Method for improving combining force of sintered Nd-Fe-B magnet and electroplated coating

Abstract

The invention discloses a method for improving combining force of a sintered Nd-Fe-B magnet and an electroplated coating. According to the method, the sintered Nd-Fe-B magnet is treated by using a dry type sand blasting method to remove an oxidation layer before the magnet enters into a groove to be electroplated without using an acid washing method to remove the oxidation layer, large current (2-4 times of normal electroplating current) impact electroplating when the electroplating enters into the groove is combined to enhance the combining force between the electroplated coating and the magnet. By adopting the method provided by the invention, the oxidation layer and dirts on the surface of the magnet can be effectively removed; the combining force of the electroplated coating and the magnet is improved; zero discharge of compounds of nitrogen and oxygen is achieved, so environment is not polluted; no hydrogen is produced, and magnet absorbing hydrogen powdering is not caused; mechanical property among crystal phase structures of the magnet is not damaged; due to the large current impact electroplating, the uniformity and sedimentation velocity of the electroplated coating can be effectively improved, the production efficiency is improved, the magnet surface corrosion caused by an electroplate liquid is avoided, and tightness of the electroplated coating, appearance of the electroplated coating and corrosion resistance of the electroplated coating also can be improved.

Description

technical field [0001] The invention provides a method for improving the bonding force between a matrix of a sintered NdFeB permanent magnet material and an electroplating layer, and belongs to the field of surface treatment of a sintered NdFeB permanent magnet material. Background technique [0002] Since the advent of NdFeB permanent magnet materials in the 1980s, they have been widely used in many fields such as electronics, electrical appliances, instruments, medical equipment, motors, sensors, automobiles, and wind power due to their excellent magnetic properties. However, due to the special preparation and processing technology of sintered NdFeB permanent magnets, the magnets have disadvantages such as poor corrosion resistance and strong self-powdering ability. [0003] For more than 30 years, the pioneers in the surface treatment industry have been unremittingly researching the surface protection technology of sintered NdFeB permanent magnets, and have developed a va...

AI Technical Summary

Problems solved by technology

However, due to the special preparation and processing technology of sintered NdFeB permanent magnets, the magnets have disadvantages such as poor corrosion resistance and strong self-powdering ability.

[0003] For more than 30 years, the pioneers in the surface treatment industry have been unremittingly researching the surface protection technology of sintered NdFeB permanent magnets, and have developed a variety of electro-galvanizing, electro-nickel, electro-copper, electrophoresis and other alloy electroplating processes. With the continuous optimization of various electroplating processes, the anti-corrosion performance of various electroplating layers has been greatly improved, but due to the poor bonding force between the electroplating layer and the sintered NdFeB permanent magnet, the electroplating layer will appear during use. Blistering, bursting and other phenomena, serious poor bonding force may even fly out of the rotor of the high-speed motor, these problems lead to a great reduction in the service life of the permanent magnet

On the one hand, because the Nd-rich phase is relatively active, it will be preferentially corroded or corroded too much in the acid solution, so that the Nd-rich grain boundary phase will be destroyed (intergranular corrosion), and the intergranular bonding force will be reduced. The binding force with the magnet is poor; on the other hand, when the oxide layer on the surface of the magnet is removed by pickling, the H produced by the reaction of Nd, Fe, etc. with the acid solution 2 It will lead to the hydrogen absorption pulverization of the main phase and the Nd-rich phase and the H in the magnet 2 The accumulation of magnets after electroplating leads to poor bonding between the magnet and the electroplating layer; on the other hand, due to the selectivity of pickling, the surface morphology of the magnet after pickling is uneven, and high and low electric regions will be formed during electroplating. With conventional current density (0.2-0.8 A / dm 2 ) control, and under the conventional current density, the low-voltage area will be plated slowly and cannot be plated in time

In the electroplating electrolyte, the potential of the Nd-rich grain boundary phase is lower than that of the main phase and the Boron-rich phase. When the magnet is electroplated in the tank, if it is not plated in time, it will be corroded by the plating solution. The Nd-rich grain boundary phase It will be used as the anode of the primary battery and will be corroded by the electroplating solution again, resulting in worse bonding between the coating and the magnet after electroplating. The short-term verification is mainly manifested in the tensile test of the coating after electroplating of the magnet. Its tensile strength is low, and it is mainly reflected in the long-term. Plating explosion