Corrosion Behavior of Sintered NdFeB Magnets in Different Acidic Solutions

Corrosion behaviors of sintered NdFeB magnets in H2SO4 solution, HCl solution and HNO3 solution of different concentrations were investigated by pickling, immersion test and electrochemical test. The results show that the corrosion mechanism of sintered NdFeB magnets in HNO3 solution is uniform corrosion, while the one in H2SO4 solution and HCl solution is selectively intergranular corrosion. The corrosion rate of NdFeB magnets increases with increasing of the concentrations of the three acid solutions, and the corrosion rate of NdFeB magnets in the HNO3 solution is the smallest among the three acid solutions both in immersion test and electrochemical test. Therefore, the HNO3 solution is more suitable to be used as the pickling solution for the surface pretreatment of sintered NdFeB magnets.