Long-term corrosion tests on Nd-Fe-B sintered magnets

Long-term corrosion tests were performed on sintered magnets in an environm ent similar to their working conditions. It was found that the corrosion pr ocess proceeds faster for magnets containing higher Nd contents. A small de gree of oxidation slows down the corrosion rate and improves the corrosion resistance. However, high oxidation of magnets leads to degradation of the microstructure and the magnetic properties during their subsequent service. Small oxygen contents, which improve the resistance to oxidation, do not a ffect the magnetic properties. The critical oxygen concentration, which cau ses deterioration of the properties, depends on both the Nd content and the solute elements added to the starting alloy. Additions of Co, Al, Zr, C or Cu substantially improve the resistance to atmospheric corrosion. (C) 1999 Elsevier Science B.V. All rights reserved.