CN110819976A - Surface rare earth passivation method for sintered NdFeB magnet metal coating - Google Patents
Surface rare earth passivation method for sintered NdFeB magnet metal coating Download PDFInfo
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- CN110819976A CN110819976A CN201911127248.3A CN201911127248A CN110819976A CN 110819976 A CN110819976 A CN 110819976A CN 201911127248 A CN201911127248 A CN 201911127248A CN 110819976 A CN110819976 A CN 110819976A
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- passivation
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- ndfeb magnet
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
- C23C22/53—Treatment of zinc or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/22—Electroplating: Baths therefor from solutions of zinc
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/34—Pretreatment of metallic surfaces to be electroplated
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/48—After-treatment of electroplated surfaces
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D7/00—Electroplating characterised by the article coated
- C25D7/001—Magnets
Abstract
The invention discloses a surface rare earth passivation method for a sintered NdFeB magnet metal coating. Aiming at the sintered NdFeB magnet surface metal Zn coating, the surface rare earth passivation of the metal coating is realized by a chemical method, so that the corrosion resistance of the coating is improved. The surface rare earth passivation method for the sintered NdFeB magnet metal coating can form a compact rare earth passivation film on the surface of the metal coating and provide a longer-acting corrosion protection effect for the sintered NdFeB magnet. Compared with the traditional hexavalent chromium and trivalent chromium passivation method, the method has better environmental adaptability and no heavy metal ion sewage discharge.
Description
Technical Field
The invention belongs to the field of surface protection and corrosion resistant coatings of magnetic materials, and particularly relates to a surface rare earth passivation method of a sintered NdFeB magnet metal coating.
Background
NdFeB, a representative of the third generation rare earth permanent magnetic materials, has extremely high magnetic energy product (BH), coercivity (Hcj), and energy density. Meanwhile, the NdFeB permanent magnetic material has good stability to heat and time and strong capability of resisting the interference of an external magnetic field. These excellent properties make ndfeb magnets a wide market in the production of electronic components in modern industries. However, the sintered NdFeB magnet prepared by the powder metallurgy method has a three-phase structure (mainly comprising a main phase, an Nd-rich phase and a B-rich phase), and the potential difference between the phases is large, particularly the Nd-rich phase has the strongest electrochemical property and is extremely easy to corrode in humid, high-temperature and electrochemical environments, so that the further expansion of the application field of the sintered NdFeB magnet is severely limited. Therefore, measures must be taken to improve the corrosion resistance of sintered NdFeB magnets. At present, the corrosion resistance of the steel is improved mainly by adjusting the chemical composition components or adopting a surface treatment method in industrial production so as to meet the requirements of practical application. However, the alloying method may reduce the magnetic properties of the magnet to some extent, and the effect is not significant. Therefore, the surface protection treatment method is mainly adopted in industrial production to add the protection coating on the surface of the magnet, so that the corrosion resistance of the magnet can be obviously improved.
Protective coatings slow the corrosion of magnets by preventing direct contact between the corrosive medium and the substrate. The most commonly used surface treatment methods at present include: electrodeposition, chemical deposition, physical vapor deposition, organic polymer resin coating, and the like. The electroplating zinc on the surface of the neodymium iron boron magnet is an effective anti-corrosion means for the neodymium iron boron magnet, has better binding force with the magnet, higher corrosion resistance and good electrochemical protection performance. The surface passivation of the metal coating is a common mode for improving the corrosion resistance, and a compact conversion coating is formed on the surface of the metal coating through the reaction with passivators such as hexavalent chromium, trivalent chromium and the like, so that the corrosion resistance of the metal coating can be effectively improved. However, the application of the chromium-containing waste liquid is limited due to serious environmental pollution, and the chromium-containing waste liquid is gradually replaced by other low-pollution processes.
Therefore, the development of the surface rare earth passivation method of the sintered NdFeB magnet metal coating has important economic benefits, social benefits and environmental protection benefits.
Disclosure of Invention
The invention provides a surface rare earth passivation method for a sintered NdFeB magnet metal coating, aiming at the problems of poor corrosion resistance of the sintered NdFeB magnet surface metal coating and serious environmental pollution of the traditional passivation process.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a surface rare earth passivation method for a sintered NdFeB magnet metal coating comprises the following specific steps:
(1) electroplating pretreatment: firstly, washing NdFeB matrix with alkali to remove oil, washing with deionized water, washing with nitric acid, activating in citric acid, and then ultrasonically cleaning in deionized water;
(2) the electrogalvanizing process comprises the following steps: electroplating in a mixed solution of zinc chloride, potassium chloride and boric acid;
(3) passivation pretreatment: putting the galvanized magnet into a nitric acid solution for acidification treatment, and carrying out ultrasonic treatment after cleaning;
(4) preparing a passivation solution: preparing a mixed aqueous solution of soluble cerium salt and hydrogen peroxide, and adding acid to adjust the pH value to obtain a passivation solution;
(5) preparing a passivation film: and (3) putting the acidified galvanized magnet into a passivation solution, and reacting at room temperature to complete surface passivation of the neodymium iron boron zinc coating.
Preferably, in the step (1), the alkali is NaOH, the pH is less than 11, the alkali washing time is 5-20min, the nitric acid washing time is 5-120s, and the nitric acid concentration is 1-10%; the citric acid activation time is 5-60s, the citric acid concentration is 1-10%, and the ultrasonic treatment time is 1-10 min.
Preferably, the concentration of zinc chloride in the step (2) is 30-60g/L, the concentration of potassium chloride is 150-300g/L, and the concentration of boric acid is 20-50 g/L.
Preferably, the current density of the plating treatment in the step (2) is 0.1 to 2A/dm2The electroplating time is 40-80 min.
Preferably, the concentration of the nitric acid in the step (3) is 0.1-6%, the acidification time is 5-60s, and the ultrasonic cleaning time is 1-10 min.
Preferably, the soluble cerium salt in step (4) is one or more of cerium nitrate, cerium chloride and cerium sulfate.
Preferably, the concentration of the soluble cerium salt in the step (4) is 0.05-0.5mol/L, and the concentration of the hydrogen peroxide is 0.5-10%.
Preferably, the acid used for adjusting the pH value in the step (4) is one of hydrochloric acid, nitric acid, sulfuric acid or a mixture thereof.
Preferably, the pH value in step (4) is in the range of 2 to 4.
Preferably, the reaction time in step (5) is 5 to 30 min.
Compared with the prior art, the invention has the beneficial effects that:
the surface rare earth passivation method for the sintered NdFeB magnet metal coating can form a compact rare earth passivation film on the surface of the metal coating and provide a longer-acting corrosion protection effect for the sintered NdFeB magnet. Compared with the traditional hexavalent chromium and trivalent chromium passivation method, the method has better environmental adaptability and no heavy metal ion sewage discharge.
Drawings
FIG. 1 is SEM topography before and after passivation of a zinc coating, (a) (b) is the surface topography of the zinc coating without rare earth passivation, and (c) (d) is the surface topography of the zinc coating after rare earth passivation of example 1;
fig. 2 is a potentiodynamic polarization curve for a zinc coating without rare earth passivation and rare earth passivated zinc coatings prepared in examples 1, 2, 3, and 4.
Detailed Description
The present invention is further described with reference to the following examples, which are intended to be illustrative and illustrative only, and various modifications, additions and substitutions for the specific embodiments described herein may be made by those skilled in the art without departing from the spirit of the invention or exceeding the scope of the claims.
The present invention will be described with reference to specific examples.
Example 1:
(1) electroplating pretreatment: the NdFeB matrix is washed with alkali to remove oil for 12min, washed with deionized water, washed with nitric acid for 40s, activated in weak acid for 20s, and then ultrasonically washed in deionized water for 1 min.
(2) The electrogalvanizing process comprises the following steps: electroplating is carried out in a mixed solution of zinc chloride, potassium chloride and boric acid, and the concentrations are 65g/L, 215g/L and 37g/L respectively. Current density 1A/dm2Electroplating time is 50 min;
(3) passivation pretreatment: acidizing the sintered NdFeB coated with the electroplated Zn coating for 10s by using 1 wt.% nitric acid solution, and carrying out ultrasonic treatment after cleaning;
(4) preparing a passivation solution: preparing a mixed aqueous solution of cerium nitrate and hydrogen peroxide, wherein the concentration of the cerium nitrate solution is 5g/L, and the concentration of the hydrogen peroxide is 3%. Adjusting the pH value to 3.0 by hydrochloric acid;
(5) preparing a passivation film: and (3) putting the acidified galvanized magnet into a passivation solution, reacting at room temperature for 20min, cleaning and drying to complete surface passivation of the neodymium iron boron zinc coating.
The comparative example is a Zn coating on the surface of a sintered NdFeB magnet without rare earth passivation, i.e., the product of step (1). The test shows that the corrosion potential in the electrochemical corrosion test is-1.3V, and the self-corrosion current density is 4.43 multiplied by 10-4A·cm-2The salt spray test time is 228 h.
The rare earth passivated Zn coating in the electrochemical corrosion test according to example 1 has a corrosion potential of-1.02V and a self-corrosion current density of 1.02X 10-5A·cm-2The salt spray test time is 360h, and the comprehensive corrosion resistance of the alloy is obviously superior to that of the comparative example.
Example 2:
this example was prepared in the same manner as in example 1, except that the concentration of the cerium nitrate solution in step (4) was 3 g/L.
As a result of the tests, the rare earth passivated Zn coating in the electrochemical corrosion test according to the example 2 has a corrosion potential of-1.2V and a self-corrosion current density of 1.44X 10-4A·cm-2The salt spray test time is 296h, and the comprehensive corrosion resistance of the alloy is obviously superior to that of the comparative example.
Example 3:
this example was prepared in the same manner as in example 1, except that the concentration of the cerium nitrate solution in step (4) was 7 g/L.
As a result of the tests, the rare earth passivated Zn coating in the electrochemical corrosion test has a corrosion potential of-1.15V and a self-corrosion current density of 2.9X 10-4A·cm-2The salt spray test time is 282h, and the comprehensive corrosion resistance of the alloy is obviously superior to that of the comparative example.
Example 4
This example was prepared in the same manner as in example 1, except that the concentration of the cerium nitrate solution in step (4) was 9 g/L.
The Zn coating after rare earth passivation according to example 2 was tested to have a corrosion potential of-1.16V and a self-corrosion current density of 2.17X 10 in an electrochemical corrosion test-4A·cm-2The salt spray test time is 256 hours, and the comprehensive corrosion resistance of the alloy is obviously superior to that of the comparative example.
The self-corrosion potentials and corrosion current densities of the non-rare earth passivated zinc coatings and the rare earth passivated zinc coatings prepared in examples 1, 2, 3, 4 are shown in table 1 below:
TABLE 1 potential for self-corrosion and corrosion current density for non-rare earth passivated galvanizes and rare earth passivated galvanizes prepared in examples 1, 2, 3, 4
| Sample (I) | Jcoor/(A·cm-2) | Ecoor/V |
| Is not passivated | 4.43×10-4 | -1.3 |
| Example 1 | 1.02×10-5 | -1.02 |
| Example 2 | 1.44×10-4 | -1.2 |
| Example 3 | 2.9×10-4 | -1.15 |
| Example 4 | 2.17×10-4 | -1.16 |
Claims (10)
1. A surface rare earth passivation method for a sintered NdFeB magnet metal coating is characterized by comprising the following steps: the method comprises the following specific steps:
(1) electroplating pretreatment: firstly, washing NdFeB matrix with alkali to remove oil, washing with deionized water, washing with nitric acid, activating in citric acid, and then ultrasonically cleaning in deionized water;
(2) the electrogalvanizing process comprises the following steps: electroplating in a mixed solution of zinc chloride, potassium chloride and boric acid;
(3) passivation pretreatment: putting the galvanized magnet into a nitric acid solution for acidification treatment, and carrying out ultrasonic treatment after cleaning;
(4) preparing a passivation solution: preparing a mixed aqueous solution of soluble cerium salt and hydrogen peroxide, and adding acid to adjust the pH value to obtain a passivation solution;
(5) preparing a passivation film: and (3) putting the acidified galvanized magnet into a passivation solution, and reacting at room temperature to complete surface passivation of the neodymium iron boron zinc coating.
2. A method of rare earth passivation of the surface of a sintered NdFeB magnet metal coating as claimed in claim 1, wherein: in the step (1), the alkali is NaOH, the pH is less than 11, the alkali washing time is 5-20min, the nitric acid pickling time is 5-120s, and the nitric acid concentration is 1-10%; the citric acid activation time is 5-60s, the citric acid concentration is 1-10%, and the ultrasonic treatment time is 1-10 min.
3. A method of rare earth passivation of the surface of a sintered NdFeB magnet metal coating as claimed in claim 1, wherein: in the step (2), the concentration of zinc chloride is 30-60g/L, the concentration of potassium chloride is 150-300g/L, and the concentration of boric acid is 20-50 g/L.
4. A method of rare earth passivation of the surface of a sintered NdFeB magnet metal coating as claimed in claim 1, wherein: the current density of the electroplating treatment in the step (2) is 0.1-2A/dm2The electroplating time is 40-80 min.
5. A method of rare earth passivation of the surface of a sintered NdFeB magnet metal coating as claimed in claim 1, wherein: in the step (3), the concentration of nitric acid is 0.1-6%, the acidification time is 5-60s, and the ultrasonic cleaning time is 1-10 min.
6. A method of rare earth passivation of the surface of a sintered NdFeB magnet metal coating as claimed in claim 1, wherein: the soluble cerium salt in the step (4) is one or a mixture of more of cerium nitrate, cerium chloride and cerium sulfate.
7. A method of rare earth passivation of the surface of a sintered NdFeB magnet metal coating as claimed in claim 1, wherein: in the step (4), the concentration of the soluble cerium salt is 0.05-0.5mol/L, and the concentration of the hydrogen peroxide is 0.5-10%.
8. A method of rare earth passivation of the surface of a sintered NdFeB magnet metal coating as claimed in claim 1, wherein: and (4) the acid for adjusting the pH value in the step (4) is one or a mixture of hydrochloric acid, nitric acid and sulfuric acid.
9. A method of rare earth passivation of the surface of a sintered NdFeB magnet metal coating as claimed in claim 1, wherein: the pH value range in the step (4) is 2-4.
10. A method of rare earth passivation of the surface of a sintered NdFeB magnet metal coating as claimed in claim 1, wherein: the reaction time in the step (5) is 5-30 min.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113445038A (en) * | 2021-06-29 | 2021-09-28 | 永新县晨阳磁电科技有限公司 | Chromium-free passivation solution and passivation method for neodymium iron boron zinc coating |
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| CN104005013A (en) * | 2014-06-11 | 2014-08-27 | 廊坊京磁精密材料有限公司 | Method for passivating galvanized neodymium iron boron magnet |
| CN104032342A (en) * | 2014-06-11 | 2014-09-10 | 安徽大地熊新材料股份有限公司 | Method for improving combining force of sintered Nd-Fe-B magnet and electroplated coating |
| CN104213162A (en) * | 2013-06-04 | 2014-12-17 | 天津三环乐喜新材料有限公司 | Surface treatment method for zinc alloy electroplating of automobile permanent magnetic material |
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- 2019-11-18 CN CN201911127248.3A patent/CN110819976A/en active Pending
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104213162A (en) * | 2013-06-04 | 2014-12-17 | 天津三环乐喜新材料有限公司 | Surface treatment method for zinc alloy electroplating of automobile permanent magnetic material |
| CN104005013A (en) * | 2014-06-11 | 2014-08-27 | 廊坊京磁精密材料有限公司 | Method for passivating galvanized neodymium iron boron magnet |
| CN104032342A (en) * | 2014-06-11 | 2014-09-10 | 安徽大地熊新材料股份有限公司 | Method for improving combining force of sintered Nd-Fe-B magnet and electroplated coating |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113445038A (en) * | 2021-06-29 | 2021-09-28 | 永新县晨阳磁电科技有限公司 | Chromium-free passivation solution and passivation method for neodymium iron boron zinc coating |
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