Rachel Boillat-Newport, a doctoral candidate in mechanical engineering, will defend their dissertation titled “Fabrication and Characterization of a High Strength Novel Aluminum Alloy for Implementation with Directed Energy Deposition.” Their advisor, Dr. Frank Liou, is the Michael and Joyce Bytnar Professor and director of manufacturing engineering in the mechanical and aerospace engineering department. The dissertation abstract is provided below.

Additive manufacturing (AM) is of significant interest due to the ability to fabricate 3D components layer-by-layer. Compared with traditional manufacturing methods, AM allows for the direct fabrication of complex, intricate parts without the need for extensive machining, reducing manufacturing time and tooling costs and minimizing material waste. Aluminum alloys are highly desired for implementation via AM due to their high strength-to-weight ratios; however, there are several challenges that complicate the situation and hinder the use of aluminum alloys. One of the most challenging issues is that the desired high-strength alloys are not compatible with AM processing methods. A method to address this is to develop new alloys that are specially designed to work with AM. Scalmalloy® is an Al-Mg-Sc-Zr-based alloy that has been developed for use with the unique processing seen with AM. During AM processing, Scalmalloy® powder is melted and solidified into a supersaturated solid solution. During postprocessing heat treatment, Scalmalloy® is aged to promote nanoprecipitation of Al3(Sc,Zr) which provides strengthening by pinning grain boundaries and preventing dislocation movement. This study focused on the application of post-processing treatments for the improvement of the properties of Scalmalloy® deposits fabricated by directed energy deposition (DED). The manufacturer recommendation for heat treating Scalmalloy® is a single-step aging treatment at 325°C for 4 hours to promote nanoprecipitation; however, this is considerably different from the multistage heat treatments commonly used in traditional manufacturing. These multistage treatments can provide many benefits, allowing the tailoring to achieve final components with the desired properties. It is theorized that multistage heat treatments are possible, but that optimization must be performed using AM rather than relying on conventional heat treatments. This study explored the application of single-stage aging treatments for DED Scalmalloy® to understand and determine whether the manufacturer’s recommendation is valid for DED processing as the alloy was developed for powder bed processing. Many studies on powder bed processing have noted the benefit of the manufacturer-recommended heat treatment, but there are few to no studies on DED. Furthermore, the influence of natural aging time between fabrication and heat treatment was investigated to identify the impact on tensile behavior. The literature shows that DED Scalmalloy® exhibits lower properties than powder bed processes. As age hardenable conventional aluminum alloys can be dramatically impacted by time held at room temperature prior to artificial aging, an exploration into the influence of natural aging is crucial for optimal properties. Lastly, heat treatment studies were conducted at low to intermediate temperatures to explore the possibility of stress relief treatments. Many studies have concluded that stress relief treatments are detrimental to mechanical behavior; however, it is proposed that a balance between stress relief and property diminishment can be found to provide a part with significantly less stress than the as-built case while maintaining properties. This work acts as the first stepping stone toward the ultimate goal of customized multistep heat treatments for DED-fabricated high-strength aluminum alloys.