Study On Technology And Property Of Electroless Plating Ni-W-P Coatings On AZ91D Magnesium Alloy

As the corrosion resistance of AZ91D magnesium alloy is very poor，which restricts thefurther development, preparing electroless Ni-W-P plating with excellent corrosion resistanceproperties has been a key issue. In the article, by establishing orthogonal experiments, stableand excellent corrosion resistance electroless plating technology was obtained and the effectsof temperature，pH，the concentration of reducing agent and NiSO4.6H2O on electrolessplating was investigated. The corrosion resistance of Ni-W-P coating was studied byelectrlchemical test. The results show that temperature makes the greatest impact onelectroless plating,and the concentration of reducing agent has the least impact. In the end,microscopic structure and the corrosion resistance of the optimized electroless plating havebeen studied by SEM, XRD, Potentiodynamic polarization curves and EIS. The results showthat the optimized Ni-W-P coating is a low phosphorous coating and the hardness is fourtimes as hard as AZ91D magnesium alloy. It has excellent corrosion-resistance.Ultrasound was applied in activation radioactivation on the basis of normal activationradioactivation。The morphology, microstructure and components of the Ni-W-P platingwere characterized by SEM, XRD and EDS, respectively. Potentiodynamic polarizationcurves and EIS were used to test electrochemical properties.The effects of ultrasound onstructure and corrosion-resistance of Ni-W-P coatings were investgated. The results show thatNi-W-P coatings with ultrasound activation have a better bond and corrosion-resistance.Through designing four electroless plating technologies: stirring, ultrasonic power60W,105W,150W and comparaing microstructure and the corrosion resistance of four differentNi-W-P coatings, the influence of ultrasonic power was investgated. The results show thatwith the increasing of the power，the deposition rate and the hardness of plating wereincreased，but when the value of power reaches105W，the deposition rate achieves themaximum. Compared with the stirring process, Ni-W-P coatings surface with ultrasonictechnology is more uniform compact.And the surface of Ni-W-P coatings with ultrasonic105W is the flattest and has the best corrosion-resistance.Double layer Ni-W-P coating was designed. The morphology, microstructure andcomponents of double layer and single layer Ni-W-P coatings were characterized by SEM,XRD and EDS. Potentiodynamic polarization curves and EIS were used to test electrochemical properties, and through comparing it showed that double layer Ni-W-Pcoating has a better corrosion resistance.