Effect of Electroless Ni-P Plating on Corrosion Resistance of NdFeB Magnets

The porosity of different types of Ni-P deposits and substrate were measured and the corrosion rates were studied in 3.5% NaCl,10% HCl and 20% NaOH solutions.The corrosion characteristics of different types of Ni-P deposites in 3.5% NaCl solution were envaluated by electrochemical potentiodynamic polarization curves.The microstructure of electroless Ni-P deposits in acidic and acidic-alkaline compositing baths were compared.The results showed that all the types of deposits could enhance the densification and corrosion resistance of substrate.The acidic-alkaline composite deposits composed of alkaline Ni-P plating as bottom film and acidic Ni-P plating as top film could provide the best protection,and the corrosion resistance of single acidic Ni-P deposit was better than that of single alkaline Ni-P deposit.