Developing superplasticity in magnesium alloys with the help of friction stir processing and its variants - A review

Friction stir processing (FSP), an adaption of the solid-state joining process friction stir welding (FSW), is now a widely recognized severe plastic deformation (SPD) technique. It induces microstructural refinement in the metallic materials which enhances their formability and other mechanical properties. Dynamic recrystallization occurs during the stirring phase which leads to reduction in the grain size and texture modification. Breaking up of the intermetallics and precipitates with their homogeneous distribution in the matrix is also accompanied. This further improves the material's ability to attain maximum ductility during plastic deformation at higher temperatures, resulting in very large uniform elongations (>200%) termed as 'superplasticity'. Optimization of FSP parameters activates superplastic behaviour in different magnesium alloys at low temperatures and high strain rates. It has become the focal point of the recent researches owing to its huge potential in the light-weight structural applications. In addition to the essential aspects of superplasticity, this article highlights the major explorations in the area of superplasticity of magnesium alloys using FSP method and it's recently developed variants.