Characteristics and corrosion behavior of nickel‐phosphorus coatings deposited by a simplified bath

An economical formulation is introduced for electroless Ni-P coating on AZ31B Mg alloy, and the multifunctional additive polyvinylpyrrolidone as the only additive is used for the electroless bath. The effect of PVP concentration on electroless Ni-P coating is researched in detail. The total deposition rate of the Ni-P coating is estimated by the gravimetric method. It is shown that with the increases of PVP concentration in electroless solution, the total deposition rate for Ni-P coatings decreases. The microstructure and surface morphologies of Ni-P coatings are characterized by X-ray diffraction and scanning electron microscopy. Moreover, electrochemical impedance spectroscopy and polarization measurement are used to evaluate the anticorrosion property of the Ni-P coatings in 3.5% NaCl solution. The results show that a mixture of crystalline and amorphous Ni-P coating with medium phosphorus content is successfully deposited on the AZ31B Mg alloy. Furthermore, the Ni-P coating displays preferable properties in both micro-hardness and corrosion resistance when the concentration of PVP is 10 g/L.