Fabrication of Vanadate-Exchanged Electrodeposited Zn-Al Layered Double Hydroxide Coating on a ZX21 Mg Alloy to Improve the Corrosion Resistance

This study presents a vanadate-exchanged Zn-Al layered double hydroxide (LDH) coating on a ZX21 Mg alloy (Mg-2.15 wt%Zn-0.97 wt%Ca) by electrodeposition and immersion anion-exchange post-treatment. With the prepared vanadate-exchanged electrodeposited Zn-Al LDH coating, the corrosion resistance of the ZX21 Mg alloy improves with a decrease in the corrosion current density from 62.4 μA/cm[sup.2] to 3.32 μA/cm[sup.2]. The fabricated vanadate-exchanged electrodeposited Zn-Al LDH coating contains complex anions in the interlayers, including mainly nitrate (NO[sub.3] [sup.−]), carbonate (CO[sub.3] [sup.2−]), and different vanadates. The coating not only serves as a physical barrier on the ZX21 Mg alloy but also absorbs chloride ions in the environment through anion exchange and inhibits corrosion with the reduction of the interlayer vanadates. Furthermore, the vanadates can also be released into the damaged area of the coating.