High temperature deformation and microstructural instability in AZ31 magnesium alloy

The high temperature deformation behaviour of AZ31 magnesium alloy is analysed by comparingnumerous investigations, including work by these authors and by other researchers. Three maindeformation 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 theconcurring effect of these different deformation mechanisms, is proposed. Grain boundary sliding isobserved to cause a superplastic behaviour in fine-grained materials, but grain growth due toexcessively prolonged high temperature exposure invariably results in a transition to either viscousglide or dislocation climb as a rate-controlling mechanism. On the basis of these considerations, thedifferences observed by testing the same material under constant strain rate or by strain rate changeexperiments are rationalised by quantifying the effect of static and dynamic grain growth and dynamicrecrystallisation. This procedure provides a unitary description of the high temperature deformation ofAZ31 in a wide range of strain rates and temperatures