Abstract:A processing scheme for preparing strips of Al-Cu-Li-Mg-Zr-based alloys microalloyed with Sc was proposed. This scheme includes a twin-roll casting of strips with a near-net-shaped 3 mm-thick gauge and a homogenization/solution treatment processing step. Two twin-roll cast Al-Cu-Li-Mg-Zr-based alloys were studied, one with an addition of 0.17 wt.% Sc, and the other without addition of Sc. Both alloys were annealed at 300 °C for 30 min, 450 °C for 30 min, and 530 °C for 30 min and quenched into room temperature water. The first two annealing steps provide a fine dispersion of Al₃Zr/Al₃(Sc,Zr) particles. The final annealing step serves as homogenization/solution treatment. A fine crystallization structure of the twin-roll cast materials enables the dissolution of primary particles containing the main alloying elements during a relatively short annealing time. Shorter soaking duration limits the depletion of surface layers from Li and significant coarsening of Al₃Zr/Al₃(Sc,Zr) dispersoids. The Sc-containing material has significantly finer grains already in the as-cast state. The Al₃(Sc,Zr) dispersoids formed during the homogenization/solution treatment step prevent grain coarsening at high temperatures. Strengthening θ′(Al₂Cu), T₁(Al₂CuLi), and rare S''''(Al₂CuMg) phases are formed during subsequent artificial aging at 180 °C. The increase in yield strength was 200 MPa in the peak-aged conditions. This value is comparable to the ones reported in similar direct-chill cast materials, thus validating the proposed processing scheme.

Key words: microstructure; mechanical properties; Al-Cu-Li-based alloy; Sc alloying; twin-roll casting