Residual stresses and microstructural evolution of ECAPed AA2017

Abstract

The mechanical behavior and microstructural evolution of an AA2017 aluminum alloy processed by ECAP with an equivalent simple shear deformation of ∼6 at 200 °C were studied. Samples were characterized by means of scanning electron microscopy (SEM-EDS- EBSD), image-assisted by focus ion beam (FIB), Vickers microhardness and X-ray diffraction (XRD) techniques. During the deformation process, the Al 2 Cu precipitates did not get fragmented or re-absorbed in the Al matrix. After the first ECAP pass, at least 50% of grains displayed an ultrafine size. The EBSD analysis showed an increment of the misorientation angle immediately after the first ECAP pass. The macrotexture evolution was explained in terms of the formation of f1: A 1θ ∗ , A θ , Ā θ , A 2θ ∗ , f2: C θ , B¯ θ , B θ , Ā θ , A θ , A 1θ ∗ and f3: C θ , B θ , B¯ θ , A θ , Ā θ , A 2θ ∗ fibers. The macro-residual stress measurements of the highly deformed samples showed linear sin 2 ψ profiles. The micro and macro-residual stresses were compatible with dislocation rearrangement, in which the annihilation and formation were in quasi-equilibrium. It was found that the highest microhardness value (1176 MPa) and grain refinement (at least 20% of grains showed a size smaller than 100 μm 2 ) appeared after the first extrusion pass. The decrease in hardness, after the second pass and the residual stress stability, could be associated to a dynamic recovery phenomenon.