The link between microstructure and creep in aluminum processed by equal-channel angular pressing

The creep life of pure ultrafine-grained aluminum produced by equal-channel angular pressing and examined at 473 K, 15-20 MPa, continually decreases with the increasing number N of passes in spite of a considerable grain refinement. In order to explain this behavior, a detailed microstructural study has been carried out by means of electron backscatter diffraction at four different lower bounds of subgrain boundary misorientation Δ = 2°, 5°, 10° and 15°. At low N = 1, 2, the misorientation of the majority of boundaries is very low (Δ < 5°); the relative fractions of the true boundary (Δ ≥ 15°) area do not exceed 10% and the creep strain is very slow. With the increasing N, the mutual misorientation of neighboring subgrains grows, the deformation processes can proceed faster and the creep life is substantially shortened (the creep fracture elongation grows only slowly).