Characterization of Mg,Al-hydrotalcite conversion film on Mg alloy and Cl− and CO32- anion-exchangeability of the film in a corrosive environment

This work explores an environmentally clean method for synthesizing chemical conversion coatings on Mg alloy. An Mg,Al-hydrotalcite (Mg6Al2(OH)16CO3 · 4H2O) layer was initially developed on Mg alloy in an HCO3-/CO32- aqueous solution to protect the alloy from corrosion. The Mg,Al-hydrotalcite-coated Mg sample had a much greater corrosion resistance than an as-die-cast sample. In a corrosive environment (chloride solution), the hydrotalcite layer exhibited CO32- for Cl− anion-exchangeability, causing that the layer protected Mg alloy against corrosion.