Corrosion behaviors and mechanism of sintered rare-earth magnets

摘要

: Sintered rare-earth magnets possessing outstanding magnetic properties are widely applied in many fields. However, corrosion resistance has been a problem with the magnets owing to the high chemical activity of the phases rich in rare earth elements. The Nd-rich phases of the Nd-Fe-B magnets can react with water vapor and oxygen in a damp and humid atmosphere. The electro-chemical corrosion occurs for Nd-Fe-B magnets in a high humidity atmosphere because of the difference of corrosion potential between the matrix Nd_2Fe14B phase and the boundary Nd-rich phase. In this article, Corrosion resistance of sintered Nd-Fe-B and Sm-Co magnets was investigated in steady-state damp heat (HH), neutral salt spray (NSS) and pressure cooker (PCT) climates. The effects of alloy composition and different corrosive environments on magnetic flux loss were discussed. It shows that the corrosion rates of sintered Nd-Fe-B magnets in HH and NSS climates exhibit a obvious parabolic trend, flux loss in the above three kinds of climates have a approximate linear trend. The corrosion resistance of sintered Nd-Fe-B magnets can be improved by Dy partially substitution for Nd and minor Co addition. The sintered Sm-Co magnets show very good corrosion resistance in the above three kinds of climates.