Abstract:The formation of Cr(III) chemical conversion coating (TCC) on Zn-Al hot-dip coating was unraveled and cathode or anode square wave potential (φ_p) was applied during the TCC construction progress in terms of comparatively investigating the effectiveness of φ_p. 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 φ_p enhanced the corrosion resistance and reduced the content of Cr(VI) on the surface of freshly-prepared TCC better than anode φ_p. Besides, the hydrophobicity of TCC and adhesion to epoxy primer were also improved due to the reconstruction of the micro-nano structure.

Key words: hot-dip coating; Cr(III) conversion coating; wave potential; surface roughness