Multiscale characterization of dislocation processes in Al 5754

Multiscale characterization was performed on an Al–Mg alloy, Al 5754 O-temper, including <i>in situ</i> mechanical deformation in both the scanning electron microscope and the transmission electron microscope. Scanning electron microscopy characterization showed corresponding inhomogeneity in the dislocation and Mg distribution, with higher levels of Mg correlating with elevated levels of dislocation density. At the nanoscale, <i>in situ</i> transmission electron microscopy straining experiments showed that dislocation propagation through the Al matrix is characterized by frequent interactions with obstacles smaller than the imaging resolution that resulted in the formation of dislocation debris in the form of dislocation loops. <i>Post</i>-<i>mortem</i> chemical characterization and comparison to dislocation loop behaviour in an Al–Cr alloy suggests that these obstacles are small Mg clusters. Previous theoretical work and indirect experimental evidence have suggested that these Mg nanoclusters are important factors contributing to strain instabilities in Al–Mg alloys. This study provides direct experimental characterization of the interaction of glissile dislocations with these nanoclusters and the stress needed for dislocations to overcome them.

本研究针对O态5754铝合金（Al 5754 O-temper）开展多尺度表征，涵盖在扫描电子显微镜与透射电子显微镜中进行的原位（in situ）力学变形测试。扫描电子显微镜表征结果显示，位错（dislocation）与镁（Mg）的分布存在对应不均匀性：镁含量越高的区域，位错密度也越高。在纳米尺度下，原位透射电子显微镜拉伸实验表明，可滑移位错（glissile dislocations）在铝基体中的传播过程以频繁与尺寸低于成像分辨率的阻碍物发生交互作用为特征，该交互作用会形成位错环形式的位错碎屑。事后（post-mortem）化学表征结果，并与铝铬（Al-Cr）合金中的位错环行为进行对比后表明，上述阻碍物为小型镁团簇。此前的理论研究与间接实验证据均指出，这类镁纳米团簇是引发铝镁合金应变不稳定性的关键诱因。本研究首次实现了可滑移位错与这类纳米团簇交互作用的直接实验表征，并测得位错克服该类阻碍物所需的临界应力。