Quantitative measurements of small scaled grain sliding in ultra-fine grained Al–Zn alloys produced by friction stir processing

An Al-15 wt.% Zn alloy was processed by friction stir processing to produce grain sizes of ~ 0.5 μm, ~ 1 μm, and ~ 2 μm. A simple and effective method was developed to determine the true strain by scribing marker lines with scaled division using focused ion beam micromachining prior to deformation. The “microscopic” grain boundary sliding, with displacements of adjacent grains of the order of a nanometer, can easily be detected by the proposed technique, providing a surface analysis with high accuracy that could be used to observe the changes in relief with increasing strains. Moreover, the occurrence of grain boundary sliding at room temperature was considered a major cause for higher strain rate sensitivity in fine-grained Al–Zn alloys.