Efficient corrosion inhibition mechanism of barbituric acid and sodium phosphate on AZ91 Mg alloys in NaCl solution

• The synergistic corrosion inhibition effect of sodium phosphate and barbituric acid on Mg alloys was systematically investigated. • Theoretical calculations were used to simulate the adsorption process of corrosion inhibitors. • SP and BA synergistically work together in the inhibition process of magnesium alloy, enhancing the corrosion inhibition efficiency by forming a protective film and adsorbing to prevent corrosion reactions. The surface of the Mg alloy develops a stable and dense film of corrosion products through the synergistic interaction of barbituric acid (BA) and sodium phosphate (SP). The combination of SP and BA exhibits a strong corrosion inhibition effect, with a corrosion inhibition efficiency of 83.67% observed in mass loss experiments. Furthermore, electrochemical tests reveal a corrosion inhibition efficiency of 94.04%. SP predominantly forms a protective Mg 3 (PO 4 ) 2 layer by reacting with Mg, effectively shielding the Mg surface from the corrosive environment. Theoretical calculations indicated that BA tends to align in a nearly parallel orientation on the Mg (0 0 1) surface. Moreover, BA inhibits the cathodic reaction by adsorbing onto the Mg surface and promotes the activation of Mg on the surface. The synergistic action of SP and BA enhances the efficacy of inhibiting Mg alloy corrosion by creating a protective film and adsorbing to prevent further reactions.