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

•Low additions of Sn remarkably improve corrosion resistance of NdFeB magnets.•Increased corrosion resistance relates to modified intergranular phases.•Nd6Fe13Sn phase improves chemical stability of anodic intergranular phases.•Nd6Fe13Sn inhibits formation of active reaction channels in grain boundaries. 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⩽0.6wt% can remarkably improve the corrosion resistance of Nd31.8FebalAl0.3B1.0 magnets and optimum addition amount is 0.3wt%. 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.