Fabrication of Magnesium Phosphate Coating by Electrochemical Cathodic Method for Corrosion Protection of Sintered NdFeB Magnets

Abstract

Phosphate coating is a commonly used anti-corrosion coating for NdFeB magnets, but its application is hindered by the intrinsic porosity and adverse impact on magnetic performance during the conventional chemical conversion process. Here, a compact magnesium phosphate coating with high protective efficiency has been successfully fabricated on the surface of NdFeB magnets. The surface properties, corrosion resistance and magnetic performance were investigated in detail. It is found that the quality of magnesium phosphate coating significantly depends on the deposition temperature. The coated sample deposited at 60\xa0°C possesses the highest impedance value and protective efficiency (94.25%), because this temperature is appropriate for sufficient deposition of magnesium phosphate crystals (MgHPO 4 ·3H 2 O) and can avoid defects induced by the excess growth of (021) plane. In addition, the magnesium phosphate coatings fabricated by electrochemical cathodic method exhibits no prejudice to the magnetic performance of NdFeB magnets. The superiority in corrosion resistance and magnetic performance of electrodeposited magnesium phosphate coating provides tremendous application prospect for developing protective coating of sintered NdFeB magnets.