Formation of Meso-Scale Roughening in 6022-T4 Al Sheets Deformed in Plane-Strain Tension

Meso-scale surface roughening evolution in 6022-T4 Al sheets was investigated using plane-strain tension. Formation of grain-scale hills and valleys and their relation to the morphologies and corresponding orientations of surface grains after deformation were examined experimentally. These observations were analyzed using various approaches based on the Schmid and Taylor crystal plasticity models. It was observed that surface grains with and without slip bands tend to form valleys and hills, respectively, wherever these two types of grains are adjacent to each other along the planestrain tension direction. When the sample was pulled along the transverse direction, the formation of hills and valleys by unbanded and banded grains was more lineally organized in the plane-strain (rolling) direction than in the sample which was pulled along the rolling direction. Slip banding and valley formation were principally observed in the surface grains with either very few (1∼2) slip systems of high Schmid factors or low Taylor factors, in contrast to non slip-banded and hillforming surface grains. Quantitative analysis using correlation coefficients showed that the Schmid factor provided slightly better agreement than the Taylor factor in predicting slip-banding (and valley-forming) and non slip-banding (and hill-forming) behaviors of surface grains. In addition, measures that quantify the image qualities of EBSPs for selected surface grains suggested that the slip-banded and valley-forming grains contain less lattice distortion than the non slip-banded and * Currently at Department of Civil and Environmental Engineering, Carnegie Mellon University, PA hill-forming grains despite the larger strains experienced by these grains. This indicates that dislocations in the slip-banded grains move out of the surface to create deformation without lattice distortion. Plastic interactions between specific neighboring grains are central to the formation of meso-scale surface roughening.