The deposition, microstructure and properties of Al protective coatings for NdFeB magnets by multi-arc ion plating

Herein, pure Al coatings have been deposited on sintered NdFeB via multi-arc ion plating method. The effect of target current and working pressure on the microstructure and properties of these coatings have been investigated using scanning electron microscopy, laser scanning confocal microscopy, X-ray diffraction, tensile testing, electrochemical tests and neutral salt spray. The results showed that the Al coating on NdFeB magnets achieved higher deposition rate of 4.85 μm/h, a maximum adhesive strength of 24 MPa and a corrosion current density of two orders of magnitude less than that of bare NdFeB substrates when processed using a target current of 60 A and a working pressure of 1.0 Pa. Electrochemical impedance spectroscopy and neutral salt spray tests further proved the excellent corrosion protection performance of such thin films with a thickness of 5 μm without any significant perturbation on the magnetic properties of the substrate.