Ambient- and high-temperature mechanical properties of isochronally aged Al-0.06Sc, Al-0.06Zr and Al-0.06Sc-0.06Zr (at.%) alloys

Ambient- and high-temperature precipitation strengthening are investigated in Al-0.06Sc, Al-0.06Zr and Al-0.06Sc-0.06Zr (at.%) alloys. Following solidification, Sc is concentrated at the dendrite peripheries while Zr is segregated at the dendrite cores. During isochronal aging, precipitation of Al3Sc (L1(2)) commences between 250 and 300 degrees C for Al-0.06Sc, and reaches a 429 MPa peak microhardness at 325 degrees C. For Al-0.06Zr, precipitation of Al3Zr (L1(2)) first occurs between 400 and 425 degrees C and reaches a 295 MPa peak microhardness at 475 degrees C. A pronounced synergistic effect is observed when both Sc and Zr are present. Above 325 degrees C, Zr additions provide a secondary strength increase that is attributed to precipitation of Zr-enriched outer shells onto the Al3Sc precipitates, leading to a peak microhardness of 618 MPa at 400 degrees C for Al-0.06Sc-0.06Zr. Upon compressive creep deformation at 300-400 degrees C, Al-0.06Sc-0.06Zr exhibits threshold stresses of 7-12 MPa; these values may be further improved by optimal heat-treatments. Published by Elsevier Ltd. on behalf of Acta Materialia Inc.