JP7634966B2 - Rare earth cobalt permanent magnet, its manufacturing method, and device - Google Patents

Description

The present invention relates to rare earth cobalt permanent magnets that are particularly applicable to variable field magnet motors, as well as manufacturing methods and devices for the same.

Variable magnetic field motors are attracting attention from the perspective of energy saving in motors. Variable magnetic field motors are motors that change magnetic flux according to the rotation speed. Variable field motors generally generate high magnetic flux when torque is required at low rotation speeds, and low magnetic flux at high rotation speeds, and there is a demand for motors that are highly energy efficient in all ranges from low to high rotation speeds.

Methods for changing the amount of magnetic flux in a variable field magnet motor include, for example, a variable magnetic force method, a magnetic field coil method, and a winding switching method.
For example, Patent Document 1 discloses a method of achieving a variable magnetic field by combining an NdFeB magnet, which has high magnetization and coercive force, with an Alnico magnet, which has high magnetization but low coercive force. However, there is a problem in that the Alnico magnet is difficult to use because its coercive force is too small.

As a variable magnetic force method, a method using samarium-cobalt magnets that allow the amount of magnetic flux to be changed is being considered. For example, Patent Document 2 proposes using samarium-cobalt magnets as magnets for variable field magnets. However, the method in Patent Document 2 requires a residual magnetization value of 80% or more in a magnetic field of 10 kOe, which is not sufficient for high torque operation that requires a strong magnetic flux.

Patent No. 4965924 International Publication No. 2009/145229

From the viewpoint of increasing the efficiency of variable magnetic field motors, it is preferable for permanent magnets to reach saturation magnetization in a low magnetic field when remagnetizing after demagnetization, and there is a demand for permanent magnets with a high squareness ratio, which is expressed as the ratio (Hk/Hcj) of the magnetic field (Hk) to the coercive force (Hcj).

The present invention aims to solve the above problems and provide a rare earth cobalt permanent magnet with high residual magnetic flux density, low coercive force, and high squareness ratio, a method for manufacturing the same, and a device having the rare earth cobalt permanent magnet.

In the rare earth cobalt permanent magnet of this embodiment, when R is a rare earth element including at least Sm,
A rare earth-cobalt permanent magnet comprising, by mass percentage, 23-27% rare earth element R, 1.0-5.0% Cu, 18-25% Fe, 1.5-3.0% Zr, and the remainder being Co and unavoidable impurities;
The alloy has a plurality of crystal grains and grain boundaries,
In the grain boundary portion, the Cu concentration is at least twice the Zr concentration.

In one embodiment of the rare earth cobalt permanent magnet, the size of the cell structure that constitutes the crystal grains is 50 to 200 nm.

One embodiment of the rare earth cobalt permanent magnet has a saturation magnetization of 1.16 T or more and an intrinsic coercivity Hcj of 120 to 800 kA/m.

One embodiment of the rare earth cobalt permanent magnet has a saturation magnetization of 1.16 T or more and an intrinsic coercivity Hcj of 240 to 800 kA/m.

In one embodiment of the rare earth-cobalt permanent magnet, the squareness ratio (Hk/Hcj) of the magnetic field Hk at 90% magnetization of the residual magnetization to the intrinsic coercivity Hcj in the demagnetization curve is 60% or more, and
When magnetized again from a demagnetization field exceeding the knickpoint of the demagnetization curve, magnetization of 95% or more of the saturation magnetization can be obtained in a magnetic field of 5 times or less the intrinsic coercivity Hcj.

In one embodiment of the rare earth-cobalt permanent magnet, the squareness ratio (Hk/Hcj) of the magnetic field Hk at 90% magnetization of the residual magnetization to the intrinsic coercivity Hcj in the demagnetization curve is 60% or more, and
When magnetized again from a demagnetization field exceeding the knickpoint of the demagnetization curve, magnetization of 95% or more of the saturation magnetization can be obtained in a magnetic field of three times or less the intrinsic coercivity Hcj.

In one embodiment of the rare earth cobalt permanent magnet, when the diffraction intensity I(006) of the (006) plane and the diffraction intensity I(303) of the (303) plane are measured by powder X-ray diffraction, the diffraction intensity ratio I(006)/I(303) is 0.225 to 0.4.

The first method for producing the rare earth-cobalt permanent magnet of the present embodiment includes the following steps:
(I) preparing an alloy containing, by mass percentage, 23-27% rare earth element R, 1.0-5.0% Cu, 18-25% Fe, 1.5-3.0% Zr, and the balance being Co and unavoidable impurities, where R is a rare earth element including at least Sm;
a pulverization step (II) of converting the alloy into powder;
A pressure molding step (III) of forming the powder into a molded body;
A step (IV) of sintering the compact at 1200 to 1250°C;
A step (V) of subjecting the sintered compact to a solution treatment;
A step (VI) of heat treating the solution-treated compact at 600 to 850°C;
A step (VII) of cooling the heat-treated molded body to 400° C. or less at a rate of 0.2 to 10° C./min;
A step (VIII) of performing a heat treatment at a temperature of 700 to 900° C. and higher than that of the step (IV);
and a step (IX) of cooling the heat-treated molded body to 400° C. or lower at a rate of 0.1 to 5° C./min.

The second method for producing the rare earth-cobalt permanent magnet of the present embodiment is as follows:
The method for producing a rare earth-cobalt permanent magnet according to the present invention includes the steps of: (I) preparing an alloy containing, by mass percentage, 23-27% rare earth elements R, 1.0-5.0% Cu, 18-25% Fe, 1.5-3.0% Zr, and the balance being Co and unavoidable impurities, where R is a rare earth element including at least Sm;
a pulverization step (II) of converting the alloy into powder;
A pressure molding step (III) of forming the powder into a molded body;
A step (IV) of sintering the compact at 1200 to 1250°C;
A step (V) of subjecting the sintered compact to a solution treatment;
A step (VI-a) of heat treating the solution-treated compact at 750 to 850 ° C.;
A step (VII-a) of cooling the heat-treated molded body to 500 to 600 ° C. at 0.5 to 10 ° C./min and maintaining the temperature at 500 to 600 ° C.;
and a step (VIII-a) of quenching the molded body after the isothermal holding.

The present invention also provides a device having the rare earth cobalt permanent magnet.

The present invention provides a rare earth cobalt permanent magnet with high residual magnetic flux density, low coercive force, and high squareness ratio, a method for producing the same, and a device having the rare earth cobalt permanent magnet.

FIG. 2 is a schematic diagram for explaining the structure of the permanent magnet. 1 is a graph showing the first and second quadrants of the hysteresis curve of the permanent magnet of Example 1. 1 is a dark-field scanning transmission electron microscope (DF-STEM) image of the permanent magnet of Example 1. 4 is a graph showing the results of composition analysis including the grain boundary portion of the permanent magnet of Example 1. 1 shows powder X-ray diffraction spectra of permanent magnets of Examples 3 and 4 and Reference Example 1.

The rare earth-cobalt permanent magnet and its manufacturing method, as well as the device according to the present invention, will be described below in order.
In addition, unless otherwise specified, the numerical range indicated by "to" includes the lower limit and the upper limit.

<Rare earth cobalt permanent magnet>
The rare earth-cobalt permanent magnet according to the present invention (hereinafter also referred to as the present permanent magnet) is a rare earth-cobalt permanent magnet containing, by mass percentage, 23-27% rare earth elements R including Sm, 1.0-5.0% Cu, 18-25% Fe, 1.5-3.0% Zr, with the balance being Co and unavoidable impurities,
The alloy has a plurality of crystal grains and grain boundaries,
In the grain boundary portion, the Cu concentration is at least twice the Zr concentration.

In general, in rare earth cobalt permanent magnets having a Sm ₂ CO ₁₇ type crystal phase (hereinafter also referred to as the 2-17 phase), it is believed that Cu increases the coercive force, and Zr increases the amount of Fe in solid solution, thereby indirectly increasing the residual magnetic flux density Br.
This permanent magnet is manufactured by two types of methods described later, which control the diffusion of Cu and Zr so that the Cu concentration in the grain boundaries is at least two times, and preferably at least three times, the Zr concentration, thereby obtaining a magnet with high residual magnetic flux density, low coercive force, and high squareness ratio.
Because this permanent magnet has magnetic properties suited to variable field motors, its application to variable field motors makes it possible to manufacture variable field motors that achieve high efficiency from low to high speeds.

The rare earth element R is a general term for Sc, Y, and lanthanoids, and in this permanent magnet, the R contains at least Sm. By containing rare earth elements in the above ratio, a permanent magnet with high magnetic anisotropy is obtained. The rare earth element R may consist of only Sm, or may be a combination of Sm and other rare earth elements. From the viewpoint of magnetic properties, the other rare earth element R is preferably one or more selected from Nd, Pr, and Ce. From the viewpoint of magnetic properties, the rare earth element R is preferably such that Sm is 70 mass% or more of the total rare earth elements, and more preferably 80 mass% or more.

The Cu content is 1.0 to 5.0 mass %. By setting the Cu content within this range, a high squareness ratio can be obtained while adjusting the coercive force within an appropriate range.
The Fe content is 18 to 25 mass%. By setting the Fe content within this range, it is easy to achieve a high residual magnetic flux density. Furthermore, by setting the Fe content to 18% or more, the saturation magnetization is improved, and by setting the Fe content to 25% or less, the coercive force is adjusted to an appropriate range.
The Zr content is 1.5 to 3.0 mass%. By keeping the Zr content within this range, the amount of Fe in solid solution is increased, which indirectly makes it easier to increase the residual magnetic flux density Br. Also, the maximum energy product (BH)max, which is the maximum magnetostatic energy that the magnet can hold, is improved.

The remainder of the permanent magnet (that is, 40 to 56.5 mass %) is Co and unavoidable impurities.
The inclusion of Co improves the thermal stability of the permanent magnet. On the other hand, if the Co content is excessive, the Fe content decreases relatively, which may result in a decrease in magnetization. From these points of view, the Co content is preferably 40 to 56.5 mass%.

Next, the structure of the permanent magnet will be described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view showing a part of the cross section of the permanent magnet. As shown in the example of FIG. 1, the permanent magnet 10 has a plurality of crystal grains 1 (areas surrounded by solid lines in the figure), and grain boundaries 2 (solid lines in the figure) are between the crystal grains 1. Each crystal grain 1 has a cell phase 3 (area surrounded by dotted lines only or dotted and solid lines in the figure) containing a crystal phase of a Th ₂ Zn ₁₇ type structure (hereinafter also referred to as a 2-17 phase), and a cell wall 4 (dotted lines in the figure) containing a crystal phase of a RCo ₅ type structure (hereinafter also referred to as a 1-5 phase) surrounding the cell phase. In the present invention, the cell structure refers to a combination of one cell phase 3 and the cell wall 4 surrounding it, and is the minimum unit that constitutes a crystal grain.

As described above, the permanent magnet has a cell phase in which the crystal phase of the Th ₂ Zn ₁₇ type structure is the main phase. The _{Th 2} Zn ₁₇ type structure is a crystal structure having an R-3m type space group, and in the permanent magnet, the Th site is occupied by rare earth elements and Zr, and the Zn site is occupied by Co, Cu, Fe, and Zr. Also, as described above, the permanent magnet has a cell wall containing a crystal phase of the RCo ₅ type structure. In the crystal phase of the RCo ₅ type structure, the R site is occupied by rare earth elements and Zr, and the Co site is occupied by Co, Cu, and Fe. In the permanent magnet 10, the size of the cell structure refers to the length of the cell wall 4 (the length of the crystal phase of the RCo ₅ type structure). In the permanent magnet, the cell size is preferably 50 to 200 nm in order to achieve low coercive force.

Next, the characteristics of this permanent magnet will be described with reference to Fig. 2. Fig. 2 is a graph showing the first and second quadrants (decay curve) of the hysteresis curve of the permanent magnet of Example 1 described below. The vertical axis represents magnetization (magnetic polarization), and the horizontal axis represents the strength of the magnetic field. Positive values on the horizontal axis represent the strength of the magnetic field applied in the direction to magnetize the permanent magnet, and negative values represent the strength of the magnetic field applied in the direction to demagnetize the permanent magnet.
When a positive magnetic field is applied to a permanent magnet, magnetic polarization occurs according to the initial magnetization curve, and the magnetization reaches saturation. When a negative magnetic field is then applied to a permanent magnet in a saturated magnetized state, the magnetization rapidly decreases through a knickpoint. The strength of the magnetic field when the magnetic polarization becomes 0 is the intrinsic coercivity (Hcj).
In the present invention, the magnetic field at 90% magnetization of the residual magnetization is defined as Hk, and the ratio of this to the intrinsic coercivity Hcj (Hk/Hcj) is defined as the squareness ratio. This permanent magnet can achieve a squareness ratio of 60% or more, preferably 70% or more.
Furthermore, when this permanent magnet is remagnetized from a demagnetization field (point A) that exceeds the knickpoint of the demagnetization curve, magnetization of 95% or more of the saturation magnetization can be achieved in a magnetic field of 5 times (absolute value) or less of the intrinsic coercivity Hcj, and preferably, magnetization of 95% or more of the saturation magnetization can be achieved in a magnetic field of 3 times (absolute value) or less of the intrinsic coercivity Hcj.
As described above, the present permanent magnet has excellent responsiveness to magnetization in response to a magnetic field, and can be suitably used in variable magnetic field motors in which the number of rotations changes frequently.

Furthermore, the permanent magnet can have magnetic properties such as a saturation magnetization of 1.16 T or more and an intrinsic coercivity Hcj of 120 to 800 kA/m, preferably 200 to 800 kA/m, and more preferably 240 to 800 kA/m.

<Manufacturing method of rare earth cobalt permanent magnet>
The rare earth-cobalt permanent magnet can be manufactured by the following two manufacturing methods. The two manufacturing methods will now be described.

(First manufacturing method)
The first method for producing the rare earth-cobalt permanent magnet (hereinafter, simply referred to as the first method for producing the magnet) is as follows:
(I) preparing an alloy containing, by mass percentage, 23-27% rare earth element R, 1.0-5.0% Cu, 18-25% Fe, 1.5-3.0% Zr, and the balance being Co and unavoidable impurities, where R is a rare earth element including at least Sm;
a pulverization step (II) of converting the alloy into powder;
A pressure molding step (III) of forming the powder into a molded body;
A step (IV) of sintering the compact at 1200 to 1250°C;
A step (V) of subjecting the sintered compact to a solution treatment;
A step (VI) of heat treating the solution-treated compact at 600 to 850°C;
A step (VII) of cooling the heat-treated molded body to 400° C. or less at a rate of 0.2 to 10° C./min;
A step (VIII) of performing a heat treatment at a temperature of 700 to 900° C. and higher than that of the step (VI);
and a step (IX) of cooling the heat-treated molded body to 400° C. or lower at a rate of 0.1 to 5° C./min.

According to the first present manufacturing method, it is possible to manufacture a rare earth-cobalt permanent magnet having a plurality of crystal grains and grain boundaries, in which the Cu concentration is at least twice the Zr concentration.
According to the first manufacturing method, it is possible to suitably manufacture rare earth-cobalt permanent magnets with a cell size of 50 to 200 nm.
According to the first manufacturing method, it is possible to suitably manufacture rare earth-cobalt permanent magnets having a saturation magnetization of 1.16 T or more and an intrinsic coercivity Hcj of 240 to 800 kA/m.
According to the first manufacturing method, it is possible to suitably manufacture rare earth cobalt permanent magnets in which the squareness ratio, expressed as the ratio (Hk/Hcj) of the magnetic field Hk at 90% magnetization of residual magnetization to the intrinsic coercivity Hcj in the demagnetization curve, is 60% or more, and which, when remagnetized from a demagnetization field that exceeds the knickpoint of the demagnetization curve, can obtain magnetization of 95% or more of the saturation magnetization in a magnetic field of three times or less the intrinsic coercivity Hcj.
Furthermore, according to the first manufacturing method, it is possible to suitably manufacture rare earth cobalt permanent magnets having a diffraction intensity ratio I(006)/I(303) of 0.225 to 0.4 when the diffraction intensity I(006) of the (006) plane and the diffraction intensity I(303) of the (303) plane are measured by powder X-ray diffraction.
In the first production method, the above steps (I) to (IX) are usually carried out in this order, and other steps may be included within the scope of the invention. Each step will be described below.

First, an alloy is prepared that contains, in mass percentage, 23-27% rare earth elements R including Sm, 1.0-5.0% Cu, 18-25% Fe, 1.5-3.0% Zr, and the balance being Co and unavoidable impurities (step (I)). The method for preparing the alloy is not particularly limited, and the alloy may be prepared by obtaining a commercially available alloy having the desired composition, or the alloy may be prepared by mixing the elements to obtain the desired composition.
A specific example of the blending of each element will be described below, but the present production method is not limited to this method.

First, the desired rare earth element, Fe, Cu, and Co metal elements, and a mother alloy are prepared as raw materials. Here, it is preferable to select a mother alloy having a composition with a low eutectic temperature, since it is easy to homogenize the composition of the obtained alloy. In this manufacturing method, it is preferable to select and use FeZr or CuZr as the mother alloy. As an example of FeZr, it is preferable to use one having about 20% Fe and 80% Zn. Also, as an example of CuZr, it is preferable to use one having about 50% Cu and 50% Zr.
These raw materials are mixed to obtain a desired composition, placed in a crucible such as an alumina crucible, and melted in a high-frequency melting furnace in a vacuum of 1×10 ⁻² torr or less or in an inert gas atmosphere to obtain a homogenized alloy. Furthermore, this manufacturing method may include a step of casting the melted alloy in a mold to obtain an alloy ingot. Alternatively, the molten alloy may be dropped onto a copper roll to produce flake-like alloys with a thickness of about 1 mm (strip casting method). In the present invention, the method of melting in a melting furnace is preferred because it is easy to obtain permanent magnets with high residual magnetic flux density and squareness ratio.

When an alloy ingot is produced by the casting, it is preferable to have a step of heat treating the alloy ingot at the solution treatment temperature for 1 hour to 20 hours before the step (II) described below. This step can make the composition more uniform. The solution treatment temperature of the alloy ingot may be appropriately adjusted depending on the composition of the alloy, etc.

Next, the alloy is pulverized to obtain a powder (step (II)). The method for pulverizing the alloy is not particularly limited, and may be appropriately selected from conventionally known methods. As an example, a suitable method is to first coarsely pulverize the alloy ingot or flakes to a size of about 100 to 500 μm using a known pulverizer, and then finely pulverize using a ball mill, jet mill, or the like. The average particle size of the powder is not particularly limited, but it is preferable to use a powder with an average particle size of 1 μm to 10 μm, preferably about 6 μm, in order to shorten the sintering time in the sintering step described below and to produce a uniform permanent magnet.

Next, the obtained powder is pressure-molded to obtain a molded body of the desired shape (step (III)). In this manufacturing method, pressure molding is preferably performed in a constant magnetic field in order to align the crystal orientation of the powder and improve the magnetic properties. The relationship between the direction of the magnetic field and the pressing direction is not particularly limited, and may be selected appropriately depending on the shape of the product, etc. For example, when manufacturing a ring magnet or a thin plate magnet, a parallel magnetic field press can be used in which a magnetic field is applied parallel to the pressing direction. On the other hand, in terms of excellent magnetic properties, a perpendicular magnetic field press in which a magnetic field is applied perpendicular to the pressing direction is preferable.

The strength of the magnetic field is not particularly limited, and may be, for example, 15 kOe or less or 15 kOe or more depending on the application of the product. In particular, from the viewpoint of excellent magnetic properties, it is preferable to perform pressure molding in a magnetic field of 15 kOe or more. In addition, the pressure during pressure molding may be appropriately adjusted depending on the size, shape, etc. of the product. As an example, the pressure may be 0.5 to 2.0 ton/cm ^2. That is, in this manufacturing method, from the viewpoint of magnetic properties, it is particularly preferable to pressure mold the powder in a magnetic field of 15 kOe or more at a pressure of 0.5 ton/cm ² or more and 2.0 ton/cm ² or less perpendicular to the magnetic field.

Next, the molded body is heated to form a sintered body (step (IV)). In this manufacturing method, the sintering conditions may be any conditions that sufficiently densify the resulting sintered body, and may be known conditions. From the viewpoint of densifying the sintered body, the sintering temperature is preferably 1200 to 1250°C. By setting the sintering temperature at 1250°C or less, evaporation of rare earth elements, particularly Sm, is suppressed, and a permanent magnet with excellent magnetic properties can be manufactured.
In terms of removing adsorbed gases contained in the compact, the temperature rise conditions in the sintering step are preferably such that evacuation is started at room temperature and the temperature is raised at a rate of 1 to 10°C/min. During the temperature rise process, a hydrogen atmosphere may be used instead of evacuation. In this case, too, it is preferable to switch to a vacuum atmosphere at a temperature of 1150°C or lower.
The sintering time is preferably 20 to 240 minutes, more preferably 30 to 180 minutes, from the viewpoint of sufficiently densifying while suppressing evaporation of Sm. Also, from the viewpoint of suppressing oxidation, the sintering step is preferably carried out in a vacuum of 1×10 ⁻² Torr or less or in an inert gas atmosphere, more preferably in a vacuum of 1×10 ⁻⁴ Torr or less.

Next, the obtained sintered body is slowly cooled at a temperature drop rate of 0.2 to 5°C/min. The slowly cooled sintered body is then subjected to a solution treatment (step (V)). The solution treatment temperature may be appropriately adjusted from the viewpoint of the sintered body and the desired magnetic properties, and it is preferable to perform the solution treatment at a temperature 20 to 50°C lower than the sintering temperature. The solution treatment time may be appropriately adjusted within the range of, for example, 2 to 20 hours.

After the solution treatment, it is preferable to rapidly cool the material to at least 400°C or less.
The sintered body is then heat-treated at 600 to 850°C (step (VI)). The heat treatment time may be adjusted appropriately from the viewpoint of the desired magnetic properties, and is preferably set to, for example, 0.5 to 3 hours. The heat-treated compact is then cooled at 0.2 to 10°C/min to 400°C or less (step (VII)). Next, heat treatment is performed at 700 to 900°C, which is a temperature higher than that of the step (VI) (step (VIII)). The heat treatment time may be, for example, 0.5 to 10 hours. Next, the heat-treated compact is cooled at 0.1 to 5°C/min to 400°C or less (step (IX)) to obtain the permanent magnet.
In the first manufacturing method, it is estimated that a cell structure is formed in the crystal grains during isothermal holding in steps (VI and VIII), but at this stage, the Cu concentration in the crystal grains is low and concentrated at the grain boundaries. On the other hand, it is estimated that Zr is dissolved in the crystal grains to form the 2-17 phase with a high Fe content. In the first manufacturing method, it is estimated that a cell structure with cell walls of 50 to 200 nm is formed in the crystal grains by two heat treatments (steps (VI) to (IX)), and further, Cu and Zr are appropriately diffused, and the Cu concentration at the grain boundaries is at least twice, preferably at least three times, the Zr concentration.

Furthermore, according to the first manufacturing method, when the diffraction intensity I(006) of the (006) plane and the diffraction intensity I(303) of the (303) plane are measured by powder X-ray diffraction, rare earth cobalt permanent magnets can be suitably manufactured in which the diffraction intensity ratio I(006)/I(303) is 0.225 to 0.4. Figure 5 shows the powder X-ray diffraction spectra of the permanent magnets of Examples 3 and 4 and Reference Example 1. It is shown that the permanent magnets obtained by the first manufacturing method have a high peak intensity of the (006) plane, which is the easy axis of magnetization (C-axis). In this way, the first manufacturing method improves the degree of orientation of the C-axis, and as a result, the magnetization is improved.

(Second manufacturing method)
The second method for producing the rare earth-cobalt permanent magnet (hereinafter, simply referred to as the second method for producing the rare earth-cobalt permanent magnet) is as follows:
(I) preparing an alloy containing, by mass percentage, 23-27% rare earth element R, 1.0-5.0% Cu, 18-25% Fe, 1.5-3.0% Zr, and the balance being Co and unavoidable impurities, where R is a rare earth element including at least Sm;
a pulverization step (II) of converting the alloy into powder;
A pressure molding step (III) of forming the powder into a molded body;
A step (IV) of sintering the molded body at 1200 to 1250 ° C.;
A step (V) of subjecting the sintered compact to a solution treatment;
A step (VI-a) of heat treating the solution-treated compact at 750 to 850 ° C.;
A step (VII-a) of cooling the heat-treated molded body to 500 to 600 ° C. at 0.5 to 10 ° C./min and maintaining the temperature at 500 to 600 ° C.;
and a step (VIII-a) of quenching the molded body after the isothermal holding.

According to the second present manufacturing method, it is possible to manufacture a rare earth-cobalt permanent magnet having a plurality of crystal grains and grain boundaries, in which the Cu concentration is at least twice the Zr concentration.
According to the second manufacturing method, rare earth cobalt permanent magnets with a cell size of 50 to 200 nm can be suitably manufactured.
Furthermore, according to the second manufacturing method, it is possible to suitably manufacture rare earth-cobalt permanent magnets having a saturation magnetization of 1.16 T or more and an intrinsic coercivity Hcj of 120 to 800 kA/m.
According to the first present manufacturing method, it is possible to suitably manufacture rare earth cobalt permanent magnets in which the squareness ratio, expressed as the ratio (Hk/Hcj) of the magnetic field Hk at 90% magnetization of residual magnetization to the intrinsic coercivity Hcj in the demagnetization curve, is 60% or more, and which, when remagnetized from a demagnetization field that exceeds the knickpoint of the demagnetization curve, can obtain magnetization of 95% or more of the saturation magnetization in a magnetic field of 5 times or less the intrinsic coercivity Hcj.
The second production method is a method in which the above steps (I) to (VIII-a) are usually carried out in this order, and may further include other steps as long as the effects of the present invention are not impaired.
In the second production method, steps (I) to (V) are the same as those in the first production method, and the preferred production conditions are also the same, so duplicated explanations will be omitted.

After the solution treatment (step (V)), the molded body is preferably rapidly cooled to at least 400° C. or less.
Next, the sintered body is heat-treated at 750 to 850°C (step (VI-a)). The heat treatment time may be adjusted appropriately from the viewpoint of the desired magnetic properties, and is preferably set to, for example, 0.5 to 10 hours. This step forms a cell structure with cell walls of 50 to 200 nm in thickness within the crystal grains, and Cu and Zr are appropriately diffused, so that the Cu concentration at the grain boundary is at least twice, preferably at least three times, the Zr concentration.
The heat-treated compact is cooled to 500-600°C at a rate of 0.5-10°C/min and isothermally held (step (VII-a)). The isothermal holding time may be adjusted appropriately within the range of, for example, 0.5-10 hours. The compact after isothermal holding is then quenched (step (VIII-a)) to obtain the permanent magnet.
In the second manufacturing method, a cell structure is formed within the crystal grains during isothermal holding in step (VI-a), but at this stage, the Cu concentration within the crystal grains is low and is presumed to be concentrated at the crystal grain boundaries. On the other hand, Zr is presumed to be dissolved in the crystal grains to form the 2-17 phase with a high Fe content. When the process shifts from the isothermal holding in step (VI-a) to slow cooling, Cu and Zr diffuse into each other, and Cu is presumed to be concentrated in the cell walls that form the cell structure within the crystal grains, resulting in an increase in coercive force.

<Device>
The present invention further provides a device having the permanent magnet. Specific examples of such devices include watches, electric motors, various instruments, communication devices, computer terminals, speakers, video disks, sensors, etc. As described above, the rare earth cobalt permanent magnet of the present invention has a high residual magnetic flux density, low coercive force, and a high squareness ratio, and therefore can be suitably applied to variable magnetic field motors, and a variable magnetic field motor that achieves high efficiency from low speed to high speed can be obtained.

The present invention will be specifically described below with reference to examples and comparative examples. Note that the present invention is not limited to these descriptions.

Example 1: Second manufacturing method
A master alloy of 20% Fe and 80% Zr and raw materials containing various elements were melted in a high-frequency melting furnace in a vacuum of 1×10 ⁻² Torr or less to obtain an alloy ingot having a composition of 25.0 wt % Sm, 4.0 wt % Cu, 21.0 wt % Fe, 2.2 wt % Zr, and the balance Co.
The alloy ingot was then heat-treated at 1170°C for 15 hours, coarsely pulverized, and finely pulverized in an inert atmosphere using a jet mill to obtain a powder with an average particle size of 6 μm. This powder was then molded into a compact with a length of 100 mm, width of 50 mm, and height of 50 mm using a die in a magnetic field of 15 kOe and a pressure of 1.0 ton/ ^cm2 .
The obtained compact was sintered at a temperature of 1200° C. in a vacuum of 1×10 ⁻² Torr or less, then cooled to 1170° C. at a rate of 1° C./min and held for 4 hours for solution treatment, after which it was immediately quenched at a cooling rate of 100° C./min.
The sintered body after quenching was heated and held at a temperature of 800°C in an inert atmosphere for 1 hour to perform isothermal aging treatment, and then continuously cooled slowly at a cooling rate of 2°C/min to 550°C or below, held at 550°C for 5 hours, and then quenched, thereby obtaining the permanent magnet of Example 1.

Example 2: Second manufacturing method
A permanent magnet of Example 2 was obtained in the same manner as in Example 1, except that the isothermal aging treatment was changed to heating and holding at a temperature of 800° C. for 5 hours.

<Comparative Example 1>
In the above-mentioned Example 1,
The isothermal aging treatment was changed to a heating and holding time of 10 hours at a temperature of 850°C.
A permanent magnet of Comparative Example 1 was obtained in the same manner as in Example 1, except that the subsequent continuous slow cooling was carried out at a cooling rate of 0.25° C./min until the temperature reached 350° C. or lower.

[evaluation]
Measurement samples were prepared by machining the permanent magnets of Examples 1 and 2 and Comparative Example 1 into shapes of 10×10×7 mm. The thickness of 7 mm corresponds to the direction of magnetic field orientation (C-axis orientation).

The hysteresis curve of Example 1 will be described with reference to FIG. 2 mentioned above. The measurement of the hysteresis curve is performed by sandwiching the measurement sample between the pole pieces of an electromagnet called a DC magnetization characteristic analyzer. Although there is no need for demagnetization correction, the apparent magnetization is reduced in the magnetic field exceeding 10 kOe in the first quadrant due to the influence of the so-called mirror effect. However, the magnetization curve is actually such that the magnetization reaches saturation magnetization. As shown in FIG. 2, it can be seen that the initial magnetization curve of Example 1 rises sharply and reaches saturation magnetization in a low magnetic field of about 10 kOe. Similarly, the measurement results of the minor loop are also shown (dotted line). Example 1 shows a magnetization curve that coincides with the initial magnetization curve at 8 to 10 kOe, and when the magnetic susceptibility is compared at 10 kOe, the Example is almost 100%. Measurements were also performed in Example 2 and Comparative Example 1 in the same manner. The results are shown in Table 1.
Table 1 also shows the measurement results of the residual magnetic flux density.

Next, FIG. 3 shows a DF-STEM image of Example 1. The left side of FIG. 3 is a DF-STEM image, and the right side of FIG. 3 is a Cu composition image with Cu extracted. A unique cell structure formed by heat treatment of _{Sm 2} Co ₁₇ alloy is observed. The inside of the cell is a 2-17 crystal phase consisting of a ferromagnetic phase, and the cell walls between the cells are a 1-5 crystal phase containing nonmagnetic Cu. Therefore, the size of the cell can be measured from the Cu composition image. When the cell size of this alloy is measured by this method, it is found to be 50 to 200 nm.
Fig. 4 shows the results of a composition analysis of the grain boundary phase between crystal grains. The "position" in the graph in Fig. 4 indicates the distance from the top end of the line LG4 in the DF-STEM image shown on the left in Fig. 4 to the measurement point, with the top end being set as 0. As shown in Fig. 4, it can be seen that Cu and Zr are concentrated in the grain boundary phase. The ratio of Cu to Zr is shown in Table 1. It can be seen that in Example 1, the ratio of Cu is higher than the ratio of Zr.

Example 3: First manufacturing method
In the same manner as in Example 1, except for the amounts of added raw materials, an alloy ingot having a composition of 21.55 wt % Fe, 25.65 wt % Sm, 4.5 wt % Cu, 2.20 wt % Zr, and the balance Co was obtained.
The obtained compact was sintered at 1210°C for 1 hour in a vacuum of ^1x10-2 Torr or less, then solution-treated at 1155°C for 15 hours, and immediately thereafter quenched at a cooling rate of 100°C/min. The quenched sintered body was heated and held at 750°C for 2 hours in an inert atmosphere to perform isothermal aging treatment, and then slowly cooled to 400°C or less at a cooling rate of 2°C/min. Further, the sintered body was heated and held at 765°C for 5.5 hours in an inert atmosphere to perform isothermal aging treatment, and continuously cooled at a cooling rate of 0.5°C/min to 700°C, at a cooling rate of 0.25°C/min to 500°C, and at a cooling rate of 0.5°C/min to 400°C or less to obtain a permanent magnet of Example 3.

Example 4: Second manufacturing method
An ingot was obtained, sintered, solution-treated, and quenched in the same manner as in Example 3. The quenched sintered body was heated and held at a temperature of 815°C for 5.5 hours in an inert atmosphere to perform isothermal aging treatment, and then continuously cooled slowly to 550°C at a cooling rate of 2°C/min, held at 550°C for 5 hours, and then quenched, thereby obtaining a permanent magnet of Example 4.

<Reference Example 1>
A permanent magnet of Reference Example 1 was obtained in the same manner as in Example 3, except that the steps subsequent to the 750° C. aging treatment in Example 3 were not carried out.

[evaluation]
Examples 3 and 4 were evaluated in the same manner as Examples 1 and 2. The results are shown in Table 2.
In addition, the spectra of the permanent magnets of Examples 3 and 4 and Reference Example 1 measured by the powder X-ray diffraction method are shown in FIG. 5. The peaks related to Sm ₂ Co ₁₇ of Reference Example 1 are marked. The diffraction intensity ratio I(006)/I(303) of the diffraction intensity I(006) of the (006) plane to the diffraction intensity I(303) of the (303) plane was 0.138 for Reference Example 1, 0.270 for Example 3, and 0.197 for Example 4. It is shown that the permanent magnet obtained by the first manufacturing method as in Example 3 has a high peak intensity of the (006) plane, which is the easy axis of magnetization (C-axis). In this way, it was shown that the first manufacturing method improves the degree of orientation of the C-axis, and as a result, the magnetization is improved.

Thus, it has become clear that the rare earth cobalt permanent magnet of the present invention, which contains, by mass percentage, rare earth elements R: 23-27%, Cu: 1.0-5.0%, Fe: 18-25%, Zr: 1.5-3.0%, with the remainder being Co and unavoidable impurities, has multiple crystal grains and grain boundaries, and in the grain boundaries, the Cu concentration is at least twice the Zr concentration, has high residual magnetic flux density, low coercive force, and a high squareness ratio, and has magnetic properties suitable for variable field magnet motors.

The present invention has been described above in accordance with the above embodiment, but the present invention is not limited to the configuration of the above embodiment, and of course includes various modifications, alterations, and combinations that a person skilled in the art could make within the scope of the invention of the claims of this patent application.

1 Crystal grain 2 Grain boundary 3 Cell phase 4 Cell wall 10 Rare earth cobalt permanent magnet

Claims (10)

When R is a rare earth element including at least Sm,
A rare earth-cobalt permanent magnet comprising, by mass percentage, 23-27% rare earth element R, 1.0-5.0% Cu, 18-25% Fe, 1.5-3.0% Zr, and the remainder being Co and unavoidable impurities;
The alloy has a plurality of crystal grains and grain boundaries,
In the grain boundary portion, the Cu concentration is equal to or more than twice the Zr concentration,
The intrinsic coercivity Hcj is 120 to 6.2×10 ³ /4π kA/m,
In the demagnetization curve, the squareness ratio, which is expressed as the ratio (Hk/Hcj) of the magnetic field Hk at 90% magnetization of the residual magnetization to the intrinsic coercivity Hcj, is 60% or more, and
When magnetized again from a demagnetization field exceeding the knickpoint of the demagnetization curve, magnetization of 95% or more of the saturation magnetization can be obtained in a magnetic field of 5 times or less the intrinsic coercivity Hcj.
Rare earth cobalt permanent magnet. The rare earth cobalt permanent magnet according to claim 1, wherein the size of the cell structure that constitutes the crystal grains is 50 to 200 nm. The rare earth cobalt permanent magnet according to claim 1 or 2, having a saturation magnetization of 1.16 T or more. 3. The rare earth-cobalt permanent magnet according to claim 1, having a saturation magnetization of 1.16 T or more and an intrinsic coercivity Hcj of 240 to 6.2×10 ³ /4π kA/m. In the demagnetization curve, the squareness ratio, which is expressed as the ratio (Hk/Hcj) of the magnetic field Hk at 90% magnetization of the residual magnetization to the intrinsic coercivity Hcj, is 60% or more, and
The rare earth cobalt permanent magnet according to any one of claims 1 to 4, which, when remagnetized from a demagnetization field that exceeds the knickpoint of the demagnetization curve, achieves magnetization of 95% or more of the saturation magnetization in a magnetic field of three times or less the intrinsic coercivity Hcj. A rare earth cobalt permanent magnet according to any one of claims 1 to 5, in which the diffraction intensity ratio I(006)/I(303) is 0.225 to 0.4 when the diffraction intensity I(006) of the (006) plane and the diffraction intensity I(303) of the (303) plane are measured by powder X-ray diffraction. When magnetized again from a demagnetization field exceeding the knickpoint of the demagnetization curve, magnetization of 95% or more of the saturation magnetization is obtained in a magnetic field of 10 kOe.
The rare earth-cobalt permanent magnet according to any one of claims 1 to 6. (I) preparing an alloy containing, by mass percentage, 23-27% rare earth element R, 1.0-5.0% Cu, 18-25% Fe, 1.5-3.0% Zr, and the balance being Co and unavoidable impurities, where R is a rare earth element including at least Sm;
a pulverization step (II) of converting the alloy into powder;
A pressure molding step (III) of forming the powder into a molded body;
A step (IV) of sintering the compact at 1200 to 1250°C;
A step (V) of subjecting the sintered compact to a solution treatment;
a step of quenching the formed body after the solution treatment to 400°C or less;
A step (VI) of heat treating the quenched compact at 600 to 850 ° C.;
A step (VII) of cooling the heat-treated molded body to 400° C. or less at a rate of 0.2 to 10° C./min;
A step (VIII) of performing a heat treatment at 700 to 900° C. and at a temperature higher than that of the step (VI) for 0.5 to 10 hours;
and (IX) cooling the heat-treated molded body to 400°C or less at 0.1 to 5°C/min.
Manufacturing method of rare earth cobalt permanent magnet. (I) preparing an alloy containing, by mass percentage, 23-27% rare earth element R, 1.0-5.0% Cu, 18-25% Fe, 1.5-3.0% Zr, and the balance being Co and unavoidable impurities, where R is a rare earth element including at least Sm;
a pulverization step (II) of converting the alloy into powder;
A pressure molding step (III) of forming the powder into a molded body;
A step (IV) of sintering the compact at 1200 to 1250°C;
A step (V) of subjecting the sintered compact to a solution treatment;
a step of quenching the formed body after the solution treatment to 400°C or less;
A step (VI-a) of heat treating the quenched compact at 750 to 850 ° C.;
A step (VII-a) of cooling the heat-treated molded body to 500 to 600 ° C. at 0.5 to 10 ° C./min and maintaining the temperature at 500 to 600 ° C.;
and a step (VIII-a) of quenching the molded body after isothermal holding.
Manufacturing method of rare earth cobalt permanent magnet. A device comprising the rare earth cobalt permanent magnet according to any one of claims 1 to 7 .

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