Formation of nanocrystalline grain structure in an Mg-Gd-Y-Zr alloy processed by high-pressure torsion.

Abstract

In this paper, the microstructural and hardness evolutions of an Mg-5.91Gd-3.29Y-0.54Zr (wt.%) alloy during high-pressure torsion (HPT) were investigated. Deformation twinning played a crucial role in the HPT-induced grain subdivision process. In the 1/8-revolution disk, {10-11} and {10-12} twins with different twin variants, {10-11}-{10-12} secondary twins and twin-twin interactions were activated. Primary twins prevailed at the very central region of the disk, while much finer multiple twins were formed at the edge region of the disk corresponding to the area subjected to a relatively large plastic strain. Besides, dislocation cell substructures were also developed. Nanocrystalline structure was attained after 5-revolution HPT processing, and the maximum hardness reached ~120 Hv at the edge region of the disk, which is much higher than that achieved from other traditional plastic deformation methods.