Electroless Ni-P plating on Mg-Li alloy by two-step method

Pretreated Mg-Li alloy sheets were pre-plated in a NiCO3·2Ni(OH)2·4H2O solution to form a thin Ni-P alloy film and then plating in a NiSO4·6H2O solution was carried out to obtain a protective coating. The surface morphology, structure and corrosion resistance of the coating were studied. The results showed that a flat, bright and compact plating layer, which was integrated into the matrix metal, was obtained. The P content of the Ni-P coating reached 13.56% (mass fraction). The hardness value of the Ni-P coating was about HV 549. The polarization curve showed that the corrosion potential of the Ni-P coating reached −0.249 V (vs SCE). A long passivation region was found on the polarization curve, and this phenomenon indicated that the coating has an excellent anti-corrosion property.