Low-temperature micromechanical properties of annealed and hydrostatic extruded Al-3.8 at. % Li alloy

The structural state of as-received course-grained (CG) and extruded ultrafine-grained (UFG) stocks of the Al-3.8 at.% Li substitution solid solution and the samples of this alloy deformed in tension to failure at the temperatures of 4.2, 77, 295 and 350 K was studied by the micro indentation method. The temperature dependence of microhardness was investigated in the range of 77 to 295 K. The measurements have revealed anisotropy of the micromechanical properties of the UFG samples which appears to be due to the texture formed during extrusion. The results reported herein revealed that in the specimens deformed by uniaxial tension to failure there was correlation between microhardness value as a measure of work hardening and magnitude of local plastic shear. The correlation breaks down for the UFG samples deformed at the temperatures of 295 and 350 K -microhardness does not depend on the amount of plastic shear. The temperature dependences of microhardness of the CG and UFG samples were analyzed in the framework of thermally activated motion of dislocations in the local obstacles array. The most probable potential barriers to the dislocation motion in the alloy studied are the impurity atoms, their small complexes and forest dislocations. Intensive plastic deformation during hydrostatic extrusion had no qualitatively effect on the energetic parameters of the obstacle spectrum.