Preparation of nanocrystalline magnesium alloy powders by high-energy ball milling

Nanocrystalline AZ31 magnesium alloy powders were prepared by high-energy ball milling under the protection of argon. The microstructure and powder morphology evolution of the alloy during high-energy ball milling was characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The results showed that, with the increase of the milling time, the grain size of the alloy decreased gradually, while both the micro-strain and the lattice parameters increased correspondingly. During milling, the powders were at first rolled into flakes and agglomerated to form coarse composite powder particles by cold welding, and then, with the further increase of the milling time, these coarse particles gradually broke down into small pieces due to the more and more accumulated strain in the powder material. After milling for 80 h, both the microstructure and the powder morphology of the alloy seemed to be stabilized, and nanocrystalline AZ31 magnesium alloy powders, with grain size of about 85 nm and particle size of 15-20 μm in average respectively, were obtained.