This paper reviews the status of nanoparticle technology as it relates to the additive manufacturing (AM) of aluminum-based alloys. A broad overview of common AM processes is given. Additive manufacturing is a promising field for the advancement of manufacturing due to its ability to yield near-net-shaped components that require minimal post-processing prior to end-use. AM also allows for the fabrication of prototypes as well as economical small batch production. Aluminum alloys processed via AM would be very beneficial to the manufacturing industry due to their high strength to weight ratio; however, many of the conventional alloy compositions have been shown to be incompatible with AM processing methods. As a result, many investigations have looked to methods to improve the processability of these alloys. This paper explores the use of nanostructures to enhance the processability of aluminum alloys. It is concluded that the addition of nanostructures is a promising route for modification of existing alloys and may be beneficial to other powder-based processes.

Scalmalloy^® is an Al-Mg-Sc-Zr-based alloy specifically developed for additive manufacturing (AM). This alloy is designed for use with a direct aging treatment, as recommended by the manufacturer, rather than with a multistep treatment, as often seen in conventional manufacturing. Most work with Scalmalloy^® is conducted using powder bed rather than powder-fed processes. This investigation seeks to fill this knowledge gap and expand beyond single-step aging to promote an overall balanced AM-fabricated component. For this study, directed energy deposition (DED)-fabricated Scalmalloy^® components were subjected to low-temperature treatments to minimize residual stresses inherent in the material due to the layer-by-layer build process. X-ray diffraction (XRD) indicated the possibility of stress minimization while reducing the detriment to mechanical strength through lower temperature treatments. Microstructural analyses consisting of energy dispersion spectroscopy (EDS) and electron backscatter diffraction (EBSD) revealed the presence of grain growth detrimentally affecting the strength and elongation made possible by very small grains inherent to AM and rapid solidification. Tensile testing determined that treatment at 175 °C for 1 h provides the best relief from the existing residual stresses; however, this is accompanied by a diminishment in the yield and tensile strength of 19 and 9.5%, respectively. It is noted that treatment at 175 °C for 2 h did not provide as great of a decrease in residual stresses, theorized to be the result of grain growth and other strengthening mechanisms further stressing the structure; however, the residual stresses are still significantly diminished compared with the as-built condition. Furthermore, a minimal reduction of the tensile strengths indicates the possibility of finding a balance between property diminishment and stress state through the work proposed here.

As high-strength aluminum alloys present several processability issues with additive manufacturing (AM), Scalmalloy^®, an Al-Mg-Sc-Zr-based alloy, has been developed. This alloy is age-hardenable, allowing it to precipitate out a strengthening precipitate phase, Al₃(Sc,Zr). The manufacturer recommends a single-stage aging treatment at 325 °C for 4 h; however, the majority of the literature studies utilize a powder bed processing known as selective laser melting (SLM) over powder-fed processing directed energy deposition (DED). This study addresses the lack of information on heat treatments for DED fabrication by exploring the application of artificial aging temperatures of 300–400 °C for 2, 4, and 6 h to: 1. determine the impact on the microstructural evolution and mechanical performance and 2. determine whether the recommended treatment for Scalmalloy^® is appropriate for DED fabrication. Tensile testing determined that low-temperature treatments exhibited no visible dependence on time (2–6 h); however, time becomes influential at higher temperatures starting at 350 °C. The temperature plays a considerable role in the mechanical and microstructural behaviors of DED Scalmalloy^®. The highest tensile strength was noted at 300 °C (384 MPa, 21.6% increase), but all heat-treated cases resulted in an improvement over the as-built case. This investigation established that increasing the treatment temperature resulted in a decreasing trend for the tensile strength that held over time. Elongation at 2 h displayed a near parabolic trend that peaks at 350 °C (20%) and falls with higher temperatures. At the 4 h treatment, a slight decreasing trend was noticed for elongation. No visible change was observed for elongation at 6 h, with elongation values remaining fairly consistent. The microstructural evolution, including micron-sized and nano-sized Al₃(Sc,Zr) and grain size, was examined, and coarsening effects were noted with the increase in the temperature. It is recommended that treatment be conducted at 300 °C to achieve the precipitation of the strengthening Al₃(Sc,Zr) phase while minimizing coarsening.

Volume 24A provides a comprehensive review of additive manufacturing (AM) design fundamentals and applications. The primary focus of the Volume is on metallic systems with limited emphasis on polymers and ceramics where applicable. The first five divisions provide an in-depth review of each of the key aspects of the entire AM value chain. The materials/process development division discusses AM process-structure-property relationships, process optimization and defects, and material/process modeling. The design principles division includes coverage of design rules, part consolidation and assemblies, and simulation-driven design. In the data management division, data analytics, data security, and data sharing through a common data model are discussed. Next, the mechanical property characterization division includes discussion on fatigue, tensile, hardness, and other property testing. The AM non-destructive evaluation (NDE) division discusses surface and geometrical characterization, ultrasonic testing, radiography, computed tomography, and resonant ultrasound spectroscopy. Included in the AM in-situ process control and monitoring division are articles on machine learning for anomaly detection, in-process thermography, laser powder-bed fusion process control, and in-situ x-ray imaging. The applications division reviews key sectors that are embracing and adopting AM technologies. The market sectors are aviation, space flight, medical, automotive, oil and gas, construction, energy, and electronics. The last two divisions cover AM standards, qualification, and certification, as well as environmental, economic, and business concerns. For information on the print version of Volume 24A, ISBN: 978-1-62708-437-6, follow this link.

Scalmalloy^® is a novel alloy designed to work with the unique processing inherent in additive manufacturing (AM). This alloy is post-processed using a single artificial aging treatment rather than a multistep heat treatment, as often noted in traditional manufacturing processes. Much of the literature details the impact of direct aging treatments around the temperature and time recommended by the manufacturer, 325 °C for 4 h; however, few studies have explored the impact of delayed artificial aging on the resulting mechanical and microstructural behavior. This study explored this missing link and determined the impact that the time between the fabrication of the component and artificial aging has on the final properties. For this study, directed energy deposition (DED) was utilized to fabricate Scalmalloy^® components. Post-processing via artificial aging was performed after fabrication to yield samples naturally aged for 0, 2, 4, 6, 8, 10, 12, and 14 days. Samples were subsequently aged at 325 °C for 4 h. Tensile testing determined that natural aging negatively impacts tensile strengths. After 6 days of delayed artificial aging (6 NA), the yield strength (YS) and tensile strength (TS) relative to day 0 (0 NA) case were diminished by 10% and 8.6%, respectively. After 12 days (12 NA), even greater property decreases were noted, with a 23% decrease in YS and an 18% decrease in TS. Microstructural characterization was performed and an increase in precipitate size and decrease in precipitate number coupled with increased grain sizes were theorized to be linked to the decrease in tensile properties. The negative impact of delayed artificial aging after AM fabrication for Scalmalloy^® highlights the importance of fast transitions from deposition to heat treatment.

Additive manufacturing (AM) simulations are effective for materials that are well characterized and published; however, for newer or proprietary materials, they cannot provide accurate results due to the lack of knowledge of the material properties. This work demonstrates the process of the application of mathematical search algorithms to develop an optimized material dataset which results in accurate simulations for the laser directed energy deposition (DED) process. This was performed by first using a well-characterized material, Ti-64, to show the error in the predicted melt pool was accurate, and the error was found to be less than two resolution steps. Then, for 7000-series aluminum using a generic material property dataset from sister alloys, the error was found to be over 600%. The Nelder–Mead search algorithm was then applied to the problem and was able to develop an optimized dataset that had a combined width and depth error of just 9.1%, demonstrating that it is possible to develop an optimized material property dataset that facilitates more accurate simulation of an under-characterized material.