JOURNAL OF MATERIALS SCIENCE, vol.30, no.23, pp.5923-5926, 1995 (SCI-Expanded)
The effects of an incoherent and of a semi-coherent dispersoid phase upon the fracture toughness of a 7000-series AlZnMg alloys has been investigated. Standard crack opening displacement tests were successfully applied, the crack propagation being shown to be predominantly intergranular. The presence of manganese bearing incoherent dispersoids lowers the fracture toughness due to their effect of promoting microvoid formation. Retrogression and re-ageing led to a coarsening of the grain-boundary phases, but because the surface-to-surface separation of these particles remained approximately constant, there was no effect of this treatment, at constant yield stress, upon the fracture toughness. The toughness was only enhanced in the system (CZH) where retrogression and re-ageing led to a reduced yield stress.