Control of the mechanical asymmetry in an extruded MN11 alloy by static annealing

An extruded Mg-1 wt pct Mn-1 wt pct Nd (MN11) alloy with a recrystallized microstructure and a weak texture was subjected to different thermal treatments at temperatures ranging from 548 K to 673 K (275 °C to 400 °C) for time intervals between 1 and 45 hours. Room-temperature mechanical tests were carried out in tension and compression at 10^-3 s^-1 in order to investigate the effect of annealing on the mechanical behavior. Microstructural examinations revealed that both the annealing temperature and time have little effect on the grain size and on the texture, which are mainly controlled by the presence of thermally stable Mn-containing particles and by the segregation of Nd to the grain boundaries. However, the composition and distribution of the Nd-containing particles vary significantly for the different annealing conditions. The annealed bars exhibit a subtle change in the tensile and compressive yield stress relative to the as-extruded bar and a somewhat larger mechanical asymmetry. The present results suggest that the Nd-containing phases, as well as Nd solute atoms, play a significant role in the mechanical behavior of the MN11 alloy by changing the relative critical resolved shear stress of the different deformation modes.