In Situ Ageing Assessment During the Manufacturing of a Large-Scale A357-AlSi7Mg0.6 Component by Laser Powder Bed Fusion

Additive manufacturing (AM) is increasingly being considered to produce large aluminum components for aeronautical applications. Larger parts lead to longer build durations, numerous lasers and may result in prolonged exposure to high temperatures if heat dissipation is insufficient, causing in situ ageing during manufacturing and a consequent reduction in the mechanical properties of as-built aluminum alloys. This study investigates the relationship between process parameters, heat dissipation, and resulting mechanical properties in large-scale A357-AlSi7Mg0.6 aluminum alloy manufactured by laser powder bed fusion (LPBF). In the context of developing geometrically complex casings or components using LPBF equipment with multiple lasers (up to 12), mechanical testing of first prototypes revealed up to a 30% reduction in mechanical properties in certain regions, attributed to insufficient heat dissipation during the build. Thermal modelling and in situ experimental measurements have shown that the high thermal mass and extended build times of large components lead to non-uniform temperature distributions, promoting undesired microstructural evolution and advanced over-ageing, effects that are generally less pronounced in smaller specimens reported in the literature. Hardness mapping on samples subjected to monitored ageing ranges, as well as on additively manufactured rods with deliberate geometries for heat accumulation, confirmed that areas with insufficiently optimized support show significant decreases in hardness due to inefficient heat dissipation. A numerical model was developed to link the hardness evolutions to both ageing time and temperature, enabling improved predictions of microstructure and properties as a function of build and heat-removal strategies. These findings emphasize the critical importance of support structure optimization for both mechanical support and thermal management during LPBF, as well as the need for tailored process and post-process heat treatments to achieve consistent and reliable mechanical properties in large, additively manufactured aluminum alloy components.