On the form of the age-hardening response in high strength aluminium alloys

The form of the age-hardening response in high strength aluminium alloys has been modelled using appropriate versions of the Orowan equation and precipitation-hardening equations developed for rationally-oriented precipitate plates. When the shape and orientation of precipitates are taken into account. the change in critical resolved shear stress (CRSS) produced following isothermal ageing of the Al-Cu-Li and Al-Cu alloys can be modelled exclusively using equations assuming interfacial strengthening and Orowan hardening. respectively. Combined with direct observations of the interaction between dislocations and the T-1 and theta' precipitates, respectively, in fractured tensile samples, these results suggest that it is not necessary to invoke a transition from predominantly dislocation shearing to Orowan looping to account for the form of the ageing curves of these alloys. (C) 2001 Elsevier Science B.V. All rights reserved.