Isothermal aging of Al-Ni-Sc alloy containing Al3Ni microfibers and Al3Sc nanoprecipitates

Binary Al-Sc alloys have excellent strength at room and elevated temperature up to 300°C due to coherent of Al₃Sc nanoprecipitates. Binary Al-Ni alloys are an alternative alloy for high-temperature applications owing to high-thermal stability of Al₃Ni microfibers. In this study, the hardness evolution at 300°C for up to 672 h for eutectic ternary Al-6Ni-0.4Sc (wt%) was studied and compared with binary Al-0.4Sc and Al-6Ni alloys. The Al-6Ni alloy maintains a constant hardness after aging at 300°C up to 672 h. Both Al-0.4Sc and Al-6Ni-0.4Sc alloys show strong precipitation strengthening response, with peak hardness reached after about 3 h aging, due to Al₃Sc precipitates. These precipitates were studied in Al-6Ni-0.4Sc via local electrode atom probe tomography and contain small amounts of Ni (0.04 at%) which do not affect the kinetics of precipitation. The microhardness evolution for Al-6Ni-0.4Sc can be explained through superposition of binary Al-0.4Sc and Al-6Ni alloys, indicating that both Al₃Sc nanoprecipitates and Al₃Ni microfibers contribute to strength.