Zn-based alloys are recognized as promising bioabsorbable materials for cardiovascular
stents, due to their biocompatibility and favorable degradability as compared to Mg.
However, both low strength and intrinsic mechanical instability arising from a strong
strain rate sensitivity and strain softening behavior make development of Zn alloys
challenging for stent applications. In this study, we developed binary Zn-4.0Ag and
ternary Zn-4.0Ag- x Mn (where x =0.2–0.6wt%) alloys. An experimental methodology
was designed by cold working followed by a thermal treatment on extruded alloys, through
which the effects of the grain size and precipitates could be thoroughly investigated.
Microstructural observations revealed a significant grain refinement during wire drawing,
leading to an ultrafine-grained (UFG) structure with a size of 700 nm and 200 nm for
the Zn-4.0Ag and Zn-4.0Ag-0.6Mn, respectively. Mn showed a powerful grain refining
effect, as it promoted the dynamic recrystallization. Furthermore, cold working resulted
in dynamic precipitation of AgZn 3 particles, distributing throughout the Zn matrix.
Such precipitates triggered mechanical degradation through an activation of Zn/AgZn
3 boundary sliding, reducing the tensile strength by 74% and 57% for Zn-4.0Ag and
Zn-4.0Ag-0.6Mn, respectively. The observed precipitation softening caused a strong
strain rate sensitivity in cold drawn alloys. Short-time annealing significantly mitigated
the mechanical instability by reducing the AgZn 3 fraction. The ternary alloy wire
showed superior microstructural stability relative to its Mn-free counterpart due
to the pinning effect of Mn-rich particles on the grain boundaries. Eventually, a
shift of the corrosion regime from localized to more uniform was observed after the
heat treatment, mainly due to the dissolution of AgZn 3 precipitates.