Effect of Polarisation Mimicking Cathodic Electrodeposition Coating on Industrially Relevant Metal Substrates with ZrO2-Based Conversion Coatings

Modern ZrO2‐based conversion coatings were deposited on an aluminium alloy (AA6014), a cold‐rolled steel, a zinc electrogalvanised steel and a Sendzimir zinc hot‐dip galvanised steel. Pretreated substrates were subjected to galvanostatic polarisation in aqueous NaNO3 to mimic deposition conditions of cathodic electrodeposition coatings. No significant structural modification of the conversion coatings was found with Raman or photoluminescence (PL) spectroscopy. After treatment, increased PL indicated an increased number of point defects. Downstream monitoring of dissolved Zr indicated an insignificant totally dissolved fraction of 0.01 % after 5 s of polarisation, which may occur through vacancy‐pair coalescence with concurrent oxide dissolution, as discussed for transpassive dissolution. Overall, the ZrO2 films remained intact after polarisation. Survival of the fittest: ZrO2‐based conversion coatings on structural materials (see picture) remain intact after cathodic polarization. Consequently, they survive the application of cathodic electrodeposition coating, a process frequently used, for example, in the automotive industry. Some surface remodeling takes place during polarization. In situ and ex situ spectroscopy show increased defect‐related luminescence.