## 5 Post-Processing
### Redesign Heat Treatment for a Sustainable PBF-LB/M Manufacturing
Higher throughputs and better use of resources further optimize production efficiency. This aligns well with the industrial goal of sustaining manufacturing with a low environmental impact. One traditional post-processing treatment in the AM sector that delivers superior mechanical properties while minimizing processing time and reducing overall costs is direct aging, also known as T5 temper [181,182]. This approach is particularly effective for alloys like Al-Cu, Al-Zn-Mg, and Al-Mg-Sc, which exhibit significant hardening potential when subjected to aging treatments [176]. Unlike solution treatment followed by aging, direct aging capitalizes on the supersaturation of alloying elements achieved through rapid solidification, enabling enhanced precipitation hardening. For instance, in Al-Mg-Sc alloys, direct aging has demonstrated a 72 HV increase in hardness due to additional Al\({}_{3}\)Sc precipitate formation [183]. T5 on Al-Mg-Sc alloys effectively improves yield strength, elevating it from 362 MPa in the as-built condition to 520 MPa after aging at 350 \({}^{\circ}\)C for 2 h [184]. Conversely, in Al-Si-Mg alloys, the effects of direct aging are more subdued, with only slight improvements in mechanical behavior and limited impact on residual stress or grain size. While T5-treated Al-Si-Mg samples exhibit the highest mechanical resistance among various heat treatments, the deviation from as-built properties is less pronounced compared to that achieved in solution-treated samples [185]. However, direct aging in Al-Si alloys can reduce toughness by 35-40%, altering the fracture behavior to be more random and less localized at melt pool boundaries [186]. The T5 treatment can also be performed in situ by leveraging platform pre-heating during the PBF-LB/M process, offering a streamlined and sustainable approach to enhance material properties directly during fabrication. For instance, [PERSON] et al. [187] investigated the precipitation of various Al-Cu-Li phases in a PBFed 209 alloy. The study compared the effects of in situ treatment, achieved by pre-heating the build platform to 220, 320, and 520 \({}^{\circ}\)C. In situ treatments successfully induced the precipitation of hardening phases. [PERSON] et al. [188] investigate the feasibility of conducting in situ heat treatments during the PBF-LB/M process for AlSi10 Mg components. Conventional PBF-LB/M systems typically operate with build plate temperature limits of 200 to 250 \({}^{\circ}\)C, restricting their application to in situ aging and low-temperature stress relief. In their work, the authors elevated the build plate temperature to 500 \({}^{\circ}\)C during 10-13 h of printing. At 220 \({}^{\circ}\)C, extended build times facilitated an in situ direct aging heat treatment, while printing at 300 \({}^{\circ}\)C enabled effective stress relief. Furthermore, temperatures of 450 and 500 \({}^{\circ}\)C allowed the implementation of in situ solution heat treatments. [PERSON] et al. [189] examine the in situ heat treatment of Scalmalloy(r) within the PBF-LB/M process. The build platform was heated to 200 \({}^{\circ}\)C, promoting the formation of Sc solute clusters. The presence of strength-enhancing secondary particles in the specimens produced under these conditions resulted in mechanical properties comparable to those of peak-aged Scalmalloy(r). The in situ heat treatments are not only efficient but also more sustainable, as they reduce the energy and time associated with separate post-processing steps. By integrating heat treatment into the printing process, energy-intensive post-build furnaces can be avoided, and the overall carbon footprint of the manufacturing process is significantly lowered, aligning with broader goals of environmental sustainability in advanced manufacturing. In addition to enhancing material properties, platform pre-heating can also help alleviate residual stresses, which are a common challenge in PBF-LB/M processes due to the rapid thermal cycling that occurs during printing.