The Corrosion Characteristics and Protection of Sintered NdFeB Magnets

NdFeB Balloy is widely used in electromotor industry and apparatus industry etc.as the third era permanent magnet.It has the advantage of distinguished magnetic,properties and comparatively low price.But it is prone to be oxidized in common atmosphere,especially be heavily electrochemical eroded at humidity environment.Corrsion becomes the obstruction to broaden applications of NdFeB.In this thesis,the corrosion characters of sintered NdFeB magnets in the common medium of acid-base solutions has been investigated. Phosphating coating and Cu/Ni composite electroplating coating on the surface of sintered NdFeB magnets were employed to enhance the corrosion resistances,based on the corrosion mechanism and anticorrosion treatment research of the papers in recent years.Various analytical instruments and methods such as scanning electron microscopy, electrochemical methods,the corrosion weight-loss method,energy dispersive spectrometer,X-ray diffraction and neutral salt spray test were used in this study.But corrosion of the magnets was accelerated in H2SO4 and NaCl solutions,owing to the formation of an occluded corrosion cell with self-catalyzing effect.Contrarily,sintered NdFeB magnets were passivated and inhibited corrosion in H3PO4 and NaOH solutions.Remanence state changed the electric double layer structure on the magnet/electrolyte interface,which was responsible for the production of the magneto overpotential and the change of electrochemical corrosion of sintered NdFeB magnets.Direct Mid-temperature phosphating treatment the surface of sintered NdFeB magnets,the results showed that a significant increase in the corrosion resistance of the magnet due to the phosphate film which cover with the magnet surface and block the pores.The phosphate film coating on the crystalline intergranular phases and main crystal phases was different in element composition:the crystalline intergranular phases include more NdPO4,and has larger thickness.HR pre-pulse copper electroplating process for the optimal level was 15%duty cycle,5000HZ pulse frequency.

Tags: neodymium magnets Corrosion,Protection,Sintered NdFeB Magnets Smco magnets