JPH07272914A - Sintered magnet, and its manufacture - Google Patents

Abstract

PURPOSE:To provide an R-T-B sintered magnet (R is a rare earth element, and T is Fe, or Fe and Co) high in coercive force and also high in residual magnetic density, and provide an inexpensive thin magnet by obviating the polishing processing after sintering by suppressing the dimensional change at sintering when manufacturing such R-T-B sintered magnet. CONSTITUTION:A mixture between powder of mother alloy for main phase, which has a phase substantially composed of R2T14B, and alloy for grain boundary phase, which contains R by 70-97wt.% and the rest of which is substantially Fe and/or Co, is heat-treated so that the mother alloy for grain boundary phase may fuse, and then, is crashed and molded and sintered. Moreover, it is sintered so that the final density may be 7.2g/cm<3> or over, with molded item density being 5.5g/cm<3> or over, whereby it is made into a magnet which contains more than 2vol.% closed voids.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth sintered magnet and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a rare earth magnet having high performance, an Sm-Co type magnet manufactured by powder metallurgy has an energy product of 32M.
GOe's are in mass production. In recent years, Nd ₂ Fe
R-T-B magnets such as _14B magnets (R is a rare earth element, T is Fe, or Fe and Co) have been developed, and are disclosed in Japanese Patent Laid-Open No.
Japanese Patent No. 46008 discloses a sintered magnet. R
The raw material of the -TB magnet is cheaper than that of the Sm-Co magnet. For manufacturing the R-T-B system sintered magnet, the conventional Sm is used.
A Co-based powder metallurgy process (melting → master alloy casting → ingot coarse grinding → fine grinding → molding → sintering → magnet) can be applied.

It has been reported in detail in various papers that the coercive force of Nd ₂ Fe ₁₄ B system sintered magnet depends on the existence of Nd-rich phase at the grain boundary. Therefore, sintering the crystal grains composed of the Nd ₂ Fe ₁₄ B phase so that the Nd rich phase is uniformly coated, that is,
It is important to uniformly disperse the Nd-rich phase in the sintered magnet. In order to uniformly disperse the Nd-rich phase in the magnet, it is preferable to use the two-alloy method. In the two-alloy method, a mixture of a powder for the main phase centered on Nd ₂ Fe ₁₄ B and a powder for the Nd-rich grain boundary phase is molded,
Sintering (JP-A-63-93841, JP-A-63
-278208, JP-A-5-21219, etc.). The powder for the grain boundary phase melts at the time of sintering and becomes Nd ₂ Fe ₁₄ B
It flows as a liquid phase with extremely good wettability with respect to the main phase, covering the periphery of the powder for the main phase and becoming the grain boundary phase of the magnet,
Improve coercive force.

However, when observing the sintered magnet manufactured by using such a two-alloy method, it cannot be said that the crystal grains are almost completely surrounded by the Nd-rich phase. Therefore, it is considered possible to further improve the coercive force by improving the texture structure of the Nd ₂ Fe ₁₄ B system sintered magnet.

By the way, in the RTB magnets, in addition to the sintered magnet, a bonded magnet in which magnet powder is bonded with a resin binder or a metal binder has been put into practical use. Since the dimensions of the bonded magnet are almost maintained during molding, the dimensional accuracy is high and no shape processing is required after manufacturing. However, since the industrialized RTB-based bonded magnet uses polycrystalline particles made of fine crystals produced by a quenching method such as a single roll method, anisotropy due to molding in a magnetic field does not occur. Have difficulty. The crushed powder of the RTB sintered magnet cannot be used as the raw material powder of the bonded magnet because the coercive force is drastically reduced due to the distortion and the oxidation due to the crushing. In addition, the crushed powder of the R-T-B type alloy ingot is reacted with hydrogen to decompose it into a rare earth hydride, a boride of T, and T, and dehydrogenate at a predetermined temperature to crystallize in individual particles. Proposals have also been made to deposit fine crystals with uniform orientation. The polycrystalline particles obtained by this method can be oriented in a magnetic field, and high coercive force can be obtained by fine crystals. However, since hydrogen is used, the process becomes complicated, and thus it has not been put to practical use.

On the other hand, in the R-T-B system sintered magnet, since powder consisting essentially of single crystal particles is molded in a magnetic field, an anisotropic magnet can be easily obtained, and a binder is not used. High characteristics can be obtained. However, in the sintering method, the molded body significantly shrinks during the sintering reaction, and the shrinkage is non-uniform, so that it is difficult to maintain the dimensional accuracy of the molded body. This shrinkage varies depending on the degree of orientation of particles in the molded body, variations in density, and the like. In an anisotropic sintered magnet, the contraction rate differs between the direction of easy magnetization and the direction perpendicular to it. For example, when the density of the molded body is 4.3 g / cm ³ , about 22% in the direction of easy magnetization, and It becomes about 15% in the vertical direction, and the density after sintering reaches 7.55 g / cm ³ .

Such a dimensional change in the anisotropic sintered magnet is particularly problematic when the ring-shaped magnet or the plate-shaped magnet is thin. This is because if the shrinkage ratio of the thin magnet becomes uneven, warpage occurs. Therefore, when commercialized, the sintered body is ground to correct such dimensional changes. However, the grinding process has the following problems.

The amount of material loss of the sintered body during grinding becomes large. For example, if a warp of 1 mm occurs when manufacturing a thin plate magnet with a thickness of 1 mm, it is necessary to first manufacture a sintered body with a thickness of about 3 mm and then grind the upper and lower surfaces of the sintered body. 2/3 of the material is lost. In order to avoid such a loss, even when cutting multiple thin plate magnets to a thickness of 1 mm from a single thick base material, if the tooth width of the grinding cutter is 0.6 mm, it will be about 40%. There will be a loss.
Further, since the thin-walled sintered body has low mechanical strength, chipping or cracking is likely to occur at the time of processing impact or handling, resulting in low yield.

Magnetic properties are degraded. As described above, the coercive force of the Nd ₂ Fe ₁₄ B-based sintered magnet depends on the existence of the Nd-rich phase at the crystal grain boundary. When processing a sintered magnet of this system, cracks are generated in the crystal grain boundaries in the region close to the processed surface due to stress, and 0.1 to 0.2 mm from the processed surface.
The coercive force is lost in the region up to the depth of. The loss of the magnet characteristics in the vicinity of the machined surface is negligible for the thick magnet, but has a large effect for the thin magnet, and the deterioration of the magnetic characteristics of the entire magnet becomes apparent. Although it is possible to remove the region where the coercive force disappears by processing by acid etching, the amount of loss of the sintered body further increases and the manufacturing cost also increases.

Under these circumstances, a thin anisotropic magnet having a longitudinal length / thickness of 10 or more is usually Sm-
Co-based bonded magnets are used, and high cost is a problem. Although there are RTB-based thin-walled sintered magnets, processing for size adjustment is indispensable, and the material yield at the time of processing is 20 to 30%, which also increases the cost. ing.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide an RTB sintered magnet having a high coercive force and a high residual magnetic flux density. Na R
An object of the present invention is to provide an inexpensive thin-walled magnet by suppressing a dimensional change at the time of sintering when manufacturing a -T-B system sintered magnet, thereby eliminating the need for grinding after sintering.

[0012]

The above object is achieved by the present invention described in (1) to (16) below. (1) A method for producing a sintered magnet containing R (R is at least one kind of rare earth element including Y), T (T is Fe, or Fe and Co) and B. , A powder of a master alloy for a main phase having a phase substantially composed of R ₂ T ₁₄ B, and a grain boundary phase containing 70 to 97% by weight of R and the balance being substantially Fe and / or Co A method for producing a sintered magnet, which comprises subjecting a mixture with a master alloy to a heat treatment so that the master alloy for the grain boundary phase is melted, then crushing, shaping and sintering. (2) The ratio of the grain boundary phase master alloy in the mixture is 2-1.
The method for producing a sintered magnet according to (1) above, wherein the content is 5% by weight. (3) The method for producing a sintered magnet according to the above (1) or (2), wherein the main phase master alloy powder is magnetized before the heat treatment. (4) The method for producing a sintered magnet according to any one of the above (1) to (3), wherein Nd occupies 50% or more of R of the grain boundary phase master alloy. (5) The method for producing a sintered magnet according to any one of the above (1) to (4), wherein the grain boundary phase master alloy is produced by a liquid quenching method. (6) Average value of major axis / minor axis of crystal grains of master alloy for main phase is 3
The method for producing a sintered magnet according to any one of the above (1) to (5), wherein the average value of the major axis / minor axis of the particles constituting the main phase master alloy powder is 3 or less. (7) The method for producing a sintered magnet according to any one of the above (1) to (6), wherein the main phase master alloy powder has an average particle size of 20 μm or more. (8) The above (1) in which the sintering temperature is 900 to 1100 ° C.
~ The method for manufacturing a sintered magnet according to any one of (7). (9) The method for manufacturing a sintered magnet according to any one of (1) to (8), wherein sintering is performed in a vacuum. (10) Sintering according to any one of the above (1) to (9), which has a step of sintering a molded body having a density of 5.5 g / cm ³ or more so that the density change becomes 0.2 g / cm ³ or more. Magnet manufacturing method. (11) The method for producing a sintered magnet according to the above (10), in which a molded body having a bending strength of 0.3 kgf / mm ² or more is sintered. (12) Molding at a pressure of 8 t / cm ² or more (10)
Alternatively, the manufacturing method of the sintered magnet according to (11). (13) A sintered magnet manufactured by the method according to any one of (1) to (12) above, which contains 2% by volume or more of closed pores. (14) The sintered magnet according to (13) above, which has a density of 7.2 g / cm ³ or less. (15) The above (13), wherein the ratio of open pores is 2% by volume or less.
Or (14) sintered magnet. (16) The above (13) to (1) which contains 27 to 40% by weight of R, 0.5 to 4.5% by weight of B, and the balance is substantially T.
5) One of the sintered magnets.

[0013]

In the conventional two-alloy method described above, the R-rich powder is melted at the time of sintering to coat the periphery of the R ₂ T ₁₄ B-based powder to obtain a high coercive force. However, according to this method, a mixture of magnetic R ₂ T ₁₄ B powder and non-magnetic R rich powder is molded in a magnetic field.
Rich powder is unevenly distributed. In a magnet obtained by sintering such a compact, the internal density and coercive force become non-uniform, resulting in shape deformation and poor magnet characteristics. Moreover, since a magnetic field is applied to the mixture of the magnetic powder and the non-magnetic powder, the orientation of the magnetic powder is hindered, and the density of the molded body becomes low.

Further, in the conventional two-alloy method, since the R-rich powder is melted in the compression-molded compact, the flow of the liquid-phase R-rich alloy is hindered, and the R-rich phase in the magnet is impaired. The uniform dispersion of is insufficient.

On the other hand, in order to produce a high coercive force R ₂ T ₁₄ B system sintered magnet by a usual powder metallurgy method other than the two-alloy method, a master alloy having a high R content is used, but the R content is high. If it is too large, the sintering proceeds and the shrinkage rate becomes high. In addition, R ₂
Nd is usually used as R of the T ₁₄ B system sintered magnet, but by replacing a part of Nd with Dy, the anisotropic magnetic field of the main phase is improved, and thus a high coercive force can be obtained. But,
Dy is more expensive than Nd.

On the other hand, in the present invention, the mixture of the powder of the master alloy for the main phase having the R ₂ T ₁₄ B phase and the R-rich grain boundary phase master alloy containing a predetermined amount of R is used for the grain boundary phase. Heat treatment is applied to melt the mother alloy. The grain boundary phase master alloy is Nd ₈₉ Fe
_It has a low melting point composition centered on ₁₁ (weight ratio). By the heat treatment, the master alloy for the grain boundary phase flows into a liquid phase having extremely good wettability with respect to the powder of the master alloy for the main phase, and flows to coat the periphery of the powder of the master alloy for the main phase.

As described above, according to the present invention, since the grain boundary phase master alloy is melted before pressure forming, the liquid phase grain boundary phase master alloy can easily flow, and in the magnet after sintering. The R-rich phase is not biased. Since the R rich phase is not biased,
Since a high coercive force can be obtained even when the R content of the entire magnet is small, the residual magnetic flux density can be increased. Also,
Even if the molding pressure is the same, a denser molded body can be obtained than when the two-alloy method is used. In addition, the orientation by forming in a magnetic field is better than that of the two-alloy method.

After cooling, the main phase master alloy particles are bonded to each other by the R-rich phase, but this bonding is extremely weak and can be easily crushed. After crushing, the periphery of the main phase mother alloy particles is almost uniformly covered with the R-rich phase.

A normal compact for producing a Nd ₂ Fe ₁₄ B system sintered magnet has a density (theoretical density: about 7.6 g / cm ³ ) of about 55% of the density (theoretical density: about 7.6 g / cm ³ ). 4.2g /
cm ³ ) and contains about 45% of holes. Then, since it is densified to about 99% of the theoretical density by sintering, the volumetric shrinkage rate becomes large. As described above, in the case of a magnetic field-oriented compact, the shrinkage during sintering becomes non-uniform, so a sintered compact with good parallelism and roundness cannot be obtained.

On the other hand, in a preferred embodiment of the present invention, by making the average diameter of the powder of the master alloy for the main phase relatively large and making the molding pressure higher than before, it is difficult to proceed with sintering, that is, A compact having a small shrinkage rate in the sintering step is produced, and the compact is magnetized without being completely sintered. Specifically, the compact density is increased to 5.5 g / cm ³ or more, and the magnet density is sintered to 7.2 g / cm ³ or less. As a result, the shrinkage rate during sintering is significantly reduced. In a high-density compact containing a large diameter master alloy powder for the main phase, it is difficult to move particles through the R-rich liquid phase, so the holding temperature in the sintering process is high (for example, the conventional complete sintering temperature range). However, the sintering reaction does not proceed before complete sintering. Therefore, a low-density sintered body can be stably obtained over a wide temperature range, and the management of the sintering process becomes extremely easy. Further, since particles having a large diameter do not easily agglomerate, they are easy to handle and particularly easy to fill in a mold during molding.

By thus suppressing the shrinkage ratio during sintering to a small value, even when manufacturing a ring-shaped or plate-shaped thin-walled anisotropic magnet, processing for correcting the shape is not required, resulting in low cost. Realization and productivity improvement. Also,
Since the high-density molded body has a high bending strength, it is easy to handle, and cracks and chips are less likely to occur between the molding step and the sintering step.

In the thus-produced sintered magnet having a small shrinkage ratio, usually 2% by volume or more of closed pores are present. Since the closed holes do not communicate with the outside of the magnet, the magnet is not corroded. Although there are open pores near the surface of such a sintered magnet, if at least a part of the sintering step is performed in a vacuum or under a reduced pressure atmosphere, a liquid phase grain boundary phase master alloy will be obtained. To block the communication path to the outside of the open hole,
The proportion of open pores is reduced and corrosion resistance is improved.

The magnetic properties of the low-shrinkage sintered magnet manufactured according to the present invention are lower than those of the RTB-based high-density sintered magnet, but the Sm-Co-based bonded magnet {(BH) max.
= About 15 MGOe}. R-T-
B-based magnets are cheaper in raw material than Sm-Co-based magnets.
Therefore, the low-shrinkage sintered magnet manufactured according to the present invention is suitable as a substitute for the Sm—Co based bonded magnet that has been conventionally used for a thin magnet.

By the way, in Japanese Patent Laid-Open No. 3-80508, in a method for producing an RFeB magnet by a powder metallurgy method, 400 to 900 ° C. after press molding of magnet powder.
It is made into a porous sintered body in the temperature range of
_{d x Fe 1-x (x} = 0.65~0.85) a method of immersing a predetermined time is disclosed. This method is intended to suppress the deformation after sintering due to the anisotropy of thermal contraction due to the magnetic field orientation. In this method, R
Since the rich molten alloy is impregnated, the effect obtained by the present invention is not considered to be realized. Moreover, the Nd ₂ Fe ₁₄ B magnet powder used in the examples of the publication is about 10
The diameter is as small as μm, and the publication does not describe the forming pressure, the density of the formed body, and the density of the porous sintered body after low temperature sintering.

[0025]

Specific Structure The specific structure of the present invention will be described in detail below.

In the present invention, the powder of the main phase master alloy having a phase substantially composed of R ₂ T ₁₄ B and R of 70 to 9 are used.
7% by weight, the balance being substantially Fe and / or Co
The mixture with the grain boundary phase master alloy is subjected to heat treatment so that the grain boundary phase master alloy is melted, then crushed, shaped, and sintered.

<Main phase master alloy> The composition of the main phase master alloy is
Depending on the intended magnet composition, it may be appropriately determined in consideration of the composition of the grain boundary phase master alloy and its mixing ratio, but usually,
It is preferable that the content of R is 26 to 35% by weight, the content of B is 0.5 to 3.5% by weight, and the balance is substantially T.

R is at least 1 of rare earth elements including Y
Species: Y, lanthanide and actinide. R is at least 1 of Nd, Pr and Tb
Species, especially Nd, are preferred, and it is further preferred to include Dy. Also, La, Ce, Gd, Er, Ho, Eu, P
One or more of m, Tm, Yb and Y may be included. A mixture of misch metal or the like can be used as the raw material of the rare earth element. If the R content is too low, a phase rich in iron precipitates and high coercive force cannot be obtained, and if the R content is too high, high residual magnetic flux density cannot be obtained.

In the R ₂ T ₁₄ B-based magnet, the R-rich phase becomes a liquid phase and flows to cause the sintering reaction to proceed. In the present invention, however, an R-rich grain boundary phase master alloy is used. Also,
Since it is preferable to suppress the progress of the sintering reaction in order to reduce the shrinkage rate, it is preferable to reduce the R content in the main phase master alloy.

T is Fe, or Fe and Co. The amount of Co in T is preferably 30% by weight or less.

If the B content is too small, a high coercive force cannot be obtained, and if the B content is too large, a high residual magnetic flux density cannot be obtained.

In order to improve the coercive force, Al, Cr, M
n, Mg, Si, Cu, C, Nb, Sn, W, V, Z
Elements such as r, Ti, and Mo may be added, but if the addition amount exceeds 6% by weight, the reduction of the residual magnetic flux density becomes a problem.

The master alloy for the main phase is usually substantially R ₂ T ₁₄
It has a crystal grain containing a phase composed of B and an R-rich grain boundary phase. The average crystal grain size of the main phase master alloy powder is not particularly limited. In the present invention, since it is anisotropy by magnetic field orientation, it is preferable that the crystal grain size is such that it becomes a single crystal grain when the grain size described later is used, but even if it is a polycrystalline grain, it is crystallized within the grain. As long as the grains are oriented, the average crystal grain size can be selected from a wide range of, for example, about 3 to 600 μm.

The average particle size of the main phase master alloy powder is not particularly limited, and may be determined so that the crystal grain size of the magnet after sintering will be a desired value, for example, appropriately selected from about 5 to 500 μm. do it. However, in order to reduce the shrinkage rate during sintering, it is preferably 20 μm or more, more preferably 5 μm or more.
0 to 350 μm. If the average particle size is too small, the above-described effect of increasing the particle size becomes insufficient. On the other hand, if the average particle size is too large, it becomes difficult to orient the magnetic field in a thin molded body. The average particle diameter of the main phase master alloy powder is the diameter when an average projected area per particle is calculated and converted into a circle. The method for measuring the projected area of the particles is not particularly limited. For example, a powder dispersion can be applied onto a glass plate so that the particles do not overlap with each other, a photograph is taken, and the projected area of the particles can be determined from this photograph. In addition, the projected area of the particles can be obtained by scanning the coated object with a light beam and detecting the change in reflectance.

The method for producing the powder of the master alloy for the main phase is not particularly limited, and any method such as a method of pulverizing the cast alloy by hydrogen occlusion pulverization or a reduction diffusion method may be used, and the sintered magnet is pulverized. You may make it into a powder. With a powder obtained by crushing a sintered magnet anisotropy by magnetic field orientation, or shavings of such a sintered magnet, large-sized polycrystalline particles composed of oriented small-sized crystal grains can be obtained. Therefore, a magnet having a high residual magnetic flux density and a high coercive force can be obtained. In addition, even in the reduction diffusion method and casting method, by controlling the manufacturing conditions,
Polycrystalline particles with good alignment of easy magnetization axes can be obtained.

When the main phase master alloy powder is mainly composed of single crystal particles, the particle shape is preferably close to an equiaxed shape. When the main phase master alloy powder is mainly composed of polycrystalline particles,
The shape of the crystal grains in the particles is preferably close to the equiaxial shape. In each of these cases, "close to equiaxed shape" means that the average value of the major axis / minor axis of the particles or crystal grains is preferably 3 or less, more preferably 2.5 or less.
Since the single crystal particles have a smaller surface area ratio per unit volume as they are closer to the equiaxial shape, the influence of damage near the particle surface in the magnet manufacturing process is reduced, and a magnet with high characteristics can be obtained. In addition, in the case of polycrystalline particles, good magnetic properties can be obtained when they have crystal grains that are close to equiaxed.

<Master Alloy for Grain Boundary Phase> The master alloy for grain boundary phase is R
Of 70 to 97% by weight, preferably 75 to 92% by weight, and the balance being substantially Fe and / or Co. R contained in the grain boundary phase master alloy is preferably Nd, and
More preferably, Nd occupies 50% or more of the
It is more preferable to use substantially only Nd. When the amount of Nd in R is small and the amount of R is small, the melting point of the grain boundary phase master alloy does not decrease, and closed voids are less likely to be formed. The melting point of Nd ₈₉ Fe ₁₁ (weight ratio) eutectic alloy is 6
40 ° C., Nd ₈₁ Co ₁₉ (weight ratio) eutectic alloy has a melting point of 56.
Although it is 6 ° C, the melting point of the Dy ₈₈ Fe ₁₂ (weight ratio) eutectic alloy is 890 ° C. The grain boundary phase master alloy used in the present invention is
Does not include B. B in the grain boundary phase master alloy does not contribute to the improvement of the magnet characteristics and does not contribute to the decrease of the melting point of the grain boundary phase master alloy.

For the grain boundary phase master alloy, in addition to R, Fe and Co, Al, Cu, Ga, Ni, Sn, Cr, V, Ti,
You may add at least 1 sort (s), such as Mo. However, the total content of these elements in the grain boundary phase master alloy,
It is preferably 20% by weight or less. This is because these elements form a non-magnetic compound and reduce the residual magnetic flux density. Al and Cu exhibit the effect of improving coercive force and corrosion resistance.

The method for producing the grain boundary phase master alloy is not particularly limited, but the liquid quenching method is preferably used. As the liquid quenching method, a method of bringing the molten alloy into contact with a cooling substrate to cool it, for example, a single roll method, a twin roll method, a rotating disk method, or the like is preferable, and a gas atomizing method may be used. The molten alloy is cooled in a non-oxidizing atmosphere such as nitrogen or Ar or in vacuum. When the cooling rate is slow, the master alloy for the grain boundary phase having the above-mentioned composition mainly undergoes phase separation into Nd and Fe ₂ Nd. Their melting points are as high as 1000 ° C. or higher, and Nd is extremely susceptible to oxidation. The grain boundary phase master alloy produced by the liquid quenching method has an amorphous phase or a microcrystalline phase.

The master alloy for grain boundary phase melted by heat treatment is
Very good wettability with respect to main phase mother alloy particles,
The shape and dimensions of the grain boundary phase master alloy before melting are not particularly limited in order to rapidly coat the periphery of the main phase master alloy particles. However, when the grain boundary phase master alloy is pulverized to a fine powder, oxidation is unavoidable, and the oxide formed during the pulverization remains in the magnet, causing deterioration of the magnetic properties. The diameter is preferably 50 μm or more. On the other hand, if the grain boundary phase master alloy is in a large bulk shape, the distance for moving or diffusing to cover the main phase master alloy particles increases, so the maximum diameter is preferably 10 mm or less.

<Mixing and Heat Treatment> The method for producing a mixture of the main phase master alloy powder and the grain boundary phase master alloy is not particularly limited. Usually, both are mixed by a V mixer or the like, but it is also possible to place the powder of the master alloy for the main phase, the coarse powder of the master alloy for the grain boundary phase, and the crushed pieces thereof on the powder of the master alloy for the main phase.

The ratio of the grain boundary phase master alloy in the mixture is preferably 2 to 15% by weight, more preferably 3 to 1%.
1% by weight. If this ratio is too low, the effect of the present invention will be insufficient, and if this ratio is too high, it will be difficult to obtain a magnet having a high residual magnetic flux density.

The mixture thus obtained is heat-treated. The heat treatment conditions are not particularly limited, as long as it is a temperature at which the powder of the grain boundary phase master alloy is melted, and the temperature of the main phase master alloy powder does not sinter or the sintering does not proceed excessively. . If the sintering proceeds too much, it becomes difficult or impossible to disintegrate after heat treatment, and it becomes difficult to anisotropy by molding in a magnetic field. Specifically, the processing temperature is preferably 600
-1000 degreeC, More preferably, it is 650-950 degreeC. If the treatment temperature is too high, sintering of the main phase master alloy powder becomes a problem. On the other hand, if the treatment temperature is too low, the fluidity of the grain boundary phase master alloy at the time of treatment becomes low, so that the dispersion of the R-rich phase in the powder of the main phase master alloy after the treatment becomes insufficient. . The grain boundary phase master alloy is melted almost instantaneously at its melting point to coat the main phase master alloy particles,
In order to sufficiently diffuse the elements between both mother alloys, the temperature is preferably maintained for 10 minutes or longer, more preferably 30 minutes or longer, and the melting point or higher.

It is sufficient that the mixture is not pressure-molded before the heat treatment and is not pressed during the heat treatment. The container holding the mixture during the heat treatment may be made of a material that does not react with the mixture during the heat treatment, for example, a refractory metal such as stainless steel or Mo.

After cooling, the particles of the main phase master alloy are bonded to each other by the solidified grain boundary phase master alloy,
Pulverize to obtain magnet powder for molding.

Before the heat treatment, it is preferable to magnetize the main phase master alloy powder. Since the fine particles smaller than the average particle diameter in the main phase master alloy powder are difficult to separate by the crushing treatment after the heat treatment, they remain bonded to the large-sized particles by the R-rich phase even after the crushing treatment, Apparently it has become polycrystalline. In the polycrystalline body formed in this way, the easy axes of magnetization of the grains are not aligned, so that the degree of orientation when molded in a magnetic field becomes insufficient. However, if the main phase master alloy powder is magnetized before the grain boundary phase master alloy is dispersed and solidified in the main phase master alloy powder, the small-diameter particles can be easily magnetized during the heat treatment. It is taken into the polycrystal in a state in which the direction is almost aligned with that of the large-diameter particles. For this reason,
The main phase master alloy powder is magnetized when the temperature is lower than the Curie temperature. The magnetic field strength when magnetizing the main phase master alloy powder is usually preferably 5 kOe or more.

<Molding> In the molding step, magnet powder is molded in a magnetic field. The density of the molded body is not particularly limited, but in order to reduce the shrinkage rate during sintering, the density of the molded body is preferably 5.5 g / cm ³ or more, more preferably 6.0 g / cm ³ or more. In the case of a compact having a low density, if sufficient magnet characteristics are to be obtained, the shrinkage rate at the time of sintering becomes large, and if the shrinkage rate at the time of sintering is made small, the magnet characteristics become insufficient. There is no particular upper limit to the density of the molded product, but 6.4 g / cm
It is difficult to achieve a density of more than ³ . For example, since an ultrahigh pressure of 20 t / cm ² or more is required at the time of molding, the molding apparatus and the mold are expensive, and the shape of the molded body is limited to a simple shape. It is effective to use a large amount of organic lubricant to improve the compact density, but it is difficult to completely remove the organic lubricant before sintering, and residual carbon in the magnet deteriorates the magnet characteristics. I will let you. The density of the molded product can be calculated from the dimensions of the molded product measured with a micrometer or the like.

The molded article having such a high density has a flexural strength of 0.3 kgf / mm ² or more, and further 0.5 kgf / cm ² or more, so that it is easy to handle, and cracks and chips are less likely to occur. Become.

The molding pressure is not particularly limited and may be appropriately determined so as to obtain a molded product having a desired density, but in order to obtain the above-mentioned high-density molded product, it is preferably 8 t / cm ^2.
Or more, more preferably 12 t / cm ² or more. The magnetic field strength during molding is usually 10 kOe or more, preferably 15 kOe.
That is all.

The magnetic field applied during molding may be a DC magnetic field or a pulsed magnetic field, or they may be used in combination. The present invention can be applied to a so-called transverse magnetic field forming method in which a pressure applying direction and a magnetic field applying direction are substantially orthogonal to each other, and a so-called longitudinal magnetic field forming method in which a pressure applying direction and a magnetic field applying direction are substantially parallel to each other.

<Sintering> The molded body obtained as described above is sintered and magnetized.

Sintering is preferably carried out under conditions such that the value obtained by subtracting the density of the molded body from the density of the sintered body (the amount of change in density during sintering) is 0.2 g / cm ³ or more. If the density change in the sintering step is too small, the sintering will be insufficient and the magnet characteristics and mechanical strength will be insufficient. In order to reduce the shrinkage rate, the above-mentioned high-density molded body is used, and the density change amount is preferably 1.5 g / cm ³ or less, more preferably 1.2 g / cm ³ or less.

There are no particular restrictions on various conditions during sintering, and it may be appropriately selected so that the density change during sintering has a desired value. The sintering temperature may be equal to or higher than the melting temperature of the grain boundary phase master alloy, but in the high-density compact using the above-mentioned powder having a relatively large diameter, it is difficult to proceed with the sintering, which is the conventional so-called semi-sintering. Even if the sintering temperature is higher than in the above case, the shrinkage ratio can be suppressed to be low. Specifically, 900 to 1100 ° C
It is preferable to heat-treat for 0.5 to 10 hours to sinter and then quench. The sintering atmosphere is preferably a vacuum or an inert gas atmosphere such as Ar gas, and as described above, it is possible to reduce the ratio of open pores, and thus the vacuum or reduced pressure inert gas atmosphere. Is more preferable. It should be noted that only part of the sintering process may be in a vacuum or reduced pressure atmosphere.

After sintering, an aging treatment is carried out as necessary to improve the coercive force.

<Sintered Magnet> The composition of the sintered magnet thus manufactured is determined by the composition of each of the main phase master alloy and the grain boundary phase master alloy, and the mixing ratio of these master alloys. A preferred magnet composition is 27 to 40 wt% R,
The content of B is 0.5 to 4.5% by weight, and the balance is substantially T.

In addition to these elements, the sintered magnet may contain unavoidable impurities or trace additives such as carbon and oxygen.

The sintered magnet has a main phase having a substantially tetragonal crystal structure, and an R-rich phase having a higher R ratio than R ₂ T ₁₄ B exists in the crystal grain boundaries. The crystal grain size of the magnet depends on the crystal grain size of the main phase master alloy, the grain size of the main phase master alloy powder, the sintering conditions, and the like.

When the shrinkage during sintering is suppressed to a low level, closed pores are included in the sintered magnet. The closed holes are holes that do not communicate with the magnet surface. The ratio of closed holes to the entire magnet is preferably 2% by volume or more, more preferably 2.5.
10 to 10% by volume. A magnet with too few closed holes contracts greatly during sintering, and good dimensional accuracy of the molded body is not maintained. A magnet having too many closed holes has insufficient magnet characteristics and insufficient strength. The total volume ratio of the closed holes in the magnet and the total volume ratio of the open holes described later can be calculated as follows.

Open hole total volume ratio K Formula I K = (WW- _W ) / V Closed hole total volume ratio H Formula II H = 1-K-W / (V · ρ) V: volume calculated from the sample geometry, W: sample weight, W _W: sample was immersed in water, after holding for 30 seconds and evacuated to 100 Torr, taking out, the sample weight after wiping off water on the sample surface, ρ: theoretical density of magnet.

The density of the sintered magnet of the present invention is 7.2 g / cm ³
The following is preferable. If a powder composed of large particles of about 200 μm is molded under high pressure, the density of the molded body can be increased to about 6.4 g / cm ^3, but with such a molded body, the particle movement during firing is Since it is difficult, it is difficult to obtain a density of more than 7.2 g / cm ³ even if it is fired at a high temperature. On the other hand, when a compact having a low density is formed by using small-diameter particles, if firing is performed until the density exceeds 7.2 g / cm ³ , the sintering proceeds excessively and the shrinkage rate increases. Even if the density of the sintered magnet is in this range, if there are many open holes communicating with the surface of the magnet, the corrosion resistance of the magnet is extremely reduced, which is not preferable. The ratio of open pores is 2% by volume
The following is preferable. The ratio of open holes can be determined by the method described above.

<Others> In order to improve the corrosion resistance of the magnet, it is preferable to close the open holes. For this purpose, for example, the magnet may be dipped in a solution in which a resin is dissolved in an organic solvent and then dried. After such a treatment, a usual anticorrosion coating may be provided by electrodeposition coating of resin, electroless plating, or the like.

The present invention is suitable for manufacturing a thin-walled ring-shaped or plate-shaped magnet as described later, and particularly for manufacturing a thin-walled magnet having a thickness of 3 mm or less. If the magnet thickness is less than 0.5 mm, molding tends to be difficult.

<Dimensional Deviation> According to the present invention, since a sintered magnet having an extremely small dimensional deviation can be obtained, it can be manufactured as a product without performing shape processing such as grinding after sintering.

That is, according to the present invention, there is a parallel portion, and the value obtained by dividing the maximum length of the parallel portion by the average thickness is 10
In the thin-walled sintered magnet as described above, the thickness deviation of the parallel portion can be 1.5% or less, and can easily be 1% or less, and the maximum length / average thickness is 15 or more. The thickness deviation of a thin magnet can be kept within such a range. The parallel part is a block sandwiched by two parallel surfaces facing each other, and the magnet having the parallel part is, for example, a plate magnet, a disk magnet, or a ring magnet. The thickness deviation of the parallel part is a value obtained by dividing the difference between the maximum value and the minimum value of the thickness of the parallel part by the maximum length of the parallel part. The thickness deviation of the parallel part is a value that is an index of the warp of the parallel part and the nonuniformity of the thickness, and in the case of the thin-walled sintered magnet having the above dimensional ratio, the warpage and the nonuniformity of the thickness are Since it becomes large, the thickness deviation is generally 2.5% or more.

Further, according to the present invention, in the thin-walled magnet having the cylindrical portion and the value obtained by dividing the average outer diameter of the cylindrical portion by the average wall thickness is 10 or more, the outer diameter deviation of the cylindrical portion and / or The inner diameter deviation can be 1.5% or less, and it is easy to set it to 1% or less. Even for a thin magnet having an average outer diameter / average wall thickness of 15 or more, the outer diameter deviation and / or the inner diameter deviation can be reduced. It is possible to fit within such a range. The cylindrical portion is a cylindrical block having an outer peripheral surface or an outer peripheral surface and an inner peripheral surface, and the magnet having the cylindrical portion is
For example, a ring-shaped magnet or a disc-shaped magnet, the outer diameter deviation and the inner diameter deviation in this case target a cylindrical portion having an outer peripheral surface and an inner peripheral surface. The outer diameter deviation of the cylindrical portion is a value obtained by dividing the difference between the maximum value and the minimum value of the outer diameter of the cylindrical portion by the average outer diameter, and the inner diameter deviation is the maximum value and the minimum value of the inner diameter of the cylindrical portion. Is the value obtained by dividing the difference of by the average inner diameter. The outer diameter deviation and the inner diameter deviation of the cylindrical portion are values that are an index of the warp and strain of the cylindrical portion and the nonuniformity of the wall thickness, and in the case of the thin-walled sintered magnet having the above dimensional ratio, the warp and strain, Since the unevenness of the wall thickness becomes large, conventionally, the outer diameter deviation and the inner diameter deviation are generally 3% or more.

Even in a thin-walled sintered magnet having a cylindrical portion having only an outer peripheral surface such as a disc magnet and having an average outer diameter / average thickness of 10 or more, further 15 or more, the deviation of the outer diameter of the cylindrical portion. Can be 1.5% or less, and can easily be 1% or less.

In the present specification, the thickness deviation of the parallel portion is measured as follows. First, the object to be measured is placed on the surface plate such that one surface forming the parallel portion is in contact with the surface plate. Then, the height from the surface plate surface of the other surface forming the parallel portion is measured at 20 points. Next, the object to be measured is turned over and placed on the surface plate so that the other surface is in contact with the surface of the surface plate, and the height is measured at 20 points in the same manner.
The measurement position divides the surface to be measured into 20 evenly,
It is set at the center point in each area. The difference (Tmax-Tmin) between the maximum value (Tmax) and the minimum value (Tmin) is determined from all the obtained measured values. This difference is the maximum value L of the lengths (lengths in the longitudinal direction) of the surfaces forming the parallel portion.
The value obtained by dividing by {(Tmax-Tmin) / L} is taken as the thickness deviation. The thickness deviation of a thin-walled magnet having two or more pairs of mutually parallel surfaces has a large value when both main surfaces are the one surface and the other surface. The average thickness in the description of the thin magnet may be the average of all the measured values obtained as described above.

The outer diameter deviation and the inner diameter deviation of the cylindrical portion are obtained as follows. First, the outer diameter or inner diameter of the cylindrical part,
The maximum value and the minimum value are obtained by continuously measuring in the axial direction of the cylindrical portion. At this time, the measured values in the range of 0.1 mm at both axial ends of the cylindrical portion are excluded. Next, after rotating the cylindrical portion by 15 ° about its axis, the same measurement is performed.
In this way, the measurement is repeated 12 times in total in the circumferential direction of 180 ° at 15 ° intervals. The maximum of the 12 maximums is φmax, and the minimum of the 12 minimums is φmi.
Let n be the value of φmax-φmin. Next, the average value φ ₀ of the average of 12 maximum values and the average of 12 minimum values is calculated, and φ
₀ is the average outer diameter or the average inner diameter. And {(φma
x −φ min) / φ ₀ } is the outer diameter deviation or the inner diameter deviation. The average outer diameter in the explanation of the dimension ratio of the thin magnet,
The above-mentioned φ ₀ may be used for the average inner diameter, and (average outer diameter−average inner diameter) / 2 may be used for the average wall thickness.

A non-contact type measuring device such as an optical type may be used to measure the dimensional deviation, and a contact type three-dimensional measuring device or a contact type measuring device such as a micrometer or an inner circumference micrometer may be used. May be used.

[0070]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

<Example 1> The sintered magnets shown in Table 1 were produced by the method of the present invention, the two-alloy method and the ordinary sintering method (indicated as "one-alloy method" in Table 1).

Method of the Present Invention First, an ingot of a master alloy for main phase was produced by casting. The composition of the ingot is shown in Table 1. The balance of the composition is Fe. These alloy ingots had an average crystal grain size of about 300 μm, and the average values of the major axis / minor axis of the crystal grains were 2.5 or less. Each alloy ingot was roughly crushed by utilizing the expansion / contraction of the volume due to hydrogen absorption / degassing reaction, and then crushed by a disc mill,
A powder having an average particle size shown in The average particle size of the powder is
It was determined from the optical micrograph of the powder coating by the method described above. The average value of the major axis / minor axis of the particles constituting the powder was 2.5 or less.

Next, the molten alloy was cooled in an Ar atmosphere by the single roll method to produce a grain boundary phase master alloy having the composition shown in Table 1. The balance of the composition shown in Table 1 is Fe. A Cu roll was used as the cooling roll. The master alloy for grain boundary phase was in the form of a ribbon having a thickness of 0.15 mm, and as a result of X-ray diffraction, it was confirmed to be in an amorphous state. Each grain boundary phase master alloy was crushed into 2 mm square or less using a stamp mill.

Next, the main phase master alloy powder and the grain boundary phase master alloy were mixed by a V mixer, and a magnetic field of 10 kOe was applied to the mixture to magnetize the main phase master alloy powder. The addition amount of the grain boundary phase master alloy (ratio of the grain boundary phase master alloy in the mixture)
It shows in Table 1.

Each mixture was placed in a Mo boat and heat-treated at 800 ° C. for 30 minutes in vacuum. All of the grain boundary phase master alloys shown in Table 1 were melted up to 800 ° C.

After the heat treatment, the main phase master alloy powder bonded with the grain boundary phase master alloy as a binder was crushed to about 500 μm.
A crushed powder composed of particles of m or less was used.

Each crushed powder was molded in a magnetic field and had a diameter of 20 mm,
A disk-shaped molded body having a thickness of 1.5 mm was obtained. Magnetic field strength is 8 kOe
The magnetic field was applied so that the axis of easy magnetization was in the thickness direction of the molded body. The molding pressure and the density of the molded body are shown in Table 1.

Next, after sintering each compact in a vacuum,
Quenched. The sintering temperature and the time kept at that temperature,
It shows in Table 1. After sintering, aging treatment was performed at 650 ° C. for 1 hour in Ar atmosphere to obtain a disc-shaped sintered magnet sample. Table 1 shows the density of each sintered magnet sample, the density change amount during sintering, the residual magnetic flux density (Br), and the coercive force (Hcj).
Shown in. For the measurement of Br and Hcj, diameter 15
A sample for measuring magnetic properties, which was produced by sintering a compact having a thickness of 10 mm and a thickness of 10 mm, was used. The manufacturing conditions of the samples for measuring magnetic properties were the same as those of the samples shown in Table 1 except for the size of the molded body. Further, the total volume ratio of open pores and the total volume ratio of closed pores of each sample were calculated by the method described above. In calculating these, the theoretical density of the magnet was 7.55 g / cm ³ . The results are shown in Table 1.

A two-alloy method grain boundary phase master alloy was produced in the same manner as described above, powdered with a pin mill, and classified with a sieve. For the sieve with a small aperture (residual sieve) that regulates the lower limit of the particle diameter, use a sieve with an aperture of 38 μm or more. I used one. The same measurement as above was performed for these. The results are shown in Table 1.

1 Alloy Method A sintered magnet was produced using only one type of master alloy without using the grain boundary phase master alloy. The same measurement as above was performed for these. The results are shown in Table 1.

[0081]

[Table 1]

From the results shown in Table 1, the effect of the present invention is clear.

Sample Nos. 1 to 3 have almost the same R content. Sample No. 2 and Sample No. 3 are formed into a compact having a relatively low density by using a mother alloy powder for a main phase having a small diameter, and are sintered to obtain a high density magnet.
Sample No. 2 according to the present invention has a significantly higher coercive force than Sample No. 3 according to the 1 alloy method. In addition, a sample No. that has a relatively high density compact using a large-diameter main phase master alloy powder and suppresses an increase in density during sintering.
Even with No. 1, the coercive force is significantly higher than that of Sample No. 3.

The sample Nos. 4 and 5 have almost the same R content, but the sample No. 4 according to the present invention has a higher coercive force than the sample No. 5 according to the two-alloy method. Moreover,
Sample No. 4 used less amount of the grain boundary phase master alloy, and the residual magnetic flux density was higher.

The samples according to the present invention other than the sample No. 2 are low-density magnets, and a high-density compact was prepared by using a master alloy powder for the main phase having a large average particle diameter, and sintered. Is. It can be seen that these contained a large amount of closed pores, and the shrinkage during sintering was small.
Moreover, since the amount of open pores is small in these samples,
Good corrosion resistance. On the other hand, Sample No. 8 by the 1-alloy method is a low-density magnet obtained by sintering a high-density compact in the same manner, and the total amount of holes is the same as that of the sample of the present invention.
The ratio of open pores is high, probably because the flow of the R-rich phase during sintering was insufficient, and the coercive force is significantly lower than that of the sample according to the present invention. Further, the sample by the two-alloy method has a small amount of open pores, but the coercive force is lower than that of the sample by the present invention.

In sample Nos. 9 and 10, Al and C were used.
Since a grain boundary phase master alloy containing u is used, high coercive force is obtained. Even in sample No. 11 by the two-alloy method,
A relatively high coercive force is obtained because the grain boundary phase master alloy contains Cu, but a coercive force lower than that of Sample Nos. 9 and 10 and a grain boundary phase master alloy containing no Cu are obtained. Coercive force is lower than the sample No. 6 used.

Next, using a JIS class 1 surface plate, the thickness deviation of each sample was determined by the method described above. As a result,
With the exception of Sample No. 2, the samples according to the present invention had a significantly small thickness deviation of 0.9% or less, and the warpage due to uneven shrinkage during sintering was extremely small. If the thickness deviation of the thin magnet having a thickness of 1.5 mm is small as described above, it is possible to commercialize the thin magnet without modifying the dimensions by grinding. Moreover, as shown in Table 1, the samples according to the present invention have obtained sufficient magnet characteristics. When calculating the thickness deviation, the diameter of the magnet was used as the maximum length of the parallel portion.

On the other hand, in sample No. 3, since the low-density compact formed by using the powder of the mother alloy having a small particle size was sintered, the sintering proceeded too much and the number of closed voids decreased. It was found that the thickness deviation was as large as 3% or more, and a large warp was generated due to uneven contraction during sintering. With such a large thickness deviation, commercialization is impossible.

The molded product having a density of 5.5 g / cm ³ or more exhibited a sufficiently high bending strength of 0.45 kgf / mm ² or more.

From the results of the above examples, the effects of the present invention are clear.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01F 41/02 G

Claims (16)

[Claims] 1. A method for producing a sintered magnet containing R (R is at least one rare earth element including Y), T (T is Fe, or Fe and Co) and B. And a powder of the master alloy for the main phase having a phase substantially composed of R ₂ T ₁₄ B, and a grain boundary containing 70 to 97% by weight of R and the balance being substantially Fe and / or Co. A method for producing a sintered magnet, which comprises subjecting a mixture with a phase master alloy to a heat treatment so that the grain boundary phase master alloy is melted, then crushing, shaping and sintering. 2. The method for producing a sintered magnet according to claim 1, wherein the proportion of the grain boundary phase master alloy in the mixture is 2 to 15% by weight. 3. The method for producing a sintered magnet according to claim 1, wherein the main phase master alloy powder is magnetized before the heat treatment. 4. 50% or more of R in the grain boundary phase master alloy is Nd
The method for manufacturing a sintered magnet according to claim 1, wherein 5. The method for producing a sintered magnet according to claim 1, wherein the master alloy for grain boundary phase is produced by a liquid quenching method. 6. The major axis / minor axis average value of crystal grains of the main phase master alloy is 3 or less, or the major axis / minor axis average value of particles constituting the main phase master alloy powder is It is 3 or less, Claims 1-5
1. A method for manufacturing a sintered magnet according to any one of 1. 7. The average particle size of the main phase master alloy powder is 20.
The method for producing a sintered magnet according to any one of claims 1 to 6, wherein the sintered magnet has a diameter of at least μm. 8. The method for producing a sintered magnet according to claim 1, wherein the sintering temperature is 900 to 1100 ° C. 9. The method for producing a sintered magnet according to claim 1, wherein sintering is performed in a vacuum. 10. The sintered magnet according to claim 1, further comprising a step of sintering a molded body having a density of 5.5 g / cm ³ or more so that a change in density is 0.2 g / cm ³ or more. Manufacturing method. 11. The method for producing a sintered magnet according to claim 10, wherein a molded body having a bending strength of 0.3 kgf / mm ² or more is sintered. 12. The method for producing a sintered magnet according to claim 10, wherein the molding is performed at a pressure of 8 t / cm ² or more. 13. A sintered magnet manufactured by the method according to any one of claims 1 to 12, wherein the sintered magnet contains 2% by volume or more of closed pores. 14. The sintered magnet according to claim 13, which has a density of 7.2 g / cm ³ or less. 15. The sintered magnet according to claim 13, wherein the ratio of open pores is 2% by volume or less. 16. R of 27 to 40% by weight and B of 0.5 to
4. The content of 4.5% by weight, the balance being substantially T.
The sintered magnet according to any one of 3 to 15.