Strain distribution and lattice rotations during in-situ tension of aluminum with a transmodal grain structure

Samples of aluminum were prepared using spark plasma sintering from a mixture of coarse (average particle size of 6 μm) and fine (average particle size of 1 μm) powders to achieve a heterogeneous transmodal grain size distribution covering a range of grain sizes from ≈1 to 10 μm. By careful choice of surface markers both electron back-scatter diffraction (EBSD) data, to track crystal rotations, and digital image correlation (DIC) data, to track local plastic deformation, were collected from the same region during in-situ tensile deformation up to a strain of ε_t = 0.126. A heterogeneous pattern of crystal rotation is observed for all grain sizes, although in some smaller grains (defined as those <4 μm diameter) no clear grain sub-division was identified. Plastic strain was more concentrated in the larger grains, but the average rotation rate of the smaller grains was found to be higher than that of larger grains, showing also a much wider spread in rotation rate. Based on the change in average orientation, a clear orientation dependence in the tensile axis rotation direction was observed for many larger grains, in agreement with previously reported data for aluminum with average grain size of 75 μm, whereas the smaller grains showed a more complex rotation behavior, with more of these grains showing unexpected tensile axis rotations. The combination of both EBSD and DIC during in-situ experiments provides a rich data set for analysis of plastic deformation in samples with a heterogeneous microstructure.