Formation of stable equiaxial nanograined Al via combined plastic deformation

Refining grains in pure aluminum (Al) to nanometerscale is difficult due to its low melting point and high stacking fault energy. Here, with a combined plastic deformation process of cold rolling and cryogenic high pressure torsion, equiaxial-nanograined pure Al with an average grain size of 65 nm was fabricated. Grain orientation statistics and high resolution transmission electron microscope observations revealed that most of the grain boundaries are high angle grain boundaries, in which there are plenty of low Σ boundaries, indicating the occurrence of grain boundary relaxation. The equiaxial nanograined Al exhibited high strength and superior thermal stability due to the grain boundary relaxation.