Twinning in rolled AZ31B magnesium alloy under free-end torsion
Twinning in rolled AZ31B magnesium alloy under free-end torsion
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DOI：
10.1016/j.msea.2020.140405
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发表时间：
2021-01-13
期刊：
影响因子：
6.4
通讯作者：
Jiang, Yanyao
中科院分区：
文献类型：
--
作者：
Carneiro, Luiz;Culbertson, Duke;Jiang, Yanyao
采用与之配套的薄壁管材试件，研究了AZ31B镁合金轧制后在自由端单调扭转载荷作用下的力学响应和组织演变。管状试件的轴线沿轧制镁板的法线方向。剪切应力-剪切应变响应呈微妙的S型，由四个不同的应变硬化阶段组成。在整个剪切变形过程中，基面滑移和拉伸孪生都在进行。拉伸孪生和压缩孪生均受青睐。多变种拉伸孪晶的生长和相互作用导致孪晶-孪晶界(TTB)的形成。孪晶界和孪晶界的集体硬化效应导致了应变硬化率在II和III阶段的独特提高。除了一次孪晶外，在拉伸孪晶有利晶中还观察到尺寸可检测的拉-压孪晶和拉-压-拉伸三次孪晶，而在拉-孪不利晶中发现了压缩-拉伸孪晶；随着剪切应变的增加，这两种现象都变得更加明显。在TTB形成耗尽的第四阶段变形中，非基面棱柱滑移变得更加明显，是导致该阶段应变硬化率逐渐降低的原因。在织构材料中普遍观察到的SWIFT效应在自由端扭转下是明显的。Swift效应的起因是位错在小于5%的剪切应变下滑移，但在较大的塑性应变下主要是由于拉伸孪晶所致。
The mechanical response and microstructure evolution in a rolled AZ31B magnesium alloy were experimentally characterized using companion thin-walled tubular specimens under free-end monotonic torsion. The tubular specimens were made with their axes along the normal direction of the rolled magnesium plate. The shear stresss-hear strain response shows a subtle sigmodal shape that is composed of four distinctive stages of strain hardening. Basal slips and tension twinning are operated throughout the shear deformation. Both tension twinning and compressing twinning are favored. Growth and interaction of tension twins with multiple variants lead to formation of twin-twin boundaries (TTBs). The collective hardening effects by twin boundary (TB) and TTB result in a unique rise of the strain hardening rate in Stage II and III. In addition to primary twins, tension-compression double twins and tension-compression-tension tertiary twins with detectable sizes are observed in the tension-twin favorable grains whereas compression-tension double twins are detected in the tension-twin unfavorable grains; all of which become more observable with the increasing shear strain. During Stage IV deformation where TTB formation exhausts, non-basal prismatic slips become more significant and are responsible for the progressive decrease in strain hardening rate in this stage. Swift effect, which is commonly observed in textured materials, is evidenced under free-end torsion. The origin of Swift effect is confirmed to be dislocation slips at a shear strain less than 5% but is predominantly due to tension twinning at a larger plastic strain.