Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China.
Mater Sci Eng C Mater Biol Appl. 2013 Aug 1;33(6):3481-8. doi: 10.1016/j.msec.2013.04.039. Epub 2013 Apr 28.
Magnesium alloys possess highly limited room-temperature formabilities. This presents a technological barrier to the fabrication of minitubes for biodegradable vascular stents. The research was aimed at developing precision forming technology to fabricate ZM21 magnesium alloy minitubes with a refined microstructure. A multipass cold drawing process with a moving mandrel was successfully developed to convert seamless hollow billets through five passes of cold drawing and an interpass annealing treatment into minitubes with an outside diameter of 2.9 mm and a wall thickness of 0.217 mm, ready for laser cutting into vascular stents. It was found that a cumulative reduction in cross-section area as much as 32% could be applied to the material without causing fracture. However, a further reduction in cross-section area required annealing at 300°C for 1h to change a twinned microstructure into a recrystallized grain structure and to regain formability. The interpass annealing treatment after the fourth pass led to a reduction in drawing force by 22%, in comparison with the drawing force at the fourth pass of drawing. The variations in the outside diameter and wall thickness of the minitubes could be kept within 5 and 12 μm, respectively. Further research is directed toward improvements in dimensional precisions.
镁合金室温成形性有限。这对可生物降解血管支架的小管制造构成了技术障碍。本研究旨在开发精密成形技术，以制造具有精细微观结构的 ZM21 镁合金小管。成功开发了带有移动心轴的多道次冷拔工艺，通过五道次冷拔和中间退火处理，将无缝空心坯料转化为外径 2.9mm、壁厚 0.217mm 的小管，准备通过激光切割成血管支架。结果发现，材料的横截面面积可以减少 32%而不会导致断裂。然而，要进一步减少横截面面积，需要在 300°C 下退火 1 小时，将孪晶结构转变为再结晶晶粒结构并恢复成形性。与第四道次的拉伸力相比，第四道次后中间退火处理可使拉伸力降低 22%。小管的外径和壁厚变化可分别保持在 5μm 和 12μm 以内。进一步的研究方向是提高尺寸精度。
