Improving both strength and ductility of a Mg alloy through a large number of ECAP passes

Ultra-fine-grained (UFG) ZE41A aeronautic magnesium alloy was achieved through multi-pass equal-channel angular pressing (EACP) at 603 K and subsequently tested in tension from room temperature (RT) to 588 K. An extraordinary phenomenon was first observed, improving both ductility and strength of hcp-structured UFG Mg alloy after a large number of ECAP passes. The results demonstrate the pressed ZE41A alloy after 8 passes has higher tensile strength but relatively lower ductility than the unpressed sample from RT to 423 K, whereas the tensile yield strength, ultimate strength, elongation to failure of UFG alloy after enough passes are all remarkably increased (about 120% higher in yield strength and 75% larger in elongation at RT after 32 passes). Multi-pass ECAP provides a simple and effective procedure for grain refinement of hcp-structured Mg alloy at elevated temperature undergoing dynamic recrystallization, while simultaneously improve its strength and ductility at service temperature owing to higher fraction of high-angle grain boundaries and lower intragranular dislocation density, making UFG Mg alloys more attractive in high strength structural applications.