Design, development and characterisation of new healable laser powder bed fusion aluminium alloys by Julie GHEYSEN

For the degree of Doctor of Engineering Sciences and Technology

Laser Powder Bed Fusion (LPBF) is an additive manufacturing technique widely used in aerospace and automotive industries which allows the production of complex geometries. Aluminium is a material of choice for these industries thanks to its excellent strength-to-weight ratio but Al alloys currently used for LPBF present a low damage resistance. In order to increase parts lifetime, one promising solution is to use healable Al alloys. The objective of this PhD thesis consists in the development, characterisation and optimisation of new healable Al alloys manufactured by LPBF. Two healing strategies were investigated:

First, the programme damage and repair strategy is based on diffusion of healing agent (HA) towards the damage sites. 6xxx series Al alloys were selected as the most promising and a new efficient methodology was developed to optimise their manufacturing. Three alloy compositions were investigated but healing of voids up to 500 nm was demonstrated by 3D X-ray nano-imaging and heating in-situ TEM only in presence of Mg. The tensile properties were significantly changed during healing heat treatment (HHT) which is not desirable.  

Second, the eutectic strategy is based on the melting of the low melting point HA phase and can heal larger defects. The 5xxx series Al alloys were selected as promising compositions due to their large solidification range. The new statistical methodology allowed to optimise their LPBF manufacturing. 3D X-ray nano-imaging showed healing of voids up to 1 µm and even a crack of 12 µm. Moreover, the HHT induced a slight increase of the mechanical properties. The healing efficiency was significantly improved by the addition of pressure during HHT which even increases the fatigue resistance up to a factor 100.

Jury members :

• Prof. Aude Simar (UCLouvain, Belgium), supervisor
• Prof. Hervé Jeanmart (UCLouvain, Belgium), chairperson
• Prof. Ernst Kozeschnik (TUWien, Austria)
• Prof. Philip Withers (University of Manchester, UK)
• Prof. Alexis Deschamps (Université Grenoble Alpes, France)
• Prof. Anne Mertens (ULiège, Belgium)
• Prof. Hosni Idrissi (UCLouvain, Belgium)

Visio conference link : https://teams.microsoft.com/l/meetup-join/19%3ameeting_YjRlMzZmYmQtMzUwNS00OTQ2LTlmNGEtYTI5M2RhYWQ3NDVh%40thread.v2/0?context=%7b%22Tid%22%3a%227ab090d4-fa2e-4ecf-bc7c-4127b4d582ec%22%2c%22Oid%22%3a%22025f9711-d2b0-45fe-b3d9-73089a40e981%22%7d