Corrosion inhibition of AZ31 magnesium alloy in NaCl solution: Role of aromatic carboxylate molecular structures

• The inhibition mechanisms of 7 aromatic carboxylates were investigated as corrosion inhibitors for AZ31 alloy. • A thin inhibitor-Mg(OH) 2 /MgO layer formed on the Mg surface. • Molecules can be arranged on the Mg surface in a flat-lying or up-right standing position, depending on the carboxylate(s) number and position(s). • The flat-lying arrangement and carboxylates unbound to Mg(OH) 2 /MgO provide corrosion protection for Mg alloy. The corrosion protection effect of aromatic carboxylates (benzoate, phthalate, isophthalate, terephthalate, 1,2,4-benzoate, trimesate, and 1,2,4,5-benzenetetracarboxylate) in NaCl solution on AZ31 alloy has been investigated. The results reveal that the inhibition mechanism is attributed to the effect of the studied molecules on the protective properties of a thin inhibitor-Mg(OH) 2 /MgO layer formed on the Mg surface. Both the number and position of carboxylate groups on the benzene ring influence the inhibition efficiencies of these inhibitors. A flat-lying molecular configuration more effectively shields the Mg surface from corrosive media. The findings confirm that the inhibitor-stabilized Mg(OH)₂/MgO layer effectively blocks Cl⁻ ingress and ensures strong corrosion protection for AZ31 alloy.