D-leucine-assisted zirconium-vanadium conversion coating for regulating interfacial electrochemical corrosion of ADC12 aluminum alloy

D-leucine-modified Zr-V coating suppresses localized corrosion of ADC12. • D-leucine seals defects and limits H 2 O/Cl – transport in the coating. • SECM reveals reduced oxygen-consuming local corrosion reactions. • DFT confirmed strong D-leucine adsorption and Zr–O interfacial anchoring on ZrO 2 . ADC12 aluminum (Al) alloy is prone to localized corrosion because its heterogeneous surface microstructure and unstable native oxide film induce spatially non-uniform electrochemical reactions at the alloy/electrolyte interface. Herein, a green D-leucine-assisted zirconium-vanadium conversion coating was fabricated on ADC12 Al alloy via a simple chemical immersion process to regulate coating formation and interfacial electrochemical corrosion behavior. D-leucine acted as a bio-derived interfacial modifier to regulate the deposition, defect evolution and interfacial bonding of Zr-containing oxide/hydroxide species. Surface analyses confirmed the incorporation of D-leucine into the conversion layer and its chemical interaction with Zr-containing species mainly through carboxyl groups, thereby promoting organic-inorganic coupling, defect sealing and coating compactification. The optimized ZRCC+0.5D-AA coating exhibited a low corrosion current density of 4.71×10 −8 A·cm −2 and a corrosion rate of 5.17×10 −4 mm·y −1 , approximately 195 times lower than those of the untreated ADC12 substrate. Scanning electrochemical microscopy further confirmed that D-leucine modification effectively suppressed localized oxygen-consuming corrosion reactions and reduced electrochemical heterogeneity on the coated surface. No visible corrosion was observed after 96 h neutral salt spray exposure. DFT calculations revealed strong dissociative adsorption of D-leucine on monoclinic ZrO 2 (−111), with the vertical bidentate configuration showing a dissociative adsorption reaction energy of −9.88 eV and pronounced interfacial charge redistribution. These results demonstrate that D-leucine-assisted interfacial modification simultaneously regulates coating defects, interfacial anchoring, and local electrochemical activity, providing an effective chromium-free surface finishing and protection strategy for Al alloys. Download: Download high-res image (411KB) Download: Download full-size image D-leucine-assisted interfacial modification suppresses localized electrochemical corrosion of zirconium–vanadium conversion coatings on ADC12 aluminum alloy. D-leucine coordinates with Zr-containing species to form a compact organic–inorganic hybrid interface, sealing defect-assisted pathways and reducing H 2 O/Cl⁻ ingress. This limits mass transfer, charge-transfer reactions, cathodic oxygen reduction, and anodic Al dissolution at the coating/substrate interface. DFT and SECM results reveal strong interfacial anchoring and reduced oxygen-consuming local corrosion activity, leading to optimal long-term protection for the coating containing 0.5 g/L D-leucine.