A combined method for producing high strength and ductility magnesium microtubes for biodegradable vascular stents application

Magnesium alloys have received significant attention as an attractive candidate for the biodegradable stent. However, the use of Mg alloys faces some difficulties in production because of the low mechanical properties. In this study, a new combined method based on cyclic expansion extrusion (CEE), direct extrusion and microtube extrusion was used to fabricate WE43 Mg microtubes. The results demonstrated a significant improvement in mechanical properties and microstructure of the processed samples. Applying large plastic strain at 400 °C led to the occurrence of dynamic recrystallization (DRX) and subsequently formation of fine and ultrafine grain microstructure. The mean grain size was reduced to 5.5 μm from the initial value of 130 μm. The ultimate strength and elongation were increased from 230 MPa to 5.1% to relatively higher values of 410 MPa and 18.5% in the final microtube, respectively. Microhardness of the final microtube was increased from the initial value of 80 Hv to 114 Hv, and good hardness homogeneity was observed along the microtubes thickness. It was demonstrated that the proposed method overcame the poor formability of Mg alloys and could be successfully applied to fabricate ultrafine grain Mg microtubes. Therefore, fabrication of high strength and high ductility microtubes from WE43 Mg alloy for biodegradable stents is possible by this combined approach and the final products showed superior properties.