Dynamic Corrosion and Material Characteristics of Mg–Zn–Zr Mini-Tubes: The Influence of Microstructures and Extrusion Parameters

In this study, magnesium–zinc–zirconium (Mg–Zn–Zr) alloy mini-tubes that fit the diameter of cardiovascular stents are successfully fabricated using an isothermal extrusion method. The influence of extrusion temperature and ram speed on the microstructure are examined. In addition, this research develops a novel dynamic-corrosion apparatus for Mg alloy mini-tube examination, and supplemented with electrochemical, and biocompatibility tests, the optimal criteria for mini-tube extrusion are defined. The optimized specimen not only retains a homogeneous fine-grained structure with a grain size of about 2 µm, but also possesses 300 MPa yielding strength and nearly 15% elongation. Compared with a coarse-grained microstructure, the fine-grained specimens significantly reduces the corrosion and oxidation rates in a dynamic-flow field, resulting in favorable characteristics of degradation, cytocompatibility, and hemocompatibility. The results suggest that precisely controlling the extrusion process can improve the mechanical properties as well as the biocompatibility of Mg alloys for application in cardiovascular implants.