Apply Ni-Co-P multi-coating to improve corrosion resistance:
Ni-Co-P coatings were deposited on the NdFeB magnets in order to improve their
corrosion resistance and decrease their loss of magnetic property. Polarization curves of
NdFeB matrix with andwithout Ni-Co-P coatings in 3.5% NaCl solution were examined.
Influence of coatings to magneticproperty was also investigated. It is found that the
adhesion between Ni-Co-P coatings to magnet substrate can be improved with the aid of
ultrasonic wave. With increasing metallic ion ratio ([Co2+]/[Ni2++Co2+]) in the solution,
deposition rate decreases, and the cobalt content of the coating increases with a
simultaneous decrease in the nickel and phosphorus contents. The polarization
curvesexhibit that the corrosion current density of NdFeB magnets decreases greatly after
electroless plating with the Ni-Co-P coating. Ni-Co-P alloy has the best corrosion resistance when the metallic
ion ratio is 0.2 in the solution. There is just a little loss of magnetic property after NdFeB
magnet deposited.