Jocelyn DELAHAYE
Thursday, 8 September 2022 at 1.30PM
How to feed and validate a phase-field model predicting the evolution of microstructures and properties in AlSi10Mg processed by Selective Laser Melting
Abstract
AlSi10Mg processed by Selective Laser Melting (SLM) exhibits an out-AlSi10Mg processed by Selective Laser Melting (SLM) exhibits an out-of-equilibrium microstructure as a result of rapid solidification. This microstructure is composed of α-Al sub-micron cells surrounded by an eutectic mixture of Si precipitates in an Al matrix. The rapid solidification also results in an extended Si solute content in solid solution inside the Al cells. The Si atoms in solid solution and the fine Si precipitates both contribute to the high strength and the thermo-physical properties of AlSi10Mg SLM, particularly its low thermal conductivity. Moreover, the microstructure and its associated properties is process parameter dependent.
The microstructure is deeply affected when submitted to a thermal field. This can happen either (i) locally due to the heat input accompanying the deposition of a new layer or (ii) in the bulk by the effect of build platform temperature or (iii) during post-treatments. At low temperature, the Si in solid solution tends to precipitate out in the α-Al cells while at intermediate or high temperature, the pre-existing Si precipitates in the eutectic coarsen. As a result, the strength and the thermo-physical properties of the alloy are modified.
The present thesis thus aims to investigate the impact of these process parameters on the microstructure evolution and the related tensile and thermo-physical properties of AlSi10Mg SLM. In a first step, microstructural characterizations and tensile tests are performed to study the influence of the laser power, scan speed and the build platform temperature. From the collected data, the preferential rupture zone in tension is identified and a hardening model connecting microstructure and tensile properties is developed. Then thermal models of the SLM process validated against experiments and able to reproduce the as-built microstructure are used to extract the thermal history in the preferential rupture zone. Thermo-physical properties are needed as inputs in the models. During their measurements, the microstructure undergoes transformations which affect in return the measured thermo-physical properties. To address the device limitation, the non-equilibrium thermo-physical properties of AlSi10Mg SLM are calculated through a CALculation of PHase Diagram (CALPHAD) model. Finally, a phase-field model tracking the nucleation, growth and coarsening kinetics of Si precipitates is developed and validated against experiment. The model investigates the effect of build platform temperature on the microstructure evolution of AlSi10Mg SLM.
Jury members
- L. DUCHENE, Université de Liège, Président ;
- Mme A. MERTENS, Université de Liège, Promotrice ;
- Mme A. HABRAKEN, Université de Liège, co-Promotrice ;
- P. DUYSINX, Université de Liège ;
- A. ROLLETT, Carnegie Mellon University (USA) ;
- B. APPOLAIRE, Institut Jean Lamour (France) ;
- Mme A. SIMAR, Université Catholique de Louvain.
