On the microstructural characteristics and mechanical properties of Al-2Li-2Cu-0.5 Mg alloy: the role of Yb additions

Potential industrial applications of high-performance cast Al-Li-Cu-(Mg) alloys micro-alloyed with Sc have been strongly limited due to the extremely high production cost and scarcity of Sc. This work aimed at evaluating the effect of substituting Yb for Sc on the microstructure characteristics, age-hardening response and mechanical performances of cast Al-2Li-2Cu-0.5 Mg-0.2Zr alloy. Varied Yb additions were tried (0%, 0.1wt%, 0.2wt%) and results indicated that no appreciable grain refinement was achieved in alloys modified with Yb, accompanied with the absence of coarse primary phases. Dissolution of Cu-rich secondary phases during solution treatment was markedly retarded as the Yb addition increased to 0.2wt%. Nucleation of Al3Li on Al-3(Yb, Zr) led to the significant reduction in the strain energy change (Delta G(S)) and interfacial energy. The addition of 0.1wt% Yb resulted in the accelerated age-hardening response and promoted precipitation of L1(2)-structured nanometric core-shell Al3Li/Al-3(Yb, Zr) precipitates, which acted as preferential nucleation sites for T-1 and S ' phases. As a result, a better mechanical characteristics and microstructural stability was obtained in alloy with 0.1Yb addition compared with the base alloy. Moreover, as compared to the Sc-modified alloy, a small reduction in mechanical properties was achieved in 0.1Yb alloy accompanied with significant reduction in production cost, revealing the feasibility of substituting Yb for Sc.

Automated summary

This study evaluated the effects of substituting Yb for Sc on the microstructure characteristics, age-hardening response, and mechanical performances of cast Al-2Li-2Cu-0.5 Mg-0.2Zr alloy. The results showed that the addition of 0.1wt% Yb accelerated the age-hardening response and promoted the precipitation of nanometric core-shell Al3Li/Al-3(Yb, Zr) precipitates, resulting in improved mechanical characteristics and microstructural stability compared to the base alloy.