Xinfeng’s experiments showed that a cubic centimeter of Sintered NdFeb Magnet would be corroded by oxidation after being exposed to air at 150℃ for 51 days. It corrodes more easily in weak acid solutions. In order to make NdFeb Permanent Magnet durable, it is required to have 20-30 years of service life, it must undergo surface corrosion treatment, so as to resist the corrosion of corrosive medium on the Magnet. And it is usually called Electroplating Permanent Magnet.
At present, sintered NdFeb permanent magnet system manufacturing industry generally adopts electroplating metal, electroplating + chemical gold-plating, electrophoretic coating and phosphating treatment, etc., on the surface of the magnet is coated with an additional layer of isolator, the magnet surface and the corrosive medium are separated, in order to prevent the damage of the medium to the magnet.
1.Generally galvanized, nickel + copper + nickel, nickel + copper + electroless nickel plating three processes, other metal plating requirements, generally in nickel plating and then other metal plating.
2.In some special cases will also use phosphating 
1) In NdFeb magnet products because of turnover, preservation time is too long and unclear follow-up surface treatment method, using phosphating is simple and easy; (2) When the magnet needs epoxy adhesive, paint, glue, paint and other epoxy organic bonding force requires the substrate to have a good infiltration performance. Phosphating process can improve the infiltration ability of magnetic surface.
3.Electrophoretic coating has become one of the most widely used anti-corrosion surface treatment techniques. Because it not only has good bonding force with the surface of porous magnet, but also has corrosion resistance of salt spray, acid and alkali, etc., excellent corrosion resistance. But compared with the spray coating, its resistance to heat and humidity is poor.
Customers can choose the coating according to their product work requirements. With the expansion of motor applications, customers have higher requirements for NdFeb corrosion resistance, and High Quality Electroplating Permanent Magnet is needed. The HAST experiment (PCT experiment) is designed to test the corrosion resistance of sintered NdFeb permanent magnets in wet and high temperature environments.
How do customers determine whether the coating meets the requirements? Salt spray experiment is the purpose of the surface of the anti-corrosion coating treated sintered NdFeb magnet to do a quick anti-corrosion experiment, at the end of the experiment, the sample from the test box, dry, with eyes or magnifying glass to observe the sample surface with spots, spots of the size of the box color changes.
To sum up, only by understanding the production process and the requirements of the product can the customer correctly judge the conformity of the product. In a nutshell, it is the grasp of performance, the control of dimensional tolerance, the detection of coating and the evaluation of appearance.
In terms of performance, Br(residual magnetism), Hcb(coercivity), Hcj(intrinsic coercivity), (BH) Max (maximum magnetic energy product) and demagnetization curve can be detected by performance. Dimensional tolerance, the accuracy can be measured by vernier calipers; On the coating, the color and brightness of the coating can be observed by naked eye and detected by binding force and salt spray test. Overall appearance, mainly with the naked eye or magnifying glass, or optical microscope (for the product line less than 0.2mm), the surface of the magnet is smooth, no visible particles and foreign bodies, no spots, no falling edge falling angle, the appearance is qualified.
Post time: Jun-08-2022