JPH0315806B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermally processed integrated permanent magnet having at least two distinct regions with different magnetic alignments. More specifically, the present invention specifically provides for thermal processing to include regions with different orientations, one having a relatively high apparent coercivity and the other having a relatively high remanence. was done,
The present invention relates to a permanent magnet containing iron, neodymium and/or praseodymium, and boron.

For example iron, neodymium and/or praseodymium,
A high energy product, high coercive force permanent magnet consisting of boron and boron, and its manufacturing method are European public authorities patent application EP
-A-0108474 and EP-A-0144112. The composition of one of these is shown in the form of atomic ratio.
Nd _0.13 (Fe _0.95 B _0.05 ) _0.87 . This is a composition containing certain safe intermetallic phases with maximum dimensions of approximately 20
It exhibits high coercive force when formed into fine crystallites of ~400 nanometers.

A suitable iron/light rare earth metal/boron composition melt can be very quickly quenched into a solid object, such as a thin ribbon, by methods such as melt spinning. By controlling the cooling rate to a suitable microcrystalline microstructure (20-400 nm), the material exhibits excellent permanent magnetic properties. On the other hand, when the cooling rate is increased (supercooling), the crystallites become smaller and the coercive force also decreases. However, as disclosed, such superquenched materials can also be annealed to suitably sized crystals with high coercivity and high energy product.

An interesting and useful property of the (for example) neodymium-iron-boron composition is that it is substantially magnetically isotropic.

The melt-spun ribbon of particulates can be crushed into fine tabular pieces. This fine piece is pressed with a die at room temperature until the density is approximately that of the material.
Can form a unified object at 85%.
A binder may be used before or after consolidation. The manufacturing method for this type of bonded magnet is
It is disclosed in European Patent Publication No. EP-A-0125752. Surprisingly, it was found that this type of coupled magnet does not exhibit a preferential magnetic orientation.
The value of the intrinsic coercive force or the highest energy product was independent of the direction of the applied magnetic field. There was no advantage to grinding the ribbon into very fine particles and magnetically aligning the particles before consolidation.

Such isotropic materials are very useful because they can be easily pressed into composite shapes (without magnetic alignment). This shaped body can be magnetized in the most convenient direction.

Iron-, neodymium-, and boron-based compositions can also be physically arranged by hot pressing or thermal processing so that at least some of the particles or crystals are arranged magnetically. Ta. As disclosed in European Patent Publication EP-A-0133758, such thermally processed materials had a preferred magnetization direction. According to one embodiment disclosed in the above-mentioned application, a molten material containing Nd _0.13 (Fe _0.95 ) _0.87 in an atomic ratio is extremely rapidly cooled by melt spinning or the like, and a thin material having no permanent magnetic properties is obtained. A ribbon-like solid material was formed. The microstructure of this material was amorphous. This ribbon was ground into strips of convenient size for thermal processing operations. The strip is heated in an argon atmosphere to about 700°C or higher in a die to a temperature of at least 68947.6KPa.
Pressed with a punch in a die under pressure (10000psi). Such heat processing operation (hereinafter referred to as hot processing)
(called a press), the pieces coagulated into a completely dense object.

If the thermal processing operation is stopped at the point where the material has agglomerated to saturation density, a slightly magnetically aligned magnet will result with the direction of easy magnetization parallel to the pressing direction.
The demagnetization curve (room temperature, second quadrant, H vs. 4πM plot) of this type of densified magnet has the form of curve A in FIG. 1 of the accompanying drawings.

When a sufficiently dense compact is pressed again in a larger die cavity under similar high temperature and pressure conditions, the compact undergoes significant plastic strain in a plane perpendicular to the pressing direction. This second thermal processing operation is called die-upsetting and results in significant magnetic alignment in the easy magnetization direction transverse to the direction of plastic strain. The demagnetization curve of such a die-upest body is shown as curve B in FIG. 1 of the accompanying drawings. Looking at the demagnetization curves in FIG. 1, it can be seen that the degree of magnetic alignment of the hot-pressed magnet (curve A) and the die-upset magnet (curve B) is significantly different. Hot-pressed magnets have a relatively higher coercive force and lower residual magnetism in the pressing direction than die-upset magnets. Die-upset magnets have a higher maximum energy product, but are more susceptible to demagnetization than hot-pressed objects of the same composition. There are several uses for magnets in which it is desirable to have both properties in an integrated magnet body.

It is an object of the present invention to provide a method of thermal processing of a permanent magnetic body that creates at least two regions located along a surface portion of the body and having different desired magnetic alignments. Generally speaking, one of the above regions has a higher apparent coercive force than the other regions, but a smaller residual magnetism. It is specifically contemplated to apply this method to quenched compositions comprising iron, neodymium and/or praseodymium and boron.

It is another object of the present invention to provide an integrated magnetic structure that can be selectively thermally processed to include discrete regions of different magnetic alignment.

An example of such a magnetic structure is an arcuate magnet for a permanent magnet motor. It is contemplated that one or both ends of the periphery of the arc may be processed so that the coercive force is relatively high, and the central portion of the arc is made to have a relatively large residual magnetism. In this case too, it is particularly contemplated that the magnet be of the iron/light rare earth/boron composition mentioned above.

In accordance with preferred embodiments of the invention, these and other objects and advantages are achieved as follows.

The starting material is a quenched composition of iron, neodymium and/or praseodymium and boron. An example of a suitable composition is Nd _0.13 expressed in atomic proportions.
(Fe _0.95 B _0.05 ) _0.78 . The starting material has an amorphous microstructure but is characterized by an extremely fine crystalline structure. Starting from something with such an amorphous or particulate microstructure,
It is desirable to be able to perform thermal processing without losing the appropriate coercivity of the final product.

A fine piece of melt-spun material is placed within the cavity of an open-ended die between two opposing punches.
The fine pieces are heated in a die to a suitable temperature (suitably about 700° C. or higher) and compacted under a suitable pressure to form a sufficiently dense object. As will be discussed later, the agglomerated body is split-ram punched in the die so that a gradual thickness change is created across its cross section.
ram punch) can be used. While the next die is still hot, the ends of each punch (of the split ram) are brought into line and moved simultaneously so that some of the agglomerated parts undergo further thermal processing. In this case, during the thermal processing operation, the hot portions of the flesh in the irregularly agglomerated portions are subjected to different strains than the thin portions.
Due to the different degrees of strain across the cross-section, two regions with different magnetic alignments generally result. The region that has received the strongest strain in the direction perpendicular to the pressing direction is more strongly aligned and draws a demagnetization curve like curve B in FIG. Areas that were not deformed (or had small deformations) due to the secondary pressing operation are:
It has a low degree of magnetic alignment and exhibits magnetic properties as shown by curve A in FIG.

The above describes an example of creating different regions in a composition of iron, onedymium and/or praseodymium and boron by thermal processing operations, thus intentionally creating different magnetic alignments. A unified object with ivy areas is formed. A typical field of application for the invention is arcuate magnets for motors, where the leading edge of the arcuate magnet (of a motor rotating in only one direction) experiences a greater demagnetizing force than the rest of the arcuate magnet.

In such applications, the leading edge of the bow magnet is engineered to have a high apparent coercivity (measured radially with respect to the bow magnet), while the rest of the bow magnet has a relatively high remanence and high energy. It is heat processed to maximize the product.

The invention will be better understood from the detailed description thereof below. This will be explained with reference to the attached drawings, in which Figure 1 shows the second quadrant of the hot-pressed magnet (curve A) and the die-leg magnet (curve B), versus room temperature H.
Figures 2a-c are partial cross-sectional views of two different die combinations illustrating the sequence of die operations during the forming of a heat-worked arcuate magnet; Figures 3a and b are 4a and 4b are schematic diagrams of a section of a split ram die showing a split ram die in two different operating states; FIGS. FIG. 5 is a cross-sectional view of a thermally processed arcuate magnet having adjacent regions with different magnetic alignments according to the present invention; FIGS. 6a and b are diagrams showing an embodiment of the present invention Figure 5 according to the example
FIG. 2 is a schematic diagram illustrating a method of manufacturing an arcuate magnet similar to that described in FIG.

FIG. 7 further illustrates another die forming method for forming a permanent magnet having regions with at least two different magnetic orientations.

The present invention can be applied to a permanent magnet composition that can be magnetically aligned by plastic deformation of the material at high temperatures. An example of a preferred group of compositions to which the method of the invention can be applied are the transition metal/rare earth metal/boron materials mentioned in the above-mentioned patent applications. The invention is particularly applicable to such compositions in which the transition metal components are iron or iron and one or more of cobalt, nickel, chromium or manganese. Cobalt is interchangeable with iron up to about 40 atomic percent. Chromium, manganese and nickel can be interchanged in smaller amounts, preferably up to 10 atomic percent. Zirconium and/or titanium can replace iron in small amounts (up to 2 atomic percent of iron). The presence of very small amounts of carbon and silicon is acceptable if the source of iron in the composition is a low carbon steel. Preferably, the composition contains from about 50 atomic percent to about 90 atomic percent of a transition metal component, primarily iron.

The composition also includes from about 10 atomic percent to about 50 atomic percent rare earth components. Neodymium and/or praseodymium are the basic rare earth constituents. As mentioned above, these can be used interchangeably. Relatively small amounts of other rare earth elements such as samarium, lanthanum, cerium, terbium and dysprosium can also be mixed with neodymium and praseodymium without significantly detracting from the desirable magnetic properties. Preferably, these components do not constitute more than about 40 atomic percent of the rare earth component. It can be expected that the rare earth component contains a small amount of impurity elements.

The supercooled composition contains about 1 to 10 atomic percent boron.

The overall composition can be expressed by the formula RE _1-X (TM _1-y B _y ) _X. The rare earth (RE) component represents 10 to 50% by weight of the composition (x=0.5 to 0.9), and at least 60 atom % of the rare earth component is neodymium and/or praseodymium. The transition metals (TM) used in the cassettes account for about 50-90% of the total composition, with iron accounting for at least 60 atomic percent of the transition metal content. As far as the above empirical formula is concerned, other constituents such as cobalt, nickel, chromium and manganese are referred to as "transition metals".

The amount of boron in the entire composition is about 1 to 10 atomic percent (y=about 0.01 to 0.11).For convenience, the composition is expressed in atomic percentages. It is clear that the numerical values in this case can be easily converted into weight ratios in the preparation of mixed compositions.

For purposes of illustration, the invention will be described using compositions having approximately the following atomic ratios.

Nd _0.13 Fe _0.95 B _0.05 ) _0.87 However, it should be understood that the method of the present invention is also applicable to other compositions such as those mentioned above.

Depending on the cooling rate, the molten composition of transition metals, rare earths, and boron can solidify into a state with a microstructure in the following range: (a) Amorphous (glass-like) with extremely fine grains; (b) microstructures containing very fine (micro) particles (e.g. 20 nm to about 400 nm) to (c) microstructures with larger particles. to.

To date, no large-grained microstructured material with useful permanent magnetic properties has been produced by a rapid solidification process from a melt. Particulate structures with particle maximum dimensions of approximately 20 to 400 nanometers possess useful permanent magnetic properties. This is not the case with amorphous materials. However, some of the glassy microstructured materials can be annealed to convert them into small-grain permanent magnets with isotropic magnetic properties. The invention applies particularly to such over-quenched glassy materials. The present invention is also applicable to high coercivity, fine-grained materials "as quenched" where the material is exposed to high temperatures above 700° C. for a short period of time, i.e., for less than 5 minutes, during thermal processing. .

Suitable superquenched compositions may be made by melt spinning. The melt spinning process is described in the above-mentioned application and will not be repeated here. This method is also used industrially to produce non-magnetic or soft magnetic alloys. It is preferred to use melt spun materials that are cooled at a rate such that an amorphous or extremely fine crystalline structure results. Iron, neodymium,
In the case of boron compositions, it is desirable to start with a rapidly solidifying structure with particle sizes less than about 20 nanometers. Next, heat these ingredients to about 700 ml.
Processing in a die at temperatures of ~750°C agglomerates the material particles into a completely dense mass and then selectively plastically deforms the agglomerated object to yield regions with different magnetic alignments. Such operations are carried out fairly quickly so that excessive particle growth does not occur and permanent magnetic properties are not lost.

Related information has already been shown in FIG. 1, which graphically illustrates the demagnetization characteristics of a hot-pressed iron-neodymium-boron magnet (curve A) and a die-upset magnet (curve B) of the same composition. Hot pressed magnets are only moderately aligned magnetically and have a relatively high coercive force in the pressing direction. The die upsetting magnet has been significantly plastically deformed. The material has reached a relatively high state of alignment. Its coercive force in the pressing direction is therefore reduced, but its residual magnetism is increased.

In this work, it was observed that the heat-processed magnets exhibited magnetic alignment in the direction perpendicular to the direction of plastic flow. When such plastic flow occurs perpendicular to the pressing direction (the direction of movement of the punch), the magnetic alignment state is parallel to the pressing direction. When measuring the magnetic properties of such an anisotropic magnet, such as coercive force and remanence, unless otherwise specified, the measured values in the preferred (alignment) direction are detected and described.

A method of forming magnetically aligned arcuate permanent magnets by die upsetting is illustrated in FIG. A fine piece of melt spun material is loaded into a cavity consisting of a through die 10 and vertically aligned opposed punches 12 and 14 as shown in Figure 2a. The die and its contacts are heated to or near 700° C. with an induction heater (not shown). The punches 12 and 14 are under a certain pressure, e.g.
The particulate material is consolidated under a pressure of 15000 psi into the substantially fully densified body shown within the die cavity of Figure 2a. The arrow within the outline of object 16 indicates that the densified compact is substantially unoriented. However, there is a slight selectivity in the direction of consolidation. The magnetic properties of this compact are as shown in curve A of FIG.

The compact 16 is then transferred to a larger die 18 having opposed punches 20 and 22, as shown in Figure 2b. The cavity is similarly heated to maintain Compact 16 at or near 700°C. Then punch 20 and 22 with compact 16.
The die is plastically deformed to form an arcuate object 24. Although the material flows laterally, the direction of alignment, the direction of easy magnetization, is perpendicular to the plastic flow, ie, generally in the direction of pressing, as indicated by the arrows in Figure 2c. The resulting arcuate magnet 24 is wider and thinner than the compact 16. The magnets 24 become highly aligned in a substantially uniform radial manner about the center of curvature. Figure 2
A cross section of the magnet 24 is shown in FIG. If shown in perspective, it would look like the magnet 36 shown in Figure 4b. Such an arcuate magnet 24 could be made in a manner similar to that described in the European patent application EP-A-0133758 mentioned above.

In accordance with the present invention, an integral arcuate magnet or other permanent magnet structure is created having at least two regions of different magnetic alignment. In one embodiment of the invention, densified compacts with different cross-sectional thicknesses are first hot pressed. One convenient procedure is to mold compacts that vary in thickness abruptly or in steps. For this purpose, a split lamb die as shown in FIG. 3 may be used. As shown, this type of die uses a conventional die body 25, but the upper and lower punches 26 and 28 are split into two parts 26', 26'' and 28', 28 of each punch. '' can work simultaneously, as shown in FIG. 3a, or separately, as shown in FIG. 3b. This type of split punch, i.e. split ram,
Using the die arrangement in a hot press, the finely divided melt-spun material can be solidified into a compact shape as shown in Figure 4a.

Hot pressed arcuate compact 3 in Figure 4a
In the case of 0, the density is almost uniform and the magnetic arrangement state is random (that is, an irregular arrangement state), but there is a stepwise difference in thickness. A perspective view (FIG. 4a) of the arcuate compact 30 shows a relatively thicker section 32 and an adjacent thinner section 34. The length of the string of Compact 30 is L. This arc can be made with a split lamb die with a moving split punch as shown in Figure 3b. By producing the hot-pressed densified compact 30 having such a configuration, it is possible to create a die-upset curved agglomerate having a uniform thickness but regions having different magnetic alignment states. As shown in Fig. 4b, Fig. 4
The compact in a is pressed in a die or cavity with a wide cross-sectional area, heated to a temperature of about 700℃,
Although it is heat-treated and has a long length (as shown in Figure 4, the length of the string is
L'>L) Use a thin arcuate magnet 36. Because cross-section 32 of compact 30 in FIG. 4a was thicker than cross-section 34, the extent of plastic deformation and flow at cross-section 32 is greater. Accordingly, the aforementioned point 32 of the compact 30 undergoes significant lateral distortion, resulting in a curved region 38 of the die upsetting magnet 36 in FIG. 4b. Thus, the area 38 of the final arcuate magnet 36 is shown in FIG. 4b.
As shown in the figure, the magnetic field becomes highly aligned. In contrast, the region 34 of the compact 30 undergoes relatively little deformation, and therefore the region 40 of the magnet 36 is hardly aligned. Region 40 has magnetic properties as in curve A of FIG. 1, and region 38 has magnetic properties as in curve B. Thus, as seen in Figure 4b, the arcuate magnet 3
The right peripheral portion 40 of 6 has a higher coercive force than the rest of the single magnet. These characteristics mean that the demagnetizing force acts most strongly on the front of the magnet.
Particularly useful for arcuate pole pieces in DC motors.

FIG. 5 is a side view of a two-area magnet 42 illustrating the general principles of the invention. One (or both) of the curved ends of the magnet 42 (region 46) is schematically shown in the direction of the arrow in the figure oriented at an angle θ (θ≠0) with respect to the radial direction of this arcuate curve. It has a certain magnetic orientation state. The rest of the magnet 44
are processed so as to be magnetically oriented in the radial direction with respect to the center of the curved line, as shown by the arrow in region 44. Thus, regions 44 and 46 are both highly oriented and exhibit relatively high remanence in the alignment direction. However, the edge region 46 is relatively difficult to demagnetize due to the countermagnetic field produced by the motor armature.

There is a two-area magnet of this type which constitutes another embodiment of the invention. A two-area magnet such as that shown in FIG. 5 can be made by the procedure illustrated in FIGS. 6a and b. A die upsetting permanent magnet 48 of a warped shape as shown in FIG. 6a is made. A hot press compact is first made and then the die is upset into the shape of Figure 6a by applying strain forces in the directions indicated. Although the die upsetting magnet 48 is warped, its magnetic orientation is
They are parallel throughout the cross section. While it's still warm,
The warped object 48 is passed through the opposing punch 52 of the die 50.
and 54 into an arcuate permanent magnet like 42 in FIG. By bending the original magnet in the opposite direction, an arcuate magnet (such as 42) with different regions (such as 44 and 46) of lateral magnetic alignment as illustrated in FIG. 5 is created. climb.

FIG. 7 also illustrates another die forming procedure for producing a two-zone permanent magnet in accordance with the present invention.
First, the non-curved compact 56 has different thicknesses in stages.
The hot pressed compact 56 has a relatively thick section 58 and a thin section 60. The compact is made in die 62 using split punches 64 and 66 operating in a stepped manner. Next, the punches are moved back slightly and used side by side to thin the inner thick part 58 of the compact and thicken the thin part 60 of the compact 56.
In this example, a flat object 6 has regions of different magnetic alignments due to different plastic flows.
8 (dashed line). In FIG. 7, the arrows indicate the direction of strain rather than the direction of magnetization. The magnetization direction will be perpendicular to the strain as mentioned before.

As described above, according to the present invention, an integrated magnetic material having two or more regions of different magnetic alignment can be produced. It is preferable for the regions to be separated along the surface direction rather than for one region to be wrapped within another region. This separation of regions along the surface dimension is illustrated by regions 38 and 40 of arcuate magnet 36 and regions 44 and 46 of arcuate magnet 42. In both cases, the regions are separated in the circumferential direction of the archwire. Regions of different magnetic alignment can be created by selectively thermally processing magnetic material objects in a variety of ways. Different parts of an object will strain to different degrees or in different directions at high temperatures. Such an effect can be achieved, for example, by starting from densified compacts of different thicknesses and molding them into products of uniform thickness in a die upsetting operation. In another specific example, magnetic material objects in a uniform parallel arrangement (Fig. 6
The two magnetic structural parts may be created by bending at high temperatures (as shown in Figure 1).

The invention can also be practiced using fine pieces from melt-spun ribbons in combination with pre-hot pressed compacts. Heat processing compacts or fine pieces from different parts of the same die, upsetting the compact (for example) into the die, hot-pressing the fine pieces and hot-pressing them together to maximum density (or near maximum density), Create an integrated object with regions with different arrangement states.
In this embodiment, different compositions could be used for the initial compact and the added fines.

The present invention is particularly useful in the production of transition metal, rare earth, and boron based magnets of the type described above. However, other magnetic compositions that can be magnetically aligned by plastic deformation at suitable elevated temperatures may also be used.

The term ``permanent magnet'' or ``hard magnet'' used in the book refers to magnets with a sufficiently large intrinsic coercive force, e.g.
It means a material with a coercive force of 1000 oersted or more.

[Brief explanation of the drawing]

Figure 1 shows the second quadrant room temperature H vs.
This is a plot of 4πM. Figures 2a-c are schematic diagrams showing partial cross-sections of two different die combinations illustrating the sequence of die operations during the forming of a thermoformed arcuate magnet. Figures 3a and 3b are schematic diagrams showing the split ram die in two different operating states. Figure 4a
and b are schematic cross-sectional views of a hot-pressed compact and a die-upset permanent magnet processed according to the invention. FIG. 5 shows a cross-section of a thermally processed arcuate magnet with adjacent regions of different magnetic alignments according to the invention. 6a and b are schematic diagrams illustrating the fabrication of an arcuate magnet similar to that described in FIG. 5 in accordance with one embodiment of the present invention. FIG. 7 further illustrates another die forming method for forming a permanent magnet having regions with at least two different magnetic orientations. [Explanation of numbers for main parts], 36, 42, 68
...Object, 38, 40, 44, 46, 58, 60
... Area, 30, 48, 56... Densified object.

Claims (1)

[Claims] 1. A permanent magnet body having first and second regions having different magnetic properties, in which the objects 36; 42; 68 have one or more compositions of iron, neodymium, and/or praseodymium and boron. the first and second regions 38; 40; 44; 46; 5;
8; 60 is arranged along the surface direction of the objects 36; 42; 68, and the objects 36; 42; 68 are heat-processed so that the magnetic arrangement states thereof are different from each other. body. 2 The arcuate object 36; 42 has one end 40; 46
said first region located in and said arcuate object 36; 42;
The second region 3 located at the center of the surface of
8; 44, and the object 36; 42 is thermally processed so that the first region has a higher coercive force than the second region when measured in the radial direction of the arcuate object 36; 42. , the object is an arcuate object 36;
42. A permanent magnet according to claim 1, wherein the permanent magnet body is 42. 3 The object 36; 42 is one end of the arcuate pole magnet 40; 4
The saturation coercive force measured in the radial direction of the arcuate pole magnet in the first region 40; is larger than the second region,
The residual magnetism measured in the radial direction is the second region 38;
Claim 1: The object is shaped into an arcuate pole magnet for an electric motor, characterized in that the object is non-uniformly thermally processed so that the first area 44 is larger than the first area 40; 46. permanent magnetic body. 4. A permanent magnetic body having first and second regions of different magnetic properties, wherein the object 36; 42; 68 comprises one or more compositions consisting of iron, neodymium and/or praseodymium and boron, and The first and second regions 38; 40; 44; 46; 5
8; 60 is arranged along the surface direction of the object 36; 42; 68, and the said object 36; 42; 68 is heat-processed so that the magnetic arrangement state mutually differs. hot-pressing fine pieces of a composition comprising iron, neodymium and/or praseodymium and boron and having an intrinsic room temperature coercivity greater than about 1000 Oersteds to produce a substantially fully densified object 30 of the same composition; 48; 56, and then nonuniformly heat-processes the object 30; 48; at least two of the above regions 38; 40;
44; 46; 58; 60; 5 Substantially fully densified object 30; 56
but at least two portions 32 having different cross-sectional thicknesses;
34; 58; 60, the object 30; 56 is thermally processed to reduce the thickness of the thick portion 32; 58, and the at least two regions 38; 40; 58 have different magnetic alignment states; 5. The method of manufacturing a permanent magnet according to claim 4, wherein the permanent magnet is heat-processed so that the permanent magnet 60 is disposed in the heat-processed object along the surface direction thereof. 6. A substantially fully densified object is charged into a die with fine pieces of a composition of iron, neodymium and/or praseodymium and boron having an inherent room temperature coercivity greater than about 1000 Oersteds, the fine pieces being The above-mentioned first and second pieces are hot-pressed and heat-processed to create magnetic alignment states that are different from each other.
5. A method of manufacturing a permanent magnet according to claim 4, characterized in that heat processing is carried out so as to produce an integrated object having a region.