A novel strategy for preparing gradient grained Mg alloy by normal extrusion process

A novel strategy for fabricating gradient-grained Mg alloys, consisting of equiaxed ultrafine grains (UFG) and bimodal grains, has been developed through normal extrusion processing of the Mg-Mn binary alloy. The gradient-grained structure was created by a gradient strain field from a stepped structure in extrusion die. The gradient strain leads to the foundation for subsequent gradient grain nucleation and also prompts the occurrence of dynamic precipitates at the low angle grain boundaries, which is also distributed in a gradient manner and plays a vital role in impeding grain boundary migration. By combining gradient nucleation and pinning effect, a gradient microstructure is successfully achieved in the Mg-2.0Mn binary alloy using the normal extrusion process. The Mg-2.0Mn alloy with a gradient-grain structure, exhibits exceptional mechanical strength and ductility. The presence of the gradient structure effectively enhances the work-hardening rate, attributed to the synergistic effect of the ultrafine and bimodal grains.