Peculiarities of Plastic Deformation of SPD Al-Li Alloy at 0.5 K

Abstract

The mechanical properties of AlLi solid solution were studied in tensile deformation tests at extremely low temperature of 0.5 K. The purpose of this study was to investigate the ow stress and work hardening rate as well as the development of serrated (jump-like) deformation for the polycrystalline samples with dierent microstructure. The samples obtained by severe plastic deformation via hydroextrusion were initially tensed up to a given intermediate deformation, then unloaded, annealed to modify their microstructure, and once again deformed to fracture. The increase of the grain size and decrease of average dislocation density due to annealing were found responsible for the work hardening rate increases and the ow stress decrease in accordance with the superposition of the HallPetch and Taylor contributions. As opposed to the ow stress, the high ductility of the samples remains rather insensitive to the microstructure properties, apparently due to suppressed recovery processes as well as the unstable deformation mode at extremely low temperature. The high ductility makes it possible to compare the work hardening rate and the scale of jump-like plastic deformation along the stress-strain curves for samples with dierent microstructures. In all cases, the average amplitude of the stress jumps was observed to increase whereas the average work hardening rate decreases with deformation. The observed correlation indicates that the nature of both phenomenons follows from the dislocation density evolution processes.

Discontinuous Flow of Fine Grained AZ31 at Extremely Low Temperature

“…Assuming the Gaussian approximation, the half-width of the distribution in A and B specimens being 0.44 and 1.13, respectively. A similar effect of the grain size on the statistics of discontinuous flow at low temperatures was previously observed in aluminum [15] and copper polycrystals [14] subjected to severe plastic deformation and subsequent annealing.…”