High ductility in solution-treated Mg-Sc-Yb-Mn-Zr alloy mediated by < c plus a > dislocations

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 alpha-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 degrees 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 profuse < c + a > dislocations, 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). (c) 2021 Published by Elsevier B.V.