Phase-Field Simulation of Microstructure Formation in Gas-Atomized Al-Cu-Li-Mg Powders

Al-Cu-Li (2xxx series) powders for additive manufacturing processes are often produced by gas atomization, a rapid solidification process. The microstructural evolution of gas-atomized powder particles during solidification was investigated by phase-field simulations using the software tool MICRESS. The following topics were investigated: (1) the microsegregation of copper and lithium in the particle, and the impact of lithium addition on the formation of secondary phases in Al-2.63Cu and Al-2.63Cu-1.56Li systems, (2) the effect of magnesium on the nucleation and final mass fraction of T₁ (Al₂CuLi) growing from the melt, and (3) the effect of increased magnesium content on the T₁ and S' (AlCu₂Mg) phase fractions. It is observed that the addition of lithium into the Al-Cu system leads to a decrease in the solid solubility of copper in the primary matrix; consequently, more copper atoms segregate in the interdendritic regions resulting in a greater mass fraction of secondary precipitates. Our result agrees with findings on the beneficial impact of magnesium on the nucleation and precipitation kinetics of T₁ precipitates in the conventional casting process with further thermomechanical heat treatments. Moreover, it is observed that the increase in magnesium from 0.28 wt.% to 0.35 wt.% does not significantly affect the nucleation and the amount of the T₁ phase, whereas a decrease in T₁ phase fraction and a delay of T₁ formation are encountered when magnesium content is further raised to 0.49 wt.%.