摘要
Mg alloys are promising lightweight materials for various applications. However, the inferior corrosion resistance limits their broader applications, underscoring the importance of surface modifications of Mg alloys. Anodization of Mg alloys provides good wear resistance but limited corrosion resistance due to their porous and cracked structure. In contrast, layered double hydroxide (LDH) coatings, typically prepared via time-consuming hydrothermal methods, offer unique ion-exchange capability but insufficient barrier protection due to their hydrophilic nature and needle-like structure. To combine the advantages and compensate for the drawbacks of each coating technique, this study develops a series of processes to fabricate a multifunctional corrosion-resistant composite coating on an AZ31 Mg alloy through sequential anodization, Zn-Al LDH electrodeposition, vanadate exchange, and myristic acid (MA) hydrophobic modification. By replacing hydrothermal methods with electrodeposition, the LDH coating process was expedited from hours to 5 min. With the multifunctional composite coating, the corrosion resistance of the AZ31 Mg alloy improves substantially, as evidenced by a 500-fold increase in polarization resistance from 393 Ωcm2 to 208,801 Ωcm2 and a 300-fold decrease in the corrosion current density from 61.87 μA/cm2 to 0.18 μA/cm2. The enhanced physical barrier protection is attributed to the pore-sealing of electrodeposited Zn-Al LDH on anodized AZ31 and to the MA hydrophobic modification, which transforms the coating surface from hydrophilic to hydrophobic. Furthermore, the incorporation of vanadate species within the LDH interlayer actively inhibits corrosion reaction through vanadate reduction. Ultimately, a multifunctional composite coating with superior corrosion resistance was prepared by an efficient sequential coating process.
•The sequential process creates a multifunctional composite coating on AZ31 Mg alloy.•Expedient electrodeposited Zn-Al LDH effectively seals pores in the anodized film.•Vanadate exchange provides active corrosion inhibition via reduction reactions.•Myristic acid modification creates a hydrophobic surface for barrier protection.•The composite coating increases the polarization resistance by over 500-fold.