The effects of ageing time and temperature on the mechanical properties and microstructure of a Duralumin-type alloy have been studied. It is shown that Kc values have an inverse relationship with proof stress values and minimum Kc values were obtained from peak aged specimens. Fractographic examination revealed that fracture changed from a transgranular to an intergranular mode with increasing ageing time. The intergranular fracture was associated with grain-boundary precipitation in overaged specimens. Some observations regarding the role of inclusions on the fracture behaviour of the material are discussed.
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