Strength-ductility Combination in Aluminum-lithium Alloy 2090 Containing Rare Earth Element

The influence of grain structure and Ce on the strength ductility combination for aluminum lithium alloy was investigated. The strength ductility combination of pancake shape unrecrystallized grains is superior to that of recrystallized grains. A significant improvement in strength ductility combination can be achieved by adding Ce to alloy 2090. According to the research results about fracture and properties of monotonic tension for Al Li alloys 2090 and 2090+Ce, the relationship among grain structure, strength differences between grain within and grain boundary, stress localization degree at grain boundary and extrinsic strengthening effect was researched. The method and mechanisms of optimizing strength ductility were discussed, including grain structure, subgrain, T 1 phase, rare earth element Ce and aging procedure.

Fatigue and Fracture Mechanisms of Aluminum-Lithium Alloy Containing Cerium

The influence of rare earth element Ce on fatigue properites and fracture toughness for Al Li 2090 alloy was studied, and the mechanism of extrinsic toughening and intrinsic toughening from Ce was explored. A significant improvement in ductility, fatigue life and fracture toughness can be achieved by adding minor Ce into 2090 alloy, which is basically attributed to intrinsic toughening effect from Ce, i.e., the role of thinning and dispersing T 1 phase. On the other hand, due to the role of restraining recrystallization by adding Ce, the fraction of recrystallized grains is decreased and the unrecrystallized grains are thinned. It is responsible for enhancing extrinsic toughening effect.

Effects of Ce and Impurities on Percentage Elongation and Recrystallization in Al-Li Alloys

The effects of the contents of Ce and deleterious impurities on the ductility and recrystallized microstructure have been investigated for Al Li based alloys 2090 and 8090 sheets. The relationships between the parameters of recrystallized microstructure and percentage elongation( δ ) in the transverse orientation of the sheets have been obtained. The beneficial behavior of Ce microalloying can be markedly shown in the alloy 2090 containing a certain amount of impurities Fe and Si or in the alloy 8090 containing a certain amount of impurities Na and K. Ce microalloying can still improve δ to a certain degree, even though impurities Fe, Si, Na and K coexist and their concentration is rather high in the alloy 8090. When the recrystallized volume, coarse grained volume and grain average width increase because of the variation in the contents of Ce element and impurities, δ decreases for the alloys 2090 and 8090. When the grain aspect ratio increases, δ increases for the alloy 2090 and decreases for the alloy 8090.

Effect of Delamination on Mechanical Properties of Al-Li Alloy Modified by Rare Earth Element Ce

Mechanisms influencing the mechanical properties and fractography of alloy 2090+Ce with different aging conditions were examined as a function of delamination and other factors. It is seen that the alloy aged at 150℃ has superior fracture resistance to the one aged at 163℃ and the practice of aging at 150℃ for 28 h renders the alloy better strength toughness combination than that of aging at 163℃ for 20 h, due to higher effect of intrinsic toughening of the former. With crack extension, failure mechanism in CT specimens changes from a tougher one to a more brittle one because of increasing strain in the frontal zone of crack tip. Moreover, a model for the improvement of toughness of the alloy, as well as monolithic laminated materials, is developed based on the observation of delamination process.

Strength and microstructure of 2091 Al-Li alloy TIG welded joint

The microstructure and tensile properties of TIG welding joints of 2091 Al Li alloy were investigated both in as welded and different postweld heat treatment condition. The results show that solution strengthening played an important role in the as welded condition, though the precipitation strengthening δ′ phase formed already in the as welded weld metal, but its effect was not apparent due to the lower volume fraction of δ′ phase. So the strength coefficient ( φ ) of the welded joint/base metal was 64%. After artificially aging heat treatment, the precipitation strengthening effect increased much due to the formation of more δ′ phase and s′ phase. Its φ value was increased up to 89%. The highest strength of the welded joints was obtained after solid solution and then artificially aged heat treatment. Due to the proper size of precipitation strengthening phases and their well distribution, the φ value was increased up to 98%.

Effect of Impurities and Cerium on Stress Concentration Sensitivity of Al-Li Based Alloys

A notch sensitivity factor was derived in order to evaluate the stress concentration sensitivity of Al Li based alloys. The factor values for the Al Li alloy sheets containing various contents of impurities and cerium addition were evaluated by determining the mechanical properties. It is found that the impurities Fe, Si, Na and K significantly enhance the stress concentration sensitivity of the alloys 2090 and 8090, whereas cerium addition reduces the stress concentration sensitivity to a certain degree for the high strength alloys. However, an excess amount of cerium addition in the high ductility alloy 1420 can significantly increase the stress concentration sensitivity. As compared with conventional aluminum alloys, the Al Li based alloys generally show high stress concentration sensitivity. Therefore, a special attention must be paid to this problem in the practical application of Al Li based alloys.

Effect of homogenization treatment in electric field on microstructure and properties of 1420 Al-Li alloy

In comparison with the homogenization treatment without an electric field prior to the same solid solution and aging treatment, the homogenization treatment in an electric field increases the hardness and strength of 1420 Al Li alloy, but somewhat decreases the elongation of the alloy. Moreover, the elongation of the alloy increases with the homogenization temperature in an electric field increasing. TEM observation showed that the homogenization treatment in an electric field can accelerate the dissolution of the coarse particles of second phase on the grain boundary as well as make δ′phase precipitated in subsequent aging process finer and more numerous.

Coupled Thermo-Mechanical Modeling of Long Cone-Shaped Forging Based on Rigid Visco-Plastic FEM

Based on synthetically considering the coupled thermo mechanical relations between temperature and deforming, a numerical simulation of the forging process for the special long cone shaped workpiece of Al 5.44Mg 2.15Li 0.12Zr alloy at high temperature was conducted by using the rigid visco plastic finite element method. The relations between the total load and the displacement during the forging, and the distributions of stress, strain, temperature and strain rate, which can provide useful information for the process design, are obtained.

Prediction of flow stresses at high temperatures with artificial neural networks

On the basis of the data obtained on Gleeble 1500 Thermal Simulator, the predicting models for the relation between stable flow stress during high temperature plastic deformation and deformation strain, strain rate and temperature for 1420 Al Li alloy have been developed with BP artificial neural networks method. The results show that the model on basis of BPNN is practical and it reflects the actual feature of the deforming process. It states that the difference between the actual value and the output of the model is in order of 5%. [

Electroplastic Tensile Behavior of 5A90 Al–Li Alloys

The electroplastic（EP） tensile properties of 5A90 Al–Li alloys compared with thermal tension were investigated.The microstructural variation at different conditions was observed by SEM and TEM.The current density significantly influences the elongation and the flow stress.With increasing current density,wider and deeper dimples on the fracture surfaces and less dislocation density and pile-ups in the EP tension samples were observed compared with roomtemperature and thermal tension,which indicates the plasticity improvement and flow stress reduction.The EP effect（EPE） mainly results from a comprehensive function of Joule heating and pure EPE.Among them,Joule heating effect is perhaps a dominant factor.

Effect of Different Ageing Processes on Microstructure and Mechanical Properties of Cast Al–3Li–2Cu–0.2Zr Alloy

The effect of different ageing processes on microstructure and mechanical properties of cast Al–3 Li–2 Cu–0.2 Zr alloy was investigated using transmission electron microscopy and tensile tests. The results showed that the mean size of δ′-Al3 Li particles and the number density of Cu-rich precipitates both increased with increasing ageing temperature from 150 to 190 °C for 24 h, resulting in increasingly high strength. In contrast, the ductility deteriorated with the increase in ageing temperature as a result of the intensified planar slip. The duplex low-to-high ageing treatment(120 °C for 6 h followed by 160 °C for 24 h) was shown to be beneficial to the ductility compared with the corresponding single-stage ageing treatment(160 °C for 24 h). The reduced slip length induced by the precipitation of θ′-Al 2 Cu phases was found to be mainly responsible for this ductility improvement.

Cu/Li Ratio on the Microstructure Evolution and Corrosion Behaviors of Al–xCu–yLi–Mg Alloys

The microstructure evolution and the corrosion feature of Al–x Cu– y Li–Mg alloys( x : y = 0.44, 1.65 and 4.2) were systematically investigated under the same artificial aging conditions. The relationships between types of precipitates and mechanical performance, as well as electrochemical behaviors, were discussed. Our results show that different types of precipitates can be obtained in alloys with different Cu/Li mass ratios, which significantly influences the mechanical performance of the alloys and substantial corrosion behaviors. Specifically, the analogous corrosion evolution in the aging Al– x Cu– y Li–Mg alloys was first ascertained to be derived from the growth mechanism of the precipitates at the grain boundary(GB). Moreover, a small number of GB precipitates can be obtained in the aged alloy with the lowest Cu/Li mass ratio, thereby resulting in the largest intergranular corrosion resistance. A higher proportion of the GB T1 phase in the continuous precipitates induces higher corrosion sensitivity in alloy with a high Cu/Li mass ratio.

Quantitative Electron Tomography for Accurate Measurement of Precipitates Microstructure Parameters in Al–Cu–Li Alloys

Mechanical theories show that properties of alloys are strongly dependent on the morphological parameters oftheir strengthening precipitates.However,accurate measurement of precipitates microstructure parameters is still a challenging task.In this article,we develop a quantitative electron tomography method by combining computer vision technology to accurately characterize the three-dimensional microstructure parameters,such as volume fractions,sizes and distributions,of the T_(1) and δ’/θ’/δ’ precipitates in Al-Cu-Li(-Mg) alloys.Since they have extremely large aspect-ratios in shape and large numbers in density upon formation in the Al matrix,these thin plate-like precipitates are difficult to be characterized quantitatively without the assistance of computer vision technology.It is shown that the property difference between two peak-aged states of the alloy can be well explained with the quantitative precipitate parameters correctly measured.Using these correct precipitate data,we also tested the validity of current mechanical models for projecting the contribution of precipitates to the strengths of the alloy,demonstrating that quantitative relations between strength and micro structure parameters still need to be refined.

Technological Aspect of Processing Maps for the AA2099 Alloy

Results of an experimental and modelling study of forming processes in the AA2099 Al–Cu–Li alloy, for a wide range of temperatures, strains and strain rates, are presented. The analyses are based on tensile testing at 20 °C at a strain rate of 0.02 s-1and uniaxial compression testing in the temperature range 400–550 °C at strain rates ranging from0.001 to 100 s-1, for constant values of true strain of 0.5 and 0.9. The stability of plastic deformation and its relationship with a sensitivity of stress to strain rate are considered. The power dissipation efficiency coefficient, g（%）, and the flow instability parameter, n B 0, were determined. The complex processing maps for hot working were determined and quantified, including process frames for basic forging processes： conventional forging and for near-superplastic and isothermal conditions. A significant aspect is the convergence of power dissipation when passing through the 500 °C peak.Deformation, temperature and strain-rate-dependent microstructures at 500 °C for strain rates of 0.1, 1, 10 and 100 s-1are described and analysed for the conventional die forging process frame, corresponding to 465–523 °C and strain rates of50–100 s-1.