Effect of refining grain size on the corrosion behavior of Cr(III) conversion layers on zinc coatings

Cr(III) conversion layers were synthesized on the nanocrystalline zinc with two grain sizes, 22 nm and 40 nm. Their corrosion behaviors were examined by potentiodynamic polarization and electrochemical impedance spectroscopy. The results shows that a more uniform and none-micro-crack conversion layer is formed on sample with grain size 22 nm compared with that formed on the sample with grain size 40 nm. Refining the grain size can markedly enhance the corrosion resistance of trivalent chromium conversion layer.