Electrodeposited Ni/AI_2O_3 Composite Coating on NdFeB Permanent Magnets

摘要

NdFeB permanent magnets are highly susceptible to corrosion in various environments. A new composite coating electrodeposited on NdFeB magnets was investigated in this paper. The Ni matrix film was firstly electrodeposited on NdFeB surface from watts nickel electrolyte, and then Ni/Al_2O_3 composite coating was successively electrodeposited on the Ni film. The microstructures of electrodeposited Ni coating and Ni/Al_2O_3 composite coating were observed by scanning electron microscopy (SEM). The corrosion behavior of Ni coating and Ni/Al_2O_3 composite coating in 3.5wt% NaCl solution was studied by polarization curves and electrochemical impedance spectroscopy (EIS). The results showed that the Ni coating and Ni/Al_2O_3 composite coating could both provide adequate protection to NdFeB substrate. But the free corrosion potential of Ni/Al_2O_3 composite coating was more positive and the passivation region was more obvious when compared with Ni coating. Meantime, the capacitance loop diameter of Ni/Al_2O_3 composite coating was significantly larger than that of Ni coating ,which suggested that the anticorrosion resistance of Ni/Al_2O_3 composite coating was better than electroplated Ni coating.