Zn-Mg and Zn-Ag Degradation Mechanism Under Biologically Relevant Conditions

Zinc (Zn) 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. The authors studied the degradation of three alloys, zinc–4 wt% silver (Ag), zinc–0·5 wt% magnesium (Mg) and zinc–3 wt% magnesium by in situ electrochemical impedance spectroscopy (EIS). After exposure for 1 h or 30 d, the samples were characterized by infrared spectroscopy and scanning electron microscopy. The presence of secondary phases in the alloy microstructure induced selective corrosion and increased the degradation rate. EIS analysis revealed an increase in surface inhomogeneity already at short (hours) immersion times. The microgalvanic corrosion of the zinc–silver alloy resulted in enrichment of the AgZn3 phase at the sample surface. The enrichment of silver and potential release of AgZn3 particles may result in complications during the tissue regeneration. The zinc–magnesium alloy surface was depleted of the magnesium-rich phase after 8–12 d. The selective dissolution caused local precipitation of corrosion products and a thicker corrosion layer with larger pore size consistent with increased corrosion rate.