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The fatigue crack propagation (FCP) behavior of a new Al–Cu–Li alloy under different aging treatments including T3, T8, and non-isothermal aging (NIA) was investigated. It was detected that the T8-24h sample exhibited the highest FCP resistance and the best mechanical performance. Compared with the T3-40D sample, the crack paths of the T8-24h sample and the C150 (non-isothermal peak-aged) sample were more tortuous and the crack width was narrower. Furthermore, the T8-24 sample had the lowest decreased FCP rate by an order of magnitude at the stress intensity factor (ΔK) of 30 MPa·m1/2. A large number of nano-scale T1 phases were precipitated in the T8-24h sample and their number density was also increased compared with the other sample. The presence of the tiny T1 phase plays a crucial role in impeding crack propagation as it can be sheared by dislocations without accumulating damage. This resulted in a substantial improvement both in the mechanical and fatigue properties of the alloy. Moreover, in the Paris stage of FCP, factors such as the size and concentration of precipitates within the grain and grain boundary play a vital role in determining the extent of crack growth. The results of transmission electron microscopy (TEM) bright field images on grain boundaries (GBs) analysis show that the variations in strength between the grain boundary and intragranular regions have a direct influence on the alloy's susceptibility to fatigue and corrosion resistance.

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]

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.

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.

Novelty: Most of the open literature research has focused on the microstructural evolution and mechanical properties of AA2050 alloy. Also, a significant study discusses the corrosion behavior of AA2050 alloy based on immersion and electrochemical characteristics. The influence of heat treatment on the microstructure and mechanical properties of friction stir processed AA2050 alloy is scarcely discussed in the open literature. The hot salt corrosion characteristics of friction stir processed AA2050 seldom exists in the available literature. This study concentrates on microhardness, tensile strength, and corrosion properties of friction stir processed AA2050. Also, the work focuses on the influence of artificial aging on the microhardness, and tensile strength of the friction stir processed AA2050.

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]

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]

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]

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.

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]

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.

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.

The anisotropy of mechanical properties limits the applications of Al-Cu-Li alloys. In this study, microstructure evolution and mechanical properties of an AleCueLi alloy via room-temperature rolling (RTR), room-temperature cross rolling (RCR), cryorolling (CR) and cross cryorolling (CCR) were investigated. The processing of AleCueLi 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. [ABSTRACT FROM AUTHOR]

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.

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• 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]

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.

The regulation of blank microstructure is the key to manufacturing high-quality ring cylinder by composite spinning - extrusion forming. In this paper, the precipitation morphologies of three Al3Zr dispersions were obtained by changing the heat treatment process, and their effects on the microstructure and mechanical properties of Al-Cu-Li alloy ring cylinder were investigated. The results show that the microstructure and mechanical properties of ring cylinder are affected by the different precipitation distribution of Al3Zr dispersoids in the blank. When the Al3Zr dispersoids precipitated and dispersed, the cracking of ring cylinder was eliminated, the thickness of coarse-grained layer decreases obviously, and the elongation is increased by 33.5%. In the T83 state, the average length of the T1 phase decreased from 100.3 to 77.5 nm, while the tensile strength and yield strength of ring cylinder increased by 16 and 20 MPa, respectively.

A friction-stir welded Al–Cu–Li alloy plate with desirable mechanical performance has been obtained using specific parameters. The microstructures of the nugget zone were systematically characterised and nano-sized phases, including δ ′ , θ ′ and T 1 were found in its matrix. These phases enhance the strength of the joint to a level comparable with the base metal. The results provide the means of obtaining a reliable and low-cost friction-stir weld (FSW) joint for T3-tempered Al–Cu–Li alloy plates without any post-welding heat treatments. This study shows that, by using appropriate parameters of FSW, the microstructures and mechanical precipitates of the nugget zone can be controlled to enhance the weld quality. [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]

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]

In the present study, the effect that superplastic deformation exerts on the microstructures, texture, and mechanical properties in 2A97 Al–Cu–Li alloy was investigated. The as-received material was deformed to a series of strains for 50%, 100%, 150%, and 200% at 430 °C with an initial strain rate of 2 × 10−3 s−1, and the grain structure, dislocation, secondary phase particles, cavities, texture, and tensile properties of deformed alloys were demonstrated and discussed comprehensively. Results show that with the increase of superplastic strain, the grain size of the alloy decreased gradually due to the dynamic recrystallization, and the Cu-rich secondary phase particles partially dissolved and partially coarsened. The initiation and growth of the cavities mainly depended on the grain boundary sliding and grain rotation, the fraction of cavities increased rapidly at higher strains (100%–200%). Superplastic deformation weakened the rolling texture (Brass, Copper, and S) and enhanced the recrystallization texture (Goss and ND-Rotated-Cube). The strength of the material decreased with increasing the superplastic strain firstly, after the strain exceeded 100%, the strength started to increase. The fracture elongation varied oppositely. The strengthening mechanism was discussed in detail. The coarsening of Cu-rich secondary phase particles and the rapid formation of cavities resulted in the drastic loss in ductility after the strain of 100%. • The microstructures and mechanical properties of an Al–Cu–Li alloy with different superplastic strains are studied. • The evolution of grain structure, secondary phases, cavities, and texture are demonstrated systematically. • The mechanical properties of the post-deformed materials are strongly related to the dramatically changed microstructures. • The formation of cavities and coarsening of secondary phase particles exert an adverse influence on the ductility. [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]

In this study, the effects of heat treatment on the microstructure and mechanical properties of extruded 2196 Al-Cu-Li alloy were examined and the precipitation behavior and strengthening mechanism were investigated. It was found that the solution treatment and artificial aging had a significant strengthening effect on the mechanical properties of the extruded alloy, which was related to the type, size, number density, and distribution of the precipitates. Most of the second phases dissolved back into the matrix after solution treatment. The precipitation sequence of 2196 alloy during aging treatment was identified as: supersaturated solid solution→ GP zone + δ′/β′ (Al3(Li,Zr)) → δ′ + θ′ (Al2Cu) + T1 (Al2CuLi) → θ′ + T1, where T1 phase played a leading role in the precipitation strengthening. The fracture mechanism changed from ductile fracture to intergranular fracture. The pre-stretching deformation can introduce a large number of vacancies and dislocations, which provide conditions for atomic diffusion and precipitation of the phases, and further improve the mechanical properties of the alloy. Besides, pre-stretching can effectively shorten the time required for peak strengthening, which is only 20% of the time needed in single-stage peak-aging (170 °C/36 h). Finally, the optimal heat treatment process of 2196 Al-Cu-Li alloy was determined as: 515 °C/90 min solution treatment+3% pre-stretching+170 °C/16 h artificial aging.

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

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

The microstructure-mechanical properties connection and strengthening contribution of Al- x Cu-1.3Li-X (x = 3.8, 4.2, 4.5 wt%) alloy sheets subjected to various heat treatments were systematically investigated. After solid-solution treatment, the decreased schmid factor value was the main factor for higher strength of Alloy-3 (4.5 wt% Cu). The number density and diameter of T 1 precipitates simultaneously increased with rising the Cu content during T8 aging, leading to the highest strength (655.4 MPa) of T8-aged Alloy-3. However, the high Cu content level resulted in the preferential precipitation of Guinier-Preston (G.P) zones during T6 aging at 165 °C. The θ' precipitates were therefore significantly increased and the nucleation of T 1 precipitates was suppressed in T6-aged Alloy-3, causing the reduced strength compared to that of T6-aged Alloy-2 (4.2 wt% Cu). Furthermore, the experimental yield strength was successfully predicted by invoking the modified precipitate strengthening model, in which the θ' precipitate-dislocation interaction was by-passing mechanism, whereas the shearable and by-passed T 1 precipitates coexisted for all alloys. The strengthening transition from by-passing to shearing occurred in T 1 precipitates with a thickness <1.9 nm or diameter <65 nm, and was particularly associated with the decrease in thickness of T 1 precipitates. • The precipitation strengthening model was modified, and the yield strength and separated precipitate strengthening contribution were successfully predicted. • The connection between the T 1 precipitates strengthening mechanism transition and detailed morphological parameters was firstly revealed in Al- x Cu-1.3Li-X alloys. • The contributions to yield strength from solid solution strengthening, grain boundary strengthening and texture were calculated. • The variation of strength sequence in Al- x Cu-1.3Li-X alloys with various heat treatments was explained in detail. [ABSTRACT FROM AUTHOR]

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

The mechanical properties of Al-Cu-Li alloys after different pretreatments were investigated through tensile testing at 25 and −196 °C, and the corresponding microstructure characteristics were obtained through optical metallography, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. An increasing mechanism of both strength and ductility at cryogenic temperatures was revealed. The results show that the hot deformation pretreatment before homogenization promoted the precipitation of Al3Zr particles, improved particle distribution, and inhibited local precipitation-free zones (PFZ). Both hot deformation pretreatment before homogenization and cryogenic temperature were able to improve strength and ductility. The former improved strength by promoting the precipitation of Al3Zr particles while enhancing the strengthening effect of the second-phase particles and reducing the thickness of the coarse-grained layer. Meanwhile, the increase in ductility is attributable to the decrease in thickness of the coarse-grained layer, which reduced the deformation incompatibility between the coarse and fine grains and increased the strain-hardening index. The latter improved the strength by suppressing dynamic recovery during the deformation process, increasing the dislocation density, and enhancing the work hardening effect. Additionally, the increase in ductility is attributable to the suppression of planar slip and strengthening of grain boundaries, which promoted the deformation in grain interiors and made the deformation more uniform.

Abstract In this study, Al-Cu-Li (5, 10 and 15 vol%) alloy particles reinforced Aluminum matrix composites were synthesized by powder metallurgy route incorporating microwave sintering and hot extrusion processes. The effects of novel Al based alloy reinforcement on the microstructure, mechanical and thermal characteristics of the Al/Al-Cu-Li composites were investigated. Uniformly distributed Al-Cu-Li alloy particles were observed in the microstructure of the composites. The synthesized materials were characterized for microhardness, co-efficient of thermal expansion, tensile and compressive properties. The results reveal that, hardness, Young's modulus, ultimate compression strength, ultimate tensile strength, yield strength and elongation of Al/15Al-Cu-Li composite improved by ∼186%, 53%, 42%, 47%, 41%, and 48%, respectively in comparison to pure Al. This increase in strength and hardness values is attributed to the distribution of hard and brittle aluminum-based alloy phases in the ductile Al matrix. Furthermore, coefficient of thermal expansion of composites revealed the better thermal stability behavior for Al/15Al-Cu-Li composite compared to pure Al. The results of the present study suggest that the Al/15Al-Cu-Li composite is a very promising candidate for aerospace applications, which are extremely demanding in terms of both comprehensive mechanical properties and lightweight. Graphical abstract Image 1 Highlights • Al/Al-Cu-Li composites were firstly synthesized by microwave sintering followed by hot extrusion. • Al/Al-Cu-Li composites exhibited superior hardness, tensile and compressive properties. • Al/Al-Cu-Li composites exhibited better ductility behavior under tensile loading when compared to pure Al. • Al/Al-Cu-Li composites showed superior dimensional stability due to decreasing thermal coefficient values. [ABSTRACT FROM AUTHOR]

Abstract Microstructure plays a crucial role on mechanical properties of materials. The as-prepared Al-Cu-Li alloy exhibits excellent thermal stability during longer aging treatment at 160 °C. Transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy and first-principle energy calculations were used to evaluate the evolution of different phases in the alloy. The results show that the microstructure evolution goes as follows: SSS→δ′, θ′, T 1 →θ′, T 1 , cubic Al 5 Cu 6 Li 2 phase. The cubic Al 5 Cu 6 Li 2 phase was not precipitated from the matrix until 104 h aging, and the number density increased with prolonging of aging time. Its formation compensates the strength loss caused by the decreased number density and coarsening of θ′(Al 2 Cu) and T 1 (Al 2 CuLi) during longer aging treatment. [ABSTRACT FROM AUTHOR]

Abstract Al–Cu–Li alloy with the thickness of 4 mm is welded by electron beam welding (EBW). Microstructure and mechanical properties of welded joint are systematically investigated. The formation mechanism of weld porosity is fully discussed. Orthogonal experiment results show that welding parameters have great effect on the generation of weld gas pore, and welding speed is the main factor affecting the porosity, followed by electron beam scanning mode, electron beam current is the minimal one. Microstructure analysis demonstrates that weldment is mainly equiaxed grains, and some dendrites exist too. Mechanical properties of welded joints indicate that, under the following welding parameters, electron beam current 13 mA, welding speed 600 mm/min, circular electron beam scanning, a welded joint with good mechanical performance can be obtained. Tensile strength of welded joint is 368.4 MPa, which is about 68% of that of the base metal (BM). SEM analysis shows that there are many fine dimples distributed on the fracture surface of welded joint, and it obviously presents the characteristic of ductile fracture. [ABSTRACT FROM AUTHOR]

The influence of aging treatment on microstructures, tensile properties and corrosion properties of Al–Cu–Li alloy was investigated. The results show that the T8 duplex aging treatment was more effective than T6 and T8 single aging treatment in enhancing the tensile properties and improving the intergranular corrosion (IGC) resistance. Based on the microstructure observation, tensile test, electrochemical experiment and IGC measurement, the factors which affect the microstructures, tensile properties and IGC behavior changing of Al–Cu–Li alloy during aging treatments were discussed in detail. [ABSTRACT FROM AUTHOR]

A large-scale billet of 2195 Al-Cu-Li alloy was prepared by spray deposition technology. The hot extrusion, solution treatment, pre-stretching, and aging treatment were performed on the deposited billet. It was found that the yield strength, ultimate tensile strength and elongation of the T83-treated alloy reach 600 MPa, 632 MPa and 10%, respectively. The microstructures of the deposited alloy in the thermo-mechanical processing were studied by optical microscopy, scanning electron microscopy and transmission electron microscopy. The mechanical properties were examined by tensile test. It was found that the spray deposited alloy presents a microstructure with fine equiaxed grains and low segregation degree. After hot extrusion, a typical fibrous structure with incomplete recrystallization is formed. After solution and aging treatments, lots of T 1 and δ ′ phases precipitate in the matrix, leading to significant increase of the tensile strength. Pre-stretch prior to aging treatment produces a fine homogeneous distribution of the T 1 plates throughout the matrix, which lead to an excellent tensile performance. The ductility of aged alloys is affected by the microstructure of grain boundary. Narrow precipitate free zone and dispersed grain boundary precipitates with small size are beneficial to improvement of alloy's ductility. [ABSTRACT FROM AUTHOR]

The microstructure and fatigue properties of Al-Cu-Li alloy sheets were investigated respectively under the conditions of without pre-deformation, 3% pre-stretching deformation and 8% pre-rolling deformation utilizing scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) in present work. Results show that the intensive Goss texture and relatively weaker Brass, Cube texture were formed in without pre-deformed alloy after aging treatment. The pole density level of Goss texture was decreased remarkably and the intensity of Brass, Cube texture was increased lightly after 3% pre-stretching deformation and 8% pre-rolling deformation. The magnitude order of fatigue crack propagation (FCP) rate of the alloy under different pre-deformation conditions was da dN pre − rolling  >  da dN pre − stretching  >  da dN non − predeformation in stage II (Paris regime). The combined contribution of T 1 phase with different size, amount and the intensity of Goss texture is the main factors affecting the FCP rate of Al-Cu-Li alloy. [ABSTRACT FROM AUTHOR]

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

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

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

The hot deformation behavior of Al-Cu-Li alloy was studied under plane strain compression in the temperature range of 400–500 °C and strain rate of 0.01–10 s − 1 . The related microstructure was studied by optical microscopy, electron back-scattered diffraction and transmission electron microscope. The results showed that the stress decreased significantly with the increase of temperature and decrease of strain rate. However, stress increase was found after peak stress at strain rate of 0.01 s − 1 and deformation temperature 440–500 °C. Constitutive equation based on the hyperbolic sine equation was established and the apparent activation energy of plane strain compression was estimated to be 226.7 KJ/mol. Precipitates decreased and finally disappeared with decreasing Z value, having an impact on the softening mechanism. Plate-shaped particles and precipitate zones restrained the proceeding of dynamic recovery but increased store energy for discontinuous dynamically recrystallization nuclei. Therefore, recrystallization nuclei more obviously occurred in the sample with higher ln Z value than the one with lower ln Z value at close ln Z value. The microstructure of all deformed specimens was composed of elongated grains and new quasi-equiaxed grains. However, the basic deformation mechanism was dynamic recovery. The mechanism of recrystallization nuclei transformed discontinuous dynamic recrystallization into continuous dynamic recrystallization with the decreasing Z values. [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]

The thermal stability of the lightweight, T83 heat treated 2099 Al-Cu-Li alloy was assessed in the temperature range 200–305 °C, through both hardness and tensile tests after overaging. After prolonged thermal exposure, the alloy exhibited a better performance compared to aluminium alloys specifically developed for high temperature applications, with the advantage of a considerable lower density. The tensile behaviour was modelled through Hollomon's equation as a function of residual hardness. The changes in the alloy performance were explained through both SEM and STEM investigations. Microstructural analyses gave evidence of Ostwald ripening, while fractographic analyses revealed a transition from an intergranular to a ductile fracture mechanism in the overaged alloy. STEM investigations highlighted the superior thermal stability of the T 1 phase compared to ϑ and S strengthening phases, which dissolved during overaging at 245 °C. The study underlines the need to enhance the formation of T 1 precipitates when high temperature strength is required. The results of the present study suggest that the 2099 alloy is a very promising candidate for automotive engine components, which are extremely demanding in terms of both thermal resistance and lightweight. [ABSTRACT FROM AUTHOR]

[Display omitted] • The T85 treated Al-Cu-Li alloy was systematically investigated under thermal exposure at 100–300 °C for up to 1000 h. • The evolution of precipitation characteristics during thermal exposure was revealed. • Fracture toughness was greatly affected by the morphology and distribution of grain boundary precipitates. • The qualitative relationship between mechanical properties and multiscale microstructure was established. 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 (Al 2 CuLi) 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′-Al 2 Cu and S-Al 2 CuMg 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-Al 6 Cu(Li, Mg) 3 and cubic C phases, leading to a dramatic decrease in strength and toughness. [ABSTRACT FROM AUTHOR]

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