FRACTURE OF 8090 AL-LI PLATE .1. SHORT TRANSVERSE FRACTURE-TOUGHNESS

Low density Al-Li alloys are attractive replacements for conventional aluminium alloys but can have a low resistance to intergranular fracture under overload and creep conditions. The effects of aging treatments and testing temperature on the short transverse fracture toughness of Al-Li-Cu-Mg-Zr 8090 alloy plate are reported in this paper (Part I). Studies of creep crack growth are reported in a companion paper (Part II). In Part I, double-aging treatments which substantially increase the toughness with only a small loss of strength are described in particular. Observations made using a variety of metallographic and fractographic techniques, consideration of the effects of temperature on toughness, and determination of the activation energy for re-embrittlement of toughened material by subsequent aging suggest that toughness is mainly determined by the extent of segregation of lithium at grain boundaries. The area fraction of grain boundary precipitates and the extent of strain localization in precipitate-free zones at grain boundaries are also significant factors.