Anti-corrosion performance of Si-surface-alloying NdFeB magnets obtained with magnetron sputtering and thermal diffusion

Abstract

Si alloying in the surface layer of NdFeB magnets was realized by thermal diffusion combined with magnetron sputtering. The surface composition, phase structure and morphology of NdFeB(S–Si) specimens were characterized by an X-ray diffractometer, an X-ray photoelectron spectrometer and a field emission scanning electron microscope, respectively. The corrosion resistance of bare NdFeB(S–Si) was analyzed by static full immersion corrosion test and electrochemical experiments. Effects of sputtering and thermal diffusion on the microstructure and corrosion resistance of the surface layer were studied. Results show that surface alloying layer can effectively improve the corrosion resistance of bare NdFeB with the optimized static total immersion corrosion test time in NdFeB(1S–Si)-800 of 36 h, which is much longer than that of the pristine NdFeB (less than 0.5 h). The Ecorr of NdFeB(1S–Si)-800 positively shifts from −1.05 to −0.92 V, indicating that the corrosion tendency is obviously lower. The Jcorr is 1.45 × 10−6 A/cm2 which is 2 orders of magnitude lower than that of the pristine NdFeB (5.25× 10−4 A/cm2). The intergranular composite oxides existing in Nd-rich phase contribute to the enhancement of corrosion resistance of Si-surface-alloying NdFeB.