Preparation method of high anti-corrosion coating on surface of sintered Nd-Fe-B magnet

Abstract

The invention discloses a preparation method of a high anti-corrosion coating on the surface of a sintered Nd-Fe-B magnet. The method comprises the steps that a machined and shaped Nd-Fe-B magnet is preprocessed, the preprocessed Nd-Fe-B product is soaked with a pre-processing solution, and the pre-processing solution is prepared by mixing distilled water, a coating agent and an accelerator; priming coating of a ZnAl coating solution is performed on the surface of the soaked Nd-Fe-B magnet, and the Nd-Fe-B magnet with the ZnAl coating obtained after priming coating is obtained; top coating ofa Al-enriched coating solution is performed on the surface of the Nd-Fe-B magnet obtained after priming coating, and the high anti-corrosion Nd-Fe-B magnet is obtained. Due to two times of coating processing, the porosity between the magnet and a corrosive medium is effectively lowered, the binding force between the coating and the magnet is improved, and the sintered Nd-Fe-B magnet has the good corrosion resistance. Due to the ZnAl coating obtained after priming coating, the quantity of a medium entering the deeper layer of the coating is greatly reduced, and therefore the high temperature and high pressure resistance and the ageing resistance of the magnet are greatly improved.

Description

Technical field [0001] The invention relates to the field of surface protection of magnetic materials, in particular to a method for preparing a high corrosion-resistant coating on the surface of a sintered neodymium iron boron magnet. Background technique [0002] Neodymium iron boron (NdFeB) permanent magnets have good magnetic properties, among which the theoretical magnetic energy product is as high as 64MGOe. They are widely used in many fields such as aerospace, medical equipment, wind power generation, energy-saving home appliances, new energy vehicles, etc. However, sintered NdFeB magnets with multi-phase structure are easily corroded in corrosive media due to the large potential difference between the phases, which severely limits the application fields of sintered NdFeB magnets. In order to improve the corrosion resistance of sintered NdFeB, there are two main types of common protective measures: (1) Alloying treatment; that is, adding trace elements to the magnet to fo...

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Problems solved by technology

[0003] For general metal substrates, the electroplated Zn coating can play a better protective role as a sacrificial anode coating, while the Nd-rich phase potential of the sintered NdFeB magnet is more negative than the Zn coating, which makes the Zn coating lose its advantage, and There is a tip effect in the electroplating process. In the electrochemical environment, hydrogen absorption corrosion occurs on the surface of the magnet at the defect of the Zn coating, resulting in loose and porous corrosion products, which lead to further corrosion of the magnet, and the waste liquid generated at the same time increases the electroplating. cost; and because the traditional electroplating process is mainly carried out in aqueous solution, hydrogen evolution reaction is prone to occur during the electroplating process, and the coating is prone to hydrogen embrittlement

The metal Al coating is also used for the surface protection of sintered NdFeB, in which the magnetron sputtering Al coating grows in a columnar crystal structure, and there are obvious gaps between the crystals, which makes it easier for the corrosive medium to contact the substrate and accelerate the corrosion of the magnet. Moreover, the existing Al film protective coatings have complex processes and relatively strict requirements on equipment, making it difficult to achieve large-scale industrial production