JPWO2004013873A1 - Rare earth-iron-boron magnet manufacturing method - Google Patents

Abstract

By utilizing shear plastic deformation, which has not been employed in the manufacture of conventional magnet alloys, rare earth-iron-boron permanent magnets or bonded magnets that do not have complicated processes and that have good yield and excellent magnetic properties can be easily obtained. This is a method for producing a permanent magnet. In the production method of the present invention, R consisting of at least one rare earth metal element containing Y is 11.3-16.5 atomic%, boron 4.7-7.4 atomic%, and the balance M containing iron, (A) which prepares the magnet raw material alloy which has the composition which consists of, and the process (B) which carries out the shear plastic deformation of the said magnet raw material alloy.

Description

  The present invention relates to a method for producing a magnet such as a rare earth-iron-boron permanent magnet or a bonded magnet containing rare earth metal, iron and boron as essential components.

Currently, high-performance rare earth-iron-boron permanent magnets are widely used for VCM for driving hard disk drive heads, small high-performance motors, MRI magnetic field generating magnets, automobile power steering motor magnets, etc. It's being used. In the future, application to various robots, electric vehicles and the like that are expected to increase dramatically is considered.
Rare earth-iron-boron permanent magnets are mainly manufactured by a sintering method. The sintering method is a method of manufacturing a magnetic material alloy obtained by melting, casting, and pulverizing a raw material by a vacuum melting method, by performing magnetic field forming, sintering, and aging treatment. In this method, in order to obtain a magnet with a high degree of anisotropy, each powder is pulverized so as not to have a crystal grain boundary and oriented in a magnetic field. In order to obtain a high coercive force, it is ideal to make the crystal grain size after sintering as small as possible. According to SW theory (Stoner-Wolfers theory), it is ideal to reduce the crystal grain size to a single domain grain size. Generally, in the pulverization process, hydrogenation occurs at about 400 ° C, and many cracks are formed inside the ingot. After being generated, it is finely pulverized to about 3 to 5 μm by a jet mill. The magnetic field shaping after pulverization is performed by shaping the magnetically easy axis in one direction in a magnetic field. In order to improve the moldability, surfactants are generally widely used. Sintering is performed by heating the molded body at approximately 1000 to 1100 ° C., and if necessary, an aging treatment is performed to finally produce a magnet.
In such a sintering method, although it is effective to obtain a high coercive force as the crystal grain size is reduced in the pulverization step as described above, oxidation or ignition of the contained rare earth metal is minimized. Therefore, it is only pulverized to an average grain size of about 3 to 5 μm in an environment controlled to a non-oxidizing atmosphere. Even if such oxidation prevention is performed, a certain degree of oxidation is unavoidable, and an oxide of an alloy component is generated during sintering. Further, mixing of the carbon component from the surfactant used at the time of molding occurs, and carbide of the alloy component is generated at the time of sintering. These oxides and carbides are non-magnetic phases and do not function magnetically at all. However, when a general sintering method is employed, oxygen is contained at 1500 ppm or more and carbon is contained at about 300 ppm.
In addition, in the sintering method, a compact is prepared in anticipation of the shrinkage rate due to sintering, but finally requires machining, and the yield is lowered particularly when the shape is small or thin. In addition, since the sintering process has a long process as a whole, it is difficult to stabilize the quality of the product and the yield is lowered.
On the other hand, in order to avoid the problems of the sintering method, a magnet obtained by pulverizing an ingot magnet raw material alloy cast by a molding method, or a slab made of amorphous or fine crystal grains cast under ultra-rapid cooling conditions such as melt span Attempts have been made to produce magnets without undergoing a sintering process, such as rolling or extruding raw material alloys by hot working.
In such a method, hot working is performed to orient the crystal axis in a specific direction and make it anisotropic to improve the magnetic properties. However, in the processing by rolling and extrusion, the crystal grains are not refined and the holding power is not sufficiently improved. In the rolling process, the crystal axis of the main phase crystal grains is oriented, so it is necessary to increase the addition amount of R, and as a result, the nonmagnetic phase increases. In addition, the R-rich phase that has become a liquid phase during processing is difficult to process, such as leakage to the outside, and is unsuitable for industrial production. In the extrusion process, the crystal axes of the main phase crystal grains are not sufficiently oriented, and sufficient magnetic properties cannot be obtained. Further, in these general hot workings, the shapes before and after the machining are different, so that the machining after a plurality of times is difficult and the shape after the machining is limited.
For the above reasons, the method of adopting the hot working is actually used only for the production of special magnets such as large radial ring magnets.
Incidentally, a metal processing method different from the hot processing has been proposed. For example, Segal et al. Gave a shear deformation by lateral extrusion (ECAP (equal-channel-angular-pressing) (also referred to as ECAE (equal-channel-angular-extension) method)) without cross-sectional area reduction. It has been proposed to accumulate large strains in the material without reducing the amount of crystal grains and to refine crystal grains by processing aluminum alloys and magnesium alloys while applying a temperature of 300 ° C. or higher by the same method. It is also known to do this (Japanese Patent Laid-Open No. 9-137244).
However, these processing methods are processing methods for improving mechanical strength by refining crystal grains, and there is no suggestion of application to a magnet alloy or action by applying to a magnet alloy.

SUMMARY OF THE INVENTION An object of the present invention is to use rare earth-iron-boron permanent magnets that do not have a complicated process by using shear plastic deformation that has not been conventionally used in the manufacture of magnet alloys, and that have good yield and excellent magnet characteristics. Alternatively, it is an object of the present invention to provide a magnet manufacturing method capable of easily obtaining a bonded magnet.
In order to solve the above-mentioned problems, the present inventor has intensively studied the relation between the processing technology of the rare earth-iron-boron magnet raw material alloy and the magnetic properties of the obtained permanent magnet, and as a result, the magnetic raw material alloy is shear plastically deformed. By performing a simple process, the crystal grain refinement and high-level orientation of the crystal axis in a specific direction can be performed more efficiently than conventional hot processing such as sintering, rolling, or extrusion. The present invention was completed by finding that permanent magnets and bonded magnets having excellent magnetic properties can be easily obtained.
According to the present invention, R consisting of at least one rare earth metal element containing yttrium is 11.3 to 16.5 atomic%, boron 4.7 to 7.4 atomic%, and the balance M containing iron. There is provided a method for producing a rare earth-iron-boron permanent magnet comprising a step (A) of preparing a magnet raw material alloy having a composition and a step (B) of shearing plastic deformation of the magnet raw material alloy.

FIG. 1 is an explanatory schematic diagram for explaining shear plastic deformation performed in the examples.
FIG. 2 is an explanatory schematic diagram for explaining plastic deformation performed in Comparative Examples 1 to 6.
FIG. 3 is an explanatory schematic diagram for explaining another plastic deformation performed in Comparative Examples 7-12.
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.
In the method for producing a rare earth-iron-boron magnet of the present invention, first, R composed of at least one rare earth metal element containing yttrium is 11.3 to 16.5 atomic%, and boron is 4.7 to 7.4. The step (A) of preparing a magnet raw material alloy (hereinafter referred to as a raw material alloy (a)) having a composition composed of atomic% and the balance M containing iron is performed.
R constituting the raw material alloy (a) is not particularly limited as long as it is a rare earth metal element containing yttrium, but preferred examples include lanthanum, cerium, praseodymium, neodymium, yttrium, dysprosium, or a mixture of two or more thereof. . When the content ratio of R is less than 11.3 atomic%, the amount of liquid phase necessary for densification of the alloy is insufficient and the magnetic properties deteriorate. When it exceeds 16.5 atomic%, the R-rich phase in the alloy is reduced. The ratio increases and the corrosion resistance decreases, and further, the volume ratio of the main phase inevitably decreases, so the residual magnetic flux density Br decreases.
When the content ratio of boron constituting the raw material alloy (a) is less than 4.7 atomic%, the ratio of the main phase decreases, the residual magnetic flux density Br decreases, and when it exceeds 7.4 atomic%, B-rich The proportion of phases increases and both magnetic properties and corrosion resistance decrease.
The iron content in the balance M containing iron is preferably 60 atomic% or more, particularly preferably 70 to 84 atomic% in the raw material alloy (a).
The balance M may contain, for example, at least one selected from the group consisting of transition metal elements, silicon, and carbon in addition to iron, and further includes inevitable impurities in industrial production such as oxygen and nitrogen. May be.
Examples of the transition metal element other than iron include titanium, nickel, vanadium, cobalt, aluminum, chromium, manganese, zirconium, hafnium, niobium, magnesium, copper, tin, tungsten, molybdenum, tantalum, ruthenium, rhodium, palladium, Examples include rhenium, osmium, iridium, platinum, gallium, or two or more of these. In particular, when the balance M includes at least one of titanium, nickel, vanadium, chromium, manganese, zirconium, hafnium, niobium, molybdenum, tantalum, tungsten, ruthenium, rhodium, palladium, rhenium, osmium, iridium and platinum, When shear plastic deformation is performed, starting from precipitates of these elements, recrystallization is induced, and refinement is promoted. As for the content rate in the case of including the element which induces these recrystallization and promotes refinement | miniaturization, 0.005-1.00 atomic% is preferable in a raw material alloy (a). If it is less than 0.005 atomic%, the amount of precipitation is small and the effect is not sufficient, and if it exceeds 1.00 atomic%, the magnetic properties are adversely affected.
The raw material alloy (a) has, for example, an ingot cast by a mold method, a thin ribbon made of amorphous or fine crystal grains cast under ultra-rapid cooling conditions such as melt span, or a plate-like crystal structure cast by a strip casting method. Examples thereof include thin ribbons, powders obtained by pulverizing them, and compacts obtained by compacting them.
In the production method of the present invention, next, the step (B) of shear plastic deformation of the raw material alloy (a) is performed.
In the step (B), the shear plastic deformation means that the raw material alloy (a) is a raw material that passes through a path bent at an angle of more than 0 ° and less than 180 ° so as to apply a strong strain along a certain shear plane. It means that the alloy (a) is extruded and deformed. Hereinafter, the alloy obtained by shear plastic deformation of the raw material alloy (a) and the pre-magnetization alloy may be referred to as shear plastic deformation alloy. For example, a deformation process as shown in FIG. Here, the shear plastic deformation includes processing in which the cross-sectional area becomes smaller in the traveling direction in which the raw material alloy (a) is extruded. However, when the cross-sectional area becomes extremely small before and after processing, the compressive stress from the mold wall surface increases, and the above-mentioned effect due to shearing force may not be sufficiently obtained. It is preferred to shear plastically deform to be the same. Examples of such a shear plastic deformation method include an ECAP method (also referred to as ECAE method) proposed by Segal et al. By applying shear plastic deformation, a large shear plastic deformation corresponding to an elongation of 200% or more, preferably 10,000% or more can be applied to the raw material alloy (a). Moreover, when using the curved channel | path like FIG. 1, the angle is preferable 60-120 degrees. If the angle is less than 60 °, the deformation resistance may be large and processing may be difficult. If the angle exceeds 120 °, the amount of strain tends to be small and the above effects tend not to be obtained.
The shear plastic deformation causes refinement of crystal grains on the shear plane, and further slipping with respect to the specific crystal plane, so that the crystal axis is highly oriented in a specific direction. As a result, a rare earth-iron-boron magnet having a high coercive force and a high anisotropic ratio can be obtained.
The shear plastic deformation can be performed by maintaining the raw material alloy (a) in a temperature range of usually 500 to 1200 ° C, preferably 800 to 1150 ° C, more preferably 850 to 1100 ° C. If the temperature is less than 500 ° C., the deformation resistance is large and uniform deformation is difficult, and the alloy is liable to break or crack. This is not preferable because it may become liquid and unworkable. . The crystal axis orientation and crystal grain refinement become more significant as the temperature is lower, but the deformation resistance increases and the workability deteriorates. Therefore, the optimum temperature is appropriately determined based on the balance between these two factors. be able to.
The shear plastic deformation can be performed a plurality of times. Although the orientation of the crystal axes is increased by shear plastic deformation, the orientation of the crystal axes can be further increased by repeating the deformation with the shear direction being constant. The shear plastic deformation is preferably performed continuously in a casting atmosphere after the casting of the magnet raw material alloy in the step (A) after the casting. For example, shear plastic deformation is performed before the alloy cast by the molding method is cooled to room temperature in a non-oxidizing atmosphere. Thus, by continuously performing the steps (A) to (B), the efficiency is improved, the contact with the atmosphere can be reduced most, and the residual heat after cooling of the cast raw material alloy (a) is utilized. Thus, shear plastic deformation can be performed, and energy required for heating can be reduced again. When using a ribbon made of amorphous or fine crystal grains cast under ultra-rapid cooling conditions such as melt span, a ribbon having a plate-like crystal structure cast by a strip casting method, or a powder thereof, before step (B) The step (A-1) of compressing and compacting (integrating) the alloy ribbon or alloy powder may be performed. In the step (A-1), the consolidation can be performed by a method of compressing the ribbon or powder at a pressure of 50 to 200 MPa while preferably heating to 600 to 1000 ° C. By carrying out such a step (A-1), uniform strain can be applied to the raw material alloy (a) in the step (B).
In the step (B), if necessary, at least one of the magnet raw material alloy before shear plastic deformation and the shear plastic deformation alloy after shear plastic deformation can be heat-treated. In short, the heat treatment can be performed before or after the shear plastic deformation, or both before and after. The heat treatment can be performed independently by heating at least one of the magnet raw material alloy and the shear plastic deformation alloy at 500 to 1150 ° C., particularly 500 to 1000 ° C., and each heat treatment time is preferably 0.5 to 10 hours. . By performing a heat treatment before the shear plastic deformation to make the structure of the magnet raw material alloy uniform, the crystal grains of the shear plastic deformation alloy obtained by shear plastic deformation become more uniform and the crystal axes are oriented. It becomes possible. Moreover, by performing heat treatment after the shear plastic deformation, the strain of the obtained shear plastic deformation alloy can be relaxed and the coercive force can be improved. The shear plastic deformation alloy obtained by the step (B) can be made into a desired permanent magnet by applying a magnetic field by a known method or the like.
In the production method of the present invention, the step (C) of pulverizing the shear plastic deformation alloy obtained by the step (B) and the step of solidifying the obtained powder with a binder (D) And can be further performed.
The step (C) is, for example, hydrogen pulverization and mechanical pulverization in which a shear plastic deformation alloy that has undergone shear plastic deformation is hydrogenated in a temperature range of room temperature to 600 ° C., a number of fine microcracks are introduced into the alloy, and then dehydrogenation is performed. Etc. can be carried out as appropriate, and a powder having a high coercive force can be obtained.
In the step (D), the powder prepared in the step (C) can be kneaded with a binder according to a known method for producing a bonded magnet and molded to obtain a bonded magnet. As a binder to be used, it can select suitably according to the kind of bond magnet, For example, a metal and an alloy other than a thermoplastic resin and a thermosetting resin can also be used. A desired permanent magnet can be obtained by applying a magnetic field by a known method at the time of molding or after molding.
The manufacturing method of the rare earth-iron-boron magnet of the present invention is not a hot process such as a sintering method, rolling, or extrusion, but is performed by shear plastic deformation. A bonded magnet can be obtained easily.

  Hereinafter, although an example and a comparative example explain the present invention still in detail, the present invention is not limited to these.

When the alloy composition is the composition (A) shown in Table 1, using rare earth metals, iron, and ferroboron as raw materials and melting by high frequency heating using an alumina crucible in an argon gas atmosphere, the molten metal becomes uniform. A slab was produced by a strip casting method of pouring on a copper water-cooled single roll. The thickness, major axis grain size and minor axis grain size of the obtained slab were measured. The thickness of the slab was determined by measuring the thickness of 50 slabs with a micrometer and calculating the average value. The major axis grain and minor axis grain size are average values of major axis axis and minor axis grain size of 50 main phase grains randomly selected by observing a cross section in the thickness direction of the slab with an optical microscope. It is. The results are shown in Table 2.
Subsequently, the obtained slab was put into a φ30 die and compacted by hot pressing at a molding pressure of 100 MPa at 900 ° C. for 2 hours. The obtained compacted body 10 was supplied to a die 13 by a press 11 as shown in FIG. In FIG. 1, the cross-sectional areas of the compact 10 before and after the shear plastic deformation are both φ30, and the traveling direction of the compact 10 is bent 90 ° before and after the shear plastic deformation. At this time, the container was preheated to 600 ° C. The same shear plastic deformation was repeated four times with the shear direction kept constant. Subsequently, the obtained shear plastic deformation alloy was heat-treated at 550 ° C. for 2 hours. The obtained shear plastic deformation alloy was magnetized with an applied magnetic field of 25 kOe using a DC sample magnetometer to form a permanent magnet, and the magnetic properties were measured. The results are shown in Table 3.

Examples 2-6

  Shear plastic deformation alloys were produced in the same manner as in Example 1 except that the alloy composition was changed to the compositions (B) to (F) shown in Table 1. About each obtained shear plastic deformation alloy, it magnetized like Example 1 and it was set as the permanent magnet, and the magnetic characteristic was measured. The results are shown in Table 3.

  The raw materials were blended and dissolved so that the alloy composition became the composition (C) shown in Table 1, and a magnet raw material alloy was produced by a φ30 copper mold. The obtained magnet raw material alloy was homogenized by heat treatment at 1100 ° C. for 20 hours. The heat-treated magnet raw material alloy was subjected to cross-sectional structure observation by EPMA composition image, and the equivalent circle diameter of each crystal grain was measured. The average equivalent crystal grain size was determined by measuring the equivalent circle diameter of 20 crystal grains at random and found to be 142 μm. The homogenized magnet raw material alloy was subjected to shear plastic deformation and heat treatment in the same manner as in Example 1 to produce a shear plastic deformation alloy. The obtained shear plastic deformation alloy was magnetized in the same manner as in Example 1 to obtain a permanent magnet, and the magnetic properties were measured. The results are shown in Table 3.

  The raw materials were blended and dissolved so that the alloy composition became the composition (C) shown in Table 1, and a slab was produced by a melt span method using a copper water-cooled single roll. When the obtained slab was measured with an X-ray diffractometer, it was amorphous. Next, the thickness of 50 slabs was measured with a micrometer, and the average value was determined to be 35 μm. A shear plastic deformation alloy was produced from the obtained slab in the same manner as in Example 1. The obtained shear plastic deformation alloy was magnetized in the same manner as in Example 1 to obtain a permanent magnet, and the magnetic properties were measured. The results are shown in Table 3.

A shear plastic deformation alloy was produced in the same manner as in Example 1 except that the shear plastic deformation was performed twice. The obtained shear plastic deformation alloy was magnetized in the same manner as in Example 1 to obtain a permanent magnet, and the magnetic properties were measured. The results are shown in Table 3.
Comparative Examples 1-6
Using a molten alloy having compositions (A) to (F) shown in Table 1, an alloy cast compact 10 was manufactured in the same manner as in Example 1. The obtained compacted body 10 was plastically deformed using a press 21 as shown in FIG. 2 and a φ23 die 23 designed with an extrusion ratio of 7. At this time, the container was preheated to 600 ° C. The obtained plastic deformation alloy was magnetized in the same manner as in Example 1 to obtain a permanent magnet, and the magnetic properties were measured. The results are shown in Table 3.
Comparative Examples 7-12
Using a molten alloy having compositions (A) to (F) shown in Table 1, an alloy cast compact 10 was manufactured in the same manner as in Example 1. As shown in FIG. 3, the obtained compacted body 10 was uniaxially compressed by a press 31 and plastically deformed at a processing rate of 80%. The obtained plastic deformation alloy was magnetized in the same manner as in Example 1 to obtain a permanent magnet, and the magnetic properties were measured. The results are shown in Table 1.

Claims (12)

Magnet raw material having a composition comprising 11.3% to 16.5 atomic% of R consisting of at least one rare earth metal element including yttrium, 4.7 to 7.4 atomic% of boron, and the balance M including iron A method for producing a rare earth-iron-boron permanent magnet comprising a step (A) of preparing an alloy and a step (B) of shearing plastic deformation of the magnet raw material alloy. The manufacturing method of Claim 1 which performs the shear plastic deformation of a process (B) by ECAP method. The manufacturing method of Claim 1 which performs the shear plastic deformation of a process (B) on the conditions by which a magnet raw material alloy is hold | maintained at the temperature range of 500-1200 degreeC. The manufacturing method according to claim 1, wherein in the step (A), the magnet raw material alloy is prepared by preparing a magnet raw material alloy by casting, and the step (B) is continuously performed following the casting. The manufacturing method according to claim 1, wherein the step (B) includes a step of heat-treating at least one of the magnet raw material alloy before shear plastic deformation and the shear plastic deformation alloy after shear plastic deformation. The manufacturing method according to claim 5, wherein the heat treatment is performed by heating at least one of a magnet raw material alloy and a shear plastic deformation alloy at 500 to 1150C. The manufacturing method of Claim 1 including the process (A-1) of compacting a magnet raw material alloy after a process (A) and before a process (B). The manufacturing method according to claim 7, wherein the consolidation in the step (A-1) is performed by pressurizing at 50 to 200 MPa while heating the magnet raw material alloy to 600 to 1000 ° C. The manufacturing method according to claim 1, wherein in the step (B), the shear plastic deformation is repeated a plurality of times. In the magnet raw material alloy prepared in the step (A), the balance M is titanium, nickel, vanadium, chromium, manganese, zirconium, hafnium, niobium, molybdenum, tantalum, tungsten, ruthenium, rhodium, palladium, rhenium, osmium, iridium and The manufacturing method of Claim 1 containing the at least 1 sort (s) of transition metal selected from the group which consists of platinum. The magnet raw material alloy prepared in step (A) is made of titanium, nickel, vanadium, chromium, manganese, zirconium, hafnium, niobium, molybdenum, tantalum, tungsten, ruthenium, rhodium, palladium, rhenium, osmium, iridium and platinum. The production method according to claim 1, comprising 0.005 to 1.00 atomic% of at least one transition metal selected from the group consisting of more than one kind. The manufacturing method of Claim 1 including the process (C) which grind | pulverizes the shear plastic deformation alloy obtained at the process (B), and the process (D) which solidifies the obtained powder with a binder and obtains a bonded magnet.

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