Microstructure and mechanical properties of casting Al-3Li-2Mg-1Zn-0.1Zr alloys modified by Sc additions

Highlights: • The Sc doping induced a more than 50% reduction in the grain size and enhanced the grain growth resistance. • Both Al₃(Sc, Zr) and Al₃Sc cores of composite particles can be observed in the Sc-containing alloys. • The coarsening exponent (n⁻¹) of the core-shell precipitates is about 0.11 probably due to the unreached quasi-steady-state. -- Abstract: In the present study, microstructure and mechanical properties of casting Al-3Li-2Mg-1Zn-0.1Zr alloys modified by Sc additions have been investigated. As-aged Al-3Li-2Mg-1Zn-0.2Sc-0.1Zr alloy possesses a desirable comprehensive mechanical performance. The YS, UTS and El reach 253 MPa, 406 MPa and 7.4% respectively. With the addition of Sc, a more than 50% reduction in the grain size was achieved by the promoted heterogeneous nucleation on primary Al₃(Sc, Zr) phases and the grain growth resistance was enhanced by the Zener pinning. After the heat treatment, core-shell composite particles precipitated from the matrix. The shell consists entirely of Al₃Li phases. In contrast, both Al₃(Sc, Zr) and Al₃Sc cores can be observed in the Sc-containing alloys. Increasing the Sc content from 0.1 wt% to 0.2 wt%, the mean radius of cores increases, while the mean width of shells and the number density of particles seem not to be affected. With the passage of ageing time, the coarsening of composite particles occurred, though the dimension of the core remained almost constant. The kinetics follows the KV model and the exponent (n⁻¹) is about 0.11, which is lower than the expected value (0.33) probably due to the unreached quasi-steady-state at the present low temperature.