Direct aging of additively manufactured A20X aluminum alloy

This study investigates the effect of direct aging on a newly developed high-performance aluminum alloy A20X for laser powder bed fusion. Three different temperatures (180 °C, 200 °C, and 220 °C) and nine different heat treatment durations (5 min to 30 h) were considered. The material exhibited significant softening (up to 23.7 % hardness drop) after direct aging. The extent of softening was proportional to the temperature and duration of heat treatment. During direct aging, incoherent Al2Cu (θ) precipitates ({110}θ ǁ {220}Al) coarsened and the volume fraction remained constant (4.52–4.63 %). The average precipitate size grew by up to ∼100 % through direct aging and no metastable precipitates (such as θ′ or Ω) formed, suggesting the absence of supersaturated matrix in as-printed A20X. Accordingly, the yield and tensile strengths of the alloy dropped by up to 27 % and 19.4 %, respectively. The continuous Mg/Ag solute wall observed at grain boundaries in the as-printed state caused serrated plastic flow due to the locking/unlocking of dislocations. Longer aging treatments generated discrete solute co-clusters along the grain boundaries and TiB2/Al interface promoting smoother plastic flow.