The processing of Mg alloy micro-tubes for biodegradable vascular stents

• High-quality Mg alloy micro-tubes for biodegradable stents are fabricated.
• Texture component and intensity vary in different Mg alloy micro-tubes.
• Three Mg alloy micro-tubes show different fracture mechanisms.
• How microstructures and textures affect mechanical properties of tubes is studied.

In this study, through a combination of hot extrusion, cold rolling and drawing, three Mg alloys, Mg–Nd–Zn–Zr (abbr. JDBM), AZ31 and WE43, were successfully fabricated into the high-quality micro-tubes with 3.00 mm outer diameter and 180 μm thickness for biodegradable stents. This processing method overcame the shortcoming of the poor workability of Mg alloys and could be applied to fabricate sufficiently long tubes with low dimensional errors within 2.8%. Microstructure observation demonstrated that the as-annealed JDBM, AZ31 and WE43 micro-tubes had more uniformly distributed grains with an average size of 10.9 μm, 12.9 μm and 15.0 μm, respectively. Tensile mechanical test results showed that the as-annealed JDBM, AZ31 and WE43 micro-tubes respectively exhibited the yield strength of 123 MPa, 172 MPa and 113 MPa, and significantly different breaking elongation of 26%, 16% and 10%. The following SEM observation showed microvoid coalescence, quasi-cleavage and cleavage fracture, respectively. In addition, EBSD analyses revealed that the as-annealed AZ31 tubes had a strong texture component 21¯1¯0 with a low Schmid factor for basal slip, while JDBM and WE43 tubes respectively exhibited weak textures 101¯0 and 101¯0+202¯1 with a similarly high Schmid factor for basal slip.