ELECTROCHEMICAL CORROSION-RESISTANCE OF FE-ND-B PERMANENT-MAGNETS

The corrosion behaviour of three permanent magnets based on the Fe-R-B system, namely Fe76.9Nd15.1 B8 (Vacodym 335), Fe76.7Nd14.3DyB8 (Vacodym 370) and Fe77Nd15B8 (Neomax 35) was investigated in 0.5 M H2SO4 using mass loss and electrochemical techniques. Differences in the chemical composition of the tested magnets did not affect the runs of polarization curves in the active dissolution range or in the cathodic one, but they influenced the runs of these curves in the passive state. The magnets show distinct lack of resistance to acid corrosion both in the magnetized and demagnetized state. Weak corrosion resistance appears also at strongly cathodic polarizations, and the rate of this abnormal dissolution increases with the rise of the hydrogen evolution rate on the surface of the magnets © 1990 Chapman and Hall Ltd.