Abstract
This thesis explores dynamic recrystallization (DRX) processes in polycrystals, using the magnesium alloy AZ31 as a model material for materials with high plastic anisotropy. An innovative experimental protocol was developed, allowing for the 2D monitoring of microstructures during deformation through tensile tests combined with in-situ EBSD mapping over a wide range of finite deformations (up to 67% engineering strain). The evolution of the microstructure was studied under different temperature and strain rate conditions (20, 150, 250, and 300◦C ; 10−3 and 10−4 s−1). The large amount of EBSD data obtained enables the study of the bulk mechanical behavior of the sample in regard to quantitative bulk microstructural evolutions datas, as well as discrete and qualitative characterizations of local processes during deformation. The results show that at 250◦C and 10−3 s−1, DRX is induced by both subgrain rotation and bulging, contributing to material softening through the reduction of geometrical hardening (induced by texture evolution) and dislocation network reorganization (polygonization). The formation of a "necklace", pockets of small recrystallized grains at the interface between two larger grains, was identified and characterized by observing the progressive local evolution. These results helped identify the impact of the grain boundary evolution initially located at the interface between the two parent grains. Additional tests at different temperatures revealed variations in the impact of DRX on deformation. Despite certain experimental limitations, this work opens up prospects for the study of DRX in other anisotropic crystalline materials, such as ice or minerals.