title: The processing of ultrafine-grained Mg tubes for biodegradable stents.
abstract: An investigation was carried out on equal-channel angular pressing (ECAP) and extrusion processing of a ZM21 Mg alloy to obtain an improved candidate material for the manufacturing of biodegradable Mg stents. Ultrafine-grain size billets of the ZM21 alloy were obtained by two-stage ECAP aimed at achieving an initial refining of the structure at 200°C and then reaching the submicrometer grain size range by lowering the processing temperature down to 150°C. The investigation revealed a significant improvement in the properties of the ECAP-treated samples compared with the starting coarse-grained ZM21 alloy. The 0.2% yield strength rose from 180 to 340 MPa after 150°C ECAP processing, while maintaining a fairly high tensile ductility. The ultrafine ZM21 alloy billets were then used for the extrusion of stent precursors having the form of small-size tubes. The grain size after extrusion remained in the submicrometer range while the hardness was revealed to be significantly higher than that of the coarse-grained ZM21 Mg alloy. It was demonstrated that processing of biodegradable Mg stent having an ultrafine-grained microstructure by ECAP and low-temperature extrusion is feasible and that the obtained products feature promising properties.
authors: Department of Mechanical Engineering, Politecnico di Milano, 20156 Milan, Italy.
authors: Qiang
authors: Q
authors: Ge
authors: David
authors: D
authors: Dellasega
authors: Ali Gökhan
authors: AG
authors: Demir
authors: Maurizio
authors: M
authors: Vedani
mesh_terms: D020341:Absorbable Implants; D000497:Alloys / Q000494:pharmacology; D001672:Biocompatible Materials / Q000737:chemistry*; D006244:Hardness; D008274:Magnesium / Q000737:chemistry*; D008422:Materials Testing / Q000379:methods*; D008855:Microscopy, Electron, Scanning; D010316:Particle Size; D015607:Stents; D013314:Stress, Mechanical; D013696:Temperature; D013718:Tensile Strength / Q000187:drug effects
chemical_list: D000497:Alloys; D001672:Biocompatible Materials; D008274:Magnesium
keywords: Biodegradable stent; ECAP; Extrusion; Mg alloy; Ultrafine grains