Phosphate conversion of electroplated Ni coatings on NdFeB magnets improving the anticorrosion property

A phosphate conversion coating was prepared on the surface of Ni-coated NdFeB magnets by a vapor-phase method to improve the anticorrosion property. The composition, microstructure and surface morphology of conversion coatings are characterized by X-ray photoelectron spectrometer, X-ray diffractometer, scanning electron microscope and transmission electron microscope, respectively. Potentiodynamic polarization curves, electrochemical impedance spectroscopy and neutral salt spray tests were used to investigate the anticorrosive properties of Ni(P)/NdFeB. Results reveal that the dense phosphate conversion coating is formed on the surface of Ni/NdFeB, which could protect the NdFeB substrate well. The corrosion potential of Ni(P)/NdFeB shifts positively and the corrosion current density decreases by 1–2 orders of magnitude. Meanwhile, the NSS time of optimized Ni(P)-300/NdFeB increases from 312 h to 648 h, further enhancing the excellent anticorrosive property of the Ni coated-specimen.