Effect of Gd on preparation of nanocrystalline Mg alloys via cold rotary swaging

The effects of Gd element on the nanocrystallization of Mg alloys during swaging were studied by means of the microhardness test, tensile test, and transmission electron microscopy. The results indicate that it is impossible to achieve nanocrystallization in pure Mg via rotary swaging, which may be attributed to the difficulty of forming dislocation arrays. In contrast, adding Gd alone can achieve a remarkable grain refinement effect after swaging. In the early stage of swaging, twin lamellae are all formed in the pure Mg and Mg−Gd alloys. As the swaging process continues, more non-basal dislocations are formed in the Mg−Gd alloys than in pure Mg. This promotes the formation of dislocation arrays and the resulting nanocrystallization in the Mg−Gd alloys. As the Gd content increases, the refinement effect is obviously enhanced. The critical content for the refinement of the grain size below 100 nm is about 5.4 wt.%.