Effect of cold compression on precipitation and conductivityof an Al–Li–Cu alloy
Transmission electron microscopy has been used to investigate the effect of increasing the degree of deformation applied by cold compression on the ageing kinetics and electrical conductivity response of an Al–Li–Cu alloy containing Mg and Ag. When cold compressed greater than 3%, the increased dislocation density accelerates the widespread precipitation of the T1 phase resulting in an enhanced age hardening response. The lengthening rate of T1 precipitates is also reduced in this cold compressed condition owing to the reduced local solute supersaturation, a result of the widespread precipitation of T1 plates. Cold compression by less than 3% does not increase the age hardening response, and the precipitation of GP zones/θ″ appears to be suppressed. Precipitation of the T1 phase is also not significantly enhanced compared with that of the more than 3% cold compressed conditions. The anomalous decrease in electrical conductivity is associated with the nucleation and growth of the T1 phase. Strain fields around T1 precipitates combined with the increased volume fraction of  T1 are thought to be the cause of the anomalous conductivity behaviour.
Independent and combined roles of trace Mg and Ag additions in properties precipitation process and precipitation kinetics of Al-Cu-Li-(Mg)-(Ag)-Zr-Ti alloys
The independent and combined roles of trace Mg and Ag additions in properties and precipitation of Al–Cu–Li–(Mg)–(Ag)–Zr–Ti alloys were studied. The independent roles of Mg additions are to promote the T1 precipitation, decrease activation energy for the growth of θ′ plates and reduce lengthening rates of T1 and θ′ plates. The independent roles of Ag additions are to retard GP-zone formation, stimulate the T1 precipitation and enhance the lengthening rates of T1 and θ′ plates. The combined additions of Mg and Ag augment and accelerate the nucleation of T1 phases. The potent role of independent Mg additions in promoting the precipitation of θ′ is still effective in the presence of Ag, but it is weakened due to the strong interaction of Mg with Ag. The role of Ag as a stimulus in the lengthening of θ′ plates is diminished in the presence of Mg additions. The growth of T1 is controlled by Cu solute diffusion along dislocations regardless of alloy contents of Mg and Ag. The growth of θ′ plates in the Ag-free alloy is controlled by vacancy-assisted diffusion of Cu.
The effect of slip distribution on the monotonic and cyclic ductility of AlLi binary alloys
Abstract The monotonic and cyclic properties of three AlLi alloys were correlated with the slip behavior. One alloy was a solid solution with short range order, one had a small volume fraction of shearable precipitates, and one had a large volume fraction of shearable precipitates. Both the monotonic and cyclic ductility were controlled by the degree of strain localization which depended on the extent of work softening on the glide plane. When a large volume fraction of precipitates were present, cracks nucleated at grain boundary ledges during tensile tests and propagated either transgranularly or intergranularly along precipitate free zones. The propagation mechanism depended on the aging treatment. Cracks most often nucleated at slip bands during cyclic deformation, and propagated either by the striated growth mechanism or by slip band decohesion; the path contingent on the extent of strain localization.