On the role of microstructure in governing fracture behavior of an aluminum-copper-lithium alloy

The influence of precipitate microstructure on fracture mechanisms is studied in a recently developed Al-Cu-Li alloy, AA2198. The intra-granular and inter-granular microstructures are varied independently by changing the quench rate from the solution heat treatment, the amount of pre-stretching and the heat treatment time. Fracture toughness is evaluated by short bar chevron tear tests that make possible to evidence clearly the mechanisms of inter-granular fracture. It is shown that intergranular ductile fracture significantly occurs in all conditions of heat treatment where substantial precipitation has taken place. This mechanism is mainly controlled by the state of inter-granular precipitation and plays a major role to determine the value of transverse fracture toughness, while the strength and ductility of the alloy are mainly controlled by the state of intra-granular precipitation.