The Preparation and Properties of ZnAl Coating for Ring-Shaped Bonded NdFeB Magnet with High Corrosion Resistance

The ZnAl coating was prepared on ring-shaped bonded NdFeB magnets (RSM) via air spraying method with silane as adhesive and flake-like Zn and Al powder as raw materials. The morphology, composition structure and element distribution of the ZnAl coating were characterized by scan electron microscopy with energy-dispersive spectroscopy and x-ray diffraction. The corrosion resistance of the ZnAl coating was analyzed by means of potentiodynamic polarization curve and neutral salt spray test (NSS). The variation in magnetic flux for RSM and ZnAl/RSM was also measured. It was found out that the Zn and Al appeared as metal elements in the coating and superimposed as sheets on the RSM and the ZnAl coating was deposited uniformly and densely with thickness of 16.7 μm. The corrosion current density of ZnAl/RSM was an order of magnitude lower than that of bare RSM and the NSS time attained to 264 h (red rust), indicating the better anticorrosion performance of the ZnAl coating. The magnetic flux of RSM was reduced by 0.15-0.55% after coated with ZnAl, indicating that the coating has little effect on the magnetic property of the RSM.