SAME

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Chinese Patent Application No. 200910106263.X, filed on March 31, 2009, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of composite material, more particularly to a composite magnetic material and a method of preparing the same.

BACKGROUND OF THE INVENTION

Because of its magnetic properties, low cost and ample reserves, Nd-Fe-B composite magnets are widely used in vehicles, computers, electronics, mechanical and medical devices, to name a few. In addition, because of its performance to price ratio, Nd-Fe-B materials have been favored to produce magnetic devices with high efficiency, small volume and light mass. However, Nd-Fe-B materials are also known to have poor coercivity and mechanical properties, thereby limiting its applications to some extent.

The polymer-bonding method is usually used for preparing a permanent magnetic material. It is easy to press and form a blank, but the polymer and other additives have different structures compared with Nd-Fe-B magnets, which lead to poor mechanical properties of the Nd-Fe-B composite magnets.

SUMMARY OF THE INVENTION In view thereof, the present invention is directed to solve at least one of the existing problems in the art. Accordingly, a composite magnetic material may be provided, which may overcome shortcomings such as low magnetic energy product or low residual magnetism in the art.

According to an embodiment of the invention, a composite magnetic material may be disclosed, which may comprise an Nd-Fe-B alloy and a nano Fe-based soft magnetic alloy having the general formula of Feioo- _x - _y - _z A _x R _a Si _y B _z . A may be at least one element selected from Cu and Au. R may be at least one element selected from the group consisting of Ti, Zr, Hf, Mo, Nb, Ta, W and V. And the x, a, y and z may satisfy: 0 < x < 3, 0 < a < 10, 0 < y < 20 and 2 < z < 25. The amount of nano Fe- based soft magnetic alloy may range from about 0.01 % to about 5 % of the Nd-Fe- B alloy by weight.

According to an embodiment of the invention, the Nd-Fe-B alloy may have the general formula of Nd _a 'R'bFeioo-a'-b-c-dM _c Bd. According to an embodiment of the invention, R' may be at least one element selected from the group consisting of Pr, Dy and Tb, M may be at least one element selected from the group consisting of Nb, Co, Ga, Zr, Al, Cu and Ti, and the a', b, c and d may satisfy: 10 < a' < 20, 0 < b < 8, 0 < c < 6 and 5 < d < 7.

Further, a method of preparing a permanent magnetic material as described above may be provided. The method may comprise the following steps: mixing an Nd-Fe-B alloy and a nano Fe-based soft magnetic alloy to form a mixture, pressing the mixture in a magnetic field to form a blank, or parison formation, sintering the blank under a first temperature, and tempering the blank under a second temperature. According to an embodiment of the invention, the sintering and tempering steps may be occurred under vacuum. According to an embodiment of the invention, the sintering and tempering steps may be occurred under an inert gas atmosphere. According to an embodiment of the invention, the average particle diameter of the nano Fe-based soft magnetic alloy may range from about 2 to about 1000 nm. According to an embodiment of the invention, the average particle diameter of the nano Fe-based soft magnetic alloy may range from about 2 to about 100 nm.

According to an embodiment of the invention, the pressing step may have an intensity ranging from about 1.2 to about 2.0 T, a pressure ranging from about 10 to about 200 MPa, and a period ranging from about 10 to about 60 seconds. According to an embodiment of the invention, the first temperature may range from about 1030 to about 1120 ⁰ C for a period ranging from about 2 to about 5 hours, while the second temperature may be from about 460 to about 920 ⁰ C for a period of from about 1.5 to about 8 hours.

According to the present invention, the composite magnetic material may have a remarkably improved residual magnetism, coercive force and magnetic energy product, especially for the residual magnetism and the magnetic energy product. Further, the mechanical properties thereof are ameliorated accordingly.

Other variations, embodiments and features of the presently disclosed permanent magnetic materials will become evident from the following detailed description, drawings and claims.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

It will be appreciated by those of ordinary skill in the art that the permanent magnetic materials can be embodied in other specific forms without departing from the spirit or essential character thereof. The presently disclosed embodiments may be therefore considered in all respects to be illustrative and not restrictive.

One embodiment of the present disclosure may disclose a composite magnetic material comprising an Nd-Fe-B (neodymium-iron-boron) alloy and a nano Fe- based soft magnetic alloy having the general formula of Feioo- _x - _y - _z A _x R _a Si _y B _z . A may be at least one element selected from Cu and Au. R may be at least one element selected from the group consisting of Ti, Zr, Hf, Mo, Nb, Ta, W and V. And x, a, y and z may satisfy: O < x < 3, O < a < 10, O < y < 20 and 2 < z < 25.

According to an embodiment of the invention, the Nd-Fe-B alloy may have the following general formula: Nd _a 'R'bFeioo-a'-b-c-dM _c Bd. In this embodiment, the R' may be at least one element selected from the group consisting of Pr, Dy and Tb, the M may be at least one element selected from group consisting of Nb, Co, Ga, Zr, Al, Cu and Ti. And a', b, c and d may satisfy: 10 < a' < 20, 0 < b < 8, 0 < c < 6 and 5 < d < 7.

According to an embodiment of the invention, the amount of nano Fe-based soft magnetic alloy may range from about 0.01 % to about 5 % of the Nd-Fe-B alloy by weight.

The adopted nano Fe-based soft magnetic alloy in the embodiment of the present invention may have soft magnetic property, having the general structural formula as mentioned above.

Further, one embodiment of the present disclosure may disclose a method of preparing a composite magnetic material. The method may comprise: mixing an Nd-Fe-B alloy and a nano Fe-based soft magnetic alloy to form a mixture, pressing the mixture in a magnetic field to form a composition, or a blank, sintering the blank under a first temperature, and tempering the blank under a second temperature.

According to an embodiment of the invention, the nano Fe-based soft magnetic alloy may be uniformly dispersed within the Nd-Fe-B alloy, the nano Fe-based soft magnetic alloy having average particle diameters ranging from about 2 to about 1000 nanometers. According to an embodiment of the invention, the boride may have average particle diameters of from about 2 to about 100 nanometers. According to an embodiment of the invention, the amount of nano Fe-based soft magnetic alloy may be from about 0.01 % to about 5 % of the Nd-Fe-B alloy by weight.

According to an embodiment of the invention, the Nd-Fe-B alloy may have the following general formula: Nd _a 'R'bFeioo-a'-b-c-dM _c B _d . In the embodiment, the R' may be at least one element selected from the group consisting of Pr, Dy and Tb. The M may be at least one element selected from a group consisting of Nb, Co, Ga, Zr, Al, Cu and Ti, and a', b, c and d may satisfy: 10 < a' < 20, 0 < b < 8, 0 < c < 6 and 5 < d < 7. The Nd-Fe-B alloy may have an average particle diameter ranging from about 2 to about 10 micrometers.

According to an embodiment of the invention, the step of pressing the mixture in a magnetic field may adopt those commonly used in the art, such as those disclosed in Chinese Patent Application CN20081006196.3, the entire content is hereby incorporated for reference. The intensity thereof may range from about 1.2 to about 2.0 T, and the pressure may range from about 10 to about 20 MPa.

According to an embodiment of the invention, the sintering and tempering steps may be occurred under vacuum having a vacuum degree of about 1.0* 10 ^"1 to about 1.0 x 10 ^"5 Pa. According to an embodiment of the invention, the sintering and tempering steps may be occurred under an inert gas atmosphere. According to an embodiment of the invention, the inert gas may include at least one member selected from a group consisting of nitrogen, helium, argon, neon, krypton and xenon.

According to an embodiment of the invention, the first temperature may range from about 1030 ⁰ C to about 1120 ⁰ C for a period ranging from about 2 to about 5 hours, while the second temperature may range from about 460 to about 920 ⁰ C for a period ranging from about 1.5 to about 8 hours.

The concrete steps of the method will be described in detail as follows: (1) According to an embodiment of the invention, the Nd-Fe-B alloy may be crushed and grounded to form a powder. The hydrogen-induced cracking or mechanical crushing may be adopted for crushing. According to an embodiment of the invention, jet milling may be utilized to produce powders with average particle diameters ranging from about 2 to about 10 microns.

According to an embodiment of the invention, the Nd-Fe-B alloy may be an alloy ingot or a strip casting alloy. According to an embodiment of the invention, the Nd-Fe-B alloy may be commercially obtained. According to an embodiment of the invention, the Nd-Fe-B alloy may be produced by casting or strip casting processes. According to an embodiment of the invention, the Nd-Fe-B alloy may have the following general formula: Nd _a 'R'bFeioo-a -b-c-dM _c Bd where the R' may be at least one element selected from the group consisting of Pr, Dy and Tb. The M may be at least one element selected from the group consisting of Nb, Co, Ga, Zr, Al, Cu and Ti, and 10 < a' < 20, 0 < b < 8, 0 < c < 6, and 5 < d < 7.

According to an embodiment of the invention, the casting process may comprise: casting a smelted alloy molten in a water-cooled, copper mold. The Nd- Fe-B alloy ingot may have a columnar, crystal structure, where the columnar crystals may be separated by Nd-rich phase layers. In these instances, the distance between the two Nd-rich phase layers may range from about 100 to about 1500 microns.

According to an embodiment of the invention, the strip casting process may comprise: pouring a smelted alloy molten on a copper roller surface. In one example, the copper roller surface may have a rotational linear velocity varying from about 1 to about 2 meters per second. The molten alloy may be cooled to form flakes in different breadths with thicknesses ranging from about 0.2 to about 0.5 mm. According to an embodiment of the invention, the columnar crystals in the flakes may have breadths ranging from about 5 to about 25 microns. According to an embodiment of the invention, hydrogen-induced cracking may comprise: placing an Nd-Fe-B alloy in a stainless steel case, filling the case with high purity hydrogen after vacuumizing, and maintaining at an atmospheric pressure. After about 20 to about 30 minutes, the alloy may blow out because of hydrogen absorption thereof to produce a hydride. According to an embodiment of the invention, the case may be vacuumized for dehydrogenation for about 2 to about 10 hours under a temperature ranging from about 400 to about 600 ⁰ C.

According to an embodiment of the invention, mechanical crushing may comprise rough crushing in a jaw crusher, followed by mechanical crushing in a fine crusher. According to an embodiment of the invention, jet milling may comprise accelerating powder grains to supersonic speed in air so that the grains are collided with each other and fall to pieces.

(2) The Nd-Fe-B alloy and the nano Fe-based soft magnetic alloy may be mixed using a mixer to obtain a powder blank. The amount of nano Fe-based soft magnetic alloy may range from about 0.01 % to about 5 % of the Nd-Fe-B alloy by weight. According to an embodiment of the invention, the nano Fe-based soft magnetic alloy may be processed in advance by dispersion treatment. According to an embodiment of the invention, the nano Fe-based soft magnetic alloy may have the general formula of Feioo- _x - _y - _z A _x R _a Si _y B _z . A may be at least one element selected from Cu and Au. R may be at least one element selected from the group consisting of Ti, Zr, Hf, Mo, Nb, Ta, W and V. And the x, a, y and z may satisfy: 0 < x < 3, 0 ≤ a < 10, 0 < y < 20 and 2 < z < 25. According to an embodiment of the invention, the nano Fe-based soft magnetic alloy may have an average particle diameter ranging from about 2 to about 1000 nanometers.

According to an embodiment of the invention, the mixture of Nd-Fe-B alloy and nano Fe-based soft magnetic alloy may further include an antioxidant and a lubricant. According to an embodiment of the invention, the amount of antioxidant may be about 0.01 % to about 5 % of the alloy by weight, and the amount of lubricant may be about 0 % to about 5 % of the alloy by weight. According to an embodiment of the invention, the antioxidant may include at least one member selected from the group consisting of polyethylene oxide alkyl ether, polyethylene oxide single fatty ester and polyethylene oxide alkenyl ether.

According to an embodiment of the invention, the lubricant may include at least one member selected from a group consisting of gasoline, oleic acid, stearic acid, polyhydric alcohol, polyethylene glycol, sorbitan and stearin.

Further, the mixing process may be that commonly used in the art, and the mixture may be evenly mixed in a mixer.

(3) The mixture may be pressed in a magnetic field to form a blank or parsion formation. According to an embodiment of the invention, the pressing process may comprise: pressing the mixture in a closed glove box within a magnetic field. According to an embodiment of the invention, the magnetic field may have an intensity ranging from about 1.2 to about 2.0 T and the blank may be pressed under a static pressure ranging from about 10 to about 200 MPa for about 10 to about 60 seconds. Further increasing of the magnetic field may further enhance the orientation degree of the magnetic powder. The blank is formed within a completely hermetic glove box, so that the magnetic powder is isolated from the air, obviating fire raised by the heat due to magnetic oxidization on one aspect, and reducing oxygen content in the final magnetic body.

(4) The blank may be sintered under a first temperature, and tempered under a second temperature. According to an embodiment of the invention, the sintering and tempering steps may occur under vacuum respectively. According to an embodiment of the invention, the sintering and tempering may occur under an inert gas filled atmosphere. According to an embodiment of the invention, the inert gas may include at least one member selected from the group consisting of nitrogen, helium, argon, neon, krypton and xenon. According to an embodiment of the invention, the mixture may be sintered under a temperature ranging from about 1030 to about 1120 ⁰ C for a period of about 2 to about 4 hours. According to an embodiment of the invention, the mixture may be tempered under a temperature ranging from about 500 to about 920 ⁰ C for a period of about 2 to about 8 hours. According to an embodiment of the invention, the mixture may be tempered in two steps, the first tempering under a temperature ranging from about 800 to about 920 ⁰ C for a period of about 1 to about 3 hours followed by a second tempering under a temperature ranging from about 500 to about 650 ⁰ C for a period of about 2 to about 4 hours. The magnetic performance of the composite magnetic material may be further enhanced by the secondary tempering.

The following provides additional details on some embodiments of the present disclosure.

EXAMPLE 1

(1) An Nd-Fe-B alloy may be made by strip casting with a rotational linear velocity of a copper roller surface at about 1.5 meters per second. The strip casting alloy may have a thickness of about 0.3 mm with the formula of Nd ₈₄ (Dy _{2 7} Tb ₃ i)Fe ₇₇₃ (Coi ₇ Al ₀ 5Cu ₀₂ Ga ₀ i)B _{5 9} .

(2) The Nd-Fe-B alloy may be crushed by hydrogen-induced cracking. And hydrogen is absorbed to saturation under room temperature. Next, hydrogen crushed powder is formed by dehydrogenating for 6 hours under a temperature of 550 ⁰ C. The alloy may be milled to produce a powder with an average particle diameter of about 5 microns by jet milling in a nitrogen-filled atmosphere.

(3) A nano Fe-based soft magnetic alloy and an antioxidant may be added to the powder. The nano Fe-based soft magnetic alloy may have the general formula of Fe ₇ 35Nb3 oCui oSii35B _{9 O} , it may be about 0.02 % of the Nd-Fe-B alloy by weight and may have an average particle diameter of about 20 nanometers. The antioxidant may be polyethylene oxide allyl ether, which may be about 3 % of the Nd-Fe-B alloy by weight. The blank may be mixed by adding gasoline, which may be about 3 % of the Nd-Fe-B alloy by weight.

(4) The powder after mixture may be pressed by a forming press in a closed glove box under nitrogen gas in a magnetic field. The intensity of the oriented magnetic field may be about 1.6 T, the pressure may be about 100 MPa, and the iso- static pressing time may be about 30 seconds.

(5) The blank after pressing may be sintered in a vacuum sintering furnace in an atmospheric pressure of 2 x 10 ^" Pa, under a sintering temperature of about 1090 ⁰ C for about 4 hours. The blank may be subsequently tempered under a temperature of about 900 ⁰ C for about 2 hours followed by tempering under a temperature of about 550 ⁰ C for about 3 hours.

The composite magnetic material can be designated as Tl.

REFERENCE 1

The sample may be substantially similar in all respects with those in EXAMPLE 1 except that the Nd-Fe-B alloy does not comprise nano Fe-based soft magnetic alloy powder.

The composite magnetic material can be designated as TCl.

REFERENCE 2

The Nd-Fe-B alloy and the nano Fe-based soft magnetic alloy may be used substantially similar to that of EXAMPLE 1 to form the mixed alloy power. The mixed alloy power as provided in the EXAMPLE 1 is further processed by bonding. A polymer bonding method may be used for forming the blank: firstly the mixed alloy powder may be encapsulated by silane, and then a bonding agent having epoxy resin of 2% by weight may be mixed in the alloy mixture, and the blank may be pressed mechanically to form a composite magnetic material with a density of about 6.27 g/cm . The composite magnetic material can be designated as TC2.

EXAMPLE 2

The sample may be substantially the same with that of EXAMPLE 1 with the exception that the nano Fe-based soft magnetic alloy of Fe _{73 5} Nb _{3 0} Cui ₀ Sii _{3 5} B _{9 0} is employed having an average particle diameter of about 100 nm.

The composite magnetic material can be designated as T2.

EXAMPLE 3

The sample may be substantially the same with that of EXAMPLE 1 with the exception that the amount of Fe _{73 5} Nb ₃ oCui oSii _{3 5} B _{9 0} may be about 5 % of the Nd- Fe-B alloy by weight.

The composite magnetic material can be designated as T3.

EXAMPLE 4

The sample may be substantially the same with that of EXAMPLE 1 with the exception that: Fe ₇ o 5Nb ₃ oCui oSiis sBio o may be incorporated as the nano Fe-based soft magnetic alloy instead of Fe ₇₃ 5Nb ₃ oCui oSii ₃ sB9 o; and the amount of Fe _{70 5} Nb ₃ oCui ₀ Sii _{5 5} B _{10 0} may be about 3 % of the Nd-Fe-B alloy by weight.

The composite magnetic material can be designated as T4.

TESTING

1. Magnetic property

A curve measurement system NIM200C for permanent magnetic materials developed by China National Institute of Metrology is used for measuring magnetic properties of materials T1-T4, TCl and TC2 with the results being recorded in Table 1. The magnetic properties tested include residual magnetism (Br) and maximum magnetic energy product (BHmax).

2. Mechanical property

Using A universal testing machine CMT5105 distributed by XinSanSi Group Company, ShenZhen, Guangdong Province, China is used for measuring mechanical properties of materials T1-T4, TCl and TC2 with the results being also recorded in Table 1. The mechanical properties tested include coercive force (Hcj) and bending strength (MPa) respectively.

Table 1. Magnetic and mechanical properties of materials T1-T4, TCl and TC2.

Based on the results as shown in Table 1, Tl exhibit better coercive force (27.65 KOe v. 25.74 KOe) and improved bending strength (253.52 MPa v. 220.14 MPa) than its counterpart TCl without the nano Fe-based soft magnetic alloy. At the same time, the composite magnetic material Tl can maintain comparable magnetic properties (residual magnetism of 12.24 KGs v. 10.91 KGs for TI v. TCl ; maximum magnetic energy product of 35.70 MGOe v. 34.41 MGOe for Tl v. TCl). Still further, Tl exhibit much better performance than its counterpart TC2 which may be prepared by polymer-bonding. In addition, the composite magnetic material according to the presently disclosed embodiments can also maintain comparable mechanical properties including coercive force and bending strength against the reference samples while keeping magnetic properties including residual magnetism and maximum magnetic energy product substantially invariant.

Although the permanent magnetic materials have been described in detail with reference to several embodiments, additional variations and modifications exist within the scope and spirit as described and defined in the following claims.