April 22, 2021
17:00
Pour l’obtention du grade de Docteur en sciences de l’ingénieur et technologie
Laser powder bed fusion (LPBF) AlSi10Mg is a promising material for lightweight structural applications in the aerospace sector. Its fine microstructure grants high mechanical strength. However, there is still a gap in the understanding of the correlation between microstructure and mechanical behaviour. Besides, the critical fatigue issue still represents a significant hurdle. Despite the relative flexibility of the LPBF additive manufacturing process, there is a limitation in the possibility of tailoring parameters to obtain a satisfactory combination of porosity and surface roughness for adequate fatigue resistance. From this quandary arises the interest for post-treatments to overcome this limitation.
First, a comprehensive microstructural characterisation was carried out. It started by looking at the as built state, including the build platform temperature and loading direction aspects. A detailed 3D microstructural analysis involving focused ion beam/scanning electron microscopy tomography was performed to describe the connectivity and size of the Si-rich eutectic network and link it to the strength and fracture strain. An analytical model was developed to exploit these microstructural features and predict the strength of the material.
The fracture and fatigue of LPBF AlSi10Mg were studied under as built and three post-processing conditions, stress relieve heat treatment, hot isostatic pressing and friction stir processing (FSP). FSP proved to be a viable solution to improve the fatigue behaviour. Indeed, thanks to this post-process that reduces overall porosity and eliminates critical defects while keeping a satisfactory fine microstructure and static mechanical behaviour, the fatigue resistance of the material was significantly enhanced. In contrast, the other studied post-processes did not have a positive impact on fatigue.
Jury members :
- Prof. Aude Simar (UCLouvain), supervisor
- Prof. Renaud Ronsse (UCLouvain), chairperson
- Prof. Pascal Jacques (UCLouvain), secretary
- Prof. Brecht Van Hooreweder (KULeuven, Belgium)
- Prof. Anne Marie Habraken (ULiège, Belgium)
- Asst. Prof. Manas Upadhyay (Ecole Polytechnique, France)
- Asst. Prof. Marie-Noëlle Avettand-Fénoël (Université Lille 1, France)
Pay attention :
The public defense of Juan Guillermo Santos Macias scheduled for Thursday 22 April at 5:00 p.m will take place in the form of a video conference Teams