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In the present work, the effect of Zn on the aging precipitates and mechanical properties of Al-Cu-Li alloys was investigated by Vickers hardness, tensile tests, transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The results indicated that the addition of Zn reduced the activation energy of the T1 phase and makes it easier to precipitate. The activation energy of the T1 phase, which was 107.02 ± 1.8 KJ/mol, 94.33 ± 1.7 KJ/mol, 90.33 ± 1.7 KJ/mol and 90.28 ± 1.6 KJ/mol for 0Zn, 0.4Zn, 0.8Zn and 1.2Zn alloy, respectively. The area number density of the T1 precipitate ranged from 97.0 ± 4.4 pcs/μm2 to 118.2 ± 2.8 pcs/μm2 as the Zn content increased from 0 to 1.2 wt.%. Consequently, the addition of Zn promoted the precipitation of the T1 phase. Therefore, the peak hardness and tensile strength of the alloy also increased with the increase in the Zn content, and the hardness of the alloy with Zn content of 1.2 wt.% increased by 16.5 ± 1.4 HV; meanwhile, the ultimate tensile strength increased by 46.5 ± 2.5 MPa. Therefore, the area number density of precipitates increased and improved the strength of the Zn-containing alloy. [ABSTRACT FROM AUTHOR]

Comparison of the precipitation characteristics of the Al-Cu-Li alloys under different processing states, especially in the presence or absence of thermoplastic deformation, was of little concern in previous studies. In this article, samples of an Al-Cu-Li alloy with different processing states were prepared, then the differences in precipitation behavior of these samples during 200 °C aging were examined, and the internal factors affecting the aging precipitation were also discussed. It was found that the processing states have a significant influence on precipitation dynamics and characteristics for the investigated alloy. The types of peak-aged precipitates and the density, size of the main strengthening phase show a great difference among the assessed states. Further analysis suggested that the integrated effect of dislocation and vacancy may be the internal reason that accounted for the differences in characteristics of precipitates between the cast alloy and the rolled alloy, as well as the different promotional effects of the pre-rolling and pre-stretching on precipitation of the T1 (Al2CuLi) phase. [ABSTRACT FROM AUTHOR]

The effects of double-step homogenization processes on the precipitation of Al3Zr dispersoids and the dissolution of the primary phases of 2196 aluminum alloy were studied by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was revealed that first-step homogenization facilitates the nucleation of Al3Zr, while second-step homogenization results in the dissolution of the primary phases and the growth of Al3Zr dispersoids. The nanosized θ' precipitates formed in the first-step homogenization are dissolved after the second-step homogenization. The optimum homogenization process was selected as 400 °C/10 h + 520 °C/24 h, which effectively dissolves the primary phases and promotes the formation of refined distribution of Al3Zr dispersoids. This phenomenon is mainly caused by the highest nucleation rate of the Al3Zr phase at 400 °C. While reducing the heating rate of the homogenization process can increase the number density of the Al3Zr dispersoids and reduce the precipitate free zone (PFZ), it does not alleviate the inhomogeneity of the Al3Zr precipitation. These results are expected to be meaningful for tailoring the industrial homogenization processing of as-cast Al-Cu-Li alloy. [ABSTRACT FROM AUTHOR]

Aluminum (Al)–copper (Cu)–lithium (Li) alloys are susceptible to environmental degradation, which limits the in-service lifetime of the components. Because of their complex composition, there are seldom studies focusing on corrosion behavior influenced by one single element, which is essential to clarify the corrosion mechanism. Herein, the sole influence of Mg on the corrosion behavior of Al–Cu–Li–xMg alloys was analyzed. Results revealed that the addition of Mg can affect the nucleation and precipitation process of the T1 precipitate, resulting in a difference of potential between grain interior and grain boundary. The precipitation of the T1 precipitate was promoted in a 0.7Mg alloy while impeded in a 1.1Mg alloy, due to the competition of Cu atoms and nucleation sites between T1 and S′. Two types of corrosion behavior of Al–Cu–Li–xMg alloys appeared due to the potential difference and continuity of grain boundaries. Continuous precipitates in grain boundaries and less precipitates within the grain are likely to cause intergranular corrosion (IGC), while more precipitates within the grain will result in pitting. [ABSTRACT FROM AUTHOR]

An optimized homogenization process for Al alloy ingots is key to subsequent material manufacturing, as it largely reduces metallurgical defects, such as segregation and secondary phases. However, studies on their exact microstructural evolution at different homogenization temperatures are scarce, especially for complex systems, such as the 2195 Al-Cu-Li alloy. The present work aims to elucidate the microstructural evolution of the 2195 Al-Cu-Li alloy during homogenization, including the dissolution and precipitation behavior of the TB (Al7Cu4Li) phase and S (Al2CuMg) phase at different homogenization temperatures. The results show that there are Cu segregation zones (Cu-SZ) at the dendrite boundaries with θ (Al2Cu) and S eutectic phases. When the temperature rises from 300 °C to 400 °C, fine TB phases precipitate at the Cu-SZ, and the Mg and Ag in the S phases gradually diffuse into the matrix. Upon further increasing the temperature to 450 °C, TB and θ phases at the grain boundaries are coarsened, and an S-θ phase transition is observed. Finally, at 500 °C, all TB and S phases are dissolved, leaving only θ phases at triangular grain boundaries. This work provides guidance for optimizing the homogenization procedure in 2195 alloys. [ABSTRACT FROM AUTHOR]

In order to reveal the precipitation behavior and strengthening mechanism of extruded 2196 Al-Cu-Li alloy plate during aging treatment, one-step and two-step age-hardening treatment with different temperatures and time were conducted. According to the mechanical property tests and microstructure observation, it was found that the strengthening effect of two-step age-hardening treatment is better than that of one-step aging, and the plasticity of the alloy is also improved. This is because the Guinier–Preston zones precipitated during low-temperature pre-aging can provide nucleation particles for T1 phases in the second-stage aging process, thus promoting the uniform precipitation of fine acicular T1 phases. In addition, the size of θ' phase and grain boundary precipitates in the two-step aged alloy is small, and the width of precipitated free zone is also narrow, which promotes the improvement of mechanical properties of the plate. The optimal two-step age-hardening treatment of 2196 alloy is finally determined as 125 °C×8 h+165 °C×32 h, the yield stress reached 455 MPa, and the fracture mechanism of the corresponding alloy shows a combination of intergranular fracture and cleavage fracture. [ABSTRACT FROM AUTHOR]

This work investigates the impact of Sc and Zr on the precipitation kinetics in an Al-Cu-Li alloy in the absence of pre-stretching. Modern Al-Cu-Li alloys usually require pre-stretching to accelerate the formation kinetics of the T 1 precipitates. A combination of in-situ Small-Angle X-ray Scattering (SAXS) and hardness are used to monitor the precipitation kinetics in an Al-Cu-Li alloy with and without Sc and Zr. The presence of Al 3 (Sc, Zr) dispersoids is found to significantly accelerate the precipitation kinetics. Surprisingly, transmission electron microscopy (TEM) reveals the absence of T 1 precipitates in the peak aged condition and instead reveals that θ ′ precipitates dominate the microstructure. Atom probe tomography (APT) and density functional theory (DFT) calculations reveals that the Al 3 Zr-shell of the dispersoids is a preferred heterogeneous nucleation sites of θ ′ precipitates. Additions of Sc and Zr can hence be a suitable solution to promote precipitation in Al-Cu-Li alloys where the pre-stretching is not applicable. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, particle-reinforced aluminum matrix composites (PRAMCs) of 2055 Al–Cu–Li alloy were prepared with nano-sized TiB 2 +TiC particles, and electron probe microanalyzer (EPMA), differential scanning calorimetry (DSC), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) were used to investigate the recrystallization and aging behavior of 2055 + TiB 2 +TiC alloy. The relationship between TiB 2 +TiC nanoparticles and the T 1 strengthening phase during aging was investigated, and the promotion effect of nanoparticles on the T 1 phase during aging was explained by the stored energy and mismatch in the coefficient of thermal expansion (CTE). The grain size of as-cast 2055, 0.5, and 1.0 alloys were 112 μm, 87 μm, and 68 μm, respectively. The TiB 2 +TiC nanoparticles were found to hinder the development of α-Al dendrites in solidification and refine the grains. The recrystallization behavior during solid solution treatment was mainly a particle stimulated nucleation (PSN) mechanism, and TiB 2 +TiC nanoparticles enhanced the recrystallization resistance. The number density of T 1 phase in the pre-deformed 2055 + TiB 2 +TiC alloy was 452 ± 12/μm−2 with an average size of 73 ± 3 nm, which was finer than 2055 alloy, resulting from the retention of more dislocations or CTE effects at the TiB 2 or TiC interface in the deformed 0.5 or 1.0 alloy. These factors cause Cu atoms to aggregate and provide favorable conditions for T 1 phase precipitation. Compared with 2055, the ultimate tensile strength of the 0.5 sample was increased from 424 MPa to 455 MPa under condition A and from 498 MPa to 550 MPa after pre-deformation. This study can be used as a reference for improving the mechanical properties of Al–Li alloys. • Al–Li alloy refinement by co-addition of TiC and TiB 2. • The addition of TiC and TiB 2 improves the recrystallization resistance. • TiC and TiB 2 particles promotes T 1 phase precipitation during the aging process. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of Al-Cu-Li alloy was studied under plane strain compression in the temperature range of 400–500 °C and strain rate of 0.01–10 s − 1 . The related microstructure was studied by optical microscopy, electron back-scattered diffraction and transmission electron microscope. The results showed that the stress decreased significantly with the increase of temperature and decrease of strain rate. However, stress increase was found after peak stress at strain rate of 0.01 s − 1 and deformation temperature 440–500 °C. Constitutive equation based on the hyperbolic sine equation was established and the apparent activation energy of plane strain compression was estimated to be 226.7 KJ/mol. Precipitates decreased and finally disappeared with decreasing Z value, having an impact on the softening mechanism. Plate-shaped particles and precipitate zones restrained the proceeding of dynamic recovery but increased store energy for discontinuous dynamically recrystallization nuclei. Therefore, recrystallization nuclei more obviously occurred in the sample with higher ln Z value than the one with lower ln Z value at close ln Z value. The microstructure of all deformed specimens was composed of elongated grains and new quasi-equiaxed grains. However, the basic deformation mechanism was dynamic recovery. The mechanism of recrystallization nuclei transformed discontinuous dynamic recrystallization into continuous dynamic recrystallization with the decreasing Z values. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy, differential scanning calorimetry and hardness tests have been performed on an in - situ TiB 2 /Al-3.3Cu-1.0Li-0.60Mg-0.40Ag-0.14Zr-0.13Si composite to study its aging behavior at 175 °C. A cubic phase suspected to be the σ (Al 5 Cu 6 Mg 2 ) phase or its variant is precipitated at all aging stages studied, and this phase is not typically observed in the Al-Cu-Li alloys. The primary hardening (aging for 3 h) phases consist of δ′ (Al 3 Li), β′ (Al 3 Zr) and the cubic phase. After aging for 18 h, all precipitates including T 1 (Al 2 CuLi), S (Al 2 CuMg), θ′ (Al 2 Cu), δ′, β′ and the cubic phase have appeared, and the formation of T 1 and S results in a rapid increase in hardness. With prolonging of aging time, the apparent coarsening of T 1 and S results in a decline in hardness. [ABSTRACT FROM AUTHOR]

The intergranular corrosion (IGC) sensitivity of an Al-3.81Cu-1.28Li-X alloy with T6 aging for different time at 150, 175, and 200 °C was investigated. With aging, the alloy potential lowers due to precipitation, accompanied with coarsening and discontinuous distribution of grain boundary precipitates, which contributes to corrosion evolution with aging time. Corrosion mode evolution with aging stage (corresponding to hardness evolution) at aging temperature of 150 and 175 °C follows the following order: pitting and local IGC (early aging), general IGC (under-aged), local IGC with pitting (near peak-aged), and pitting (over-aged). At elevated aging temperature of 200 °C, the corrosion mode evolves much faster. IGC only appears in the intensively under-aged stage, but the later under-, peak-, and over-aged stage are featured with pitting corrosion. As IGC occurs, its depth is initially increased and then decreased with aging time. [ABSTRACT FROM AUTHOR]

Pre-strain deformation before artificial aging is preferred for fabricating high-performance Al-Cu-Li alloy plates. The precipitation and mechanical properties of rapidly solidified Al-Cu-Li alloy as a function of pre-rolling deformation from 4% to 20% were investigated. The increase in pre-rolling deformation leads to higher dislocation density, which provides more nucleation sites for the T 1 phase. As a result, higher density and finer diameter of the T 1 phase in grains and mitigated enrichment of T 1 phase at the subgrain boundaries were obtained. Meanwhile, more T 1 phase consumes more Cu atoms, thus suppressing the precipitation of θ' phase. Due to strain hardening and precipitation strengthening, the yield strength of alloy increases with the pre-rolling deformation, reaches a maximum value of 641.6 MPa after 20% pre-rolling. The strength model shows that increasing the pre-rolling deformation leads to a decrease in the strengthening contribution of the T 1 phase, which results from the failure of the dislocation bypass mechanism. While the increase in yield strength is attributed to larger strain hardening from high levels of pre-rolling deformation. • Precipitation behavior and mechanical properties of rapidly solidified and pre-rolled Al-Cu-Li alloy were studied. • Pre-rolling deformation reduced the diameter of T1 platelets and increased the number density of T1 phase. • Contribution of the precipitation strengthening to yield strength decreased with increasing pre-rolling deformation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The dominant recrystallization mechanism gradually changed from DDRX to CDRX/GDRX with increasing temperature, decreasing strain rate and solid solubility of the alloy. • A lamellar grain nucleated was discovered in the 〈1 1 0〉 fiber during the R-cube transformation to copper, and its growth induced the GDRX. • Precipitation only affected the volume fraction of recrystallization and did not alter the recrystallization mechanism. • The coupling effect of DPN and solution strengthening in as-soluted alloys exhibited strong recrystallization resistance. Dynamic recrystallization (DRX) is one of the more convenient and effective means of refining grains during hot deformation, which is closely related to the precipitation behavior. Three alloys with varying pre-precipitations are designed by carrying out different heat treatment processes to explore the effects of precipitation on the recrystallization behavior of an Al–Cu–Li alloy during compression. It is indicated that the recrystallization behavior of the as-extruded alloy is quite sensitive to the precipitation. Precipitation does not change the recrystallization mechanism, but it could significantly affect the recrystallization volume fraction (V DRX). Meanwhile, the diverse extruded texture fibers coordinate deformation through different softening mechanisms during compression, which stimulates the nucleation of the lamellar grain in R–cube textures. Furthermore, the influence mechanism of microstructure on the material flow behavior is also discussed for the three heat-treated alloys. Therefore, this work is expected to provide new insights for Al–Cu–Li alloy to design high-performance products through grain refinement and texture modification in the subsequent processing. [ABSTRACT FROM AUTHOR]

This paper presents a systematic study where the distribution of precipitate microstructures is mapped in the cross-section of a friction stir weld made with an AA2050 Al–Cu–Li alloy in the naturally aged temper, as well as the evolution of this microstructure during subsequent post-welding heat treatment (PWHT). This study is carried out using spatially resolved small-angle X-ray scattering, supported by transmission electron microscopy, differential scanning calorimetry and microhardness mapping. The as-welded microstructure is dominated by solute clusters, while very little precipitation has taken place during the welding operation. During PWHT, the precipitation kinetics in the different zones of the weld is mainly controlled by the local dislocation density inherited from welding, and by the amount of solute available for precipitation, which depends on the volume fraction of welding-induced intermetallics. Pre-deforming the weld before the PWHT results in a very effective strength recovery and a nearly homogeneous distribution of hardness. [ABSTRACT FROM AUTHOR]

The effects of different ageing treatments on microstructure evolution, properties and fracture are investigated in the present study. 2198 alloy exhibits strong ageing response during ageing. It is found that tensile properties, hardness and conductivity of 2198 alloy are very sensitive to ageing temperatures, which corresponds to different microstructures. In the naturally-aged condition (T3), only &#948' (Al3Li) was detected. After artificial ageing (T8), large amounts of precipitates emerged and major precipitates that were detected turned to be &#948', θ' (Al2Cu) and T1 (Al2CuLi) phase. Exposure to higher temperature caused greater amounts of the precipitation. The constitution and morphology of precipitates varies with different ageing temperature; the major precipitates are &#948', θ' when ageing below 160 °C, while above 160 °C, T1 phase comes out in large numbers, becoming dominate strengthening phases gradually. Fracture transforms from a typical dimple type to a dimple-intergranular mixed type with the rise of ageing temperature. [ABSTRACT FROM AUTHOR]

Abstract: Yield strength of an Al–3.7Cu–1.5Li–0.50Zn–0.37Mg–0.30Mn–0.14Zr alloy aged at 165°C has been examined as a function of time. Phases existing in this alloy were identified by selected area electron diffraction analysis. Microstructure evolution was examined by transmission electron microscopy (TEM). The peak-ageing time determined is 50h with yield strength of 453MPa. Beside commonly distributed precipitates T 1, δ′ and θ′, σ phase has been observed too. This is the first experimental evidence for the existence of σ in Al–Cu–Li alloys. The strength of the alloy increases rapidly during the first 24h of ageing due to the combinative hardening effect of T 1, θ′, θ″, δ′ and σ. Additional strengthening was obtained for further ageing up to 50h due to evolution of T 1 and θ′ plates. Finally, coarsening led to strength decrease at prolonged ageing process. [Copyright &y& Elsevier]

Abstract: The precipitations of Al–3.5Cu–0.7Li alloy aging at 175°C were studied by HREM and 3DAP. A new cubic phase precipitate has been discovered as the dominant phase, which is assumed having a cubic structure with a ≈0.83nm and the orientation relationship with the matrix is: (001)p//(001)α, [010]p//[010]α. Considering the good match of observed and simulated HREM images, we suggest that the studied cubic phase is a variant of Al5Cu6Mg2 with Li substituting the Mg positions. [Copyright &y& Elsevier]