Activation Energy in Hot Forming and Recrystallization Models for Magnesium Alloy AZ31

Kinetics of the dynamic, as well as postdynamic recrystallization of the wrought magnesium alloy AZ31, was ascertained. Continuous compression tests associated with the study of dynamic recrystallization were realized at temperatures from 523 to 723 K and at the strain rates from 0.001 to 10 s⁻¹. The activation energy in hot forming was determined as Q = 158 kJ/mol for stress-strain curves of conventional shape, or Q = 146 kJ/mol for stress-strain curves with the concave initial phase affected by twinning. If the Zener-Hollomon parameter Z > 9.1 × 10¹² s⁻¹ the deformation necessary for the initiation of dynamic recrystallization is almost independent on the forming parameters. Using the results of the stress relaxation tests, equations describing the kinetics of metadynamic recrystallization and the grain size originated in such a way were developed and the effect of individual variables was evaluated.