铝锂合金夹杂物形成机理相关文献汇报

Aluminum‐lithium (Al‐Li) alloy is one of the most promising lightweight structural materials in the aeronautic and aerospace industries. The key to achieving their excellent mechanical properties lies in tailoring T1 strengthening precipitates; however, the nucleation of such nanoparticles remains unknown. Combining atomic resolution HAADF‐STEM with first‐principles calculations based on the density functional theory (DFT), here, we report a counterintuitive nucleation mechanism of the T1 that evolves from an Eshelby inclusion with unstable stacking faults. This precursor is accelerated by Ag‐Mg clusters to reduce the barrier, forming the structural framework. In addition, these Ag‐Mg clusters trap the free Cu and Li to prepare the chemical compositions for T1. Our findings provide a new perspective on the phase transformations of complex precipitates through solute clusters in terms of geometric structure and chemical bonding functions.

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This study investigates the effect of TiC particles regarding the properties of aluminium–lithium alloys under high-temperature conditions, focusing on the reinforcing effect of TiC and TiB2 particles in the aluminium matrix and the effect on the coarsening process of T1 precipitates. Aluminium–lithium alloys are widely used in aerospace applications, especially as skin materials for fast vehicles, due to their excellent high specific strength and corrosion resistance. However, conventional aluminium alloys are inadequate in meeting the elevated temperature service requirements associated with supersonic flight. Consequently, there is a significant scientific imperative to investigate the heat resistance of novel aluminium–lithium alloys. The inclusion of TiC and TiB2 nanoparticles has been demonstrated to enhance the mechanical properties of the alloys, particularly at high temperatures of 200 °C. These particles have been shown to enhance the strength and toughness of the alloy through mechanisms such as grain refinement and increased dislocation density. Concurrently, this study determined that the coarsening phenomenon of T1 precipitates occurs at elevated temperatures. The inclusion of TiC particles, however, has been shown to inhibit the coarsening process, delay the coarsening of the T1 phase, and enhance the mechanical properties of the material. This outcome is of considerable significance for the composition design of aluminium–lithium alloys and their performance optimisation in high-temperature applications.

ABSTRACT Aluminium-Lithium (Al-Li) alloys are known for its properties that are superior to conventional ones. The inclusion of graphene reinforcements to the metal matrix improved strength, stiffness, density reduction, tensile properties, wear, creep, and fatigue resistance. This study examined the combined result of graphene nanoparticles (GNP) and the Al-Li2099 alloy with an ultrasonic-aided stir-casting process. The nano-particulate metal matrix composites with various weight percentages (wt. %) of GNP were fabricated and investigated for physical, mechanical, and microstructural properties. The nanocomposites’ mechanical properties were examined in detail, and significant improvements in hardness, tensile, and compressive strength were observed with higher wt. % of GNP. Theoretical and empirical densities were measured, revealing that the nanocomposite’s densities decrease with the increase in wt. % of nano-reinforcements. Material characterisation of the composites was carried out using XRD, EDAX, SEM, and Fourier-Transformation Infrared Spectroscopy (FTIR). SEM and EDAX confirmed the presence of GNP particulates in the matrix microstructure and elemental composition. The XRD results confirmed the presence of GNP particulates in the Aluminium Alloy (AA) 2099 and the composite, and no other intermetallic elements were detected. The results demonstrated that the GNP addition to the AA2099 significantly enhanced the mechanical and microstructural characteristics of the nanocomposite.

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The evolution of hydrogen microporosity in Al–Li alloy during superheating has been observed using synchrotron X-ray radiography. The growth kinetics of microporosity are investigated to elucidate the evolution mechanism. The results demonstrate that microporosity is susceptible to migration, merging, and dissolution during its growth. In addition, microporosity diameters conform to a Gaussian distribution during the initial stage of superheating. However, the evolution of group microporosity is controlled by Lifshitz-Slyozov-Wagner (LSW) diffusion during the final stage. The nucleation and growth of microporosity during superheating are primarily influenced by the competition between hydrogen diffusion and dissolution. GRAPHICAL ABSTRACT

Precipitate phase characteristics in Al–Li alloy sheet significantly influence damage evolution during fatigue crack propagation. To investigate the influence mechanisms, the present work establishes a cross‐scale model that integrates the extended finite element method (XFEM) and the crystal plasticity finite element method (CPFEM) to elucidate the damage evolution at the crack tip. The results reveal that the T1 phase facilitates the dislocation slip reversibility, with non‐hardening slip retracting back to the crack tip, thereby reducing the cumulative damage. The accumulated shear strain could effectively predict the crack propagation paths. The planar slip effect of the δ′ phase significantly enhances the accumulated shear strain of the (1‐11)[110] slip system, promoting single slip and resulting in a serrated propagation path. Conversely, the T1 phase inhibits planar slip, enhancing the accumulated shear strain of multiple systems, and promoting multiple slip, leading to a relatively straight crack propagation path.

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The softening of aluminum–lithium alloy welded joints generally leads to a reduction in mechanical properties. In this study, a piece of 2A97-T3 aluminum–lithium alloy with a thickness of 2.8 mm was selected as the test material, and the tool and process used for wire-filled stationary shoulder friction stir welding (SSFSW) were developed. By increasing the bearing area of the softening zone, an equal-strength T-joint was manufactured. Good weld formation was obtained when the rotation speed was set to 2000 rpm and the welding speed ranged from 100 to 120 mm/min. The thickness of the softening zone was controlled by adjusting the reserved gap between the shoulder and the workpiece. The softening mechanism of the weld joint was revealed. The softening was attributed to the coarsening of the main precipitated phases (T1 and θ′ phases) in the heat-affected zone (HAZ) and the dissolution of precipitated phases in the thermo-mechanically affected zone (TMAZ). Grain refinement in the nugget zone (NZ) led to a certain fine-grained strengthening effect, although the precipitated phase was almost completely dissolved. Due to the thermal effect of second-pass welding, the hardness value of the NZ and HAZ in the center of the skin further decreased, and the minimum hardness was approximately 70% that of the base material. Tensile testing results indicated that the softening effect was largely offset by the increased bearing area of the softening zone, resulting in the successful welding of high-strength Al-Li alloy T-joints with equal strength. The strength coefficient was found to be 0.977.

Al–Li–Cu–Mg–Zr alloys are widely used in the aerospace industry for different applications and make an excellent concurrent to high-performance composites. This family of alloys has remarkable properties like low density, high elastic modulus, high strength and specific stiffness, fracture toughness, fatigue crack growth resistance, and improved corrosion resistance. The present work aims to investigate a family of Al–Li alloys by employing suitable characterization techniques such as computer-aided cooling curve analysis and thermal dilatometry to characterize the as-cast alloy. The characterization temperatures of the alloy were obtained and the phase transformation temperatures were concluded as thermal expansion inflection points as well. Furthermore, the homogenization heat treatment effect of the alloy is examined through optical microscopy (OM), scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Vickers microhardness testing to determine the optimum heat treatment time. The results reveal the formation of δ′, δ and β’ precipitates in the alloy after different hours of homogenization heat treatment. Notably, our investigation identifies the optimum heat treatment time for the alloy as 26h at 515 °C, resulting in reduced hardness and barely any chemical segregation. These findings contribute to the characterization of as-cast Al–Li alloys and the understanding of microstructure evolution and mechanical properties during homogenization heat treatment that offer a valuable insight for enhancing their performance in aerospace applications.

A combination of high hardness values and a low energy–consumption preparation method was used to induce the precipitation of the T1 phase in the Al alloy AA2195. This combination was obtained by subjecting the alloy samples to sequential and early stages of prestretching. Hardness testing and differential scanning calorimetry were employed to explore the behaviours of the hardness and enthalpy values as functions of the prestretching level applied before aging. Results demonstrated that the optimal aging thermomechanical conditions are (1) 150 °C for 10 h after applying prestretching levels of 0%, 1%, and 2% and (2) 150 °C for 20 h after applying prestretching levels of 3% and 4%. Under these conditions, the recorded enthalpy values for the formation of the T1 phase at prestretching levels of 0%, 1%, and 2% were 2.86, 1.72, and 1.14 J g−1, respectively and those obtained at prestretching levels of 3% and 4% were 1.43 and 1.27 J g−1, respectively.

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In-situ TEM investigation of aging response in an Al–7.8 at.% Li was performed at 200 °C up to 13 hours. Semi-spherical δ′ precipitates growing up to an average radius of 7.5 nm were observed. The size and number of individual precipitates were recorded over time and compared to large-scale phase-field simulations without and with a chemo-mechanical coupling effect, that is, concentration dependence of the elastic constants of the matrix solid solution phase. This type of coupling was recently reported in theoretical studies leading to an inverse ripening process where smaller precipitates grew at the expense of larger ones. Considering this chemo-mechanical coupling effect, the temporal evolution of number density, average radius, and size distribution of the precipitates observed in the in-situ experiment were explained. The results indicate that the mechanism of inverse ripening can be active in this case. Formation of dislocations and precipitate-free zones are discussed as possible disturbances to the chemo-mechanical coupling effect and consequent inverse ripening process.

The influence of Cu content (3.10, 3.50, and 3.80 wt.%) on the precipitation behavior and mechanical properties of Al-Cu-Li alloys under two aging conditions (direct aging at 175 °C vs. 3.5% pre-stretching followed by aging at 155 °C) was systematically investigated. The alloys were characterized using hardness testing, tensile property evaluation, and transmission electron microscopy (TEM) to correlate microstructural evolution with performance. The results revealed that increased Cu content accelerated early-stage hardening kinetics and elevated peak hardness and strength. Aging at 175 °C/36 h produced T1 phase-dominated microstructures with θ′ phases. With the increase of Cu content, the enhancement effect on the precipitation of T1 and θ′ phases becomes more pronounced, gradually overshadowing the initial promotion effect on precipitate growth. Pre-deformation prior to 155 °C/36 h aging induced significant T1 phase refinement and proliferation, with increasing Cu content continuously reducing T1 phase sizes while moderately enlarging θ′ precipitates. Precipitation-strengthening analysis revealed a transition in T1 strengthening from bypass to shearing dominance under 155 °C/36 h aging after pre-deformation, enhanced by Cu-promoted T1 refinement, which collectively drove superior strength in high-Cu alloys. These findings provide valuable insights for the composition design and mechanical property optimization of Al-Cu-Li alloys.

In the present study, 2195 aluminium–lithium (Al–Li) alloy joints were welded by laser-metal inert gas (laser-MIG) hybrid welding. The effect of different laser powers (700, 1000, and 1300 W) on the microstructures and mechanical properties of the weld joints was investigated. The dendritic solidification structure of the weld joint comprised the α-Al, θ-(Al2Cu), and T-(AlLiSi) phases. When the laser power increased, the grains coarsened, and the amount of the precipitated phase decreased. Consequently, the micro-hardness of the weld decreased. The heat input also increased with the increase in laser power. This increased the fluidity and solidification time of the liquid metal at the bottom of the molten pool. Therefore, the deposition of the particles of the refractory metal compounds and the formation of the equiaxed grain zone (EQZ) was hindered.

Through a systematic study involving combined pre-deformation (ranging from 0% to 6%) and aging treatment at 175 °C, the influence of precipitates on intergranular corrosion behavior was investigated. The results indicate that, in the under-aged stage, unpredeformed alloys undergo generalized intergranular corrosion due to the continuous distribution of Cu/Li-rich phases along grain boundaries. During peak aging, the uniform precipitation of the T1 phase within grains inhibits intergranular corrosion propagation, while in the over-aged stage, the coarsening of grain boundary phases and the formation of the precipitate-free zone (PFZ) lead to a transition to pitting corrosion. Upon introducing pre-deformation at 4%-6%, high-density dislocations promote the uniform and dispersed precipitation of the T1 phase within grains, inhibiting the aggregation of Cu-rich phases at grain boundaries and significantly reducing the tendency towards intergranular corrosion. As the level of pre-deformation increases, the corrosion mode dynamically shifts from localized intergranular corrosion to pitting corrosion. Pre-deformation improves the susceptibility to intergranular corrosion by optimizing the distribution of precipitates (dense within grains and discontinuous at grain boundaries) and balancing the potential difference between grain boundaries and grains.

This work investigates the effect of small (5 and 10%) cold rolling reductions on the microstructure, crystallographic texture, and hardness of a solution-treated Al-Cu-Li alloy (AA2055). It was found that deformation initiates the intensive accumulation of crystal defects and the formation of a uniform, dense dislocation substructure. This is confirmed by a sharp increase in the density of geometrically necessary boundaries (GNBs) and a significant rise in hardness in the as-rolled conditions. It is shown that deformation intensifies the β-fiber texture components and suppresses recrystallization orientations. The obtained results demonstrate a clear quantitative correlation between the thermomechanical processing parameters, the evolution of the substructure, and the distribution of geometrically necessary dislocations. This provides a scientific basis for optimizing the aging kinetics and achieving an optimal balance of mechanical properties in the AA2055 alloy.

The influence of Cu and Li content on the formation and evolution of the second phase in Al-Cu-Li alloys was investigated under as-cast conditions and homogenization treatment regimes. The second phase was characterized via SEM, EDS, XRD and DSC analysis. The results revealed that elevated Cu content promoted the formation of all three resolvable phases in the as-cast microstructures. Increased Li content significantly enhanced the Al7Cu4Li phases while suppressing the Al2Cu phases. During the homogenization treatment, the low-melting-point AlCuMgAg eutectic structure exhibited preferential dissolution kinetics and higher temperatures facilitated the complete dissolution of both Al7Cu4Li and Al2Cu phases. The double-step homogenization treatment of 495°C/24 h+515°C/24 h is universally applicable to all the investigated alloys in this study.

Al–Cu–Li (2xxx series) powders for additive manufacturing processes are often produced by gas atomization, a rapid solidification process. The microstructural evolution of gas-atomized powder particles during solidification was investigated by phase-field simulations using the software tool MICRESS. The following topics were investigated: (1) the microsegregation of copper and lithium in the particle, and the impact of lithium addition on the formation of secondary phases in Al-2.63Cu and Al-2.63Cu-1.56Li systems, (2) the effect of magnesium on the nucleation and final mass fraction of T1 (Al2CuLi) growing from the melt, and (3) the effect of increased magnesium content on the T1 and Sʹ (AlCu2Mg) phase fractions. It is observed that the addition of lithium into the Al–Cu system leads to a decrease in the solid solubility of copper in the primary matrix; consequently, more copper atoms segregate in the interdendritic regions resulting in a greater mass fraction of secondary precipitates. Our result agrees with findings on the beneficial impact of magnesium on the nucleation and precipitation kinetics of T1 precipitates in the conventional casting process with further thermomechanical heat treatments. Moreover, it is observed that the increase in magnesium from 0.28 wt.% to 0.35 wt.% does not significantly affect the nucleation and the amount of the T1 phase, whereas a decrease in T1 phase fraction and a delay of T1 formation are encountered when magnesium content is further raised to 0.49 wt.%.

Oxide films in Al–Li alloy diffusion bonding joints hinder atomic diffusion, reducing bond strength. A new electrodeposition process applies a nano-Cu coating, achieving a peak shear strength of 102.8 MPa at 1 μm and 520 °C. Cu atoms from the coating diffuse into the Al matrix, forming intermetallic compounds (IMCs) that enhance Al–Al mutual diffusion. However, thinner coatings (<0.5 μm) fail to prevent oxide film formation, while thicker ones (>4 μm) hinder Al diffusion due to continuous IMC structures. Low temperatures (<480 °C) result in coarse, non-diffusive IMCs, while high temperatures (>540 °C) promote IMC growth and increase void and crack risks. This study introduces a novel nano-coating concept for Al–Li alloy bonding, with practical engineering applications.

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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.

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In this study, 2198 Al-Li alloy, a low density and high-performance material for aerospace equipment, was welded using ultrahigh-frequency pulse alternating current with cold metal transfer (UHF-ACCMT). Influence of different ultrahigh-frequency on the formation, porosity, microstructure, microhardness and tensile strength of the welded joints were investigated. The results showed that the coupled ultrahigh-frequency current generated electromagnetic force to stir the liquid metal of molten pool. The weld formation became much better with metallic luster and uniform ripples at frequency of 60 kHz and 70 kHz. The porosity was the minimum at frequency of 60 kHz. Furthermore, the molten pool was scoured and stirred by the electromagnetic force which provided the thermal and dynamic conditions for nucleation and grain refinement, the width of fine equiaxed grain zone became larger, and the number of equiaxed non-dendrite grains increased. With the grain refining and crystallize transition, the average microhardness and tensile strength of the joints at frequency of 60 kHz reached up the highest value, 116 HV0.1 and 338 MPa, respectively. The fracture of the welded joints presented the characteristics of quasi-cleavage fracture.

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With the development of society, there is an increasingly urgent demand for light-weight, high-strength, and high-temperature-resistant structural materials. High-entropy alloys (HEAs) owe much of their unusual properties to the selection among three phases: solid solution (SS), intermetallic compound (IM), and mixed SS and IM (SS and IM). Therefore, accurate phase prediction is crucial for guiding the selection of element combinations to form HEAs with desired properties. Light high-entropy alloys (LHEAs), as a significant branch of HEAs, exhibit excellent performance in terms of specific strength. In this study, we employ a machine learning (ML) method to realize the design of light-weight high-entropy alloys based on solid solutions. We determined the Gradient Boosting Classifier model as the best machine learning model through a two-step feature and model selection, in which its accuracy and F1_Score achieve 0.9166 and 0.8923. According to the predicted results, we obtained Al28Li35Mg15Zn10Cu12 LHEAs, which are mainly composed of 90% solid solution. This alloy accords with the prediction results of machine learning. But it is made up of a two-phase solid solution. In order to obtain a light-weight high-entropy alloy dominated by a single solid solution, we designed Al24Li15Mg26Zn9Cu26 LHEAs on the basis of machine learning prediction results accompanied by expert experience. Its main structure includes a single-phase solid solution. Our work provides an alternative approach to the computational design of HEAs and provides a direction for future exploration of light-weight high-entropy alloys.

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Al-Li alloys with a high Li content have the advantages of low density and high stiffness but usually suffer from poor strength, instability of nanoprecipitates, and severe anisotropy, limiting their practical application. Here, we introduce a stable multilayer core-shell nanostructure in aluminum-lithium alloy castings to address these challenges. By quantifying the precipitates' composition and structures using atom probe tomography (APT) and small angle neutron scattering (SANS), it was found that there exists a unique type of Li-rich, coherent, nanoscale single-core double-shell particles in this alloy, which is different from the previously reported core-shell structures. First-principles calculations reveal that this complex core-shell structure possesses both the advantage of low mismatch-induced nucleation and highly stable characteristics under service conditions. Compared with traditional core-shell structures, this core-shell structure exhibits the lowest critical nucleation radius and free energy within the solidification range, enabling the cast Al-Li alloy to achieve a strength approaching 500 MPa.

To address the challenges of poor chemical stability and safety hazards in aluminum‐lithium (Al‐Li) alloys with high Li content for metal fuel applications, this study pioneers a ternary Al‐Li‐Mg system, synergistically optimizing structure and oxidation/combustion. The spherical Al‐Li‐Mg alloy powders (3 wt.% Li, 10 and 20 wt.% Mg) were prepared via high‐speed centrifugal atomization. Composition and structural characterization revealed a hierarchical structure: an α‐Al matrix with interconnected channels enriched in Al3Mg2 and Al2LiMg intermetallics. Compared to Al‐Li alloys, the ternary alloying significantly lowered the initial oxidation temperature by 125.2°C in thermogravimetric‐differential thermal analysis and enabled staged heat release. Combustion in perchlorate composites showed shortened ignition delays, and AlLi3Mg20/KP achieved a 3.22 mm/s burning rate with intensified gas‐phase reactivity and smaller residues. Mg enables dual‐stage melting‐oxidation, disrupting the passivation layer for complete core combustion while suppressing Al agglomeration. These synergistic effects concurrently shorten ignition delays and elevate combustion efficiency. This work establishes a theoretical and technological framework for advancing the compositional design and performance optimization of high‐energy metal fuels.

Aluminum alloys are widely sought for different applications due to their high strength-to-weight ratio. Most often this increased strength of the alloy is achieved by specific alloying elements and heat treatment processes which give rise to second phases intermetallic particles (IMPs) also known as intermetallic compounds (IMCs). These second phases play a dominant role in the corrosion susceptibility of aluminum alloys. This review provides a systematic survey of the electrochemical, and galvanic corrosion behavior of IMPs in the context of aluminum alloys. A discussion of the electrochemical/galvanic corrosion behavior of selected/important intermetallic compounds that are commonly found in aluminum alloys such as the Q-phase (Al4Cu2Mg7Si8), π-phase (Al8Mg3FeSi6), θ-phase (Al2Cu), S-phase (Al2CuMg), the β-phase (Mg2Si), β-phase (Al3Mg2), δ (Al3Li), η-phase (MgZn2), and β-phase (Al3Fe) is provided. In addition, the limitations in the electrochemical characterization of intermetallic compounds, the research gap, and prospects are also provided in addition to the phenomenon of galvanic polarity reversal and self-dissolution of IMPs.

With the increasing demand for premium-quality aluminum alloy castings that can be used as safety-critical structural components, as well as the rising urge to utilize sustainable materials during the manufacturing process, novel technologies need to be developed and implemented during the treatment of liquid alloys. Impurity and alloying elements accumulate in recycled aluminum alloys, which frequently results in the formation of coarse intermetallic compound (IMC) particles in the microstructure that have a detrimental effect on the ductility of cast products. One successful approach to alleviate this negative effect relies on affecting the phase selection and refinement of IMC phases. A growing body of literature has shown that the crystallization process of IMCs is affected by the native oxide phases present in the liquid alloys. It has also been demonstrated that by appropriate technologies, harmful oxide inclusion (like oxide bifilms) can be transformed into small-sized oxide particles that can be dispersed throughout the liquid alloy to serve as heterogeneous nucleation sites for different phases. In this way, the adverse effects of oxide inclusions and IMCs are simultaneously mitigated. This contribution aims to review the recent progress of experimental and theoretical work related to intermetallic particle refinement by oxide phases. Emerging technological solutions capable of refining intermetallics through transforming harmful oxide inclusions into numerous, well-dispersed heterogeneous nucleation sites are comprehensively reviewed. Besides analyzing the current state of these techniques, this discussion evaluates their future implications and the potential challenges that may arise in their application and development.

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Thin twin-roll cast strips from a model Al-Cu-Mg-Li-Zr alloy with a small addition of Sc were prepared. A combination of a fast solidification rate and a favorable effect of Sc microalloying refines the grain size and the size of primary phase particles and reduces eutectic cell dimensions to 10–15 μm. Long-term homogenization annealings used in conventionally cast materials lasting several tens of hours followed by a necessary dimension reduction through rolling/extruding could be substituted by energy and material-saving procedure. It consists of two-step short annealings at 300 °C/30 min and 450 °C/30 min, followed by the refinement and hardening of the structure using constrained groove pressing. A dense dispersion of 10–20 nm spherical Al3(Sc,Zr) precipitates intensively forms during this treatment and effectively stabilizes the structure and inhibits the grain growth during subsequent solution treatment at 530 °C/30 min. Small (3%) pre-straining after quenching assures more uniform precipitation of strengthening Al2Cu (θ′), Al2CuMg (S′), and Al2CuLi (T1) particles during subsequent age-hardening annealing at 180 °C/14 h. The material does not contain a directional and anisotropic structure unavoidable in rolled or extruded sheets. The proposed procedure thus represents a model near net shape processing strategy for manufacturing lightweight high-strength sheets for cryogenic applications in aeronautics.

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Thermal stability and mechanical properties of Al alloys can be critically influenced by the coarsening mechanism of their precipitates, where interfacial chemical variations play significant roles. Here, we reveal that the coupling of solutes Ag, Cu and Li at the T1/Al interface results in the formation of Li-rich layers with different separations from the pre-existing T1 unit cell. Such Li-rich layers would template the thickening of T1 phase, and their different positions are identified to determine the thickening paths of different T1 phases. These findings provide insights that can benefit the modification of high-temperature performances of Al alloys via interface engineering. GRAPHICAL ABSTRACT

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: A processing scheme for preparing strips of Al−Cu−Li−Mg−Zr -based alloys microalloyed with Sc was proposed. This scheme includes a twin-roll casting of strips with a near-net-shaped 3 mm-thick gauge and a homogenization/solution treatment processing step. Two twin-roll cast Al−Cu−Li−Mg−Zr -based alloys were studied, one with an addition of 0.17 wt.% Sc, and the other without addition of Sc. Both alloys were annealed at 300 °C for 30 min, 450 °C for 30 min, and 530 °C for 30 min and quenched into room temperature water. The first two annealing steps provide a fine dispersion of Al 3 Zr/Al 3 (Sc,Zr) particles. The final annealing step serves as homogenization/solution treatment. A fine crystallization structure of the twin-roll cast materials enables the dissolution of primary particles containing the main alloying elements during a relatively short annealing time. Shorter soaking duration limits the depletion of surface layers from Li and significant coarsening of Al 3 Zr/Al 3 (Sc,Zr) dispersoids. The Sc-containing material has significantly finer grains already in the as-cast state. The Al 3 (Sc,Zr) dispersoids formed during the homogenization/solution treatment step prevent grain coarsening at high temperatures. Strengthening θ′ (Al 2 Cu), T 1 (Al 2 CuLi), and rare S' (Al 2 CuMg) phases are formed during subsequent artificial aging at 180 °C. The increase in yield strength was 200 MPa in the peak-aged conditions. This value is comparable to the ones reported in similar direct-chill cast materials, thus validating the proposed processing scheme.

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In this work, the effects of the Cu/Li ratio on the mechanical properties and corrosion behavior of Sc-containing Al-Cu-Li alloys were systematically investigated by utilizing age-hardening behavior, tensile property, corrosion behavior, and electrochemical behavior, complemented by microstructural characterization through EBSD and TEM. The results show that the peak aging strength of the alloys remained relatively consistent but slightly decreased with the decrease in Cu/Li ratio, and the yield strengths were 585 MPa, 578 MPa, and 573 MPa, respectively. The changes in the Cu/Li ratio caused different matching patterns of precipitates in the peak aging alloys. The cumulative precipitation strengthening by T1, θ′, δ′, and S′ phases are equal within the alloys with different Cu/Li ratios. However, the strength contribution of the T1 phase decreases from 81% to 66% with the decrease in the Cu/Li ratio. Concurrently, the precipitates of LAGBs gradually increase in number and are continuously distributed, and the precipitates of HAGBs become larger in size with lower Cu content as the Cu/Li ratio decreases, all of which leads to a weakening of the intergranular corrosion (IGC) resistance within the low Cu/Li ratio alloy.

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The research aim was to optimize post-weld heat-treatment (PWHT) modes for a laser-welded joint of the Al–Cu–Li alloy and improve their respective strength properties. As a result, the ultimate tensile strength, yield point, and elongation of the joint were enhanced up to 95%, 94%, and 38%, respectively, of those inherent in the base metal. Before and after PWHT, both microstructures and phase compositions have been examined by optical and scanning electron microscopy, as well as synchrotron X-ray diffractometry. In the as-welded metal, the α-Al and T1(Al2CuLi) phases were found, along with the θ′(Al2Cu) and S′(Al2CuMg) phases localized at the grain boundaries, significantly reducing the mechanical properties of the joint. Upon quenching, the agglomerates dissolved at the grain boundaries, the solid solution was homogenized, and both Guinier–Preston zones and precipitates of the intermediate metastable θ″ phase were formed. After subsequent optimal artificial aging, the (predominant) hardening θ′ and (partial) T1(Al2CuLi) phases were observed in the weld metal, which contributed to the improvement of the strength properties of the joint.

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