Study on Preparation and Property of Ni-Co-P Coatings of AZ31B Magnesium Alloy

AZ31B was used as the basic material in electroless Plating of Ni-Co-P, The optimium formula and process conditions were obtained by using the orthogonal experiment methods. XRD, SEM and EDS were used to characterize phase structure, compositon and morphology of Ni-Co-P coating. The morphology, corrosion resistance, composition, hardness, thickness and binding force of coating are measured and analysed. The optimum formula and the technological conditions were gained as follows: 26.0g/L NiSO4 center dot 6H(2)O,28.0g/L CoSO4 center dot 7H(2)O, 24.0g/L NaH2PO2 center dot H2O, 80.0g/L Na3C6H5O7 center dot 2H(2)O, 60.0g/L NH4F, temperature of 90.0., 0.001g/L KI, 0.05g/L SDBS, the plating time of 2.0 h and pH of 8.0. Under this condition, the coating had stronger corrosion resistance, drop time for KMnO4 solution was 272s; The hardnesses was 229.60HV; the deposition rate was faster, up to 53.33 g.m(-2).h(-1); thickness was 12.43 mu m; the surface of the coating was uniform; the distribution of porosity was smaller; there was well-bonded with the substrate.