Scandium is the element of choice for creating stable L12 precipitates in aluminum, with Al3Sc having the same gamma-prime (L12) structure as Ni3Al in nickel-base superalloys and the same strengthening effect by blocking dislocations. We present various strategies for partially replacing Sc with less expensive transition metals (TM = Zr, Ti, Hf), where the resulting core-shell Al3(Sc, TM) nano-precipitates display better coarsening resistance due to the lower TM diffusivity in Al. Scandium can also partially be replaced with even numbered heavy rare-earth elements (RE = Er, Yb). The resulting Al3(Sc, TM, RE) precipitates have a larger lattice parameter mismatch with the matrix, thus enhancing the alloys’ creep resistance. We discuss the nucleation effect of Si upon the trialuminides, and describe industrial applications for these alloys, taking advantage of the unique combination of coarsening and creep resistance up to 400 ºC, excellent thermal and electrical conductivity, high corrosion and oxidation resistance, and high ductility, combined with good castability and cold- and hot-working. The important roles of atom-probe tomography (APT) in understanding the coarsening and creep resistance is strongly emphasized.
