Soutenance de thèse : Maureen PUYBRAS

« Development of 5xxx Aluminium Alloys for Additive Friction Stir Deposition »

Doctorante : Maureen PUYBRAS

Laboratoire INSA : MATEIS

École doctorale :  ED34 : Matériaux de Lyon

Additive Friction Stir Deposition (AFSD) is gaining significant attention for its ability to fabricate large-scale aluminum components without requiring melting, making it an attractive technique for reducing energy consumption. Given the challenges associated with post-heat treatment of large components, this work seeks to minimize the need for such thermal treatments. In this context, Al- Mg alloys—specifically the 5XXX series, which are predominantly strengthened by magnesium in solid solution—were studied. These alloys, widely used in marine applications such as boat hulls, are prone to the formation of Al₃Mg₂ precipitates at grain boundaries. This precipitation process leads to "sensitization," making the alloy susceptible to intergranular corrosion and stress corrosion cracking in corrosive environments.
To counter-strike this issue, the study investigated the incorporation of (Sc, Zr) as Al₃(Sc,Zr) core- shell dispersoids. These dispersoids serve as heterogeneous nucleation sites for Mg, potentially influencing both magnesium precipitation and the AFSD process. Using isothermal artificial aging treatments, combined with thermoelectric power measurements, it was demonstrated that Al₃(Sc,Zr) dispersoids accelerate the precipitation of magnesium.
This thesis further explores the effects of AFSD on (i) alloy microstructure, (ii) Mg precipitation, and (iii) the stability of Al₃(Sc,Zr) dispersoids under various process parameters, with a particular focus on the rotational rate. Microstructural changes were analyzed through Electron Backscatter Diffraction (EBSD), revealing significant grain refinement due to the presence of dispersoids. Additionally, Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT) were used to assess the dispersoid structure and behavior before and after the AFSD process, shedding light on the impact of AFSD on second-phase particles. Finally, the study evaluated the sensitization resistance of these alloys, providing insights into their performance in corrosive environments.