Continuous observation of twinning and dynamic recrystallization in ZM21 magnesium alloy tubes during locally heated dieless drawing
Continuous observation of twinning and dynamic recrystallization in ZM21 magnesium alloy tubes during locally heated dieless drawing
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DOI：
10.1016/j.jma.2021.06.001
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发表时间：
2021-07
影响因子：
17.6
通讯作者：
Peihua Du;Shusaku Furusawa;T. Furushima
中科院分区：
文献类型：
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作者：
Peihua Du;Shusaku Furusawa;T. Furushima
与冷拉相比，无模拉拔由于单程获得的面积大大减少，在制造可生物降解镁合金微管方面显示出巨大的潜力。但由于无模拉拔过程中存在局部加热和局部变形，变形机理尚不清楚，给无模拉拔管材的组织控制带来困难。为了获得理想的组织，通过对ZM21镁合金管材无模拉拔过程中组织演变的连续观察，阐明了ZM21镁合金管材的变形机制。结果表明，无模拉伸过程中既发生了应力再结晶，又发生了动态再结晶。SRX发生在塑性变形之前，使无模拉拔管材软化。随着进给速度的增加，变形机制发生相应变化：（1）在0.02 mm/s的低速下，变形机制以孪晶滑移为主，在此过程中，晶粒内部产生{10 - 12}拉伸孪晶，通过改变晶粒取向来适应塑性变形。(2)在2 mm/s的中速下，观察到与{10 - 12}拉伸孪晶相关的孪晶动态再结晶过程，其特征是大量{10 - 12}拉伸孪晶的产生和{10 - 12}拉伸孪晶取向差角的演变。在塑性变形后期，由于无模拉伸条件的不均匀性，可以观察到双动态再结晶向双动态再结晶的转变。(3)在5mm/s的高速下，观察到一个CDRX过程，在该过程中，除了观察到亚晶的逐渐旋转之外，还观察到晶界滑动和晶粒倾斜。结果表明，在无模拉伸过程中，动态再结晶不仅是一个温度依赖性现象，而且还受到进给速度变化的影响。
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.