Tunable corrosion protection of calcium carbonate (CaCO3) coating on biomedical Mg2Zn0.2Ca alloy.

[Display omitted] • Corrosion of the substrate was effectively inhibited by the presence of MgSO 4 during coating preparation. • MgSO 4 results in the transformation of the middle calcite from cubic to spindle-shaped crystals. • Mg2+ and SO 4 2− promote the precipitation of metastable aragonite and vaterite in the outer layer. • The corrosion resistance of CaCO 3 coating for Mg substrate can be adjusted by MgSO 4 concentration. • CaCO 3 could be transformed into Ca-P products during immersion. Too fast corrosion of magnesium(Mg)-based materials is one of main concerns prior to their applications as biodegradable biomaterials. In present study, a CaCO 3 coating on Mg alloy is developed via hydrothermal method to control the corrosion of Mg2Zn0.2Ca alloy. The morphology and anti-corrosion property of the CaCO 3 protective coating are adjusted by the concentration of MgSO 4 in coating preparation electrolyte. The results reveal that the presence of MgSO 4 stabilizes the precipitation of metastable CaCO 3 crystalline (aragonite and vaterite) and affects the structure and growth rate of the middle calcite layer on Mg alloy surface, which leads to the transformation of cubic calcite into small rhombohedral aggregates in the middle layer as the concentration of MgSO 4 increases. Consequently, the corrosion protection property of the coating is significantly enhanced due to the increased compactness of the coating as the concentration of MgSO 4 increases from 0 mM to 20 mM. Whereas, with further increase of MgSO 4 concentration, the spindle-shaped calcite crystalline formed in the middle layer provides more penetrable boundaries, leading to a lower resistance for Mg substrate. Long-term immersion tests indicate the transformation of CaCO 3 into calcium phosphate, which exhibits a great prospect for Mg alloys as orthopedic implants. [ABSTRACT FROM AUTHOR]