MAGNETIC MATERIAL

Abstract

There is disclosed a magnetic material having a composition in atomic percentage of: (MM1-aRa)uFe100-u-v-w-x-yYvMwTxBy wherein MM is a mischmetal or a synthetic equivalent thereof; R is Nd, Pr or a combination thereof; Y is a transition metal other than Fe; M is one or more of a metal selected from Groups 4 to 6 of the periodic table; and T is one or more of a metal other than B, selected from Groups 11 to 14 of the periodic table, wherein 0≦a≦1, 7≦u≦13, 0≦v≦20, 0≦w≦5; 0≦x≦5 and 4≦y≦12.

Description

TECHNICAL FIELD

The present invention relates to a magnetic material, a bonded magnet incorporating the magnetic material and to a method of making a magnetic material.

BACKGROUND

Isotropic Nd₂Fe₁₄B-type melt spun materials have been used for making bonded magnets for many years. Although Nd₂Fe₁₄B-type bonded magnets are found in many cutting edge applications, their market size is still much smaller than that of magnets made from anisotropic sintered ferrites (or ceramic ferrites). One of the means for diversifying and enhancing the applications of Nd₂Fe₁₄B-type bonded magnets and increasing their market is to expand into the traditional ferrite segments by replacing anisotropic sintered ferrite magnets with isotropic bonded Nd₂Fe₁₄B-type magnets.

Direct replacement of anisotropic sintered ferrite magnets with isotropic bonded Nd₂Fe₁₄B-type bonded magnets would offer at least three advantages: (1) cost saving in manufacturing, (2) higher performance of isotropic bonded Nd₂Fe₁₄B magnets, and (3) more versatile magnetizing patterns of the bonded magnets, which allow for advanced applications. Isotropic bonded Nd₂Fe₁₄B type magnets do not require grain aligning or high temperature sintering as required for sintered ferrites, so the processing and manufacturing costs can be drastically reduced. The near net shape production of isotropic bonded Nd₂Fe₁₄B bonded magnets also represents a cost savings advantage when compared to the slicing, grinding, and machining required for anisotropic sintered ferrites.

The higher B_r values (typically 5 to 6 kG for bonded NdFeB magnets, as compared to 3.5 to 4.5 kG for anisotropic sintered ferrites) and (BH)_max values (typically 5 to 8 MGOe for isotropic bonded NdFeB magnets, as compared to 3 to 4.5 MGOe for anisotropic ferrites) of isotropic Nd₂Fe₁₄B-type bonded magnets also allows a more energy efficient usage of magnets in a given device when compared to that of anisotropic sintered ferrites. Finally, the isotropic nature of Nd₂Fe₁₄B-type bonded magnets enables more flexible magnetizing patterns for exploring potential new applications.

To enable direct replacements of anisotropic sintered ferrites, however, the isotropic bonded magnets should exhibit certain specific characteristics. For example, the Nd₂Fe₃₄B materials should be capable of being produced in large quantity to meet the economic scale of production for lowering costs. Thus, the materials must be highly quenchable using current melt-spinning or jet casting technologies without additional capital investments to enable high throughput production. Also, the magnetic properties, e.g., the B_r, H_ci, and (BH)_max values, of the Nd₂Fe₁₄B materials should be readily adjustable to meet the versatile application demands. Therefore, the alloy composition should allow adjustable elements to control the B_r, H_ci, and/or quenchability. In addition, the isotropic Nd₂Fe₁₄B-type bonded magnets should exhibit comparable thermal stability when compared to that of anisotropic sintered ferrite over similar operating temperature ranges. For example, the isotropic bonded magnets should exhibit comparable B_r and H_ci characteristics compared to that of anisotropic sintered ferrites at 80 to 100° C. and low flux aging losses.

Conventional Nd₂Fe₁₀B type melt spun isotropic powders exhibit typical B_r and H_ci values of around 8.5 to 8.9 kG and 9 to 11 kOe, respectively, which make these type of powders unsuitable for direct replacement of anisotropic sintered ferrite. The higher B_r values could saturate the magnetic circuit and choke the devices, thus preventing the realization of the benefit of the high values. To solve this problem, bonded magnet manufacturers have usually used a non-magnetic powder, such as Cu or Al, to dilute the concentration of magnetic powder and to bring the B_r values to the desired levels. However, this represents an additional step in magnet manufacturing process and thus adds costs to the finished magnets.

The high H_ci values, especially those higher than 10 kOe, of conventional Nd₂Fe₁₄B type bonded magnets also present a common problem for magnetization. As most anisotropic sintered ferrites exhibit H_ci values of less than 4.5 kOe, a magnetizing field with peak magnitude of kOe is sufficient to fully magnetize the magnets in devices. However, this magnetizing field is insufficient to fully magnetize certain conventional Nd₂Fe₁₄B type isotropic bonded magnets to reasonable levels. Without being fully magnetized, the advantages of higher B_r or H_ci values of conventional isotropic Nd₂Fe₁₄B bonded magnet can not be fully realized. To overcome the magnetizing issues, bonded magnet manufacturers have used powders having low H_ci values to enable a full magnetization using the magnetizing circuit currently available at their facilities. This approach, however, does not take full advantage of the high H_ci value potential.

Many improvements of melt spinning technology have also been documented to control the microstructure of Nd₂Fe₁₄B-type materials in an attempt to obtain materials of higher magnetic performance. However, many of the attempted efforts have dealt only with general processing improvements without focusing on specific materials and/or applications.

Highly quenchable Fe-based rare earth isotropic (Pr—Nd—La or Pr—Nd—Ce)—Fe—B type magnetic material alloys which exhibit B_r values between 7 to 8.5 and H_ci values between 6.5 to 9.9 kOe are known. However, a major drawback with these materials is that the Praseodymium (Pr), Neodymium (Nd), and Lanthanum (La) or Cerium (Ce) of which the magnetic alloys are constituted are in highly purified form. The high purity of the Pr, Nd and La or Ce raw material constituents renders the cost of manufacturing the magnetic alloy expensive due to the high cost of refining the Pr, Nd, La and Ce from their natural occurrence in mineral deposits.

Therefore, there is still a need for isotropic Nd—Fe—B type magnetic materials with relatively high B_r and H_ci values and exhibiting good corrosion resistance and thermal stability. There is also a need for such materials to have good quenchability during rapid solidification processes, such that they are suitable for replacement of anisotropic sintered ferrites in many applications. There is also a need for isotropic Nd—Fe—B type magnetic materials that are not made from highly pure refined Pr, Nd, and La or Ce and which are simpler and possibly less expensive to produce compared to other known magnetic alloys made of refined Pr and Nd.

SUMMARY

In a first aspect, there is provided a magnetic material alloy that has the composition, in atomic percentage, of

(MM_1-aR_a)_uFe_{100-u-v-w-x-y}Y_vM_wT_xB_y

wherein

• • MM is a mischmetal or a synthetic equivalent thereof,
  • R is Nd, Pr or a combination thereof,
  • Y is a transition metal other than Fe,
  • M is one or more of a metal selected from Groups 4 to 6 of the periodic table, and
  • T is one or more of a metal other than B, selected from Groups 11 to 14 of the periodic table,
  • wherein 0≦a<1, 7≦u≦13, 0≦v≦20, 0≦w≦5, 0≦x≦5, and 4≦y≦12.

Advantageously, in one embodiment the MM is a mischmetal, which is a naturally occurring mineral which is comprised of Nd, Pr, Ce and La. Accordingly, in such embodiments it is not necessary to refine the Nd, Pr, Ce or La from the mischmetal mineral and hence, the production cost of producing the magnet can be reduced compared to alloys which incorporate Nd, Pr, Ce and La in purified form and does not require the presence of Yttrium to impart magnetic properties on the alloy. Hence, in one embodiment, the magnetic alloy excludes Yttrium. In another embodiment, the magnetic alloy may exclude metals selected from the group consisting of Co, Zr, Nb, Ti, Cr, V, Mo, W, Hf, Al, Mn, Cu and Si.

Advantageously, the disclosed MM-TM-B-type (Mischmetal-Transition Metal-Boron) magnetic materials disclosed in the first aspect may be made in a rapid solidification process. Furthermore, bonded magnets may be produced from the disclosed MM-TM-B-type magnetic materials. The disclosed magnetic materials exhibit relatively high B_r and H_ci values and good corrosion resistance and thermal stability. The materials also have good quenchability during rapid solidification processes. These qualities of the materials make them suitable for replacement of anisotropic sintered ferrites in many applications.

In a specific embodiment, the mischmetal is a cerium-based mischmetal. In yet another embodiment, the mischmetal or synthetic equivalent thereof has the composition of 20% to 30% La, 2% to 8% Pr, 10% to 20% Nd and the remaining being Ce and any incidental impurities. More specifically, the mischmetal or synthetic equivalent thereof has the composition of 25% to 27% La, 4% to 6% Pr, 14% to 16% Nd and 47% to 51% Ce.

In a specific embodiment, the transition metal Y is selected from Group 9 or Group 10 of the periodic table. More specifically, the transition metal Y is Co. In another specific embodiment, the metal M is one or more of Zr, Nb, Ti, Cr, V, Mo, W and Hf. In yet another specific embodiment, T is one or more of Al, Mn, Cu and Si. In specific embodiments of the present invention, M is selected from Zr, Nb, or a combination thereof and T is selected from Al, Mn, or a combination thereof. More specifically, M is Zr and T is Al.

In one embodiment, the values for a, u, v, w, x, and y are independent of each other and fall within the following ranges: 0.2≦a≦0.8, 8≦u≦13, 0≦v≦15, 0.1≦w≦4, 1≦x≦5, and 4≦y≦11. Other specific ranges include: 0.4≦a≦0.8, 10≦u≦13, 0≦v≦10, 0.1≦w≦3, 2≦x≦5, and 4≦y≦10; 0.5≦a≦0.75, 11≦u≦12, 0≦v≦5, 0.2≦w≦2, 2.5≦x≦4.5, and 5≦y≦6.5; and 0.55≦a≦0.7, 11.3≦u≦11.7, 0≦v≦2.5, 0.3≦w≦1, 3≦x≦4, and 5.7≦y≦6.1. In another specific embodiment, the values of a and x are as follows: 0.9≦a≦0.99 and 0.1≦x≦1.

In one embodiment, the values for a, u, v, w, x, and y are independent of each other and fall within the following ranges: 8≦u≦13, 0≦v≦15, 0.1≦w≦4, 1≦x≦5, 4≦y≦11 and a=0. Other specific ranges include: 10≦u≦13, 0≦v≦10, 0.1≦w≦3, 2≦x≦5, 4≦y≦10 and a=0; 11≦u≦12, 0≦v≦5, 0.2≦w≦2, 2.5≦x≦4.5, 5≦y≦6.5 and a=0; and 11.3≦u≦11.7, 0≦v≦2.5, 0.3≦w≦1, 3≦x≦4, 5.7≦y≦6.1 and a=0. In another specific embodiment, the values of a and x are as follows: 0.1≦x≦1 and a=0.

In another embodiment, the magnetic material exhibits a B_r value of from about 7.0 kG to about 9.0 kG and H_ci value of from about 4.0 kOe to about 10.6 kOe. Specifically, the magnetic material exhibits a B_r value of from about 7.0 kG to about 7.8 kG and an H_ci value of from about 4.0 kOe to about 6.8 kOe.

Other specific embodiments include that the material exhibits, as determined by X-Ray diffraction, crystal grain sizes ranging from about 1 nm to about 80 nm.

In a second aspect, there is provided a bonded magnet comprising a magnetic material and a bonding agent, said magnetic material having been prepared by a rapid solidification process, followed by a thermal annealing process, said magnetic material having the composition, in atomic percentage, of

(MM_1-aR_a)_uFe_{100-u-v-w-x-y}Y_vM_wT_xB_y

wherein

• • MM is a mischmetal or a synthetic equivalent thereof;
  • R is Nd, Pr or a combination thereof;
  • Y is a transition metal other than Fe;
  • M is one or more of a metal selected from Groups 4 to 6 of the periodic table; and
  • T is one or more of a metal other than B, selected from Groups 11 to 14 of the periodic table,
    wherein 0≦a≦1, 7≦u≦13, 0≦v≦20, 0≦w≦5; 0≦x≦5 and 4≦y≦12.

The magnetic material of the bonded magnet may have been prepared by a rapid solidification process, followed by a thermal annealing process.

In one specific embodiment, the bonding agent is epoxy, polyamide (nylon), polyphenylene sulfide (PPS), a liquid crystalline polymer (LCP), or combinations thereof. In another specific embodiment, the bonding agent further comprises one or more additives selected from a high molecular weight multi-functional fatty acid ester, stearic acid, hydroxy stearic acid, a high molecular weight complex ester, a long chain ester of pentaerythritol, palmitic acid, a polyethylene based lubricant concentrate, an ester of montanic acid, a partly saponified ester of montanic acid, a polyolefin wax, a fatty bis-amide, a fatty acid secondary amide, a polyoctanomer with high trans content, a maleic anhydride, a glycidyl-functional acrylic hardener, zinc stearate, and a polymeric plasticizer.

Other specific embodiments of the present invention include that the bonded magnet comprises, by weight, from about 1% to about 5% epoxy and from about 0.01% to about 0.05% zinc stearate; that the bonded magnet has a permeance coefficient or load line of from about 0.2 to about 10; that the magnet exhibit a flux-aging loss of less than about 5.0% when aged at 80° C. for 1000 hours.

The bonded magnet may be made by compression molding, injection molding, calendering, extrusion, screen printing, or a combination thereof. In one embodiment, the magnet is made by compression molding at a temperature range of 40° C. to 200° C.

In a third aspect, a method of making a magnetic material comprising:

forming a melt comprising the composition, in atomic percentage, of

(MM_1-aR_a)_uFe_{100-u-v-w-x-y}Y_vM_wT_xB_y

rapidly solidifying the melt to obtain a magnetic powder; and thermally annealing the magnetic powder; wherein

• • MM is a mischmetal or a synthetic equivalent thereof;
  • R is Nd, Pr or a combination thereof;
  • Y is a transition metal other than Fe;
  • M is one or more of a metal selected from Groups 4 to 6 of the periodic table; and
  • T is one or more of a metal other than B, selected from Groups 11 to 14 of the periodic table,
    wherein 0≦a≦1, 7≦u≦13, 0≦v≦20, 0≦w≦5; 0≦x≦5 and 4≦y≦12.

In a specific embodiment, the step of rapidly solidifying comprises a melt-spinning or jet-casting process at a nominal wheel speed of from about 10 meter/second to about 60 meter/second. In yet another specific embodiment, the nominal wheel speed is from about 15 meter/second to about 50 meter/second. More specifically, the nominal wheel speed is from about 35 meter/second to about 45 meter/second. Preferably, the actual wheel speed is within plus or minus 0.5%, 1.0%, 5. 0%, 10%, 15%, 20%, 25% or 30% of the nominal wheel speed and that the nominal wheel speed is an optimum wheel speed of producing the magnetic material by the rapid solidification process, followed by the thermal annealing process.

In a specific embodiment, the thermal annealing process used for the preparation of the magnetic material is at a temperature range of about 350° C. to about 800° C. for about 0.5 to about 120 minutes. More specifically, the thermal annealing process used is at a temperature range of about 600° C. to about 700° C. for about 2 to about 10 minutes.

DEFINITIONS

The following words and terms used herein shall have the meaning indicated:

The term “refined” in the context of a metal such as Nd and Pr, means that the metals are substantially pure or have minimal impurities. The maximum amount of impurities present in a refined metal may be less than 10% impurities, more preferably less than 5% impurities, more preferably less than 1% impurities. For example, a “refined Nd” may be a metal which comprises Nd and up to 10% non-Nd impurities such as other non-Nd metals and non-metals.

The term “mischmetal” refers to mischmetal ore as known in the art and also includes within its scope the oxidized form of mischmetal ore. The specific combination of rare earth metals in the mischmetal ore varies depending on the mine and vein from which the ore was extracted. Mischmetal generally has a composition, based on 100% of weight, of about 30% to about 70% Ce by weight, about 19% to about 56% La by weight, about 2% to about 6% Pr by weight and from about 0.01% to about 20% Nd by weight, and incidental impurities. A mischmetal in “natural form” means a mischmetal ore which is not refined as defined above.

Unless specified otherwise, the terms “comprising” and “comprise”, and grammatical variants thereof, are intended to represent “open” or “inclusive” language such that they include recited elements but also permit inclusion of additional, unrecited elements.

As used herein, the term “about”, in the context of concentrations of components of the formulations, typically means +/−5% of the stated value, more typically +/−4% of the stated value, more typically +/−3% of the stated value, more typically, +/−2% of the stated value, even more typically +/−1% of the stated value, and even more typically +/−0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the magnetic properties of the disclosed magnetic material alloys: FIG. 1A is a graph showing the variation of B_r with varying NdPr substitution in [(MM_1-x (Nd_0.75Pr_0.25)_x]_11.65Fe_82.75B_5.6; FIG. 1B is a graph showing the variation of H_ci with varying NdPr substitution in [(MM_1-x(Nd_0.75Pr_0.25)_x]_11.65Fe_82.75B_5.6; and FIG. 1C is a graph showing the variation of (BH)_max with varying NdPr substitution in [(MM_1-x(Nd_0.75Pr_0.25)_x]_11.65Fe_82.75B_5.6.

FIG. 2 illustrates demagnetization curves of [(MM_1-x(Nd_0.75Pr_0.25)_x]_11.65Fe_82.75B_5.6 powder with varying proportions of NdPr substituted from 0% to 100%, melt-spun at a wheel speed between 22 m/s and 27 m/s followed by annealing at 640° C. for 2 minutes.

FIG. 3 illustrates the optimal-quench wheel speed of the magnetic material in [(MM_1-x(Nd_0.75Pr_0.25)_x]_11.65Fe_82.75B_5.6 as the proportion of NdPr in the composition is varied from 0% to 100%.

DETAILED DESCRIPTION

The magnetic alloys disclosed herein have compositions near the stoichiometric Nd₂Fe₁₄B and exhibiting nearly single-phase microstructure. Further, the material contains one or more of Al, Si, Mn, or Cu to help in manipulating the value of B_r; La or Ce inherently present in the mischmetal to help in manipulating the value of H_ci, and one of more of refractory metals such as Zr, Nb, Ti, Cr, V, Mo, W, and Hf, to improve the quenchability or to reduce the optimum wheel speed required for melt spinning. The combination of Al, La, and Zr may also improve the wetting behavior of liquid metal to wheel surface and broadens the wheel speed window for optimal quenching. If necessary, a dilute Co-addition can also be incorporated to improve the reversible temperature coefficient of B_r (commonly known as a). Thus, compared to conventional attempts, the disclosed MM-TM-B type magnetic material provides a more desirable multi-factor approach and uses a novel alloy composition that allows manipulation of key magnetic properties and a broad wheel speed window for melt spinning without modifying current wheel configurations. Furthermore, the mischmetal (MM) can be unrefined in that the mineral form of the MM is used rather than a purified Nd, Pr, La, or Ce, which significantly reduces the cost of production of the magnetic material alloy.

Bonded magnets made from the disclosed MM-TM-B type magnetic material may be used for replacement of anisotropic sintered ferrites in many applications.

The disclosed MM-TM-B type magnetic material alloy compositions of this invention are “highly quenchable” which, within the context of this disclosure, means that the materials can be produced by a rapid solidification process at a relatively low optimal wheel speed with a relatively broad optimal wheel speed window, as compared to the optimal wheel speed and window for producing conventional materials. For example, when using a laboratory jet caster, the optimum wheel speed required to produce the highly quenchable magnetic materials of the present invention is less than 25 meter/second (m/s), with an optimal quenching speed window of at least ±15%, preferably ±25% of the optimal wheel speed. Under actual production conditions, the optimum wheel speed required to produce the highly quenchable magnetic materials of the present invention is less than 60 meter/second, with an optimal quenching speed window of at least ±15%, preferably ±30% of the optimal wheel speed.

Within the meaning of the present disclosure, “optimum wheel speed (V_ow)” means the wheel speed that produces the optimum B_r and H_ci values after thermal annealing. Further, as actual wheel speed in real-world processes inevitably varies within a certain range, magnetic materials are always produced within a speed window, rather than a single speed. Thus, within the meaning of the present invention, “optimal quenching speed window” is defined as wheel speeds that are close and around the optimum wheel speed and that produce magnetic materials with identical or almost identical B_r and H_ci values as that produced using the optimum wheel speed. Specifically, the magnetic material of the present disclosure can be produced at an actual wheel speed within plus or minus 0.5%, 1.0%, 5.0%, 10%, 15%, 20%, 25% or 30% of the nominal optimal wheel speed.

As discovered by the present disclosure, the optimum wheel speed (V_ow) may vary according to factors such as the orifice size of the jet casting nozzle, the liquid (molten alloy) pouring rate to the wheel surface, diameter of the jet casting wheel, and wheel material. Thus, the optimum wheel speed for producing the highly quenchable magnetic materials of the present disclosure may vary from about 15 to about 25 meter/second when using a laboratory jet-caster and from about 25 to about 60 meter/second under actual production conditions. The unique characteristics of the materials of the present invention enable the materials to be produced with these various optimal wheel speed within a wheel speed window of plus or minus 0.5%, 1.0%, 5.0%, 10%, 15%, 20% 25% or 30% of the optimum wheel speed. This combination of flexible optimal wheel speed and broad speed window enables the production of the highly quenchable magnetic materials of the present invention. Moreover, this highly quenchable characteristic of the materials enables one to increase the productivity by making it possible for one to use multiple nozzles for jet casting. Alternatively, one may also increase the liquid pouring rate, e.g., by enlarging the orifice size of the jet casting nozzle, to the wheel surface if a higher wheel speed is desirable for high productivity.

Typical room temperature magnetic properties of the present invention's materials include a value of B_r from about 7.0 kG to about 9.0 kG and a value of H_ci from about 4.0 kOe to about 10.6 kOe. Although the material of the present invention often exhibits a single-phase microstructure, the materials may also contain the R₂Fe₁₄B/α—Fe or R₂Fe₁₄B/Fe₃B type nanocomposites and still retain most of its distinct properties. The magnetic powders and bonded magnets of the present disclosure include very fine grain sizes, e.g., from about 1 nm to about 80 nm and even finer sizes from about 10 nm to about 40 nm. The typical flux aging loss of the bonded magnets made from powders, e.g., epoxy bonded magnets with PC (permeance coefficient or load line) of 2, are less than 5% when aged at 80° C. for 1000 hours.

The specific composition of the magnetic material can be defined as, in atomic percentage, (MM_1-aR_a)_uFe_{100-u-v-w-x-y}Y_vM_wT_xB_y wherein MM is a mischmetal or a synthetic equivalent thereof, R is Nd, Pr or a combination thereof, Y is a transition metal other than Fe, M is one or more of a metal selected from Groups 4 to 6 of the periodic table and T is one or more of a metal other than B, selected from Groups 11 to 14 of the periodic table. Further, the values for a, u, v, w, x, and y are as follows: 0≦a≦1, 7≦u≦13, 0≦v≦20, 0≦w≦5, 0≦x≦5, and 4≦y≦12.

In specific embodiments, the mischmetal is a cerium-based mischmetal. The mischmetal or synthetic equivalent thereof has the composition of 20% to 30% La, 2% to 8% Pr, 10% to 20% Nd and the remaining being Ce and any incidental impurities. More specifically, the mischmetal or synthetic equivalent thereof has the composition of 25% to 27% La, 4% to 6% Pr, 14% to 16% Nd and 47% to 51% Ce.

In yet another specific embodiment of the present invention, the transition metal Y is selected from Group 9 or Group 10 of the periodic table. More specifically, the transition metal Y is Co. In another specific embodiment, the metal M is one or more of Zr, Nb, Ti, Cr, V, Mo, W and Hf. In yet another specific embodiment, T is one or more of Al, Mn, Cu and Si. In specific embodiments of the present invention, M is selected from Zr, Nb, or a combination thereof and T is selected from Al, Mn, or a combination thereof. More specifically, M is Zr and T is Al.

The present disclosure also encompasses specific magnetic materials wherein the values for a, u, v, w, x, and y are independent of each other and fall within the following ranges: 0.2≦a≦0.8, 8≦u≦13, 0≦v≦15, 0.1≦w≦4, 1≦x≦5, and 4≦y≦11. Other specific ranges include: 0.4≦a≦0.8, 10≦u≦13, 0≦v≦10, 0.1≦w≦3, 2≦x≦5, and 4≦y≦10; 0.5≦a≦0.75, 11≦u≦12, 0≦v≦5, 0.2≦w≦2, 2.5≦x≦4.5, and 5≦y≦6.5; and 0.55≦a≦0.7, 11.3≦u≦11.7, 0≦v≦2.5, 0.3≦w≦1, 3≦x≦4, and 5.7≦y≦6.1. In another specific embodiment, the values of a and x are as follows: 0.9≦a≦0.99 and 0.1≦x≦1.

In another specific embodiment of the present invention, the values for a, u, v, w, x, and y are independent of each other and fall within the following ranges: 8≦u≦13, 0≦v≦15, 0.1≦w≦4, 1≦x≦5, 4≦y≦11 and a=0. Other specific ranges include: 10≦u≦13, 0≦v≦10, 0.1≦w≦3, 2≦x≦5, 4≦y≦10 and a=0; 11≦u≦12, 0≦v≦5, 0.2≦w≦2, 2.5≦x≦4.5, 5≦y≦6.5 and a=0; and 11.3≦u≦11.7, 0≦v≦2.5, 0.3≦w≦1, 3≦x≦4, 5.7≦y≦6.1 and a=0. In yet another specific embodiment, the values of a and x are as follows: 0.1≦x≦x≦1 and a=0.

Magnetic materials of the disclosed MM-TM-B type magnetic material can be made from molten alloys of the desired composition which are rapidly solidified into powders/flakes by a melt-spinning or jet-casting process. In a melt-spinning or jet-casting process, a molten alloy mixture is flowed onto the surface of a rapidly spinning wheel. Upon contacting the wheel surface, the molten alloy mixture forms ribbons, which solidify into flake or platelet particles. The flakes obtained through melt-spinning are relatively brittle and have a very fine crystalline microstructure. The flakes can also be further crushed or comminuted before being used to produce magnets.

The rapid solidification suitable for the present invention includes a melt-spinning or jet-casting process at a nominal wheel speed of from about 10 meter/second to about 25 meter/second, or more specifically from about 15 meter/second to about 22 meter/second, when using a laboratory jet-caster. Under actual production conditions, the highly quenchable magnetic materials of the present invention cab be produced at a nominal wheel speed of from about 10 meter/second to about 60 meter/second, or more specifically from about 15 meter/second to about 50 meter/Second, and from about 35 meter/second to about 45 meter/second. Because a lower optimum wheel speed usually means that the process can be better controlled, the decrease in V_ow in producing the magnetic powders of the present invention represents an advantage in melt spinning or jet casting as it in indicates that a lower wheel speed can be used to produce powder of the same quality.

The disclosed MM-TM-B type magnetic material can be produced at a broad optimal wheel speed window. Specifically, the actual wheel speed, used in the rapid solidification process is within plus or minus 0.5%, 1.0%, 5.0%, 10%, 15%, 20%, 25% or 30% of the nominal wheel speed of the nominal wheel speed and, preferably, the nominal wheel speed is an optimum wheel speed of producing the magnetic material by the rapid solidification process, followed by the thermal annealing process.

Therefore, the highly quenchable characters of the disclosed MM-TM-B type magnetic material may also enable higher productivity by permitting increased the alloy pour rate to the wheel surface, such as through enlarging the orifice size of jet casting nozzle, using multiple nozzle, and/or using higher wheel speeds. The disclosed MM-TM-B type magnetic material, may be in the form of powders obtained by the melt-spinning or jet-casting process, are heat-treated to improve their magnetic properties. Any commonly employed heat treatment method can be used, although the heat treating step preferably comprises annealing the powders at a temperature between 350° C. to 800° C. for 0.5 to 120 minutes, or preferably between 600° C. to 700° C., for about 2 to about 10 minutes to obtain the desired magnetic properties.

In another specific embodiment, the magnetic material exhibits a B_r value of from about 7.0 kG to about 9.0 kG and H_ci value of from about 4.0 kOe to about 10.6 kOe. More specifically, the magnetic material exhibits a B_r value of from about 7.0 kG to about 7.8 kG and an H_ci value of from about 4.0 kOe to about 6.2 kOe.

FIG. 1 illustrates an example of the variation of B_r, H_ci and (BH)_max with varying NdPr substitution from 0% to 100% in [(MM_1-x(Nd_0.75Pr_0.25)_x]_11.65Fe_82.75B_5.6. The new MM-based MM-Fe—B powder has a magnetic performance of B_r=706 mT, H_ci=332 kA/m, and (BH)_max=58 kJ/m³. Higher magnetic performance can be achieved by increasing substitution of MM with NdPr from 0% to 100%. Magnetic performance of B_r=893 mT, H_ci=848 kA/m, and (BH)_max=132 kJ/m³ is achieved in MM-free (Nd_0.75Pr_0.25)_11.65Fe_82.75B_5.6. This demonstrates that magnetic performance of the new MM-Fe—B can be tailored within a wide range by substituting MM with NdPr, enabling the new materials suitable for various applications.

FIG. 2 illustrates demagnetization curves of [(MM_1-x(Nd_0.75Pr_0.25)_x]_11.65Fe_82.75B_5.6 powders with varying proportions of NdPr substituted from 0% to 100%, melt-spun at a wheel speed between 22 m/s and 27 m/s followed by annealing at 640° C. for 2 minutes. It can be seen that all the materials exhibit normal demagnetization curve with very good squareness. It also indicates that all materials have single-phase and nano-sized crystalline structure.

FIG. 3 illustrates the optimal-quench wheel speed of the magnetic material in [(MM_1-x(Nd_0.75Pr_0.25)_x]_11.65Fe_82.75B_5.6 as the proportion of NdPr in the composition is varied. It can be observed that MM-Fe—B has a much lower optimal-quench wheel speed (about 22 m/s) than the NdPr—Fe—B counterpart (about 26.5 m/s). This means that MM-Fe—B has much better quenchability than NdPr—Fe—B.

A bonded magnet can be made from the disclosed MM-TM-B type magnetic material. The bonded magnet can be produced from the magnetic material through a variety of pressing/molding processes, including, but not limited to, compression molding, extrusion, injection molding, calendering, screen printing, spin casting, and slurry coating. The bonded magnet can be made, after the magnetic powders have been heat treated and mixed with the binding agent, by compression molding. The bonded magnet can also be made by injection molding, calendering, extrusion, screen printing, or a combination thereof; and the bonded magnet made by compression molding can be made at a temperature range of 40° C. to 200° C.

The bonded magnet may comprises, by weight, from about 1% to about 5% epoxy and from about 0.01% to about 0.05% zinc stearate; a bonded magnet that has a permeance coefficient or load line of from about 0.2 to about 10; a bonded magnet that exhibits a flux-aging loss of less than about 5.0% when aged at 80° C. for 1000 hours. In a specific embodiment, the thermal annealing process used for the preparation of the magnetic material of the present invention is at a temperature range of about 350° C. to about 800° C. for about 0.5 to about 120 minutes. More specifically, the thermal annealing process used is at a temperature range of about 600° C. to about 700° C. for about 2 to about 10 minutes.

Further, the various embodiments disclosed and/or discussed herein, such as the compositions of the magnetic material, rapid solidification processes, thermal annealing processes, compression processes, and magnetic properties of the magnetic material and the bonded magnet, are encompassed by the method.

EXAMPLES

Non-limiting examples of the invention, including the best mode, and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1

The purpose of this example is to compare the magnetic performance between samples made with MM as source of RE (Rare Earth) raw material and that made with pure Nd, Pr, La and Ce as source of RE raw materials. For this purpose, two alloy ingots having same composition in atomic percentage of (Nd_0.16Pr_0.05La_0.28Ce_0.51)_11.65Fe_82.75B_5.6 were prepared by arc melting. One ingot was made using MM (natural mixture of Nd, Pr, La and Ce; MM=16 at % Nd+5 at % Pr+28 at % La+51 at % Ce) as source of RE raw material; and another was made using pure Nd, Pr, La, and Ce as source of RE raw materials. A laboratory jet caster with a metallic wheel of good thermal conductivity was used for melt-spinning. A wheel speed of 20-22 meter/second (m/s) was used to prepare the samples. Melt-spun ribbons were crushed to less than 40 mesh and annealed at a temperature in the range of 600 to 700° C. for about four minutes to develop the desired values of B_r and H_ci. Table I lists the compositions in weight percent of the components present in the two samples prepared. Table II lists the corresponding magnetic performance B_r, H_ci and (BH)_max values of the powders prepared.

TABLE I
		Nd	Pr	La	Ce	Fe	B
Composition (at %)	RE source	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)
MM11.65Fe82.75B5.6	Pure MM	4.19	1.34	7.09	13.28	73.14	0.96
(Nd0.16Pr0.05La0.28Ce0.51)11.65Fe82.75B5.6	Pure Nd, Pr,	4.19	1.34	7.09	13.28	73.14	0.96
	La, and Ce

TABLE II
			Hci
	RE	Br	(kA/	(BH)m
Composition (at %)	source	(mT)	m)	(kJ/m3)
MM11.65Fe82.75B5.6	Pure	706	332	58
	MM
(Nd0.16Pr0.05La0.28Ce0.51)11.65Fe82.75B5.6	Pure	715	326	60
	Nd, Pr,
	La, and
	Ce

It can be seen from Table II that similar magnetic high magnetic performance is achieved in both samples, with B_r=706-715 mT, H_ci=326-332 kA/m, and (BH)_max=58-60 kJ/m. This demonstrates that it is possible to use MM as source of RE raw material to produce high-performance melt-spun MM-Fe—B powders.

Example 2

Alloy ingots having compositions, in atomic percentage, of [(MM_1-x(Nd_0.75Pr_0.25)_x]_11.65Fe_82.75B_5.6 were prepared by arc melting. A laboratory jet caster with a metallic wheel of good thermal conductivity was used for melt-spinning. A wheel speed of 20 to 30 meter/second (m/s) was used to prepare the samples. Melt-spun ribbons were crushed to less than 40 mesh and annealed at a temperature in the range of 600 to 700° C. for about four minutes to develop the desired values of B_r and H_ci. Table III lists the proportions in weight percent of the components present in the magnetic material compositions prepared. Table IV lists the corresponding magnetic performance B_r, H_ci and (BH)_max values of the powders prepared.

TABLE III
	MM/TRE	Nd	Pr	La	Ce	Fe	B
Composition (at %)	(%)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)
MM11.65Fe82.75B5.6	100	4.19	1.34	7.09	13.28	73.14	0.96
(MM0.9Nd0.075Pr0.025)11.65Fe82.75B5.6	90	5.76	1.86	6.38	11.95	73.10	0.96
(MM0.8Nd0.15Pr0.05)11.65Fe82.75B5.6	80	7.33	2.37	5.67	10.61	73.06	0.96
(MM0.7Nd0.22Pr0.075)11.65Fe82.75B5.6	70	8.90	2.88	4.95	9.28	73.02	0.96
(MM0.5Nd0.38Pr0.12)11.65Fe82.75B5.6	50	12.04	3.91	3.54	6.62	72.94	0.96
(MM0.25Nd0.56Pr0.19)11.65Fe82.75B5.6	25	15.94	5.19	1.77	3.31	72.84	0.96
(Nd0.75Pr0.25)11.65Fe82.75B5.6	0	19.84	6.46	0.00	0.00	72.75	0.95

TABLE IV
	MM/
	TRE	Br	Hci	(BH)m
Composition (at %)	(%)	(mT)	(kA/m)	(kJ/m3)
MM11.65Fe82.75B5.6	100	706	332	58
(MM0.9Nd0.075Pr0.025)11.65Fe82.75B5.6	90	734	390	68
(MM0.8Nd0.15Pr0.05)11.65Fe82.75B5.6	80	758	432	79
(MM0.7Nd0.22Pr0.075)11.65Fe82.75B5.6	70	779	491	88
(MM0.5Nd0.38Pr0.12)11.65Fe82.75B5.6	50	828	603	107
(MM0.25Nd0.56Pr0.19)11.65Fe82.75B5.6	25	861	721	120
(Nd0.75Pr0.25)11.65Fe82.75B5.6	0	893	848	132

In this example, it is demonstrated that magnetic performance of MM-Fe—B material can be significantly improved by substitution of MM with NdPr. The higher the substitution percentage of NdPr, the higher the magnetic performance. Magnetic performance of Br=893 mT, Hci=848 kA/m, and (BH)max=132 kJ/m3 is achieved when MM is 100% substituted by NdPr. This means that magnetic performance of the new MM-Fe—B can be tailored within a wide range by substituting MM with NdPr, enabling the new materials suitable for various applications.

Example 3

Alloy ingots having compositions, in atomic percentage, of [(MM_x(Nd_0.75Pr_0.25)_1-x]_11.65Fe_82.75B_5.6 were prepared by arc melting. A laboratory jet caster with a metallic wheel of good thermal conductivity was used for melt-spinning. Wheel speeds of 20 to 30 meter/second (m/s) were used to prepare the samples. Melt-spun ribbons were crushed to less than 40 mesh and annealed at a temperature in the range of 600 to 700° C. for about four minutes to develop the desired values of B_r and H_ci. Table V lists the optimal-quench wheel speeds obtained as MM is substituted with increasing proportions of NdPr in the composition.

TABLE V
	MM/TRE	Optimal-quench
Composition (at %)	(%)	wheel speed (m/s)
MM11.65Fe82.75B5.6	100	22
(MM0.9Nd0.075Pr0.025)11.65Fe82.75B5.6	90	22.9
(MM0.8Nd0.15Pr0.05)11.65Fe82.75B5.6	80	23.6
(MM0.7Nd0.22Pr0.075)11.65Fe82.75B5.6	70	24
(MM0.5Nd0.38Pr0.12)11.65Fe82.75B5.6	50	24.2
(MM0.25Nd0.56Pr0.19)11.65Fe82.75B5.6	25	25.4
(Nd0.75Pr0.25)11.65Fe82.75B5.6	0	26.5

In this example, it can be observed that MM-Fe—B has the lowest optimal-quench wheel speed (22 m/s). As the MM is substituted by increasing percentage of NdPr in the composition, the optimal-quench wheel speed increases. When MM is fully substituted by NdPr, a much higher optimum wheel speed (26.5 m/s) is observed. Therefore, this example demonstrates that MM-Fe—B has much better quenchability than NdPr—Fe—B magnetic materials.

Claims

1. A magnetic material having a composition in atomic percentage of:

(MM1-aRa)uFe100-u-v-w-x-yYvMwTxBy

wherein

MM is a naturally occurring mischmetal comprised of Nd, Pr, Ce and La; R is Nd, Pr or a combination thereof; Y is a transition metal other than Fe;

M is one or more of a metal selected from Groups 4 to 6 of the periodic table; and

T is one or more of a metal other than B, selected from Groups 11 to 14 of the periodic table,

wherein 0≦a<1, 7≦u≦13, 0≦v≦20, 0≦w≦5; 0≦x≦5 and 4≦y≦12.

2. A magnetic material as claimed in claim 1, wherein the mischmetal is a cerium-based mischmetal.

3. A magnetic material as claimed in claim 1, wherein said mischmetal has the following composition in weight percent:

20% to 30% La;

2% to 8% Pr;

10% to 20% Nd; and

the remainder being Ce and any incidental impurities.

4. A magnetic material as claimed in claim 3, wherein said mischmetal has the following composition in weight percent:

25% to 27% La;

4% to 6% Pr;

14% to 16% Nd; and

47% to 51% Ce.

5. A magnetic material as claimed in claim 1 wherein the transition metal Y is selected from Group 9 or Group 10 of the periodic table.

6. A magnetic material as claimed in claim 5 wherein the transition metal Y is Co.

7. A magnetic material as claimed in claim 1 wherein the metal M is one or more of Zr, Nb, Ti, Cr, V, Mo, W, and Hf.

8. A magnetic material as claimed in claim 1 wherein the T is one or more of Al, Mn, Cu and Si.

9. A magnetic material as claimed in claim 1, wherein M is Zr, Nb, or a combination thereof and T is Al, Mn, or a combination thereof.

10. A magnetic material as claimed in claim 9, wherein M is Zr and T is Al.

11. A magnetic material as claimed in claim 1, wherein 0.2≦a≦0.8, 8≦u≦13, 0≦v≦15, 0.1≦w≦4, 1≦x≦5, and 4≦y≦11.

12. A magnetic material as claimed in claim 11, wherein 0.4≦a≦0.8, 10≦u≦13, 0≦v≦10, 0.1≦w≦3, 2≦x≦5, and 4≦y≦10.

13. A magnetic material as claimed in claim 12, wherein 0.5≦a≦0.75, 11≦u≦12, 0≦v≦5, 0.2≦w≦2, 2.5≦x≦4.5, and 5≦y≦6.5.

14. A magnetic material as claimed in claim 13, wherein 0.55≦a≦0.7, 11.3≦u≦11.7, 0≦v≦2.5, 0.3≦w≦1, 3≦x≦4, and 5.7≦y≦6.1.

15. A magnetic material as claimed in claim 1, wherein 0.9≦a≦0.99 and 0.1≦x≦1.

16. A magnetic material as claimed in claim 15, wherein 8≦u≦13, 0≦v≦15, 0.1≦w≦4, 1≦x≦5, 4≦y≦11 and a=0.

17. A magnetic material as claimed in claim 16, wherein 10≦u≦13, 0≦v≦10, 0.1≦w≦3, 2≦x≦5, 4≦y≦10 and a=0.

18. A magnetic material as claimed in claim 17, wherein 11≦u≦12, 0≦v≦5, 0.2≦w≦2, 2.5≦x≦4.5, 5≦y≦6.5 and a=0.

19. A magnetic material as claimed in claim 18, wherein 11.3≦u≦11.7, 0≦v≦2.5, 0.3≦w≦1, 3≦x≦4, 5.7≦y≦6.1 and a=0.

20. A magnetic material as claimed in claim 1, wherein 0.1≦x≦1 and a=0.

21.-37. (canceled)