The influence of iron content on the plane strain fracture behaviour of AA 5754 Al–Mg sheet alloys

The effects of impurity iron content and a change from uniaxial to plane strain tension on AA 5754 Al-Mg sheet alloys were investigated. This was done by studying the fracture evolution in each case. These alloys do not exhibit the progressive damage accumulation often found in ductile commercial metals, because of a relatively low second-phase iron intermetallic volume fraction and a propensity for shear localization at large plastic strains. Necking strains and the strains at which intense shear localization occurred were not influenced by iron content. Once void nucleation has occurred, an increase in iron content causes a reduction in the strain necessary to attain failure. In addition, an increase in iron content also changes the fracture mode from double cup fracture to void sheet fracture. A change from uniaxial to plane strain tension reduces the strain to fracture and creates conditions for shear localization to occur more readily. Finally, the negative strain rate sensitivity exhibited at room temperature further increases the tendency toward shear localization. (C) 2002 Elsevier Science B.V. All rights reserved.