Study of the in situ growth mechanism of Mg–Al hydrotalcite conversion film on AZ31 magnesium alloy

By means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), open circuit potential (OCP) measurement and scanning electronic microscope (SEM), the in situ growth mechanism of the Mg–Al hydrotalcite film has been proposed. The composition and morphology of the films undergo a series of variations during the growth processes. The added Al compounds are a vital contribution to the formation of hydrotalcite. The film formation involves the dissolution of the AZ31 substrate, adsorption of the ions from solution, nucleation of the precursor, followed by the dissolution of Al3+, exchanging of OH− by CO32− and growth of the hydrotalcite film.

► The status of Al3+ and Mg2+ during the formation of HT was illustrated.
► The effect of the added Al compounds on the formation of HT film was discussed.
► The model for two-step in situ growth of Mg–Al HT film on AZ31 has been proposed.