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

Long-term corrosion tests were performed on sintered magnets in an environment similar to their working conditions. It was found that the corrosion process proceeds faster for magnets containing higher Nd contents. A small degree 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 affect the magnetic properties. The critical oxygen concentration, which causes 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.