Study on preparation and characterization of the Zinc-Manganese black electrolytic phosphate coating

A steady the black Zinc-Manganese electrolytic phosphate bath for carbon steel was obtained with an orthogonal trial.Electrochemical Impedance Spectroscopy and Tafel Polarization curves were used to evaluate the corrosion resistance of phosphate coatings, scanning electron microscope (SEM) techniques were applied for crystal morphology of the electrolytic phosphate films,while the XRD method was used for the electrolytic phosphate films analysis.The results have shown that electrochemical techniques can accurately characterize the high corrosion resistance of phosphate coatings.the results show that after electrolytic phosphate, the crystal morphology dense strip flake-shaped structure of the electrolytic phosphate films. 25μm phosphate coatings could be formed in this solution and the coatings could withstand over 260 s corrosion in CuSO₄ test, electrolytic phosphate coatings is constituted mainly by Zn₃(PO₄)₂, Fe(H₂PO₃)₃, Mn(HPO₄) · 3H₂O, Mn₃(PO₄)₂.