Enhancing strength-ductility synergy in a Mg-Gd-Y-Zr alloy at sub-zero temperatures via high dislocation density and shearable precipitates

The strength-ductility trade-off dilemma is hard to be evaded in high-strength Mg alloys at sub-zero temperatures, especially in the Mg alloys containing a high volume fraction of precipitates. In this paper, we report an enhanced strength-ductility synergy at sub-zero temperatures in an aged Mg-7.37Gd-3.1Y- 0.27Zr alloy. The tensile stress-strain curves at room temperature (RT), -70 & DEG;C and -196 & DEG;C show that the strength increases monotonically with decreasing temperature, but the elongation increases first from RT to -70 & DEG;C then declines from -70 & DEG;C to -196 & DEG;C. After systematic investigation of the microstructure evolutions at different deformation temperatures via synchrotron X-ray diffraction, electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM), it is found that a high dislocation density with sufficient dislocations promotes good tensile ductility at -70 & DEG;C, which is attributed to the minimized critical resolved shear stress (CRSS) ratio of non-basal to basal < a > dislocations. In ad-dition, more shearable precipitates can further improve the ductility via lengthening the mean free path of dislocation glide. The present work demonstrates that an excellent strength-ductility synergy at sub -zero temperatures can be achieved by introducing a high dislocation density and shearable precipitates in high-strength Mg alloys. & COPY; 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.