Development of an Advanced Aluminum Alloy for Additive Manufacturing

Traditional aluminum alloys for use in additive manufacturing have been developed from old foundry technologies. There is a need for the development of an aluminum alloy which takes full advantage of the benefits additive manufacturing has to offer, i.e. rapid solidification and cooling. Preliminary research conducted in 2016 had shown that Al-Cu-Mg-Ag precipitation-hardenable alloys achieved hardness exceeding 140 VHN after deposition and heat treatment, compared to the traditional Al-10Si-0.5Mg alloy which provided hardness near 100 VHN. A correlated improvement of strength was also seen with the advanced alloy, which approached the typical yield strength of 7075-T651 alloy. To better refine the target composition for commercialization, the alloy system is currently being evaluated to optimize mechanical properties and insensitivity to solidification cracking.

Three metal powders were used to blend 9 characteristic Al-Cu-Mg-Ag compositions to determine optimum chemistry for this advanced aluminum alloy. Manufactured test specimens were printed by multiple deposition tracks using the blended experimental material. Solidification crack sensitivity was assessed through a special design that imposed varying levels of residual stress during the additive manufacturing process. Specimens were examined for surface appearance. An additional sample was subjected to post process heat treatment to study the effect of solution treating and aging for achieving precipitation strengthening. Samples were tested for mechanical properties and examined to determine precipitate formation. The Al-Cu-Mg-Ag alloys are primarily strengthened by Ω phase precipitates, which were evident in transmission electron microscopy. The relationship between composition, precipitate formation, and crack sensitivity were analyzed to determine the optimal composition.