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The butt joints of AA2099-T86 alloy were prepared by friction stir welding process under four different environments, i.e. conventional (C-FSW), liquid nitrogen (LN-FSW), ultrasonic vibration welding (U-FSW), and ultrasonic vibration with liquid nitrogen (ULN-FSW). The welding tool rotational speed of 650 rpm and tool traverse speed of 80 mm/min were fixed for all experiments. The microstructural characterization of the welded samples is examined with optical microscopy, SEM, and XRD. Higher tensile strength and microhardness were obtained in the ULW-FSW welded samples. The ultrasonic vibrations promote plastic deformation and material mixing, increasing the dislocation density and improving the weld strength. In addition, liquid nitrogen restricts the grain size and dissolution of strengthening precipitates due to the rapid welding cooling rate, resulting in higher hardness. Comparative analysis of weld joint efficiencies revealed that the ULN-FSW welded sample achieved an impressive efficiency of 87.12%. In contrast, U-FSW, LN-FSW, and C-FSW displayed efficiencies of about 86.17%, 83.01%, and 74%, respectively. [ABSTRACT FROM AUTHOR]

The present study investigates the tensile properties, activation of slip, and grain boundary cracks in Al–Cu–Li ternary alloys with varying precipitations resulting from different aging treatments. The size and distribution of precipitations were ascertained using transmission electron microscopy. The slip activtiy with tensile strain was observed by the electron back-scatter diffraction and scanning electron microscopy. Furthermore, the influence of precipitated strengthening was quantitatively evaluated. The presence of precipitations hinders dislocation movement, increasing strength but reducing the appearance of deformation mechanisms like slip activity, slip transfer, intragranularly misoriented grain boundaries, and lattice rotation, ultimately resulting in reduced ductility. In the sample of T6 aging for 72 h, the coarsed θ′ phase promotes the formation of dislocation rings, resulting in a decrease in the percentage of grains activated with slip to 9.7%. The percentage of grain boundaries with crack initiation reaches 6.9%. On the contrary, in the sample dominated by the T1 phase, the percentage of grains that activate slip is 14.6%, and the percentage of grain boundaries that initiate cracks is only 1.4%. This is because the continuous shear of the T1 phases helps disperse coplanar slip, thereby avoiding cracking caused by excessive stress concentration. Hence, to enhance alloy strength while preserving a certain level of ductility, it is vital to promote the precipitation of the T1 phase and avoid the coarsening of the θ′ phase. This study provides a new insight into the influence of precipitations on the strength and plasticity of Al–Cu–Li alloys. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The microstructures and mechanical properties of Al-2.8 wt%Cu-1.4 wt%Li-T87 alloy after thermal exposure at 125, 150 and 175 °C were measured and characterized by universal testing machine, scanning electron microscope and transmission electron microscope. The thermal stability of microstructures and mechanical properties of T87 heat-treated Al-2.8 wt%Cu-1.4 wt%Li alloy was investigated. The results show that the tensile strength of Al-2.8 wt%Cu-1.4 wt%Li-T87 alloy increased first and then decreased with the increase of thermal exposure temperature, which is due to the change of the number and size of precipitates. After thermal exposure at 125 °C, the alloy exhibited higher strength due to further precipitation of θ′ phase and stable size of T1 phase. After thermal exposure at 175 °C, the mechanical properties of Al-2.8 wt%Cu-1.4 wt%Li-T87 alloy decreased obviously, which was related to the dissolution of θ' phase and thickening of T1 phase. [ABSTRACT FROM AUTHOR]

In this work, the tribological behavior of the friction pair composed of 2297 Al-Cu-Li alloy and GCr15 stainless steel ball under dry friction conditions at different applied loads and sliding speeds was studied by a ball-on-disk configuration. The effects of applied load and sliding speed on wear characteristics of Al-Cu-Li alloy were analyzed, including wear coefficient, wear rate and morphology of wear surface and wear debris. The wear mechanism of 2297 alloy under different conditions was analyzed and discussed. The results show that the wear rate of 2297 alloy generally increases with the increase in the sliding speed. The wear mechanism of the 2297 alloy changes with sliding speed and applied load. The friction coefficient of 2297 alloy decreases with increasing applied load and sliding speed. The friction coefficient changes more significantly as the applied load increases at 400 rpm. When the rotation speed is large, the friction coefficient is stable in the range of 0.5 to 0.6 regardless of the applied load. [ABSTRACT FROM AUTHOR]

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

Optimization of forging process to improve the microstructure and mechanical properties of 2195 Al–Cu–Li alloy forgings is an urgent issue. In this study, a homogenized 2195 alloy ingot was subjected to multi-directional forging (MDF), annealing, and forging at 500 °C, 420 °C, and 240 °C with a 50% reduction in cross-sectional area, followed by a T8 heat treatment (involving solution, quenching, cold compression, and aging). The microstructural evolution during the process and the final mechanical properties in three orthogonal directions were examined. The results showed that the grain structures of the alloy were significantly refined after MDF by dynamic recrystallization (DRX), but the structure was thermally unstable and formed coarse grains during subsequent annealing by static recrystallization (SRX). The T8-treated samples forged at 500 °C, 420 °C, and 240 °C obtained fine and uniform grain structures by DRX, inhomogeneous grain structures by partial SRX, and uniform, equiaxed grain structures by full SRX, respectively. The average grain size of the forging increased with decreasing forging temperature because more significant SRX occurred for the forging that was deformed at lower temperatures. The grain structures had minimal influence on precipitation behavior and strength but had a significant influence on elongation. The fine and uniform grain structures improved the elongation; whereas, the inhomogeneous grain structures, which contained extremely large grains, significantly deteriorated the elongation. The uniform, equiaxed grain structures decreased the anisotropy in three orthogonal directions and maintained fine elongation even though the average grain size of the forging was the largest. [ABSTRACT FROM AUTHOR]

The microstructure, mechanical properties, and intergranular corrosion (IGC) susceptibility of peak-aged 2195 Al-Cu-Li alloy at different temperatures were investigated. The results showed that the microhardness and tensile properties of the alloy were significantly improved by increasing the aging temperature, while the ductility and corrosion resistance decreased. The medium-temperature aged sample could obtain optimal mechanical properties and acceptable corrosion resistance in comparison with other samples. A competitive relationship was observed between T1 (Al2CuLi) and θ' (Al2Cu) phases during aging treatment, where a higher aging temperature promoted nucleation of the T1 phase, which played the dominant role in strengthening the alloy. However, the θ' phase precipitation was inhibited. The improvement of corrosion susceptibility was mainly related to fine intragranular precipitates, continuous grain boundary precipitates, and a narrow precipitate-free zone. Furthermore, the relationship between the open circuit potential and the IGC sensitivity was discussed to determine the corrosion mechanism of the alloy. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The flow stress behavior of an innovative spray-formed aluminum–copper–lithium (Al–Cu–Li) alloy was successfully investigated via isothermal compression tests under a deformation temperature range of 350–450 °C (25 °C interval) and a strain rate range of 0.01, 0.1, 1, 5, 10 s−1. The constitutive relationship was established based on backpropagation artificial neural network (BP-ANN) algorithm. And the 3D processing maps were constructed as well. The results show that the constitutive model is in great agreement with the experiment data where the correlation coefficient goes up to 0.99963 and the average residual error lies only 1.06%. Moreover, from the 3D processing maps, the area of the instable regions tends to enlarge by virtue of the increasing strain, and the optimum processing domain is advised to be 440–450 °C. The microstructure evolution is found consistent with the prediction of the processing map. [ABSTRACT FROM AUTHOR]

Al–Cu–Li alloy is a huge potential alloy for aerospace industry due to its low density and excellent comprehensive performances. In this study, the microstructures and mechanical properties of a novel cast Al–Cu–Li alloy during the heat treatment were investigated. Results showed that most of the secondary phases along grain boundaries in as-cast state were dissolved into the Al matrix after homogenization and solution treatment, while the Cu-rich phases were slightly segregated once again on grain boundaries after aging. A relatively good combination of strength and ductility (average ultimate tensile strength of 430 MPa and elongation of 8.9%) was obtained after natural aging. Transmission electron microscopy (TEM) results revealed that there was a complicated precipitate distribution in this cast alloy after natural aging. Compared with the similar alloys which introduced dislocations before aging, the density of T1 (Al2CuLi) phases was decreased but the size was increased. The low volume fraction of δ′ phase, medium density of needle-shaped precipitates and relativity narrow precipitates-free zone with varying widths near grain boundary are the reasons accounting for the improvement of performances. [ABSTRACT FROM AUTHOR]

In this study, different pre-stretching and aging processes were applied to spray-formed Al-Cu-Li alloy 2195. The effects of different processes on the microstructures, mechanical properties, and corrosion behaviors of the alloy were examined. The strengthening and corrosion mechanisms were investigated. The samples treated with pre-stretching and aging have higher strength than the only aged samples. However, the strength is not significantly improved with the increase in the amount of pre-stretching. The pre-stretching treatment can suppress the formations of grain boundary precipitates (GBPs) and precipitate-free zones (PFZ), and the intergranular corrosion (IGC) sensitivity of the alloy is therefore reduced. The increase in pre-stretching promotes massive precipitation of the T1 phase, which leads to the negative shift of open-circuit potential. The over-aging treatment after pre-stretching leads to the growth of the PFZ and GBPs as well as the coarsening of the T1 phase. These changes in microstructure cause a decrease in mechanical properties and the re-sensitivity to the IGC. Under the same pre-stretching deformation, the two-step aging treatment (110 °C/12 h + 160 °C/24 h) can result in more intensive precipitation of the T1 phase, which enhanced the strength to a higher level. Meanwhile, the two-step aged alloy was immune to the IGC. The evolution mechanism of IGC for the alloy with different pre-stretching and aging processes was proposed based on the TEM characterization and the observation of IGC morphology. [ABSTRACT FROM AUTHOR]

Hot gas forming with an integrated heat treatment was utilized to form complex-shaped components in one operation that obtain full strength. The effects of the pressurizing rate on the deformation and strengthening behaviors were critical. Free-bulging tests were conducted at different pressurizing rates (0.0088–2.37 MPa/s) to reveal the corresponding deformation and strengthening behaviors of an Al–Cu–Li alloy sheet and for choosing appropriate pressurizing conditions. The profile and thickness were analyzed to describe the deformation behaviors. The Vickers hardness under different pressurizing and deformation conditions was measured to evaluate the strengthening behavior. The microstructure evolution was observed to reveal the deformation and strengthening mechanisms. An excellent bulging ability was obtained under the full solution condition, with a maximum strain of 0.88 at a pressurizing rate of 0.034 MPa/s. The thickness distribution became more uniform under rapid pressurizing conditions because of the increasing strain and strain-rate hardening abilities. The hardness increased with increasing deformation and was not affected by the pressurizing rate. Dynamic recovery was the main deformation mechanism, and dynamic recrystallization occurred at a low pressurizing rate. Fine precipitates comprising the T1 phase (Al2CuLi, hexagonal structure) were the main strengthening phase. The pressurizing condition was only considered to obtain the maximum improvement in formability and microstructure, regardless of its effect on strengthening during hot gas forming with an integrated heat treatment. [ABSTRACT FROM AUTHOR]

The effect of acid pickling pretreatments prior to cerium conversion coating process on the corrosion behavior of AA2198-T851 alloy substrates was investigated. Three acid pretreatments were employed: nitric acid (HNO3), phosphoric acid (H3PO4) and sulfuric acid (H2SO4). The cerium conversion coating process was performed using a batch solution composed of cerium nitrate and hydrogen peroxide. Microscopic techniques, electrochemical impedance spectroscopy, polarization resistance and open-circuit potential measurements were employed to investigate the effect of each acid pretreatment. The untreated and nitric acid pretreated substrates presented more defective cerium conversion layers than the substrates treated with phosphoric and sulfuric acids. Accordingly, the corrosion resistance of the untreated and nitric acid-treated substrates was very low, while that of the substrates treated with phosphoric acid and sulfuric acids were greatly improved. The sulfuric acid pickling treatment was the best pretreatment before cerium conversion coating among the investigated pretreatments on the AA2198-T851 Al-Cu-Li alloy. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of Al–Cu–Li alloy was investigated by hot compression tests in the temperature range of 340–500 °C with strain rate of 0.001–10.000 s−1. Based on the dynamic materials model (DMM), processing maps of the test alloy were developed for optimizing hot processing parameters. The optimum parameters of hot deformation for Al–Cu–Li alloy are at temperature of 400–430 °C and strain rate of about 0.100 s−1, with efficiency of power dissipation of around 30%. The microstructural manifestation of the alloy deformed in instability domains is flow localization, and dynamic softening first occurs in flow localizations structure. In stable domains, dynamic recovery (DRV) and dynamic recrystallization (DRX) are the main microstructural evolution mechanism. DRX is gradually strengthened with the increase in deformation temperature and the decrease in strain rate. During hot deformation, the DRX mechanism of Al–Cu–Li alloy is dominated by continuous DRX (CDRX). A DRX model of Al–Cu–Li alloy is proposed based on the microstructural evolution process of the test alloy. [ABSTRACT FROM AUTHOR]

Abstract: The morphology of the intermetallic phases and their contents in the welded joint zones of a V‑1469 alloy (Al-Cu-Li system) are studied by X-ray diffraction and transmission electron microscopy. Welding is shown to change the phase composition, the crystallographic texture, and the microhardness of the alloy. According to quantitative X-ray diffraction analysis, the T1-phase content decreases and the δ'-phase content increases in the weld metal. As a result, the microhardness in the weld zone decreases, since the T1 phase is much stronger hardener than the δ' phase. This effect weakens when the weld root is approached. [ABSTRACT FROM AUTHOR]

The effect of small rare earth (RE) addition of 0.11%Ce, 0.2%Er and 0.082%Sc on aging precipitates and mechanical strength of an Al-(3.3-4.2)Cu-1.2Li-X alloy were investigated. It is found that Cu-rich residual particles containing RE element exist in the solutionized alloy, which leads to a decrease of dissolved Cu concentration in the solutionized matrix. Like RE-free alloy, the main aging precipitate types in RE-containing alloy are T1 (AlCuLi) and θ′ (AlCu), but their fraction is decreased. The strength of the corresponding alloys is therefore lowered by the small RE addition. Combined with the analysis of some reported references, it is proposed that the effect of small RE addition on Al-Cu-Li alloy strength is also associated with the Cu and Li concentrations and their ratio. [ABSTRACT FROM AUTHOR]

Texture and tempered condition combined effects on fatigue behavior in an Al-Cu-Li alloy have been investigated using tensile testing, cyclic loading testing, scanning electron microscope (SEM), transmission electron microscopy (TEM) and texture analysis. Results showed that in near-threshold region, T4-tempered samples possessed the lowest fatigue crack propagation (FCP) rate. In Paris regime, T4-tempered sample had similar FCP rate with T6-tempered sample. T83-tempered sample exhibited the greatest FCP rate among the three tempered conditions. 3% pre-stretching in T83-tempered sample resulted in a reducing intensity of Goss texture and facilitated T precipitation. SEM results showed that less crack deflection was observed in T83-tempered sample, as compared to other two tempered samples. It was the combined effects of a lower intensity of Goss texture and T precipitates retarding the reversible dislocation slipping in the plastic zone ahead the crack tip. [ABSTRACT FROM AUTHOR]

In order to study the workability of a Al-Cu-Li alloy, isothermal hot compressive deformation was investigated in the temperature range of 350-500 °C at strain rates in the range of 0.01-10/s up to a true strain of 0.9 on Gleeble-1500 mechanical testing machine. The flow stress increased rapidly to a peak value. The peak stress decreased with increasing deformation temperature and decreasing strain rate. The effects of strain rate and temperature on hot deformation behavior can be represented by a Zener-Hollomon parameter including an Arrhenius term. The influence of the strain has also been incorporated in the constitutive equation and four material constants α, n, A, and the activation energy Q were calculated by compensation of strain. The proposed constitutive equation (considering the compensation of strain) gives an accurate description for the flow stress of the Al-Cu-Li alloy. [ABSTRACT FROM AUTHOR]

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]