Growth behaviour of cerium‐based conversion coating on Zn‐5%Al alloy

Cerium‐based conversion coatings were deposited on a Zn‐5%Al alloy by immersing the alloy in cerium nitrate aqueous solutions with various immersion times. The growth behaviour of the cerium‐based conversion coating on the Zn‐5%Al alloy was investigated by the electrochemical impedance spectroscopy (EIS), SEM, energy dispersive spectroscopy (EDS), and XPS techniques. The results reveal that the coating mainly consists of ZnO, Zn(OH) 2 , Ce(OH) 4 , Ce(OH) 3 , CeO 2 , and Ce 2 O 3 . The growth of the cerium‐based conversion coating is accompanied by metal dissolution. The dissolution mainly occurs on the η‐Zn surface of the phase boundary and continues to extend to the Zn‐rich phase as the coating grows. EIS results show that with increasing immersion time, the corrosion resistance of the Ce conversion coating gradually increases in the early growth stage and then decreases when the cracks appear.