Effects of the aluminum concentration on twin boundary motion in pre-strained magnesium alloys

We investigated the effects of Al concentration on the reciprocated motion of twin boundaries in pre-strained Mg-Al-Zn alloys through a combination of applied compression and tension, in-situ electron-backscattering diffraction observations, and high-angle annular dark-field scanning transmission electron microscopy observations. The twin growth was restricted by increased Al concentration, which resulted in the occurrence of smaller-sized twins. The reverse motion of twin boundaries was also restricted, resulting in the formation of higher fractions of secondary twins and 2–5° boundaries during reverse tension. The secondary twins and 2–5° boundaries mainly contributed to the increased ultimate tensile strength of the pre-strained Mg alloys. This effect is more significant in Mg alloys with larger pre-compression. Moreover, the increased amount of the Al solute atoms, rather than the precipitates, mainly contributed to the increased strengthening effect on the twin boundary motion. Our research contributes to development of high-strength Mg alloys by stabilizing twin boundaries.