Additive manufacturing (AM) can be particularly advantageous to manufacture components designed to meet challenging structural requirements. Selective laser melting (SLM) microstructure is different than that obtained by traditional manufacturing process; in particular, mechanical and microstructural features achieved herein are influenced by the entire thermal history, including the manufacturing process and the heat treatment (HT) with relevant role of the slow cooling rate adopted. In fact, both the process and the HTs can significantly modify the microstructure and related mechanical and tribological properties. To better understand how mechanical response can be tuned to meet different requirements, in this article the effects of four different vacuum HTs on microstructures, mechanical properties, and wear behavior of Inconel 625 produced with SLM are deeply investigated. In general, the results confirm that HT can significantly change the microstructure and mechanical or tribological properties of Inconel 625. Among the examined HT, solution + aging and direct aging improve the strength of the alloy, whereas annealing leads to recrystallization, reducing strength in favor of ductility. Stress relieving does not significantly change the microstructure and mechanical properties. Considering tribological behavior, only direct aging HT leads to a remarkable improvement, with a reduction in friction coefficient and wear rate.

Additive manufacturing (AM) could be used to reduce the production times of prototypes; however, further research is required to address metals structural parts. To obtain the correct properties, some relevant factors to be considered are the build volume, shape factor, and the need for specific heat treatments. This study aims to evaluate the reliability of AM prototypes applied at a new powertrain system developed to reduce vehicle emissions. Firstly, it was investigated the mechanical behavior, microstructure, and the effect of sample size and heat treatments on both specimens and prototypes made of AM 17-4PH steel. Finite Element Analysis (FEA) was performed to evaluate the structural resistance. Finally, the prototypes were produced, analyzed, and tested on a functional engine test bench to evaluate their reliability. The mechanical properties decreased with an increase in the sample volume. After heat treatment, the yield strength increased, due to the transformation of δ-ferrite in martensite and the reduction of retained austenite. The engine test bench was successfully completed. The conclusions set the basis for similar future applications of time-effective prototypes that can be dimensioned owing to appositely developed postprocesses that guarantee the required resistance.

Hybrid lightweight structures increasingly combine cast, wrought, and additively manufactured aluminum alloys, but the mechanical response of their welded joints remains strongly material-dependent. In this study, cast EN AC-42100-T6, wrought EN AW-6082-T6, and laser powder bed fusion (LPBF) AlSi10Mg stress-relieved plates were welded in 4 and 8 mm configurations using cold metal transfer and pulsed multi-control processes over two campaigns. Weld defects, microstructure, hardness profiles, and tensile properties were analyzed using a framework combining a hardness derived local yield-stress descriptor (σ_y,loc), a cumulative hardness deficit (ID_HV), and a porosity increment metric (ΔP). The second campaign eliminated fusion and penetration related defects, but did not mitigate fusion zone porosity in LPBF-related joints, which reached 13.7% in the 8 mm LPBF–Cast joint. Hardness analysis showed the widest hardness-affected region in the wrought alloy, an intermediate response in the cast alloy, and localized alteration in LPBF. Tensile results identified three degradation modes: strength loss associated with heat-affected zone (HAZ) softening in wrought-containing joints, ductility limitation associated with the initial cast condition, and porosity-associated ductility loss in LPBF-related joints. The lower yield strength reduction in LPBF-related joints does not imply improved performance, as fracture remains strongly influenced by fusion zone porosity. The results support material specific mitigation and design strategies for hybrid welded aluminum structures.