A corrosion-resistant NdFeB magnetic material and its preparation process

Abstract

The present invention discloses a corrosion-resistant NdFeB magnetic material and a preparation process thereof, relating to the technical field of NdFeB magnets, including the following processes: NdFeB is mixed with a grain boundary additive, oriented and formed in a magnetic field to form a blank; sintering, heat treatment, to obtain a NdFeB magnetic material; surface aluminum plating, to obtain a corrosion-resistant NdFeB magnetic material; the grain boundary additives include magnesium, silicon, and magnesium oxide. The present invention sinters the NdFeB together with the grain boundary additive, wherein silicon forms a high-melting-point silicide with neodymium, refines the grain boundary phase, forms a dense oxide layer on the magnet surface, and improves the corrosion resistance of the magnet; low-melting-point magnesium forms a magnesium-neodymium phase, reduces the melting point of the Nd-rich phase, improves the grain boundary wettability, densifies the grain boundary structure, and can purify the grain boundary, thereby improving the resistance of the magnet to intergranular corrosion; magnesium oxide forms an Nd‑O‑Fe‑Mg phase at the grain boundary, refines the grains, and hinders the grain boundary corrosion of the magnet.

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 The Nd-rich phase is relatively active and has a large potential difference with the main phase, which makes the magnet prone to intergranular corrosion. This 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, so as to solve the problems raised in the above background technology.

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

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

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

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

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

[0009] Furthermore, 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 made by melting pure neodymium, iron-boron alloy, pure iron, pure cobalt and other raw materials in an argon atmosphere, rapidly solidifying and spinning the strip, and then 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] Furthermore, the NdFeB and the grain boundary additive are placed in a mixer and mixed for 90 to 120 minutes under a nitrogen atmosphere to obtain a mixture;

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

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

[0015] The heat treatment process is as follows: primary tempering at 890-960°C for 90-120 minutes; secondary 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 pulverization 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 weight: 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-mentioned technical solution, during the co-sintering process of the grain boundary additive and NdFeB, elemental silicon forms a high-melting-point silicide with the rare earth element (Nd), inhibiting abnormal grain growth, refining the grain boundary phase, and increasing coercivity. Silicon also forms a dense oxide layer on the magnet surface, enhancing its corrosion resistance. The addition of low-melting-point magnesium forms a magnesium-Nd phase, lowering the melting point of the rare earth-rich phase and improving its grain boundary wettability. This facilitates liquid-phase sintering of the magnet and fills the voids and defects between grain boundaries, making the grain boundary structure denser and more uniform, thereby enhancing the magnet's magnetic properties. The resulting NdFeB magnetic material (hereinafter referred to as the magnet) has a high density and fewer pores, reducing the specific surface area of the magnet in contact with the external environment, which contributes to improved corrosion resistance. Magnesium is also highly reactive and readily reacts with oxygen and nitrogen, purifying grain boundaries, reducing impurities, and increasing the energy barrier for domain wall motion, contributing to the overall improvement of the magnet's performance. Adding magnesium oxide to the grain boundaries acts as an inert additive, pinning the grain boundaries and inhibiting grain growth. At high temperatures, it provides a small amount of oxygen to the grain boundaries, forming a Nd-O-Fe-Mg phase at the grain boundaries. This inhibits grain growth and refines the grains, which in turn refines the intergranular corrosion channels and hinders grain boundary corrosion. The standard electrode potential of Mg2+ / Mg is higher than that of Nd3+ / Nd, which increases the electrode points of the grain boundary phases and improves the magnet's corrosion resistance. Furthermore, as the grain size decreases, the coercivity of the magnet increases. The synergistic addition of silicon and magnesium forms a magnesium-silicon-neodymium ternary phase, further stabilizing the magnet's grain boundaries. Furthermore, magnesium preferentially binds to oxygen impurities, reducing silicon loss and allowing silicon to more effectively modify the magnet's grain boundaries. The magnesium oxide and the resulting silicides together improve the thermal stability of the magnet's grain boundary phases and reduce their high-temperature irreversible demagnetization rate. The addition of grain boundary additives can also reduce the internal stress generated during magnet sintering, minimizing the loss of magnetic properties caused by internal stress. However, the increase in non-magnetic phases (MgO, silicide) may lead to a decrease in the magnet's remanence, so it is necessary to optimize the ratio of the various components 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] Furthermore, the calcium fluoride composite sol is prepared by the following process;

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

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

[0026] The mass ratio of calcium fluoride sol and 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 solution, calcium fluoride and silicon dioxide assist in grain boundary reconstruction, forming dense protection on the surface of the magnet. At the sintering temperature, calcium fluoride can form a Ca-Nd-F compound with the rare earth-rich phase, which has better thermal stability and can generate silicate (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, enhancing 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: aluminum is used as the target material, and 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 magnet's oxidation resistance, corrosion resistance and mechanical strength.

[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 NdFeB with a grain boundary additive, wherein silicon forms a high-melting-point silicide with neodymium, refines the grain boundary phase, forms a dense oxide layer on the surface of the magnet, and improves the corrosion resistance of the magnet; low-melting-point magnesium forms a magnesium-neodymium phase, lowers the melting point of the neodymium-rich phase, improves the wettability of the grain boundary, densifies the grain boundary structure, purifies the grain boundary, and improves the resistance of the magnet to intergranular corrosion; and magnesium oxide forms an Nd-O-Fe-Mg phase at the grain boundary, refines the grains, and hinders the grain boundary corrosion of the magnet.

[0037] 2. A preparation process for corrosion-resistant NdFeB magnetic materials of the present invention comprises the following steps: coating the surface of the green body with a calcium fluoride composite sol before sintering, utilizing calcium fluoride and silicon dioxide to assist in grain boundary reconstruction, thereby forming dense protection on the surface of the magnet; at the sintering temperature, calcium fluoride forms a Ca-Nd-F compound with a rare earth-rich phase, which has better thermal stability and can generate silicates, 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, increasing the coercive force, reducing the corrosion rate of the magnet in a corrosive medium or a high-temperature environment, and improving the overall mechanical properties of the magnet.

[0038] 3. The present invention provides a process for preparing corrosion-resistant NdFeB magnetic materials, which 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 magnet's oxidation resistance, corrosion resistance and mechanical strength. DETAILED DESCRIPTION

[0039] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0040] In the following specific embodiments,

[0041] NdFeB includes the following mass composition: 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 with a roller speed of 1.0m / s and a sheet thickness of 0.3mm, and then pulverized by hydrogen crushing and air flow grinding to obtain NdFeB powder with a particle size of 4-5μm.

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

[0044] Example 1: A process for preparing a corrosion-resistant NdFeB magnetic material, comprising the following steps:

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

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

[0047] Step 3: Slowly add 2M potassium fluoride solution to 1M calcium nitrate solution at a rate of 10 mL / min, stir and react for 90 minutes, age for 24 hours, and dilute to obtain a calcium fluoride sol with a solid content of 40%; add 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; and the calcium fluoride composite sol is coated on the surface of the green body to a coating thickness of 1 μm;

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

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

[0050] Step 6: Surface aluminum plating. The process is as follows: aluminum is used as the target material, and 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 aluminum film thickness is 0.5 μm; then it is annealed at 300°C for 2h to obtain a corrosion-resistant NdFeB magnetic material.

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

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

[0053] Step 2: placing the mixture in a magnetic field pressing 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 add 2M potassium fluoride solution to 1M calcium nitrate solution at a rate of 10 mL / min, stir and react for 105 minutes, age for 24 hours, and dilute to obtain a calcium fluoride sol with a solid content of 40%; add 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; and the calcium fluoride composite sol is coated on the surface of the green body to a coating thickness of 3 μm;

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

[0056] Step 5, heat treatment, the heat treatment process is: primary tempering and holding at 925 ° C for 105 minutes; secondary tempering and holding at 480 ° C for 3.5 hours, cooling to 50 ° C in argon gas, and 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 with a flow rate of 50 sccm, and the aluminum film thickness is 3 μm; then it is annealed at 320°C for 3.5h to obtain a corrosion-resistant NdFeB magnetic material.

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

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

[0060] Step 2: placing the mixture in a magnetic field pressing 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 add 2M potassium fluoride solution to 1M calcium nitrate solution at a rate of 10 mL / min, stir and react for 120 minutes, age for 24 hours, and dilute to obtain a calcium fluoride sol with a solid content of 40%; add 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; and the calcium fluoride composite sol is coated on the surface of the green body to a coating thickness of 5 μm;

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

[0063] Step 5, heat treatment, the heat treatment process is: primary tempering at 960 ° C for 120 minutes; secondary tempering at 500 ° C for 5 hours, 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: aluminum is used as the target material, and 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 with a flow rate of 50 sccm, and the aluminum film thickness is 5 μm; then it is annealed at 350°C for 5 hours to obtain a corrosion-resistant NdFeB magnetic material.

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

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

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

[0068] Step 3: Slowly add 2M potassium fluoride solution to 1M calcium nitrate solution at a rate of 10 mL / min, stir and react for 90 minutes, age for 24 hours, and dilute 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; and coat the calcium fluoride sol on the surface of the green body to a coating thickness of 1 μm;

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

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

[0071] Step 6: Surface aluminum plating. The process is as follows: aluminum is used as the target material, and 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, with a mass ratio of NdFeB to the grain boundary additive being 100:0.1, and the grain boundary additive comprising the following mass components: 1 part magnesium, 2 parts silicon, and 0.5 parts magnesium oxide; mixing for 90 minutes under nitrogen atmosphere to obtain a mixture;

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

[0075] Step 3: Coating silica sol on the surface of the green body with a coating thickness of 1 μm;

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

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

[0078] Step 6: Surface aluminum plating. The process is as follows: aluminum is used as the target material, and 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 process for preparing a corrosion-resistant NdFeB magnetic material, comprising the following processes:

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

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

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

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

[0084] Step 5: Surface aluminum plating. The process is as follows: aluminum is used as the target material, and 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, with a mass ratio of NdFeB to the grain boundary additive being 100:0.1, and the grain boundary additive comprising the following mass components: 1 part magnesium, 2 parts silicon, and 0.5 parts magnesium oxide; mixing for 90 minutes under nitrogen atmosphere to obtain a mixture;

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

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

[0089] Step 4, heat treatment, the heat treatment process is: primary tempering and holding at 890°C for 90 minutes; secondary tempering and holding 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 process for preparing a corrosion-resistant NdFeB magnetic material, comprising the following processes:

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

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

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

[0094] Step 4, heat treatment, the heat treatment process is: primary tempering and holding at 890°C for 90 minutes; secondary tempering and holding 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 process for preparing a corrosion-resistant NdFeB magnetic material, comprising the following processes:

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

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

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

[0099] Step 4, heat treatment, the heat treatment process is: primary tempering and holding at 890°C for 90 minutes; secondary tempering and holding 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 to obtain a mixture;

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

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

[0104] Step 4, heat treatment, the heat treatment process is: primary tempering and holding at 890°C for 90 minutes; secondary tempering and holding at 460°C for 2 hours, cooling to 50°C in argon, 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: Place the NdFeB in a magnetic field pressing and orienting machine, and press it into shape by cold isostatic pressing at 17 MPa. The external magnetic field strength is 1.5 T, so that the magnetization axis of the mixture is consistent with the direction of the external magnetic field. Cold isostatic pressing is performed at 100 MPa to obtain a green body.

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

[0108] Step 4, heat treatment, the heat treatment process is: primary tempering and holding at 890°C for 90 minutes; secondary tempering and holding at 460°C for 2 hours, cooling to 50°C in argon, 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, the remanence (Br) and intrinsic coercive force (Hcj) of the test are detected;

[0111] Corrosion resistance test: Based on GB / T10125 as the reference standard, a neutral salt spray test was conducted, in which a 3.5 wt% sodium chloride aqueous solution was sprayed and deposited on the sample surface. The test temperature was 35°C, and the salt spray deposition rate was 1-2 mL / (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: Based on GB / T31967.2 as the reference standard, an electronic universal mechanical testing machine was used to test the bending strength of the specimens. The specimen 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 were 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. This fully demonstrates that the present invention achieves improved corrosion resistance and magnetic properties of NdFeB magnetic materials.

[0117] Compared with Example 1, the corrosion-resistant NdFeB magnetic material obtained in Comparative Example 1 has a surface coated with calcium fluoride sol; the corrosion-resistant NdFeB magnetic material obtained in Comparative Example 2 has a surface coated with silica sol; the corrosion-resistant NdFeB magnetic material obtained in Comparative Example 3 has a surface coated with no sol; the corrosion-resistant NdFeB magnetic material obtained in Comparative Example 4 has a surface coated with no sol and no surface aluminum plating process; 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 additive in Comparative Example 7 is magnesium; and no grain boundary additive is provided in Comparative Example 8. The corrosion-resistant NdFeB magnetic materials obtained in Comparative Examples 1-8 have lower coercivity, remanence data, and salt spray corrosion resistance time. It can be seen that the setting of the preparation process of the NdFeB magnetic material of 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 invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A process for preparing corrosion-resistant NdFeB magnetic material, characterized by: Including the following processes: Mixing NdFeB with grain boundary additives, and orienting and shaping in a magnetic field to form a green body; Sintering and heat treatment to obtain NdFeB magnetic material; The surface is aluminum-plated to obtain corrosion-resistant NdFeB magnetic material; 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; Before the green body is sintered, a calcium fluoride composite sol is coated on its surface; The mass ratio of the NdFeB and the grain boundary additive is 100:(0.1-0.8); The calcium fluoride composite sol contains calcium fluoride sol and silica sol in a mass ratio of (1-3): (0.5-2).

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

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

4. The process for preparing a corrosion-resistant NdFeB magnetic material according to claim 1, wherein: The process of aluminum plating on the surface is as follows: aluminum is used as a target material, and 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; Then anneal at 300-350°C for 2-5h.

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

6. A corrosion-resistant NdFeB magnetic material obtained according to the preparation process according to any one of claims 1 to 5.

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