Micromechanical modelling of fracture toughness in overaged 7000 alloy forgings

In this article, a multiple micromechanisms-based model that quantitatively relates the plane-strain fracture toughness, KIC, of overaged 7000 alloy forgings to their microstructural attributes, fracture surface morphology and basic tensile properties is developed. To verify the proposed model, extensive microstructural and fractographic analyses along with mechanical tests are carried out using three industrially produced alloys with different contents of Fe and Si impurities. The fracture mechanisms are identified and individual contributions to the overall fracture are quantitatively assessed. The fracture toughness is then calculated using the experimentally obtained average values of relevant mechanical properties, area fractions of main fracture modes and microstructural parameters such as volume fraction of coarse intermetallic (IM) particles, their size and spacing, density of intragranular precipitates, number and width of the precipitate-free zones (PFZ). The proposed model correctly predicts the effect of individual microstructural parameters on the overall fracture behaviour.