5A90 Al-Li Alloy Research Articles

Effect of bath temperature on corrosion resistance of electroless Ni-P coating on 5A90 Al-Li alloy

Abstract The Al-Li alloy exhibits outstanding characteristics, including remarkable specific strength, elevated specific stiffness, and heightened susceptibility to localized corrosion. Electroless Ni-P coating is extensively applied over the appearance of aluminum alloys to enhance their corrosion resistance. Electroless Ni-P coating was applied to 5A90 Al-Li alloy at various plating temperatures for the study presented in this publication. The coating’s surface, composition, and cross-sectional morphology were examined using SEM/EDS. The corrosion behavior of coating was studied using the potentiodynamic polarization curve. Results showed that coating on the surface of 5A90 Al-Li alloy was uniform and smooth. Ni and P elements were evenly distributed in the coating. The thickness of coatings at 80°C, 85°C, 90°C and 95°C was about 3.98 μm, 5.5 μm, 11.2 μm, and 10.29 μm, respectively. As the temperature of the bath increased, the corrosion resistance of the coating first increased and afterward decreased. The corrosion resistance of the coating might be correlated with its thickness.

Effect of the hot forming with synchronous quenching process on high cycle fatigue properties of the 2A97 Al-Li alloy

The 2A97 Al-Li alloys have been used in aircraft to achieve lightweight, its high cycle fatigue performance is one of the important factors that determines aircraft safety. The 2A97-T8 Al-Li alloy is obtained through the 2A97-T3 Al-Li alloy undergoes the hot forming with synchronous quenching process. The 2A97-T3 and 2A97-T8 Al-Li alloys are tested for high cycle fatigue under different stress amplitudes. The fatigue crack propagation path of the 2A97-T3 Al-Li alloy is not only along the direction of maximum shear stress at 45° to the stress direction but also along the direction perpendicular to the stress axis. The fatigue crack propagation path of the 2A97-T8 Al-Li alloy propagates along the direction perpendicular to the stress axis. Under high amplitude stress, the characteristics of quasi-cleavage fracture are found in the fracture morphology of 2A97-T3 Al-Li alloy. However, the characteristics of cleavage fracture are found on the fracture morphology of 2A97-T3 Al-Li alloy under low amplitude stress. Under high amplitude stress, the quasi-cleavage characteristics and the dimples are found on the fracture morphology of 2A97-T8 Al-Li alloy. Under low amplitude stress, the small voids and the dimples are found on the fracture morphology of 2A97-T8 Al-Li alloy. The precipitated phases of the 2A97-T3 Al-Li alloy are multitudinous, fine, and dispersed δ’ phases and a few T1 phases. The precipitates of the 2A97-T8 Al-Li alloy are large, fine, and acicular T1 phases and a few δ’ phases. The hot forming with synchronous quenching process significantly improves the high cycle fatigue properties of the 2A97 Al-Li alloy. In addition, the fatigue cycles, the fatigue life rise and fall plots, the S-N curves, and the fatigue crack growth behaviors of the 2A97-T3 and 2A97-T8 Al-Li alloys are obtained.

Effect of Thermal Exposure on the Microstructure and Mechanical Properties of 2A97 Al-Li Alloy

Effect of Thermal Exposure on the Microstructure and Mechanical Properties of 2A97 Al-Li Alloy

Corrosion Behavior of 2A97 Al–Li Alloy in Cl− and SO42− Mixed Salt Spray

Corrosion Behavior of 2A97 Al–Li Alloy in Cl− and SO42− Mixed Salt Spray

Effect of laser remelting and heat treatment on microstructure and wear resistance of 2A97 Al-Li alloy

Effects of laser surface remelting and heat treatment on microstructure and wear resistance of 2A97 Al-Li alloy were studied. The results show that hardening layer with fine grain and small size eutectic phase is easily prepared by laser remelting technique with rapid solidification characteristics. The cross section of molten pool after laser remelting is mainly composed of fine equiaxed grains (about 10 μm in size) close to fusion line, elongated columnar grains and coarse equiaxed grains on top of molten pool. Divorced eutectic phase Al2Cu is formed at grain boundary, and T2 phase (Al6CuLi3) with five times symmetric axis is observed. Fine grain strengthening and solution strengthening are main reasons for higher microhardness (105 HV) of remelting sample than that of matrix (85 HV). Hardness and wear resistance of remelting alloy are improved significantly by simple heat treatment. After 520 °C/1.5 h + 175 °C/24 h, discontinuous Al2Cu eutectic phase is no longer reticular distribution, and the size is greatly reduced. δ' phase (Al3Li), T1 phase (Al2CuLi) and σ (Al5Cu6Mg2) phase are precipitated during aging. Due to precipitation of reinforcements, microhardness of laser remelted Al-Li Alloy is increased from 105 HV to 142 HV, and elastic modulus is increased from 79.734 GPa to 91.962 GPa. The wear forms of Al-Li alloy are mainly abrasive wear and adhesive wear. Simple heat treatment significantly improves wear resistance of remelted Al-Li alloy, and wear rate is only 39.62 % of matrix.

Study of icosahedral quasi-crystalline phase T2-Al6CuLi3 and transformation in 2A97 Al-Li alloy fabricated by laser additive manufacturing

Precipitated phases of 2A97 Al-Li alloy fabricated by laser additive manufacturing with thermal input are mainly composed of quasicrystal T2 phase gathered around grain boundary and TB phase in grain interior. Diffraction patterns of quasi-crystalline T2 phase show two-fold, three-fold and five-fold symmetry, respectively. Under condition of thermal cycling, T2 phase transforms into a face-centered cubic Y phase with a lattice constant of 2 nm. Y phase can grow into twins, and the twin plane is (111). After solution treatment at 515 °C for 1.5 h, δ' phase, T1 phase and TB phase are completely dissolved in matrix, while quasi-crystalline T2 phase transforms into orthorhombic O phase. The size of O phase is similar to that of T2, with length of about 400 nm and rougher surface.

Microstructure characterization and evaluation of mechanical properties in 2A97 aluminum-lithium alloys welded by stationary shoulder friction stir welding

2A97 Al–Li alloy joints with the thickness of 1.5 mm were fabricated by stationary shoulder friction stir welding (SSFSW) under rotational speeds of 600–1000 rpm and a fixed welding speed of 200 mm/min. As the rotational speeds increased, the grain sizes of the nugget zone (NZ) kept almost constant with the presence of zigzag defects. The electron backscattered diffraction (EBSD) analysis suggested that the initial crystal orientation with near <001>‖TD and <001>‖WD textural components exhibited weaker anisotropy induced by the severe shearing deformation. The dynamic recrystallization (DRX) mechanisms were clarified in the transition from low-angle grain boundaries (LAGBs) to high-angle grain boundaries (HAGBs). In contrast to the conventional FSW joints of Al–Li alloys, the dispersions were indexed as Al11Cu5Mn3, Al2Cu within the grains, and Al–Cu–Mn–Zn phase at the grain boundaries in the SSFSW joints. The T1, δ′/β' and θ′ precipitates were detected in the base metal (BM), and the θ′ precipitates were dissolved in the heat affected zone (HAZ). However, those strengthening precipitates were absent in the NZ. The variation of the ultimate tensile strength first increased and then decreased with the increasing rotational speeds. Moreover, the joint obtained at a rotational speed of 1000 rpm exhibited the best combination of strength and ductility. The defect-free joints failed in the thermo-mechanically affected zone (TMAZ), which corresponded to the hardness minima positions (HMP). However, an abnormal fracture occurred in the NZ due to the presence of weak-bonding areas and curved band structures.

New insights into fine equiaxed zone of laser-welded 2A97 Al-Li alloy

In this study, the concept of fine equiaxed band (FEQB) was proposed for the first time, and the distribution range of the fine equiaxed zone (FEQZ) was redefined. Characterization techniques including scanning electron microscopy, electron backscattered diffraction, energy dispersive spectroscopy, and transmission electron microscopy were employed to analyse the microstructures, orientations, micro-segregations, and precipitates within the grain of the FEQZ. The results indicate the existence of tiny precipitates, mainly T1 and θ′ along with a small amount of δ′ within the randomly oriented fine equiaxed grain with spherical morphology, and no obvious dendrite structure was observed. The micro-segregation of Cu and Mg occurred at the grain boundaries, resulting in the generation of intermetallic phases at grain boundaries derived mainly by eutectic action. The dominant intermetallic phase enveloping that grain is T1, and a small amount of plate-like precipitate S′ is formed at the junction of three or more grains. The bands formed by these closely connected grains are called FEQB. Furthermore, the region covered by the FEQBs is called FEQZ.

Buckling fatigue behavior of 2A97 Al-Li alloy stiffened panels under shear loading

In order to study buckling fatigue behavior and failure modes of 2A97 Al-Li alloy stiffened panels under shear loading, 1.2 mm and 1.5 mm thick 2A97 Al-Li alloy stiffened panels were designed and manufactured. The static and fatigue tests were performed under shear loading. The results indicate that the shear failure modes of stiffened panels are global buckling wave, skin cracks and rivets falling off. The effect of skin thickness on the buckling load is greater than that on the ultimate load. The fatigue failure processes of stiffened panels include gradual failure and catastrophic failure. The fatigue failure modes are complex and rivet falling off is most dangerous. Panels with cracks or broken rivets still has residual life. Once the skin tears, the panel will immediately fail. The total fatigue life and initial fatigue life of 1.5 mm stiffened panel are 28.87% and 59.88% higher than those of 1.2 mm stiffened panel respectively, while the residual life is 87.68% lower. The finite element models were established to simulate the buckling and post-buckling process of the stiffened panels, and the local stress spectrum of the fatigue dangerous point was obtained. Goodman's theory and nominal stress method was combined to predict the fatigue life and to explain the experimental findings.

Effect of thermal cycling on microstructure and mechanical properties of 2A97 Al–Li alloy fabricated by direct laser deposition

Direct laser deposition (DLD) is a potential approach to prepare large-scale metal component. This work focuses on understanding microstructural characteristics and mechanical properties along deposition direction of 2A97 Al–Li alloy fabricated by direct laser deposition. As-deposited sample showed coarse equiaxed grains at top and columnar crystals at middle and bottom. Growth texture of as-deposited sample along <001> was relatively obvious, value of which increased first and then decreased from bottom to top. Thermal cycle led to different kinds and distribution of precipitated phases along deposition direction, which affected microhardness and tensile strength. T1 phase and a small amount of T2, TB phase precipitated at top. Effect of thermal cycle from top to bottom gradually increased, resulted in δ′, T2, TB phase coarsened. As a result, microhardness decreased from top (99 HV) to bottom (75HV). The sample in bottom showed an ultimate tensile strength (UTS) of 232.9 ± 4.3 MPa, and elongation of 9.5 ± 1.4%. While, ultimate tensile strength was increased to 268.5 ± 5.2 MPa, and elongation was 12.5 ± 0.9% in middle part, which was close to that of sample at top.

Study on Microstructure Formation in Non-autogenous Laser Welded 2A97 Al-Li Alloy

Study on Microstructure Formation in Non-autogenous Laser Welded 2A97 Al-Li Alloy

Investigation on the ageing behaviour and hardening mechanisms of 5A90 Al–Li alloy U-shaped parts formed by electric resistance heating forming-quenching process

The electric resistance heating technology was introduced into the solution heating, forming-quenching with cold die integrated process for improving the dimensional accuracy of the 5A90 Al–Li alloy U-shaped parts. In order to evaluate the effect of current density on the forming quality of U-shaped parts, the springback and mechanical properties of formed parts were analyzed. The dimensional accuracy of formed parts increased with the current density. The U-shaped part with the minimum springback angle (0.43°) was obtained under the current density of 12.76 A/mm 2 . The increase in hardness of the typical positions of U-shaped parts was mainly due to the spherical δ′ phase with the proper matching of volume fraction and size. The hardness of the bottom fillet increased from 82.4 HV to 113.53 HV after ageing at 160 °C for 10 h. A mechanistic model referring to grain boundaries, dislocation accumulation, solid solution and precipitation was established to describe the hardening mechanisms. The δ′ phase not only contributed to the precipitation hardening mechanism but also affected the solid solution hardening by changing the concentration of solute atoms. The precipitate hardening caused by δ' phase with the perfect antiphase boundaries was the dominant mechanism, which afforded 35.6 HV with the volume fraction of 31.51% in the peak-aged sample. • The EHFQ process improves the dimensional accuracy of the 5A90 Al-Li alloy U-shaped parts. • The precipitation behavior and matching relation of δ′ phase are studied, which affect the mechanical properties of parts. • A mechanistic model is established to describe the hardening mechanisms and the contribution of each mechanism is analyzed.

Mechanisms and microstructures of 2A97 Al-Li alloy under the hot forming with synchronous quenching process.

Aluminum-lithium alloy is regarded as the most promising light material in the aircraft and aerospace industries. For the production of complex and high-precision parts, the hot forming with synchronous quenching (HFSQ) process has become an effective and attractive forming method. In order to achieve the performance and microstructure evolution of the 2A97 Al-Li alloy under the HFSQ process, the specimens were subjected to solution treatment at 520°C and held at 90 min in the Gleeble 3,500 thermal simulator. Then the hot tensile test with simultaneous quenching was conducted directly at a temperature of 300-500°C and a strain rate of 0.1-0.001 s-1 with the same equipment. Through analyzing the macroscopic stress-strain curves and microscopic fractures, it was concluded that the optimal forming temperature was 450°C with the strain rate being 0.1 s-1 and its forming mechanism under the process was presented. To obtain the microstructure evolution of 2A97 Al-Li alloy under the HFSQ process, the material was subjected to constant strain tensile test with synchronous quenching and then treated with two-stage artificial aging 200°C and 6 hr + 165°C and 6 hr. The microstructure of the alloy was observed by means of electron backscattering diffraction (EBSD). And its evolution process and the influence of temperature, strain rate, and strain on the microstructure under the process were attained.

Effect of temperature alternating load on stripping performance of Al-Li alloy T-joint manufactured by dual laser beam bilateral synchronous welding

In this work, the temperature alternating load (TAL) with four cycles is performed to the 5A90 Al-Li alloy T-joint produced by dual laser beam bilateral synchronous welding (DLBSW). The grain details, stripping strength, fracture micro-morphology and elemental composition of the samples are analyzed by optical microscope, self-designed specific fixture, scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS), respectively. The experiment results indicate that the TAL treatment has a slight decrease on the width of non-dendritic equiaxed zone (EQZ) near the fusion line. The average striping strength and post-break elongation of the TAL treated samples are separately 126.01 MPa and 3.60%, which are both reduced compared with the values 145.61 MPa and 5.54% of the untreated samples. Meanwhile, the results of fracture micro-morphology and elemental composition are utilized to investigate the decline of the tensile performance of the T-joint with the TAL treatment. It is found that the fracture features such as tear layers, shear dimples and torn pores are relatively insignificant compared to the T-joint without the TAL treatment. The non-uniformity of element distribution exists in the TAL treated and untreated sample.

Evolution of aging precipitates in an Al–Li alloy with 1.5 wt% Li concentration

Transmission electron microscope and selected area electron diffraction were employed to characterise the precipitates in 2A97 Al–Li alloy with 1.5 wt% Li concentration, which were aged at 150°C (with 6% pre-deformation) and 165°C (without pre-deformation) for various time. The diameter of the plate-like T1, δ′/GP/δ′ and δ′/θ'/δ′ precipitates were measured to analyse the precipitate evolution during ageing treatment. We find the pre-deformation has a significant effect on the T1, δ′/GP/δ′, δ′/θ'/δ′ and cubic precipitates, which improves the nucleation of T1 precipitates but suppress the other precipitates. The findings herein provide the guidance to tailor the microstructure of 2A97 alloy through artificial ageing treatment, which can facilitate the future alloy design.

The effect of temperature alternating load on residual stresses for Al-Li alloy T-joints welded by dual laser beam bilateral synchronous welding

The finite element (FE) simulation is employed to predict the residual stresses, which is induced by the welding and the temperature alternating load. The simulation of 5A90 Al-Li alloy T-joint welded by the dual laser beam bilateral synchronous welding (DLBSW) is carried out. Then the evolution of the residual stresses is obtained under the temperature alternating load which is achieved by changing the ambient temperature on T-joint. In addition, the accuracy of simulation model has been verified by comparing the experimental results with the simulation results. According to the comparison, the simulation results are consistent with the experimental results, which shows that the residual stresses of 5A90 T-joints decrease under the temperature alternating load. Besides, the FE simulation is a relatively efficient and accurate method to predict the change of residual stresses under the temperature alternating load.

Study on micro-structure, solid solubility and tensile properties of 5A90 Al–Li alloy cast by low-frequency electromagnetic casting processing

In this paper, the low-frequency electromagnetic casting (LFEC) processing was introduced as an efficient pollution-free casting technique, and how it influenced the micro-structure and mechanical properties of 5A90 Al–Li alloy was investigated. The mechanical properties of the alloy had a close connection with the casting metallurgical quality and the precipitation phases. Compared to the conventional direct chill casting (DCC), the LFEC could promote the precipitate of the δ′ (Al3Li)/β′ (Al3Zr) and reduce the width of PFZ, which enhanced the effect of the precipitation strengthen and alleviated the strain localization. Meanwhile, the micro-structure of the ingot was refined significantly and the metallurgical quality was improved after LFEC treatment due to the modification of the flow and temperature field of the sump that caused by the application of low-frequency electromagnetic field. Maximum yield strength and ultimate tensile strength of as-aged alloy cast by LFEC with 150 A/15 Hz could reach 371.85 MPa and 495.5 MPa, while elongation remained at 9.82%.

Influence of Laser Power on Grain Size and Tensile Strength of 5A90 Al–Li Alloy T-joint Fabricated by Dual Laser-Beam Bilateral Synchronous Welding

Dual laser-beam bilateral synchronous welding is introduced to produce the 2.5 mm thick 5A90 Al–Li alloy T-joint. The grain morphology and grain size of weld metal (WM) in the T-joint are analyzed and calculated. The tensile experiment, scanning electron microscopy and energy disperse spectroscopy are respectively employed to study the tensile strength, fracture morphology and chemical composition of the T-joint. The results reveal that when the laser power is increased from 2500 to 3000 W, the grain sizes of fine-grained layers and columnar dendrites near the fusion line are significantly reduced. Conversely, that of equiaxed dendrites at the WM center is not sensitive to the variety of laser power. Moreover, the degree of elemental segregation in WM near the fusion line is also aggravated with the increasing of the laser power. The tensile strength of the T-joint with the laser power of 2500 W is significantly higher than that with the laser power of 3000 W. The tensile fracture locations are occurred in the weld toe with obvious pores, shear dimples and tear ridges, which are the typical characteristics of ductile fracture. Besides, the chemical compositions of the second phase particles in the WM are more sensitive to than the variation of laser power compared with that of the matrix.

Micro-Structure and Mechanical Properties of 2A97 Al-Li Alloy Cast by Low-Frequency Electromagnetic Casting

In this paper, the micro-structure and solid solubility of 2A97 aluminum-lithium alloy ingots prepared by conventional direct chill (DC) casting and low frequency electromagnetic casting (LFEC) as well as the density of precipitates and tensile properties of 2A97 alloy after T6 treatment were investigated. The results show that the low-frequency electromagnetic field during casting had a remarkable effect on the refinement of micro-structure and solid solubility of alloying elements within the grains, which is very helpful to obtain a large number of fine, uniformly-distributed T1 phases. The mechanical properties of 2A97 alloy prepared by low frequency electromagnetic casting after T6 treatment were improved by obtaining a larger number T1 phases.

Effect of Intermediate Thermomechanical Treatment on Microstructure and Mechanical Properties of 2A97 Al-Li Alloy

Effect of intermediate thermomechanical treatment on tensile properties at short-transverse direction, fracture mechanism and microstructure of 2A97 Al-Li alloy thick plate were studied by tensile testing, SEM, EBSD and TEM.The results show that with the increasing of compression deformation, the strength and elongation of the alloy increase first and then decrease slightly. The fracture mode of the alloy changes from quasi-cleavage fracture to high energy ductile fracture. When the compression deformation rises to 20%, the elongated structure are replaced by a more uniform and equiaxial structure. The distribution of δ phase distribute more homogeneously in the grains.