Novel Ti/Zr Based Non-Chromium Chemical Conversion Coating for the Corrosion Protection of Electrogalvanized Steel

摘要

A novel Ti/Zr based chemical conversion coating was developed for improving the corrosionresistance of electrogalvanized steel using fluotitanate acid, fluozirconate acid and hydrofluoric acid,etc. The surface morphology was investigated by SEM. Coating composition was analyzed using XPSand FTIR. EIS and potentiodynamic polarization curves were used to evaluate the corrosion behavior.The results showed that the conversion coating was compact with the thickness of about 500 nm, andhad a uniform amorphous composition that consisted of nanoscale complicated oxides or hydroxidesand zinc fluorides. The Ti/Zr based conversion coating exhibited a relatively better protection for theelectrogalvanized steel because the corrosion current (Icorr) was about two orders of magnitude lowerthan the zinc coating substrate. EIS results indicated that the corrosion reaction of the preparedconversion coating was mixed-controlled by charge transition and diffusion charge during its threecorrosion stages.