Segregation Behavior and Microstructure Evolution of 2219 Aluminum Alloy by Directed Energy Deposition-Arc

Abstract

Segregation affects the solute content within the grains, as well as the content and distribution of the secondary phases at grain boundaries, leading to structural and property inhomogeneity. It also influences the microstructure evolution during the remelting and post-heating in directed energy deposition-arc (DED-Arc), ultimately impacting product performance in both as-built and heat-treated states. In this study, a 2219 aluminum alloy wall was fabricated using DED-Arc. Numerical simulation was employed to calculate the temperature field of the additive manufacturing process and solidification parameters. The segregation behavior and microstructure characteristics were analyzed. Both macrosegregation and microsegregation were observed in the as-built wall. Within a single layer, the Cu content is higher at the top where the metal solidifies last, than at the bottom where it solidifies first. The microsegregation is more severe in the first few layers due to the higher cooling rate. As the DED-Arc process progresses, eutectics enriched in the interlayer form a reticular network due to remelting, while a finer grain size is achieved through Cu enrichment and Al3Zr nucleants. As the layer-by-layer deposition process continues, the as-built wall alternates between coarse-grained unmelted intralayers, coarse-grained partially remelted intralayers with network-distributed eutectics, fine-grained remelted interlayers with network-distributed eutectics and fine-grained newly deposited interlayers.

Keywords: 2219 aluminum alloy, Cu segregation, Microstructure evolution, directed energy deposition-arc, numerical simulation