The objective of the study was to characterize the properties of a magnesium alloy welded by friction stir welding. The results led to a better understanding of the relationship between this process and the microstructure and anisotropic properties of alloy materials. Welding principally leads to a large reduction in grain size in welded zones due to the phenomenon of dynamic recrystallization. The most remarkable observation was that crystallographic textures appeared from a base metal without texture in two zones: the thermo-mechanically affected and stirwelded zones. The latter zone has the peculiarity of possessing a marked texture with two components on the basal plane and the pyramidal plane. These characteristics disappeared in the thermo-mechanically affected zone (TMAZ), which had only one component following the basal plane. These modifications have been explained by the nature of the plastic deformation in these zones, which occurs at a moderate temperature in the TMAZ and high temperature in the SWZ.

International audienceA thermo-mechanical plasticity material model, which consists of a hardening and a temperature sensitivity term, is built to describe the dual phase DP600 steel behavior. For the hardening term, a synthesis Ludwik–Voce hardening law is proposed, identified and compared with the classical Ludwik and the Voce hardening laws. For the temperature sensitivity function, a new proposed expression together with a classical Johnson–Cook term and an improved Chen term are analyzed and identified. Moreover, the plate anisotropy of DP600 is also taken into account using Hill-48 theory. Based on the plasticity material model, a numerical sequential coupled thermo-mechanical model is applied to investigate the residual stresses of laser welding process. It is shown that the material anisotropy and the thermo-mechanical elastic-plastic model have an important influence on numerical residual stresses results. An experiment is also carried out to verify the numerical model. Simulation results of residual stresses are in good accordance with neutrons diffraction measurements

International audienceThis study aimed at characterizing the residual stresses distribution of a DP600 undergoing a laser beam welding. The residual stresses in the ferritic phase have been experimentally determined by the use of the neutron diffraction technique. The results confirmed a gradient of residual stresses among different zones both on the top and below surfaces but also through the thickness of the fusion zone. Low compressive stresses were observed in the BM (Base metal) close to the HAZ zone (heat affected zone) whereas high tensile stresses were observed in the FZ (fusion zone). Two numerical modelling strategies were conducted: first with elastic plastic model (EP) and then with a visco-elastic plastic model (VEP) which takes into account the effect of phase transformation-induced volumetric strain. Both models allowed highlighting the residual stresses evolution through the different zones. Numerical results showed a difference in the residual stresses distribution depending on the model used. In the end, it appears that the high temperature, specific to the laser beam, is the main factor governing the residual stresses. When comparing simulation results with experimental data, the values converge well in some zones, in particular the FZ and the others less

No abstract