Effect of Rare Earth on the Corrosion Resistance of Electroless Ni-Mo-P Composite Coatings

A kind of corrosion-resistant Ni-Mo-P composite coating was deposited on the surface of AZ91D magnesium alloy substrate by electroless plating method with different concentration of Ce(NO₃)₃ and Nd(NO₃)₃. The deposition mechanism of Ni-Mo-P composite coating was explored. Furthermore, the effects of Ce(NO₃)₃ and Nd(NO₃)₃ concentration on the microstructure and properties of Ni-Mo-P composite coatings were studied. Results indicated that the Ni-Mo-P composite coatings prepared by adding the optimal concentration of Ce(NO₃)₃ and Nd(NO₃)₃ had few defects. Meanwhile, the deposition rate of the composite coatings and the adhesion between the coating and the magnesium alloy substrate were improved. When the concentration of Ce(NO₃)₃ and Nd(NO₃)₃ were 0.10 and 1.00 g/L, the Ni-Mo-P composite coatings had the minimum corrosion rate of 0.826 and 0.681 g/m²·h, respectively. Herein, compared with the addition of Ce(NO₃)₃, the Nd(NO₃)₃ added Ni-Mo-P composite coating has the maximum arc radius of capacitive resistance and significant improvement corrosion resistance.

Keywords:
AZ91D magnesium alloy; Electroless plating; Ni-Mo-P composite coatings; Rare earth; Microstructure; Corrosion resistance