Study On Process And Properties Of Zn-Mn-Ni Alloy Coating By Pulse Electroplating

With the purpose of improving corrosion resistance, Zn-Mn-Ni alloy coating was prepared by pulse electroplating on the surface of Q235 steel from sulfate-sodium citrate bath. The effects of bath composition and technological parameters on the surface morphology, each element content, and deposition rate of Zn-Mn-Ni alloy coating were studied by scanning electron microscope and glow discharge optical emission spectrometer. The phase compositions and corrosion resistance of Zn-Mn-Ni alloy coating under the optimal technological parameters were characterized by X-ray diffractometer and Tafel curve. Electrochemical reduction of Zn-Mn-Ni alloy coating was studied through electrochemical measurement by using cathodic polarization, cyclic voltammetry and chronoamperometry with three electrode system. This provided theoretical basis for preparing Zn-Mn-Ni alloy coating.Studies of bath composition and technological parameters showed that Zn-Mn-Ni alloy coating of bight, smooth, uniform, dense, fine grain, relatively high manganese content and deposition rate could be obtained under the conditions of ZnSO₄·7H₂O0.15mol/L,MnSO₄·H₂O 0.35mol/L,NiSO₄·6H₂O 0.10mol/L,NH₄ Cl 30g/L,H₃BO₃30g/L, Na3C6H5O7·2H₂O 0.6mol/L, Sodium lauryl sulfate 0.1g/L, compound additive10ml/L, temperature 30?, current density 30 m A/cm², pH 5.0, duty cycle 20% and cycle1000?s. The result is quite good.Zn-Mn-Ni alloy coating was consisted of Zn, Ni Zn, FeMn₄ and Fe₄Zn₉. Tafel curves of Zn-Ni alloy coating and Zn-Mn-Ni alloy coating in 3.5% NaC1 solution showed that corrosion resistance of Zn-Mn-Ni alloy coating was better than Zn-Ni alloy coating.Results of electrochemical reduction showed that Zn-Mn-Ni alloy coating was more easier deposited in a sulfate-sodium citrate path than any single metal ion, which belonged to anomalous codeposition. Nucleation way of Zn-Mn-Ni alloy coating was three-dimensional Progressive nucleation and controlled by diffusion.