Microstructure and performance of biodegradable magnesium alloy tubes fabricated by local-heating-assisted dieless drawing

•Dieless drawing is efficient in manufacturing magnesium alloy ZM21 microtubes.•Three types of microstructure are clarified, as TM, NM and TNM.•Twins generated during dieless drawing will not cause harden effect.•Grain refinement can increase of elongation, 0.2% proof stress and UTS.•Refined grains and less twins can alleviate the local corrosion. Magnesium (Mg) alloy stents are expected to be the next generation of stents because of good biocompatibility and biodegradability. Compared with cold drawing, dieless drawing with local heating is an effective method for manufacturing the Mg alloy microtubes since a large reduction in area can be achieved in a single pass. However, the microstructure and properties of dieless drawn tubes have not been clarified, leading to the problems in practical application of dieless drawn tubes. In this study, the microstructure and performance of dieless drawn tubes are clarified. The results show that temperature and speed in the dieless drawing process are two factors in determining the grain size of dieless drawn tubes since decreasing the temperature or increasing the speed promotes the generation of fine-grained microstructure. Twins are also generated during the dieless drawing process, which 1) disintegrates grains leading to refinement and 2) causes Hall–Petch law effect on dieless drawn tubes. Tensile tests show that grain size is the main factor in determining the mechanical properties of dieless drawn tubes, namely, 0.2% proof stress 135–180 MPa, ultimate tensile strength (UTS) 200–250 MPa, and elongation 8–12%. In 0.9 wt% NaCl solution, localized corrosion is the key factor in initiating the corrosion of dieless drawn tubes, but refined grains and fewer twins can alleviate local corrosion. These results imply that dieless drawn tubes are promising in the clinical application of Mg alloy stents for cardiovascular disease.