Results of Phase II Research to Develop an Advanced Aluminum Alloy for Additive Manufacturing

There is a significant desire for an aluminum alloy for additive manufacturing that exhibits improved mechanical properties over the current Al-10Si-0.5Mg alloy. This presentation will describe the results of current research directed at fulfilling this need. Based on a sound alloy design philosophy, alloys within the Al-Cu-Ag-Mg system are being developed for additive manufacturing with the objectives of minimizing solidification cracking, maximizing mechanical properties, and providing good processing characteristics. A master alloy was obtained that enabled the blending of pure Cu and Ag to achieve several compositions necessary for selective characterization with the ultimate goal of defining a compositional range for a commercial alloy. These blends were utilized within a laser-based directed energy deposition process, operating at 2 kW of laser power, to produce specimens for characterization and testing that were approximately 2 cm wide by 10 cm long by 10 cm wide. Chemical analysis of the completed specimens indicated that some departure from the desired compositions was displayed; however, the compositions of the alloys that were produced were sufficient for identifying candidate alloys of interest. Results of characterization and testing of these alloys have been extremely positive. The high strength exhibited by this system is based on the participation of Cu, Ag, and Mg in the concomitant nucleation and growth of two precipitate phases, θ’ and Ω. Peak strengthening was found to occur when employing post-process solution heat treatment and aging at 160°C for 20 hours, and resulted in an evenly distributed network of extremely fine q’ and Ω precipitates. Alternate compositions also indicated the ability to respond to aging only. These results indicate that two of the experimental alloys may individually achieve strength comparable to alloy 7075-T6 in the as-built and aged condition or in as-built and solutionized and aged condition, while no solidification cracking was observed.