Texture and microstructural evolution in an Al-6061 alloy processed by high-pressure torsion.

Abstract

A commercial Al-6061 alloy was processed by high-pressure torsion at room temperature over equivalent strains in the range of εeq = 0–205 and the evolutions of the microstructure, texture and mechanical properties were investigated using electron backscatter diffraction and Vickers microhardness measurements. The mean grain size decreased significantly from ~121 ± 5 μm in the initial state to ~0.45 ± 0.15 μm after a strain of εeq = 205 and this grain refinement occurred in three distinct stages. First, the grain size decreased and saturated in the strain range of εeq = 0–4.2 accompanied by the development of an A-fiber shear texture and an increase in the microhardness. Continuous and discontinuous dynamic recrystallization were the main mechanisms for this grain refinement. Second, the grain size increased and the texture changed to a B-fiber texture between εeq = 4.2 and 10.2 producing a drop in the microhardness, where this grain growth was attributed to a strain-induced grain boundary migration. The mean grain size decreased and saturated again over the strain range of εeq = 10.2–205 where there was a weak but stable texture and a microhardness evolution following a model of hardening without recovery. Finally, the separate contributions of grain size, dislocation and texture strengthening to the overall hardening behavior were critically examined.