AZ31镁合金中的{10-12}孪生行为及其与滑移的交互作用

发布时间：2018-05-07 00:21

本文选题：镁合金 + 拉伸孪晶　；参考：《重庆大学》2016年博士论文

【摘要】：{10-12}拉伸孪晶具有较低的临界分切应力,是镁合金最为常见的变形机制之一,拉伸孪晶启动的难易程度及变体选择与镁合金的力学性能和微观组织演化密切相关。本文以AZ31镁合金为研究对象,采用电子背散射衍射(EBSD)技术和晶体学计算,系统研究了两种变形方式(单轴拉伸和压缩)和两种变形温度下的孪生行为,重点分析了初始织构和晶粒尺寸对孪生行为的影响规律,以及滑移与孪晶的交互作用。沿与镁合金轧板ND成0?、30?、45?、60?和90?五个方向进行室温拉伸变形,对比研究孪晶启动与变体选择行为。发现0?样品孪晶的施密特因子排序(SF rank)分布较散,这主要与其六个理论孪晶变体的SF相近有关。30?到90?样品中六个理论孪晶变体最大和最小SF的差值逐渐变大,孪晶变体选择受Schmid法则的影响越来越明显,样品中SF rank为1或2的孪晶比例逐渐增大。镁合金力学各向异性与主导变形机制的临界分切应力及不同取向下的SF有关,拉伸变形过程孪晶和滑移的启动共同决定了材料的r-value,通过晶体塑性分析,揭示了30?-60?样品的宏观变形特征(即r-value1)与基面滑移启动的相关性。对滑移主导变形的样品(45?拉伸样品),利用EBSD技术和迹线分析,深入研究了滑移与孪晶的交互作用,通过对二者之间应变协调因子m?的统计分析,发现大部分孪晶的启动能够很好的协调相邻晶粒中的位错滑移,因此认为滑移与晶界的交互作用刺激了孪晶形核,即滑移诱导了孪晶形核。在孪生主导变形的样品中(0?拉伸样品),发现孪晶更倾向于在晶界上成对出现,通过对孪晶对的应变协调因子m?进行统计分析,发现孪晶对之间具有很好的局部应变协调,因此认为孪晶与晶界的交互作用刺激了新孪晶的形成从而形成了孪晶对,即发生了孪晶诱导孪晶。上述滑移诱导孪晶和孪晶诱导孪晶行为显著影响了孪晶的变体选择。比较研究了五类初始织构样品在250?C压缩变形中的孪生行为,证实孪晶倾向于在SF较大的晶粒中启动,然而每类样品中都有一定数量的non-Schmid孪晶(即实际启动的变体不具有6个理论变体中最大或第二大的SF)。统计分析了孪晶与滑移的应变协调因子m?,证实了滑移与晶界的交互作用是90?样品中出现non-Schmid孪晶的主要原因。60?样品变形过程中产生了大量的小角度晶界(2-10?),成为孪晶择优形核位置,而实际启动的孪晶变体受SF和局部应变协调的共同作用。对比研究了粗晶和细晶两种镁合金材料在拉伸变形过程中的孪生行为,发现细晶样品中孪晶形核受晶界处应变协调的影响更大,更易在相邻晶粒中形成长的孪晶链或带,而粗晶样品中晶界较长,启动的孪晶变体数量较多,从而形成相互平行或交叉的孪晶片层。针对具有细晶组织的搅拌摩擦焊接样品进行研究,分析了样品中晶粒c轴变化对孪晶与滑移启动和相互竞争的影响,揭示了镁合金焊接接头宏观塑性变形不均匀性特征与基面滑移的对应关系。
[Abstract]:The tensile twinning of {10-12} has a lower critical shear stress. It is one of the most common deformation mechanisms of magnesium alloys. The difficulty and selection of the initiation of tensile twins are closely related to the mechanical properties and microstructure evolution of magnesium alloys. In this paper, the AZ31 magnesium alloy was used as the research object, and the electronic backscatter diffraction (EBSD) technology and crystallography were used. The twin behavior of two types of deformation (uniaxial tension and compression) and two kinds of deformation temperatures are studied systematically. The influence of the initial texture and grain size on twin behavior and the interaction between the slip and the twin are emphatically analyzed. The tensile deformation of the two?, 30?, 45, 60? And 90? Five directions of the magnesium alloy rolling plate is made in 0?, 30?, 45?, 60? And 90? The Schmidt factor ordering (SF rank) of 0? Sample twins is scattered, which is mainly related to the six theoretical twin variants of SF, which is related to.30? To 90? The difference between the largest and the smallest SF of the six theoretical twins is increasing, and the choice of the twins is more and more influenced by the Schmid rule. It is obvious that the ratio of SF rank to 1 or 2 in the sample increases gradually. The mechanical anisotropy of the magnesium alloy is related to the critical shear stress of the dominant deformation mechanism and the SF under different orientations. The R-value of the material is determined by the initiation of twinning and slippage in the process of tensile deformation. The macroscopic deformation of the samples of 30? -60? Is revealed by the plastic analysis of the crystal. The correlation between the sign (r-value1) and the ground slip initiation. The interaction between slip and twinning is studied by EBSD technique and trace analysis for the sample of slip leading deformation (45? Tensile samples). By statistical analysis of the strain coordination factor M between the two, it is found that most twins can be well coordinated in the adjacent grain. Dislocation glide, so the interaction between the slip and grain boundary stimulates the twin nucleation, that is, the twin crystal nucleus is induced by slip. In the twin led deformation sample (0? Tensile sample), the twins tend to appear on the grain boundary. By statistical analysis of the strain co modulation factor of twin pairs, the twin pairs are found to have a pair. Good local strain coordination, so the interaction of twin and grain boundary stimulates the formation of the new twin and forms twin pairs, that is, twin induced twins are formed. The twin crystal twins and twin induced twins have significant influence on the selection of twins. The five types of initial texture samples have been studied in 250? C compression. The twin behavior in the shape shows that the twins tend to start in the larger SF grains, however, there are a certain number of non-Schmid twins in each class of samples (that is, the actual starting variant does not have the largest or second SF in the 6 theoretical variants). The statistical analysis of the strain coordination factor M of the twin and slippage confirms the interaction between the slip and the grain boundary. It is the main reason for the appearance of non-Schmid twins in 90?.60? A large number of small angle grain boundaries (2-10?) were produced during the deformation of the sample, which became the preferred nucleation position of the twins, and the actual starting twins were co ordinated by SF and local strain. The tensile deformation process of two kinds of magnesium alloys with coarse and fine grain were compared and studied. It is found that the twin nucleation in the fine crystal is more influenced by the strain coordination at the grain boundary, the twin chains or bands are more likely to grow in the adjacent grain, while the grain boundary of the coarse grain is longer and the number of twinning variants starts to be more, thus forming a parallel or cross twin wafer layer. The effect of the change of C axis on the twinning and sliding initiation and the mutual competition in the sample was analyzed. The relationship between the non uniformity of the macroscopic plastic deformation of the welded joint of magnesium alloy and the slip of the base surface was revealed.

【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG146.22

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