Improvement of corrosion resistance in Nd-Fe-B sintered magnets by intergranular additions of Sn

Sn powders as grain boundary modifiers were applied to improve the corrosion resistance of Nd-Fe-B sintered magnets. Effects of additions of Sn on the corrosion behavior in sulphuric acid and sodium chloride solutions were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy experiments as well as SEM observation. It was found that additions of Sn ⩽ 0.6 wt% can remarkably improve the corrosion resistance of Nd31.8FebalAl0.3B1.0 magnets and optimum addition amount is 0.3 wt%. The improved corrosion resistance is attributed to the increase of chemical stabilization and the microstructural modification of grain boundaries. Also the effect mechanism of additions of Sn on the corrosion resistance of magnets was discussed based on experimental results.