Manufacturing and mechanical characterization of Mg-4Y-2Nd-0.4Zr-0.25La magnesium microtubes by combined severe plastic deformation process for biodegradable vascular stents

Using biodegradable magnesium microtubes for producing vascular stent have received a great deal of attention during the last decade. However, poor workability and low mechanical properties of Mg and its alloys pose an obstacle to manufacturing microtubes for stent application. In this article, a combined method including equal channel angular pressing), direct extrusion, and microtube extrusion processes are employed to produce WE43 magnesium microtubes. Thus, microtubes with an outside diameter of 3.3 mm and a wall thickness of 0.22 mm are successfully manufactured. The results demonstrate a significant improvement in mechanical properties and microstructure of the processed samples. The ultimate strength and elongation are increased from 240 MPa and 6% to 340 MPa and 20% in the final microtube, respectively. In addition, the microhardness of the final microtube is enhanced from an initial value of 85 Hv to 102 Hv and the grain size is reduced to 3.5 mu m from the initial value of 135 mu m. Therefore, the proposed method overcomes the poor formability of Mg alloy and can be used to fabricate high-strength microtubes with ultrafine-grained structure.