Microstructural transformation and elemental distribution of 2319 aluminum alloy in droplet hybrid arc additive manufacturing

Droplet hybrid arc additive manufacturing (DAAM) is a novel low-cost technique with high deposition efficiency for aluminum alloys. This study investigates the deposition and solidification mechanisms of 2319 Al alloy in DAAM, focusing on molten pool temperature fields, microstructural evolution, and solute redistribution. First, the deposition principle and influences of process parameters on the bead morphology of DAAM were analyzed. A coupled heat-mass transfer model is developed to simulate the molten pool thermal field and solidification parameters. Then, the solidification data was input into the microscopic phase-field model to obtain the microstructural evolution and elemental redistribution. Columnar crystals and epitaxial growth were generated at the lower part of the deposition layer. The thermal gradient reduced obviously while the solidification rate raised from the down to up of the deposition layer. Therefore, in the middle and upper parts the development of columnar to equiaxed transition occurred. Finally, metallographic analysis was conducted and showed the similar microstructural transformation patterns. In addition, the solute (Cu) was primarily distributed on the grain boundary according to the Energy-dispersive spectroscopy results. The simulations were well validated by the experimental analyses.