Influence of Solute Elements on The Protective Layer Properties of MG-1.06AL-0.046CA in Alkaline Electrolytes

Abstract The formation of surface films and local alkalization during the aqueous corrosion of Mg alloys significantly influences their corrosion properties across various electrolytes. This study provides new insights into the layer formation on a Mg-1.06Al-0.046Ca alloy immersed in an alkaline electrolyte (pH = 11.5) for 72 h, utilizing (electro-)chemical analysis. This study contributes new evidence supporting the formation of a subsurface Al-enriched interlayer (~4 at.%) in a Mg–Al–Ca alloy under alkaline conditions. Atom probe tomography and scanning transmission electron microscopy show the absence of Ca segregation at the metal and corrosion product interface. The corrosion product itself is a three-layer structure: next to the substrate a Mg(OH)2_dense layer, followed by an Al-enriched interlayer 2, and an outer Mg(OH)2_flake layer. Changes in diffusion-related transport properties are observed after 20.5 h of immersion, as indicated by the impedance response associated with the Mg(OH)2_dense layer and the subsurface Al interlayer 1.