existing in the magnet and not higher than the sintering temperature of the magnet so that the grain boundary phase components are diffused onto the grinding surface of the magnet thus forming a thin film layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３２】
【発明の効果】
本発明によれば、研削加工による磁気特性の劣化を防止して良好な磁気特性を示すＳ／Ｖ＝６ｍｍ^−１以上の小型あるいは薄型の永久磁石を提供することができる。
【図面の簡単な説明】
【図１】本発明により作製された磁石体の減磁曲線（曲線Ｈ１）及び研削加工のみの磁石体の減磁曲線（曲線Ｋ１）を示した図である。
【図２】本発明により作製された磁石体の減磁曲線（曲線Ｈ２）及び研削加工のみの磁石体の減磁曲線（曲線Ｋ２）を示した図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing an R—Fe—B permanent magnet in which deterioration of magnetic properties due to grinding of the surface of a sintered magnet body or the like is prevented, and in particular, the specific surface area (S (surface area) / V ( The present invention relates to a method for producing a small or thin high-performance permanent magnet material having a volume (volume) of 6 mm ⁻¹ or more.
[0002]
[Prior art]
Nd-Fe-B-based permanent magnets have been increasingly used because of their excellent magnetic properties. In recent years, Nd-Fe-B magnets, especially high-performance, have been developed with computer-related equipment using magnets, CD players, DVD players, mobile phones, and other electronic devices that are becoming lighter, thinner, smaller, more efficient, and more energy efficient. There is a demand for smaller and thinner Nd-Fe-B based sintered magnets, and the demand for small or thin magnets whose specific surface area S / V exceeds 6 mm ^-1 is also increasing. .
[0003]
In order to process a small or thin Nd-Fe-B based sintered magnet into a practical shape and mount it on a magnetic circuit, it is necessary to grind a shaped and sintered block-shaped sintered magnet. An outer edge cutting machine, an inner edge cutting machine, a surface grinding machine, a centerless polishing machine, a lapping machine and the like are used.
[0004]
However, it is known that when the Nd-Fe-B based sintered magnet is ground by the above-described apparatus, the magnetic properties deteriorate as the magnet body becomes smaller. It is considered that the field structure is missing on the magnet surface due to processing. In order to prevent the deterioration of the magnetic characteristics, for example, by preventing the growth of crystal grains in the sintering process of the magnet, the magnetic characteristics do not deteriorate even if the grinding process is performed until the specific surface area S / V becomes 2.6 mm ^−1. A magnet material has been proposed (see Patent Document 1: Japanese Patent No. 2514155). However, when the S / V exceeds 6 mm ⁻¹ , there is a problem that the magnetic characteristics are significantly deteriorated.
[0005]
As a method of preventing the characteristic deterioration of such an extremely small magnet, a thin film layer mainly composed of a rare earth element is formed on the surface to be ground, and further subjected to a heat treatment so that the deteriorated surface to be ground has the same high coercive force as the inside of the magnet. A method has been proposed to prevent the deterioration of the properties of the magnet body by modifying the grain boundary structure necessary for the above (Patent Document 2: Japanese Patent Publication No. 5-60241, Patent Document 3: Japanese Patent Publication No. 6-63086). Gazette). Patent Literature 2 employs a method in which a magnet body after grinding is vacuum-sealed together with a rare earth metal in a quartz tube and heated at 1,000 ° C. so that the evaporated rare earth metal is adhered to the magnet body. However, it is difficult to apply to mass production due to extremely low productivity. Patent Literature 3 employs a method of depositing a thin film on the surface of a magnet body by sputtering using a rare earth metal as a target. In a conventional technique, a thin film can be applied to only one surface of the magnet body by one sputtering. It is considered to be applicable if there is only one surface to be ground. However, since the entire surface of a normal magnet body is the surface to be ground, recoating of the magnet and sputtering are repeated to deposit a thin film on the entire magnet body. There must be.
[0006]
As described above, it is difficult to apply the prior art because of extremely low productivity with respect to mass production. Therefore, there is no deterioration in magnetic characteristics and the S / V exceeds 6 mm ^−1. Was considered virtually impossible.
[0007]
[Patent Document 1]
Japanese Patent No. 2514155 [Patent Document 2]
Japanese Patent Publication No. 5-60241 [Patent Document 3]
Japanese Patent Publication No. 6-63086
[Problems to be solved by the invention]
The present invention has been made in view of the above-described conventional problems, and provides a method of manufacturing an R—Fe—B based sintered magnet material with high productivity, in which deterioration of magnetic properties due to grinding is prevented. It is intended for that purpose.
[0009]
Means for Solving the Problems and Embodiments of the Invention
The appearance of coercive force in an R—Fe—B sintered magnet represented by an Nd—Fe—B based sintered magnet depends on the structure of the crystal grain boundaries, and the R-rich phase existing around the main phase. It is well known that a high coercive force is exhibited when the surface covers the main phase surface and has a flat interface even at the atomic level. The R-rich phase melts at 400 to 700 ° C. or higher, depending on the type and composition of the added element or constituent element. When this melting start temperature is expressed as _TE ° C, the present inventors have found that when the magnet body after grinding is heated to _TE ° C or higher, the R-rich phase becomes a liquid phase, and its fluidity is significantly increased. The inventors have found that the component of the R-rich phase is diffused on the entire surface to be ground and that a thin film rich in R can be deposited on the entire surface of the magnet body, thereby completing the present invention.
[0010]
That is, the present invention provides a sintered magnet body having an R—Fe—B composition (R is one or more selected from rare earth elements including Y) and having a specific surface area of 6 mm ⁻¹ or more. Is subjected to a surface diffusion heat treatment for 1 minute to 10 hours in a vacuum or an inert gas at a temperature equal to or higher than the melting start temperature of the R-rich grain boundary phase present inside the magnet and equal to or lower than the sintering temperature of the magnet. Thus, a method of manufacturing a permanent magnet material is provided, in which a grain boundary phase component is diffused on a surface to be ground of the magnet body to form a thin film layer.
[0011]
In this case, it is preferable to perform an aging treatment for 1 minute to 10 hours in a vacuum or an inert gas at a temperature lower than the melting start temperature of the grain boundary phase after the surface diffusion treatment.
Before the surface diffusion treatment, it is preferable to wash with one or more of an alkali, an acid and an organic solvent, or to remove a surface layer by shot blasting.
[0012]
Hereinafter, the present invention will be described in more detail.
The present invention is directed to a small or thin high-performance permanent magnet having a specific surface area S / V of 6 mm ^-1 or more, which prevents deterioration of magnetic properties due to grinding of the surface of an R-Fe-B based sintered magnet body. The present invention relates to a method for manufacturing a magnet material.
Here, the R—Fe—B based sintered magnet body can be obtained by coarsely pulverizing, finely pulverizing, molding, and sintering the master alloy according to a conventional method.
In this case, the master alloy contains R, Fe, and B. R is one or more selected from rare earth elements including Y, and specifically, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu Nd, Pr, and Dy are preferred. The content of the rare earth element containing Y is preferably 10 to 20 at%, particularly 12 to 15 at% of the entire alloy, and more preferably, R contains Nd and Pr or any one of them at 10 at% or more, particularly 50 at%. It is preferable to contain at least atomic%. B is preferably contained in an amount of 3 to 15 atomic%, particularly 4 to 8 atomic%. In addition, Al, Cu, Zn, In, Si, P, S, Ti, V, Cr, Mn, Ni, Ga, Ge, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta, One or more selected from W may be contained in an amount of 0 to 11 atomic%, particularly 0.1 to 5 atomic%. The balance is Fe or inevitable impurities such as C, N, and O, but Fe is preferably contained at 50 at% or more, particularly at least 65 at%. Further, a part of Fe, for example, 0 to 40 atomic%, particularly 0 to 15 atomic% of Fe may be replaced with Co.
[0013]
The mother alloy is obtained by melting a raw metal or alloy in a vacuum or an inert gas, preferably an Ar atmosphere, and then casting it in a flat mold or book mold, or casting it by strip casting. It should be noted that an alloy close to the R ₂ Fe ₁₄ B compound composition, which is the main phase of the present alloy, and an R-rich alloy, which is a liquid phase aid at the sintering temperature, are separately prepared, weighed and mixed after coarse pulverization. The two-alloy method is also applicable to the present invention. However, for an alloy having a composition close to the main phase, α-Fe tends to remain depending on the cooling rate during casting and the alloy composition, and is homogenized as necessary for the purpose of increasing the amount of the R ₂ Fe ₁₄ B compound phase. A chemical treatment is performed. The heat treatment is performed at 700 to 1,200 ° C. for 1 hour or more in a vacuum or Ar atmosphere. For an R-rich alloy serving as a liquid phase aid, a so-called liquid quenching method can be applied in addition to the casting method.
[0014]
The above alloy is usually coarsely pulverized to 0.05 to 3 mm, particularly 0.05 to 1.5 mm. A brown mill or hydrogen pulverization is used in the coarse pulverization step, and hydrogen pulverization is preferable for an alloy produced by strip casting. The coarse powder is usually finely pulverized to, for example, 0.2 to 30 μm, particularly 0.5 to 20 μm by a jet mill using high-pressure nitrogen. The fine powder is formed by a compression molding machine in a magnetic field, and put into a sintering furnace. The sintering is performed in a vacuum or an inert gas atmosphere, usually at 900 to 1,250 ° C, especially 1,000 to 1,100 ° C.
[0015]
The sintered magnet obtained here contains the tetragonal R ₂ Fe ₁₄ B compound as a main phase in an amount of 60 to 99% by volume, particularly preferably 80 to 98% by volume, and the balance is 0.5 to 20% by volume of R. At least one of carbides, nitrides, oxides, and hydroxides formed by unavoidable impurities, and a mixture or composite thereof.
[0016]
The obtained sintered block is ground into a practical shape. However, in order to minimize the influence of processing strain, it is preferable to reduce the processing speed within a range where productivity is not reduced. In this case, the grinding method can be performed according to a conventional method, but the processing speed is specifically 0.1 to 20 mm / min, particularly preferably 0.5 to 10 mm / min.
[0017]
In this case, as the grinding amount, the specific surface area S / V (surface area mm ² / volume mm ³ ) of the sintered block is 6 mm ⁻¹ or more, preferably 8 mm ⁻¹ or more. The upper limit is appropriately selected and is not particularly limited, but is usually 40 mm ^-1 or less, particularly 30 mm ^-1 or less.
[0018]
The ground magnet body is subjected to surface diffusion treatment in a vacuum or an inert gas atmosphere such as Ar or He. The treatment temperature is equal to or higher than the melting start temperature ( _TE ° C.) of the R-rich grain boundary phase and equal to or lower than the sintering temperature of the sintered magnet. T _E can know in advance the sintered body by differential thermal analysis. The reasons for limiting the processing temperature are as follows.
First, it is less than T _E ° C. for rich phase R does not become a liquid phase, the surface diffusion process of the present invention does not proceed, T _E ° C. or higher, preferably (T E ₊₅₀₎ ℃ or higher. Further, if the treatment is performed at a temperature higher than the sintering temperature of the sintered magnet, (1) the structure of the sintered magnet is deteriorated and high magnetic characteristics cannot be obtained, and (2) the specific surface area of the magnet body is large, so that it is inevitable. The oxidation temperature and the evaporation of components are remarkable, and the surface layer is rather deteriorated. (3) The processing dimensions cannot be maintained due to thermal deformation. Is (T _E +200) ° C. or less. The surface diffusion treatment time is 1 minute to 10 hours. If the time is less than 1 minute, the surface diffusion treatment is not completed, and if the time exceeds 10 hours, the structure of the sintered magnet is deteriorated, and unavoidable oxidation and evaporation of components adversely affect the magnetic properties. More preferably, it is 5 minutes to 8 hours, particularly 10 minutes to 6 hours.
[0019]
By the surface diffusion heat treatment as described above, the R-rich grain boundary phase component is diffused on the surface, and a R-rich thin film layer is formed.
In this case, the composition of the thin film layer is almost the same as that of the R-rich grain boundary phase existing inside the magnet, and contains 50 to 95 atomic% of R.
The thickness of the thin film layer is preferably 1 nm to 10 μm, particularly preferably 10 nm to 5 μm. Furthermore, an unavoidable oxide film layer formed through the surface diffusion treatment and the aging treatment described below is present at the outermost portion of the thin film layer, and this thickness occupies 0.01 to 90% of the entire thin film layer.
[0020]
After the surface diffusion heat treatment as described above, it is preferable to perform an aging treatment. This aging treatment is performed at a temperature lower than the melting start temperature of the grain boundary phase, preferably 200 ° C. or higher and 5 ° C. lower than the melting start temperature, more preferably 350 ° C. or higher and 5 ° C. lower than the melting start temperature. It is desirable. Preferably, the atmosphere is vacuum or in an inert gas such as Ar or He. The time of the aging treatment is 1 minute to 10 hours, preferably 10 minutes to 5 hours, particularly 30 minutes to 2 hours.
[0021]
When using a water-based coolant for the grinding machine during the above-described grinding, or when the ground surface is exposed to a high temperature during the processing, an oxide film is easily formed on the surface to be ground. It may hinder the surface diffusion of R-rich phase components on the body surface. In such a case, appropriate surface diffusion treatment can be performed by washing with one or more of an alkali, an acid, and an organic solvent, or by performing shot blasting to remove the oxide film.
[0022]
Incidentally, as the alkali, potassium pyrophosphate, sodium pyrophosphate, potassium citrate, sodium citrate, potassium acetate, sodium acetate, potassium oxalate, sodium oxalate, etc., as the acid, hydrochloric acid, nitric acid, sulfuric acid, acetic acid, Citric acid, tartaric acid and the like can be used, and as an organic solvent, acetone, methanol, ethanol, isopropyl alcohol and the like can be used. In this case, the alkali or acid can be used as an aqueous solution having an appropriate concentration that does not corrode the magnet body.
[0023]
The permanent magnet material obtained as described above can be used as a small or thin permanent magnet with no characteristic deterioration. In this case, as an example of a specific size of the permanent magnet, 1 mm × 1 mm × 1 mm (S / V = 6 mm ⁻¹ ), 0.8 mm × 0.8 mm × 0.25 mm (S / V = 13 mm ⁻¹⁾ ), 0.8 mm × 0.8 mm × 0.13 mm (S / V = 20 mm ⁻¹ ), 0.8 mm × 0.3 mm × 0.13 mm (S / V = 25 mm ⁻¹ ), and the like.
[0024]
【Example】
Hereinafter, specific embodiments of the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.
[0025]
[Example 1]
Strip casting method in which a predetermined amount of Nd, Dy, Co, Al, Fe metal and ferroboron having a purity of 99% by weight or more and ferroboron are weighed in a high frequency and melted in an Ar atmosphere, and the molten alloy is poured into a copper single roll in an Ar atmosphere. Thus, a thin plate-shaped alloy was obtained. The composition of the obtained alloy was such that Nd was 11.0 atomic%, Dy was 1.5 atomic%, Co was 1.0 atomic%, Al was 1.0 atomic%, B was 4.5 atomic%, and Fe was the balance. And this is referred to as alloy A. After absorbing hydrogen in the alloy A, the alloy A was heated to 500 ° C. while performing evacuation to partially release hydrogen, so-called hydrogen pulverization to obtain coarse powder of 30 mesh or less. Further, a predetermined amount of Nd, Dy, Fe, Co, Al, Cu metal and ferroboron having a purity of 99% by weight or more was weighed, and after high frequency melting in an Ar atmosphere, casting was performed. The composition of the obtained alloy was 20 atomic% of Nd, 10 atomic% of Dy, 24 atomic% of Fe, 6 atomic% of B, 1 atomic% of Al, 2 atomic% of Cu, and the balance of Co. Is referred to as alloy B. The alloy B was coarsely pulverized to 30 mesh or less using a brown mill in a nitrogen atmosphere.
[0026]
Subsequently, 90% by weight of the alloy A powder and 10% by weight of the alloy B powder were weighed and mixed in a nitrogen-purged V blender for 30 minutes. This mixed powder was finely pulverized by a jet mill using high-pressure nitrogen gas to a powder having a median particle diameter of 4 μm. The obtained mixed fine powder was molded at a pressure of about 1 ton / cm ² while being oriented in a magnetic field of 15 kOe under a nitrogen atmosphere. Next, this compact was put into a sintering furnace in an Ar atmosphere, and sintered at 1,060 ° C. for 2 hours to produce a magnet block having a size of 10 mm × 20 mm × 15 mm. The magnet block was entirely ground into a rectangular parallelepiped having a predetermined size so that the specific surface area S / V became 22 mm ⁻¹ by an inner peripheral blade cutting machine. The magnet body after this processing is called magnet body P1.
[0027]
After the ground magnet body was washed with an alkaline solution, it was washed with an acid and dried.
Before and after each cleaning, a cleaning step using pure water is included.
This was subjected to the surface diffusion treatment according to the present invention in an Ar atmosphere at 600 ° C. for 2 hours, and further subjected to aging treatment at 500 ° C. for 1 hour and rapidly cooled to obtain a magnet body. This is called a magnet M1. Incidentally, the results of differential thermal analysis, the temperature T _E ° C. for rich phase R starts to melt was 525 ° C..
[0028]
The demagnetization curves of the magnet bodies M1 and P1 are shown in FIG. 1 as curves H1 and K1, respectively, and their magnetic properties are shown in Table 1. Further, Table 1 also shows the magnetic properties of the block magnet before processing. When the grinding process is performed until the specific surface area becomes S / V = 22 mm ⁻¹ , it can be seen that the coercive force _HcB is reduced by about 20%, but is hardly reduced in the present invention.
[0029]
[Example 2]
Strip casting method in which a predetermined amount of Nd, Dy, Co, Al, Fe metal and ferroboron having a purity of 99% by weight or more and ferroboron are weighed in a high frequency and melted in an Ar atmosphere, and the molten alloy is poured into a copper single roll in an Ar atmosphere. Thus, a thin plate-shaped alloy was obtained. The composition of the obtained alloy was such that Nd was 11.0 atomic%, Dy was 4.2 atomic%, Co was 1.0 atomic%, Al was 1.0 atomic%, B was 4.5 atomic%, and Fe was the balance. And this is referred to as alloy A. After absorbing hydrogen in the alloy A, the alloy A was heated to 500 ° C. while performing evacuation to partially release hydrogen, so-called hydrogen pulverization to obtain coarse powder of 30 mesh or less. Further, a predetermined amount of Nd, Dy, Fe, Al, Cu, Co metal and ferroboron having a purity of 99% by weight or more were weighed, melted by high frequency in an Ar atmosphere, and then cast. The composition of the obtained alloy was 20 atomic% of Nd, 10 atomic% of Dy, 24 atomic% of Fe, 6 atomic% of B, 1 atomic% of Al, 2 atomic% of Cu, and the balance of Co. Is referred to as alloy B. The alloy B was coarsely pulverized to 30 mesh or less using a brown mill in a nitrogen atmosphere. Subsequently, 90% by weight of the alloy A powder and 10% by weight of the alloy B powder were weighed and mixed in a nitrogen-purged V blender for 30 minutes. This mixed powder was finely pulverized by a jet mill using high-pressure nitrogen gas to a weight median particle diameter of 6 μm. The obtained mixed fine powder was molded at a pressure of about 1 ton / cm ² while being oriented in a magnetic field of 15 kOe. Next, this compact was put into a sintering furnace in an Ar atmosphere, and sintered at 1,070 ° C. for 2 hours to produce a magnet block having a size of 10 mm × 20 mm × 15 mm. The magnet block was entirely ground into a rectangular parallelepiped having a predetermined size so that the specific surface area S / V was 24 mm ⁻¹ by an inner peripheral blade cutting machine. The magnet body after this processing is called magnet body P2.
[0030]
After the ground magnet body was washed with an alkaline solution, it was washed with an acid and dried. Before and after each cleaning, a cleaning step using pure water is included.
This was subjected to the surface diffusion treatment according to the present invention in an Ar atmosphere at 600 ° C. for 2 hours, and further subjected to aging treatment at 500 ° C. for 1 hour and rapidly cooled to obtain a magnet body. This is called magnet body M2.
FIG. 2 shows the demagnetization curves of the magnet bodies M2 and P2 as curves H2 and K2, respectively. Table 1 also shows the magnetic properties of the magnet bodies M2 and P2 and the block magnet before processing. Note that the coercive force _{HcJ is} described as ">30", which means that _HcJ exceeds the maximum applied magnetic field of the measuring apparatus. When the grinding process is performed until the specific surface area becomes S / V = 24 mm ⁻¹ , the coercive force _HcB is reduced by about 17%, but is hardly reduced in the present invention.
[0031]
[Table 1]

[0032]
【The invention's effect】
According to the present invention, it is possible to provide a small or thin permanent magnet of S / V = 6 mm ⁻¹ or more that exhibits good magnetic characteristics while preventing deterioration of magnetic characteristics due to grinding.
[Brief description of the drawings]
FIG. 1 is a diagram showing a demagnetization curve (curve H1) of a magnet body manufactured according to the present invention and a demagnetization curve (curve K1) of a magnet body only subjected to grinding.
FIG. 2 is a diagram showing a demagnetization curve (curve H2) of a magnet body manufactured according to the present invention and a demagnetization curve (curve K2) of a magnet body only subjected to grinding.

Claims (4)

A sintered magnet body made of an R-Fe-B-based composition (R is one or more kinds selected from rare earth elements including Y) and having a specific surface area of 6 mm ^-1 or more is ground inside the magnet. By subjecting the surface diffusion heat treatment for 1 minute to 10 hours in a vacuum or an inert gas at a temperature equal to or higher than the melting start temperature of the existing R-rich grain boundary phase and equal to or lower than the sintering temperature of the magnet, the grain boundary phase component A permanent magnet material, wherein the thin film layer is applied by diffusing the thin film layer to the ground surface of the magnet body. A sintered magnet body having an R-Fe-B composition (R is one or more selected from rare earth elements including Y) and having a specific surface area of 6 mm ^-1 or more is subjected to the surface diffusion treatment. 2. The method for producing a permanent magnet material according to claim 1, wherein an aging treatment is performed for 1 minute to 10 hours in a vacuum or an inert gas at a temperature lower than the melting start temperature of the grain boundary phase. A sintered magnet body having an R-Fe-B composition (R is one or more selected from rare earth elements including Y) and having a specific surface area of 6 mm ^-1 or more is subjected to the surface diffusion treatment. 3. The method for producing a permanent magnet material according to claim 1, wherein the substrate is washed with at least one of an alkali, an acid, and an organic solvent. The surface-deteriorated layer of the sintered magnet body, which is composed of an R-Fe-B-based composition (R is one or more selected from rare earth elements including Y) and has a specific surface area of 6 mm ^-1 or more, 3. The method for manufacturing a permanent magnet material according to claim 1, wherein the material is removed by shot blasting before the surface diffusion treatment.

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