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AA2195, an Al-Cu-Li alloy in the T8P4 age-hardened condition, is a candidate aluminum armor for future combat vehicles, as this material offers higher static strength and ballistic protection than current aluminum armor alloys. However, certification of AA2195 alloy for armor applications requires initial qualification based on the ballistic performance of welded panels in the as-welded condition. Currently, combat vehicle manufacturers primarily use gas metal arc welding (GMAW) process to meet their fabrication needs. Unfortunately, a matching GMAW consumable electrode is currently not commercially available to allow effective joining of AA2195 alloy. This initial effort focused on an innovative, low-cost, low-risk approach to identify an alloy composition suitable for effective joining of AA2195 alloy, and evaluated transverse-weld tensile properties of groove butt joints produced using the identified alloy. Selected commercial off-the-shelf (COTS) aluminum alloy filler wires were twisted to form candidate twisted filler rods. Representative test weldments were produced using AA2195 alloy, candidate twisted filler rods and gas tungsten arc welding (GTAW) process. Selected GTA weldments produced using Al-4wt.%Cu-2wt.%Si alloy as filler metal consistently provided transverse-weld tensile properties in excess of 275 MPa (40 ksi) UTS and 8% El (over 25 mm gage length), thereby showing potential for acceptable ballistic performance of as-welded panels. Further developmental work is required to evaluate in detail GMAW consumable wire electrodes based on the Al-Cu-Si system containing 4.2-5.0 wt.% Cu and 1.6-2.0 wt.% Si. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anisotropic hardness evolution appears during artificial aging when changing the loading axis of samples. • Due to fiber texture and inhomogeneous distribution of T 1 (Al 2 CuLi) variants, different amounts of face-on/inclined T 1 will be encountered in different loading directions. • The face-on/inclined T 1 has a higher resistance ability to hardness loading compared to edge-on T 1. • The pre-stretching prior to aging can effectively facilitate the isotropy of hardness evolution. Anisotropy of mechanical properties has limited the further application of Al–Cu–Li alloys. Previous research efforts were mostly focused on the anisotropic tensile properties. In the present study, significant hardness anisotropy evolution, measured during artificial aging, was also established when loading in different directions. It was found that different amounts of inclined/face-on would be encountered when loading along different directions, resulting from the fiber texture and inhomogeneous distribution of T 1 (Al 2 CuLi) variants along different directions for the samples without pre-stretching. The resistance to hardness loading is different between the face-on/inclined T 1 and edge-on T 1 due to its high aspect ratio, so the measured anisotropic hardness is obtained. Moreover, the characteristics of precipitates also play an important role in the anisotropic hardness evolution, the strong anisotropy of hardness only appears in the alloys that contained large diameters and a low density of T 1 phase or θ' (Al 2 Cu) phase. After applying pre-stretching, the predominant T 1 phase precipitates with small diameters and a high density, which helps to facilitate the isotropic hardness evolution during artificial aging. These findings provide a necessary supplement for the hardness evaluation where a high aspect ratio of precipitate is involved. [ABSTRACT FROM AUTHOR]

Effect of electropulsing has been investigated on the microstructures and precipitation kinetics of an Al-Cu-Li alloy during artificial ageing. Electropulsing assisted ageing (EAA) and conventional ageing (CA) were carried out under various ageing temperature and time conditions. The maximum stable plateau of EAA samples happens for less ageing times, than that of CA samples from ageing hardening curves. It was found that precipitation activation energy in EAA is remarkably reduced by ~45% compared to CA. Dislocation reconfiguration was firstly found to happen via electropulsing during artificially ageing. Specifically, both the larger dislocation lines and the resultant dislocation network configuration were observed in the EAA sample of ageing for 1 h. Before the peak statue, the average length and number density of T 1 plates in the EAA samples were much larger than those of the CA sample at the same ageing time. Based on the results analyzed, a new mechanism, which considering the formation of dislocation network configuration induced by electropulsing and the reduced average diffusion field size via dislocation network resulting in the absorption among T 1 precursors in a shorter timescale, has been established to successfully explain an accelerated T 1 precipitation during ageing assisted by electropulsing. • A new mechanism is revealed on an acceleration in T 1 precipitation kinetics during ageing assisted by electropulsing. • T 1 precipitation activation energy is remarkably reduced by ~45% via electropulsing effects. • Dislocation reconfiguration was firstly found to happen via electropulsing during artificially ageing. • This beneficial 3D dislocation network can result in accelerated nucleation and growth of T 1 precipitates. [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: 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 mechanical properties of Al-Cu-Li alloys after different pretreatments were investigated through tensile testing at 25 and −196 °C, and the corresponding microstructure characteristics were obtained through optical metallography, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. An increasing mechanism of both strength and ductility at cryogenic temperatures was revealed. The results show that the hot deformation pretreatment before homogenization promoted the precipitation of Al3Zr particles, improved particle distribution, and inhibited local precipitation-free zones (PFZ). Both hot deformation pretreatment before homogenization and cryogenic temperature were able to improve strength and ductility. The former improved strength by promoting the precipitation of Al3Zr particles while enhancing the strengthening effect of the second-phase particles and reducing the thickness of the coarse-grained layer. Meanwhile, the increase in ductility is attributable to the decrease in thickness of the coarse-grained layer, which reduced the deformation incompatibility between the coarse and fine grains and increased the strain-hardening index. The latter improved the strength by suppressing dynamic recovery during the deformation process, increasing the dislocation density, and enhancing the work hardening effect. Additionally, the increase in ductility is attributable to the suppression of planar slip and strengthening of grain boundaries, which promoted the deformation in grain interiors and made the deformation more uniform. [ABSTRACT FROM AUTHOR]

Cryogenic deformation can improve the strength and plasticity of Al–Li alloy, although the underlying mechanism is still not yet well understood. The effects of cryogenic temperature on the tensile properties and microstructure of an Al–Cu–Li alloy were investigated by means of tensile property test, roughness measurement, scanning electron microscope (SEM), optical microscope (OM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM). The results indicated that the strength and elongation of the as-annealed (O-state) and solution-treated (W-state) alloys increased with the decrease in deformation temperature, where the increasing trend of elongation of the W-state alloy was more significant than that of the O-state alloy. In addition, a temperature range was observed at approximately 178 K that caused the strength of the W-state alloy to slightly decrease. The decrease in temperature inhibited the dynamic recovery of the Al–Cu–Li alloy, which increased the dislocation density and the degree of work hardening, thus improving the strength of the alloy. At cryogenic temperatures, the internal grain structure was more involved in the deformation and the overall deformation was more uniform, which caused the alloy to have higher plasticity. This study provides a theoretical basis for the cryogenic forming of Al–Li alloy. [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]

• 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]

[Display omitted] • The microstructures of homogenized alloy are greatly affected by the cooling rates. • The air-cooled sample is dominated by T phase and δ′/β′ phase. • In the furnace cooling, numerous large size T 1 phases and some θ′ liked phases are precipitated. The microstructure of homogenized Al–Cu–Li alloy is greatly affected by cooling rates. The air-cooled sample is dominated by high temperature precipitated T (Al 20 Cu 2 Mn 3) phase and β′ (Al 3 Zr) phase, accompanied by naturally aged δ′ (Al 3 Li) phase. But for the furnace cooled sample, except for the T phase and δ′/β′ phase, the predominant phases are numerous micrometer-scale T 1 (Al 2 CuLi) phase and some of θ′ (Al 2 Cu) liked phase. [ABSTRACT FROM AUTHOR]

The effects of re-solution (RST) and re-aging (RA) treatment on the mechanical property, microstructure, corrosion resistance and electrochemical behavior of 2196 Al-Cu-Li alloy were investigated by tensile testing, conductivity testing, intergranular corrosion and electrochemical corrosion testing. The results show that RST and RA treatment can improve the corrosion resistance without sacrificing the strength compared to T6 temper. The aging precipitation process is reversible, and the number and distribution of δ', T 1 and θ' precipitates can be effectively regulated by the RA treatment, so that the strength of the alloy approximately reaches the level of T6 temper and the ductility is improved. The corrosion mode of the alloy changed from pitting into intergranular corrosion during RST and RA treatment. The coarsening and discontinuous distribution of grain boundary precipitates as well as the increase of precipitate-free zone (PFZ) width inhibit the generation and propagation of stress corrosion cracking and thereby improve the corrosion resistance of the alloy. The increase of Cu content in grain boundary reduces the electrochemical corrosion sensitivity of the alloy. The optimal process parameters of RST and RA treatment for 2196 Al-Cu-Li alloy are finally determined to be 515 °C for 90 min and 170 °C for 24 h. [Display omitted] • RST and RA can improve corrosion resistance without sacrificing the strength. • Corrosion mode changes from pitting to intergranular corrosion during RST and RA. • Coarse discontinuous GBPs and wide PFZ improve corrosion resistance of alloy. • Increase of Cu content in GBs reduces electrochemical corrosion sensitivity. [ABSTRACT FROM AUTHOR]

In this work, a Al-Cu-Li alloy plate with outstanding mechanical properties was successfully prepared with electromagnetic twin-roll casting (TRC) technology. The microstructure of Al-Cu-Li alloy manufactured by conventional mold casting, TRC, and electromagnetic TRC was studied in detail. The action mechanism of electromagnetic oscillation field (EOF) in the TRC process was studied by systematic experimental characterization and numerical simulation. The results show that the EOF will enlarge the circumfluence area in the cast-rolling zone, accelerate the mass transfer and heat transfer in the molten pool, and make the solute field and flow field in the liquid cavity tend to be evenly distributed. Further, the introduction of the EOF will produce the electromagnetic body force F with the maximum strength of 14 N/m3. The F acting on the solidification front will eliminate the accumulation and deposition of Cu2+, Li+, Mg2+, Zn2+, Mn2+ at the dendrite tip and inhibit the growth of dendrites. At the same time, the F can refine the microstructure of the TRC plate, promote the formation of equiaxed crystals, improve the supersaturated solid solubility of solute elements in the α(Al) matrix, and avoid the appearance of obvious solute segregation area or the formation of excessive solute enrichment area. Therefore, the macro-segregation in TRC plate was significantly reduced, the solidification structure was dramatically refined, and the comprehensive properties of the alloy were remarkably improved. [ABSTRACT FROM AUTHOR]

The mechanical properties and microstructure evolution of an Al-Cu-Li alloy sheet processed via hot rolling (HR) (at 400 °C and 500 °C) or cryorolling (CR) (at −100 °C and −190 °C) and subsequence aging at 160 °C for 10 h were investigated. Before aging, the highest ultimate tensile strength of 502 MPa was achieved when the sheets were cryorolled at −190 °C, while the better ultimate tensile strength of 476 MPa and the best elongation rate of 11.1% was achieved simultaneously when the sheets were cryorolled at −100 °C. The refined grains and numerous uniform deformation-induced dislocations microstructures were responsible for the improved strength and enhanced ductility of the cryorolled sheets compared to that of the alloy processed by hot rolling with a low dislocation density zone (LDDZ) and high dislocation density zone (HDDZ). After aging at 160 °C for 10 h, the ultimate tensile strength further improved resulted from the greater precipitation strengthening, and the increased precipitates provided greater resistance to dislocations movement resulting in the increased ductility although the dislocation density decreased. The uniform dislocation microstructures in the cryorolled sheets provide numerous nucleation sites for the precipitates, leading to higher strength after aging. [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 unique chemical and phase compositions of aluminum‑copper‑lithium (Al-Cu-Li) alloys call for a new surface treatment process parallel to the conventional anodizing one. Thus, in this work, a layered double hydroxides (LDHs) coating was formed on an AA2099-T83 Al-Cu-Li alloy in a Li 2 CO 3 solution via an in-situ growth method; further, the LDH coating was modified with 1H, 1H, 2H, 2H- Perfluorodecyltrimethoxysilane (PFDTMS). Scanning electron microscopy, ultramicrotomy, scanning vibrating electrode technique, potentiodynamic polarization and electrochemical impedance spectroscopy were employed to characterize the structure and corrosion resistance of the alloy after different treatments. It was found that a uniform and compact LDH coating of 1.25 μm thickness was formed on the alloy surface at 70 °C in 60 min. The Li-Al-LDH coating showed active corrosion protection behavior in 0.5 M NaCl solution, associated with re-healing of the coating and/or re-passivation of the alloy. Compared with the as-formed LDH coating, the coating after the PFDTMS modification showed greatly enhanced corrosion resistance due to its superhydrophobic characteristic as well as active corrosion protection behavior. It is suggested that the superhydrophobic LDH coating is a promising alternative surface treatment for corrosion protection of the AA2099-T83 Al-Cu-Li alloy. • A Li-Al-LDH-CO 3 coating of 1.25 μm thickness was formed on AA2099-T83 alloy. • The coating was anodic relative to the alloy substrate. • The coating became superhydrophobic after silane modification. • The silane-modified coating showed two passivation zones in NaCl solution. • The overall coating system decreased corrosion current density by 2 orders of magnitude. [ABSTRACT FROM AUTHOR]

In the present work, attempts have been made to control the yield strength anisotropy in an Al–Cu-Li alloy by implementing a novel processing route combining multi-axial forging (MAF) and rolling with an aim to weaken the texture. It has been observed that continuous destabilization of deformation texture during MAF results in weakening of texture. Further weakening of texture could be achieved upon post MAF cold cross rolling, which has been attributed to (i) the geometry induced shear in the roll gap, and (ii) the change in strain path during rolling. Such a weak texture is in contrast to strong Brass-type texture, generally observed in these alloys. Further annealing in the solution treatment regime led to even more weakening of texture. Uniaxial tensile tests along different directions of the as-processed sheets confirmed the weak dependency of yield strength on orientation of tensile axis. • Novel processing route of multiaxial forging and rolling is proposed for texture weakening of Al-Cu-Li alloys. • Texture weakening is due to continuous change in reference frame during multiaxial forging. • Further weakening of texture occurs due to geometric induced shear and change in strain path imposed during rolling. • Highly isotropic mechanical properties are obtained via the proposed processing method. [ABSTRACT FROM AUTHOR]

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]

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]

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]

The evolution of precipitate microstructures of the Al-1.0wt%Cu-2.5wt%Li alloys with different micro-alloyed elements addition was investigated during ageing at 175 °C together with the mechanical properties and corrosion resistance. It was found that the Al-Cu-Li alloy with Zn addition possesses not only higher yield strength but also improved intergranular corrosion resistance, compared with the alloy with Mg addition. The corresponding precipitate microstructures were greatly affected by Zn or Mg micro-alloyed element addition, for example, with Zn addition the δ′-Al 3 Li, T 1 -Al 2 CuLi and θ′-Al 2 Cu (and θ″) phases were formed within grains, whereas the coarse T B -Al 7 Cu 4 Li phase and the T 1 phases appeared at grain boundaries (GBs). In contrast, the Al-Cu-Li alloy with Mg addition possessed the δ′, T 1 and S′-Al 2 CuMg phases within grains, while the coarse Al Cu phase and T 1 phases were present at GBs. The alloy with combined Zn + Mg addition exhibited a duplex microstructure of the two alloys, resulting in lower mechanical strengths but the intermediate corrosion resistance. Therefore, the increased amount of Zn-containing coarsened T B phase at GBs was found to improve the corrosion resistance of the alloy with Zn addition, due to the smaller potential difference between the GB precipitates and the adjacent zones. • The Al-Cu-Li alloy with 0.74Zn addition possesses higher yield strength and improved intergranular corrosion resistance. • Zn addition alloy possessed higher strength and intergranular corrosion resistance comparing with only Mg addition. • Zn containingalloy, δ′-Al 3 Li, T 1 -Al 2 CuLi and θ′-Al 2 Cu (and θ′′) phases were formed in grains, coarse T B -Al 7 Cu 4 Li and T 1 phases at GBs. • The Mg containing alloy possessed δ′, T 1 and S′-Al 2 CuMg phases in grains, the coarse Al Cu phase and T 1 phases at GBs. • The alloy with combined Zn+Mg exhibited a duplex microstructure, causing lower strengths but intermediate corrosion resistance. [ABSTRACT FROM AUTHOR]

In this study, the hot compression bonding (HCB) tests of 2196 Al-Cu-Li alloy were carried out under different temperatures, strain rates and strains. The interfacial microstructure evolution and bonding mechanism were investigated in detail. The effects of deformation parameters on the bonding quality were revealed, and the processing window for HCB was determined. The preconditions of realizing interfacial bonding are the discontinuous dynamic recrystallization (dDRX) induced by grain boundary bulging or particle-stimulated nucleation (PSN), and the subsequent migration of interface grain boundary (IGB). As strain increases, the bonding quality is improved significantly. The elevated interfacial pressure and quick dDRX behavior under high strain rate are also favorable for bonding. The optimal processing window for HCB was determined as temperatures ranging from 470 to 525 °C and strain rates of 0.6 to 1 s−1. An expression of activation energy (Q w) for HCB was proposed to quantitatively evaluate the combined effects of strain, bonding time and interfacial pressure on the bonding quality. It was found that the strength of most bonding joints can be more than 80% of strength of the base material when the Q w is larger than 1.2. Unlabelled Image • The interfacial microstructure and bonding mechanism of 2196 alloy were investigated. • The effects of deformation parameters on the bonding quality were revealed. • The bonding quality can be improved by increasing strain and strain rate. • The processing window for bonding of 2196 Al-Cu-Li alloy was determined. • An evaluation method for bonding quality based on activation energy was proposed. [ABSTRACT FROM AUTHOR]

The structure and corrosion resistance of anodized AA2099-T83 Al-Cu-Li alloy after layered double hydroxides (LDH) sealing and hot water sealing (HWS) were studied using scanning electron microscopy (SEM), X-ray diffraction, electrochemical impedance spectroscopy (EIS) and neutral salt spray test (NSST). Particularly, the corrosion resistance of the LDH-based coating system with reduced anodic film thicknesses was compared with that of the normal HWS-based coating system. It was found that LDH could be formed over the surface and within the pores of the anodic film within 30 min. With other conditions the same, the LDH-sealed alloy passed 1000 h of NSST without evident localized corrosion, contrasting with the HWS alloy, which showed severe localized corrosion after NSST for 120 h. Further, when the anodic film thickness was reduced from 3.7 to 1.3 μm, the LDH-sealed alloy still showed much better corrosion resistance than the normal HWS alloy. This work clearly demonstrates that it is possible to obtain high corrosion resistance for the anodized AA2099-T83 Al-Cu-Li alloy at much reduced anodic film thickness. • The anodic film was successfully sealed with layered double hydroxides (LDH). • The process of LDH sealing is different from that of hot water sealing. • LDH-sealed AA2099-T83 alloy passed 1000 h of neutral salt spray test. • Good corrosion resistance was achieved at an anodic film thickness of 1.3 μm. [ABSTRACT FROM AUTHOR]

In this study, the effects of heat treatment on the microstructure and mechanical properties of extruded 2196 Al-Cu-Li alloy were examined and the precipitation behavior and strengthening mechanism were investigated. It was found that the solution treatment and artificial aging had a significant strengthening effect on the mechanical properties of the extruded alloy, which was related to the type, size, number density, and distribution of the precipitates. Most of the second phases dissolved back into the matrix after solution treatment. The precipitation sequence of 2196 alloy during aging treatment was identified as: supersaturated solid solution→ GP zone + δ′/β′ (Al 3 (Li,Zr)) → δ′ + θ′ (Al 2 Cu) + T 1 (Al 2 CuLi) → θ′ + T 1 , where T 1 phase played a leading role in the precipitation strengthening. The fracture mechanism changed from ductile fracture to intergranular fracture. The pre-stretching deformation can introduce a large number of vacancies and dislocations, which provide conditions for atomic diffusion and precipitation of the phases, and further improve the mechanical properties of the alloy. Besides, pre-stretching can effectively shorten the time required for peak strengthening, which is only 20% of the time needed in single-stage peak-aging (170 °C/36 h). Finally, the optimal heat treatment process of 2196 Al-Cu-Li alloy was determined as: 515 °C/90 min solution treatment+3% pre-stretching+170 °C/16 h artificial aging. Unlabelled Image • The precipitation sequence of this alloy during aging was: SSS → GP zone + δ′/β′ → δ′ + θ′ + T 1 → θ′ + T 1. • The optimum heat treatment process of extruded 2196 Al-Cu-Li alloy was determined, the strength was significantly improved. • The pre-stretching can effectively shorten the time required for peak strengthening, only 20% of the T6 peak-aging state. • The dimple fracture was transformed to intergranular fracture with aging time, accompanied by partial cleavage fracture. [ABSTRACT FROM AUTHOR]

The quantitative effects of pre-treatments, namely pre-stretching and natural ageing (NA), on the precipitation sequence, precipitation kinetics and mechanical properties of an Al–Cu–Li–Mg–Ag alloy during artificial ageing were systematically investigated, aiming to elucidate the mechanisms by which these effects proceed. At the early ageing stage, pre-stretching could inhibit the formation of GP zones by restricting the Mg–Cu co-clustering, and could result in a higher nucleation rate of the T 1 precipitates due to an increase in the quantity of dislocations covered by solute segregations. The introduction of NA after pre-stretching could further increase the number density of T 1 by providing more nucleation sites, which evolved from the much more Mg–Ag co-clusters forming during the NA process. With prolonging ageing time, the precipitation kinetics for T 1 were strongly enhanced by pre-stretching due to a more efficient nucleation of T 1 and a more rapid growth rate of this phase, which was attributed to the combination of the suppression effect on the GP zone precipitation and the pipe diffusion effect derived from the introduced dislocations. When applying NA after pre-stretching, a further acceleration of the precipitation kinetics was observed, which was related to the formation of much more T 1 nuclei. At the peak-aged condition, both the two pre-treatments could not only refine the precipitates but also result in a higher T 1 volume fraction. Mechanisms of the strength changes induced by the pre-treatments under various ageing conditions were discussed in detail in view of these experimental results. [ABSTRACT FROM AUTHOR]

Friction stir welds (FSWs) can be considered as an ensemble of elements of material with composite microstructures connected in series. In the present study, bead-on-plate FSW runs were made on an Al–Cu–Li alloy with varying rotation speeds ranging from 400 to 800 rpm. Microstructure of the FSW region was investigated by using optical microscope, electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). Thermal stability of various precipitates was evaluated with differential scanning calorimetry (DSC) measurements. Strength variation across FSW cross sections was mapped by microhardness measurements. Average as well as local mechanical properties were evaluated using a digital image correlation (DIC) technique. Irrespective of the process parameters, FSW samples showed similar tensile and strain hardening behaviour along with serrations in stress-strain curves while local strength values showed increasing trend with rotation speed. The FSW alloy produced at intermediate rotation speed exhibited different mechanical behavior and is correlated with the resultant substantial changes in the microstructure. Strain localization occurred at the boundary of nugget zone and thermo-mechanically affected zone which led to failure of the FSW tensile specimens within weld regions. Fractography investigation revealed that the failure is initiation controlled, that is void nucleation at coarse precipitate-matrix interfaces. • Bead-on-plate FSW runs were made on an Al–Cu–Li alloy with varying rotation speeds. • Microstructure of the FSW region was investigated by using optical microscope, EBSD and TEM. • Average as well as local mechanical properties were evaluated using a DIC technique. • We report detailed microstructure-mechanical property correlation of the weld specimens. • Data presented is useful for the design of large sized cryogenic propellant tanks of satellite launch vehicles. [ABSTRACT FROM AUTHOR]

The corrosion behavior of the 1445 aged alloy was studied by analysis of microstructure characteristics and grain structure characteristics achieved from TEM, STEM, and EBSD. Three corrosion modes including intergranular corrosion (IGC), sub-intergranular corrosion (SIGC), and sub-intragranular corrosion (SGC) were found in the aged samples. In contrast with the conventional Al-Cu-Li alloy, the increased corrosion resistance was derived from the lower chemical potential difference between δ′ phase in matrix and S′ phase at GBs. The grain stored energy can significantly affect the SGC especially under a specific grain orientation thus the corrosion resistance of deformed grains can be increased. • The corrosion behaviors of aged 1445 Al-Li alloy includes IGC, SIGC and SGC, not uniform to that of the normal Al-Li alloy. • The IGC is due to the T 1 phase on the high grain boundary. The SIGC is attributed to S′ phase on the low grain boundary. • The SGC is linked to copper-rich nanoparticles, located on dislocation bands of deformation with high grain stored energy. • In the zone of un-recrystallize grains, the corrosion appeared on the prioritization of the specific grain orientation. [ABSTRACT FROM AUTHOR]

A layered double hydroxides (LDH) film was formed on AA2099-T83 Al-Cu-Li alloy in a mixed solution containing 0.05 M Zn (NO 3) 2 ·6H 2 O and 0.3 M NH 4 NO 3 at 75 °C. Field emission scanning electron microscope, ultramicrotomy and electrochemical impedance spectroscopy were employed to characterize the structure and corrosion properties of the alloy after different treatments. It was found that the LDH film preferred to form on coarse intermetallic particles; the thickness of the LDH film and its corrosion resistance initially increased with increasing preparation time (up to 12 h); micro-cracks then developed in the LDH film after 24 h formation, leading to deterioration of its corrosion resistance; loading vanadate ions significantly improved the long-term corrosion resistance of the LDH film. It is suggested that the LDH film is a promising substitute for anodizing treatment of Al-Cu-Li alloys. • A LDH film up to 8 μm thickness was formed on AA2099 Al-Cu-Li alloy. • The LDH film preferentially formed on the surfaces of Al-Fe-Mn-Cu particles. • Loading vanadate anions greatly improved the corrosion resistance of the LDH film. • The LDH film is a promising substitute for anodizing treatment of Al-Cu-Li alloy. [ABSTRACT FROM AUTHOR]

After aging heat treatment, Al-Cu-Li alloy, in general, contains a variety of precipitated phases that jointly influence the age-strengthening effect on the alloy. In this work, a multiphase-coupled strengthening model has been established on the basis of a dislocation bypassing mechanism. The model considered situations with different proportions of two strengthening phases, T1 and θ′, and then obtained the dimension and volume fractions of these two strengthening phases via experiments. The values predicted by the multiphase-coupled strengthening model and the classical strengthening superposition model were compared with the measured results. The multiphase-coupled strengthening model established in this work had better consistency with the measured results. Moreover, the modeling method proposed in the paper can also be extended to the system having over two primary strengthening phases. Hence, the model can contribute towards the development of a multi-component precipitation strengthening process for aluminum alloys. [ABSTRACT FROM AUTHOR]

Regulating the deformation and property synchronously is a key point of creep aging process. And pre-deformation has been considered to be a good regulating method. In this paper, the laws of the influence of pre-stretching degree on creep strain, strength property, precipitate during creep aging process of Al–Cu–Li alloy were studied, and the pre-stretching design methods suitable for creep aging process were explored. The results indicate that the introduction of different pre-stretching degrees can have various influences on the creep strain of Al–Cu–Li alloy and the nucleation, growth and composition of the precipitates, so as to possess the capacity to regulate deformation and property. The introduction of proper pre-stretching can significantly prolong the duration of the initial creep stage, therefore, the total creep strain in 24 h are 2 times greater than that of the un-pre-stretched specimen. Besides, appropriate pre-stretching can effectively inhibit the orientation precipitation effect of T 1 phase and promote a large deal of nucleation and dense distribution. However, when the pre-stretching degree is too large, the composition of the precipitates will be changed, so that the number of θ′ precipitates increases and T 1 precipitates decreases, and the alloy strengthening effect is obviously reduced. [ABSTRACT FROM AUTHOR]

The effects of the addition of 0.29 wt% Ce on the high-temperature mechanical properties of an Al–Cu–Li alloy were investigated. Ce addition contributes to T1 (Al2CuLi) phase coarsening inhibition and Ce-containing intermetallic refinement which greatly improved the thermal stability and high-temperature deformation uniformity of this alloy. On the one hand, small Ce in solid solution and segregation at phase interface can effectively prevent the diffusion and convergence of the main element Cu on T1 phase during thermal exposure. Therefore, the thermal stability of Ce-containing alloy substantiality improves during thermal exposure at the medium-high-temperature stage (170 °C to 270 °C). On the other hand, the increment of the tensile elongation in Ce-containing alloy is much greater than that in Ce-free alloy at high temperatures tensile test, because the refined Al8Cu4Ce intermetallic phase with high-temperature stability are mainly located in the fracture area with plastic fracture characteristics. This work provides a new method for enhancing high-temperature mechanical properties of Al–Cu–Li alloy which could be used as a construction material for high-temperature structural components. [ABSTRACT FROM AUTHOR]

The effects of pre-stretching on creep behavior, mechanical properties and microstructure during the creep aging process of Al-Cu-Li alloy were investigated. AA2195 was taken as the representative of Al-Cu-Li alloys. It is found that the total creep strain and strength property of creep aged AA2195 specimens can be improved through effective pre-stretching. Unlike with artificial aging, yield strength increased increasing by 47%. The TEM images show that the constitution of aging precipitates in the creep-aged specimens are obviously changed by pre-stretching. Precipitates in the 2% pre-stretched specimen are mainly composed of T1 phase, while a great amount of θ' phase accompanied with a few T1 phase were found in the non-pre-stretched specimen. Moreover, pre-stretching introduces many dislocations which benefit the creep deformation, but the increasing dislocation density also accelerates the nucleation and growth of the precipitates as well. The premature T1 phase has a great blocking effect to the dislocation motion, creating a lower decrease rate but a longer duration in the early creep stage. Except for the initial dislocations, the dislocation motion in the creep aging process is also a favorable factor to precipitate the T1 phase. [ABSTRACT FROM AUTHOR]

The effects of the addition of 0.29 wt % Ce on the recrystallization behavior of an Al–Cu–Li–0.13Zr (wt %) alloy during isothermal annealing were investigated. Ce addition greatly improved inhibition of recrystallization in this alloy compared with that in the Ce-free alloy. The texture of the Ce-containing alloy contained a large amount of β-fibers and fibrous unrecrystallized grain microstructures distributed along the rolling direction in the overall annealing process. The improved recrystallization resistance endowed by Ce addition can be attributed to the large number of small Al8Cu4Ce species formed on the grain boundary. These fine particles with high-temperature stability can exert a Zener pressure on the Al3Zr dispersoid-free grain boundary. The yield strength of the Ce-containing alloy increased significantly, to 38 MPa, and the fracture toughness improved by 56.28% compared with those of the Ce-free alloy. This work provides a convenient and economical method for enhancing the overall performance of an Al–Cu–Li–Zr alloy via recrystallization inhibition by Ce addition. [ABSTRACT FROM AUTHOR]

The microstructural evolution and properties of an Al-Cu-Li alloy with Mg and Zn microalloying (Al-3.5Cu-1.5Li-0.5Mg-0.4Zn-0.3Mn-0.12Zr-0.06Ti) ingot subjected to homogenization (second-step annealing at 500 °C for 24 h following first-step annealing at 400 °C for 8 h) were investigated. Mg-Zn atom clusters were enriched at the end of dendrites as well as low-melting eutectic phases such as S (Al2CuMg), T2 (Al6CuLi3), TB (Al7.5Cu4Li) and T1 (Al2CuLi) in the as-cast alloy. During homogenization, Mg-Zn atom clusters diffused from the segregation to the vacancies, leading to the dissolution of the low-melting eutectic phases. Not only Al3Zr particles were observed at 500 °C, but more fine and uniform spherical dispersoids appeared, which were assumed as Al3(ZrxTiyLi1−x−y). Mg and Zn microalloying can promoted the nucleation of Al3Zr and Al3(ZrxTiyLi1−x−y) dispersoids, as well as T (Al20Cu2Mn3) phases, which all inhibited recrystallization effectively and improve the uniformity of the grains due to the strong pinning effect. The yield ratio was decreased from 0.81 to 0.52 with the yield strength decreased from 172 MPa to 61 MPa, which showed better plastic deformation ability of the alloy subjected to homogenization. In addition, the dissolution of low-melting eutectic phases and formation of Al3(ZrxTiyLi1−x−y) dispersoids resulted in the significant improvement on thermal stability. [ABSTRACT FROM AUTHOR]