Effect of Sc addition on downstream processing of twin-roll cast Al-Cu-Li-Mg-Zr-based alloys
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 ℃ for 30 min,450 ℃ for 30 min,and 530 ℃ 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.Strengtheningθ'(Al2Cu),T1(Al2CuLi),and rare SS'(Al2CuMg)phases are formed during subsequent artificial aging at 180 ℃.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.
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