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Friction stirred materials have unavoidable heterogeneity in the processed microstructure, which is more severe in the transverse direction of the run and deteriorates structural strength. Effect of post friction stir pre-stretching and aging on this microstructural heterogeneity in an Al-Cu-Li alloy sheet is investigated using highly resolved local tensile behaviour. Local stress-strain curves, at 1 mm spacing were obtained using transverse tensile tests accompanied by a continuous strain measurement using digital image correlation and the hybrid model was used for strain hardening analysis. Local mechanical and strain hardening behaviour is correlated with microstructural information obtained from transmission electron microscopy and differential scanning calorimetry. Aging with and without pre-stretch, both effectively increased the global strength, but the aging response was heterogeneous in all the cases due to variation in solute content and the strain hardening ability within the processed region. Direct aging enhanced the microstructural heterogeneity and led to strain localization, while strain hardening during pre-stretch contributed more strength to the weaker regions, enhanced T1 precipitation and thus effectively reduced the strength heterogeneity. This study provides insight into detailed mechanical behaviour information within a friction stir processed material which can be applied to strengthen structures produced with friction stir technology. • Aging response of friction stirred Al-Cu-Li sheet improves with pre-stretch. • Precipitate phases are pre-stretch sensitive and control flow heterogeneity. • The aging response is limited by the local solute availability. • Dislocation accumulation during pre-stretch strengthens weaker regions. [ABSTRACT FROM AUTHOR]

The hexagonal T 1 (Al 2 CuLi) phase is the main strengthening precipitate in Al-Cu-Li alloys and is usually considered to be formed heterogeneously at dislocations during artificial aging. The precipitation scenario in Al-Cu-Li-Mg alloy has been revisited using high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and in-situ heating inside TEM. Octahedral nano-complexes consisting of T 1 precursors (T 1p) on {111} facets of early-precipitated δ'(Al 3 Li) particles form at under-aging stage in the investigated alloy. This nano-complex with an average diameter of 5–10 nm is a transitional structure, which gradually dissolve to facilitate the transformation of a small portion of large precursors toward T 1 precipitates. The T 1p is determined to be isostructural to orthorhombic Ω phase based on atomic-resolution HAADF-STEM observations. The subsequent inward diffusion of Li is believed to promote the transition from Ω-like T 1p to T 1. An alternative precipitation path toward the key hardening T 1 precipitate is thus proposed and could explain the formation of T 1 precipitates apart from those at the dislocations. Our findings suggest complex multiple precipitation pathways for T 1 phase should exist in Al-Cu-Li alloys. • A new precipitation path toward the key hardening T 1 precipitate is proposed. • Octahedral nano-complexes formed by T 1 precursors on δ'(Al 3 Li) particles are observed. • The T 1 precursor is isostructural to orthorhombic Ω phase. • The inward diffusion of Li is believed to promote the transition from Ω-like T 1p to T 1. • Multiple precipitation pathways for T 1 phase should exist in Al-Cu-Li alloys. [ABSTRACT FROM AUTHOR]

An improved thermomechanical treatment (N-ITMT) containing electrically-assisted recrystallization annealing (EARA) was proposed for manufacturing fine-grained Al-Cu-Li alloys, based on overaging, cold asymmetric rolling and EARA. The corresponding microstructure evolution and mechanical properties were investigated. The coarse precipitates introduced by overaging changed the deformed microstructure, produced particle affected zones and weakened the shear band (SB) compared with that with no precipitates. The combined action of electric current and coarse precipitates completed the recrystallization within 5 s and the solution process within 180 s, refined the grain size, and improved the strength and ductility. Discontinuous static recrystallization (dSRX) and continuous static recrystallization (cSRX) were both considered recrystallization mechanisms for specimens with or without coarse precipitates. The dSRX for specimens with coarse precipitates mainly featured particle-stimulated nucleation (PSN), while it featured shear band nucleation for specimens with no precipitates. The athermal effect of electric current not only decreased the activation energy, increasing the nucleation rate during dSRX, but also accelerated the diffusion of atoms and vacancies, promoting recrystallization and solution treatment. The proposed N-ITMT containing EARA possesses the synergetic capacity of optimizing the microstructure and improving the strength and ductility of Al-Cu-Li alloys. [Display omitted] • EARA accomplished rapidly grain refinement, solution and texture weakening. • The joint improvement of strength and ductility of the Al-Cu-Li alloy was achieved. • The recrystallization mechanism of specimen with coarse particles was dSRX by PSN and cSRX. • Athermal effect reduced the activation energy and improved the diffusion of atoms. [ABSTRACT FROM AUTHOR]

The 2195 Al-Cu-Li alloy is widely utilized in the aerospace industry due to its lightweight nature and high strength. Consequently, gaining a comprehensive understanding of techniques to enhance its microstructural and mechanical properties is crucial for the consistent production of reliable and high-strength aerospace components. In this investigation, a pristine 2195 industrial ingot was subject to three distinct forging pretreatments: PT1, which involved a direct three upsetting and three stretching (3U3S) process; PT2, which combined double stage homogenization (DH) with 3U3S; and PT3, which involved DH along with six upsetting and six stretching (6U6S). Subsequent warm deformation and T8 aging treatment were applied to the pretreated forgings. The microstructure evolution during the processes and the final mechanical properties in three orthogonal dimensions were examined. The findings revealed that the combination of DH and multi-dimensional forging (MDF) facilitated the dissolution of non-equilibrium phases to a greater extent. Consequently, the main strengthening phase transformed from the T 1 + δ' phase observed in PT1 to the denser T1 + little θ' phase observed in PT2 and PT3 after T8 aging treatment. Notably, the tensile strength and yield strength of PT2 and PT3 specimens increased by 20–30 MPa in all three directions. Moreover, the MDF process accelerated the recrystallization behavior from PT1 to PT3, resulting in a gradual reduction in the average grain size of the pretreated samples from 356 µm to 186 µm. Following warm forging and T8 aging, the grains exhibited a finer and equiaxed structure. Additionally, the coarse phase was identified as the primary source of transgranular cracking. The coarse phases within the matrix became more homogeneous and finer from PT1 to PT3, with a gradual decrease in their area fraction. On the fracture surfaces, the aggregation of coarse phases diminished. Consequently, the elongation in the z-direction improved, and the elongation anisotropy and standard deviation decreased in all three directions for PT3 specimens. The findings presented in this study provide valuable insights into the high-performance manufacturing of Al-Cu-Li alloys. • The DH and doubling the strain of MDF both promoted the dissolution of non-equilibrium phases. • Combine DH treatment with MDF enhanced the precipitation kinetics of the T 1 phase, increasing the strength by 20–30 MPa. • The coarse phase was the main transgranular cracking sources, which was diminished gradually by the improved process. [ABSTRACT FROM AUTHOR]

In the present work, the shear stress required to move a dislocation through an array of randomly distributed T 1 precipitates (Al 2 CuLi), forest dislocations and solutes was computed using the circle rolling method. The evolution of shear stress as a function of swept area was determined to calculate the shear resistance of T 1 precipitates, forest dislocations and solutes for different ageing conditions. The inputs for the circle rolling simulations, such as the critical breaking angle of the obstacles, were obtained by performing detailed microstructural analysis at different length scales to estimate forest dislocation density, diameter, thickness, and number density of T 1 precipitates. The individual shear resistance of precipitates, dislocations and solutes were suitably superimposed using a flow stress addition law, where the superposition exponent is dependent on the critical breaking angles of the T 1 precipitates, forest dislocations and solutes. The present approach outperforms previous models based on the linear superposition of strengthening components in predicting the yield strength evolution of AA 2195 alloy as a function of pre-strain. • Circle rolling simulations for calculating shear resistance of precipitates, dislocations, and solutes. • Obstacle strength-based superposition of strengthening contributions for flow stress prediction. • Proposed modeling framework outperforms linear superposition-based yield strength models. • Circle rolling method outperforms strength models based on uniform distribution of obstacles on glide plane. [ABSTRACT FROM AUTHOR]

2195 Al-Li alloy billet was prepared by gas atomization (GA) and hot isostatic pressing (HIP), followed by hot extrusion and different heat treatments. Microstructural evolution and mechanical properties of the alloy were investigated. The results show that the HIPed alloy presents a fine microstructure, but with clear powder boundaries and Mg element segregation. Hot extrusion breaks the powder boundary and eliminates the element segregation, thus improving the mechanical properties of the alloy. After solution and aging treatments, a large number of T 1 and θ' phases are precipitated, and the alloy strength is significantly improved. The introduction of pre-deformation before artificial aging produces a high density of fine T 1 phase and suppresses the formation of the σ phase. The T8 specimen exhibits an excellent mechanical property with the ultimate tensile strength of 600 MPa, yield strength of 576 MPa, and elongation of 9%. The improved ductility is ascribed to the narrow precipitate free zone, the discontinuous and small grain boundary phase, and the moderate enrichment of the T 1 phase at the sub-grain boundaries in the alloy. [ABSTRACT FROM AUTHOR]

Abstract The hot compression tests for spray deposited alloy 2195 were performed on Gleeble-1500 thermomechanical simulator at different conditions. The constitutive models and processing map of the alloy were established. The deformation mechanisms at different areas of the processing map were revealed via metallographic and electron backscatter diffraction examinations of the compressed samples. The results showed that dynamic precipitation of Al 2 CuLi phase occurred at low deformation temperatures (400–450 °C). The precipitation caused significant reduction in solution strengthening effect, resulting in rapid decrease of flow stress. The instability domain at low temperature was induced by the decreasing flow stress. Moreover, the stacking faults with the precipitation of Al 2 CuLi caused the discontinuous dynamic recrystallization. The precipitation and recrystallization led to the high dissipation efficiency at low temperature and low strain rate. At high temperatures (500–550 °C), the deformation mechanisms varied with the imposed strain rates. The dynamic recovery and recrystallization occurred at strain rate of 0.1–1 s−1, which led to the high dissipation efficiency. At low strain rate (0.01–0.1 s−1), the alloy exhibited strong dynamic recovery characteristic, which caused the decrease in dissipation efficiency. The deformation instability occurred when the strain rate is about 10 s−1, and intergranular cracking was the main instability mechanism. Graphical abstract Image 1 Highlights • Arrhenius-type constitutive equation of spray deposited 2195 alloy was established. • Processing maps with different strain levels were constructed. • The precipitation of Al 2 CuLi occurred at low temperature, causing many changes. • Strong DRV causes decrease of efficiency η at high temperature and low strain rate. • The available hot working window of the deposited alloy 2195 was obtained. [ABSTRACT FROM AUTHOR]

Effects of creep aging on strength and toughness and microstructure evolution of Al-Cu-Li alloy were investigated by tensile test and Kahn tear test at room temperature, combined with fractograph and transmission microstructure analysis. The specimens of pre-strain creep aging state (CA) have been studied and compared with artificial aging state (AA) and pre-strain artificial aging state (PA). It is demonstrated that pre-strain before artificial aging process can improve the strength property and the fracture toughness of Al-Cu-Li alloy. On top of that, both of them can be further improved by creep aging process: the yield strength was increased by 8.7% and the unit initiation energy of Kahn tear was increased by 11.7%. The increasing of fracture toughness has also been verified by Kahn tear fractographs that the dominating fracture type changes from the ductile intergranular fracture to the ductile transgranular fracture. Transmission electron microscopy revealed that creep aging promotes the nucleation of T 1 phase, resulting in a fine and dense distribution of precipitates in the matrix, and the enrichment of subgrain boundary T 1 precipitates was greatly reduced. [ABSTRACT FROM AUTHOR]

It has been known for decades that dislocation density can significantly affect the precipitation of the strengthening phases for the age-hardening alloys. However, an understanding of the relationship between dislocation morphology and their ageing precipitation is still far limited. Here we study the impacts of especially helical dislocation morphology on the T 1 precipitation of an Al-Cu-Li alloy. We find that this "opened out" helical dislocation line, tailored by pulsed currents, can markedly accelerate T 1 precipitation during ageing of 155 °C. It is also revealed that a new and beneficial dislocation configuration, formed by these heavily deformed helices, can effectively decrease the field size of interacting among T 1 precursors, and the resultant enhancement in nucleation and growth of T 1 phases. This study is the first to propose an innovative method, tailoring helical dislocation morphology, to accelerate ageing precipitation process. [Display omitted] • This study is the first to propose an innovative method to affect ageing precipitation process. • Our findings have shown that such an "opened out" morphology can facilitate T 1 ageing precipitation. • It is revealed that the mechanism of acceleration on nucleation and growth of T 1 phases. [ABSTRACT FROM AUTHOR]

The fatigue crack propagation (FCP) characteristics of two Al-Cu-Li-Mg-Ag alloys were investigated with regard to the grain boundaries (GBs) and crystal orientation. The Sc-added alloy showed much lower FCP rate than the Sc-free alloy at the same values of stress intensity factor range (ΔK). In the Paris stage of ΔK= 20 MPa∙m1/2, FCP rates of Sc-free alloy and Sc-added alloy were 1.52 × 10−3 mm/cycle and 7.65 × 10−4 mm/cycle, respectively. In the Al-Cu-Li alloys, EBSD examinations suggested that Goss, Q, Cube and random orientation grains with large twist angle component boundary could elicited large crack deflection to enhance the crack propagation resistance. Even if the cubic grain with adjacent grain had a great tilt angle boundary, the crack deflection caused by it was still little when the twist angle was small. Additionally, it also showed Sc-added alloy had more tortuous crack propagation path in the Paris stage. Besides, coarse Fe-, Mn-, Sc-, Zr-rich inclusions were detrimental to tensile strength and fatigue fracture, but the finer, globular and dispersive distribution of these particles could meliorate fatigue performances. • The addition of 0.09Sc (wt%) dramatically improved the fatigue crack propagation resistance of Al-Cu-Li alloy sheet. • Due to the influence of grain orientation, cracks tended to propagate along grain boundaries. • The presence of AlCu(Sc, Zr) particles reduced a few proportion of the mechanical properties of the Al-Cu-Li alloy sheet. • The fine, globular and dispersive distribution of Fe-, Mn-, Sc-, Zr-rich inclusions particles could improve fatigue properties. [ABSTRACT FROM AUTHOR]

The formation mechanism of T 1 (Al 2 CuLi) precipitate in an Al-Cu-Li alloy was investigated by using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging, atom probe tomography (APT) and first-principles energy calculations. The HAADF-STEM images reveal the existence of the T 1 precursor phase, which is termed as T 1p in this study. The T 1p phase has a lattice structure identical to the Al matrix, and consists of a stacking of Li-rich and Cu-rich layers along the {111} Al planes. APT analysis further confirms the existence of T 1p phase, in which the concentrations of Li and Cu are significantly lower than those in T 1 plate. Based on the first-principles energy calculations, the structural evolution from T 1p phase to T 1 phase is proved to be energetically favorable. Correspondingly, one possible evolution process from T 1p phase to T 1 phase involving the change of stacking sequence is proposed and discussed. [ABSTRACT FROM AUTHOR]

The 2195 Al-Cu-Li alloy is widely utilized for the fabrication of key aerospace vehicle components; hence, an in-depth understanding of its hot deformation behavior is essential for consistently achieving high-performance products. In this study, isothermal compression tests were performed on 2195 Al-Cu-Li alloy ingots in the temperature and strain rate ranges of 250–500 °C and 10−3-1 s−1, respectively. A processing map was established to predict the workability under different conditions. The corresponding microstructures were examined to reveal their hot deformation mechanism. Results demonstrated that the processing map was divided into four distinct domains. The unstable zone was located in the 250–375 °C/10−1.5-1 s−1 and 250–275 °C/10−2.5–10−1.5 s−1, temperature/strain rate regimes, in which deformation bands and flow localization were observed. The deformation bands blocked dislocations and compromised the dynamic recrystallization (DRX) behavior, hence damaging the microstructure. Further, large coarse T 1 phases precipitated in the 325–410 °C/10−2.5–10−3 s−1 regime, which led to the formation of heterogeneities in the microstructure, corresponding to a minimum workability in the processing map. The optimal hot-working domain for the 2195 alloy was determined to be 460–500 °C/10−3–10−2 s−1, and the dominating hot deformation mechanisms were DRX and dynamic recovery (DRV). Specifically, continuous and discontinuous DRX behaviors dominated in the 300–400 °C/10−3 s−1 and 450–500 °C/10−3 s−1 regimes, respectively. DRX gradually weakened as the strain rate increased at 500 °C. Further, the weakening of DRX was only minimally affected by temperature at 400–500 °C during high-speed deformation (1 s−1). The results reported herein can provide valuable insights into the hot working of Al-Cu–Li alloys. • A processing map (PM) was established to accurately predict the hot deformation behavior of the 2195 alloy. • Deformation bands and flow localization were the main microstructure response in the unstable domain. • Large coarse T 1 phases precipitated in the precipitation sensitive domain, leading to heterogeneity deformation. • The optimal hot working domain was 460–500 °C/10−3–10−2 s−1, which was dominated by DRX and DRV. • Within the 300–400 °C/10−3 s−1 regime, CDRX was the main DRX mechanism, whereas DDRX predominant at 450–500 °C/10−3 s−1. [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]

The quenching expansion tests in the temperature range 350–500 ℃ and isothermal compression tests in the range 350–500 ℃ & 0.01–10 s−1 of a homogenized Al-Cu-Li alloy were conducted to investigate the flow behavior and thermal expansion behavior. The corresponding microstructures of the tested specimens were characterized by back-scattered electron-scanning electron microscope (BSE-SEM), electron back-scattered diffraction (EBSD) and transmission electron microscope (TEM). Coarse secondary phases including Al 2 CuLi (T 1), Al 2 (Cu-Ag)(Li-Mg) (Ω), Al 2 Cu (θ), Al 2 CuMg (S) dissolve with increasing temperature, which is likely to increase the coefficient of thermal expansion. The temperature rising induced by deformation heat varies from 2.29 ℃ to 38.32 ℃ with increasing strain rate and decreasing temperature. Three different constitutive models were calculated, evaluated and optimized, based on which, the two-step optimized Johnson-Cook model showed the highest precision. At the temperature ≤ 400 ℃, the existences of undeformable coarse phases (especially T 1 or Ω phase) promote particle stimulated nucleation (PSN), which pronouncedly increases the volume fraction of dynamic recrystallization (DRX) and decreases the flow stress. At temperature of 450 ℃, most of undeformable coarse phases dissolved, cutting-off mechanism of S and θ phase was observed, which is no longer beneficial to PSN, and CDRX becomes the main DRX mechanism. • Flow behavior and hot expansion behavior of the homogenized Al-Cu-Li alloy were analyzed. • Microstructures before and after compression at high temperature of the homogenized Al-Cu-Li alloy were compared. • A novel two-step optimized Johnson-Cook model with high prediction precision was proposed. • Cut-off mechanism of Al 2 CuMg phase during deformation were identified. • PSN and CDRX were characterized and the effects of precipitates on them were discussed. [ABSTRACT FROM AUTHOR]

The effects of minor Sc additions on the formation of various precipitates and mechanical properties of a new Al-Cu-Li alloy have been experimentally investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), three dimensional atomic probe (3DAP) analysis and tensile tests. Under T8 temper, the introduction of 0.092 wt% Sc accelerates the aging response of Al-Cu-Li alloy and induces a little reduction in the tensile and yield strength due to the decrease of solid solubility of Cu in Al alloy matrix and number density of T 1 (Al 2 CuTi) strengthening phase, which are closely linked with the formation of insoluble Sc-containing W(AlCuSc) phase by consuming Cu solutes for the precipitation of T 1 phase. Except for T 1 and W phase, Nanoscale Al 3 (Sc,Zr) and S′ phases are also found after minor Sc addition. The 3DAP tomography indicates that the Al 3 (Sc,Zr) precipitates have a core-shell structure with Zr atoms mainly close to the shell and Sc atoms enriched in the core. It is believed that such precipitate is only probably composed of Al and Sc at the initial stage, and then Zr enters into them at the later stage, which hinders the diffusion of Sc in the matrix through the boundary into the interior of the particle and thus makes the coarsening rate of Al 3 Sc decrease. • Minor Sc addition accelerates aging response of Al-Cu-Li alloy and induces change in alloy strength and elongation. • W phases inhibit precipitation of T1 phase by consuming the available Cu solutes for T1 phase. • Length range of T1 phase slightly increases and its number density obviously decreases after Sc addition. • Zr aggregation at the interface inhibits the diffusion of Sc from alloy matrix to the precipitate interior. • Zr aggregation also makes coarsening rate of Al3(Sc, Zr) particle decrease. [ABSTRACT FROM AUTHOR]

The Al-Cu-Li alloys with different grain sizes were manufactured through different routes and treated with T34 before the creep aging process. Their creep-aging behaviors at 160 °C under 175 MPa were investigated and their corresponding mechanical properties were tested. Their microstructure was characterized by EBSD and HAADF-STEM. The results show that the total creep strains increase with increasing grain size. The creep strain of specimens with an average grain size of 53.4 µm is twice as that with an average grain size of 12.2 µm. However, their yield and tensile strengths are grain size independent. This appearance could be explained by the large creep strain achieved before the secondary primary creep stage, which is contributed by dislocation motion and increases with increasing grain size. When strengthening precipitates start to nucleate and grow, the creep resistance of dislocations sharply increases and Harper-Dorn creep becomes the main creep mechanism. The alloys with different grain sizes have similar precipitates and substructures in their peak-creep-aged state, leading to their similar yield and tensile strengths at room temperature. • A new thermomechanical treatment was used to fabricate sheets with fine grains. • The creep mechanism of the complex four-stage creep age test in the Al-Cu-Li alloy has been clarified. • Grain refinement was proven to have a negative influence on the total creep strain in this work. • GND densities was used to characterize the distribution evolution of dislocations during creep age test. [ABSTRACT FROM AUTHOR]

• An Al-Cu-Li alloy was rolled at 25 °C, − 100 °C, −190 °C respectively. • Heterogeneous grain structure occurs in samples by cryorolling at − 100 °C. • Sheets by cryorolling at − 100 °C have higher strength and better ductility. • A back stress model was used to explain the highest strength of cryorolled sheets. An Al-Cu-Li alloy was selected as the model material to get insight into the mechanism of deformation strengthening at cryogenic temperatures. The mechanical properties and microstructure evolution of the alloy fabricated by symmetric rolling and asymmetric rolling (the rolling ratio was 1.3) at different temperatures (25 °C, − 100 °C, − 190 °C) were investigated. Smaller grains and denser dislocations were observed in the cryorolled samples, leading to strength enhancement compared to the samples processed at room temperature. The heterogeneous grain structure was made of coarse and fine grains in the samples processed by cryorolling (CR) at − 100 °C, which resulted in higher strength and better ductility than those processed by CR at − 190 °C and room temperature rolling. Finally, a new back stress model was employed to calculate the yield strength of the heterogeneous structure, which could explain the highest strength of samples processed by CR at − 100 °C. [ABSTRACT FROM AUTHOR]

• Corrosion occurs preferentially in non-recrystallized regions. • Subgrain boundaries decorated with T 1 precipitates are preferred sites for corrosion initiation. • Local corrosion susceptibility is strongly correlated to grain stored energy. • Cu-enriched layer is developed at the crevice wall of attacked grain boundaries. In the present study, correlative corrosion testing and electron microscopy, including quasi-in-situ electron microscopy, are employed to investigate the corrosion behaviour of 2A97-T8 Al-Cu-Li alloy extrusion in 3.5 wt% NaCl solution. It is found that the corrosion behaviour of the alloy is influenced by synergetic effect of the plastic deformation introduced by the thermomechanical processing during alloy fabrication and the precipitation of T 1 phase during T8 treatment. Localized corrosion initiates and propagates preferentially within non-recrystallized regions of the partially recrystallized alloy. Corrosion initiated at coarse constituent intermetallic particles is confined to its periphery, which doesn't develop further when the particles are disconnected from alloy matrix. [ABSTRACT FROM AUTHOR]

• The equiaxed zone shows the highest sensitivity to localized corrosion. • Aging treatment decreases the corrosion resistance of the fusion zone. • The weld transforms from intergranular corrosion to pitting corrosion after aging. • Aging strengthens the fusion zone but lowers its ductility. The present work analyzed the effect of aging on the corrosion and mechanical properties of laser beam remelted 2A97 Al-Cu-Li alloy. Electrochemical measurements and immersion tests were performed to study the corrosion behavior. Tensile and microhardness tests were used to investigate the strength, ductility, and hardness of the specimens. We found that the corrosion degree declines dramatically from the edge to center of the fusion zone, and the EQZ is most sensitive to localized corrosion. The corrosion resistance of the fusion zone is lowered by aging treatment. Moreover, the dominant corrosion feature transforms from intergranular corrosion to pitting corrosion by 175 °C of aging. The strength and hardness increase with aging temperature while the ductility declines distinctly. Our work can provide an in-depth understanding of the effect of aging on the corrosion and mechanical behaviors of laser beam remelted Al-Cu-Li alloys. [ABSTRACT FROM AUTHOR]

● A promising method is proposed to attain a sound sheet metal forming/property synergy. ● Creep strain increases by ~27.2% and an increased elongation by ~27.4% induced by electropulsing process. ● An increased creep strain ascribes promoting dislocation motion by electropulse, which first proven by larger dislocations. ● A raised elongation attributes to dissolution of GP zones/θ´precipitates and Cu-rich phases induced by electropulsing. Electrically assisted creep age (ECA) forming of an Al-Cu-Li alloy, when applied electropulsing during the different stages, has been experimentally investigated under the applied stress of 160 MPa at 160 °C for 20 h. Creep strain of the sample assisted by electropulsing when introduced during the initial creep stage increased by ~27.2% comparing with that of conventional creep ageing test (CCA) at the end of 20 h. However, there is almost no effect on creep strain when applied electropulsing at the beginning of 4, 8 and 19 h. Tensile tests indicate that strength of the aged specimens assisted by electropulsing when applied during the different creep stages is almost the same, but a slight reduction in elongation for the ECA specimen when introduced electropulsing during the initial stage and an increase by ~27.4% in elongation of the ECA specimen when introduced electropulsing during the last stage, compared to that of the CCA specimen. The fractograph of aged samples assisted by electropulsing when applied during the various creep stages, was observed to an obvious difference. Transmission electron microscopy (TEM) observations show that applying electropulsing during the early creep stage can accelerate dislocation motion, which for the first time proven by the observed larger dislocation structure, and promote Li solutes diffusion to grain-boundary, which is responsible for an increased creep strain and a decreased elongation, respectively. And dissolution of the Cu-rich at grain-boundary and GPI zone/θ ´ precipitates within the grain, induced by electropulsing when applied during the last creep stage, is considered as the cause of an increased elongation. Thus, applying electropulsing during both the initial and last creep age forming stages is a promising method to control the microstructure to attain a sound sheet metal forming/property synergy. [ABSTRACT FROM AUTHOR]

Abstract: To clarify the corrosion mechanism associated with T1 and T2 precipitates in Al–Cu–Li alloys, the simulated bulk precipitates of T1 and T2 were fabricated through melting and casting, their electrochemical behaviors and coupling behaviors with α(Al) in NaCl solution were investigated. Meanwhile, simulated Al–Cu–Li alloys containing T1 and T2 particles, respectively, were prepared and their corrosion morphologies were observed. A corrosion conversion mechanism associated with the precipitates of T1 and T2 was advanced. The precipitates of T1 and T2 are anodic to the alloy base and corrosion occurs on their surface at the beginning. While, during their corrosion process, the preferential dissolution of Li and the enrichment of noble element Cu make their potential move to a positive direction. As a result, the corroded T1 and T2 precipitates become cathodic to the alloy base at a later stage, leading to the anodic dissolution and corrosion of the alloy base at their adjacent periphery. However, due to more amount of active element Li and much less amount of noble element Cu in the precipitate of T2, the electrode conversion of T2 from anode to cathode is more superficial than that of T1, and the corrosion mainly occurs in T2. [Copyright &y& Elsevier]

Abstract: Based on Thomas–Fermi model, the calculation method of Gibbs free energy for atom cluster with electric field had been found. The change trend of Gibbs free energy of Al–Cu–Li alloy under the effect of electric field had been calculated systemically and quantitatively. And following results had been given: near the zero electric field and the side of positive electric field, the Gibbs free energy of Cu4LiAl7 compound at aging temperature 460K was higher than that of Gibbs free energy at solid solution temperature 725K, but once the negative electric field increased to a certain degree there would be an opposite result. The Gibbs free energy of binary solid solution was increased with the addition of third element lithium or copper, and with the increase of electric field intensity the Gibbs free energy margin of two kinds of solid solution became bigger. [Copyright &y& Elsevier]

• The abnormal grains formed during extrusion were Cube orientated, while that formed in solution treatment were random. • The strain-free Cube orientated grains located at the frontier of different textures have growth advantage in extrusion. • The migration and annihilation of dislocations resulted in abnormal grain growth in solution treatment. • The weld seam had higher thermal stability in solution treatment when formed at higher extrusion temperature and speed. • The matrix area kept fine grainsin extrusion and heattreatment due to the flat grain boundaries and many sub-structures. The porthole die extrusion processes of 2196 Al-Cu-Li alloy were carried out at billet temperatures of 420–510 °C and ram speeds of 0.25–5.0 mm/s, then the extruded profiles were subjected to the solution and aging treatment. Abnormal grain growth (AGG) was observed along longitudinal weld of profiles during the extrusion and solution treatment. The fine equiaxed grains with Copper orientation were formed in the welding area when extruded at low temperature and low extrusion speed, and some Copper orientated grains transformed into recrystallization textures with the increase of deformation temperature. When extruded at high temperature and speed, AGG occurred in the junction area of Copper texture and recrystallization textures, and some strain-free Cube orientated grains in this area transformed into AGG structures due to the high growth-driving force and growth priority. During the solution treatment, the migration and annihilation of dislocations were repeated inside the equiaxed grains of the welding area, resulting in the coalescence of the subgrains and the formation of AGG. The abnormal grains formed during extrusion were mainly Cube orientated, while those occurred during solution treatment were randomly orientated. The weld seam had higher thermal stability during solution treatment if profiles were extruded at higher extrusion temperature and speed. In the matrix area, most of the dislocations migrated along the same direction, and the dislocations were hard to meet and annihilate. Besides, little driving force for grain growth could be provided by the flat grain boundaries of the matrix area. Hence, the Brass orientated grains in the matrix area possessed high thermal stability during the extrusion and solution treatment. The AGG structure led to the intergranular fracture and poor elongation of samples in the tensile test. [ABSTRACT FROM AUTHOR]

The mechanical properties and microstructures of the extruded 2196 Al-Cu-Li alloy plates under different heat treatment parameters are tested and characterized along different directions. It is found that the mechanical property anisotropy of 2196 Al-Li alloy is significantly affected by heat treatment. The anisotropy is mainly caused by the differences of grain morphology, microtexture, recrystallization degree and secondary particles characteristics in different directions. The specimens in 0° and 90°directions have high strength, while the specimen in 45° direction has the best ductility. The main microtexture of alloy are {111}<112>oriented A* 1 and A* 2 shear textures, and aging treatment has little effect on the grain morphology and microtexture. The decrease of mechanical property anisotropy after aging treatment is mainly due to the increase of number density and distribution uniformity of T 1 phase. The elimination of PFZ and the increase of grain boundary strength are also conducive to the decrease of anisotropy. The dislocations introduced by pre-stretching is beneficial to the uniform precipitation of the fine phases, resulting in the optimal mechanical property homogeneity of the alloy. The ductility in different directions is also anisotropic, and the fracture mechanism changes from ductile to intergranular and cleavage fracture modes after heat treatment. ga1 • The anisotropy is caused by the difference of grain morphology, microtexture and precipitates. • Heat treatment has obvious influence on the anisotropy where T8 state can obtain the optimal isotropy. • Increasing density and distribution uniformity of T 1 phase is the main factor reducing the anisotropy. • The main texture of alloy is A* 1 and A* 2 , and heat treatment has little effect on microtexture. • Heat treatment promotes the ductile fracture changing into intergranular and cleavage fracture. [ABSTRACT FROM AUTHOR]

The segregation feature and its influence on the aging behavior of laser beam remelted 2A97 Al–Cu–Li alloy were investigated. Scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrum methods were employed to analyze the microstructures, segregations, and structures of precipitates. It is revealed that segregations of Cu, Mn, and Zn occurred at the grain and dendrite boundaries of the as remelted and aged alloy, and co-segregation of Mg and Zn took place after aging. The dominant intermetallic phases at the segregation bands varied from T B (equiaxed zone) + θ (columnar dendrite zone) for the as remelted specimen to T B for the 155 °C-aged to T 1 for the 175 °C-aged. Our results can provide an in-depth insight into the mechanism of the segregation effect on aging precipitation in laser beam welded Al–Cu–Li alloys. • The fusion zone is comprised of equiaxed zone, columnar dendrite zone, and equiaxed dendrite zone. • Cu, Mn, and Zn are segregated at grain and dendrite boundaries. • Co-segregation of Mg and Zn took place after 24 h of aging at 155 and 175 °C. • The dominant phases varied from T B + θ (as remelted) to T B (155 °C-aged) to T 1 (175 °C-aged). [ABSTRACT FROM AUTHOR]

The influence of asymmetric cold rolling (ASR) and subsequent ageing on microstructures and mechanical properties of the Al–Cu–Li alloy was investigated systematically in this work. Both the hardness and yield strength increased with the asymmetric cold rolling degree. The peak hardness, yield strength and ultimate tensile strength of aged samples increased from 138 HV, 380 MPa, 430 MPa of the conventional hot rolled sheet (CHR) to 162 HV, 420 MPa and 480 MPa of 90% ASR sheet (ACR90), respectively, while the elongation keeps near 10%. The grain size decreased and the recrystallization degree increased with the asymmetric rolling degree. Textures of four rolled sheets, such as solid solute of conventional hot rolled sheet (CHR), conventional cold rolling with reduction of 50% (CCR50), asymmetric cold rolling with reduction of 50% and 90% (ACR50 and ACR90) were mainly Copper, S, and Brass types along the β fiber. In particular, volume fractions of textures were different, and CCR50, ACR50, ACR90 samples had similar average Taylor factors (M), which was lower than the CHR sample. The number density and the average diameter of T 1 precipitates in matrix increased with the ASR degree. The CHR sample with higher average M value in the tensile direction at room temperature can sufficiently compensates for the loss of strengthening due to less precipitates as compared with the CCR50 sample. The strength of two ASR samples is higher than the CHR sample due to the coupling effect of textures and precipitation strengthening. • The effect asymmetric rolling on the subsequent ageing behaviors has been studied. • The texture and Taylor factor of aged Al-Cu-Li sheets were analyzed and compared. • Amount of T 1 precipitates increasing gradually with asymmetric deformation degree. • The textures and precipitation are the main reasons causing the strength difference. [ABSTRACT FROM AUTHOR]