NdFeB磁体前处理工艺、电镀Ni-W-P合金性能及其退镀工艺研究.docx

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Abstract
NdFeB magnetic materials are widely used in various fields due to their unique magnetic properties. However, the instability of NdFeB magnets in corrosive environments and their brittleness are major challenges. Surface treatment methods, such as electroplating, are used to improve the anti-corrosion and mechanical properties of NdFeB magnets. This paper reviews the literature on the surface treatment of NdFeB magnets with a focus on the pre-treatment process, electroplating of Ni-W-P alloy, as well as its characteristics and removal process.
Keywords: NdFeB magnet, pre-treatment process, electroplating, Ni-W-P alloy, removal process.
Introduction
NdFeB magnets are made with rare earth metals that have become essential for many advanced technological applications due to their excellent magnetic properties. However, the corrosion and brittleness of NdFeB magnets limit their application in harsh environments. Therefore, it is necessary to develop surface treatment methods, especially electroplating, to improve the corrosion resistance and mechanical properties of NdFeB magnets.
This paper focuses on the pre-treatment process, electroplating of Ni-W-P alloy, as well as its characteristics and removal process.
Pre-treatment process
The pre-treatment process is an essential step before electroplating, which can efficiently improve the adhesion of the electroplated coating. Acid etching and alkaline degreasing are typical pretreatment processes for NdFeB magnet surface treatment. In acid etching, hydrochloric acid or sulfuric acid can be used to remove the residual oil on the surface and form a rough surface to increase the contact area of the electroplated layer. In alkaline degreasing, an appropriate amount of surfactant is added to the alkali solution to effectively remove the oil on the surface.
Electroplating of Ni-W-P alloy
Ni-W-P alloy plating is an essential coating for NdFeB magnets as it not only improves the corrosion resistance but also enhances the mechanical properties of the surface. The Ni-W-P alloy coating is formed by electroplating with a soluble anode method at a current density of 1-2 A/dm2. In this process, nickel sulfate, tungstate, and sodium hypophosphite are used as the main plating solution, and the nickel concentration can range from 20 to 40 g/L.
Characteristics of Ni-W-P alloy plating
Ni-W-P alloy plating has unique characteristics such as excellent corrosion resistance, high hardness, and good wear resistance. The alloy plating process adopts the electroless plating method, which can uniformly cover the surface of the NdFeB magnet. The composition of Ni-W-P alloy depends on the concentration of the solution and the deposition time. The phosphorus content can range from 6% to 12%, and the tungsten content can range from 5% to 6%.
Removal process of Ni-W-P alloy plating
The removal of the Ni-W-P alloy plating is necessary when a defect is detected during the surface treatment process. The conventional methods for alloy plating removal are mechanical grinding, chemical oxidation, and electrochemical method. The chemical oxidation method is preferred due to its high efficiency, low cost, and easy operation. In this method, a mixture of sulfuric acid, nitric acid, and hydrogen peroxide is used to remove the Ni-W-P alloy plating film from the NdFeB magnet surface.
Conclusion
NdFeB magnets are widely used in various fields, but their brittleness and susceptibility to corrosion limit their application in harsh environments. Surface treatment methods such as electroplating can significantly enhance the anti-corrosion and mechanical properties of NdFeB magnets. The pre-treatment process and electroplating of Ni-W-P alloy are critical steps in surface treatment, and their characteristics and removal process should be carefully considered. Further research on the surface treatment of NdFeB magnets is necessary to expand their application in modern industries.