Origin of plastic anisotropy in (ultra)-fine-grained Mg–Zn–Zr alloy processed by isothermal multi-step forging and rolling: Experiments and modeling
Origin of plastic anisotropy in (ultra)-fine-grained Mg–Zn–Zr alloy processed by isothermal multi-step forging and rolling: Experiments and modeling
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DOI：
10.1016/j.msea.2017.12.045
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发表时间：
2018-01
期刊：
影响因子：
6.4
通讯作者：
D. Nugmanov;M. Knezevic;Milovan Zecevic;O. Sitdikov;M. Markushev;I. Beyerlein
中科院分区：
文献类型：
--
作者：
D. Nugmanov;M. Knezevic;Milovan Zecevic;O. Sitdikov;M. Markushev;I. Beyerlein
研究了多道次锻造（MIF）+高温等温轧制（IR）工艺对ZK60镁合金屈服应力的影响。在MIF阶段之后，屈服应力在轧制方向（RD）上比在横向方向（TD）上略高。在300 °C下IR之后，各向异性保持较小。相比之下，在较低温度200 °C下IR之后，观察到RD和TD方向之间的屈服应力的显著差异，发现该差异随着轧制应变而增加，并且在200 °C下轧制压下量时，RD方向的屈服应力甚至从高于TD方向的屈服应力变为远低于TD方向的屈服应力。为了帮助确定各向异性及其随应变的演变的可能原因，我们使用多尺度弹塑性自洽多晶体模型，该模型考虑了位错密度（泰勒硬化），沉淀硬化，纹理和晶粒尺寸。该模型在这里扩展到还包括I型和II型残余应力的影响。结合建模和电子显微镜，我们发现，纹理，晶粒尺寸分布，残余应力，泰勒硬化，和Orowan硬化只有适度的影响，塑性各向异性，不能完全解释的意见。我们合理化的屈服各向异性的主要起源是二次析出物的演变，这成为分布在轧制过程中的轧制板的平面。它们在IR期间在RD平面中变得更加对齐，从而导致TD中的拉伸屈服应力超过RD中的拉伸屈服应力。
This paper reports a strong effect of multi-step forging (MIF) followed by elevated temperature isothermal rolling (IR) on the yield stress in ZK60 Mg alloy. After the MIF stage, the yield stress is slightly higher in the rolling direction (RD) than in the transverse direction (TD). After IR at 300 °C, the anisotropy remains small. In contrast, after IR at a lower temperature 200 °C, a significant difference in yield stress between the RD and TD directions is observed, found to increase with rolling strain, and even reverse from being higher to being much lower in the RD than in the TD with rolling reduction at 200 °C. To help determine the possible causes for the anisotropy and its evolution with straining, we use a multi-scale elasto-plastic self-consistent polycrystal model that accounts for dislocation density (Taylor hardening), precipitate hardening, texture, and grain size. The model is extended here to also include the effects of type I and type II residual stresses. With a combination of modeling and electron microscopy, we find that texture, grain size distribution, residual stresses, Taylor hardening, and Orowan hardening only have moderate effects on the plastic anisotropy and cannot fully explain the observations. We rationalize that the primary origin of the yield anisotropy is the evolution of the secondary precipitates, which become distributed in the plane of the rolled sheet during rolling. They become more aligned in the RD plane during IR, causing strengthening in tensile yield stress in the TD over that in the RD.