The effect of Ti addition on microstructure evolution of AZ61 Mg alloy during mechanical milling

AZ61 Mg and AZ61 Mg with 10 at. %Ti addition (AZ61-10 at. %Ti) were mechanically milled and a comparative study on microstructure evolution was performed. During mechanical milling, Mg grain refining/nanocrystallization and the dissolving of Mg17Al12 precipitates, with the formation of Al supersaturated Mg solid solution, were observed for both materials due to mechanical milling. As analyzed by density dislocation, Ti dispersions hinder the movement of dislocations and grain boundaries and accelerate the dislocation pile-up. Therefore, Ti addition accelerated Mg grain refining, meanwhile, the ultimate Mg grain (43.47 nm) with Ti dispersions was smaller than that (69.19 nm) without Ti dispersions based on X-ray diffraction and transmission electron microscopy results. As the scanning electron microscope and X-ray diffraction exhibiting, the dissolving of Mg17Al12 precipitates was expedited by Ti dispersions and the dissolving of Al in Ti phase was verified by high angle annular dark field. Moreover, during mechanical milling, Ti particulates entranced Mg particles gradually by the welding and cracking effect. After mechanical milling, Ti phase, dispersed in Mg matrix, were smashed to approximately 274.0 nm and Ti supersaturated Mg solid solution was synthesized with the solid solubility being 1.07 at. %.