Zirconia-engineered semiconducting LDH/MgO composites on AZ31 Mg alloy for enhanced corrosion resistance

This work reports the fabrication of zirconia-engineered semiconducting CoFe-layered double hydroxide (CoFe-LDH) architectures on MgO layers formed by micro-arc oxidation (MAO) of AZ31 Mg alloys for enhanced corrosion protection. Two strategies were investigated: (i) incorporation of ZrO 2 nanoparticles during MAO and (ii) post-modification of LDH layers with ZrO 2 via hydrothermal treatment. ZrO 2 incorporation during MAO produced denser MgO layers that facilitated LDH nucleation, while post-treatment effectively sealed surface defects in the LDH matrix. Electrochemical tests demonstrated remarkable improvements: the corrosion current density decreased from 1.43 × 10 -6 A·cm -2 for MAO to 7.60 × 10 -10 A·cm -2 for LDH-ZrO 2 , accompanied by significant increases in both outer- and inner-layer resistances. Mott–Schottky analysis confirmed that MAO and MAO-ZrO 2 coatings are predominantly p-type, while LDH-containing composites display dual p-/n-type behavior due to their heterogeneous layered structure. Mott–Schottky analysis further revealed that MAO and MAO-ZrO 2 coatings exhibit p-type behavior with relatively high carrier densities, while LDH-containing composites display dual p-/n-type responses due to their heterogeneous layered structure. Among these, LDH–ZrO 2 exhibited the lowest carrier density (1.102 × 10 12 cm -3 ), indicating the formation of a highly resistive electronic barrier that effectively suppresses charge transfer and chloride ingress. Density functional theory (DFT) calculations further confirmed the strong interfacial interactions between ZrO 2 particles and the LDH matrix, which contribute to enhanced structural stability and improved charge-blocking capability. Overall, zirconia-modified LDH hybrids act as compact semiconducting barriers that markedly improve magnesium alloy corrosion resistance in chloride-rich environments.