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Mechanical properties, precipitate microstructures and textures of AA 2195 Al-Cu-Li alloy with different rolling schedules and subsequent artificial ageing heat treatment have been investigated. The highest ultimate tensile strength (UTS) and yield strength (YS) were obtained in a longitudinal direction of the hot-rolled alloy at 280 °C due to a higher number density of the T 1 phase and the increased volume fraction of the textures with rolling textures. In contrast, the second highest UTS and YS in the longitudinal direction and the highest UTS and YS in the transverse direction was clarified in the cold-rolled and hot-rolled alloys at 225 °C. This 'anomalous' anisotropy can be explained not only by a higher number density of the θ' phase within fine and equiaxed recrystallized grains but also by grain boundary precipitates at low-angle grain boundaries. Therefore, textures control was suggested to be a useful method to improve mechanical properties in addition to the conventional precipitation strengthening. • The highest volume fraction of rolling textures was present in hot-rolled at 225 °C. • The highest volume fraction is due to the suppressed formation of recrystalized grains by smaller driving force. • The highest strength in longitudinal of the hot-rolled at 280 °C, but lower in transverse lead 'normal' anisotropy. • The 'normal' anisotropy is explained by the texture because of the larger average Taylor factors in transverse. • The 'anomalous' anisotropy with lower UTS and YS in longitudinal was clarified in the cold- and hot-rolled at 225 °C. [ABSTRACT FROM AUTHOR]

In this paper, the microstructure evolution of the 2195 Al-Li alloy under different isothermal annealing schedules and ramp heating-up heat treatments prior to solution heat treatment and the tensile properties of the aging alloy were investigated. The grain structure characteristics of the aging alloy could be influenced by the change of different heat treatment schedules prior to the solution heat treatment. Meanwhile, the mechanical properties of the aging alloy including strength, heterogeneity, and anisotropy were closely related to the grain structure characteristics. There were evident differences in the mechanical properties of aging samples, attributed to the mutual effect of grain structure evolution and texture change. Annealing at a lower temperature (300–350 °C) resulted in the growth of the grain size and the aspect ratio as well as the decrease of the deformation texture components, related to the decline of the strength and the heterogeneity. While grains refined and the deformation texture components increased as the annealing temperature rose (350–400 °C), the strength along the transverse direction decreased, and the heterogeneity increased. Fibrous and overall texture components significantly strengthened in the grain structure of aging samples treated with the low heating-up rate, resulting in a higher strength in the longitudinal direction. [ABSTRACT FROM AUTHOR]

The fatigue crack propagation (FCP) rates of the Al- x Cu-1.2Li-X (x =4.2, 4.5 wt%) alloys with various heat treatment states were systematically investigated and correlated crack growth mechanism was further elucidated. The finer recrystallized grains and more equivalent slip system numbers provided more beneficial conditions for crack deflection and bifurcation, leading to the decreased FCP rate in short-term natural-aged (ST-T4) MC alloy. Moreover, the crack tips hardly activated the slip system within the adjacent grains when their twist angle differences for four slip surfaces were >10°, and the crack tended to propagate along the grain boundaries. With increasing Cu content of T8-aged alloy, the number density and dimension of T 1 and θ′ precipitates are simultaneously increased, and the strengthening mechanism of T 1 precipitates transformed from shearing to by-passing. Thus, the crack tips required more energy for transgranular propagation, causing the tendency of propagation to the grain boundaries and increased FCP rate in T8-aged HC alloy. However, the high Cu content levels resulted in the preferential precipitation of Guinier-Preston (G.P) zones during T6 aging. The δ′ and θ′ precipitates are increased and the nucleation of by-passed T 1 precipitates is suppressed in T6-aged HC alloy, leading to a significantly decreased FCP rate compared to that of MC alloy. [Display omitted] • The relationship of the twist and tilt angles within the adjacent grains and crack bifurcation and propagation paths was explained. • The effect of texture on FCP behavior was intensively explained by introducing the equivalent slip system number. • The effect of the strengthening mechanism transition and precipitation behavior on the FCP rate was revealed. • The effect of Cu content on FCP rates in Al- x Cu-1.2Li-X alloys with various heat treatment states was firstly studied. [ABSTRACT FROM AUTHOR]

The influences of grain thickness and T 1 precipitate on the strength anisotropy of extruded Al-4.0Cu-1.0Li-0.4Mg-0.4Ag-xZr alloys (x = 0, 0.1, and 0.14 wt%) were investigated. The alloys were subjected to different heat-treatment conditions to obtain distinct grain morphologies adjusted by different Zr content and to induce T 1 precipitate. The results demonstrated that grain morphology, particularly the grain thickness influenced by various Zr content, is the primary factor affecting strength anisotropy under different heat treatment conditions. In solution heat-treated alloys (SHT), reduced grain thickness, extended length of low-angle grain boundaries (LAGBs), and more uniformly distributed dislocations due to increasing Zr content led to a decrease in strength anisotropy. Conversely, in T6-aged alloys, the combined interaction between T 1 precipitate and substructures in thinner grains with more LAGBs may aggravate the degree of strength anisotropy. In addition, the T 1 precipitate further amplified the anisotropy induced by the Brass texture component also increasing strength anisotropy. The findings highlight the significance of grain thickness, LAGBs length, dislocation distribution, and the interaction between T 1 precipitate and these factors in influencing the strength anisotropy of Al-Li alloys. Moreover, after solution heat treatment, adding 0.1 wt% Zr in the alloy reinforced the intensity of β-fiber texture while adding 0.14 wt% Zr wakened the β-fiber texture intensity due to the particle-simulated recrystallization process. • Effects of grain thickness and T 1 precipitate on the strength anisotropy of extruded Al-Cu-Li-xZr alloys were discussed. • Mechanism of gran thickness on the strength anisotropy of solution heat-treated alloys was revealed. • Combined effect of grain thickness and T 1 precipitate on the strength anisotropy of T6-aged alloys was discussed. [ABSTRACT FROM AUTHOR]

The microstructure-mechanical properties connection and strengthening contribution of Al- x Cu-1.3Li-X (x = 3.8, 4.2, 4.5 wt%) alloy sheets subjected to various heat treatments were systematically investigated. After solid-solution treatment, the decreased schmid factor value was the main factor for higher strength of Alloy-3 (4.5 wt% Cu). The number density and diameter of T 1 precipitates simultaneously increased with rising the Cu content during T8 aging, leading to the highest strength (655.4 MPa) of T8-aged Alloy-3. However, the high Cu content level resulted in the preferential precipitation of Guinier-Preston (G.P) zones during T6 aging at 165 °C. The θ' precipitates were therefore significantly increased and the nucleation of T 1 precipitates was suppressed in T6-aged Alloy-3, causing the reduced strength compared to that of T6-aged Alloy-2 (4.2 wt% Cu). Furthermore, the experimental yield strength was successfully predicted by invoking the modified precipitate strengthening model, in which the θ' precipitate-dislocation interaction was by-passing mechanism, whereas the shearable and by-passed T 1 precipitates coexisted for all alloys. The strengthening transition from by-passing to shearing occurred in T 1 precipitates with a thickness <1.9 nm or diameter <65 nm, and was particularly associated with the decrease in thickness of T 1 precipitates. • The precipitation strengthening model was modified, and the yield strength and separated precipitate strengthening contribution were successfully predicted. • The connection between the T 1 precipitates strengthening mechanism transition and detailed morphological parameters was firstly revealed in Al- x Cu-1.3Li-X alloys. • The contributions to yield strength from solid solution strengthening, grain boundary strengthening and texture were calculated. • The variation of strength sequence in Al- x Cu-1.3Li-X alloys with various heat treatments was explained in detail. [ABSTRACT FROM AUTHOR]

The effects of Zr addition on microstructure evolution and mechanical properties of extruded Al-Cu-Li-Mn alloy were investigated during heat treatment processing. The recrystallization and grain growth were profoundly inhibited in solid solution-treated (SST) Al-Cu-Li-Mn-Zr alloy (Zr-containing), and massive substructures were retained, which were attributed to the higher Zener pinning pressure provided by Al 3 Zr dispersoids. But, complete recrystallization and considerable grain growth occurred in SST Al-Cu-Li-Mn alloy (Zr-free). Besides, the deformation textures containing Brass and S components were predominant in Zr-containing alloy, which contributed to a higher average Talyor factor (M) value. The higher strength behavior in SST Zr-containing alloy mainly originated from the extra Al 3 Zr dispersoids apart from the higher M value and dislocation density. The higher dislocation density and Al 3 Zr dispersoids in Zr-containing alloy promoted the precipitation of T1 phases and narrowed the width of precipitate-free zones (PFZs). Compared with Zr-free alloy, the enhanced combination of good strength and ductility shown in T6-aged Zr-containing alloy was mostly due to the higher T1 phase density and M value, higher dislocation density, and extra Al 3 Zr dispersoids. • Effects of Zr addition on microstructures and mechanical properties of extruded Al-Cu-Li-Mn alloy were discussed in depth. • The influence mechanism of dispersoids on the recrystallization behavior of extruded Al-Cu-Li-Mn-xZr alloys was revealed. • The strength improvement of Zr-containing alloy under different heat-treatment conditions was confirmed. • The higher strength behavior of Zr-containing alloy has been discussed through different strengthening mechanisms. [ABSTRACT FROM AUTHOR]