Precipitation behavior of the secondary L1₂-Al₃(Sc, Zr) phase in the SLM fabricated Al-4Cu-2Mg-0.3Sc-0.7Zr alloy during aging process

The precipitation behavior of the secondary L1₂-Al₃(Sc, Zr) precipitates in the selective laser melting (SLM) fabricated Al-4Cu-2Mg-0.3Sc-0.7Zr alloy is investigated. And the distribution of Sc and Zr atoms in the secondary Al₃(Sc, Zr) precipitates at different aging temperatures was studied by HAADF-STEM. The secondary L1₂-Al₃(Sc, Zr) precipitates are predominantly comprise Al and Sc atoms after direct aging at 225 °C for 2.5 h, and this indicating that Sc elements primarily control the nucleation and the growth of the L1₂-Al₃(Sc, Zr) phase at 225 °C. The distinct Al₃Sc-rich core and Al₃Zr-rich shell structure were observed when the aging temperature increases to 440 °C, and both Sc atoms and Zr atoms actively participate in the nucleation and growth of Al₃(Sc, Zr) particles at 440 °C. Furthermore, Cu element enriched at the interface between Al₃(Sc, Zr) precipitate and Al matrix following direct aging treatment at 440 °C for 0.5 h. And during non-isothermal aging process, the oxidation was observed occurs at the grain boundary mainly when the aging temperatures were higher than 440 °C.