Strain rate sensitivity and fracture behavior of severely deformed Al–Mn alloy sheets

Wrought sheets of an Al–Mn alloy are subjected to severe plastic deformation using constrained groove pressing (CGP) method. After applying CGP passes on the sheets, tensile tests at different strain rates are carried out and the strain rate sensitivity values are calculated. Results show that strain rate sensitivity is increased from 0.0081 in annealed sheets to 0.019 after three passes of constrained groove pressing. This arises from intrinsic decrease in grain size due to severe straining. Experimental results reveal that after three CGP passes, the rate of increasing in strain rate sensitivity is decreased. Fracture surfaces of the tensile samples are observed using scanning electron microscopy. It is found that with increasing pass number, shear fracture angle is increased from 45° for annealed sample to 60° after three passes of CGP. This is due to the change in the mechanism of fracture from tensile fracture to shear fracture which is detectable from the formation of parabolic dimple instead of hemispherical equiaxed ones.