Precipitation evolution in Al–0.1Sc, Al–0.1Zr and Al–0.1Sc–0.1Zr (at.%) alloys during isochronal aging

Precipitation strengthening is investigated in binary Al–0.1Sc, Al–0.1Zr and ternary Al–0.1Sc–0.1Zr (at.%) alloys aged isochronally between 200 and 600 C. Precipitation of Al3Sc (L12) commences between 200 and 250 C in Al–0.1Sc, reaching a 670 MPa peak microhardness at 325 C. For Al–0.1Zr, precipitation of Al3Zr (L12) initiates between 350 and 375 C, resulting in a 420 MPa peak microhardness at 425–450 C. A pronounced synergistic effect is observed when both Sc and Zr are present. Above 325 C, Zr additions provide a secondary strength increase from the precipitation of Zr-enriched outer shells onto the Al3Sc precipitates, leading to a peak microhardness of 780 MPa at 400 C for Al–0.1Sc–0.1Zr. Compositions, radii, volume fractions and number densities of the Al3(Sc1 xZrx) precipitates are measured directly using atom-probe tomography. This information is used to quantify the observed strengthening increments, attributed to dislocation shearing of the Al3(Sc1 xZrx) precipitates. Published by Elsevier Ltd. on behalf of Acta Materialia Inc.