Effect of square wave potential polarity and amplitude on property of trivalent chromium conversion coating applied on Zn−Al hot-dip coating

The formation of Cr(III) chemical conversion coating (TCC) on Zn−Al hot-dip coating was unraveled and cathode or anode square wave potential (φp) was applied during the TCC construction progress in terms of comparatively investigating the effectiveness of φp. Corrosion resistance of TCC in chloride-containing solution was obtained by EIS and polarization curve measurements, combined with the discussion of macro/micro-morphology using 3D microscope and chemical composition distribution analysis using XPS, AES, FTIR and Raman spectra. The results showed that the cathode φp enhanced the corrosion resistance and reduced the content of Cr(VI) on the surface of freshly-prepared TCC better than anode φp. Besides, the hydrophobicity of TCC and adhesion to epoxy primer were also improved due to the reconstruction of the micro−nano structure.