## 5 Post-Processing
### Redesign Heat Treatment for a Sustainable PBF-LB/M Manufacturing
The high temperatures and rapid cooling cycles inherent in these processes induce residual stresses that can lead to distortion, warping, or cracking if not properly managed. Pre-heating the platform helps mitigate these stresses by providing a more controlled thermal gradient, reducing the cooling rates that contribute to stress accumulation. However, while pre-heating can offer some relief,it is often still necessary to apply a dedicated post-processing heat treatment at elevated temperatures to fully alleviate residual stresses. Such heat treatments must be carefully designed to balance stress reduction with the preservation of the material microstructure and mechanical properties. For example, in Al-Si-Mg alloys, stress-relieving temperatures are often a challenge because precipitation hardening typically occurs at temperatures between 150-200 \({}^{\circ}\)C, which is insufficient to effectively relieve residual stresses after PBF-LB/M. While a typical stress-relieving treatment of 2 h at 300 \({}^{\circ}\)C helps soften the alloy, it also reduces strength, necessitating a subsequent solution heat treatment to regain mechanical properties [190]. While it is true that the current literature is progressively shifting toward shorter, simpler, and more sustainable heat treatments to align with environmental and economic demands, more comprehensive treatments, such as the T6 process, which includes solution heat treatment followed by aging, remain essential in some instances. Specifically, the T6 treatment is often necessary to mitigate the effects of microstructural anisotropy introduced by the PBF-LB/M process. This anisotropy, inherent to layer-by-layer manufacturing, can lead to heterogeneities in mechanical performance, such as reduced toughness or non-uniform elongation. Moreover, T6 treatments are particularly beneficial for enhancing the toughness and elongation at fracture of additively manufactured components, properties that are frequently challenging to optimize in metal AM. Despite the increasing emphasis on leaner thermal treatments, the trade-off in mechanical performance must be carefully evaluated to ensure the reliability and functionality of components in demanding applications. However, the as-printed SSSS condition of additively manufactured components can significantly reduce the duration required for the solutionizing step in the T6 treatment. This feature allows for shorter heat treatment cycles, reducing energy consumption and enhancing the overall sustainability of the process, without compromising the benefits of the T6 approach. For example, [PERSON] et al. investigated the effects of a shortened T6 heat treatment on PBF-LB/M AlSi7 Mg samples [191]. The procedure involved a 15 min solution treatment at 540 \({}^{\circ}\)C, followed by water quenching and artificial aging at 170 \({}^{\circ}\)C for 2-8 h. The results demonstrate that the shorter solution treatment effectively dissolves the fine phases generated during the PBF-LB/M process. However, the subsequent aging at 170 \({}^{\circ}\)C for 6 h leads to tensile properties that are slightly lower than those obtained with the standard T6 treatment. [PERSON] et al. examined a novel rapid T6 heat treatment for AlSi10 Mg alloy produced via PBF-LB/M, comparing its performance with T5 and conventional T6 heat treatments [192]. This rapid T6 process includes a brief solution treatment (10 min at 510 \({}^{\circ}\)C) followed by artificial aging (6 h at 160 \({}^{\circ}\)C). The objective of this treatment is to homogenize the microstructure and relieve residual stresses in the as-built alloy while preserving its fine microstructural features and associated strengthening mechanisms. The shortened solution treatment reduces porosity growth typically seen at elevated temperatures, resulting in a uniform dispersion of fine globular Si particles within the aluminum matrix. Moreover, this approach limits diffusion, increasing the amount of Mg and Si in solid solution, thereby enhancing precipitation hardening while preventing microstructural coarsening.