2-methylimidazole coordinated LDH/PEO hybrid coatings for high-performance corrosion protection of AZ31 Mg alloy

This study explores the use of 2-methylimidazole (2MIM) to engineer high-performance hybrid coatings for AZ31 Mg alloy. A porous oxide layer was first fabricated via plasma electrolytic oxidation (PEO), followed by the growth of MgAl layered double hydroxide (LDH) nanosheets. To improve coating compactness and corrosion resistance, 2MIM was introduced through two distinct coordination routes: (i) in-situ coordination during LDH formation (LDH+2MIM), and (ii) post-synthetic coordination after LDH growth (LDH-2MIM). Structural and chemical analyses confirmed that 2MIM effectively coordinated with surface-exposed Mg 2+ and Al 3+ sites without disrupting LDH crystallinity. Among the two, the LDH-2MIM coating exhibited superior surface densification with the smallest interflake spacing (0.209 μm), enhanced chemical stability, reduced surface wettability as indicated by an increased water contact angle (∼80°), and the most compact cross-sectional structure. Electrochemical tests demonstrated that LDH-2MIM achieved the lowest corrosion current density (6.99 × 10 -10 A/cm 2 ), outperforming both the unmodified LDH and 2MIM-LDH samples. Impedance analysis further revealed the highest film impedance and the most stable phase response in LDH-2MIM, attributed to its dense, well-coordinated surface layer. These findings demonstrate the role of 2MIM coordination in tailoring LDH/PEO morphology, chemistry, and durability, while providing a scalable and eco-friendly strategy for Mg alloy protection.