Effect of Phosphorus Contents on Structure and Properties of Electroless Ni-P Plating on AZ31 Magnesium Alloy

The phosphorus content of Ni-P coatings could be controlled by changing the pH value and concentrations of reducing agent and complexing agent,and the different performance coatings could be obtained.Effects of phosphorus content on the morphology,chemical composition,phase structure and corrosion resistance of the electroless Ni-P plating coatings were studied by methods of optical microscopy,SEM,EDS,XRD and electrochemical polarization.The results showed that the cellular microstructure of high phosphorus coatings was small and compact.The bonding area of coating and substrate was uniform.The structure of the coatings changed from amorphous plus crystalline to amorphous with the increase of phosphorus content.Electrochemical results indicated that the coatings with high phosphorus content had more excellent pitting corrosion resistance in NaCl solution.