METHOD FOR PREPARING RARE-EARTH PERMANENT MAGNET BY HOT PRESS MOLDING

Abstract

The present invention relates to a method for preparing a neodymium-iron-boron rare-earth permanent magnetic material, in particular to a hot press molding-based method for preparing a rare-earth permanent magnet. The problem that the residual magnetism and coercive force of a rare-earth permanent magnet prepared in the prior art cannot be both high is solved. An RTM alloy infiltrates same during an HD treatment. RTM sticks to the surface of coarse powder and infiltrates into the interior of the coarse powder along a grain boundary. The temperature of hot press sintering is relatively low, and grains barely grow. In the absence of Dy and Tb, a higher coercive force is obtained. If an alloy containing Dy and Tb is used for infiltration, these atoms diffuse into the surface layer of a main phase during preheating and heat treatment, achieving grain boundary hardening. Under the premise of a very small reduction in the residual magnetism, the coercive force is greatly improved.

Claims

1. A method for preparing a rare-earth permanent magnet by hot press molding, comprising steps of: 1) smelting an RFeB alloy, where R is any one of Nd, Pr, Dy, Tb, Ce, La, Gd, Ho and Y, or any combination of two or more of Nd, Pr, Dy, Tb, Ce, La, Gd, Ho and Y, and the content of the rare-earth R in the RFeB alloy is 27.5% to 30.5% by mass; the RFeB alloy further contains 0.2% to 2% by mass of a metal composition; the metal composition is any one of Al, Cu, Ga, Zr and Nb, or any combination of two or more of Al, Cu, Ga, Zr and Nb in any ratio; and 1% to 10% Fe is replaced with Co; 2) performing HD treatment on the master alloy, and permeating an R.sub.TM alloy during this process, where R.sub.T is any one of Nd, Pr, Dy, Tb, Gd, Ho, Y and Sc, or any combination of two or more of Nd, Pr, Dy, Tb, Gd, Ho, Y and Sc in any ratio, and M is any one of Cu, Al and Ga, or any combination of two or more of Cu, Al and Ga in any ratio; 3) performing jet pulverization on the product obtained in the step 2); 4) molding under a magnetic field at room temperature; 5) preheating the green body in vacuum; 6) performing hot pressing on the green body to further improve the density; and 7) aging to obtain the magnet.

2. The method for preparing a rare-earth permanent magnet by hot press molding according to claim 1, wherein, in the R.sub.TM alloy in the step 2), R.sub.T accounts for 65% to 100%, and M accounts for 0% to 35%.

3. The method for preparing a rare-earth permanent magnet by hot press molding according to claim 1, wherein, in the step 2), the permeation amount of the R.sub.TM alloy is 0.5% to 4.5% of the mass of the RFeB alloy.

4. The method for preparing a rare-earth permanent magnet by hot press molding according to claim 1, wherein, in the step 2), the HD treatment process comprises steps of: a) mixing the R.sub.TM alloy powder in 1 μm to 100 μm with a quick-setting sheet alloy and loading the mixture into an HD treatment furnace; b) filling with hydrogen after the vacuum degree reaches 0.1 Pa, maintaining the pressure at 0.05 MPa to 0.2 MPa, and performing saturated hydrogen absorption; c) permeating and dehydrogenating for 60 min to 240 min at 750° C. to 950° C.; d) stopping heating; and e) cooling, then sealing and taking out from the furnace.

5. The method for preparing a rare-earth permanent magnet by hot press molding according to claim 1, wherein, during the jet pulverization in the step 3), compressed N.sub.2 is used as power, and grinding is performed until the average particle size is 1 μm to 6 μm.

6. The method for preparing a rare-earth permanent magnet by hot press molding according to claim 1, wherein, in the step 4), pressing is performed under an orientation magnetic field with an intensity greater than 1.2 T, the pressing density is 3.6 to 4.2 g/cm.sup.2, and the oxygen concentration in the exposed space is less than 500 PPM.

7. The method for preparing a rare-earth permanent magnet by hot press molding according to claim 1, wherein the R.sub.TM alloy is replaced with an R.sub.TFeB alloy, where R.sub.T is any one of Nd, Pr, Dy, Tb, Gd, Ho, Y and Sc, or any combination of two or more of Nd, Pr, Dy, Tb, Gd, Ho, Y and Sc in any ratio, and the content of R.sub.T exceeds 50% of the mass of the R.sub.TFeB alloy.

8. The method for preparing a rare-earth permanent magnet by hot press molding according to claim 1, wherein, in the steps 5) and 6), the hot press molding comprise steps of: preheating for 1 h to 10 h at 650° C. to 950° C. and at a vacuum degree of 10.sup.−1 to 10.sup.−4 Pa, immediately loading into a mold cavity having a temperature close to the preheating temperature at the end of preheating, applying a pressure of 25 to 120 MPa, maintaining the pressure for 0.3 min to 10 min, hot pressing in an inert gas having an oxygen content less than 200 PPM, naturally or forcedly cooling to the room temperature.

9. The method for preparing a rare-earth permanent magnet by hot press molding according to claim 1, wherein the cross-section size of the hot pressing mold in the step 6) is increased by 0.05 mm to 0.2 mm according to the size of the preheated green body after shrinkage, so as to facilitate molding.

10. The method for preparing a rare-earth permanent magnet by hot press molding according to claim 1, wherein the hot-pressed product is aged at an aging temperature of 450° C. to 950° C.

Description

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0022] A method for preparing a rare-earth permanent magnet by hot press molding is provided, including steps of:

[0023] 1) smelting an RFeB alloy, where R is any one of Nd, Pr, Dy, Tb, Ce, La, Gd, Ho and Y, or any combination of two or more of Nd, Pr, Dy, Tb, Ce, La, Gd, Ho and Y, and the content of the rare-earth R in the RFeB alloy is 27.5% to 30.5% (e.g., optionally 27.5%, 28%, 28.5%, 29% or 30.5%) by mass; the RFeB alloy further contains 0.2% to 2% (e.g., optionally 0.2%, 0.5%, 0.8%, 1.0%, 1.5% or 2%) by mass of a metal composition; the metal composition is any one of Al, Cu, Ga, Zr and Nb, or any combination of two or more of Al, Cu, Ga, Zr and Nb in any ratio; and 1% to 10% Fe is replaced with Co;

[0024] 2) performing HD treatment on the master alloy, and permeating an R.sub.TM alloy during this process, where R.sub.T is any one of Nd, Pr, Dy, Tb, Gd, Ho, Y and Sc, or any combination of two or more of Nd, Pr, Dy, Tb, Gd, Ho, Y and Sc in any ratio, and M is any one of Cu, Al and Ga, or any combination of two or more of Cu, Al and Ga in any ratio;

[0025] 3) performing jet pulverization on the product obtained in the step 2);

[0026] 4) molding under a magnetic field at room temperature;

[0027] 5) preheating the green body in vacuum;

[0028] 6) performing hot pressing on the green body to further improve the density; and

[0029] 7) aging to obtain the magnet.

[0030] In the step 2), the permeation amount of the R.sub.TM alloy is 0.5% to 4.5% (e.g., optionally 0.5%, 1%, 2%, 3%, 3.5%, 4% or 4.5%) of the mass of the RFeB alloy.

[0031] In the R.sub.TM alloy in the step 2), R.sub.T accounts for 65% to 100%, and M accounts for 0% to 35% (e.g., optionally, R.sub.T accounts for 65% and M accounts for 35%; R.sub.T accounts for 100% and M accounts for 0%; R.sub.T accounts for 75% and M accounts for 25%; R.sub.T accounts for 85% and M accounts for 15%; or, R.sub.T accounts for 95% and M accounts for 5%).

[0032] The R.sub.TM alloy may be replaced with an R.sub.TFeB alloy. R.sub.T is any one of Nd, Pr, Dy, Tb, Gd, Ho, Y and Sc, or any combination of two or more of Nd, Pr, Dy, Tb, Gd, Ho, Y and Sc in any ratio, and the content of R.sub.T exceeds 50% of the mass of the R.sub.TFeB alloy.

[0033] In the step 1), the RFeB alloy is obtained by smelting RFeB alloy quick-setting sheets in which the content of rare-earth R is 27.5% to 30.5% by mass.

[0034] In the step 2), the HD treatment process includes steps of:

[0035] a) mixing the R.sub.TM alloy powder in 1 μm to 100 μm with a quick-setting sheet alloy and loading the mixture into an HD treatment furnace;

[0036] b) filling with hydrogen after the vacuum degree reaches 0.1 Pa, maintaining the pressure at 0.05 MPa to 0.2 MPa (e.g., optionally 0.05 MPa, 0.1 MPa, 0.15 MPa or 0.2 MPa), and performing saturated hydrogen absorption;

[0037] c) permeating and dehydrogenating for 60 min to 240 min (e.g., optionally 60 min, 120 min, 180 min or 240min) at 750° C. to 950° C. (e.g., optionally 750° C., 800° C., 850° C., 900° C. or 950° C.);

[0038] d) stopping heating, cooling to 200° C., and performing secondary hydrogen absorption, where the hydrogen absorption amount is 500 to 1000 ppm (e.g., optionally 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm or 1000 ppm); and

[0039] e) feeding Ar, cooling with water to room temperature, sealing and taking out from the furnace.

[0040] During the jet pulverization in the step 3), compressed N.sub.2 is used as power, and grinding is performed until the average particle size is 1 μm to 6 μm (e.g., optionally 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or 6 μm).

[0041] In the step 4), molding is performed under a magnetic field at room temperature. Pressing is performed under an orientation magnetic field with an intensity greater than 1.2 T. The density is 3.6 to 4.2 g/cm.sup.2, and the exposed space has an oxygen concentration less than 500 PPM. To further improve the density, it is possible to perform secondary molding, i.e., isostatic pressing. The pressure for isostatic pressing is 150 MPa to 300 MPa (e.g., optionally 150 MPa, 210 MPa, 250 MPa or 300 MPa).

[0042] During the preheating in the step 5), preheating is performed for 1 h to 10 h (e.g., optionally 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h) at 650° C. to 950° C. (e.g., optionally 650° C., 700° C., 800° C., 900° C. or 950° C.).

[0043] In the step 6), at the end of preheating, the green body is immediately loaded into a mold cavity having a temperature close to the preheating temperature, and a pressure of 25 to 120 MPa (e.g., optionally 25 MPa, 40 MPa, 50 MPa, 60 MPa, 90 MPa or 120 MPa) is applied and maintained for 0.3 min to 10 min (e.g., optionally 0.3 min, 0.5 min, 0.8 min, 1 min, 3 min, 5 min, 6 min, 8 min, 9 min or 10 min). Hot pressing is performed in an inert gas having an oxygen content less than 200 PPM, and the pressure is 0 MPa, that is, there is no pressure difference between the inert gas and the outside. The green body is naturally or forcedly cooled to the room temperature.

[0044] The cross-section size of the hot pressing mold in the step 6) is increased by 0.05 mm to 0.2 mm according to the size of the preheated green body after shrinkage, so as to facilitate molding.

[0045] In the step 7), the hot-pressed product may be aged at an aging temperature of 450° C. to 950° C. (e.g., optionally 450° C., 500° C., 600° C., 700° C., 800° C., 900° C. or 950° C.).

Embodiment 1

[0046] The material formulation of the RFeB alloy was as follows:

TABLE-US-00001 Composition Nd + Pr Co B Cu Nb Al Zr Ga Fe Mass ratio 27.8 0.9 1.05 0.2 0.2 0.2 0.1 0.1 The remaining

[0047] The materials were smelted in vacuum according to the formulation, and treated by quick-setting spinning to obtain the RFeB alloy, i.e., quick-setting sheets, having a thickness of 0.20 mm to 0.45 mm.

[0048] The quick-setting sheets were processed by the method of the present application. The R.sub.TM alloy infiltrated during the HD process was DyCu alloy powder, where Nd accounted for 90% and Cu accounted for 10%.

[0049] To ensure the performance, it was required that there was no oxide layer on the surfaces of the quick-setting sheets and the discharging of the quick-setting furnace was performed in a sealed barrel. When loaded into a hydrogen pulverizating furnace, the quick-setting sheets should be strictly protected from contact with air.

[0050] The quick-setting sheets and the DyCu alloy powder in an amount that was 1% of the total mass of the quick-setting sheets were loaded into a treatment furnace. After the vacuum degree reached 0.1 Pa, saturated hydrogen absorption was performed at a hydrogen pressure of 0.05 MPa to 0.2 MPa. Subsequently, dehydrogenation was performed for 120 min at 900° C. Then, heating was stopped, and the vacuum state was maintained. Cooled to 200° C. and subjected to secondary hydrogen absorption in a hydrogen absorption amount of 800 ppm, and then cooled, sealed and discharged. Thejet pulverization was performed until the average particle size was 2 μm to 4 μm.

[0051] The experimental mold was 25*50 mm in size, and the mold cavity was 150 mm in depth. Molding was performed under a magnetic field in a low-oxygen environment having an oxygen concentration less than 500 ppm, 525 g of magnetic powder was added, a pressure of 15 Ton was applied, to obtain a green body in 25*50*50. The green body was preheated in vacuum at a vacuum degree of 0.01 Pa and at 900° C., then placed into the mold cavity, and maintained for 60 s at 40 MPa to realize a density of 7.6 g/cm.sup.2. Cooled and aged at 900° C. to obtain the product with magnetic performance 55 H. The residual magnetism was 14.5 KGs, and the HcJ was 1350 KA/m.

Embodiment 2

[0052] The material formulation of the RFeB alloy was as follows:

TABLE-US-00002 Composition Nd + Pr Co B Cu Nb Al Zr Ga Fe Mass ratio 27.8 0.9 1.05 0.2 0.2 0.2 0.1 0.1 The remaining

[0053] The materials were smelted in vacuum according to the formulation, and treated by quick-setting spinning to obtain the RFeB alloy, i.e., quick-setting sheets, having a thickness of 0.20 mm to 0.45 mm.

[0054] A TbCuAl alloy and powder thereof were prepared, where Tb accounted for 80%, Cu accounted for 10%, and Al accounted for 10% (mass percentage).

[0055] The same implementation method as Embodiment 1 was executed. During this process, part of TbCuAl adhered to the surfaces of coarse particles subjected to hydrogen pulverizating, while part of TbCuAl diffused into coarse powder.

[0056] Jet pulverization, molding under a magnetic field, vacuum preheating, hot pressing and tempering were performed by methods the same as those in Embodiment 1. The product with magnetic performance 50 EH was obtained. The residual magnetism was 14.0 KGs, and the HcJ was 2388 KA/m.