| Although Al-Li-X alloys showed initial promise for aerospace applications, implementation has not proceeded swiftly in part due to anisotropic mechanical properties and unusual fracture behavior. In this study, a concerted effort is made to design and develop microstructures with good fracture and fatigue crack growth resistance without sacrificing the high strength of the Al-Cu-Li-Ag-Mg-Zr alloy X2095.; Deformation behavior is predicted by combining slip intensity calculations for shearable precipitates ({dollar}deltaspprime{dollar}) with critical particle size estimates for strong precipitates (T{dollar}sb1{dollar}). The deformation behavior of the various microstructures correlates fairly well with the predictions. T{dollar}sb1{dollar} plates appear to be bypassed by dislocations in X2095 alloys, in contrast to previous results for AA2090. This indicates a significant volume fraction of shearable precipitates may influence the shearability of strong precipitates.; The influence of deformation behavior on fracture and fatigue properties is also addressed. However, in addition to encouraging {dollar}deltaspprime{dollar} precipitation, lower aging temperatures reduced the density of T{dollar}sb1{dollar} plates on subgrain boundaries compared to T8 microstructures. As a result, intersubgranular fracture is suppressed, leading to significant increases in both plane strain fracture toughness and stable crack growth resistance. Since subgrain boundary T{dollar}sb1{dollar}is implicated in environmentally assisted cracking, intrinsic fatigue crack growth resistance also improves in tempers heat treated at lower temperatures.; The short transverse fracture toughness of AA8090 is dramatically improved by double aging treatments. Although failure is due to intergranular separation in most cases, a transition from coarse planar slip to homogeneous deformation occurs after double aging, reducing stress concentrations across the weak, high angle boundaries, increasing fracture toughness. This behavior is attributed to dissolution of the shearable phase ({dollar}deltaspprime{dollar}) and growth of the strong precipitate (S{dollar}spprime{dollar}). A number of tempers with improved strength-toughness relationships were developed. |
