Optimization of Nickel-Phosphorous Electroless Plating Technology for Whisker-Reinforced Magnesium-Matrix Composite and Study of Corrosion Resistance of Coatings

Conventional nickel-phosphorous electroless plating technology was applied to whisker-reinforced A291D Mg alloy-matrix composite so as to improve its corrosion resistance.Thus four kinds of electroless plating conditions were primarily screened,and then further optimized in relation to the morphology of electroless Ni-P coatings and the properties of the electroless plating bath.Moreover,the surface morphology of as-plated Ni-P coatings was observed with a scanning electron microscope,and their corrosion resistance was evaluated by electrochemical method(potentialtime curve,potential-dynamic polarization curve,and alternating current impedance spectrum).The adhesion to substrate was determined by file test.Results indicated that conventional nickelphosphorous electroless plating technology applicable to Mg alloys was also suitable for whisker-reinforced Mg alloy-matrix composite.The optimized electroless plating bath consisted of 20 g/L 2NiCO_3?Ni(OH)_2?H_2O_3 10 g/L NH_4 HF_2,and 20 g/L NaH_2 PO_2 ?H_2O;and the optimized electroless plating condition was suggested as pH value of 6.5,temperature of 65 ?,and time of 2 h.Relevant electroless Ni-P coating obtained under the optimized condition was free of surface defects and had good compactness as well as good adhesion to Mg alloy substrate.Besides, the corrosion potential of electroless Ni-P coating was higher than that of Mg alloy substrate by 0.41 V,showing mildly improved corrosion resistance.