Elastic wave amplitudes in shock-compressed thin polycrystalline aluminum samples

Thin polycrystalline aluminum (1050 and 6061-T6 alloys) samples were shocked to 4 GPa to examine elastic wave attenuation not observed in thicker samples (1–10 mm). Using laser interferometry in plate impact experiments, particle velocity histories were obtained for 0.08–1 mm thick samples, thinned from bulk material. Unlike past work on thicker samples, thin 1050 Al samples reveal large and rapidly attenuating elastic wave amplitudes, indicating a time-dependent elastic-plastic response. Extrapolation of measured elastic wave amplitudes to larger sample thicknesses agrees well with previously observed amplitudes for thicker 1050 and 1060 Al samples. Thus, all of the results for relatively pure polycrystalline Al can be reconciled into a single consistent picture: elastic wave attenuation, due to time-dependent elastic-plastic response, is confined to material close to the impact surface. In contrast to the 1050 Al results, thin 6061-T6 Al samples reveal an elastic wave amplitude of $∼0.7GPa$ with no attenuation, in quantitative agreement with previous results for thick 6061-T6 Al samples. The lack of elastic wave attenuation even in thin samples suggests that elastic wave amplitudes in shocked 6061-T6 Al are governed by different plastic deformation mechanisms than those for shocked pure Al.