Anti-corrosion neodymium iron boron magnetic material and preparation process thereof

Abstract

The invention discloses a corrosion-resistant NdFeB magnetic material and a preparation process thereof, and relates to the technical field of NdFeB magnets, and the preparation process comprises the following steps: mixing NdFeB with a grain boundary additive, and carrying out orientation molding in a magnetic field to form a green body; and sintering and carrying out heat treatment to obtain the neodymium iron boron magnetic material. And plating aluminum on the surface to obtain the corrosion-resistant neodymium iron boron magnetic material. And the grain boundary additive comprises magnesium, silicon and magnesium oxide. The grain boundary additive and neodymium iron boron are sintered together, silicon and neodymium form a high-melting-point silicide, a grain boundary phase is refined, a compact oxide layer is formed on the surface of the magnet, and the corrosion resistance of the magnet is improved; the low-melting-point magnesium forms a magnesium-neodymium phase, so that the melting point of the neodymium-rich phase is reduced, the grain boundary wettability is improved, the grain boundary structure is densified, the grain boundary can be purified, and the resistance of the magnet to intergranular corrosion is improved; the magnesium oxide forms an Nd-O-Fe-Mg phase at the grain boundary, grains are refined, and grain boundary corrosion of the magnet is hindered.

Description

Technical Field

[0001] The invention relates to the technical field of NdFeB magnets, in particular to a corrosion-resistant NdFeB magnetic material and a preparation process thereof. Background Art

[0002] Nowadays, with the advocacy of sustainable development and green energy in today's society, NdFeB magnetic materials are widely used in various fields, such as medicine, refrigeration, green energy, etc. Among NdFeB magnetic materials, sintered NdFeB magnets mainly have the main phase (Nd2Fe 14 B) and grain boundaries (Nd-rich phase). The Nd-rich phase is more active and has a larger potential difference with the main phase, which makes the magnet prone to intergranular corrosion, which limits the application of NdFeB magnetic materials. Therefore, we propose a corrosion-resistant NdFeB magnetic material and its preparation process. Summary of the invention

[0003] The object of the present invention is to provide a corrosion-resistant NdFeB magnetic material and a preparation process thereof to solve the problems raised in the above-mentioned background technology.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] A preparation process of corrosion-resistant NdFeB magnetic material, comprising the following processes:

[0006] Mixing NdFeB with grain boundary additives, orienting and molding in a magnetic field to obtain a green body; sintering and heat treating to obtain NdFeB magnetic materials;

[0007] The surface is plated with aluminum to obtain corrosion-resistant NdFeB magnetic material.

[0008] Furthermore, the mass ratio of NdFeB to grain boundary additive is 100:(0.1-0.8).

[0009] Further, NdFeB includes the following mass components: neodymium (Nd): 29.0% to 32.5%, boron (B): 1.1% to 1.2%, cobalt (Co): 0 to 0.25%, and the balance is iron (Fe);

[0010] NdFeB is obtained by melting pure neodymium, iron-boron alloy, pure iron, pure cobalt and other raw materials in an argon atmosphere, rapidly solidifying and spinning, and powdering.

[0011] Furthermore, the NdFeB or grain boundary additives include the following components: a mixture of two or more of magnesium, silicon, copper, aluminum, praseodymium, zinc, magnesium oxide, and aluminum nitride.

[0012] Further, the NdFeB and the grain boundary additive are placed in a mixer and mixed for 90 to 120 minutes under the protection of a nitrogen atmosphere to obtain a mixture;

[0013] The mixed material is placed in a magnetic field pressing and orienting machine, and is pressed into shape by cold isostatic pressing at 17-40 MPa. The strength of the external magnetic field is 1.5-2.8 T, so that the magnetization axis of the mixed material is consistent with the direction of the external magnetic field. The mixed material is cold isostatic pressed at 100-200 MPa to obtain a green body.

[0014] Further, the sintering process is as follows: placing the green body in a vacuum sintering furnace, heating the temperature to 1067-1085°C at a heating rate of 3-5°C / s, sintering for 3-4h, and air cooling to room temperature;

[0015] The heat treatment process is as follows: tempering at 890-960°C for 90-120 minutes; tempering at 460-500°C for 2-5 hours, cooling to 50°C in argon and taking out.

[0016] Furthermore, the melting temperature is 1400-1450°C, and the casting temperature is 1380-1400°C.

[0017] Furthermore, the process of quick-setting belt throwing is as follows: roller speed 0.8-4.0 m / s, sheet thickness 0.2 mm-0.4 mm.

[0018] Furthermore, the pulverizing is hydrogen crushing-air flow milling to obtain NdFeB powder with a particle size of 4 to 5 μm.

[0019] Furthermore, the grain boundary additive includes the following components by mass: 1 to 5 parts of magnesium, 2 to 8 parts of silicon, and 0.5 to 3 parts of magnesium oxide.

[0020] Furthermore, the grain boundary additive is nanoscale.

[0021] In the above technical scheme, during the sintering process of the grain boundary additive and NdFeB, elemental silicon can form high-melting-point silicide with rare earth elements (neodymium), which can inhibit abnormal grain growth, refine grain boundary phases, and improve coercivity. Silicon can also form a dense oxide layer on the surface of the magnet to improve the corrosion resistance of the magnet. The addition of low-melting-point magnesium can form a magnesium-neodymium phase, reduce the melting point of the rare earth-rich phase, improve its grain boundary wettability, facilitate the liquid phase sintering of the magnet, fill the gaps and defects between the grain boundaries, make the grain boundary structure more dense and uniform, and improve the magnetic properties of the magnet; the prepared NdFeB magnetic material (referred to as magnet) has a high density and fewer holes, which reduces the specific surface area of ​​the contact surface between the magnet and the external environment, which helps to improve its corrosion resistance. Magnesium is also highly active and easily reacts with oxygen and nitrogen elements. It can purify the grain boundaries, reduce impurities, increase the domain wall movement energy barrier, and help improve the comprehensive performance of the magnet. Adding magnesium oxide to the grain boundary as an inert additive can pin the grain boundary and inhibit grain growth. At high temperatures, it can provide a small amount of oxygen to the grain boundary region, forming a Nd-O-Fe-Mg phase at the grain boundary, thereby inhibiting grain growth and refining the grains, which can refine the intergranular corrosion channel of the magnet and hinder the grain boundary corrosion of the magnet. The standard electrode potential of Mg2+ / Mg is higher than that of Nd3+ / Nd, which improves the electrode point position of the grain boundary phase in the magnet and improves the magnet's resistance to corrosion; and as the grain size decreases, the coercive force of the magnet is improved. The synergistic addition of silicon and magnesium can form a magnesium-silicon-neodymium ternary phase, which helps to further stabilize the grain boundary of the magnet. At the same time, magnesium will preferentially combine with oxygen impurities to reduce the loss of silicon, so that the silicon element can act more effectively on the grain boundary modification of the magnet. Magnesium oxide and the formed silicide can jointly improve the thermal stability of the magnet grain boundary phase and reduce its high-temperature irreversible demagnetization rate. The addition of grain boundary additives can also reduce the internal stress generated during the sintering process of the magnet and reduce the loss of magnetic properties caused by internal stress. The increase of non-magnetic phases (MgO, silicide) may lead to a decrease in the remanence of the magnet, so it is necessary to optimize the proportion of each component in the crystal additive.

[0022] Furthermore, before the green body is sintered, a calcium fluoride composite sol is coated on its surface with a coating thickness of 1 to 5 μm.

[0023] Further, the calcium fluoride composite sol is prepared by the following process;

[0024] The potassium fluoride solution is slowly added to the calcium nitrate solution, and the mixture is stirred for reaction for 90 to 120 minutes and aged for 24 hours to obtain a calcium fluoride sol; and the silica sol is added to obtain a calcium fluoride composite sol.

[0025] Further, the molar ratio of potassium fluoride to calcium nitrate is (1.05-1.10):1;

[0026] The mass ratio of calcium fluoride sol to silica sol is (1-3): (0.5-2);

[0027] Further, the concentration of the potassium fluoride solution is 2M;

[0028] The concentration of calcium nitrate solution is 1M;

[0029] The rate of addition of potassium fluoride solution was 10 mL / min;

[0030] The solid content of silica sol is 10% to 40%.

[0031] In the above technical scheme, calcium fluoride and silicon dioxide assist in grain boundary reconstruction to form dense protection on the surface of the magnet. At the sintering temperature, calcium fluoride can form Ca-Nd-F compounds with the rare earth-rich phase, which has better thermal stability and can generate silicates (CaSiO3), further stabilizing the grain boundaries, enhancing the grain boundary isolation effect, forming a barrier layer, reducing the oxidation of neodymium, hindering the formation of the non-magnetic phase Nd-O, inhibiting the expansion of the reverse magnetization domain, improving the coercive force, reducing the corrosion rate of the magnet in corrosive media or high temperature environments, and improving the overall mechanical properties of the magnet.

[0032] Furthermore, the process of surface aluminum plating is as follows: using aluminum as the target, magnetron sputtering is performed on the surface of the NdFeB magnetic material to form an aluminum film; the target-substrate distance is 80 mm, and the vacuum degree is 6.5×10 -4 ~8.0×10 -4 Pa, the working gas is high-purity argon, the flow rate is 50sccm, and the thickness of the aluminum film is 0.5-5μm;

[0033] Then anneal at 300-350°C for 2-5h.

[0034] In the above technical solution, magnetron sputtering is used to form aluminum film on the surface of the NdFeB magnetic material (barrier layer), which is then annealed to form aluminum oxide, which can further improve the oxidation resistance, corrosion resistance and mechanical strength of the magnet.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. A preparation process of a corrosion-resistant NdFeB magnetic material of the present invention comprises the following steps: sintering the NdFeB with a grain boundary additive, wherein silicon forms a high-melting-point silicide with neodymium to refine the grain boundary phase, and forms a dense oxide layer on the surface of the magnet, thereby improving the corrosion resistance of the magnet; low-melting-point magnesium forms a magnesium-neodymium phase, thereby lowering the melting point of the neodymium-rich phase, improving the wettability of the grain boundary, densifying the grain boundary structure, purifying the grain boundary, and improving the resistance of the magnet to intergranular corrosion; and magnesium oxide forms an Nd-O-Fe-Mg phase at the grain boundary, thereby refining the grains and hindering the grain boundary corrosion of the magnet.

[0037] 2. A preparation process of a corrosion-resistant NdFeB magnetic material of the present invention comprises the following steps: before sintering the green body, a calcium fluoride composite sol is coated on the surface of the green body, and calcium fluoride and silicon dioxide are used to assist in grain boundary reconstruction to form a dense protection on the surface of the magnet. At the sintering temperature, calcium fluoride and the rare earth-rich phase form a Ca-Nd-F compound, which has better thermal stability and can generate silicates, further stabilize the grain boundaries, enhance the grain boundary isolation effect, form a barrier layer, reduce the oxidation of neodymium, hinder the formation of the non-magnetic phase Nd-O, inhibit the expansion of the reverse magnetization domain, enhance the coercive force, reduce the corrosion rate of the magnet in a corrosive medium or a high temperature environment, and improve the overall mechanical properties of the magnet.

[0038] 3. The preparation process of a corrosion-resistant NdFeB magnetic material of the present invention forms an aluminum film on the surface of the NdFeB magnetic material (barrier layer) by magnetron sputtering aluminum plating, and annealing to form aluminum oxide, which can further improve the oxidation resistance, corrosion resistance and mechanical strength of the magnet. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] In the following specific implementations,

[0041] NdFeB includes the following mass components: neodymium: 23.1%, praseodymium: 6.1%, boron: 1.18%, cobalt: 0.24%, and the balance is iron;

[0042] NdFeB is made of pure neodymium, iron-boron alloy (Fe80B20), pure iron, pure cobalt and pure praseodymium raw materials (purity ≥99.9%), which are melted at 1420±10℃ in an argon atmosphere and cast at 1390℃±10℃; the powder is quickly solidified and spun off with a roller speed of 1.0m / s and a sheet thickness of 0.3mm, and then pulverized by hydrogen crushing-air flow grinding to obtain NdFeB powder with a particle size of 4-5μm.

[0043] Magnesium, silicon and magnesium oxide are all nanometer-grade powders with a purity of ≥99.5% and particle sizes of 50-90nm, 30-60nm and 30±10nm respectively.

[0044] Embodiment 1: A preparation process of a corrosion-resistant NdFeB magnetic material, comprising the following process:

[0045] Step 1, placing NdFeB and a grain boundary additive in a mixer, wherein the mass ratio of NdFeB to the grain boundary additive is 100:0.1, and the grain boundary additive includes the following mass components: 1 part of magnesium, 2 parts of silicon, and 0.5 parts of magnesium oxide; mixing for 90 minutes under nitrogen atmosphere protection to obtain a mixture;

[0046] Step 2, placing the mixture in a magnetic field pressing and orienting machine, pressing and molding at 17MPa cold isostatic pressing, applying a magnetic field strength of 1.5T, so that the magnetization axis of the mixture is consistent with the direction of the external magnetic field, and cold isostatic pressing at 100MPa to obtain a green body;

[0047] Step 3, slowly adding 2M potassium fluoride solution to 1M calcium nitrate solution at a rate of 10mL / min, stirring the reaction for 90min, aging for 24h, and diluting to obtain a calcium fluoride sol with a solid content of 40%; adding silica sol with a solid content of 40% to obtain a calcium fluoride composite sol; the molar ratio of potassium fluoride to calcium nitrate is 1.05:1; the mass ratio of calcium fluoride sol to silica sol is 1:0.5; coating the calcium fluoride composite sol on the surface of the blank with a coating thickness of 1μm;

[0048] Step 4, sintering, the sintering process is: placing the green body in a vacuum sintering furnace, heating to 1067°C at a heating rate of 3°C / s, sintering for 3h, and air cooling to room temperature;

[0049] Step 5, heat treatment, the heat treatment process is: first tempering and heat preservation at 890℃ for 90min; second tempering and heat preservation at 460℃ for 2h, cooling to 50℃ in argon gas, taking out; obtaining NdFeB magnetic material;

[0050] Step 6: Surface aluminum plating. The process is as follows: using aluminum as the target, magnetron sputtering is performed on the surface of the NdFeB magnetic material to form an aluminum film; the target-substrate distance is 80 mm, and the vacuum degree is 6.5×10 -4 Pa, the working gas is high-purity argon with a flow rate of 50 sccm and the thickness of the aluminum film is 0.5 μm; then it is annealed at 300°C for 2h to obtain a corrosion-resistant NdFeB magnetic material.

[0051] Embodiment 2: A process for preparing a corrosion-resistant NdFeB magnetic material, comprising the following process:

[0052] Step 1, placing NdFeB and a grain boundary additive in a mixer, wherein the mass ratio of NdFeB to the grain boundary additive is 100:0.4, and the grain boundary additive includes the following mass components: 3 parts of magnesium, 5 parts of silicon, and 1.8 parts of magnesium oxide; mixing for 105 minutes under nitrogen atmosphere protection to obtain a mixture;

[0053] Step 2, placing the mixture in a magnetic field pressing and orienting machine, cold isostatic pressing at 30 MPa, applying a magnetic field strength of 2.1 T, so that the magnetization axis of the mixture is consistent with the direction of the external magnetic field, and cold isostatic pressing at 150 MPa to obtain a green body;

[0054] Step 3, slowly adding 2M potassium fluoride solution to 1M calcium nitrate solution at a rate of 10 mL / min, stirring the reaction for 105 min, aging for 24 h, and diluting to obtain a calcium fluoride sol with a solid content of 40%; adding a silica sol with a solid content of 40% to obtain a calcium fluoride composite sol; the molar ratio of potassium fluoride to calcium nitrate is 1.08:1; the mass ratio of calcium fluoride sol to silica sol is 2:1.2; coating the calcium fluoride composite sol on the surface of the blank with a coating thickness of 3 μm;

[0055] Step 4, sintering, the sintering process is: placing the green body in a vacuum sintering furnace, heating to 1076°C at a heating rate of 4°C / s, sintering for 3.5h, and air cooling to room temperature;

[0056] Step 5, heat treatment, the heat treatment process is: first tempering and heat preservation at 925℃ for 105min; second tempering and heat preservation at 480℃ for 3.5h, cooling to 50℃ in argon gas, taking out; obtaining NdFeB magnetic material;

[0057] Step 6: Surface aluminum plating. The process is as follows: using aluminum as the target, magnetron sputtering is performed on the surface of the NdFeB magnetic material to form an aluminum film; the target-substrate distance is 80 mm, and the vacuum degree is 7.4×10 -4 Pa, the working gas is high-purity argon, the flow rate is 50sccm, and the aluminum film thickness is 3μm; then it is annealed at 320℃ for 3.5h to obtain corrosion-resistant NdFeB magnetic material.

[0058] Embodiment 3: A process for preparing a corrosion-resistant NdFeB magnetic material, comprising the following process:

[0059] Step 1, placing NdFeB and a grain boundary additive in a mixer, wherein the mass ratio of NdFeB to the grain boundary additive is 100:0.8, and the grain boundary additive includes the following mass components: 5 parts of magnesium, 8 parts of silicon, and 3 parts of magnesium oxide; mixing for 120 minutes under nitrogen atmosphere protection to obtain a mixture;

[0060] Step 2, placing the mixture in a magnetic field pressing and orienting machine, cold isostatic pressing at 40 MPa, applying a magnetic field strength of 2.8 T, so that the magnetization axis of the mixture is consistent with the direction of the external magnetic field, and cold isostatic pressing at 200 MPa to obtain a green body;

[0061] Step 3, slowly adding 2M potassium fluoride solution to 1M calcium nitrate solution at a rate of 10mL / min, stirring the reaction for 120min, aging for 24h, and diluting to obtain a calcium fluoride sol with a solid content of 40%; adding a silica sol with a solid content of 40% to obtain a calcium fluoride composite sol; the molar ratio of potassium fluoride to calcium nitrate is 1.10:1; the mass ratio of calcium fluoride sol to silica sol is 3:2; coating the calcium fluoride composite sol on the surface of the blank with a coating thickness of 5μm;

[0062] Step 4, sintering, the sintering process is: placing the green body in a vacuum sintering furnace, heating to 1085°C at a heating rate of 5°C / s, sintering for 4 hours, and air cooling to room temperature;

[0063] Step 5, heat treatment, the heat treatment process is: first tempering and heat preservation at 960°C for 120min; second tempering and heat preservation at 500°C for 5h, cooling to 50°C in argon gas, and taking out; obtaining NdFeB magnetic material;

[0064] Step 6: Surface aluminum plating. The process is as follows: using aluminum as the target, magnetron sputtering is performed on the surface of the NdFeB magnetic material to form an aluminum film; the target-substrate distance is 80 mm, and the vacuum degree is 8.0×10 -4 Pa, the working gas is high-purity argon, the flow rate is 50sccm, and the aluminum film thickness is 5μm; then it is annealed at 350℃ for 5h to obtain corrosion-resistant NdFeB magnetic material.

[0065] Comparative Example 1: A preparation process of a corrosion-resistant NdFeB magnetic material, comprising the following processes:

[0066] Step 1, placing NdFeB and a grain boundary additive in a mixer, wherein the mass ratio of NdFeB to the grain boundary additive is 100:0.1, and the grain boundary additive includes the following mass components: 1 part of magnesium, 2 parts of silicon, and 0.5 parts of magnesium oxide; mixing for 90 minutes under nitrogen atmosphere protection to obtain a mixture;

[0067] Step 2, placing the mixture in a magnetic field pressing and orienting machine, pressing and molding at 17MPa cold isostatic pressing, applying a magnetic field strength of 1.5T, so that the magnetization axis of the mixture is consistent with the direction of the external magnetic field, and cold isostatic pressing at 100MPa to obtain a green body;

[0068] Step 3, slowly adding 2M potassium fluoride solution to 1M calcium nitrate solution at a rate of 10 mL / min, stirring the reaction for 90 min, aging for 24 h, and diluting to obtain a calcium fluoride sol with a solid content of 40%; the molar ratio of potassium fluoride to calcium nitrate is 1.05:1; coating the calcium fluoride sol on the surface of the blank with a coating thickness of 1 μm;

[0069] Step 4, sintering, the sintering process is: placing the green body in a vacuum sintering furnace, heating to 1067°C at a heating rate of 3°C / s, sintering for 3h, and air cooling to room temperature;

[0070] Step 5, heat treatment, the heat treatment process is: first tempering and heat preservation at 890℃ for 90min; second tempering and heat preservation at 460℃ for 2h, cooling to 50℃ in argon gas, taking out; obtaining NdFeB magnetic material;

[0071] Step 6: Surface aluminum plating. The process is as follows: using aluminum as the target, magnetron sputtering is performed on the surface of the NdFeB magnetic material to form an aluminum film; the target-substrate distance is 80 mm, and the vacuum degree is 6.5×10 -4 Pa, the working gas is high-purity argon with a flow rate of 50 sccm, the aluminum film thickness is 0.5 μm, and then annealed at 300 °C for 2 h to obtain corrosion-resistant NdFeB magnetic material.

[0072] Comparative Example 2: A process for preparing a corrosion-resistant NdFeB magnetic material, comprising the following processes:

[0073] Step 1, placing NdFeB and a grain boundary additive in a mixer, wherein the mass ratio of NdFeB to the grain boundary additive is 100:0.1, and the grain boundary additive includes the following mass components: 1 part of magnesium, 2 parts of silicon, and 0.5 parts of magnesium oxide; mixing for 90 minutes under nitrogen atmosphere protection to obtain a mixture;

[0074] Step 2, placing the mixture in a magnetic field pressing and orienting machine, pressing and molding at 17MPa cold isostatic pressing, applying a magnetic field strength of 1.5T, so that the magnetization axis of the mixture is consistent with the direction of the external magnetic field, and cold isostatic pressing at 100MPa to obtain a green body;

[0075] Step 3, coating silica sol on the surface of the blank with a coating thickness of 1 μm;

[0076] Step 4, sintering, the sintering process is: placing the green body in a vacuum sintering furnace, heating to 1067°C at a heating rate of 3°C / s, sintering for 3h, and air cooling to room temperature;

[0077] Step 5, heat treatment, the heat treatment process is: first tempering and heat preservation at 890℃ for 90min; second tempering and heat preservation at 460℃ for 2h, cooling to 50℃ in argon gas, taking out; obtaining NdFeB magnetic material;

[0078] Step 6: Surface aluminum plating. The process is as follows: using aluminum as the target, magnetron sputtering is performed on the surface of the NdFeB magnetic material to form an aluminum film; the target-substrate distance is 80 mm, and the vacuum degree is 6.5×10 -4 Pa, the working gas is high-purity argon with a flow rate of 50 sccm, the aluminum film thickness is 0.5 μm, and then annealed at 300 °C for 2 h to obtain corrosion-resistant NdFeB magnetic material.

[0079] Comparative Example 3: A preparation process of a corrosion-resistant NdFeB magnetic material, comprising the following processes:

[0080] Step 1, placing NdFeB and a grain boundary additive in a mixer, wherein the mass ratio of NdFeB to the grain boundary additive is 100:0.1, and the grain boundary additive includes the following mass components: 1 part of magnesium, 2 parts of silicon, and 0.5 parts of magnesium oxide; mixing for 90 minutes under nitrogen atmosphere protection to obtain a mixture;

[0081] Step 2, placing the mixture in a magnetic field pressing and orienting machine, pressing and molding at 17MPa cold isostatic pressing, applying a magnetic field strength of 1.5T, so that the magnetization axis of the mixture is consistent with the direction of the external magnetic field, and cold isostatic pressing at 100MPa to obtain a green body;

[0082] Step 3, sintering, the sintering process is: placing the green body in a vacuum sintering furnace, heating to 1067°C at a heating rate of 3°C / s, sintering for 3h, and air cooling to room temperature;

[0083] Step 4, heat treatment, the heat treatment process is: first tempering and heat preservation at 890℃ for 90min; second tempering and heat preservation at 460℃ for 2h, cooling to 50℃ in argon gas, taking out; obtaining NdFeB magnetic material;

[0084] Step 5: Surface aluminum plating. The process is as follows: using aluminum as the target, magnetron sputtering is performed on the surface of the NdFeB magnetic material to form an aluminum film; the target-substrate distance is 80 mm, and the vacuum degree is 6.5×10 -4 Pa, the working gas is high-purity argon with a flow rate of 50 sccm, the aluminum film thickness is 0.5 μm, and then annealed at 300 °C for 2 h to obtain corrosion-resistant NdFeB magnetic material.

[0085] Comparative Example 4: A process for preparing a corrosion-resistant NdFeB magnetic material, comprising the following processes:

[0086] Step 1, placing NdFeB and a grain boundary additive in a mixer, wherein the mass ratio of NdFeB to the grain boundary additive is 100:0.1, and the grain boundary additive includes the following mass components: 1 part of magnesium, 2 parts of silicon, and 0.5 parts of magnesium oxide; mixing for 90 minutes under nitrogen atmosphere protection to obtain a mixture;

[0087] Step 2, placing the mixture in a magnetic field pressing and orienting machine, pressing and molding at 17MPa cold isostatic pressing, applying a magnetic field strength of 1.5T, so that the magnetization axis of the mixture is consistent with the direction of the external magnetic field, and cold isostatic pressing at 100MPa to obtain a green body;

[0088] Step 3, sintering, the sintering process is: placing the green body in a vacuum sintering furnace, heating to 1067°C at a heating rate of 3°C / s, sintering for 3h, and air cooling to room temperature;

[0089] Step 4, heat treatment, the heat treatment process is: first tempering and keeping at 890°C for 90 minutes; second tempering and keeping at 460°C for 2 hours, cooling to 50°C in argon, and taking out; to obtain corrosion-resistant NdFeB magnetic material.

[0090] Comparative Example 5: A preparation process of a corrosion-resistant NdFeB magnetic material, comprising the following processes:

[0091] Step 1, placing NdFeB and a grain boundary additive in a mixer, wherein the mass ratio of NdFeB to the grain boundary additive is 100:0.1, and the grain boundary additive includes the following mass components: 1 part of magnesium and 0.5 part of magnesium oxide; mixing for 90 minutes under nitrogen atmosphere protection to obtain a mixture;

[0092] Step 2, placing the mixture in a magnetic field pressing and orienting machine, pressing and molding at 17MPa cold isostatic pressing, applying a magnetic field strength of 1.5T, so that the magnetization axis of the mixture is consistent with the direction of the external magnetic field, and cold isostatic pressing at 100MPa to obtain a green body;

[0093] Step 3, sintering, the sintering process is: placing the green body in a vacuum sintering furnace, heating to 1067°C at a heating rate of 3°C / s, sintering for 3h, and air cooling to room temperature;

[0094] Step 4, heat treatment, the heat treatment process is: first tempering and keeping at 890°C for 90 minutes; second tempering and keeping at 460°C for 2 hours, cooling to 50°C in argon, and taking out; to obtain corrosion-resistant NdFeB magnetic material.

[0095] Comparative Example 6: A preparation process of a corrosion-resistant NdFeB magnetic material, comprising the following processes:

[0096] Step 1, placing NdFeB and a grain boundary additive in a mixer, wherein the mass ratio of NdFeB to the grain boundary additive is 100:0.1, and the grain boundary additive includes the following mass components: 2 parts of silicon and 0.5 parts of magnesium oxide; mixing for 90 minutes under nitrogen atmosphere protection to obtain a mixture;

[0097] Step 2, placing the mixture in a magnetic field pressing and orienting machine, pressing and molding at 17MPa cold isostatic pressing, applying a magnetic field strength of 1.5T, so that the magnetization axis of the mixture is consistent with the direction of the external magnetic field, and cold isostatic pressing at 100MPa to obtain a green body;

[0098] Step 3, sintering, the sintering process is: placing the green body in a vacuum sintering furnace, heating to 1067°C at a heating rate of 3°C / s, sintering for 3h, and air cooling to room temperature;

[0099] Step 4, heat treatment, the heat treatment process is: first tempering and keeping at 890°C for 90 minutes; second tempering and keeping at 460°C for 2 hours, cooling to 50°C in argon, and taking out; to obtain corrosion-resistant NdFeB magnetic material.

[0100] Comparative Example 7: A process for preparing a corrosion-resistant NdFeB magnetic material, comprising the following processes:

[0101] Step 1, placing NdFeB and a grain boundary additive in a mixer, wherein the mass ratio of NdFeB to the grain boundary additive is 100:0.1, and the grain boundary additive includes the following mass components: 1 part of magnesium; mixing for 90 minutes under nitrogen atmosphere protection to obtain a mixture;

[0102] Step 2, placing the mixture in a magnetic field pressing and orienting machine, pressing and molding at 17MPa cold isostatic pressing, applying a magnetic field strength of 1.5T, so that the magnetization axis of the mixture is consistent with the direction of the external magnetic field, and cold isostatic pressing at 100MPa to obtain a green body;

[0103] Step 3, sintering, the sintering process is: placing the green body in a vacuum sintering furnace, heating to 1067°C at a heating rate of 3°C / s, sintering for 3h, and air cooling to room temperature;

[0104] Step 4, heat treatment, the heat treatment process is: first tempering and keeping at 890°C for 90 minutes; second tempering and keeping at 460°C for 2 hours, cooling to 50°C in argon gas, and taking out; to obtain corrosion-resistant NdFeB magnetic material.

[0105] Comparative Example 8: A process for preparing a corrosion-resistant NdFeB magnetic material, comprising the following processes:

[0106] Step 1, placing the NdFeB in a magnetic field pressing and orienting machine, cold isostatic pressing at 17MPa, applying a magnetic field strength of 1.5T, so that the magnetization axis of the mixture is consistent with the direction of the external magnetic field, cold isostatic pressing at 100MPa, to obtain a green body;

[0107] Step 2, sintering, the sintering process is: placing the green body in a vacuum sintering furnace, heating to 1067°C at a heating rate of 3°C / s, sintering for 3h, and air cooling to room temperature;

[0108] Step 4, heat treatment, the heat treatment process is: first tempering and keeping at 890°C for 90 minutes; second tempering and keeping at 460°C for 2 hours, cooling to 50°C in argon gas, and taking out; to obtain corrosion-resistant NdFeB magnetic material.

[0109] Experiment: The corrosion-resistant NdFeB magnetic materials obtained in Examples 1-3 and Comparative Examples 1-8 were used to prepare samples, and their properties were tested and the test results were recorded:

[0110] Magnetic performance test: using a precise measurement system for permanent magnetic materials and the principle of electromagnetic induction to detect the residual magnetism (Br) and intrinsic coercive force (Hcj) of the test;

[0111] Corrosion resistance test: Based on GB / T10125 as the reference standard, a neutral salt spray test was conducted, in which a 3.5wt% sodium chloride aqueous solution was sprayed and deposited on the surface of the sample. The test temperature was 35°C, and the salt spray deposition was 1-2mL / (h·cm 2), the salt spray time corresponding to the first visible rust point on the sample surface is taken as the salt spray life of the sample, in hours (h);

[0112] Mechanical properties test: GB / T31967.2 was used as the reference standard, and an electronic universal mechanical testing machine was used to test the bending strength of the sample. The sample size was 5mm×6mm×20mm (magnetization direction), the span was 14.5mm, and the loading speed was 0.5mm / min.

[0113]

[0114] According to the data in the above table, we can clearly draw the following conclusions:

[0115] The corrosion-resistant NdFeB magnetic materials obtained in Examples 1-3 are compared with the corrosion-resistant NdFeB magnetic materials obtained in Comparative Examples 1-8. The test results show that:

[0116] Compared with the comparative example, the corrosion-resistant NdFeB magnetic materials obtained in Examples 1-3 have higher coercivity and remanence data and longer salt spray corrosion resistance time, which fully demonstrates that the present invention improves the corrosion resistance of NdFeB magnetic materials and improves their magnetic properties.

[0117] Compared with Example 1, the corrosion-resistant NdFeB magnetic material obtained in Comparative Example 1 is coated with calcium fluoride sol on the surface of the blank; the corrosion-resistant NdFeB magnetic material obtained in Comparative Example 2 is coated with silica sol on the surface of the blank; the corrosion-resistant NdFeB magnetic material obtained in Comparative Example 3 is not sol-coated on the surface of the blank; the corrosion-resistant NdFeB magnetic material obtained in Comparative Example 4 is not sol-coated on the surface of the blank, and no surface aluminum plating process is performed; compared with Comparative Example 4, the grain boundary additives in Comparative Example 5 are magnesium and magnesium oxide; the grain boundary additives in Comparative Example 6 are silicon and magnesium oxide; the grain boundary additives in Comparative Example 7 are magnesium; and no grain boundary additives are provided in Comparative Example 8. The corrosion-resistant NdFeB magnetic materials obtained in Comparative Examples 1-8 have lower coercive force, remanence data and salt spray corrosion resistance time. It can be seen that the setting of the preparation process of NdFeB magnetic materials in the present invention can promote the improvement of its corrosion resistance and maintain good magnetic properties.

[0118] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A preparation process of corrosion-resistant NdFeB magnetic material, characterized in that: Including the following processes: The NdFeB is mixed with a grain boundary additive and oriented and molded in a magnetic field to form a green body; Sintering and heat treatment to obtain NdFeB magnetic material; The surface is plated with aluminum to obtain corrosion-resistant NdFeB magnetic material.

2. The preparation process of a corrosion-resistant NdFeB magnetic material according to claim 1, characterized in that: The grain boundary additive includes the following components by weight: 1 to 5 parts of magnesium, 2 to 8 parts of silicon, and 0.5 to 3 parts of magnesium oxide.

3. The preparation process of a corrosion-resistant NdFeB magnetic material according to claim 1, characterized in that: The mass ratio of the NdFeB to the grain boundary additive is 100:(0.1-0.8).

4. The preparation process of a corrosion-resistant NdFeB magnetic material according to claim 1, characterized in that: Before the green body is sintered, the surface of the green body is coated with calcium fluoride composite sol.

5. The process for preparing a corrosion-resistant NdFeB magnetic material according to claim 1, characterized in that: The sintering process is as follows: placing the green body in a vacuum sintering furnace, heating the temperature to 1067-1085°C at a heating rate of 3-5°C / s, sintering for 3-4h, and air cooling to room temperature; Temper once at 890-960°C for 90-120 min; temper twice at 460-500°C for 2-5 h, cool to 50°C in argon and take out.

6. The process for preparing a corrosion-resistant NdFeB magnetic material according to claim 4, characterized in that: The calcium fluoride composite sol contains calcium fluoride sol and silica sol in a mass ratio of (1-3): (0.5-2).

7. The process for preparing a corrosion-resistant NdFeB magnetic material according to claim 1, characterized in that: The green body is prepared by the following process: NdFeB and the grain boundary additive are placed in a mixer and mixed for 90 to 120 minutes under the protection of a nitrogen atmosphere to obtain a mixture; The mixed material is placed in a magnetic field pressing and orienting machine, and is pressed into shape by cold isostatic pressing at 17-40 MPa. The strength of the external magnetic field is 1.5-2.8 T, so that the magnetization axis of the mixed material is consistent with the direction of the external magnetic field. The mixed material is cold isostatic pressed at 100-200 MPa to obtain a green body.

8. The process for preparing a corrosion-resistant NdFeB magnetic material according to claim 1, characterized in that: The surface aluminum plating process is as follows: using aluminum as a target, magnetron sputtering is performed on the surface of the NdFeB magnetic material to form an aluminum film; the target-substrate distance is 80 mm, the vacuum degree is 6.5×10-4 to 8.0×10-4 Pa, the working gas is high-purity argon gas, the flow rate is 50 sccm, and the aluminum film thickness is 0.5 to 5 μm; Then anneal at 300-350°C for 2-5h.

9. The process for preparing a corrosion-resistant NdFeB magnetic material according to claim 1, characterized in that: The grain boundary additive is nanometer-scale.

10. A corrosion-resistant NdFeB magnetic material obtained according to the preparation process according to any one of claims 1 to 9.

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