High ductility in solution-treated Mg-Sc-Yb-Mn-Zr alloy mediated bydislocations

Due to their unique crystal structure, preparation of high-ductility Mg alloys is still a great challenge, especially high-ductility as-cast or heat-treated Mg alloys. Here, the effect of Sc on the microstructure, second phases, and mechanical properties of as-cast and heat-treated Mg-xSc-3Yb-1Mn-0.5Zr (x = 2, 3, 4, 6 wt%) alloys was investigated systematically. The results indicated that as-cast samples mainly consisted of α-Mg, MgSc, Mg2Yb, Mn2Zr and Mn2Sc phases. Moreover, the average grain sizes of all alloys clearly decreased with the addition of Sc. After solid-solution treatment at 525 °C for 12 h, the tensile elongation (El.) of Mg-xSc-3Yb-1Mn-0.5Zr (x = 2, 3, 4, 6 wt%) alloys improved and the 6 wt% Sc-containing solution-treated sample demonstrated the maximum El. of 28%. Examination of high-ductility solution-treated alloy microstructure revealed that dislocation slip was the primary deformation mechanism during tensile testing. In particular, the high ductility was primarily associated with the activation of profusedislocations, which can significantly accommodate c-axis strain to improve plasticity. Besides, both grain refinement and solid-solution strengthening were also responsible for the large El. of the Mg-6Sc-3Yb-1Mn-0.5Zr alloy. This work can provide useful insights into developing high-ductility Mg alloys using Sc alloying and solution treatment (T4).