Samples of Zn-21Al-2Cu alloy (Zinalco) that will be heavily deformed were prepared using five different manual mechanical metallographic methods. Samples were analyzed before tensile testing using the orientation imaging microscopy-electron backscatter diffraction (OIM-EBSD) technique. The effect of type and particle size during the final polishing stages for this material were studied in order to identify a method that produces a flat, damage free surface with a roughness of about 50 nm and clean from oxide layers, thereby producing diffraction patterns with high image quality (IQ) and adequate confidence indexes (CI). Our results show that final polishing with alumina and silica, as was previously suggested by other research groups for alloys that are difficult to prepare or alloys with low melting point, are not suitable for manual metallographic preparation of this alloy. Indexes of IQ and CI can be used to evaluate methods of metallographic preparation of samples studied using the OIM-EBSD technique.

Electron backscatter diffraction (EBSD) has become a common technique for measuring crystallographic orientations at spatial resolutions on the order of tens of nanometers and at angular resolutions <0.1°. In a recent search of EBSD papers using Google Scholar™, 60% were found to address some aspect of deformation. Generally, deformation manifests itself in EBSD measurements by small local misorientations. An increase in the local misorientation is often observed near grain boundaries in deformed microstructures. This may be indicative of dislocation pile-up at the boundaries but could also be due to a loss of orientation precision in the EBSD measurements. When the electron beam is positioned at or near a grain boundary, the diffraction volume contains the crystal lattices from the two grains separated by the boundary. Thus, the resulting pattern will contain contributions from both lattices. Such mixed patterns can pose some challenge to the EBSD pattern band detection and indexing algorithms. Through analysis of experimental local misorientation data and simulated pattern mixing, this work shows that some of the rise in local misorientation is an artifact due to the mixed patterns at the boundary but that the rise due to physical phenomena is also observed.

Image quality (IQ) maps constructed from electron backscatter diffraction data provide useful visualizations of microstructure. The contrast in these maps arises from a variety of sources, including phase, strain, topography, and grain boundaries. IQ maps constructed using various IQ metrics are compared to identify the most prominent contrast mechanism for each metric. The conventional IQ metric was found to provide the superior grain boundary and strain contrast, whereas an IQ metric based on the average overall intensity of the diffraction patterns was found to provide better topological and phase contrast.