Dynamic recrystallization and mechanical behavior of Mg alloy AZ31: Constraints from tensile tests with in-situ EBSD analysis
Résumé
We conducted tensile tests on AZ31 samples with in-situ SEM-EBSD acquisi- tion at 250°C and 10−3 s−1 to study the evolution of dynamic recrystallization and its effect on the mechanical behavior. To investigate the entire deforma- tion range up to failure at 65-67% engineering strain, stepwise experiments were conducted with in-situ EBSD acquisition at 2-5% strain intervals and repolishing of the samples at 15% strain intervals. All experiments show a consistent mechanical behavior characterized by a transition from harden- ing to quasi-steady state at ∼10% strain, followed by softening for strains greater than 35%. The bulk intragranular misorientation, quantified by the mean kernel average misorientation, increases steadily. Analysis of the EBSD maps shows that the quasi-steady state is associated with dominant disloca- tion reorganization (polygonization), whereas the onset of softening is linked to a net and continuous increase in the recrystallized fraction. In situ EBSD mapping documents the local discontinuous nature of continuous dynamic recrystallization: (1) nucleation of strain-free grains by bulging and subgrain rotation, (2) grain growth, (3) re-accumulation of dislocations substructures and formation of new nuclei. Analysis of the textures shows that dynamic re- crystallization slows down rotation and strengthtening of the textures. The observed steady state and softening behaviors result therefore from both geometrical (texture-induced) and microstructural (dislocation-related) soft- ening due to dynamic recrystallization.
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