PhD defence of Saoussen Ouhiba

– Prof. Knut Marthinsen, Norwegian University of Science and Technology, rapporteur

– MC. Myriam Dumont, Arts et Métiers Lille, rapporteur

– Prof. Franck Montheillet, Mines Saint Etienne, examinateur

 

Abstract:

 

The increasing need for weight reduction in automotive applications has led to paying increasing attention to aluminum alloys, especially to age-hardenable 6xxx (Al-Mg-Si) alloys. Although these alloys are known for their good formability, good corrosion resistance and sufficient strengthening potential, they are sometimes prone to the appearance of sheet surface defects. A better understanding of the microstructural evolutions occurring during the hot rolling process is needed to optimize the final properties of the material. Particularly, the interaction between precipitates and solutes with dynamic recovery, dynamic and post-dynamic recrystallization processes is studied. In this context, different initial precipitation states are generated prior to deformation and are subsequently submitted to hot compression tests. Microstructural analyses are performed using Scanning Electron Microscopy and crystal orientation mapping by EBSD. The factors possibly leading to the anisotropic development of coarse recrystallized grains during holding after deformation are also investigated through sequential annealing using a fast heating stage coupled to SEM. This is followed by 2D full field simulations based on the Level Set method in order to discuss the validity of specific assumptions regarding the anisotropic overgrowth of some recrystallized grains. Finally, the influence of different thermomechanical parameters on microstructure evolution is studied, determining thus the thermomechanical parameters promoting the formation of a finer final recrystallized grain size.

 

 

Keywords: aluminium alloys, hot rolling, recrystallization, coarse recrystallized grains, effect of precipitates/solutes