Effects of Zr on the Microstructure and Mechanical Properties of Al-Sc- Yb Alloys

Cast, coarse-grained Al-Sc alloys are interesting candidates for high temperature, creepresistant applications due to the formation of a high number density of nanometer sized Al3Sc precipitates [1]. Upon addition of Yb to Al-Sc alloys, Yb replaces the Sc forming Al3(Sc1-xYbx) precipitates (L12 structure) [2]. The resulting alloys have higher creep resistance due to the larger lattice parameter mismatch between the matrix and precipitate phases as a result of the substitution of Yb for Sc. The precipitates in Al-Sc-Yb alloys form rapidly at 300 ̊C and the coarsening kinetics are not slowed when compared with binary Al-Sc alloys [3]. Additions of Zr to Al-Sc alloys do, however, retard the coarsening kinetics of the Al3(Sc1-xZrx) precipitates [4]. In the present study, Zr is added to an Al-Sc-Yb alloy. The compositions of the alloys studied are Al-0.06Sc-0.02Yb0.02Zr (at.%) and Al-0.06Sc-0.02Yb-0.005Zr (at.%).