Electropolishing is the most common method of preparing samples of aluminium alloys for scanning and transmission electron microscopy, as it yields a good surface quality and large flat, electron-transparent areas. Like many chemical surface treatment procedures, the electropolishing process can create a Cu-rich layer between the aluminium matrix and the outermost aluminium oxide layer. The Cu layer is shown to be crystalline, which causes several distinct effects on electron images and diffraction patterns, that can easily be misinterpreted as originating from features inside the aluminium matrix. The layer is a modified θ’–Al₂Cu phase, with a semi-coherent interface with aluminium. A θ’ superstructure suggested in this paper can explain lattice modulations with a 1 nm spacing that have been observed in the [011]_Al zone axis of electropolished specimens. Evidence of Cu diffusion into the Al matrix was also found. The surface enrichment can also occur in Cu-free aluminium alloys, as small amounts of Cu can be introduced from outside sources through the electrolyte solution.

电抛光是制备用于扫描和透射电子显微镜的铝合金样品的最常用方法，因为它具有良好的表面质量和较大的平坦，电子透明区域。像许多化学表面处理程序一样，电抛光过程可以在铝基体和最外层的氧化铝层之间形成富Cu层。铜层显示为晶体，这会对电子图像和衍射图样产生一些明显的影响，很容易将其误解为源自铝基质内部的特征。该层是修正的θ'–Al ₂铜相，与铝具有半相干界面。本文提出的θ'超结构可以解释在电抛光试样的[011] _Al区域轴中观察到的1 nm间距的晶格调制。还发现了铜扩散到Al基体中的证据。在无铜铝合金中也可能发生表面富集，因为少量铜可以从外部源通过电解液引入。