A new approach to achieving high strength and ductility of ultrafine grained commercial Al-Mg alloys

Ultrafine grained (UFG) high strength Al-Mg alloys generally suffer from low ductility. This paper proposes a new approach involving extremely short annealing at enhanced temperature followed by small additional deformation to achieve both high ductility (-10 %) and high strength (625 MPa) in high-pressure torsion processed commercial Al-5Mg (wt%) alloy. Extremely short annealing alone at various temperatures leads to either high strength with low ductility or vice versa. Annealing combined with additional deformation changes the dislocation structure of grain boundaries and promotes the formation of a significant fraction (-30 %) of higher grains, allowing for active plastic deformation and enhancing ductility. High strength is due to UFG structure with large fraction of small grains, high dislocation density, as well as with Mg-segregations in grain boundaries, providing additional strengthening by-100 MPa. The resulting combination of strength and ductility significantly exceeds such characteristics achieved to date for similar alloys with UFG structures.