Superplastic Behaviour of Selected Magnesium Alloys

Abstract

Superplastic materials exhibit anomalous plasticity, achieving strain until several thousand per cent. The phenomenon of plasticity is limited on special microstructure, temperatures and strain rates. Magnesium and magnesium alloys are known as materials with limited plasticity. This is due to their hexagonal structure of these materials. Finding the superplasticity conditions has a crucial importance for applications of magnesium alloys. In this chapter, we will deal with the superplastic behaviour of AZ91, QE22, AE42 and EZ33 magnesium alloys. Materials were prepared by various techniques: thermomechanical treatments, equal channel angular pressing, hot extrusion, rolling, friction stirring and high-pressure torsion. Strain rate sensitivity and elongation to fracture were estimated at various temperatures. Mechanisms of superplastic flow are discussed. Grain boundary sliding and diffusional processes were depicted as the main mechanisms responsible for high plasticity of these alloys. On the other hand, cavitation at elevated temperatures deteriorates the superplastic properties.

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“…Most of the Mg-alloys have been found to be super-plastic in nature due to their hexagonal structure. Though no material can be termed perfectly plastic, Mg-alloy can be assumed to be nearly perfectly plastic for the purpose of design analysis because of its super-plastic nature [29,30].Generally, most of the generated stresses in any structural design are based on elastic behaviour of materials corresponding to safe limits with respect to yield strength and the design analysis doesn't go beyond the safe elastic region.…”