阅读说明：本技术 一种烧结NdFeB磁体金属涂层的表面稀土钝化方法 (Surface rare earth passivation method for sintered NdFeB magnet metal coating ) 是由 徐光青 陈婧 杨振宇 张鹏杰 吕珺 李炳山 汪冬梅 孙威 刘辉 张威峰 吴玉程 于 2019-11-18 设计创作，主要内容包括：本发明公开了一种烧结NdFeB磁体金属镀层的表面稀土钝化方法。针对烧结NdFeB磁体表面金属Zn涂层,通过化学方法实现金属涂层的表面稀土钝化,从而提高涂层的耐蚀性能。本发明的烧结NdFeB磁体金属镀层的表面稀土钝化方法,可以在金属镀层表面形成致密的稀土钝化膜,为烧结NdFeB磁体提供更长效的腐蚀防护作用。相较于传统的六价铬、三价铬钝化法,本发明具有更好的环境适应性,无重金属离子的污水排放。(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.)

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.

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.