High temperature deformation and microstructural instability in AZ31 magnesium alloy

The high temperature deformation behaviour of AZ31 magnesium alloy is analysed by comparing numerous investigations, including work by these authors and by other researchers. Three main deformation mechanisms are observed, i.e grain boundary sliding, solute drag creep and climb-controlled dislocation creep. A combined set of constitutive equations, which takes into account the concurring effect of these different deformation mechanisms, is proposed. Grain boundary sliding is observed to cause a superplastic behaviour in fine-grained materials, but grain growth due to excessively prolonged high temperature exposure invariably results in a transition to either viscous glide or dislocation climb as a rate-controlling mechanism. On the basis of these considerations, the differences observed by testing the same material under constant strain rate or by strain rate change experiments are rationalised by quantifying the effect of static and dynamic grain growth and dynamic recrystallisation. This procedure provides a unitary description of the high temperature deformation of AZ31 in a wide range of strain rates and temperatures.