Compared to cold drawing, dieless drawing has shown great potential for manufacturing biodegradable Mg alloy microtubes due to the large reduction in area acquired in a single pass. However, owing to the local heating and local deformation, the deformation mechanism during dieless drawing is not clear, and thus causing difficulties in controlling the microstructure of dieless drawn tubes. For the purpose of acquiring a desired microstructure, in this study the deformation mechanism of ZM21 Mg alloy tube was clarified by conducting continuous observation of the microstructural evolution during dieless drawing. The results show that both SRX and DRX occurred during dieless drawing. SRX occurred before the plastic deformation to soften dieless drawn tubes. With increase of feeding speed, the deformation mechanism changed accordingly: (1) At the low-speed of 0.02 mm/s, the deformation mechanism was dominated by twin-slip sliding, during which {10–12} tension twins were generated inside grains to accommodate the plastic deformation by changing the crystal orientation. (2) At the intermediate-speed of 2 mm/s, a twin-DRX process related to {10–12} tension twin was observed, which was characterized by the generation of abundant {10–12} tension twins and the evolution of misorientation angle of {10–12} tension twins. Moreover, the transformation from twin-DRX to CDRX can be observed at the late stage of plastic deformation, which was attributed to the inhomogeneous conditions of dieless drawing. (3) At the high-speed of 5 mm/s, a CDRX process was observed, during which grain boundary sliding and grain tilting were observed, in addition to the gradual rotation of subgrains. These results show that during dieless drawing, DRX is not only a temperature-dependent phenomenon, but also influenced by the variation of feeding speed.

与冷拉相比，无模拉丝在制造可生物降解的镁合金微管方面显示出巨大的潜力，因为单次获得的面积大大减少。然而，由于局部加热和局部变形，无模拉拔过程中的变形机制尚不清楚，从而导致无模拉拔管的显微组织难以控制。为了获得所需的显微组织，本研究通过连续观察无模拉拔过程中的显微组织演变，阐明了 ZM21 镁合金管的变形机制。结果表明，无模拉伸过程中同时出现了SRX和DRX。SRX 发生在塑性变形以软化无模拉管之前。随着进给速度的增加，变形机制也随之发生变化：(1) 在 0.02 mm/s 的低速下，变形机制以双滑滑动为主，在此期间在晶粒内部产生 {10-12} 张力孪晶，通过改变晶体取向来适应塑性变形。(2) 在 2 mm/s 的中速下，观察到与 {10-12} 张力孪晶相关的孪生 DRX 过程，其特征是大量的 {10-12} 张力孪晶的产生和演化{10-12} 张力孪晶的错误取向角。此外，在塑性变形后期可以观察到双DRX向CDRX的转变，这归因于无模拉伸条件的不均匀。(3) 在 5 mm/s 的高速下，观察到 CDRX 过程，在此过程中，除了亚晶粒的逐渐旋转外，还观察到晶界滑动和晶粒倾斜。