Influence of Ca 2+ and Dissolved Ozone in Phosphating Solution on Phosphate Coating on A3 Carbon Steel

Phosphate coating on the surface of A3 carbon steel was prepared through the addition of Ca2+ and ozone as an accelerator of phosphating treatment at low temperature, and was characterized by SEM, XRD, EDS, FT-IR and corrosion electrochemical testing. The effects of Ca2+ and dissolved ozone in phosphating solution on the structure and performance of phosphate coating were investigated. The results show that the coating mass decreases with increasing the Ca2+ concentration in phosphating solution. Ca2+ can reduce the crystal size of coating and increase the density and corrosion resistance of coating. The dissolved ozone in phosphating solution can reduce the crystal size of coating and promote the growth of crystal, so the nucleation and formation rates are increased and the corrosion resistance of coating is improved. When pH=2.70, concentration of Ca2+ and ozone were 1.8 g/L and 2.50 mg/L respectively, the mass of phosphate coating was 5.46 g/m2, the corrosion-resistance time of coating with CuSO4 dripping was >122 s, and the corrosion current of phosphating sample was 0.50 μA/cm2 in 5% NaCl solution.