The influence of Nb and Ga addition on the corrosion resistance of permanent magnets in marine environments-part 2

摘要

This paper deals with the effect of alloying elements such as Nb and Ga on the corrosion behaviour of Nd-Fe-B permanent magnetic alloy. The results show that these alloying elements do not help in improving the corrosion resistance of the base magnet; rather, their presence makes the base alloy highly vulnerable to corrosion in marine environments. In particular, the Ga addition along with 7% Co and 4% Dy is highly detrimental to corrosion, as evidenced from potentiodynamic, cyclic polarization, E{sub}(corr) vs time, ac impedance, and SEM results. The studies also showed that the degradation of the alloys with and without alloy addition takes place by preferential dissolution of grain boundaries. Based on these results, the importance of surface-engineering techniques in exploiting the base Nd-Fe-B magnet for a variety of applications by improving the corrosion resistance under marine environments has been highlighted. Part 1 was published in our September issue and, having introduced the subject, dealt with the experimental details of the investigation and a discussion of some of the results. It ended with the discussion of the degradation mechanism, related to the alloys' composition.