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

Abstract

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 µm from the initial value of 135 µm. Therefore, the proposed method overcomes the poor formability of Mg alloy and can be used to fabricate high-strength microtubes with ultrafine-grained structure.

Review on Advances in Metal Micro-Tube Forming

“…In this study, the tensile strength could be increased from 240 MPa of the initial workpiece to 340 MPa of the final micro-tube. An important achievement in this context was the determined increase in ductility, with an increase from 6% to 20% for the elongation of the fracture [104]. This is worth mentioning, as in many cases, SPD processing diminishes ductility [101].…”

“…On the background, an improvement of the mechanical properties and corrosion resistance of tubular materials for stent manufacture by grain refinement, a process sequence of equal-channel angular pressing (ECAP, or sometimes abbreviated as ECAE [99]), direct extrusion, machining, and micro-tube extrusion, was developed and presented by [104]. With this strategy, micro-tubes made from the magnesium alloy WE43, with d o = 3.3 mm and t = 220 µm, were fabricated, showing an average grain size of d g = 3.5 µm.…”

“…This is worth mentioning, as in many cases, SPD processing diminishes ductility [101]. According to the authors, the significant grain refinement within the equal-channel angular pressing step, initiated by recrystallization under the selected processing temperature, was assumed to be one of the main reasons for the increase in ductility [104].…”

Study of Hydroxyapatite-coated High-strength Biodegradable Magnesium-based Alloy in Repairing Fracture Damage in Rats

“…both grains' interior and grain boundaries, and some HA heterogeneous deposits (36). Following 14 days of soaking, the fraction of the white deposits increased, but the entire specimen surface was not covered with an apatite-like coating (Figure 3B).…”

Machinability of pure copper before and after processing by severe plastic deformation method

“…12,13 Also, significant large specimens can be built made from bulk without internal porosity, making processed SPD specimens the most popular type of material for industrial use among other UFG/NS materials. [14][15][16][17] Based on these methods, there are different SPD methods. The outstanding behavior of these materials is only related to their defect structures.…”