Electroless nickel plating on ZM6 (Mg–2.6Nd–0.6Zn–0.8Zr) magnesium alloy substrate

To improve the corrosion resistance of ZM6 (Mg–2.6Nd–0.6Zn–0.8Zr) magnesium alloy, electroless nickel plating on ZM6 alloy with a new pretreatment process and nickel carbonate bath was investigated in this paper. The morphology, component, chemical composition and structure of the pretreatment layers and electroless nickel coating were analyzed using scanning electronic microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction spectroscopy. The adhesion and corrosion resistance of the Ni–P coating were evaluated by means of thermal shock, potentiodynamic polarization, and salt spray test. The results showed that a compact zinc immersion layer was formed on the surface of the ZM6 alloy in a new zinc dipping solution. The subsequent amorphous electroless nickel coating was uniform, in which the content of P was 9.7 wt.%. Its thickness reached about 62 μm at 2 h deposition. Compared with the bare substrate, the corrosion potential of the coated alloy shifted by 1075 mV positively and the corrosion current density decreased two orders of magnitude in 3.5 wt.% NaCl solution. The salt spray test time of Ni–P coating was 158 h. These results suggest that the electroless nickel plating procedure developed in the study is available for ZM6 alloy and the Ni–P coating obtained with good adhesion could protect the substrate effectively.