WO2023197621A1

WO2023197621A1 - Preparation method for heterojunction-containing sintered aluminum-nickel-cobalt doped with cast aluminum-nickel-cobalt

Info

Publication number: WO2023197621A1
Application number: PCT/CN2022/136370
Authority: WO
Inventors: 冯建涛; 赵宇; 于京京; 张其雪; 舒曾昌
Original assignee: 杭州永磁集团有限公司
Priority date: 2022-04-11
Filing date: 2022-12-02
Publication date: 2023-10-19
Also published as: CN114855056B; CN114855056A

Abstract

A preparation method for heterojunction-containing sintered aluminum-nickel-cobalt doped with cast aluminum-nickel-cobalt. Cast aluminum-nickel-cobalt fine powder is doped into a sintered aluminum-nickel-cobalt material, and process details such as the particle size and sintering of the powder are optimized in a targeted manner, so that a heterojunction-containing sintered aluminum-nickel-cobalt material having improved magnetic properties is obtained.

Description

A method for preparing heterojunction sintered AlNiCo doped with cast AlNiCo

Technical field

The invention relates to the field of permanent magnet materials, and in particular to a method for preparing heterojunction sintered AlNiCo doped with cast AlNiCo.

Background technique

According to different production processes, Alnico magnets are generally divided into sintered Alnico and cast Alnico. Among them, sintered alnico magnets adopt a pressing-sintering process and can be made into materials with various special-shaped structures and are widely used in various small devices. The disadvantages of sintered alnico magnets are low density and poor magnetic properties, which greatly limits its range of use. Unlike sintered AlNiCo magnets, cast AlNiCo magnets are directly cast from molten steel and have high magnetic properties. However, their disadvantages are poor toughness and high processing difficulty. The specific manifestations are that corner breakage, crystal dropout and other phenomena are easily produced during the processing, and the yield after processing is unstable. At present, in the production process, such scrapped cast aluminum-nickel-cobalt finished products are often used as recycled materials to improve the utilization rate of raw materials. However, considering the effects of re-smelting burnout and inclusion of impurities, such scrap magnetic steel used as recycled materials can generally only be used as supplementary materials for low-grade products, or new materials need to be added, such as new cobalt, aluminum, nickel and other raw materials. The performance of the new magnet can be restored.

From the perspective of raw material utilization and cost, in order to further improve the magnetic properties of powder sintered alnico magnets, the formula needs to further increase the content of cobalt, titanium, etc., and the pressing process needs to pursue higher pressure in order to obtain higher density. Regardless of the difficulty and space of formula adjustment, if you want to obtain higher-performance powder-sintered alnico, the cost obviously needs to increase accordingly. In addition, for cast aluminum nickel cobalt, although the processed scrap products are used as re-melted materials, the utilization rate of materials is improved to a certain extent. However, the smelting process will still cause volatilization loss of internal low melting and boiling point components, such as aluminum. Moreover, compared with powder sintered AlNiCo, the raw material cost of cast AlNiCo is lower. Taking the material cobalt as an example, the price difference between cobalt powder in powder-sintered alnico and cast cobalt flakes/beans is 100,000 yuan/ton. Therefore, if scrapped, low-cost cast AlNiCo magnets can be used in powder sintered AlNiCo products to obtain a powder sintered AlNiCo material with superior performance, it will have great economic benefits and practicality. value.

Contents of the invention

In order to solve the above technical problems, the present invention provides a method for preparing heterojunction sintered AlNiCo doped with cast AlNiCo. The present invention obtains a heterojunction sintered aluminum with superior magnetic properties by doping cast AlNiCo fine powder into the sintered AlNiCo material and simultaneously optimizing the powder particle size, sintering and other process details in a targeted manner. Nickel cobalt material.

The specific technical solution of the present invention is: a preparation method of heterojunction sintered AlNiCo doped with cast AlNiCo, which includes the following steps:

(1) Weighing and mixing powder: Weigh the following mass percentage of powder, including: Ni 12-14%, Cu 3-4%, Co 5-6%, CoAl alloy 32-35%, NbFe alloy 4-5 %, TiFe alloy 1.5-2%, the balance of elemental iron powder; mix all the powder materials evenly.

(2) Pressing and pre-sintering: The powder obtained in step (1) is pressed and formed, and then vacuum-sintered at 900 to 1000°C to obtain a pre-sintered blank.

(3) Pulverizing: coarsely crush the pre-sintered blank obtained in step (2), sieve, and air-flow mill to obtain pre-sintered fine powder with an average particle size of 15-20 μm, which is recorded as A powder.

(4) Preparation of casting powder: Take the cast aluminum nickel cobalt alloy blank, clean it and then melt it, add aluminum, and after the smelting is complete, cast the caster; coarsely crush the obtained caster, sieve, and airflow grinding to obtain average particles. Cast alloy fine powder with a diameter of 18-25 μm is recorded as B powder; the particle size distribution of the A powder and B powder satisfies the following conditions: D ₅₀ (B) > D ₅₀ (A), and D ₉₀ /D ₁₀ (B )>D ₉₀ /D ₁₀ (A).

(5) Powder mixing and pressing: Mix the A powder and B powder and press them into shape to obtain a pressed blank of corresponding shape.

(6) Sintering: The pressed blank is vacuum sintered, cooled and released from the furnace to obtain a sintered blank.

(7) Heat treatment and tempering: The sintered blank obtained in step (6) is subjected to magnetic field heat treatment, and then a semi-finished product blank is obtained after three-stage tempering treatment.

(8) Finishing: The semi-finished product blank is finely ground to remove surface impurities and defects, and the finished product is obtained after cleaning.

In the present invention, a sintered AlNiCo permanent product with a heterogeneous structure and enhanced magnetic properties is produced by doping cast AlNiCo waste products (which can also be qualified products) into the sintered AlNiCo material, and through powder mixing and sintering. Magnetic materials. The present invention fully takes into account the performance characteristics of cast Alnico and sintered Alnico. Among them, cast Alnico has dense crystals and high magnetic properties (remanence), while sintered Alnico has relatively low magnetic properties, but the material It has high utilization rate and can be directly formed by pressing and can be prepared into a variety of shapes. And compared with cast AlNiCo, the raw material requirements for sintered AlNiCo are more stringent. Slightly lighter impurities can easily cause pores and affect performance, resulting in a higher price. When preparing cast AlNiCo, the molten alloy liquid has a stronger coating of impurities and oxides, and its cost is lower. Therefore, using it to replace raw materials of the same quality in sintered AlNiCo has huge economic benefits. Moreover, doping the sintered AlNiCo alloy with an appropriate proportion of cast AlNiCo alloy powder can effectively reduce the sintering temperature and time and prevent deformation. Finally, a composite material containing a heterogeneous structure is formed, which has the advantages of high density, strong magnetism, and can be pressed.

In terms of the composition of a single smallest microstructural unit, the composite material containing a heterostructure finally obtained by the present invention has the core of the unit formed by the incorporated cast AlNiCo material, and the periphery of the structure is formed of the sintered AlNiCo material. In terms of microstructure, the melted cast Alnico material is more thorough and dense than the sintered Alnico material. However, there is no significant difference in the overall composition of the permanent magnet material from conventional sintered AlNiCo (the composition is still AlNiCo).

In addition, in order to form the above-mentioned special unit structure, and taking into account the impact of incorporating cast AlNiCo on sintered AlNiCo, the present invention specifically adjusts the preparation process to make it different from traditional sintered AlNiCo. The preparation process is specifically reflected in the following aspects:

(1) In the preparation process of traditional sintered AlNiCo, no pre-sintering process is required, but the present invention takes into account the continuity of the composite material structure to prevent internal cracks and incompatibility. In the present invention, in step (2), the A powder is pre-sintered once, and the particle size of the A powder is controlled to be smaller than the particle size of the B powder, which is beneficial to the growth and remelting of the material in subsequent sintering. Specifically, the coercive force of powder-sintered AlNiCo permanent magnet materials comes from the growth of internal crystals. Therefore, controlling the particle size of the powder and refining its particle size range are beneficial to subsequent sintering to form large grains. And we found that the temperature required for complete melting of cast AlNiCo is much higher than that of the unformed powder (A powder is not yet complete AlNiCo). In order to form a heterogeneous structure, the present invention only needs to cast aluminum nickel cobalt powder to form a molten state, and powder A needs to be melted to completely form aluminum nickel cobalt. During the sintering process, powder A is completely converted into aluminum nickel cobalt and mixed with the molten cast aluminum nickel. Cobalt (B powder) is coupled, so it is necessary to ensure that the temperatures of the two are as close as possible without being too different to avoid causing abnormal volatilization of a single component (compared to normal powder sintered body), such as Al. Or, the two cannot be coupled due to the large temperature difference, resulting in faults or local deformations (as shown in Figure 1). Therefore, the present invention controls the particle size of the cast alloy fine powder (B powder) to be slightly larger than the pre-sintered fine powder (A powder).

(2) In addition, the present invention compensates for the excessive addition of aluminum powder during the melting process of casting AlNiCo. Part of it can be used as the burning loss of smelting and powdering, and part of it can be used as the liquid phase component of subsequent sintering to fill the gaps in the powder particles. , further improving the overall density and performance of the material.

(3) Since the present invention incorporates an appropriate amount of cast AlNiCo alloy powder into the sintered AlNiCo, the sintering temperature is appropriately reduced and the sintering time is shortened (the traditional sintering AlNiCo temperature and time are 1360 to 1380°C , 6~8h), which can prevent material deformation.

Preferably, in step (1), the Co content in the CoAl alloy is 70-80%, the Nb content in the NbFe alloy is 60-70%, and the Ti content in the TiFe alloy is 25-35%.

Preferably, in step (1), mix all the powders, add 0.3-0.7wt% aluminum stearate, and continue mixing for 10-20 minutes. Preferably, in step (2), the vacuum sintering conditions are: heating to 450-550°C at a temperature rise rate of 3-7°C/min and holding for 1-2 hours, and then raising the temperature to a sintering temperature of 900-1000°C and sintering for 1-2 hours. 2h, cool to room temperature.

Preferably, in step (3), the sieving is 50 mesh sieve.

Preferably, in step (4), the elemental composition of the cast AlNiCo alloy blank is Al 8~9%; Ni 12~14%; Co 24~26%; Cu 3~4%; Nb 0.7~0.9% ;The balance is Fe.

Preferably, in step (4), the added amount of aluminum is 0.5-1.0% of the total weight of the cast AlNiCo alloy blank.

Preferably, in step (5), the mass ratio of the A powder and B powder is 4 to 8:1.

Preferably, in step (5), mix A powder and B powder, add 0.3-0.7wt% aluminum stearate, and continue mixing for 15-30 minutes.

Preferably, in step (6), the vacuum sintering conditions are: heating to 450-500°C at a temperature rise rate of 3-5°C/min at room temperature, holding for 1-2 hours, and then raising the temperature to 800-900°C for holding. 1~2h, continue to raise the temperature to 1330~1360℃, keep warm for 0.2~0.5h, then continue to raise the temperature to 1340~1370℃, keep warm for 6.5~7h, and finally cool to room temperature.

Preferably, step (7) specifically includes: placing the sintered blank in an environment of 800-900°C for 30-50 minutes, and then transferring it to a solid solution heat treatment of 1260-1280°C for 20-40 minutes; then taking out the sintered blank and waiting for After the surface is cooled to 800-900°C, transfer it to a magnetic field and place it for 20-30 minutes; after taking it out and cooling it to room temperature, perform three-level tempering treatment: first keep it at 610-625°C for 3-4 hours, and then keep it at 580-595°C for 4-6 hours. , then keep it at 550-565℃ for 4-6 hours, and finally cool it to obtain a semi-finished product blank.

Compared with the existing technology, the present invention has the following technical effects:

(1) The present invention makes full use of the characteristics of cast AlNiCo and sintered AlNiCo materials. By doping cast AlNiCo fine powder into the sintered AlNiCo material, a sintered AlNiCo material with a heterogeneous structure is obtained. Cobalt material. The composite material has the advantages of high density, strong magnetism, and can be pressed. In addition, scrapped cast aluminum nickel cobalt materials are recycled and used, which is beneficial to reducing costs.

(2) In order to form a composite AlNiCo material with an ideal crystal phase structure, the present invention specifically optimizes the powder particle size, sintering and other process details, and the AlNiCo material finally obtained has excellent magnetic properties.

Description of the drawings

Figure 1 is a photograph of the magnet obtained in Example 1 (left) and Comparative Example 3 (right).

Detailed ways

The present invention will be further described below in conjunction with examples.

General embodiment

A method for preparing heterojunction sintered AlNiCo doped with cast AlNiCo, including the following steps:

(1) Weighing and mixing powder: Weigh the following mass percentage of powder, including: Ni 12-14%, Cu 3-4%, Co 5-6%, CoAl alloy (Co content 70-80%) 32- 35%, NbFe alloy (Nb content 60-70%) 4-5%, TiFe alloy (Ti content 25-35%) 1.5-2%, the balance of elemental iron powder; mix all the powder materials, add 0.3-0.7 wt% aluminum stearate, continue mixing for 10 to 20 minutes.

(2) Pressing and pre-sintering: Press the powder obtained in step (1) into shape, and then sinter it in a vacuum. The conditions are: heating to 450-550°C at a heating rate of 3-7°C/min and holding for 1-2 hours, and then raising the temperature to sintering. Sintering at a temperature of 900 to 1000°C for 1 to 2 hours, and then cooled to room temperature; a pre-sintered blank is obtained.

(4) Preparation of casting powder: Take the cast AlNiCo alloy blank (elemental composition is Al 8~9%; Ni 12~14%; Co 24~26%; Cu 3~4%; Nb 0.7~0.9%; remainder (Fe), clean and melt, add 0.5-1.0% aluminum of the total weight of the cast alnico alloy blank, after complete smelting, cast the strips; coarsely crush the resulting strips, pass through a 50-mesh sieve, and airflow grinding into powder , obtain casting alloy fine powder with an average particle size of 18-25 μm, recorded as B powder; the particle size distribution of the A powder and B powder satisfies the following conditions: D ₅₀ (B) > D ₅₀ (A), and D ₉₀ / D ₁₀ (B)>D ₉₀ /D ₁₀ (A).

(5) Powder mixing and pressing: Mix the A powder and B powder at a mass ratio of 4 to 8:1, add 0.3-0.7wt% aluminum stearate, and continue mixing for 15 to 30 minutes; press and shape to obtain the corresponding Shape pressed blank.

(6) Sintering: The pressed blank is vacuum sintered under the following conditions: at room temperature, it is heated to 450-500°C at a heating rate of 3-5°C/min, kept for 1-2 hours, and then heated to 800-900°C for heat preservation. 1~2h, continue to raise the temperature to 1330~1360℃ and keep it for 0.2~0.5h, then continue to raise the temperature to 1340~1370℃, keep it for 6.5~7h, finally cool to room temperature, take it out of the furnace, and obtain the sintered blank.

(7) Heat treatment and tempering: Place the sintered blank in an environment of 800-900°C for pretreatment for 30-50 minutes, and then transfer it to an environment of 1260-1280°C for solid solution heat treatment for 20-40 minutes; then take out the sintered blank and wait for its surface to cool After reaching 800~900℃, transfer it to a magnetic field and place it for 20~30 minutes; take it out and cool it to room temperature, then perform three-level tempering treatment: first keep it at 610~625℃ for 3~4h, then keep it at 580~595℃ for 4~6h, and then Insulate at 550-565℃ for 4-6 hours, and finally cool to obtain a semi-finished product blank.

Example 1

1. Weigh the elemental powder and alloy powder, including elemental powder: Ni: 12%, Cu: 4%, Co: 5%; alloy powder: CoAl (Co content 75%): 32%, NbFe (Nb content 60%): 4%, TiFe (Ti content 25%): 1.5%; the rest is elemental iron powder; mix all the powders, add 0.5% aluminum stearate, and continue mixing for 20 minutes.

2. Use a molding press to press the above powder into a D20*8mm cake shape, then heat it to 450°C at a heating rate of 3°C/min and keep it for 2 hours, then raise the temperature to the sintering temperature of 900°C and sinter for 2 hours, and cool to room temperature to obtain Pre-sintered blank.

3. Coarsely crush the above pre-sintered blank, pass it through a 50-mesh sieve, and then grind it into powder by airflow. D50=15μm, D90/D10=6, recorded as A powder.

4. Remove the five types of casting alloy blanks that need to be scrapped after appearance defects such as crystals and broken corners. Its elemental composition is Al 8%; Ni 13%; Co 25%; Cu 3%; Nb 0.8%; the balance is Fe, clean it Clean it, add it to the vacuum rapid solidification belt throwing furnace, add aluminum with 0.5% of the total weight of the alloy, and cast the throwing plate after the melting is complete. The prepared belt-throwing piece is put into a mortar, crushed with a punch, and the coarsely crushed powder obtained by the crushing is sieved to obtain the cast alloy coarse powder. Further jet milling was performed to obtain the fine powder of cast alloy with D50=21μm and D90/D10=8.2, which was recorded as B powder.

5. Mix the A/B powder prepared above according to the mass ratio of 5:1, add 0.5% aluminum stearate, and continue mixing for 30 minutes. Press forming to obtain a pressed blank of corresponding shape.

6. Put the above-mentioned pressed blank into a vacuum sintering furnace, heat it to 500°C at a heating rate of 5°C/min, keep it for 1 hour, then raise it to 900°C and keep it for 1 hour, continue to heat it to 1330°C and keep it for 0.2 hours, and then continue to heat it to 1340℃, keep warm for 7h, and finally cool to room temperature with the furnace.

7. Perform magnetic field heat treatment on the product obtained in step 6. First, pretreat the blank in a box-type resistance furnace at 800°C for 50 minutes, and then transfer the blank to a high-temperature furnace at 1260°C for solid solution heat treatment for 40 minutes. Then, take out the blank, wait until the surface of the magnetic steel is cooled to 800°C, then transfer it to the magnetic field, cover it with insulation cotton, and place it in the magnetic field for 30 minutes. After taking it out and cooling it to room temperature, perform tempering treatment. The process is 610°C for 4 hours, 580°C for 5 hours, 550°C for 6 hours, and finally cooled in the furnace.

8. Finely grind the semi-finished product blank to remove defects such as oxide scale on the surface, clean it, and obtain the finished product after passing the inspection.

Example 2

1. Weigh the elemental powder and alloy powder, including elemental powder: Ni: 13%, Cu: 3%, Co: 6%; alloy powder: CoAl (Co content 75%): 33%, NbFe (Nb content 60%): 5%, TiFe (Ti content 25%): 1.5%; the rest is elemental iron powder; mix all the powders, add 0.5% aluminum stearate, and continue mixing for 20 minutes.

2. Use a molding press to press the above powder into a D20*8mm cake shape, then heat it to 500°C at a heating rate of 5°C/min and keep it for 1.5h, then raise the temperature to the sintering temperature of 950°C and sinter for 1.5h, and cool to room temperature. , to obtain the pre-sintered blank.

3. Coarsely crush the above pre-sintered blank, pass it through a 50-mesh sieve, and then air-flow mill it into powder. The average particle size is controlled at D50 = 18 μm, D90/D10 = 5.8, and is recorded as A powder.

4. Remove the five types of casting alloy blanks that need to be scrapped after appearance defects such as crystals and broken corners. Its elemental composition is Al 8%; Ni 13%; Co 25%; Cu 3%; Nb 0.8%; the balance is Fe, clean it Clean it, add it to the vacuum rapid solidification belt throwing furnace, add aluminum with 1.0% of the total weight of the alloy, and cast the throwing plate after the melting is complete. The prepared belt-throwing piece is put into a mortar, crushed with a punch, and the coarsely crushed powder obtained by the crushing is sieved to obtain the cast alloy coarse powder. Further jet milling was performed to obtain cast alloy fine powder with D50=24μm and D90/D10=6.5, which was recorded as B powder.

5. Mix the A/B powder prepared above according to the mass ratio of 6:1, add 0.5% aluminum stearate, and continue mixing for 30 minutes. Press forming to obtain a pressed blank of corresponding shape.

6. Put the above-mentioned pressed blank into a vacuum sintering furnace, heat to 500°C at a heating rate of 5°C/min, hold for 1 hour, then heat to 900°C for 1 hour, continue to heat to 1340°C and hold for 0.2 hours, and then continue to heat to 1340°C for 0.2 hours. 1360℃, keep warm for 6.5h, and finally cool to room temperature with the furnace.

Example 3

1. Weigh the elemental powder and alloy powder, including elemental powder: Ni: 14%, Cu: 4%, Co: 6%; alloy powder: CoAl (Co content 75%): 35%, NbFe (Nb content 60%): 5%, TiFe (Ti content 25%): 2.0%; the rest is elemental iron powder; mix all the powders, add 0.5% aluminum stearate, and continue mixing for 20 minutes.

2. Use a molding press to press the above powder into a D20*8mm cake shape, heat it to 550°C at a heating rate of 6°C/min and keep it for 1 hour, then raise the temperature to the sintering temperature of 1000°C and sinter for 1 hour, cool to room temperature, and obtain the preform. Sintered blank.

3. Coarsely crush the above pre-sintered blank, pass it through a 50-mesh sieve, and then air-flow grind it into powder to obtain D50=20μm, D90/D10=5.0, which is recorded as A powder.

4. Remove the five types of casting alloy blanks that need to be scrapped after appearance defects such as crystals and broken corners. Its elemental composition is Al 8%; Ni 13%; Co 25%; Cu 3%; Nb 0.8%; the balance is Fe, clean it Clean it, add it to the vacuum rapid solidification belt throwing furnace, add aluminum with 1.0% of the total weight of the alloy, and cast the throwing plate after the melting is complete. The prepared belt-throwing piece is put into a mortar, crushed with a punch, and the coarsely crushed powder obtained by the crushing is sieved to obtain the cast alloy coarse powder. Further jet milling was performed to obtain the fine powder of cast alloy with D50=25μm and D90/D10=6.4, which was recorded as B powder.

5. Mix the A/B powder prepared above at a mass ratio of 8:1, add 0.5% aluminum stearate, and continue mixing for 30 minutes. Press forming to obtain a pressed blank of corresponding shape.

6. Put the above-mentioned pressed blank into a vacuum sintering furnace, heat to 500°C at a heating rate of 5°C/min, hold for 1 hour, then heat to 900°C for 1 hour, continue to heat to 1360°C and hold for 0.2 hours, and then continue to heat to 1360°C for 0.2 hours. 1370℃, keep warm for 6.5h, and finally cool to room temperature with the furnace.

7. Perform magnetic field heat treatment on the product obtained in step 6. First, pretreat the blank in a box-type resistance furnace at 800°C for 50 minutes, and then transfer the blank to a high-temperature furnace at 1270°C for solid solution heat treatment for 40 minutes. Then, take out the blank, wait until the surface of the magnetic steel is cooled to 800°C, then transfer it to the magnetic field, cover it with insulation cotton, and place it in the magnetic field for 30 minutes. After taking it out and cooling it to room temperature, perform tempering treatment. The process is 615°C for 4 hours, 585°C for 5 hours, 555°C for 6 hours, and finally cooled in the furnace.

Comparative Example 1 (the difference from Example 1 is: undoped cast aluminum nickel cobalt)

1. Weigh the elemental powder and alloy powder, including elemental powder: Ni: 12%, Cu: 4%, Co: 5%; alloy powder: CoAl (Co content 75%): 32%, NbFe (Nb content 60%): 4%, TiFe (Ti content 25%): 1.5%; the rest is elemental iron powder; mix all the powders (D50=15μm, D90/D10=6), add 0.5% aluminum stearate, and continue mixing for 20 minutes .

2. Press and form to obtain a pressed blank of corresponding shape.

3. Put the above-mentioned pressed blank into a vacuum sintering furnace, heat to 500°C at a heating rate of 5°C/min, hold for 1 hour, then heat to 900°C for 1 hour, continue to heat to 1330°C and hold for 0.2 hours, and then continue to heat to 1340℃, keep warm for 7h, and finally cool to room temperature with the furnace.

4. Perform magnetic field heat treatment on the product obtained in step 3. First, pretreat the blank in a box-type resistance furnace at 800°C for 50 minutes, and then transfer the blank to a high-temperature furnace at 1260°C for solid solution heat treatment for 40 minutes. Then, take out the blank, wait until the surface of the magnetic steel is cooled to 800°C, then transfer it to the magnetic field, cover it with insulation cotton, and place it in the magnetic field for 30 minutes. After taking it out and cooling it to room temperature, perform tempering treatment. The process is 610°C for 4 hours, 580°C for 5 hours, 550°C for 6 hours, and finally cooled in the furnace.

5. Finely grind the semi-finished product blank to remove defects such as oxide scale on the surface, clean it, and obtain the finished product after passing the inspection.

Comparative Example 2 (the difference from Example 1 is that powder A is not pre-sintered)

1. Weigh the elemental powder and alloy powder, including elemental powder: Ni: 12%, Cu: 4%, Co: 5%; alloy powder: CoAl (Co content 75%): 32%, NbFe (Nb content 60%): 4%, TiFe (Ti content 25%): 1.5%; the rest is elemental iron powder; mix all the powders, pass through a 50-mesh sieve, and then airflow grind them into powder. Powder particle size: D50=15μm, D90/D10=6 , recorded as A powder.

2. Remove the five types of casting alloy blanks that need to be scrapped due to appearance defects such as crystals and broken corners. The element composition is Al 8%; Ni 13%; Co 25%; Cu 3%; Nb 0.8%; the balance is Fe, clean it Clean it, add it to the vacuum rapid solidification belt throwing furnace, add aluminum with 0.5% of the total weight of the alloy, and cast the throwing plate after the melting is complete. The prepared belt-throwing piece is put into a mortar, crushed with a punch, and the coarsely crushed powder obtained by the crushing is sieved to obtain the cast alloy coarse powder. Further jet milling was performed to obtain the fine powder of cast alloy with D50=21μm and D90/D10=8.2, which was recorded as B powder.

3. Mix the A/B powder prepared above according to the mass ratio of 5:1, add 0.5% aluminum stearate, and continue mixing for 30 minutes. Press forming to obtain a pressed blank of corresponding shape.

4. Put the above-mentioned pressed blank into a vacuum sintering furnace, heat it to 500°C at a heating rate of 5°C/min, keep it for 1 hour, then raise it to 900°C and keep it for 1 hour, continue to heat it to 1330°C and keep it for 0.2 hours, and then continue to heat it to 1340℃, keep warm for 7h, and finally cool to room temperature with the furnace.

5. Perform magnetic field heat treatment on the product obtained in step 4. First, pretreat the blank in a box-type resistance furnace at 800°C for 50 minutes, and then transfer the blank to a high-temperature furnace at 1260°C for solid solution heat treatment for 40 minutes. Then, take out the blank, wait until the surface of the magnetic steel is cooled to 800°C, then transfer it to the magnetic field, cover it with insulation cotton, and place it in the magnetic field for 30 minutes. After taking it out and cooling it to room temperature, perform tempering treatment. The process is 610°C for 4 hours, 580°C for 5 hours, 550°C for 6 hours, and finally cooled in the furnace.

6. Finely grind the semi-finished product blank to remove defects such as oxide scale on the surface, clean it, and obtain the finished product after passing the inspection.

Comparative Example 3 (the difference from Example 1 is that the particle size of A/B powder is equivalent)

3. Coarsely crush the above pre-sintered blank, pass it through a 50-mesh sieve, and then grind it into powder by airflow. D50=18μm, D90/D10=6.1, recorded as A powder.

4. Remove the five types of casting alloy blanks that need to be scrapped after appearance defects such as crystals and broken corners. Its elemental composition is Al 8%; Ni 13%; Co 25%; Cu 3%; Nb 0.8%; the balance is Fe, clean it Clean it, add it to the vacuum rapid solidification belt throwing furnace, add aluminum with 0.5% of the total weight of the alloy, and cast the throwing plate after the melting is complete. The prepared belt-throwing piece is put into a mortar, crushed with a punch, and the coarsely crushed powder obtained by the crushing is sieved to obtain the cast alloy coarse powder. Further jet milling was performed to obtain fine powder of cast alloy with D50=17μm and D90/D10=6.0, which was recorded as B powder.

Performance Testing

The magnetic property test results of the alnico magnets obtained in each embodiment and comparative example are as shown in Table 1:

Table 1 Performance test results of magnets of different embodiments/comparative examples

It can be seen from the above data:

Compared with Comparative Example 1, Example 1-3 is due to the addition of cast Alnico powder sintered Alnico product (Example 1-3), because the magnetic properties of the cast magnet are better than those of the powder, and due to the casting Due to the coupling effect between the powder and the pre-sintered powder, the density of the sintered sample with a heterogeneous structure generated is improved compared to the pure powder sintered sample, and the performance is better.

Compared with Comparative Example 2, Examples 1-3 can effectively ensure that the sintered powder surrounding the cast AlNiCo forms a single small unit of "AlNiCo" structure by pre-sintering the A powder to prevent other local components from appearing. The structural composition of the alloy affects the performance; and through the coupling effect with the casting powder, the consistency of the overall structure is ensured.

In addition, compared with Comparative Example 3, the optimization of particle size in Examples 1-3 ensures that the temperatures of the casting powder and the sintered powder are more consistent, and the density during the pressing process is more uniform, further ensuring the overall performance.

In addition, Figure 1 shows photos of alnico magnets produced according to the methods of Example 1 (left) and Comparative Example 3 respectively. By comparing the two magnets in the figure, it can be seen that the magnet on the left (Example 1) has no fault phenomenon. There are obvious faults in the magnet on the right. The reason is that the A/B powder did not select the appropriate particle size, resulting in faults during sintering.

In summary, the present invention provides a preparation method for manufacturing heterostructured powder sintered AlNiCo material using cast AlNiCo magnet scrap, which effectively improves the magnetic properties of the sintered AlNiCo material and expands the range of cast AlNiCo magnet waste. The range of use greatly increases the added value of the material. It is of great significance to increase the use scope of AlNiCo materials and reduce their material costs.

The raw materials and equipment used in the present invention, unless otherwise specified, are all commonly used raw materials and equipment in this field; the methods used in the present invention, unless otherwise specified, are all conventional methods in this field.

The above are only preferred embodiments of the present invention and do not limit the present invention in any way. Any simple modifications, changes and equivalent transformations made to the above embodiments based on the technical essence of the present invention still belong to the technical solutions of the present invention. scope of protection.

Claims

A method for preparing heterojunction sintered AlNiCo doped with cast AlNiCo, which is characterized in that it includes the following steps:

(1) Weighing and mixing powder: Weigh the following mass percentage of powder, including: Ni 12-14%, Cu 3-4%, Co 5-6%, CoAl alloy 32-35%, NbFe alloy 4-5 %, TiFe alloy 1.5-2%, the balance of elemental iron powder; mix all powder materials;

(2) Pressing and pre-sintering: The powder obtained in step (1) is pressed and formed, and then vacuum sintered at 900 to 1000°C to obtain a pre-sintered blank;

(3) Pulverizing: coarsely crush the pre-sintered blank obtained in step (2), sieve, and air-flow mill to obtain pre-sintered fine powder with an average particle size of 15-20 μm, which is recorded as A powder;

(4) Preparation of casting powder: Take the cast aluminum nickel cobalt alloy blank, clean it and then melt it, add aluminum, and after the smelting is complete, cast the caster; coarsely crush the obtained caster, sieve, and airflow grinding to obtain average particles. Cast alloy fine powder with a diameter of 18-25 μm is recorded as B powder; the particle size distribution of the A powder and B powder satisfies the following conditions: D 50 of B powder > D 50 of A powder, and D 90 /D of B powder 10 >D 90 /D 10 of A powder;

(5) Powder mixing and pressing: Mix the A powder and B powder, and press them into shape to obtain a pressed blank of the corresponding shape;

(6) Sintering: The pressed blank is vacuum sintered, cooled and released from the furnace to obtain a sintered blank;

(7) Heat treatment and tempering: Subject the sintered blank obtained in step (6) to magnetic field heat treatment, and then undergo three-stage tempering treatment to obtain a semi-finished product blank;

(8) Finishing: The semi-finished product blank is finely ground to remove surface impurities and defects, and the finished product is obtained after cleaning.
The preparation method according to claim 1, characterized in that: in step (1), the Co content in the CoAl alloy is 70-80%, the Nb content in the NbFe alloy is 60-70%, and the Ti content in the TiFe alloy is 25-35%.
The preparation method according to claim 1 or 2, characterized in that: in step (1), all powders are mixed, 0.3-0.7wt% aluminum stearate is added, and mixing is continued for 10-20 minutes.
The preparation method according to claim 1, characterized in that: in step (2), the vacuum sintering conditions are: heating to 450-550°C at a heating rate of 3-7°C/min and holding for 1-2 hours, and then Raise the temperature to the sintering temperature of 900-1000°C and sinter for 1-2 hours, then cool to room temperature.
The preparation method according to claim 1, characterized in that: in step (4), the elemental composition of the cast AlNiCo alloy blank is Al 8~9%, Ni 12~14%, Co 24~26%, Cu 3～4%, Nb 0.7～0.9%, the balance is Fe.
The preparation method according to claim 1 or 5, characterized in that: in step (4), the added amount of aluminum is 0.5-1.0% of the total weight of the cast alnico alloy blank.
The preparation method according to claim 1, characterized in that in step (5), the mass ratio of the A powder and B powder is 4 to 8:1.
The preparation method according to claim 1 or 7, characterized in that: in step (5), mix A powder and B powder, add 0.3-0.7wt% aluminum stearate, and continue mixing for 15-30 minutes.
The preparation method according to claim 1, characterized in that: in step (6), the vacuum sintering conditions are: heating to 450-500°C at a temperature rise rate of 3-5°C/min at room temperature, and holding for 1 ~2h, then raise the temperature to 800~900℃ and keep it for 1~2h, continue to raise the temperature to 1330~1360℃ and keep it for 0.2~0.5h, then continue to raise the temperature to 1340~1370℃, keep it for 6.5~7h, and finally cool to room temperature.
The preparation method according to claim 1, wherein step (7) specifically includes: placing the sintered blank in an environment of 800-900°C for pretreatment for 30-50 minutes, and then transferring it to a solution heat treatment in an environment of 1260-1280°C. 20~40min; then take out the sintered blank, wait until its surface is cooled to 800~900℃, transfer it to a magnetic field and place it for 20~30min; after taking it out and cooling it to room temperature, perform three-level tempering treatment: first keep it at 610~625℃ for 3~ 4h, then keep it at 580~595℃ for 4~6h, then keep it at 550~565℃ for 4~6h, and finally cool it to get the semi-finished product blank.