Microstructure and low-temperature plastic deformation of Al–Li alloy

Abstract

Features of the plastic deformation of solid Al–Li solutions with microstructures formed by direct and angular hydroextrusion are studied under tension at temperatures of 4.2–350 K. It is found that the grain size reductions, increases in the average density of defects, and changes in the orientational textures during combined hydroextrusion lead to increased strength and reduced plasticity of the microcrystalline alloy relative to initially large-grained samples. The high yield stress of the microcrystalline alloy is explained by a higher grain density and the evolution of an orientational texture. The strong temperature dependence of the yield stress is typical of thermally activated interactions between dislocations and local obstacles in the form of deformation defects produced during hydroextrusion. The low plasticity of the microcrystalline alloy, which already shows up as a localization of plastic deformation with small deformations, is caused by a low rate of work hardening owing to enhanced dynamic recovery of fine grains even at low temperatures. The rate of dynamic recovery decreases, while uniform deformation increases, at temperatures of 77 K and below. Based on data on the high stress rate sensitivity at temperatures above 77 K and the low activation volume for plastic deformation of microcrystalline Al–Li, it is proposed that high-angle grain boundaries may serve as highly efficient sources and sinks of mobile dislocations.