Corrosion characteristics of Nd–Fe–B permanent magnets in different environments

The corrosion behaviour of Nd–Fe–B, a permanent magnetic alloy, has been studied in two different solutions chosen to simulate the effects of marine and industrial environments. The results showed that the corrosion rate of the alloy was about nine times higher in the simulated industrial (sulphate) environment when compared to the marine (chloride) environment. The studies also revealed that the alloy could not form a protective layer on its surface in either of the environments studied, but was resistant to pitting corrosion. Scanning electron microscopy results indicated that the magnetic alloy undergoes preferential grain boundary corrosion in both environments although the corrosion rate varies considerably. A sequence of steps that result in the loss of magnetic properties under corrosive conditions has been proposed. Furthermore, the effect of alloying elements on the corrosion behaviour and magnetic properties of the alloy was also discussed. The importance of surface engineering techniques for improving the corrosion resistance of Nd–Fe–B permanent magnets was highlighted and a suitable surface coating system was proposed.