The effects of scandium heterogeneous distribution on the precipitation behavior of Al3(Sc, Zr) in aluminum alloys.

Sc-containing Al alloys have excellent mechanical properties, which provide the foundation for their applications. The precipitation of the Al 3 Sc/Al 3 (Sc, Zr) is generally considered to be a key factor for the performance boost. However, the performances of the alloy in different production batches often exhibit unstable and fluctuation, which may be related to the heterogeneous of scandium. Herein, we investigated the precipitation behaviors of Al 3 Sc/Al 3 (Sc, Zr) phases in the Al-0.5Sc and Al-0.5Sc-0.25Zr alloys at 340 °C. Results shown that the high scandium‑zirconium ratio not only lead to the discontinuous precipitation, but also contribute to the abnormal continuous Al 3 (Sc, Zr) precipitation in Al-0.5Sc-0.25Zr alloy. The morphology of abnormal Al 3 (Sc, Zr) is similar to the common secondary Al 3 (Sc, Zr) phase with a coffee-bean like morphology. With the aid of Three-Dimensional Atomic Probe (3DAP), the core-shell structures of Al 3 (Sc, Zr) phases are quantitatively analyzed. In the shell layer of abnormal Al 3 (Sc, Zr) phase, the atomic concentration ratio of Sc to Zr is much higher than the common continuous precipitated Al 3 (Sc, Zr) phase. The abnormal Al 3 (Sc, Zr) phase may be one of the key factors for the structure heredity of Sc-containing Al alloys. [Display omitted] • The discontinuous precipitated Al 3 Sc phases are related to the partial high ratio of Sc/Zr (at.%) in Al alloys. • The discontinuous precipitated Al 3 Sc phases form at the casting process and gradually decompose at annealing process. • The high scandium-zirconium ratio leads to the decrease of coarsening resistance of the secondary Al 3 (Sc, Zr) phase. [ABSTRACT FROM AUTHOR]