Twinning characteristics in rolled AZ31B magnesium alloy under three stress states
Twinning characteristics in rolled AZ31B magnesium alloy under three stress states
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DOI：
10.1016/j.matchar.2021.111050
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发表时间：
2021-05
影响因子：
4.7
通讯作者：
Luiz Carneiro;D. Culbertson;Xianyun Zhu;Qin Yu;Yanyao Jiang
中科院分区：
文献类型：
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作者：
Luiz Carneiro;D. Culbertson;Xianyun Zhu;Qin Yu;Yanyao Jiang
研究了AZ31B镁合金在沿法向拉伸(NDT)、沿轧制方向压缩(RDC)和沿法向扭转(NDTOR)三种不同应力状态下的应力应变响应和孪生特征。拉伸孪生在双胞胎中被广泛诱导，有利于NDT和RDC。在无损检测下，张力双胞胎的所有六个变种都被激活，而在RDC下，最多激活四个变种。在NDTOR下，拉伸孪晶和压缩孪晶在相对较大的应变下都被激活，孪晶发生在一小部分受欢迎的颗粒中，而不是在大多数颗粒中。在高应变水平下，在择优取向的晶粒中观察到二次孪晶和三次孪晶。每种应力状态下的变形呈现三个阶段：应变硬化率快速降低(阶段I)、依次增加(阶段II)和逐步降低(阶段III)。硬化率的提高是由于孪晶界的硬化效应和孪生织构诱发的滑移活动所致，在NDT和RDC下的硬化率比NDTOR下的更显著。孪晶界的硬化效应包括孪晶界(TBS)和孪生孪晶界(TTB)相乘引起的动态Hall-Petch硬化，以及与TTB形成不利的能量相关的硬化效应。当施加的塑性应变大于0.05时，拉伸孪晶体积分数大于50%。孪生织构导致非基面滑移的激活主要发生在孪生体积中，即NDT下的棱柱形滑移和RDC下的锥形滑移。NDTOR下加工硬度低是由于NDTOR下普遍存在的基面滑移和孪生活动减少所致。
Stress-strain responses and twinning characteristics are studied for a rolled AZ31B magnesium alloy under three different stress states: tension along the normal direction (NDT), compression along the rolled direction (RDC), and torsion about the normal direction (NDTOR) using companion specimens interrupted at incremental strain levels. Tension twinning is extensively induced in twinning-favorable NDT and RDC. All the six variants of tension twin are activated under NDT, whereas a maximum of four variants is activated under RDC. Under NDTOR, both tension twins and compression twins are activated at relatively large strains and twinning occurs in a small fraction of favored grains rather than in the majority of grains. Secondary and tertiary twins are observed in the favorably-orientated grains at high strain levels. Deformation under each stress state shows three stages of strain hardening rate: fast decrease (Stage I), sequential increase (Stage II), and progressive decrease (Stage III). The increase in the hardening rate, which is more significant under NDT and RDC as compared to NDTOR, is attributed to the hardening effect of twin boundaries and twinning texture-induced slip activities. The hardening effect of twin boundaries include the dynamic Hall-Petch hardening induced by the multiplication of twin boundaries (TBs) and twin-twin boundaries (TTBs) as well as the hardening effect associated with the energetically unfavorable TTB formation. When the applied plastic strain is larger than 0.05 under NDT and RDC, the tension twin volume fraction is higher than 50%. The twinning-induced texture leads to the activation of non-basal slips mainly in the twinned volume,i.e.prismatic slips under NDT and pyramidal slips under RDC. The low work hardening under NDTOR is due to the prevailing basal slips with reduced twinning activities under NDTOR.