Processing Magnesium and Its Alloys by High-Pressure Torsion: An Overview

Magnesium and its alloys have attracted significant attention in recent years because they display high strength-to-density ratios, they are biodegradable and they provide a potential for hydrogen storage. Many investigations have examined the effect of high-pressure torsion processing on the microstructures and properties of these materials so that numerous reports are now available. This overview provides a summary of the observations reported to date on the structure and mechanical property evolution including the nature of grain refinement, the grain boundary misorientation distributions, texture evolution, and the minimum grain size. For convenience, the mechanical properties are separated into hardness, tensile behavior, and superplastic properties. It is shown that the mechanism of grain refinement differs from other metallic materials processed by severe plastic deformation but high strength may be achieved in magnesium alloys and exceptional ductility in pure magnesium. Hydrogen storage and corrosion behavior are also examined together with a discussion of recent attempts to produce magnesium-based nanocomposites through processing by high-pressure torsion.