The fundamental relationships between grain orientation, deformation-induced surface roughness and strain localization in an aluminum alloy

Polycrystalline AA6022 tensile specimens were cut from sheet stock, mechanically polished, and uniaxially strained in situ under a scanning laser confocal microscope (SLCM) using a sub-sized universal testing apparatus. Prior to deformation, electron backscatter diffraction (EBSD) was performed on the gauge sections of one specimen in the rolling direction of the sheet and one in the transverse direction. Maps of the largest displacements in the surface morphology were constructed from the SLCM data and overlaid onto maps derived from the crystallographic orientation data to examine the strength of the influence that grain orientation effects have on critical strain localization. The roles of Taylor factors, grain boundary misorientation, largest Schmid factors, grain sizes, coincident site lattice orientations, and local grain breakup were considered. The largest surface displacements were observed to be concentrated at triple junctions where there is a large difference between the Taylor factors of the individual grains. The high degree of correlation between the density and location of these large surface displacements and the local plasticity conditions indicate that a critical localization event is most likely to initiate in grain boundary regions where unfavorable slip interactions produce the largest plastic strains.