Degradation Mechanism of the Biomedical Mg-3Zn-0.5Zr Alloy in a Simulated Physiological Environment Containing Different Anions

The interaction and synergetic effects of four corrosive anions (Cl−, HPO42-, HCO3−, and SO42-) on the degradation behavior of a Mg-3wt%Zn-0.5wt%Zr (Mg-3Zn-0.5Zr) alloy were investigated using electrochemical tests, such as potentiodynamic polarization, open circuit potential evolution, and electrochemical impedance spectroscopy (EIS). We find that chloride ions induce porous pitting corrosion on the alloy. The corrosion pits expand on the surface and become much deeper. Hydrogen phosphate ions decrease the degradation rate and restrain the pitting corrosion. However, the degradation rate of the Mg-3Zn-0.5Zr alloy is accelerated at early time points during immersion in solutions containing hydrogen carbonate ions; never the less, precipitation of the magnesium carbonate results in passivation, and the corrosion products totally inhibit the pitting corrosion. In addition sulfate ions could also corrode the Mg-3Zn-0.5Zr alloy; due to its low concentration in the physiological environment, however, the effects of sulfate on the degradation rate and corrosion morphology are limited.