Improvement of toughness and ductility of a cryomilled Al-Mg alloy via microstructural modification

The effect of annealing treatment on microstructure, fracture toughness, and tensile and compression behavior of a cryomilled Al-7.5 pct Mg alloy was investigated in the present study. Inspection of the mechanical performance reveals that there is a significant effect of annealing on fracture toughness and ductility. After annealing treatment, the value of fracture toughness increases from 8.3 to 17.5 MPa , and the value of ductility increases from 4.4 to 14 pct, while the decrease of strength is slight. The improvement of ductility and toughness is attributed to the existence of lamellar coarsegrain bands that effectively blunt the crack tip and slow propagation. These bands have widths of approximately 500 nm and are parallel to the extrusion direction. They were produced in the microstructure, which has a typical grain size of approximately 260 nm as a result of the annealing at 773 K.