Fabrication and Corrosion Resistance of a Superhydrophobic Ni–P/Ni3(NO3)2(OH)4 Multilayer Protective Coating on Magnesium Alloy

A superhydrophobic multilayer coating with excellent corrosion resistance has been fabricated on an AZ61 magnesium alloy through electroless plating and hydrothermal treatment. The surface morphologies, chemical characteristics, wettabilities, and corrosion resistance of the multilayer coating were characterized and discussed. The results show that the electroless Ni-P coating on the magnesium alloy exhibits a nodular structure with micropores and lower corrosion resistance. However, a dense Ni 3 (NO 3 ) 2 (OH) 4 layer, a porous Ni 3 (NO 3 ) 2 (OH) 4 nanostructure layer, and a stearic absorbing layer are grown on the surface of the Ni-P coating with superhydrophobic characters and higher corrosion resistance after hydrothermal treatment. Furthermore, the water contact angle and corrosion resistance of the multilayer coating showed a trend of first increasing and then decreasing as the hydrothermal reaction time increases. The optimum hydrothermal reaction time is 15 h, and the multilayer coating prepared under this condition has the highest corrosion resistance and the highest contact angle. In addition, the protection mechanism of the multilayer coating is discussed, and the formation of the dense Ni 3 (NO 3 ) 2 (OH) 4 layer and the stearic absorbing layer effectively improved the corrosion resistance of the multilayer coating.