Ambient- and elevated temperature properties of Sc- and Zr-modified Al-6Ni alloys strengthened by Al₃Ni microfibers and Al₃(Sc, Zr) nanoprecipitates

The eutectic Al-6Ni (wt.%) alloy exhibits excellent strength at ambient and elevated temperature, provided by a high volume fraction of Al₃Ni microfibers formed during solidification. Here, Al-6Ni is micro-alloyed with Sc and Zr (with 0.1Sc+0.2Zr, 0.2Sc+0.4Zr and 0.3Sc+0.2Zr, wt.%), creating two additional populations of primary and secondary Al₃(Sc,Zr) precipitates. The fully eutectic microstructure (α-Al + Al₃Ni) observed in Al-6Ni alloy changes, with Sc and Zr addition to hypoeutectic microstructure with primary α-Al grains nucleated on solidification by primary Al₃(Sc,Zr) precipitates. Upon subsequent aging, fully-coherent Al₃(Sc,Zr) nano-precipitates form in the α-Al matrix between Al₃Ni microfibers, providing substantial precipitation strengthening, which is maintained for up to 1 month at 350 °C. Alloy strength - both at ambient temperature and during creep at 300 °C - can be quantitatively described through a superposition of precipitation strengthening by Al₃(Sc,Zr) nanoprecipitates and load-transfer strengthening by Al₃Ni microfibers.