Improvement of the corrosion resistance on Nd-Fe-B magnet with nickel plating

Three kinds of corrosion tests, a humidity test (80°C, 90% RH), an autoclave test (120°C, 2 atm saturated with water vapor), and a salt spray test (35°C, 5% NaCl), were performed on a sintered magnet treated with nickel plating. For comparison, samples with epoxy resin coating, Al ion plating, and without coating were also exposed to the corrosion test. After specified periods of corrosion testing, the permanent flux loss of the remagnetized sample was measured. Changes in appearance were also observed. It was found that the epoxy resin coating could not prevent the penetration of moisture in the humidity and autoclave tests because of its hygroscopic properties. The nickel plating and Al ion plating withstood the humidity and autoclave tests reasonably well, but they suffered slight corrosion in the salt spray test. It is concluded that the use of nickel plating can provide high corrosion resistance and low cost of production