Two-step diffusion method for preparing high-performance dual-main-phase sintered mischmetal-iron-boron magnet

Abstract

A two-step diffusion method for preparing high-performance dual-main-phase sintered mischmetal-iron-boron magnet belongs to the preparing technical field of rare earth permanent magnet materials. The compositions of the two main phase alloys are RE-Fe—B (RE is Nd or Pr) and (Nd, MM)-Fe—B (MM is mischmetal), respectively. First, PrHoFe strip-casting alloy is used as a diffusion source. Next, a PrHo-rich layer is uniformly coated on the surface of (Nd, MM)-Fe—B hydrogen decrepitation powders. The higher anisotropic fields of Pr.sub.2Fe.sub.14B and Ho.sub.2Fe.sub.14B are used to improve the coercivity. Then, the ZrCu strip-casting alloy is used as a diffusion source. A Zr-rich layer is uniformly coated on the surface of the powders after the first-step diffusion, which prevents the growth of the MM-rich main phase grains during the sintering process and the inter-diffusion between the two main phases, thus obtaining high coercivity.

Claims

1. A two-step diffusion method for preparing high-performance dual-main-phase sintered mischmetal-iron-boron magnet, wherein the high-performance dual-main-phase sintered mischmetal-iron-boron magnet comprises a Pr/Nd.sub.2Fe.sub.14B main phase A and a (E, Nd).sub.2Fe.sub.14B main phase B, hydrogen decrepitation coarse powders of the main phase B is subjected to two-step rotating diffusion treatment, then mixed with hydrogen decrepitation coarse powders of the main phase A, a mass ratio of the main phase A to the main phase B is 1:9-5:5 with the sum being 10; wherein nominal composition of the main phase A is Pr/Nd.sub.xFe.sub.100-x-y-zM.sub.yB.sub.z (wt. %), and nominal composition of the main phase B is [E.sub.aNd.sub.1-a].sub.xFe.sub.100-x-y-zM.sub.yB.sub.z (wt. %), where E is mischmetal, and mass percent of each component is Ce: 48-58%, La: 20-30%, Pr: 4-6%, and Nd: 15-17%; M is one or more of Nb, Ti, V, Co, Cr, Mn, Ni, Zr, Ga, Ag, Ta, Al, Au, Pb, Cu, Si, a x, y, z satisfies the following relationships: 0≤a≤1, 25≤x≤35, 0.5≤y≤3, 0.3≤z≤1.5; the two-step diffusion method comprising the following steps: (1) according to the main phase A with the nominal composition of Pr/Nd.sub.xFe.sub.100-x-y-zM.sub.y B.sub.z, and the main phase B with the nominal composition of [E.sub.aNd.sub.1-a].sub.x Fe.sub.100-x-y-zM.sub.yB.sub.z, praseodymium, mischmetal (E), other metals (M), neodymium, iron, and iron boron alloy are selected and put into a crucible; after drying under vacuum and filling argon, mixed metals are smelted and then poured on a rotating water-cooled copper roller with a rotation speed of 1-4 m/s; A and B strip-casting alloys with a thickness of 180-400 μm are obtained, respectively; (2) a PrHoFe alloy and a ZrCu alloy are prepared into PrHoFe strip-casting alloys and ZrCu strip-casting alloys using a vacuum induction rapid-quench furnace, respectively; then the PrHoFe strip-casting alloys and the ZrCu strip-casting alloys are roughly broken into square pieces with a size of (0.5-1.5) cm*(0.5-1.5) cm; (3) the A and B strip-casting alloys of step (1) are broken by hydrogen decrepitation, respectively, and coarsely crushed powders are obtained after dehydrogenation; (4) the hydrogen decrepitation coarse powders of the B strip-casting alloys of step (3) and the PrHoFe strip-casting alloys of step (2) are respectively placed in inner and outer cavities of a coaxial double-layer circular barrel for a first step diffusion treatment; a mass ratio of the B strip-casting alloys and the PrHoFe strip-casting alloys is 2:1 to 1:2; a molybdenum mesh separates the inner cavity and the outer cavity; first-step diffusion coarse powders are obtained by diffusion heat treatment at a speed of 1-10 r/min and 500-700° C. for 3-6 h in a rotary heat treatment furnace; an external shell of the coaxial double-layer circular barrel is made of solid material plates; a coaxial inner layer is a molybdenum mesh cylinder; an annular cavity structure between the molybdenum mesh cylinder and the external shell of the coaxial double-layer circular barrel is the outer cavity; a cavity in the molybdenum mesh cylinder is the inner cavity; a mesh diameter of the molybdenum mesh cylinder is less than 5 μm; (5) the first-step diffusion coarse powders of step (4) and the broken ZrCu strip-casting alloys of step (2) are respectively placed in the inner and outer cavities of the coaxial double-layer circular barrel for a second-step diffusion treatment to obtain second-step diffusion coarse powders; a mass ratio of the first-step diffusion coarse powders and the broken ZrCu strip-casting alloys is 2:1 to 1:2; a diffusion heat treatment is carried out in a rotary heat treatment furnace at a speed of 1-10 r/min and 800-950° C. for 2-5 h; the rotary heat treatment furnace is connected with a glove box filled with inert gas to protect raw materials during moving in and out of the rotary heat treatment furnace in the glove box; (6) the hydrogen decrepitation coarse powders of the A strip-casting alloys of step (3) are mixed with the second-step diffusion coarse powders after two-step diffusion treatment of step (5) to make a mass ratio of main phases A and B between 1:9 and 5:5; fine powders with a diameter of 1-5 μm are obtained by jet milling after adding 0.01-5 wt. % lubricant and 0.01-5 wt. % antioxidant; the weight percentage of the lubricant and the antioxidant is based on a total weight of the hydrogen decrepitation coarse powders of the A strip-casting alloys of step (3) and the second-step diffusion coarse powders after two-step diffusion treatment of step (5); (7) the fine powders of step (6) adding 0.01-5 wt. % lubricant and 0.01-5 wt. % antioxidant again are mixed well, then aligned and compacted under a magnetic field of 1.5-2.0 T in an inert gas to obtain compacts; the compacts are vacuum-encapsulated and subjected to cold isostatic pressing; the weight percentage of the lubricant and the antioxidant is based on the weight of the fine powders of step (6); (8) the compacts of step (7) are put into a vacuum sintering furnace for sintering at 980-1080° C. for 1-4 h and then cooled by argon; to restrain inter-diffusion between the two phases, the high-performance dual-main-phase sintered mischmetal-iron-boron magnet is only annealed at low temperature at 400-600° C. for 2-5 h.

2. The method for preparing high-performance dual-main-phase sintered mischmetal-iron-boron magnet by two-step diffusion according to claim 1, wherein composition and mass percentage of the PrHoFe alloy are: a mass fraction of Pr is 40-80%, a mass fraction of Ho is 10-40%, and a mass fraction of Fe is 10-20%.

3. The method for preparing high-performance dual-main-phase sintered mischmetal-iron-boron magnet by two-step diffusion according to claim 1, wherein composition and mass percentage of the ZrCu alloy are: a mass fraction of Zr is 35-65%, a mass fraction of Cu is 35-65%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of a double-layer circular barrel used for diffusion in the invention.

(2) In the FIGURE: 1—the outer wall of the barrel, 2—inner metal molybdenum mesh, 3—(E,Nd)—Fe—B hydrogen decrepitation coarse powders, 4—PrHoFe or ZrCu strip-casting alloys for diffusion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(3) The following examples describe this disclosure, but do not limit the coverage of the disclosure.

Comparative Example 1

(4) The nominal composition of main phase A was Pr.sub.31.5Fe.sub.ba1Al.sub.0.4Cu.sub.0.2Co.sub.1Ga.sub.0.2Zr.sub.0.22B.sub.0.98 (wt. %), and the nominal composition of main phase B was (Nd.sub.0.5E.sub.0.5).sub.31.5Fe.sub.ba1Al.sub.0.4Cu.sub.0.2Co.sub.1Ga.sub.0.2Zr.sub.0.22B.sub.0.98 (wt. %) (E including about 27.49 wt. % La, 53.93 wt. % Ce, 1.86 wt. % Pr and 16.72 wt. % Nd). The rotation speed of the copper roller was 1.25 m/s. The A and B strip-casting alloys with a thickness of 210 μm were obtained.

(5) The A and B strip-casting alloys were broken by hydrogen decrepitation, respectively. The coarsely crushed powders were obtained after dehydrogenation. The powders of A and B with the mean diameter (X.sub.50) of 2.10 μm were obtained by jet milling after adding 0.05 wt. % lubricant and 0.1 wt. % antioxidant.

(6) In the glove box, the A and B jet milling powders added 0.1 wt. % lubricant and 0.2 wt. % antioxidant were mixed evenly, respectively. Next, the A and B magnetic powders were aligned and compacted under a magnetic field of 2.0 T in inert gas. The A and B green compacts were vacuum packaged for isostatic pressing and then placed in a vacuum sintering furnace for sintering at 1060° C. and 1050° C. for 2 h and then cooled by argon respectively.

(7) Subsequently, two-stage heat treatments were carried out. The first-stage tempering temperature was 900° C. for 3 h; the second-stage tempering temperature was 450° C. for 4 h.

(8) The magnetic properties of the A and B magnets were measured by the permanent magnetic measurement system (BH tester), the results were as follows:

(9) Magnet A: B.sub.r=13.69 kG, H.sub.cj=20.18 kOe, (BH).sub.max=45.72 MGOe, H.sub.k/H.sub.cj=97.7%.

(10) Magnet B: B.sub.r=12.29 kG, H.sub.cj=9.02 kOe, (BH).sub.max=36.86 MGOe, H.sub.k/H.sub.cj=92.0%.

Comparative Example 2

(11) The nominal composition of main phase A was Pr.sub.31.5Fe.sub.ba1Al.sub.0.4Cu.sub.0.2Co.sub.1Ga.sub.0.2Zr.sub.0.22B.sub.0.98 (wt. %), and the nominal composition of main phase B was (Nd.sub.0.5E.sub.0.5).sub.31.5Fe.sub.ba1Al.sub.0.4Cu.sub.0.2Co.sub.1Ga.sub.0.2Zr.sub.0.22B.sub.0.98 (wt. %) (E including about 27.49 wt. % La, 53.93 wt. % Ce, 1.86 wt. % Pr and 16.72 wt. % Nd). The rotation speed of the copper roller was 1.25 m/s. The A and B strip-casting alloys of with a thickness of 210 μm were obtained.

(12) The A and B strip-casting alloys were broken by hydrogen decrepitation, respectively. The coarsely crushed powders were obtained after dehydrogenation.

(13) The A and B hydrogen decrepitation coarse powders were mixed with the mass ratios of 1:9 and 3:7. And the powders of two components C and D with a mean diameter (X.sub.50) of 2.10 μm were obtained by jet milling after adding 0.05 wt. % lubricant and 0.1 wt. % antioxidant.

(14) In the glove box, the C and D jet milling powders added 0.1 wt. % lubricant and 0.2 wt. % antioxidant were mixed evenly, respectively. Next, the C and D magnetic powders were aligned and compacted under a magnetic field of 2.0 T in inert gas. The C and D green compacts were vacuum packaged for isostatic pressing and then placed in a vacuum sintering furnace for sintering at 1050° C. for 2 h and then cooled by argon. Subsequently, only low-temperature heat treatment was carried out, and the tempering temperature was 450° C. for 4 h.

(15) The magnetic properties of the C and D magnets were measured by the permanent magnetic measurement system (BH tester), the results were as follows:

(16) Binary-main-phase magnet C: B.sub.r=12.53 kG, H.sub.cj=9.53 kOe, (BH).sub.max=38.11 MGOe, H.sub.k/H.sub.cj=93.4%.

(17) Binary-main-phase magnet D: B.sub.r=12.68 kG, H.sub.cj=12.05 kOe, (BH).sub.max=39.50 MGOe, H.sub.k/H.sub.cj=94.2%.

Example 1

(18) The nominal composition of main phase A was Pr.sub.31.5Fe.sub.ba1Al.sub.0.4Cu.sub.0.2Co.sub.1Ga.sub.0.2Zr.sub.0.22B.sub.0.98 (wt. %), and the nominal composition of main phase B was (Nd.sub.0.5E.sub.0.5).sub.31.5Fe.sub.ba1Al.sub.0.4Cu.sub.0.2Co.sub.1Ga.sub.0.2Zr.sub.0.22B.sub.0.98 (wt. %) (E including about 27.49 wt. % La, 53.93 wt. % Ce, 1.86 wt. % Pr and 16.72 wt. % Nd). The rotation speed of the copper roller was 1.25 m/s. The A and B strip-casting alloys with a thickness of 210 μm were obtained.

(19) The PrHoFe alloy and ZrCu alloy were prepared into strip-casting alloys using a vacuum induction rapid-setting furnace, respectively. Then they were roughly broken into 1 cm*1 cm square pieces.

(20) The A and B strip-casting alloys were broken by hydrogen decrepitation, respectively, and the coarsely crushed powders were obtained after dehydrogenation.

(21) The B hydrogen decrepitation coarse powders and the crushed Pr.sub.65Ho.sub.20Fe.sub.15 strip-casting alloys were placed in the inner and outer cavities of a coaxial double-layer circular barrel with a mass ratio of 1:1, respectively. A metal molybdenum mesh separated the inner and outer cavities of the barrel with a diameter less than 5 μm. The first-step diffusion heat treatment was carried out in a rotary heat treatment furnace with a speed of 5 r/min at 630° C. for 4 h. Then, the hydrogen decrepitation coarse powder obtained by the first-step diffusion and the crushed Zr.sub.55Cu.sub.45 strip-casting alloys were put into a rotary heat treatment furnace with a mass ratio of 1:1. And the second-step diffusion heat treatment was carried out at 885° C. for 3 h with a speed of 5 r/min. In the above heat treatment process, the furnace was first evacuated to 5×10.sup.−3 Pa, and then filled with argon to 65 kPa. The subsequent experiment was carried out in an argon protective atmosphere. The rotary heat treatment furnace is connected with a glove box filled with inert gas to protect the raw materials during moving in and out of the furnace in the glove box.

(22) The A and diffused B hydrogen decrepitation coarse powders were mixed with the mass ratios of 1:9 and 3:7. And the powders of two components C1 and D1 with a mean diameter (X.sub.50) of 2.10 μm were obtained by jet milling after adding 0.05 wt. % lubricant and 0.1 wt. % antioxidant.

(23) In the glove box, the C1 and D1 jet milling powders added 0.1 wt. % lubricant and 0.2 wt. % antioxidant were mixed evenly, respectively. Next, the C1 and D1 magnetic powders were aligned and compacted under a magnetic field of 2.0 T in inert gas. The C1 and D1 green compacts were vacuum packaged for isostatic pressing and then placed in a vacuum sintering furnace for sintering at 1050° C. for 2 h and then cooled by argon. Subsequently, only low-temperature heat treatment was carried out, the tempering temperature was 450° C. for 4 h.

(24) The magnetic properties of the C1 and D1 magnets were measured by the permanent magnetic measurement system (BH tester), the results were as follows:

(25) Binary-main-phase magnet C1: B.sub.r=12.65 kG, H.sub.cj=14.87 kOe, (BH).sub.max=39.76 MGOe, H.sub.k/H.sub.cj=96.7%.

(26) Binary-main-phase magnet D1: B.sub.r=12.92 kG, H.sub.cj=16.95 kOe, (BH).sub.max=41.31 MGOe, H.sub.k/H.sub.cj=96.5%.

Example 2

(27) The nominal composition of main phase A was Pr.sub.31.5Fe.sub.ba1Al.sub.0.4Cu.sub.0.2Co.sub.1Ga.sub.0.2Zr.sub.0.22B.sub.0.98 (wt. %), and the nominal composition of main phase B was (Nd.sub.0.5E.sub.0.5).sub.31.5Fe.sub.ba1Al.sub.0.4Cu.sub.0.2Co.sub.1Ga.sub.0.2Zr.sub.0.22B.sub.0.98 (wt. %) (E including about 27.49 wt. % La, 53.93 wt. % Ce, 1.86 wt. % Pr and 16.72 wt. % Nd). The rotation speed of the copper roller was 1.25 m/s. The A and B strip-casting alloys with a thickness of 210 μm were obtained. The PrHoFe alloy and ZrCu alloy were prepared into strip-casting alloys using a vacuum induction rapid-setting furnace, respectively. Then they were roughly broken into 1 cm*1 cm square pieces.

(28) The A and B strip-casting alloys were broken by hydrogen decrepitation, respectively, and the coarsely crushed powders were obtained after dehydrogenation.

(29) The B hydrogen decrepitation coarse powders and the crushed Pr.sub.65Ho.sub.20Fe.sub.15 strip-casting alloys were placed in the inner and outer cavities of a coaxial double-layer circular barrel with a mass ratio of 1:1, respectively. A metal molybdenum mesh separated the inner and outer cavities of the barrel with a diameter less than 5 μm. The first-step diffusion heat treatment was carried out in a rotary heat treatment furnace with a speed of 5 r/min at 630° C. for 4 h. Then, the hydrogen decrepitation coarse powder obtained by the first-step diffusion and the crushed Zr.sub.55Cu.sub.45 strip-casting alloys were put into a rotary heat treatment furnace with a mass ratio of 1:1. And the second-step diffusion heat treatment was carried out at 915° C. for 3 h with a speed of 5 r/min. In the above heat treatment process, the furnace was first evacuated to 5×10.sup.−3 Pa, and then filled with argon to 65 kPa. The subsequent experiment was carried out in an argon protective atmosphere. The rotary heat treatment furnace is connected with a glove box filled with inert gas to protect the raw materials during moving in and out of the furnace in the glove box.

(30) The A and diffused B hydrogen decrepitation coarse powders were mixed with the mass ratios of 1:9 and 3:7. And the powders of two components C2 and D2 with a mean diameter (X.sub.50) of 2.10 μm were obtained by jet milling after adding 0.05 wt. % lubricant and 0.1 wt. % antioxidant.

(31) In the glove box, the C2 and D2 jet milling powders added 0.1 wt. % lubricant and 0.2 wt. % antioxidant were mixed evenly, respectively. Next, the C2 and D2 magnetic powders were aligned and compacted under a magnetic field of 2.0 T in inert gas. The C2 and D2 green compacts were vacuum packaged for isostatic pressing and then placed in a vacuum sintering furnace for sintering at 1050° C. for 2 h and then cooled by argon. Subsequently, only low-temperature heat treatment was carried out, the tempering temperature was 450° C. for 4 h.

(32) The magnetic properties of the C2 and D2 magnets were measured by the permanent magnetic measurement system (BH tester), the results were as follows:

(33) Binary-main-phase magnet C2: B.sub.r=12.71 kG, H.sub.cj=14.89 kOe, (BH).sub.max=39.92 MGOe, H.sub.k/H.sub.cj=96.3%.

(34) Binary-main-phase magnet D2: B.sub.r=12.94 kG, H.sub.cj=17.06 kOe, (BH).sub.max=41.57 MGOe, H.sub.k/H.sub.cj=96.4%.

Example 3

(35) The nominal composition of main phase A was Pr.sub.31.5Fe.sub.ba1Al.sub.0.4Cu.sub.0.2Co.sub.1Ga.sub.0.2Zr.sub.0.22B.sub.0.98 (wt. %), and the nominal composition of main phase B was (Nd.sub.0.5E.sub.0.5).sub.31.5Fe.sub.ba1Al.sub.0.4Cu.sub.0.2Co.sub.1Ga.sub.0.2Zr.sub.0.22B.sub.0.98 (wt. %) (E including about 27.49 wt. % La, 53.93 wt. % Ce, 1.86 wt. % Pr and 16.72 wt. % Nd). The rotation speed of the copper roller was 1.25 m/s. The A and B strip-casting alloys with a thickness of 210 μm were obtained.

(36) The PrHoFe alloy and ZrCu alloy were prepared into strip-casting alloys using a vacuum induction rapid-setting furnace, respectively. Then they were roughly broken into 1 cm*1 cm square pieces.

(37) The A and B strip-casting alloys were broken by hydrogen decrepitation, respectively, and the coarsely crushed powders were obtained after dehydrogenation.

(38) The B hydrogen decrepitation coarse powders and the crushed Pr.sub.65Ho.sub.20Fe.sub.15 strip-casting alloys were placed in the inner and outer cavities of a coaxial double-layer circular barrel with a mass ratio of 1:1, respectively. A metal molybdenum mesh separated the inner and outer cavities of the barrel with a diameter less than 5 μm. The first-step diffusion heat treatment was carried out in a rotary heat treatment furnace with a speed of 5 r/min at 630° C. for 4 h. Then, the hydrogen decrepitation coarse powder obtained by the first-step diffusion and the crushed Zr.sub.55Cu.sub.45 strip-casting alloys were put into a rotary heat treatment furnace with a mass ratio of 1:1. And the second-step diffusion heat treatment was carried out at 915° C. for 3 h with a speed of 10 r/min. In the above heat treatment process, the furnace was first evacuated to 5×10.sup.−3 Pa, and then filled with argon to 65 kPa. The subsequent experiment was carried out in an argon protective atmosphere. The rotary heat treatment furnace is connected with a glove box filled with inert gas to protect the raw materials during moving in and out of the furnace in the glove box.

(39) The A and diffused B hydrogen decrepitation coarse powders were mixed with the mass ratios of 1:9 and 3:7. And the powders of two components C3 and D3 with a mean diameter (X.sub.50) of 2.10 μm were obtained by jet milling after adding 0.05 wt. % lubricant and 0.1 wt. % antioxidant.

(40) In the glove box, the C3 and D3 jet milling powders added 0.1 wt. % lubricant and 0.2 wt. % antioxidant were mixed evenly, respectively. Next, the C3 and D3 magnetic powders were aligned and compacted under a magnetic field of 2.0 T in inert gas. The C3 and D3 green compacts were vacuum packaged for isostatic pressing and then placed in a vacuum sintering furnace for sintering at 1050° C. for 2 h and then cooled by argon. Subsequently, only low-temperature heat treatment was carried out, the tempering temperature was 450° C. for 4 h.

(41) The magnetic properties of the C3 and D3 magnets were measured by the permanent magnetic measurement system (BH tester), the results were as follows:

(42) Binary-main-phase magnet C3: B.sub.r=12.76 kG, H.sub.cj=15.04 kOe, (BH).sub.max=40.13 MGOe, H.sub.k/H.sub.cj=97.3%.

(43) Binary-main-phase magnet D3: B.sub.r=13.03 kG, H.sub.cj=17.31 kOe, (BH).sub.max=42.05 MGOe, H.sub.k/H.sub.cj=97.8%.

(44) The lubricants used in all the above comparative examples and examples are conventional in the field, and the antioxidant is conventional in the field.

(45) TABLE-US-00001 TABLE 1 The B.sub.r, H.sub.cj, (BH).sub.max, and H.sub.k/H.sub.cj of the magnets in the comparative examples and examples. B.sub.r H.sub.cj (BH).sub.max H.sub.k/H.sub.cj (kG) (kOe) (MGOe) (%) Comparative Magnet A 13.69 20.18 45.72 97.7 Example 1 Magnet B 12.29  9.02 36.86 92.0 Comparative BMP magnet C 12.53  9.53 38.11 93.4 Example 1 BMP magnet D 12.68 12.05 39.50 94.2 Examples 1 Powder diffusion 12.65 14.87 39.76 96.7 BMP magnet C1 Powder diffusion 12.92 16.95 41.31 96.5 BMP magnet D1 Examples 2 Powder diffusion 12.71 14.89 39.92 96.3 BMP magnet C2 Powder diffusion 12.94 17.06 41.57 96.4 BMP magnet D2 Examples 3 Powder diffusion 12.76 15.04 40.13 97.3 BMP magnet C3 Powder diffusion 13.03 17.31 42.05 97.8 BMP magnet D3