Process for Ehxtroless Nickel Plating of AM60 Magnesium Alloy in Nickel Sulfate Bath and Properties of the Coating

The process for electroless nickel plating of AM60 magnesium alloy in a nickel sulfate bath, based on etching in acidic molybdate and activation in alkali molybdate,was studied. The morphology of the resulting electroless Ni - P coating was observed using a scanning electron microscope, while its composition was analyzed by means of energy dispersive spectroscopy. Moreover, the adhesion of the Ni - P coating to the Mg alloy substrate was measured using file test, and the corrosion resistance of the Ni - P coating was evaluated by measuring the open - circuit - potential versus time curve and potentiodynamic polarization curve using electrochemical method. It was found that the electroless Ni - P coating was uniform and compact and had no obvious defects on the surface, with the content of P ( mass fraction) to be about 10% - 14%. The corrosion potential of the electroless Ni-P coating in the solution of 3.5%NaCl was about -0.4 V (vs SCE), and the anodic polarization curve showed evidences to the existence of a passivation region. Besides, the electroless Ni - P coating was well adhered to the Mg alloy substrate and had good corrosion resistance.