Review on ultrafined/nanostructured magnesium alloys produced through severe plastic deformation: microstructures

Abstract

A review on the microstructural evolution in magnesium alloys during severe plastic deformation was<br />presented. The challenges deserved to achieve ultrafine/ nanostructured magnesium were discussed.<br />The characteristics of the processed materials are influenced by three main factors, including i)<br />difficult processing at low temperatures, ii) high temperature processing and the occurrence of<br />dynamic recrystallization and grain growth processes, and iii) a combined effect of grain refinement<br />and crystallographic texture changes. Reviewing the published results indicate that there are two<br />potential difficulties with severe deformation of magnesium alloys. First, it is very hard to achieve<br />homogeneous ultrafined microstructure with initial coarse grains. The second is the dependency of<br />microstructure development on the initial grain size and on the imposed strain level. It was clarified<br />that different grain refining mechanisms may be contributed along the course of multi-pass severe<br />deformation. It was clarified that discontinuous recrystallization takes places during the first stages of<br />deformation, whereas continuous refinement of the recrystallized grain may be realized at consecutive<br />passes. Shear band formation as well as twinning were demonstrated to play a significant role in grain<br />refinement of magnesium alloy. Also, the higher the processing temperature employed the more<br />homogeneous microstructure may be achieved with higher share of low angle grain boundaries.