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

Abstract Sc-containing Al alloys have excellent mechanical properties, which provide the foundation for their applications. The precipitation of the Al3Sc/Al3(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 Al3Sc/Al3(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 Al3(Sc, Zr) precipitation in Al-0.5Sc-0.25Zr alloy. The morphology of abnormal Al3(Sc, Zr) is similar to the common secondary Al3(Sc, Zr) phase with a coffee-bean like morphology. With the aid of Three-Dimensional Atomic Probe (3DAP), the core-shell structures of Al3(Sc, Zr) phases are quantitatively analyzed. In the shell layer of abnormal Al3(Sc, Zr) phase, the atomic concentration ratio of Sc to Zr is much higher than the common continuous precipitated Al3(Sc, Zr) phase. The abnormal Al3(Sc, Zr) phase may be one of the key factors for the structure heredity of Sc-containing Al alloys.