## 5 Post-Processing  
### Redesign Heat Treatment for a Sustainable PBF-LB/M Manufacturing  
The rapid advancements in PBF-LB/M technology have driven significant interest in optimizing post-processing methods, particularly heat treatments, to enhance the performance of aluminum components. Unlike conventional methods, the PBF-LB/M process induces unique metallurgical characteristics due to its extremely high cooling rates (in the range of 10\({}^{3}\)-10\({}^{7}\) K/s), and successive heating and cooling cycles due to the layer-by-layer construction. These features lead to the formation of strongly supersaturated solid solutions (SSSSs), generation of residual stresses, and epitaxial growth on the underlying layers, which results in directional solidification and mechanical anisotropy and in situ heat treatment of previously solidified material, which in turn causes local phase transformations and precipitation [176]. Given these distinctive characteristics, conventional heat treatments, which are typically optimized for slowly solidified alloys, may not be directly applicable. Their long durations and high temperatures, though effective for conventional alloys, are likely not suitable for PBFed components, as they do not account for the microstructural peculiarities induced by rapid solidification. Moreover, the environmental impact of traditional heat treatments, which require significant energy and extended processing times, adds an additional layer of concern. Therefore, there exists a pressing need to develop novel heat treatments specifically tailored to PBFed aluminum alloys that must be shorter and more energy-efficient to reduce the environmental footprint while simultaneously being capable of achieving the desired microstructural and mechanical properties. As mentioned above, the PBF-LB/M process enables a favorable SSSS condition in the as-built state, thanks to the high cooling rates characteristic of this technology. This feature allows an increased amount of solute in solution, even for elements with low solubility in aluminum, sometimes exceeding the levels achievable through conventional solution treatment and quenching. For example, it has been demonstrated that Al-Si-Mg alloys processed via PBF-LB/M exhibit higher supersaturation compared to that obtained with traditional thermal treatments [177]. In addition, [PERSON] et al. exploited this PBF-LB/M peculiarity to produce a high solute Al-Zn-Mg alloy with 14 wt% Zn and 3 wt% Mg where excess manganese was added to improve the solid solution strengthening of the alloy, in addition to second-phase strengthening produced by Sc [178]. Furthermore, [PERSON] et al. observed that the exceptionally high cooling rates achievable in the PBF-LB/M process can retain up to 4.3 wt% of Mn in supersaturated solid solution within Al-Mn alloys--significantly surpassing its equilibrium solubility of approximately 1.8 wt% [179]. This phenomenon was leveraged by [PERSON] et al. to develop a novel Al-Mn-Cr-Zr alloy containing 5 wt% Mn, which exhibited exceptional solid solution strengthening and achieved high hardness in the as-built condition [180]. The increased SSSS characteristic of the PBF-LB/M process opens up the possibility of using aluminum-based alloys in the as-built state or with reduced treatments, leveraging supersaturation to achieve fast and effective strengthening through artificial aging. In this context, mechanical strengthening occurs via the precipitation of coherent and semi-coherent nanometric particles, making some Al-based alloys particularly suitable for direct use after faster heat treatment without requiring preliminary long solution treatment. Reducing heat treatments required on PBFed Al-based alloys further lessens energy consumption and reduces greenhouse gas emissions due to energy being produced by fossil fuels. Such direct processes preserve the material properties, reduce the occurrence of defects, and limit reprocessing requirements; hence, the whole circle of manufacturing time is reduced and greener.