Zn-Mg and Zn-Ag degradation mechanism under biologically relevant conditions

Zinc alloys form a promising new class of biodegradable metals that combine suitable mechanical properties with the favorable degradation properties of pure zinc. However, the current understanding of the influence of alloying elements on the corrosion of zinc alloys, in biologically relevant media, is limited. We studied the degradation of three alloys, Zn 4 wt% Ag, Zn 0.5 wt% Mg and Zn 3 wt% Mg by in situ electrochemical impedance spectroscopy (EIS). After exposure for 1h or 30 days the samples were characterized by infrared spectroscopy and scanning electron microscopy (SEM). The presence of secondary phases in the alloy microstructure induced selective corrosion and increased degradation rate. An increase in surface inhomogeneity was evident by EIS analysis both at short (hours) as well as long immersion times (days). The microgalvanic corrosion of the Zn-Ag alloy resulted in enrichment of the AgZn3 phase at the sample surface. The enrichment of Ag and potential release of AgZn3 particles may result in complications during the tissue regeneration. The Zn-Mg alloy surface was depleted of the Mg-rich phase after 8-12 days. The selective dissolution caused local precipitation of2corrosion products and a thicker corrosion layer with larger pore size consistent with increased corrosion rate.QC 20171017