In situ monitoring of dislocation, twinning, and detwinning modes in an extruded magnesium alloy under cyclic loading conditions
In situ monitoring of dislocation, twinning, and detwinning modes in an extruded magnesium alloy under cyclic loading conditions
复制标题
DOI：
10.1016/j.msea.2021.140860
复制
发表时间：
2021-02
期刊：
影响因子：
6.4
通讯作者：
D. Xie;Z. Lyu;Yuan Li;P. Liaw;H. Chew;Yang Ren;Yan Chen;K. An;Yanfei Gao
中科院分区：
文献类型：
--
作者：
D. Xie;Z. Lyu;Yuan Li;P. Liaw;H. Chew;Yang Ren;Yan Chen;K. An;Yanfei Gao
本文采用中子衍射原位测量方法研究了挤压沉淀强化AZ 80镁合金应变控制低周疲劳的微观变形机制。结果表明，在循环加载过程中的塑性变形是由交替的{10.2}延伸孪生和退孪生机制。观察到的变形模式是强烈的织构和沉淀依赖。对于初始织构，测试材料具有两个主要织构组分，这导致在前两个循环中在压缩和反向拉伸期间发生拉伸孪晶。在随后的循环中，长时间的退孪晶过程被认为是为了缓解{00.2}晶粒的剪切应力场，从而导致孪晶的消失。析出强化使AZ 80镁合金的拉伸孪晶临界分辨剪切应力（CRSS）提高了约33 MPa。初始织构、沉淀强化和各种晶粒族和相的载荷分担的协同效应有助于主导变形机制的复杂演变，其中升高的位错活动被认为是与其他镁合金相比时相对较差的低周疲劳寿命的原因。
This work investigates the microscopic deformation mechanisms of an extruded, precipitation-strengthened AZ80 magnesium (Mg) alloy subjected to strain-controlled low-cycle fatigue using in situ neutron diffraction measurements. Results demonstrate that the plastic deformation during cyclic loading is dominated by the alternating {10.2} extension twinning and detwinning mechanisms. The observed deformation mode is strongly texture and precipitate dependent. For the initial texture, the tested material has two major texture components which result in the occurrence of extension twinning during both compression and reverse tension in the first two cycles. The prolonged detwinning process in the following cycles is proposed to relieve the shear stress field of {00.2} grains, leading to the disappearance of twinning. The precipitation strengthening results in an increase of the critical resolved shear stress (CRSS) by ~33 MPa for the extension twinning in this AZ80 alloy. The synergistic effects of the initial texture, precipitation strengthening, and load sharing of various grain families and phases contribute to the complicated evolution of dominant deformation mechanisms, among which elevated dislocation activities are believed to be responsible for the relatively poor low-cycle-fatigue lifetime when compared to other Mg alloys.