Evaluation of corrosion resistance and self-healing behavior of zirconium-cerium conversion coating developed on AA2024 alloy

In the present investigation, a zirconium-cerium conversion coating (ZrCeCC) was developed on aerospace aluminum alloy (AA2024) by simple immersion technique. Zirconium conversion coating (ZrCC) was also prepared for comparison. Surface morphology of ZrCC and ZrCeCC specimens exhibited smooth and cracked patterns respectively. Elemental analysis showed the presence of Zr and Ce in ZrCeCC specimen. XPS results indicated the presence of multiple oxidation states of Zr and Ce in the developed coatings. Potentiodynamic polarization results revealed the corrosion current density (icorr) values obtained for both coatings (between 0.6 and 0.85 μA/cm2) were lower than bare specimen (1.2 μA/cm2). However, ZrCeCC specimen exhibited the lowest icorr value of about 0.46 μA/cm2 after 168 h of immersion in 0.6 M NaCl solution. EIS studies showed that higher coating resistance (Rcoat) value was obtained for ZrCeCC even after 168 h of immersion. The results obtained from simulated scratch cell test revealed a continuous increase in charge transfer resistance (Rct) value for bare specimen which was exposed along with ZrCeCC in 0.1 M NaCl solution. The self-healing behavior of ZrCeCC was confirmed from all electrochemical tests. After 168 h of neutral salt spray exposure, the surface of ZrCeCC was almost comparable with the conventional chromate conversion coating.