Controlled Grain Refinement of Biodegradable Zn-Mg Alloy: The Effect of Magnesium Alloying and Multi-Pass Hydrostatic Extrusion Preceded by Hot Extrusion

To satisfy the most stringent criteria in terms of new cardiovascular stents, pure Zn was alloyed with 1 wt pct of Mg and subsequently subjected to plastic deformation, using conventional hot extrusion followed by multi-pass hydrostatic extrusion. A detailed microstructural and textural characterization of the obtained materials was conducted, and mechanical properties were assessed at each pass of deformation process. In contrast to pure Zn, hydrostatically extruded low-alloyed Zn is characterized by a remarkable increase in strength and ductility (YS = 383 MPa, E = 23 pct), exceeding the values needed for stents. Such behavior is associated with a dual microstructure containing fine-grained Zn, alternatively arranged with bands of a fragmented eutectic. Extensive grain refinement was achieved due to the process of continuous dynamic recrystallization. Hydrostatic extrusion changes the initial < 10 (1) over bar0 > fiber texture to a < 0002 > and < 10 (1) over bar1 > double fiber texture in which the < 0002 > component decreases with each pass of hydrostatic extrusion. The gradual evolution of texture components was simulated using a visco-plastic self-consistent model, which confirmed that, during hydrostatic extrusion, secondary slip systems were activated involving mostly the pyramidal one.