Papers by Keyword: Aluminium-Lithium (Al-Li) Alloy

Abstract: Utilization of aluminium-lithium alloys in aerospace applications requires an understanding of how processing and product geometry impact their microstructure, crystallographic texture and mechanical properties. In this paper, the effect of various microstructural features as well as deformation textures on the static mechanical properties of Al-Li extruded components has been investigated. These relationships are discussed with regard to two 2099-T83 extruded sections, i.e. a cylindrical extrusion and an integrally stiffened panel (ISP). The ISP typically shows an unrecrystallized microstructure with varying texture depending on the location along its cross section while the cylindrical extrusions present a strong fibre texture. The anisotropy is noticeable in tensile and compressive tests for both types of extrusions.

Abstract: Aluminum-lithium (Al-Li) alloys are of interest to the aerospace and aeronautical industries as rising fuel costs and increasing environmental restrictions are promoting reductions in vehicle weight. However, Al-Li alloys suffer from several issues during fusion welding processes including solute segregation and depletion. Solid freeform fabrication (SFF) of materials is a repair or rapid prototyping process, in which the deposited feedstock is built-up via a layering process to the required geometry. Recent developments have led to the investigation of SFF processes via Gas Metal Arc Welding (GMAW) capable of producing functional metallic components. A SFF process via GMAW would be instrumental in reducing costs associated with the production and repair of Al-Li components. Furthermore the newly developed Controlled-Short-Circuit-MIG (CSC-MIG) process provides the ability to control the weld parameters with a high degree of accuracy, thus enabling the optimization of the solidification parameters required to avoid solute depletion and segregation within an Al-Li alloy. The objective of this study is to develop the welding parameters required to avoid lithium depletion and segregation. In the present study weldments were produced via CSC-MIG process, using Al-Li 2199 sheet samples as the filler material. The residual lithium concentration within the weldments was then determined via Atomic Absorption (AA) and X-ray Photoelectron Spectroscopy (XPS). The microstructure was analyzed using High Resolution Scanning Electron Microscopy (HR-SEM). Finally the mechanical properties of welded samples were determined through the application of hardness and tensile testing.

Abstract: The electromagnetic micro-gravity simulation smelting is a new preparation technology of Al-Li alloy containing high Li. In the aluminum lithium binary system, based the principle of electromagnetic force applied on the metal alloy melt, the Al-Li alloy was smelt and cast at 0.5T and 800°C with home-made apparatus. Through composition analysis by means of XPS, surface microscopic morphology with SEM and density measurement, the results show that the low density, 10wt% of Li in Al, homogeneous lithium distribution and compact and uniform and compact microstructure Al-Li alloy can prepared by using the technique of electromagnetic simulating micro-gravity method.

Abstract: The laser welding of Aluminum-Lithium alloy (Al-Li) alloy were conducted to investigate the weld porosity features in this paper. The results show that there are two kinds of weld porosity existing for laser welding Aluminum-Lithium alloy sheet. They are can be divided into metallurgical porosity and unstable keyhole porosity according to their different reason causing them. The mechanism of unstable keyhole porosity occurring was discussed according to the results of YAG laser welding processing. The methods how to reduce weld porosity for laser welding of Aluminum-Lithium alloy was also described.

Abstract: The cylindrical cup drawing of 5A90 Aluminum-Lithium alloy sheets at various forming conditions was studied by both the experimental approach and the finite element analysis. The uniaxial tensile tests and forming limit tests of 5A90 Al-Li alloy sheets at various temperatures were first carried out. The tests results were then employed in the finite element simulations to investigate the effects of process parameters, such as forming temperature, holder force, and die corner radius, on the formability of cylindrical cup drawing with 5A90 sheets. In order to validate the finite element analysis, the corresponding deep drawing tests were also carried out. It is shown that the simulation results are in qualitative agreement with the experimental observations. The optimal forming temperature, diameter of blank, holder force, punch radius and die corner radius were then determined for the cylindrical cup drawing of 5A90 sheets, and the limit drawing ratio (LDR) reached 2.4 in the optimal parameter conditions.

Abstract: Uniaxial tensile deformation behavior of 5A90 aluminium-lithium alloy sheet is investigated in the hot forming with the temperature range of 200-450°C and strain rate range of 0.3×10^-3-0.2×10^-1s^-1. It is found that the flow stress of 5A90 Al-Li alloy in uniaxial tension increase with increasing strain rate and decrease with increasing temperature, however, the tendency of total elongation is just the reverse, and the optimum forming temperature is 400°C. The strain rate sensitivity index (m-value) remarkably increases with increasing temperature for a given strain rate. It is shown that 5A90 Al-Li alloy sheet displays the sensitivity to the strain rate at elevated temperatures. For a given strain rate, the strain hardening index (n-value) decreases with increasing temperature, whereas the n-value increases above 350°C. The constitutive equation of stress, strain and strain rate for 5A90 Al-Li alloy at any temperature is obtained by fitting the experimental data, which gave a good flow stress model for the FEM simulation of hot forming.

Abstract: As a heat treatable aluminum alloy to be used in T6 and T8 temper, belongs to Al-Cu-Li system, a novel high-strength aluminum-lithium alloy 2A97 was developed. In order to improve the relationships of strength and ductility and fracture toughness, and to urge the applications in the aeronautical and aerospace industries, the effects of normal heat treatments and thermomechanical heat treatments on the mechanical properties and fracture toughness were investigated by Transmission Electron Microscope(TEM), Scanning Electronic Microscope (SEM), tensile test, and fracture toughness test. The results show that for the alloy aged at 135 °C for 24 h after quenching and 4 percent plastic deformation, its microstructures are strengthened by strain hardening and precipitation hardening, consisting of fine T₁ phase, θ″/θ′ phase and δ′ phase densely and homogeneously distributed in the matrix. It yields optimum relationship of strength and ductility, fracture toughness, its σ_0.2, σ_b and δ₅ are 454 MPa, 536 MPa, and 11.8%, respectively. It yields 43.5 MPa·m^1/2 of K_q values higher than that of 42.5 MPa·m1/2 in T6 temper. The fracture morphologies of impact tensile samples of fracture toughness test and normal tensile test were observed, indicating the dominance of intergranular failure and subintergranular failure with some dimples and trangranular failure.

Abstract: Laser forming is a new flexible sheet metal forming process. By means of the theory of orthogonal experimental design method, design of experiment and optimization were carried out on thin aluminum-lithium alloy AA2090 sheet metal laser forming under the condition of water-cooling. And through the calculation and analysis of the experiments, the effect of the four process parameters related to the energy of laser beam on bending angle under the condition of water-cooling were ranked in order of laser power, number of scan, scan speed and beam diameter. Furthermore, the optimum process parameters were obtained, and experiment verifications were carried out.

Abstract: The quality of full penetration laser welding 5A90 Al-Li alloy can be evaluated by weld width, especially the ratio of weld back width to weld surface width (Rw), according to the results from laser welding experiment. And Rw will influence the joint properties, such as tensile strength and fatigue. In this paper, the effect of Rw on joint properties of 5A90 Al-Li alloy sheet are discussed, these joint welded by laser welding, dual beam laser welding .

Abstract: The critical resolved stresses (CRSS) of two kinds of Al-Li alloys 2090 and 2090+Ce in which contained trace addition of cerium are examined. The three heat treatment conditions (solution, peak aging and reversion after peak aging) are used in order to identify the influence of precipitates to CRSS. The experimental results show that the strengthening contribution of T1 Phase is greatly different at various orientation with respect to rolling direction, and the precipitation of T1 phase can weaken the anisotropy of mechanical properties. The T1 phase precipitated in subgain boundaries in peak aged and reverted specimens produce a stronger tendency of delaminating along grain boundary, which is a direct reason for the decrease of anisotropic yield strength.