On the evolution of surface roughness during deformation of polycrystalline aluminum alloys

Surface roughening of polycrystalline Al–Mg alloys during tensile deformation is investigated using white light confocal microscopy. Materials are tested that differ only in grain size. A height–height correlation technique is used to analyze the data. The surface obeys self-affine scaling on length scales up to a correlation length which approximately equals the grain size and above which no height correlation is present. The self-affine scaling exponent increases initially with strain and saturates at a value around 0.9. A linear relation is observed between root-mean-square roughness and both strain and grain size. The observed roughness is explained as the result of the combined effect of a self-affine roughening on a subgrain scale and a grain scale roughening caused by orientation differences between neighboring grains.