Study of the corrosion mechanism of the in situ grown Mg–Al–CO32− hydrotalcite film on AZ31 alloy

The corrosion mechanism of Mg–Al–CO32− hydrotalcite film is discussed based on its corrosion behavior and the anion-exchange or adsorption effect of Cl−. The results demonstrate that the film is very compact and acts as a barrier against Cl− attack in the early stage. Then the surface of the film is dissolved gradually due to its instability in aqueous solutions. Only after eliminating CO32−, Cl− can insert into the hydrotalcite interlayer to balance charges. Cl− cannot substitute CO32− just in NaCl solution, but can adsorb on active spots of the film to accelerate the decomposition.

► The anion-exchange or adsorption of Cl− on CO32-–hydrotalcite was illustrated.
► It indicates that Cl− cannot substitute CO32- just in NaCl solution.
► Cl− could insert into the CO32-–hydrotalcite interlayer after eliminating CO32-.
► The corrosion mechanism of hydrotalcite film on AZ31 alloy was discussed.