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Purpose: The criteria importance through intercriteria correlation (CRITIC) and range of value (ROV) combined methods were used to determine a single index for all multiple responses. Design/methodology/approach: This paper used cold metal transfer (CMT) and pulse metal-inert gas (MIG) welding processes to study the weld-on-bead geometry of AA2099-T86 alloy. This study used Taguchi's approach to find the optimal setting of the input welding parameters. The welding current, welding speed and contact-tip-to workpiece distance were the input welding parameters for finding the output responses, i.e. weld penetration, dilution and heat input. The L9 orthogonal array of Taguchi's approach was used to find out the optimal setting of the input parameters. Findings: The optimal input welding parameters were determined with combined output responses. The predicted optimum welding input parameters were validated through confirmation tests. Analysis of variance showed that welding speed is the most influential factor in determining the weld bead geometry of the CMT and pulse MIG welding techniques. Originality/value: The heat input and weld bead geometry are compared in both welding processes. The CMT welding samples show superior defect-free weld beads than pulse MIG welding due to lesser heat input and lesser dilution. [ABSTRACT FROM AUTHOR]

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

T1 (Al2CuLi) nano-phase precipitation has been a major focus in developing new multi-microalloyed Al–Cu–Li alloys. Nevertheless, more understanding is required. This work investigated the effect of Zn alloying on the microstructure and mechanical properties of multi-element Al–Cu–Li alloys with a high Cu/Li ratio using a combination of advanced electron microscopy and first-principles calculations. Zn alloying (i) induced a higher density of geometrically-necessary dislocations after solid-solution treatment, which increased the T1 nucleation rate during the early aging stage; (ii) promoted T1 growth by substituting Al or Cu atoms in the T1 structure; and (iii) profoundly increased the aging kinetics, the age hardening response, and the strength. In addition, the co-segregation of Zn, Mg and Cu at the T1/Al interface helped to stabilize the fine T1 nano-platelets. These structural insights into T1 precipitation and age hardening by Zn alloying can help to guide the optimal design of high-performance Zn micro-alloyed multi-element Al–Cu–Li alloys.

The effect of pre-rolling on the microstructure and fatigue crack (FC) propagation resistance of the Al-Cu-Li alloy was studied using tensile testing, fatigue testing, transmission electron microscopy (TEM), X-ray diffractometer (XRD), and scanning electron microscopy (SEM). The results revealed that reducing the alloy thickness through pre-rolling by up to 12% enhanced both tensile strength and yield strength, albeit at the expense of reduced elongation. In addition, the FC growth rate decreased by up to 9% pre-rolling, reaching the minimum, while the application of additional mechanical stress during the pre-rolling increases this parameter. Deformations in the Al-Cu-Li alloy with less than a 9% thickness reduction were confined to the surface layer and did not extend to the central layer. This non-uniform deformation induced a compressive stress gradient in the thickness direction and led to an inhomogeneous distribution of T1 phase, resembling the structure generated by shot peening. The superior FC propagation resistance in the 9% pre-rolled alloy could be primarily attributed to the optimum balance of compressive residual stress and work hardening. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department 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 thermal stability of Al–Cu–Li alloy is critical to the quality and reliability of aerospace structural components. In this work, the microstructure and properties of rapidly solidified Al–Cu–Li alloy (T84) thermally exposed at 150 °C, 175 °C, 200 °C and 225 °C for 500 h were systematically studied. The results show that the T84 alloy exhibits excellent thermal stability with increased strength after thermally exposed at 150 °C, which is attributed to the increased number density of the T1 phase -Al2CuLi. With the further increase of thermal exposure temperature, the size of the T1 phase increases, the number density decreases significantly, and coarse precipitates such as T2 phase-Al6CuLi3 are formed. Meanwhile, the grain boundary precipitates coarsen and the precipitation free zones widen. The strengthening mechanism of the T1 phase transforms from shear mechanism to by-passing mechanism, and its contribution to yield strength decreases dramatically. In addition, the calculated activation energy indicates that coarsening of the T1 phase is controlled by the diffusion of Cu atoms.

In the present work, the anisotropic creep aging (CA) behavior and microstructural evolution of Al–Cu–Li alloy are investigated under different stress levels. The results indicate that as the stress level increases, the anisotropic creep behavior of Al–Cu–Li alloy changes significantly. As the applied stress level increases, the in-plane anisotropy (IPA) value of creep strain decreases and then increases. In addition, the strength also exhibits significant anisotropy, and as the applied stress level increases, there are differences in the strength changes of samples with different orientations at different creep aging times. Electron backscatter diffraction (EBSD), Energy-dispersive x-ray spectroscopy (EDS) and transmission electron microscopy (TEM) methods are used to study the evolution of texture and microstructure, as well as their effects on the anisotropy evolution of materials. Microscopic observation reveals that the anisotropy changes in creep and strength can be attributed to the difference in dislocation density and grain boundary slip phenomenon during the initial creep stage in samples with different orientations, as well as the stress orientation effect of precipitated phases, especially T1 phase. The study reveals a new mechanism of anisotropic CA mechanism in Al–Cu–Li alloy under different applied stress levels.

The evolution of the microstructure, texture and mechanical properties of the Al–Cu–Li alloy sheets by nanoscale TiC + TiB2 ceramic particles during solid solution treatment was systematically investigated by characterization, texture measurements and mechanical performance tests. The yield strength, tensile strength, and elongation of the A1 alloy with the addition of nanoscale TiC + TiB2 ceramic particles under T4P conditions were 312 MPa, 420 MPa, and 21.9%, respectively, which were 35.6%, 27.6%, and 2.8% higher than those of the A0 alloy, respectively. The recrystallization mechanism of both alloys was mainly the particle stimulated nucleation (PSN) mechanism, but the nanoscale TiC + TiB2 in the A1 alloy led to a stronger Zener dragging effect, which hindered the growth of CubeND nuclei, and P-oriented grains dominated. Thus, the A0 alloy sheet was dominated by CubeND components, while the A1 alloy sheet was dominated by P recrystallized grains, which led to the two alloy sheets showing opposite variation trends of the deep drawing properties with increasing solid solution treatment time. The short-time solid-solution process is more likely to provide better properties to the alloy with TiC + TiB2 added particles better properties in terms of various aspects, such as microstructure, mechanical properties, and electrical conductivity.

The precise control of forming in the new generation Al–Li alloy is challenged by the anisotropic creep aging behaviors. This anisotropy is influenced by coupling effect the microstructure and process parameters during creep age forming, where process parameters such as creep aging temperature and stress play a crucial role. Taking the 2195 Al–Cu–Li alloy as an example material, the study aimed to investigate the effect of creep aging temperatures (140–200 °C) and stresses (150–200 MPa) on the anisotropic creep aging behaviors. The findings revealed that with increasing temperature and stress, the in planar anisotropy (IPA) value of creep deformation decreased from 19.1% to 9.4%, the IPA value of strength decreased from 10.3% to 5.1%. The study uncovered the anisotropy of creep aging and its mitigation mechanisms. The analysis revealed the crucial role of the initial texture and precipitation. By regulating the type and size of precipitates, the process parameters can mitigate anisotropic creep aging behavior. The stress-oriented precipitation of GPI (θ″) zones intensifies creep aging anisotropy, while the homogeneous precipitation of T1 phase hinders creep aging anisotropy, the smaller and more uniform the T1 phase, the stronger the hindering effect. The coarsened T1 phase have a relatively small effect on creep aging anisotropy. In conclusion, the optimal combination of low deformation anisotropy (9.4%) and excellent yield strength (527 MPa) can be achieved when the creep aging temperature is set at 170 °C under 200 MPa.

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

The microstructure and mechanical properties of Al-Cu-Li alloy with different aging processes have been investigated. The experimental results indicate that increasing aging temperature enhances the precipitation kinetics of the alloy, which is beneficial for T1 phase precipitation. The average size of δ' phase is decreased from 18.2 to 11.6 nm when aging process changes from 200 °C singlestage aging to 150 °C/200 °C two-stage aging. The two-stage aging can effectively suppress the coarsening of δ' phase because T1 phase competes with δ' phase for Li atoms. The past researches have pointed out that T1 phase thickens when aging temperature exceeds 190 °C. However, the results indicate that two-stage aging can not only retard thickening but also increase number density of T1 phase. The alloy reaches maximum strength in two-stage aging, and the ultimate tensile strength, yield strength, and elongation are 415 MPa, 376 MPa, and 5.9%, respectively. When the diameter of T1 phase reaches a critical value, the strengthening mechanism of T1 phase has changed from shear mechanism to bypass mechanism. The diameter distribution range of T1 phase is large in this paper, and the strengthening mechanism of T1 phase is a mixed strengthening mechanism of shear mechanism and bypass mechanism. [ABSTRACT FROM AUTHOR]

This work investigated the influence of cooling rate (0.04, 0.87, 15.2 and 156.2 K/s) on the microstructure and compressive properties of Al–4Cu–3Li-0.7 Mg–1Zn alloys fabricated by several casting molds. The experiment results revealed that the microstructure cooled at low cooling rates of 0.04, 0.87 and 15.2 K/s is composed of α-Al, α(Al)+T2, θ (Al2Cu), T1 phases and core-shell configuration (Al13Fe4/Al7Cu2Fe phase). This core-shell structure is observed for the first time in an Al–Cu–Li alloy. However, T1 and core-shell configuration vanish at the high cooling rate of 156.2 K/s due to the insufficient diffusion time of Cu, Li and Fe elements. As the cooling rate increases, the average secondary dendrite arm spacing (SDAS) decreases significantly from 110.3 to 7.5 μm and the relationship between SDAS and cooling rate has been established. The average diameter/thickness of the α(Al)+T2, Al2Cu and Al13Fe4/Al7Cu2Fe phases decreases dramatically from 16.9 to 1.0 μm, 8.1 to 0.8 μm and 7.5 to 0.7 μm with the increase of cooling rate, respectively. Fine spherical Al13Fe4/Al7Cu2Fe and Al2Cu phases are beneficial to the improvement of comprehensive compressive properties. Additionally, the solute concentration in the matrix decreases, while the hot-tear resistance and volume fraction of secondary phases increase with increasing cooling rate. The empirical equations are established between (compressive properties, SDAS) and cooling rate. The fracture failure is responsible for the initial hot tearing at low cooling rates, the α(Al)+T2 or Al2Cu or Al13Fe4/Al7Cu2Fe phases at the moderate cooling rate, and the α(Al)+T2 phase at the high cooling rate.

In this study, the effect of Sc content on the microstructural characteristics and phase evolution of an Al–Cu–Li alloy under as-cast and homogenization conditions was investigated. The results show the grain refinement effect was distinct when the content of Sc was 0.16 wt%. However, further increased in Sc content resulted in a limited decrease in grain size. Besides, In the 0.16Sc alloy, the flocculent phase with primary Al3(Sc,Zr) phase coexisting with W (Al8-xCu4+xSc) phase appeared, and in the 0.32Sc alloy, the additional blocky primary Al3(Sc,Zr) phase was observed. With the increased of Sc content, the proportion of primary Al3(Sc,Zr) and W phases gradually increased, and the number and size of Al2Cu and Ag-containing Al2CuMg phases at grain boundaries gradually decreased. Two different morphologies of the primary W phase, flocculent and long strip shaped, were revealed within the Sc-containing alloy. The formation of the core-shell structure formed by Al3(Sc,Zr) particles and W phase was generated by the peritectic-eutectic reaction (Liquid + Al3(Sc,Zr)→α-Al + W) and the long strip of W phase was generated by the eutectic reaction (Liquid→α-Al + Al2Cu + W). During the homogenization process, the Al2Cu and Ag-containing Al2CuMg phases were completely re-dissolved after the two previous stages of homogenization, and only a small amount of the spheroidal residual W phase persisted. A subsequent low temperature treatment was employed to allow the Sc atoms that had diffused into the Al matrix to precipitate as Al3(Sc,Zr) dispersoids, resulting in a higher number density of Al3(Sc,Zr) particles for more efficiently utilizing the Sc elements.

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

The intergranular corrosion behaviour of Al-Cu-Li-Sc alloy with different microstructures was systematically investigated in this work. The SKPFM characterisation revealed that the AlCuSc (W) phase has more negative potential compared to the Al matrix and undergoes dealloying in the intergranular corrosion solution. The dealloying rate of the W phase in the corrosive solution is relatively slow, which does not lead to serious pitting characteristics. As denser anodic T1 precipitates formed on low-angle grain boundaries of the partially recrystallised sample will reduce the precipitates on the sub-grain interior, resulting in the low-angle boundary being prone to preferential corrosion and reduced intergranular corrosion resistance. The complete recrystallised sample exhibits corrosion of grain interior and propagates along corroded bands parallel to {111}Al habit planes of T1 precipitates, reducing the expansion rate of corrosion along the grain boundaries. Restraining the IGC along the low-angle grain boundary and inducing crystallographic corrosion to improve the intergranular corrosion resistance. [ABSTRACT FROM AUTHOR]

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

In this work, AA2050 alloy was friction stir processed at various tool rotation speeds and feed rates. The material was subjected to artificial aging to investigate its influence on macrostructure, microstructure, microhardness, and tensile strength of friction stir processed AA2050. In addition, a hot salt corrosion test was done on the test specimens at 130°C for 168 hours. The results indicated that grain refinement and dispersion of secondary phase particles improved the microhardness and strength of friction stir processed specimens. The artificial aging of the friction stir processed specimens improved the ductility by 81.5%. However, the tensile strength of the specimens decreased by 2.8%. The corrosion (mass loss per unit area) of the specimen processed with a single pass at a speed of 600 rpm and feed rate of 60 mm/min decreased by 90% compared to the base material. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of a novel Al–Cu–Li alloy is investigated by isothermal compression with a temperature range of 350–510 °C and a strain rate range of 0.001–10 s−1. Constitutive analysis and hot processing maps are used to analyze the influence of deformation parameters on hot deformation behavior, and the related microstructure evolution is characterized by scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM) observations. The results indicate that the microstructure evolution of the alloy during deformation was dominated by dislocation movement and substructure evolution. With the increase in temperature or the decrease in strain rate, the dislocations introduced by deformation gradually transform into dislocation walls and substructures, showing distinct dynamic recovery (DRV) and slight dynamic recrystallization (DRX) characteristics. The degree of DRX is very low, while it is more sensitive to strain rate than temperature. According to the analysis of hot processing maps and microstructure, the optimum deformation temperature and strain rate of the alloy are determined as at least 430 °C and 0.008–0.15 s−1, respectively. These results can be referable for the industrial thermomechanical processing of this novel Al–Cu–Li alloy. [ABSTRACT FROM AUTHOR]

Precipitation-strengthened Al–Cu–Li alloys are commonly used as structural materials in aerospace equipment. The present work focused on investigating the characteristics of grain boundary T1 precipitate in a rolled Al–Cu–Li alloy. It was found that the T1 phase with a multilayer structure will precipitate at the grain boundary after artificial aging, and it is nearly continuously distributed along grain boundaries in the pre-rolled samples. The habit plane of the intergranular T1 normally parallels a (111) plane of the matrix on one side of the grain boundary. And compared to the preferential growth of platelet edges for the intragranular T1, the grain boundary T1 phase is also prone to thickening via the stacking of successive unit-cell-thick (0.935 nm) layers on the existing broad surface of the plate, resulting in the significant coarsening in the direction perpendicular to its habit plane. In addition, the reason for the obvious thickening of the grain boundary T1 phase was also discussed.

Al–Cu–Li cast alloy components also show a promising application in the aerospace industry due to their relatively good combination of density and performance. According to the conventional processing procedures for cast products, a novel cast Al–Cu–Li alloy was directly solution treated and aged after homogenization, then the aging precipitation behavior and its effect on the mechanical properties of the alloy were investigated in this article. It was found that the naturally aged precipitates are rapidly dissolved during artificial aging at 175 °C, and the cubic phase, θ′ phase, T1 phase, Ω phase, and S phase will precipitate successively. In the early stage of artificial aging, the cubic phase and θ′ phase are formed prior to the T1 phase. With the aging time increasing, numerous T1 phases also precipitate with relatively large diameters, so the hardness of the alloy keeps rising until to the peak value. The naturally aged specimens show good plasticity and relatively low strength. After artificial aging, the tensile strength of the cast alloy can be increased to 423 MPa, but the corresponding elongation has a significant reduction. Moreover, the predominant precipitates—T1 phase and cubic phase show excellent thermal stability during 175 °C aging, they still exist with a large population even aged for 40 days.

The anisotropy of mechanical properties limits the applications of Al–Cu–Li alloys. In this study, microstructure evolution and mechanical properties of an Al–Cu–Li alloy via room-temperature rolling (RTR), room-temperature cross rolling (RCR), cryorolling (CR) and cross cryorolling (CCR) were investigated. The processing of Al–Cu–Li alloy by CCR gave the highest ultimate tensile strength of 471 MPa and an elongation of 8.4% along rolling direction (RD). The elongation of the CCR alloy along the diagonal direction (DD) was higher than those processed by CR, RCR, and RTR. The in-plane anisotropy (IPA) factor of the ultimate tensile strength (3.26%) of the CCR alloy indicated its relatively low anisotropy of the strength. Kernel average mapping (KAM) showed that the deformation was relatively uniform for the CCR alloy. A prominent local low KAM zone appeared in the alloy processed by RCR and RTR. The alloy in the CCR condition exhibits the highest strain hardening rate, progressively decreasing in a sequence of CR, RCR, and RTR. The refined grains and the texture, including mainly copper texture, little Cube texture, little Goss texture and little S texture, are the main reasons for the excellent mechanical properties and balanced strength-ductility of the CCR alloys.

The aim of this work is to investigate the effect of different second phases on the composite spinning-extrusion forming and mechanical properties of Al–Cu–Li alloy. With that purpose, four kinds of second phases blanks were controlled using preheating treatment, composite spinning-extrusion forming and mechanical properties test. Then, the correlation between the second phases and mechanical properties was further analyzed using electron backscattered diffraction and transmission electron microscopy. The results indicated that different second phases of Al–Cu–Li alloy can be regulated via reasonable preheating treatment. In addition, different second phases in the blank have various influences on composite spinning-extrusion forming, microstructure and mechanical properties of cylindrical parts. Dissolving the coarse second phases particles and precipitating the Al3Zr dispersoid in the blank can effectively improve the composite spinning-extrusion forming, inhibit the abnormal growth of recrystallized grains, and significantly enhance the mechanical properties of cylindrical parts with ribs. After regulation, the average grain size of the cylindrical parts is refined from about 90 μm to about 45 μm, and the average diameter of T1 phase is refined from 107 nm to 77 nm. In addition, the ultimate tensile strength, yield strength and elongation of cylindrical parts are increased from 555 MPa to 588 MPa, 530 MPa to 564 MPa, and 9.1% to 11%, respectively. [ABSTRACT FROM AUTHOR]

In this paper, the effects of compressive pre-deformation and successive pre-artificial aging on the compressive creep aging behavior and microstructure evolution of the Al-Cu-Li alloy have been studied. Severe hot deformation mainly occurs near the grain boundaries during the compressive creep initially, which steadily extends to the grain interior. After that, the T1 phases will obtain a low radius–thickness ratio. The secondary T1 phases in pre-deformed samples usually only nucleate on dislocation loops or Shockley incomplete dislocations induced by movable dislocations during creep, which are especially prevalent in low plastic pre-deformation. For all pre-deformed and pre-aged samples, two precipitation situations exist. When pre-deformation is low (3% and 6%), solute atoms (Cu and Li) can be consumed prematurely during pre-aging at 200 °C, with dispersed coherent Li-rich clusters in the matrix. Then, the pre-aged samples with low pre-deformation no longer have the ability to form secondary T1 phases in large quantities during subsequent creep. When dislocation entangles seriously to some extent, a large quantity of stacking faults, together with a "Suzuki atmosphere" containing Cu and Li, can provide the nucleation sites for the secondary T1 phase, even when pre-aged at 200 °C. The sample, pre-deformed by 9% and pre-aged at 200 °C, displays excellent dimensional stability during compressive creep because of the mutual reinforcement of entangled dislocations and pre-formed secondary T1 phases. In order to decrease the total creep strain, increasing the pre-deformation level is more effective than pre-aging. [ABSTRACT FROM AUTHOR]

The aerospace industry is constantly looking for innovative materials that exhibit good mechanical and corrosion properties. The 2198-T851 (Al-Cu-Li) alloy was developed to replace the conventional Al-Cu-Mg in aircraft structures. Despite the usefulness of the 2198-T851 alloy, its performance may be affected when subjected to an aggressive medium containing chloride ions. The deposition of Nb2O5 coatings by using the reactive sputtering technique on the 2198-T851 alloy surface appears as a powerful tool to improve the corrosion resistance of this material. Recently, groundbreaking research findings have demonstrated the positive effect of Nb2O5 coatings on corrosion protection of alloy 2198-T851. However, the corrosion products originated from the 2198-T851 aluminium alloy are poorly understood. The use of Raman spectroscopy and XPS techniques may help to shed some light on the corrosion products of 2198-T851 alloy. Results demonstrated the corrosion products are mainly composed by CuCl2 x H2O, CuCl, Cu2Cl(OH)3, Al(OH)3, and AlO(OH).

The Al–Cu–Li alloy has poor plasticity and hot workability, making it difficult to form by single-pass working, so the multi-stage thermomechanical processing is usually required. However, there is a general distinctly heterogeneous fiber structure in deformed alloys, which has non-negligible effects on the stability and formability of subsequent deformation. Therefore, the deformation mechanism of heterogeneous fibers and intergranular deformation compatibility mechanism are investigated for as-extruded Al–Cu–Li alloys with and fibers in this work. The results show that more slip systems are activated in the fiber, forming LAGBs through dislocations cross-slip and entanglement, thereby stimulating the CDRX. The number of slip systems that be activated in the fiber is relatively smaller, and the dislocations are dominated by single-slip and are easily pinned by the coarsening precipitate, thus activating the DDRX mechanism to force the grains to transform into the fiber. To coordinate the fiber deformation, the DDRX driven by dislocations from precipitate pinning is activated to relieve stress concentration. This study can provide theoretical guidance for rationally formulating the multi-stage thermomechanical processing regime of Al–Cu–Li alloys.

In this study, the T85-treated Al-3.78Cu-1.17Li-0.7 Mg-0.32Ag-0.25Mn-0.33Zn-0.12Zr alloy thermally exposed at a series of temperatures (100–300 °C) for 100 h, 500 h, and 1000 h was systematically investigated. The results show that the thermal stability of the alloy is more closely correlated with thermal exposure temperature than with exposure duration. Excellent thermal stability in strength is obtained below 150 °C, which can be linked to the diameter and number density of T1 (Al2CuLi) precipitates continually increasing with a thickness less than 2 nm. However, the widened precipitation-free zones (PFZs) associated with continuous grain boundary precipitates (GBPs) benefit intergranular fracture, contributing to a decrease in toughness and elongation. In the window of 175–200 °C, T1 precipitates tend to thicken and are gradually substituted by coarse θ′-Al2Cu and S-Al2CuMg with elevating temperature. Simultaneously, the continuous GBPs transverse to discrete circle-like shapes, and thus intergranular ductile fracture becomes dominant. Therefore, the related hardness and strength decrease, while the electrical conductivity and toughness are the opposite. At temperatures over 250 °C, thermal exposure can reduce the dislocation density and dissolve T1 phases to form T2-Al6Cu(Li, Mg)3 and cubic C phases, leading to a dramatic decrease in strength and toughness.

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

In this work, the effects of Ce content (0.1%, 0.2%, and 0.3 wt%) on the microstructures and mechanical properties of Al-Cu-Li alloys were investigated. The results show that the grains of Al-Cu-Li alloy are refined by adding Ce element. When Ce content is less than 0.1%, the ultimate strength of the alloy increases with the increase of Ce content. However, the ultimate strength of the alloy decreases when Ce content is above 0.1%. For Al-Cu-Li alloy with different Ce content, the aging precipitation of T1 and θ′ phases play the main strengthening role. When Ce content increases from 0.1 to 0.3%, dynamic recrystallization is promoted during hot deformation. The recrystallization of the alloys is inhibited after T6 treatment with the increase of Ce content, which can be attributed to existence of the Al8Cu4Ce phases on the grain boundary. This work provides an economical and convenient method for improving the properties of Al-Cu-Li alloys by Ce addition. [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]

Al-Cu-Li alloys are widely used in aerospace due to their excellent mechanical properties. However, the surface of Al-Cu-Li alloy components is prone to localized corrosion, when it serves in humid environments such as the ocean, due to the action of moisture in the air and Cl− in the atmosphere. Therefore, it is significant to study the corrosion performance of typical third-generation Al-Cu-Li alloys in a marine environment. The corrosion tests of the experimental materials are carried out in different concentrations of NaCl solution, and their morphology and maximum corrosion depth are characterized to evaluate their corrosion resistance at a particular time. The corrosion behavior of the third generation typical Al-Cu-Li alloys (2A97-T3, 2A97-T6, 2060-T8, and 2099-T83) and high-strength Al alloy 2024-T4 in solution containing Cl− is investigated using correlative immersion testing. The results show that 2A97-T3 possesses the best corrosion resistance performance of all under the same concentration of NaCl solution and soaking time. The corrosion resistance performance of 2024-T4 is respectively stronger than that of 2060-T8 and 2099-T83, but weaker than that of 2A97 (T3, T6). The corrosion morphologies of 2060-T8 and 2099-T83 are characterized by deep pits and large areas of exfoliation corrosion, while the corrosion morphology of 2099-T83 is the worst, indicating that its corrosion resistance is the weakest of all. The local corrosion preferentially occurred in the boundary region between intermetallic compounds or precipitates and alloy matrix in NaCl solution, and the lithium is selectively dissolved during the dissolution process, which brings about the enrichment of copper-containing residues. Subsequently, the copper-rich residue serves as the cathodic relative to the Al matrix, which leads to the anodic dissolution of the peripheral Al matrix occurs. [ABSTRACT FROM AUTHOR]

The local tensile mechanical properties of laser beam-welded joints of AA2198 alloy with Al–Si filler wire were experimentally investigated. For this purpose, micro-flat tensile specimens were extracted from the fusion zone and the heat-affected zone. The chemical composition of the filler wire affects the local mechanical properties in the fusion zone, showing an approximately 26% decrease in yield strength from the radiation exposure side to the weld root side. The effect of post–weld heat treatment on the tensile mechanical behavior was additionally investigated for different heat treatment artificial ageing conditions. The maximum yield strength increase was noticed for 48 h of artificial ageing for the weld root side of the fusion zone. Several approximations were proposed to correlate the hardness measurements with the local tensile mechanical properties of the welded joint that allow for a fast assessment of the global tensile mechanical behaviour of the welded joint. To evaluate the effect of (i) artificial ageing and (ii) geometrical imperfections of the weld on the mechanical behavior of the welded joint, finite element analyses were performed, using the local mechanical properties as input to the model. It is shown that the local mechanical properties of the fusion zone play a pivotal role on the strain localization and fracture of the welded joint.

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

Dynamic recrystallization (DRX) is one of the more convenient and effective means of refining grains during hot deformation, which is closely related to the precipitation behavior. Three alloys with varying pre-precipitations are designed by carrying out different heat treatment processes to explore the effects of precipitation on the recrystallization behavior of an Al–Cu–Li alloy during compression. It is indicated that the recrystallization behavior of the as-extruded alloy is quite sensitive to the precipitation. Precipitation does not change the recrystallization mechanism, but it could significantly affect the recrystallization volume fraction (VDRX). Meanwhile, the diverse extruded texture fibers coordinate deformation through different softening mechanisms during compression, which stimulates the nucleation of the lamellar grain in R–cube textures. Furthermore, the influence mechanism of microstructure on the material flow behavior is also discussed for the three heat-treated alloys. Therefore, this work is expected to provide new insights for Al–Cu–Li alloy to design high-performance products through grain refinement and texture modification in the subsequent processing.

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]

Copyright of Transactions of Nanjing University of Aeronautics & Astronautics is the property of Editorial Department of Journal of Nanjing University of Aeronautics & Astronautics 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.)

In this study, Al–Li alloys containing TiC + TiB2 particles were successfully prepared by mechanical stirring method. The alloy organisation and nanoparticles were investigated by scanning electron microscopy (SEM) and electron probe microanalyser (EPMA). The number of T1 phases in the alloy matrix after different pre-deformation was investigated by transmission electron microscopy (TEM). The results showed that TiC and TiB2 acted as nucleation plasmas for grains during solidification, promoting non-uniform nucleation and refining the grains in the 0.5 samples, the main recrystallisation mechanism of the alloy during solidification was the particle-stimulated nucleation (PSN) mechanism, and the incorporation of nanoparticles improved the recrystallisation resistance of the alloy, while the yield strength of the alloy firstly increased and then decreased as the amount of pre-deformation increased, and the best tensile properties occurred The yield strength and tensile strength of 0.5 samples after 5% pre-deformation were 580 MPa and 603 MPa, respectively. [ABSTRACT FROM AUTHOR]

• The dynamic evolution of T 1 phase during the hot deformation of Al-Cu-Li alloy has been completely revealed for the first time. • The mechanism interaction of T 1 phase with dislocation and grain boundary is elucidated. • The dynamic precipitation of T 1 phase greatly promoted the CDRX behavior by pinning dislocation walls and sub-grain boundaries. The T 1 phase is the highest density and most prominent strengthening effect precipitate in Al–Cu–Li alloys, and it undergoes a complex dynamic evolution during hot deformation, which has significant effects on microstructure development and hot working. This study comprehensively characterizes and analyzes the dynamic evolution of the T 1 phase at 400 °C/0.01 s−1 and its influence on continuous dynamic recrystallization (CDRX). The results indicate that the T 1 phase successively undergoes coarsening, fracture, dissolution, dynamic precipitation, recoarsening, and spheroidization during deformation. A shear-coupled diffusion mechanism is proposed to explain the ultrafast coarsening rate of the T 1 phase in early deformation. During the dynamic precipitation of the T 1 phase, an anomalous inhomogeneous size and spatial distribution of the T 1 phase are observed, and a high number density of fine T 1 phases form in the matrix (with a denser, thinner and shorter size at the dislocation wall). The dynamically precipitated T 1 phase is affected by the octahedral slip system during the coarsening process and exhibits a selective ripening phenomenon. The T 1 phase formed by aging increases the inhomogeneity of the deformation and induces many substructures intragranularly, decreasing the percentage of CDRX grains but increasing the CDRX potential. Conversely, the dynamically precipitated T 1 phase and its evolution accelerate CDRX development by promoting the transformation of LAGBs to HAGBs. In addition, the effects of dynamically evolving precipitates on the dislocations and formation modes of LAGBs at various deformation stages are elucidated. The results can provide valuable insights into the regulation of microstructure, and the development of high-performance Al–Cu–Li alloys, and also offer a theoretical and experimental basis for microstructure modeling. [Display omitted] [ABSTRACT FROM AUTHOR]

The study systematically investigated the impact of asymmetric rolling (AR) and subsequent aging treatment on the microstructure and mechanical properties of Al–Cu–Li–TiC/TiB 2 alloy. The average grain size of the as-cast A0 and A1 alloys was 249.87 μm and 38.2 μm, respectively. The grain size was significantly refined by TiC and TiB 2 particles. The texture of A0 and A1 samples after symmetric rolling (SR) was dominated by the β-fiber, including typical Copper, S, and Brass rolled textures. The core of the board has a relatively high proportion of Brass texture. The grain size of the AR sheet increases gradually from the surface to the center, with the middle to fast (MF) layer having the largest grain size. The middle to slow (MS) layer has the highest strength of Goss texture, indicating that the shear bands formed by AR are mostly located in the MS layer. A significant amount of T 1 precipitate was observed in the aged sample, and a new T 1 phase composite with a thickness of 1.426 nm was found in the AR sample. The structure of the composite consists of two parallel T 1 precipitates with Al–Cu layer atoms at the center. The growth behavior of the composite is such that the new T 1 precipitate adheres to one side of the original T 1 precipitate and grows parallel in the form of T 1P -T 1. In the T85 state, the A0SR samples exhibit a yield strength, tensile strength, and elongation of 503 MPa, 518 MPa, and 7.5%, respectively. The A1-SR samples exhibit a yield strength, tensile strength, and elongation of 520 MPa, 526 MPa, and 8.2%, respectively. The A0-AR samples exhibit a yield strength, tensile strength, and elongation of 553 MPa, 572 MPa, and 4.5%, respectively, while the A1-AR samples exhibit a yield strength, tensile strength, and elongation of 580 MPa, 605 MPa, and 5.2%, respectively. The increase in yield strength can be attributed to fine-grained strengthening, precipitation strengthening, and Orowan strengthening brought about by nano TiC/TiB 2 particles. [ABSTRACT FROM AUTHOR]

A novel method involving twin-wire pulsed VPPA (P-VPPA) welding was combined with Ti–Zr microalloying to improve the mechanical properties of AA2195-T8 Al–Cu–Li alloy variable polarity plasma arc (VPPA) welded joints. This method aimed to increase the width of the equiaxial cellular grain zone (ECZ) by adding higher content of Ti–Zr and reducing heat input. The microstructure evolution process was established to understand the formation and strengthening mechanism of the ECZ. The results showed that the strength of the ECZ was higher than that of the dendrite in the weld zone (WZ). The twin-wire VPPA welding led to the formation of a wider ECZ near the fusion zone (FZ). This ECZ was continuously distributed throughout the thickness direction of the welded joint. Combined with higher Ti–Zr microalloying, the maximum width of ECZ increased to 2.5 mm and extended to the WZ. Consequently, the proportion of cracks passing through the ECZ during tensile fracture increased from 27.6% to 88.7%. Moreover, the ultimate tensile strength (UTS) of the welded joint exhibited a notable improvement, rising from 328 MPa to 370 MPa, while the elongation also increased to 5%. The UTS of the welded joint achieved 66% of the base metal. Additionally, the average grain size in the ECZ was 14 μm. The formation of the ECZ was primarily attributed to the nucleation precursors of Al 3 (Ti, Zr) and β′ phase, as well as less welding heat input near the FZ. The widening of the ECZ was mainly due to the presence of more Al 3 (Ti, Zr) phases. Moreover, the grain boundary of the ECZ exhibited the distribution of Al–Cu eutectic, θ(Al 2 Cu), Ω, T2(Al 6 CuLi 3), and ω(Al 7 Cu 2 Fe) phases, while a small amount of T1(Al 2 CuLi) phase precipitated within the grain. The strengthening mechanism of ECZ is the result of multiple strengthening effects, including the reduction of element segregation and microcracks, the precipitation of the T1 phase, and the fine grain strengthening. [Display omitted] • The twin-wire P-VPPA welding and higher Ti–Zr microalloying was proposed. • The width of ECZ was obviously increased by improving VPPA welding process. • The mechanical properties of the welded joint were improved by widening ECZ. • The microstructure of ECZ was analyzed comprehensively. • The study explained the formation and strengthening mechanism of ECZ. [ABSTRACT FROM AUTHOR]

An appropriate friction stir welding (FSW) tool has been developed to perform high-quality joining of 12 mm thick Al-Li alloy plates. Threads and triple facets were machined on the stirring pin to improve the material flow. The differences in microstructure characteristics, recrystallization mechanisms, and precipitate evolution along the stir zone (SZ) thickness were systematically clarified. The results indicated that microstructures in SZ were refined by dynamic recrystallization (DRX) and showed an apparent top-to-bottom gradient distribution in grain size. The geometric topology of the stirring pin results in periodic ultrafine-grained bands throughout SZ. At the top and middle regions of SZ, high-density vacancies and dislocations were formed due to elevated temperature and strain rate, facilitating the precipitation of T 1 (Al 2 CuLi) phases through a dislocation-induced heterogeneous nucleation mechanism. In comparison, icosahedral quasi-crystalline T 2 (Al 6 Cu(Li, Mg) 3) phases, which can be attributed to the segregation of atoms and high cooling rate, were detected along grain boundaries at SZ-bottom. Furthermore, the ultimate strength values of tensile specimens sectioned from the top, middle, and bottom parts of SZ are 452, 457, and 406 MPa, respectively. Studying the inhomogeneous microstructure and properties of welded joints provides a theoretical basis for manufacturing high-load components. [ABSTRACT FROM AUTHOR]

Pre-rolling deformation is a preferable procedure in practice, compared to pre-stretching, to improve the performances of the rolled Al–Cu–Li plates. In the present work, the different strains of pre-rolling were applied to a rolled Al–Cu–Li alloys before aging. The influence of pre-rolling on mechanical properties and precipitates during 200 °C aging was carefully investigated through hardness test, tensile test, and microstructure characterization. It was found that the aging precipitation behavior was rather complicated for the not pre-rolled samples, various abnormal precipitates were precipitated along with the large diameter and low-density of T1 (Al2CuLi) phase after a period of aging. After pre-rolling, the nucleation of T1 phase was greatly promoted while the formation of other phases was inhibited, resulting in the precipitation behavior became dominated by the high density and tiny T1 phase. Furthermore, the precipitation kinetics of the T1 phase was continually accelerated by increasing the pre-stain, which facilitated the more rapid aging response, higher T1 phase density and continuous improvement of mechanical properties. The strain of pre-rolling could be increased to 20% to obtain the optimal properties, and the tensile strength of the 20% pre-rolled samples increased to ∼520 MPa in peak aged state, compared to ∼360 MPa of the samples only T6 tempered.

A 2297 aluminum-lithium alloy was subjected to multi-axial compression (MAC) at 160 °C to obtain different cumulative strains. The room temperature tensile test, transmission electron microscopy and X-ray diffraction techniques were used to study the microstructural evolution and mechanical properties of Al–Cu–Li alloy. It was observed that the ultimate tensile strength was increased from 267 MPa to 480 MPa and the hardness was increased from 55 HV to 141 HV by high-density dislocations and precipitation phases. Due to the massive amount of precipitation occurring at dislocations and the subsequent high strain introduced to destroyed it, the size of the precipitates was effectively reduced, the fine precipitates delayed the strain localization, the alloy obtained high elongation (~11.2 %).