Fracture toughness tests have been carried out on two Al alloys (7075 and 7475) containing different amounts of Fe and Si. These materials were tested in T3, T6 and T7 conditions, along six orientations (LT, LS, TL, TS, SL and ST). Large variations in the fracture toughness (20-60 MPaVm) were measured. Mechanical tests on notched specimens were also performed to determine the influence of stress triaxiality ratio on ductility. These specimens were calculated by finite element method. Quantitative metallography was largely used to measure the volume fraction of intermetallic particles (Mg2Si and Fe-rich precipitates) and llie statistical distribution of these particles. The Qurson potential is used to interpret these test resulls carried out on volume elements and on cracked specimens. It is shown that the ductility of notched specimens and the measured variations in fracture toughness can be interpreted with the Gurson potential provided that the non homogeneous distribution of intermetallic particles is taken into account. A model has been developed to relate the toughness of the alloys to the yield strength, the critical void growth rate calculated on notched specimen from Rice and Tracey equation and to the mean distance between the clusters of second phase particles.
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