Comparative microstructural characterization of a friction-stir-welded aluminum alloy using TEM and SEM-based techniques

Abstract

Comparison is made between images collected using four different transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques from the same region of a commercial Al alloy processed by friction-stir welding. The techniques include conventional bright-field TEM, electron-channeling contrast (ECC) imaging using SEM, gallium-enhanced microscopy (GEM), and the electron backscattered diffraction (EBSD) technique. It is found that for a microstructure with a large range of misorientations, only investigation with TEM is capable of revealing all the dislocation boundaries present in a given region, although this requires careful tilting. Single-tilt TEM images, EBSD maps, as well as ECC and GEM images miss a certain population of boundaries, which can lead to erroneous results when the boundary spacing is evaluated. For the EBSD data, the calculated fraction of high-angle boundaries can vary over a large range, depending on the choice of data-processing parameters. The number of missed boundaries is relatively small for the single-tilt TEM images, GEM images, and postprocessed (filtered) EBSD maps. These images can, therefore, be considered to give a good compromise between the required experimental effort and the resulting data quality.