Pretreatment process and corrosion resistance of electroless nickel plating on ZM6 magnesium alloy

Nickel coating was prepared on ZM6 magnesium alloy by electroless nickel plating in nickel carbonate bath with pretreatment of zinc immersion.The morphology and composition of zinc coating and electroless nickel coating were studied by scanning electronic microscopy(SEM) and energy dispersive spectroscopy(EDS).The structure of nickel coating was studied by X-ray diffraction spectroscopy(XRD).Potentiodynamic polarization analysis was used to study the corrosion resistance of the coating.The results indicate that a compact,well-distributed zinc coating is obtained on the surface of ZM6 alloy in a new zinc immersion solution with addition of Sn2+.The subsequent amorphous electroless nickel coating is uniform and the thickness is 8.74 μm after 1 h deposition.Phosphorus mass fraction is 9.29%.The corrosion potential is-0.609 V,and the corrosion current density is about 1/10 of substrate in 3.5% NaCl solution.