Low temperature plasticity of microcrystalline Al–Li alloy

Abstract

The plastic deformation of Al-3.8 at.% Li polycrystals processed by the equal-channel angular hydroextrusion (ECAH) were investigated during tension in the temperature range of 4.2–400 K. The evolution of the microstructure during loading was studied by the electron backscatter diffraction (EBSD) method, including the orientation and kernel average misorientation (KAM) mappings. In as-prepared state the microstructure characterized by grains with small misorientation angles and a high density of dislocations. The deformation of a sample at 120 K leads to increase in the density of deformation defects while at 290 K to their decrease. The strong temperature sensitivity of the yield strength indicates the thermally activated nature of the plastic deformation. An increase in the plasticity and strength of polycrystals with decreasing temperature is explained by a decrease in the dislocation annihilation due to a decrease in the mobility of atoms, resulting in increase in the strain hardening rate. A nonmonotonic dependence of the activation volume Va(T) with a maximum at 180 K was established from stress relaxation data. The analysis of stress-strain curves and microstructure evolution indicate a dominance of thermally activated mechanism of intersection of the forest dislocations below 180 K and an increase in the activity of recovery processes at moderate temperatures.