理解钇对挤压镁-钇合金中主导孪生模式和局部机械场演变的影响
Understanding the influence of yttrium on the dominant twinning mode and local mechanical field evolution in extruded Mg-Y alloys
AI总结：
本研究通过实验和建模揭示了钇对镁-钇合金中孪晶模式及局部机械行为的影响，发现钇含量增加会抑制TT1孪晶并促进TT2孪晶，同时影响滑移与孪晶的CRSS比。
摘要：
孪生是镁合金中的主要变形机制。本研究聚焦于镁-钇合金在单轴压缩中的张应力孪生，有三个关键方面：孪晶晶粒的取向特异性、随着钇含量增加CRSS的相对演变，以及孪晶区域的局部应力和应变演变。进行了实验表征和晶体塑性建模。在Mg-7wt.%Y中，除了常见的TT1-{101-2}孪晶外，还观察到TT2-{112-1}张应力孪晶。增加钇会抑制TT1的形成，同时促进TT2的活动。识别出一组以前未报告的晶体学取向，其对于<c+a>滑移具有更高的全局Schmid因子，这些取向在压缩应变增加时表现出TT1孪晶。为了阐明钇对孪晶活动和局部机械场的影响，将TT1和TT2张应力孪晶模式纳入PRISMS-Plasticity，这是一个开源的基于有限元的晶体塑性求解器。四种二元镁-钇合金在压缩下进行了建模，并进行了统计分析，以关联初始取向、应力-应变分布和孪晶活动作为钇浓度函数的关联。塑性分析表明，随着钇的增加，普鲁士滑移和金字塔滑移的CRSS比TT1孪晶相对降低，而TT2的滑移-孪晶CRSS比增加，从而成为潜在的差异化孪晶活动指示器。此外，尽管体积分数较小，TT2孪晶区域被预测在局部具有更高的应变积累，相对于代表性体积元素和TT1孪晶，这表明其可能对局部现象如再结晶或孪晶成核产生影响。这些发现提供了对镁合金局部机械行为的见解，并支持为先进工程应用设计合金。
英文摘要：
Twinning is a primary deformation mechanism in Mg alloys. This study focuses on tension twins during uniaxial compression of Mg-Y alloys, with three key aspects: the orientation specificity of twin grains, the relative evolution of CRSS with increasing Y content, and the local stress and strain evolution at twin sites. Experimental characterization and crystal plasticity modeling were performed. In Mg-7wt.%Y, TT2-{112-1} tension twins were observed in addition to the common TT1-{101-2} twins. Increasing Y suppressed TT1 formation while promoting TT2 activity. A previously unreported group of crystallographic orientations with a higher global Schmid factor for <c+a> slip was identified, which exhibited TT1 twinning with increasing compression strain. To elucidate Y effects on twin activity and local mechanical fields, both TT1 and TT2 tension twin modes were incorporated into PRISMS-Plasticity, an open-source, finite element-based crystal plasticity solver. Four binary Mg-Y alloys were modeled under compression, and statistical analysis was conducted to correlate initial orientations, stress-strain distributions, and twin activities as functions of Y concentration. The plasticity analysis revealed that increasing Y decreases the CRSS ratio of prismatic and pyramidal slip relative to TT1 twinning, while the slip-to-twin CRSS ratio for TT2 increases, thereby serving as a potential indicator of differential twin activity with Y addition in Mg alloys. Additionally, despite their small volume fraction, TT2 twin sites were predicted higher local strain accumulation locally, relative to the representative volume element and TT1 twins, suggesting their potential influence on localized phenomena such as recrystallization or twin nucleation. These findings provide insight into local mechanical behavior in Mg alloys and support alloy design for advanced engineering applications.
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