Densification and anticorrosion performances of vacuum evaporated aluminium coatings on NdFeB magnets

Abstract Al coated NdFeB magnets obtained by vacuum evaporation technique have been densified by high energy ball milling method. The surface morphology, metal composition and microstructure of the coatings were characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectrometer, respectively. The anticorrosive properties were investigated by potentiodynamic polarization curves and neutral salt spray test. The pores in the Al coatings of columnar crystals (Al) induced by the evaporation technique, have been apparently filled in the following ball milling process, leading to the densification of Al coatings and the evident improvement of the anticorrosive performances. When treated with the ball milling time of 30 min, the sample achieves the best anticorrosive performances with the self-corrosion potential of –0.87 V, self-corrosion current density of 1.65 μA/cm2 and the NSS time of 144 h (red rust). The improvement of the anticorrosive performances of vacuum evaporated Al coating mainly lies in the densification effect of the coating, which depends on different loading conditions of ball milling process.