All industrial unrecrystallized AI-Li-X alloys exhibit a strong tendency to intergranular failure leading to a slaty fracture of the specimens, associating transgranular shear and intergranular delamination in L-LT planes. The level of alkali impurities measured in industrial metal quality cannot explain this fracture behaviour. In the opposite, the studies conducted on bending specimens indicate that the slip heterogeneity within the grains induce the delamination through a severe and detrimental shear localization at grain boundaries. This behaviour is stifl possible in strongly aged tempers because of the heterogeneity of the precipitation. In order to avoid or reduce the stress localization at grain boundaries, increasing the homogeneity of deformation has become the guideline for the metallurgy of industrial AI-Li-X alloys, illustrated by the following three examples.An efficient means to reduce or even suppress slatiness consists in underageing alloys like 2091 or CP 276 which offer a high potential of matrix coprealpitation. These underqged tempers maximize short transverse properties as well as the resistance against exfoliation corrosion. In addition, toughness and crack growth resistance reach higher levels.
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