Competitive anion precipitation governs corrosion product film evolution on corrosion-resistant magnesium alloys in physiological solutions

In solutions containing Cl − as the base electrolyte, adding either H 2 PO 4 − /HPO 4 2− or HCO 3 − markedly lowers the corrosion rates of Mg-Al-Y alloy wires, suppresses severe localized corrosion and promotes more uniform degradation. When both anions are present, their competitive interactions alter early corrosion product evolution and lead to a less continuous and less protective corrosion product film. Thermodynamic calculations indicate that phase accessibility depends on local pH and ion activities, while quasi-in situ FTIR reveals distinct early interfacial evolution of P- and C-containing species. Subsequent product retention may additionally depend on dissolution tendency and interfacial bonding. First-principles calculations further show that, in the selected idealized models, the carbonate-containing interface exhibits a higher Cl − migration barrier, whereas the phosphate-containing interface exhibits stronger interfacial adhesion.