Nanocrystallization and strengthening of Mg-Dy-Zr alloys by room temperature rotary swaging

In this study, bulk Mg-Dy-Zr alloys with an average grain size of 78.8 nm and a diameter of 12.1 mm were prepared by room temperature rotary swaging (RTRS). The evolution of the microstructure and texture during the grain refinement process was investigated using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that the original texture consisting of arbitrarily oriented recrystallized grains and ED∥[10 0] deformed grains is transformed into an ED∥[10 0] texture after the alloy processed by RTRS. The formation of nanograins is induced by a large number of tensile twins, deformation bands, and dislocation arrays synergistically adapting to the strain. The yield strength and ultimate tensile strength of the nanograin alloys obtained are substantially increased to 281% and 190% of those of the as-extruded alloys. The strength improvement of the alloys is a result of the combined effect of grain refinement and dislocation strengthening, in which nanograin strengthening dominates.