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New aluminum-lithium alloys for aerospace applications

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Abstract

This paper discusses two aluminum-lithium alloys for aerospace applications, 2099 and 2199, including the relationship between their alloying elements and thermal-mechanical processing, to the alloy's properties. The paper also includes selected properties of these alloys in sheet, plate and extrusion forms. Finally, a trade study conducted between Alcoa and Bombardier using these alloys is discussed which highlights the weight and performance benefits to an aircraft when alloys with optimized properties are selected for specific aircraft applications.

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... Aluminum-Lithium (Al/Li) alloys were developed to serve as potential replacements to traditional aluminum alloys (e.g., 2024 and 7075) in aerospace structures [1][2][3][4]. Al/Li alloys offer a reduction in density, and therefore introduce a corresponding weight savings [2,[4][5][6][7]. These alloys show good resistance to corrosion [2,3,8], better weldability [5,[7][8][9][10], and superior fatigue benefits [2,5,11,12] compared to the traditional counterparts. ...
... Al/Li alloys offer a reduction in density, and therefore introduce a corresponding weight savings [2,[4][5][6][7]. These alloys show good resistance to corrosion [2,3,8], better weldability [5,[7][8][9][10], and superior fatigue benefits [2,5,11,12] compared to the traditional counterparts. By introducing 1 wt% (wt%) lithium, the Al/Li alloy density is reduced by approximately 3% while increasing by 6% the elastic modulus [2,5]. ...
... The more recent, third generation, Al/Li alloys addresses these drawbacks by lowering the weight percent of lithium to less than 2 wt.%, while introducing additional alloying elements (e.g., Zn, Mn, Cu, Mg, Ag, Zr, Sc) during the manufacturing process to better control the microstructure [14]. Alloying elements, such as zinc (Zn), have been used to improve the resistance to corrosion [2,3], while copper (Cu) and silver (Ag) have been added to improve strength [15]. It has been shown that Zirconium (Zr) and Manganese (Mn) are responsible mainly for grain recrystallization properties, specifically to the newest generation of Al/Li alloys [2,3,16,17]. ...
Article
A comparative study on the fatigue crack growth behavior in a typical third generation Al/Li alloy (AA2198-T8) and traditional aerospace aluminum alloy (AA2024-T3) was conducted. Fatigue crack growth history was reconstructed using marker band loading sequences (i.e., applying two different R-ratios). Effect of alloying and loading direction (relative to the rolling direction) was discerned from the fatigue fracture surface morphologies, which were markedly different in the two alloys. The marker band imprints aided in identifying suspected fatigue crack initiation region and estimating crack growth rate. A data reduction scheme was used to estimate crack initiation cycle.
... Fracture mechanics-based fatigue testing was performed on samples excised from a 50.8 mm thick plate of 2199-T86 supplied by Arconic. The nominal composition of the 2199 alloy is shown in Table 1 [73]. The expected strengthening precipitates in the aluminum alloy are the T 1 (Al 2 CuLi), θ' (Al 2 Cu),T 2 (Al 6 CuLi 3 ), and the δ' (Al 3 Li) [73]. ...
... The nominal composition of the 2199 alloy is shown in Table 1 [73]. The expected strengthening precipitates in the aluminum alloy are the T 1 (Al 2 CuLi), θ' (Al 2 Cu),T 2 (Al 6 CuLi 3 ), and the δ' (Al 3 Li) [73]. The yield strength was 423 MPa in the rolling direction. ...
... The yield strength was 423 MPa in the rolling direction. The nominal plane strain fracture toughness is 47 MPa√m in the Transverse (T)-Longitudinal (L) loading orientation and 59.5 MPa√m in the L-T orientation [73]. The grain sizes and texture of the plate was not quantified. ...
Article
The objective of the study is to evaluate the fatigue crack growth of a third-generation Al-Li-Cu alloy (2199-T86) in environments relevant to high-altitude flight. Reduction of PH2O at 23 ◦C resulted in a general reduction of crack growth rates. A local minimum in growth rates were observed at intermediate ΔK and PH2O and was attributed to roughness induced impedance of water transport through the crack wake. Decreasing temperature had no effect on growth kinetics down to -15 ◦C, but decreased crack rates were observed at -30 ◦C and -50 ◦C.
... Recent alloy developments have produced a new generation of Al-Li alloys which provide not only density weight savings, but also many property benefits such as excellent corrosion resistance, good spectrum fatigue crack growth performance, a good strength and toughness combination and compatibility with standard manufacturing techniques. This results in well-balanced, light-weight aluminum alloys [9]. Finally, Al-Li alloys provide many property benefits over previous Al alloys and are often competitive with the performance composites can offer for many aerospace applications. ...
... Recent alloy developments have produced a new generation of Al-Li alloys which provide not only density weight savings, but also many property benefits such as excellent corrosion resistance, good spectrum fatigue crack growth performance, a good strength and toughness combination and compatibility with standard manufacturing techniques. This results in well-balanced, light-weight aluminum alloys[9]. Finally, Al-Li alloys provide many property benefits over previous Al alloys and are often competitive with the performance composites can offer for many aerospace applications. Chronology of the development Aluminum alloys and latest Al-Lithium alloys development by Alcoa Company is shown inFig. ...
Article
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New developments in material science and its technologies find their best implementation areas in aircraft and space vehicles. Since the beginning of the powered flight, weight of airframes and systems are needed to be reduced. They are developed and built by light, durable and affordable materials through highly disciplined design, development, test and certification as well as manufacturing processes. Besides airframes, engineers are challenged to develop more efficient engines; both by reducing their weights and improving their aero-thermodynamic properties, sustaining higher operational and safety reliabilities along with complying stringent emission and noise restrictions. These conditions are increasing the demand for the development and the utilization of advanced lighter, stronger and durable materials and alloys, ceramic coatings and relevant manufacturing processes. In this study, current trends and future expectations from material technologies in general; for accomplishing higher expectations for future lighter airframes, aircraft systems and engines, are reviewed.
... The properties of these alloys are also adjusted by certain heat treatments, which is generally a sequence of solution heat treatment, cold working either followed by natural ageing (T3X) or by artificial ageing (T8X). According to Giummarra et al. [3], the strengthening is provided by the stable T 1 (Al 2 CuLi), the metastable Θ'-type (Al 2 Cu) and δ' (Al 3 Li) precipitates. Whereas the stable T 2 (Al 6 CuLi 3 ) precipitates increase the toughness. ...
Article
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AA2198 is a relatively new light-weight and high-performance Al-Cu-Li alloy considered for aviation and space applications. However, Al-Cu-Li alloys generally exhibit severe weldability problems for all fusion-welding techniques, such as laser-beam welding. In particular, porosity formation and hot cracking are observed for the laser-beam welding of these alloys. A common remedy for hot cracking is the use of an appropriate filler wire with a high Si content. In the present study, three different approaches for improving the hot cracking susceptibility of AA2198 laser beam welded without any filler material are presented. For this purpose, pre-heating of the weld samples to elevated temperatures, pre-loading of the weld samples perpendicular to the welding direction, or an optimization of the laser-beam welding parameters were conducted. The autogenously welded samples were assessed with regard to the resulting total crack length and their mechanical properties. It was demonstrated that all of the presented approaches led to a reduction of hot cracking. However, the largest effect was observed for the use of low levels of laser power and welding velocity. The mechanical properties of the optimised autogenously welded samples are only marginally inferior as for the samples laser welded with the Al-Si filler wire AA4047.
... Moreover, launch costs have strong restrictions on the overall mass of spacecraft, so the mass of aeronautical structures must be minimized as far as possible. Severe contradiction between strength and mass spurs extensive utilization of advanced alloy material and composite material in aerospace applications, such as aluminum lithium (Al-Li) alloys [1], titanium alloy [2] [3], carbon fiber/epoxy composites, and aramid fiber/epoxy composites [4] [5]. The Al-Li products offer opportunities for significant improvements in aerostructural performance through density reduction, stiffness increase, increases in fracture toughness and fatigue crack growth resistance, and enhanced corrosion resistance [6]. ...
Article
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Al-Li alloy and aluminum honeycomb panel (AHP) are both excellent materials for aeronautical structures. In this paper, a plate-type aeronautical structure (PAS), which is a base mounting structure for 172 kg functional devices, is selected for comparative analysis with different materials. To compare system-level performance under multidisciplinary constraints, mathematical models for optimization are established and then structural optimization is carried out using Altair OptiStruct. For AHP, its honeycomb core is regarded as orthotropic material and its mechanical properties are calculated by Allen’s model in order to establish finite element model (FEM). The heights of facing sheet and honeycomb core are selected as design variables for size optimization. For Al-Li alloy plate, topology optimization is carried out to obtain its most efficient load path; and then a reconstruction process is executed for practical manufacturing consideration; to obtain its final configuration, accurate size optimization is also used for reconstructed model of Al-Li alloy plate. Finally, the optimized mass and performance of two PASs are compared. Results show that AHP is slightly superior to Al-Li alloy.
... The rod-shaped Mn-rich precipitates (Fig. 6a) were identified as Al 20 Cu 2 Mn 3 , and the spherical-shaped Zr-rich precipitates (Fig. 6b) were judged to be b 0 (Al 3 Zr)282930. It is published [31] that the dispersed phases of Al 20 Cu 2 Mn 3 and b 0 (Al 3 Zr) mainly determine the size of recrystallised grains. ...
... Previous generations of aluminium-lithium alloys contained a higher concentration of lithium (Li) and had a lower density than the new Gen3 alloys. However, these earlier alloys suffered from high anisotropy, lower toughness, and manufacturing issues, associated with the high Li level and precipitation of the metastable d 0 and coarser equilibrium Li containing phases, such as T 2 [3,5,7]. New Gen3 alloys typically contain lower Li levels of 1e1.8 wt.%, which suppresses d 0 formation, and have chemistries designed to promote T 1 as the dominant strengthening phase. ...
Article
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The effect of increasing pre-stretching to higher levels, than are currently used in industrial practice, has been investigated on the strength, microstructure, and precipitation kinetics seen during artificial ageing an Al–Cu–Li alloy AA2195 - focussing on the behaviour of the main strengthening phase, T1. Increasing the pre-strain level, to the maximum obtainable before plastic instability (15%), resulted in an increase in the T8 yield strength to ∼ 670 MPa with a corresponding reduction in ductility from ∼11 to 7.5%. Microstructure data have been used to deconvolute and model the effects of increasing pre-strain on the main strengthening components that contribute to this large strength increase. The precipitation strengthening model proposed by Dorin et al. [1] has been successfully employed to calculate the strengthening contribution of the T1 phase and the increase in strength due to strain hardening has been modelled using X-ray line broadening measurements of dislocation density, using the modified Williamson–Hall approach. Refinement of the T1 phase was observed to continue to higher pre-strains than previously thought, but it is predicted that this leads to a reduction in the strengthening contribution from precipitation. In contrast a low level of recovery was observed during stretching, and artificial ageing, resulting in an increasing contribution form strain hardening with pre-strain. Thus, it is shown that increasing the pre-strain prior to ageing results in a reduction in the strengthening provided by the T1 phase, in favour of an increase in the strain hardening contribution.
... Initially these alloys did not achieve widespread use due to properties anisotropy, low toughness, poor corrosion resistance and/or manufacturing issues. New generation of Al-Li alloys provides not only density weight savings, but also many property benefits such as excellent corrosion resistance, good fatigue crack growth performance, a good strength and toughness combination and compatibility with standard manufacturing techniques [3]. ...
Article
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The analysis of isothermal forging process of ribbed plates made of multicomponent (Al-Cu-Li-Zn-Mg system) third generation 2099 aluminium alloy is presented in the paper. Numerical simulation of forging was performed by finite elements method (FEM) using the QForm v.7 commercial software. Obtained results were the base for selection of conditions of isothermal forging for examined aluminium alloy. It was assumed in the work that ribbed plates could be produced by one-step forging. The isothermal forging at the temperature of 450ºC was conducted on designed test bed. Satisfactory shape accuracy and high quality surface of the forging were found. Evaluation of alloy’s microstructure before (T-83 condition) and after forging was performed by microscopic examination. It was found that obtained results of numerical simulation and experimental research can be a base for elaboration of industrial process of plastic forming of complex geometry flat structural parts made of 2099 aluminium alloy.
... Welded joints can be used instead of riveted joints due to their lower production costs, better corrosion resistance and weight savings. Consequently, in recent time the FSW process has been known as a fundamental technology for fuselage and wing manufacturing by major aircraft manufactures [10]. FSW of dissimilar metals and alloys is becoming popular particularly for systems that are troublesome or impossible to weld by conventional fusion welding [11,12]. ...
Article
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In the present study, butt joints of aluminum (Al) 8011-H18 and pure copper (Cu) were produced by friction stir welding (FSW) and the effect of plunge depth on surface morphology, microstructure and mechanical properties were investigated. The welds were produced by varying the plunge depth in a range from 0.1 mm to 0.25 mm. The defect-free joints were obtained when the Cu plate was fixed at the advancing side. It was found that less plunging depth gives better tensile properties compare to higher plunging depth because at higher plunging depth local thinning occurs at the welded region. Good tensile properties were achieved at plunge depth of 0.2 mm and the tensile strength was found to be higher than the strength of the Al (weaker of the two base metals). Microstructure study revealed that the metal close to copper side in the Nugget Zone (NZ) possessed lamellar alternating structure. However, mixed structure of Cu and Al existed in the aluminum side of NZ. Higher microhardness values were witnessed at the joint interfaces resulting from plastic deformation and the presence of intermetallics.
... Welded joints can be used instead of riveted joints due to their lower production costs, better corrosion resistance and weight savings. Consequently, in recent time the FSW process has been known as a fundamental technology for fuselage and wing manufacturing by major aircraft manufactures [10]. FSW of dissimilar metals and alloys is becoming popular particularly for systems that are troublesome or impossible to weld by conventional fusion welding [11,12]. ...
Article
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Aluminium matrix surface composites are gaining alluring role especially in aerospace, defence, and marine industries. Friction stir processing (FSP) is a promising novel solid state technique for surface composites fabrication. In this study, AA6061/SiC surface composites were fabricated and the effect of tool plunge depth on pattern of reinforcement particles dispersion in metal matrix was investigated. Six varying plunge depths were chosen at constant levels of shoulder diameter and tool tilt angle to observe the exclusive effect of plunge variation. Process parameters chosen for the experimentation are speed of rotation, travel speed and tool tilt angle which were taken as 1400 rpm, 40 mm/min, and 2.5°respectively. Macro and the microstructural study were performed using stereo zoom and optical microscope respectively. Results reflected that lower plunge depth levels lead to insufficient heat generation and cavity formation towards the stir zone center. On the other hand, higher levels of plunge depth result in ejection of reinforcement particles and even sticking of material to tool shoulder. Thus, an optimal plunge depth is needed in developing defect free surface composites.
... Since the first and second generations of Al-Li alloys presented some other characteristics that were found to be undesirable by aircraft manufacturers, with the progress of technology however, the third generation Al-Li alloys have received much attention for weight savings of aircrafts due to their more outstanding comprehensive performance than previous models. Among them, relatively new Al-Li alloys AA2060 and AA2099 are more promising candidates for fuselage panels of jetliners [4][5][6][7]. In Airbus Germany, double-sided laser beam welding (LBW) of skinstringer T-joints in lower fuselage areas partly instead of using the dominant riveting technique has led to a certain reduction of aircrafts' weight. ...
... For example, the two alloys AA2099 and AA2199 recently commercialized by ALCOA Inc. (AL- COA Technical Center, Pittsburgh, PA, USA), are the results of these continuous improvements (Rioja & Liu, 2012). These two alloys were the basis of this study and their elemental compositions are listed inTable 1 (Giummarra et al., 2007). In these alloys, in addition to Li and copper (Cu), minor elements like magnesium (Mg), zinc (Zn) and manganese (Mn) enable the formation of potent nanosized strengthening ppts during thermal treatments. ...
Article
Precipitates (ppts) in new generation aluminum-lithium alloys (AA2099 and AA2199) were characterised using scanning and transmission electron microscopy and atom probe tomography. Results obtained on the following ppts are reported: Guinier-Preston zones, T1 (Al2 CuLi), β' (Al3 Zr) and δ' (Al3 Li). The focus was placed on their composition and the presence of minor elements. X-ray energy-dispersive spectrometry in the electron microscopes and mass spectrometry in the atom probe microscope showed that T1 ppts were enriched in zinc (Zn) and magnesium up to about 1.9 and 3.5 at.%, respectively. A concentration of 2.5 at.% Zn in the δ' ppts was also measured. Unlike Li and copper, Zn in the T1 ppts could not be detected using electron energy-loss spectroscopy in the transmission electron microscope because of its too low concentration and the small sizes of these ppts. Indeed, Monte Carlo simulations of EEL spectra for the Zn L2,3 edge showed that the signal-to-noise ratio was not high enough and that the detection limit was at least 2.5 at.%, depending on the probe current. Also, the simulation of X-ray spectra confirmed that the detection limit was exceeded for the Zn Kα X-ray line because the signal-to-noise ratio was high enough in that case, which is in agreement with our observations.
... This is the main dispersoid used to control recrystallization. In aluminium-lithium, the strengthening δ' (Al 3 Li) phase also precipitates epitaxialy on the surface of Al 3 Zr dispersoids [40,108]. PFZs may be detrimental for the mechanical properties of a material as well as for corrosion resistance. ...
Article
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Co-encadrement de la thèse : Yazid Madi
... As previously reported, 1 wt. % of Li decreases the density of the resultant Al alloy by approximately 3% and increases the elastic modulus by approximately 6%, as depicted in Fig. 2a and b, respectively [4,6,7]. Since Al is a lightweight metal (2.7 g/cm 3 ), few alloying addition choices exist for a further weight reduction. ...
Article
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Al-Li alloys are attractive for military and aerospace applications because their properties are superior to those of conventional Al alloys. Their exceptional properties are attributed to the addition of Li into the Al matrix, and the technical reasons for adding Li to the Al matrix are presented. The developmental history and applications of Al-Li alloys over the last few years are reviewed. The main issue of Al-Li alloys is anisotropic behavior, and the main reasons for the anisotropic tensile properties and practical methods to reduce it are also introduced. Additionally, the strengthening mechanisms and deformation behavior of Al-Li alloys are surveyed with reference to the composition, processing, and microstructure interactions. Additionally, the methods for improving the formability, strength, and fracture toughness of Al-Li alloys are investigated. These practical methods have significantly reduced the anisotropic tensile properties and improved the formability, strength, and fracture toughness of Al-Li alloys. However, additional endeavours are required to further enhance the crystallographic texture, control the anisotropic behavior, and improve the formability and damage tolerance of Al-Li alloys.
... Although the difference between both substrate materials is with 15 HV0.1 small and identical LMD process parameters were used, the difference between both Al coatings is with approximately 30 HV0.1 about 2 times larger. This can be explained on the one hand by the presence of porosity in the Al coatings of the AA2198 substrate and on the other hand by the reduced homogeneity of Li during the LMD processing, since the main strengthening phases are Al 3 Li and Al 2 CuLi (besides Al 2 CuMg) [13]. ...
Article
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The application of coatings to structures is generally done in order to locally tailor properties. For this purpose, powder-based laser metal deposition (LMD) can be utilized. The resulting properties of the coatings are not only affected by the LMD process parameters, but also by the substrate material. In this regard, the chemical composition as well as its initial microstructure of the substrate has a significant influence. In the present study two Al-Cu alloy substrates, 2139 and 2198, are used for the LMD of pure Al powder. The resulting coatings possess clearly different properties, although the same process parameters are used.
... The deep understanding of the relations between the microstructure and mechanical characteristics of these materials matured much later in the 1990s, leading to the production of the third generation (GEN3), a family of alloys with an outstanding combination of properties for aeronautic applications. The former generations of Al-Li alloys had a higher Li content and a lower density than GEN3 alloys, but suffered from high anisotropy associated with the precipitation of coarse Li phases, such as T 2 [22,23]. ...
Article
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In recent years, a great effort has been devoted to developing a new generation of materials for aeronautic applications. The driving force behind this effort is the reduction of costs, by extending the service life of aircraft parts (structural and engine components) and increasing fuel efficiency, load capacity and flight range. The present paper examines the most important classes of metallic materials including Al alloys, Ti alloys, Mg alloys, steels, Ni superalloys and metal matrix composites (MMC), with the scope to provide an overview of recent advancements and to highlight current problems and perspectives related to metals for aeronautics.
... The specimens exhibited similar fracture behaviours and crack propagation profiles. The key difference lies in the fracture load and subsequent fracture toughness seen by each specimen, with values ranging between 36 and 50 MPa Á (Dorward and Pritchett, 1988;Giummarra et al., 2007;Heinz et al., 2000;Starke and Staley, 1996;Wanhill, 2013). The experimental results were also compared against a number of published articles (Chen et al., 2015;Narayana et al., 2004;Reid, 1974), which included typical K IC magnitudes for these alloys ranging between 29 and 53 MPa Á ffiffiffiffi ffi m p . ...
Article
Purpose - A key challenge found in additive manufacturing is the difficulty to produce components with replicable microstructure and mechanical performance in distinct orientations. This study aims to investigate the influence of build orientation on the fracture toughness of additively manufactured AlSi10Mg specimens. Design/methodology/approach - The AlSi10Mg specimens were manufactured using the selective laser melting (SLM) technology. The fracture toughness was experimentally determined (under ASTM E399-09) using C(T) specimens manufactured in different orientations. The microstructure of the specimens was examined using metallography to determine the effects of grain orientation on fracture toughness. Findings - The fracture toughness magnitude of manufactured specimens ranged between 36 and 50 MPa m^1/2 , which closely matched conventional bulk material and literature values regarding AlSi10Mg components. The C(T) specimens printed in the T-L orientation yielded the highest fracture toughness. The grain orientation and fracture toughness values confirm the anisotropic nature of SLM parts where the T-L-oriented specimen obtained the highest K IC value. A clear interaction between the melt pool boundaries and micro-slipping during the loading application was observed. Originality/value - The novelty of this paper consists in elucidating the relationship between grain orientation and fracture toughness of additively manufactured AlSi10Mg specimens because of the anisotropy generated by the different melting pool boundaries and orientations in SLM. The findings show that melt pool boundaries can behave as easier pathways for cracks to propagate and subsequently reduce the fracture toughness of specimens with cracks perpendicular to the build direction.
... Al-Li alloys are attractive to aviation and aerospace applications because of their excellent properties, such as low density, high specific strength and elastic modulus [1][2][3][4] . However, in moist environments, corrosion will occur in Al-Li alloys and deteriorate their mechanical properties, which can reduce the service life of Al-Li structures. ...
Article
2198 and 5A90 Al-Li alloys were anodized with a constant DC potential in 18%H2SO4 solution (Solu.A) and the mixture solution of 18%H2SO4+5%C2H2O4 (Solu.B) at room temperature. 12 and 11 V was optimized as the applied oxidation potential for 2198 and 5A90 alloys, respectively. Cross-sectional morphology, surface morphology and elements distribution of anodic oxidation coatings were observed by scanning electron microscope equipped with energy dispersive X-ray analysis (SEM/EDX). Corrosion resistance was tested by potentiodynamic polarization plot in 3.5%NaCl solution. The results showed that the thicknesses of coatings obtained at the selected potential in Solu.A and Solu.B were about 50 μm/110 μm for 2198 alloy and 80 μm/110 μm for 5A90 alloy. In both solutions, anodic oxidation coatings of 2198 alloy were primarily composed of Al oxides; those of 5A90 alloy were mainly consisted of Al oxides and a small amount of Mg oxides. The results of potentiodynamic polarization showed that anodic oxidation coatings of 2198 and 5A90 Al-Li alloys had better corrosion resistances than that of untreated alloys.
... When addition 1wt%Li reduces the density of the Al alloy by about 3% and increase the elastic modulus by about 6%. [2,4,5]. Addition Li to Al improvement the solubility of Al create very fine precipitates at high temperature [8]. ...
Research
Aluminum-lithium alloys used in the aerospace industry as structural components and strengthened by age-hardening
... The low ductility and fracture toughness of the first generation of the Al-Li alloys, as well as their strong anisotropy, kept the researchers in the search for improved Al-Li alloys 2,3 . The second generation was developed aiming weight saving by low density, however, it was also characterized by short-transverse fracture toughness, lower plane stress (K c ) fracture toughness/residual strength in sheet and higher anisotropy of tensile properties 4,5 . This generation also presented higher damage tolerance due to pronounced slip reversibility and large crack path deviation when compared with that of conventional aluminum alloys. ...
Article
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Fatigue and corrosion-fatigue tests were performed to quantify the fatigue properties of AA2524-T3 and AA2198-T851 Al alloys. High cycle axial fatigue tests were carried out under air and salt-water fog conditions. In air, the specimens were fatigue tested at a frequency of 50 Hz, using specimens with and without preconditioning in a salt spray chamber, and for the corrosion fatigue condition, the tests took place at a frequency of 30 Hz in a salt-water fog condition. In all cases it was used a sinusoidal waveform and a stress ratio (R) of 0.1. The results indicate that the saline environment had a deleterious effect on the fatigue life of the two aluminum alloys. AA2524-T3 exhibited a better fatigue strength than AA2198-T851 when fatigue tested in air. However, considering the corrosion fatigue test in a saline fog environment an inverse behavior was observed with the AA2198-T851 exhibiting higher fatigue strength.
Article
Aluminum lithium alloys are new materials developed for lightweight aircraft parts. However, as compared with conventional aluminum alloys in high-speed machining, problems such as tool wear, machining distortion, and cutting ability arise. This study presents the machining distortion characteristics of an Al-Li alloy wing tip in relation to the cutting heat in high-speed machining. A machining experiment was conducted with high-speed machining equipment for an evaluation of the machining distortion characteristics, with each machining stage temperature change of the workpiece machining surface, and the inside and outside temperature changes of the equipment measured. By measuring the amount of distortion of the workpiece before and after machining, the cutting heat was analyzed with regard to its effect on machining distortion in the product.
Article
Aluminum-lithium alloys are widespread in the aerospace industry. The new 2099 and 2199 alloys provide improved properties, but their microstructure and texture are not well known. This article describes how state-of-the-art field-emission scanning electron microscopy (FE-SEM) can contribute to the characterization of the 2099 aluminum-lithium alloy and metallic alloys in general. Investigations were carried out on bulk and thinned samples. Backscattered electron imaging at 3 kV and scanning transmission electron microscope imaging at 30 kV along with highly efficient microanalysis permitted correlation of experimental and expected structures. Although our results confirm previous studies, this work points out possible substitutions of Mg and Zn with Li, Al, and Cu in the T1 precipitates. Zinc and magnesium are also present in "rice grain"-shaped precipitates at the grain boundaries. The versatility of the FE-SEM is highlighted as it provides information in the macro- and microscales with relevant details. Its ability to probe the distribution of precipitates from nano- to microsizes throughout the matrix makes FE-SEM an essential technique for the characterization of metallic alloys.
Article
Al-Cu-Li alloys are extensively used for aerospace applications. The main hardening phase is the T1 phase that precipitates as thin platelets on {111}Al planes. To facilitate its nucleation, different minor alloying elements are added and dislocations are introduced by cold deformation before the ageing treatment. The impact of these additions in combination with the presence of dislocations on precipitate nucleation and growth needs a deeper understanding. In this work, we investigated the precipitation kinetics of the T1 phase in alloys containing a common content of Cu and Li and different contents of minor solutes (Mg, Ag) where these elements are present either together or independently. A general overview on the precipitation kinetics was achieved by in-situ small-angle X-ray scattering and hardness measurements. The evaluation of precipitation kinetics reveals that magnesium plays an important role during precipitation by enhancing nucleation kinetics. Additionally, a smaller yet measureable effect of Ag, both in the presence and absence of Mg has been evidenced.
Article
This paper discusses two Al-Cu alloys for aerospace applications, one which has a high concentration (>1.8 wt.%) of Li. These alloys are AA2024-T3 (Al-Cu) and AA2099-T8E77 (Al-Cu-Li) and are both in the plate format. Anodic polarisation and immersion in a 3.5 wt.% NaCl solution have been carried out and a comparison of the corrosion mechanisms have been made. Both alloys showed extensive corrosion over the surface, AA2024-T3, however, had areas of pitting that had joined together forming large corrosion regions, whereas AA2099-T8E77 had numerous corrosion pits that had not merged. The pits on AA2099-T8E77 propagated to a depth ~120 µm whereas on AA2024-T3 the maximum depth was ~85 µm. Intergranular and transgranular corrosion was also observed on the AA2024-T3 alloy following anodic polarisation. AA2099-T8E77 had reduced corrosion resistance with regards to Epit-Ecorr values. For both alloys, dissolution of matrix material surrounding the Cu-rich intermetallic particles was observed, highlighting the particles’ cathodic nature.
Article
Environmental fatigue crack propagation (EFCP) is alloy-inhibited in under aged Al–Cu–Mg and peak aged Al–Cu–Li alloys stressed in pure aqueous chloride solution. Counter to H diffusion and H-embrittlement rate limited step considerations which predict fatigue crack growth rate (da/dN) to be either independent of fatigue loading frequency (f) or increase with decreasing f, da/dN declines with decreasing f. The mechanism for such alloy induced inhibition and decreasing da/dN with decreasing f is reduced crack tip H production and uptake due to stabilization of the native aluminum passive film resulting from: (1) dissolution of anodic Cu-containing GP zones or precipitates (Al2CuLi or Al2CuMg) by dealloying, (2) crack surface Cu enrichment, and (3) enhanced crack wake cathodic reaction kinetics on Cu enriched sites that increase crack solution pH. Peak aged Al–Zn–Mg–Cu alloy 7075 does not exhibit alloy induced inhibition because the predominant anodic phase, Mg(Cu,Zn)2, does not provide a source for Cu surface enrichment. Alloy induced inhibition is similar to ion-assisted inhibition by molybdate or chromate addition into bulk chloride solution which provides an alternate path to stabilize a crack tip passive film. Both alloy-induced and ion-assisted inhibition of EFCP are promoted by reduced f and crack tip strain rate which favor repassivation of the crack tip passive film over film rupture.
Article
Controlled short circuiting gas metal arc welding (CSC-GMAW) was investigated as a potential solid freeform fabrication (SFF) process for AA2199. The low heat input of the CSC-GMAW process resulted in a cooling rate on the order of 840-3500°C s-1 being realised during deposition. The solidification time was then calculated to range between 2-5 ms depending on the location within the weldment. The depositedmaterial displayed a fine (4·3±1 μm) cellular structure, comparable to that previously reported for electron beam welding. Through comparison with the Kurz-Giovanola- Trivedi (KGT) model for microstructural development during solidification, the solidification front velocity (SFV) of the CSC-GMAW process was estimated to be 2-4·5 × 10-4 m s-1. Chemical analysis revealed lateral segregation of copper to the cell walls. TOF-SIMS revealed a homogeneous lateral lithium distribution, however depth profiling displayed some extent of lithium enrichment at the surface of the deposited material.
Article
A charge-coupled device camera of an electron backscattered diffraction system in a scanning electron microscope was positioned below a thin specimen and transmission Kikuchi patterns were collected. Contrary to electron backscattered diffraction, transmission electron forward scatter diffraction provides phase identification and orientation mapping at the nanoscale. The minimum Pd particle size for which a Kikuchi diffraction pattern was detected and indexed reliably was 5.6 nm. An orientation mapping resolution of 5 nm was measured at 30 kV. The resolution obtained with transmission electron forward scatter diffraction was of the same order of magnitude than that reported in electron nanodiffraction in the transmission electron microscope. An energy dispersive spectrometer X-ray map and a transmission electron forward scatter diffraction orientation map were acquired simultaneously. The high-resolution chemical, phase and orientation maps provided at once information on the chemical form, orientation and coherency of precipitates in an aluminium-lithium 2099 alloy.
Article
Addition of molybdate (MoO42-) to aqueous chloride solution effectively inhibits environmental fatigue crack propagation (EFCP) in peak aged Al–2.6Cu–1.6Li (wt pct, C47A-T86) which also exhibits alloy-induced inhibition in pure chloride solution. MoO42- inhibits EFCP at frequencies below an upper bound and eliminates the effect of environment at sufficiently low loading frequencies by yielding crack growth rates equivalent to those for fatigue in ultra-high vacuum. Ion-assisted inhibition is attributed to MoO42- stabilizing a crack tip passive film which reduces H production and uptake due to a diffusion barrier film, reduced crack acidification by hydrolysis, and buffered pH. Inhibition is governed by the balance between passive film rupture by crack tip strain and repassivation. As such, inhibition is promoted by reduced loading frequency and potentials at or anodic to free corrosion; each of which favors passivity over film rupture. Alloy-induced inhibition is destabilized by addition of molybdate. This is likely due to molybdate inhibiting localized corrosion of Al2CuLi precipitates in the crack wake which otherwise leads to Cu enrichment required for alloy-induced EFCP inhibition in C47A-T86. The inhibiting effect of molybdate for this Al–Cu–Li alloy parallels chromate and molybdate inhibition of EFCP in 7075-T651, establishing molybdate as a viable chromate replacement inhibitor.
Article
This paper discusses two Al-Cu alloys for aerospace applications, one of which has an addition of between 1.6 and 2.0 wt.% of Li. The alloys are AA2024-T3 (Al-Cu) and AA2099-T8E77 (Al-Cu-Li). Microstructural analysis via Field Emission Gun Transmission Electron Microscope (FEGTEM) and Field Emission Gun Scanning Electron Microscope (FEGSEM) utilising Energy Dispersive Spectroscopy (EDS) and Electron Backscatter Detector (EBSD) techniques have been used to characterise the two microstructures and phases contained within them. Anodic polarisation and immersion testing in a 3.5 wt.% NaCl solution have been carried out and a comparison of the corrosion mechanisms has been made. AA2024-T3 had a fine, equiaxed grain structure, whereas AA2099-T8E77 had a substantial amount of recrystallized grains. Finer grains were also observed on AA2099-T8E77, however, the vast majority were larger than the maximum detection limit of the EBSD technique. Intergranular and pitting corrosion were observed on both alloys following immersion testing, however, the intergranular corrosion (IGC) was more prominent on AA2099-T8E77. Anodic polarisation indicated that AA2024-T3 was more noble, highlighting that the Li-containing AA2099-T8E77 alloy was more susceptible to corrosion. The T1 (Al2CuLi) phase within AA2099-T8E77 was seen to be highly active following immersion and anodic polarisation tests. The corrosion pits on AA2099-T8E77 were seen to propagate to a depth of ~ 80 to 100 μm, with a maximum of 126 μm recorded. For AA2024-T3 the maximum depth recorded was 77 μm and the average depth was between 60 and 70 μm.
Article
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The paper presents the results of investigations of a multicomponent third-generation aluminium alloy, classified as AA2099. The actual forging conditions were determined basing on the assessment of the quality of side surface of specimens subjected to compression in Gleeble 3800 simulator and on flow curves of the alloy, as well as numerical modelling of forging process performed with application of QForm 3D v.7 software. Compression tests were realized at temperatures 400-500 °C, with a strain rate of 0.001-100 s
Article
Full-text available
The ever increasing utilization of Al-Li alloys for light weight structural applications is limited chiefly due to their lower room temperature formability compared to their Li-free counterparts. In the present work, the effect of 1, 2 and 3 wt.% Li addition to Al-Mg-Si alloy (containing 0.5 wt.% Mg and 0.2 wt.% Si) was studied. Experimental work showed that microstructural features of the second phase particles and mechanical properties changed substantially with Li addition. It was observed that 1 wt.% Li addition resulted in significantly large elongation of over 38 % resembling a super-plastic behavior with decent strength and hardness due to the formation of second phase precipitates uniformly dispersed in alpha (Al) matrix. Scanning electron microscopy and X-ray diffraction analysis revealed that the addition of Li promotes the formation of second phase precipitates, which strongly affect the mechanical properties of Al-Mg-Si alloy. Quite surprisingly, the alloys containing 2 and 3 wt.% Li showed a much reduced ductility and a much higher hardness after aging.
Chapter
Al-Li alloys are the focus of attention in the aviation industry with their high modulus of elasticity, high hardness, high fatigue crack growth resistance, and low density. These specially designed alloys are used in fuselage, fuselage beam, lower wing, and upper wing structures in aircraft. The use of Al–Li alloys is thought to be extended to different sections in aircraft due to the effort of weight reduction. However, various drawbacks are encountered in either the production or material properties of these alloys. In this chapter, the progressive advantages and disadvantages of Al–Li alloys that are used in aviation are explained. Historical development, aviation usage, microstructural properties, processing metallurgy, corrosion, and mechanical properties of Al–Li alloys are expressed.
Chapter
This chapter describes the basic concepts related to the application of cerium compounds as a main alternative to the already restricted approaches of the use of toxic and environmentally unacceptable compounds. The chapter begins with a brief description of the importance of aluminium alloys for the aircraft industry and the basic corrosion forms and damages typical for these alloys. Besides the indispensability of the coating procedures for providing long-term corrosion protection, the basic multilayered coatings systems are also discussed. Following this, the basic stages and factors of deposition of cerium conversion coatings (CeCCs) as primer coating layers are described. Subsequently, various methods that involve cerium compounds as active components in upper and finishing coating layers are proposed based on the literature analysis. Furthermore, some alternatives of the cerium compounds as environmentally friendly active coating ingredients, such as organic corrosion inhibitors, are also proposed. The chapter finishes with the recent and the most actual directions for further improvement of coatings. Finally, the development of dense, self-healing, sun-light-protected, hydrophobic coatings are described.
Conference Paper
Aluminum lithium alloy will likely become the material of choice over composites as the fuselages of the next generation of narrow-body aircraft due to its high strength to weight ratio and excellent corrosion resistance. In this paper, aluminum lithium alloy samples are milled under air coolant condition and liquid nitrogen condition. Surface integrity factors including roughness and residual stress are measured. The results show that the angle between feed direction and rolling orientation dominates in the formation of surface finish, which is often neglected in previous study. The results also demonstrate the capacity of liquid nitrogen on improving the surface integrity followed by an increase of material removal rate in face milling of aluminum lithium alloy. Finally, the regression models for roughness and residual stress are established and the effectiveness of these models are validated.
Chapter
As well as improvements in the propulsive efficiency of aircraft (Chapter 23) there are a number of other technological developments, which enable the reduction in anthropogenic greenhouse gas emissions from aviation. Some are ‘tweaks’ to current design methodologies; others involve a more radical approach to aviation, all resulting in significant savings in fuel burn and therefore a reduction of emissions from aviation. This chapter will cover developments in materials, aerodynamics and some more radical options for the reduction of the impact of aviation on climate change.
Chapter
Introduction Materials and Methods Results and Discussion Conclusions
Article
In the present study, correlative corrosion testing and electron microscopy, including quasi-in-situ electron microscopy, are employed to investigate the corrosion behaviour of 2A97-T8 Al-Cu-Li alloy extrusion in 3.5 wt. % NaCl solution. It is found that the corrosion behaviour of the alloy is influenced by synergetic effect of the plastic deformation introduced by the thermomechanical processing during alloy fabrication and the precipitation of T1 phase during T8 treatment. Localized corrosion initiates and propagates preferentially within non-recrystallized regions of the partially recrystallized alloy. Corrosion initiated at coarse constituent intermetallic particles is confined to its periphery, which doesn’t develop further when the particles are disconnected from alloy matrix.
Chapter
The evolution of the microstructure during friction stir welding of a third generation AA2199 Al-Li alloy has been described and related to the mechanical properties of welds. The coupling of electron microscopy and micro-hardness have helped generate an understanding of the relationship between grain structure, precipitate density and morphology behind the observed changes in mechanical properties during post weld artificial ageing. The ability of welds to recover hardness and strength during post weld heat treatment was linked to the limited formation of large scale precipitates which act as sinks for alloying elements. Welds obtained with high tool rotation speed (within parameters studied) showed ultimate tensile strength levels of about 93% of the base metal, an elongation of 6% at fracture, and hardness values ranging between 120–140 HV in the stir zone, thermo-mechanically affected zone, and heat affected zone upon post weld heat treatment.
Chapter
This paper describes how state-of-the-art Field-Emission Scanning Electron Microscopy (FE-SEM) can contribute to the characterization of the 2099 aluminum-lithium alloy, and metallic alloys in general. Investigations were carried out on bulk and thinned samples. BSE imaging at 3kV and STEM imaging at 30kV along with highly efficient microanalysis permitted to correlate experimental and expected structures. Although our results confirm previous studies, this work points out possible substitutions of Mg and Zn with Li, Al and Cu in the T1 precipitates. Zinc and magnesium are also present in “rice grain” shaped precipitates at the grain boundaries. The versatility of the FE-SEM is highlighted in that it can provide information at the macro and micro scales with relevant details. Its ability to probe the distribution of precipitates from nano-to micro-sizes throughout the matrix makes Field-Emission Scanning Electron Microscopy a suitable technique for the characterization of metallic alloys.
Article
Laser shock peening can improve the damage tolerance of metallic materials by introducing deep compressive residual stress that inhibits crack initiation and growth. This study investigates the laser peening of aluminium alloy in a product form – an extruded T-section – that has different crystallographic textures in different locations. The alloy studied is Al 2099, an aluminium-lithium alloy that shows anisotropy in the mechanical properties when texture is present. Specimens extracted from different regions of the extrusion were laser shock peened with a power density of 3 GW/cm² in single shocks as well as in a pattern. Residual stresses were characterized primarily using incremental hole drilling. The results show 20% higher residual stresses in the web area of the extrusion compared to the flange after peening with a single laser shock, with this difference decreasing as the number of shocks increases. This effect can be explained by the difference in yield strength between those locations. No significant differences were observed in the residual stresses from peening onto different planes of a textured sample at a given location.
Article
Increasing space activities produce a high number of space objects and lead to increasing collision risks which urges leading industries to look for future removal strategies. Material substitution in order to raise demisability during atmospheric reentry is a possible solution. Modern aluminum lithium alloys are under consideration to replace high-temperature melting materials like titanium. Further, friction stir welding was proposed as suitable joining technology in order to avoid high heat inputs during manufacturing. In this work, two modern Al-Li-Cu alloys, AA 2060 and AA 2196, in peak-aged temper were welded using the stationary shoulder variant of bobbin tool friction stir welding. Identical process parameters led to defect-free welds in both alloys. The macrostructural and microstructural features are shown and analyzed. The welds were mechanically tested to an efficiency of 78 and 70% of the base metal ultimate tensile strength for AA 2060 T8 and AA 2196 T8, respectively. The process forces as well as the thermal cycle experienced by the workpiece material were used to explain the mechanical performance. The difference in composition regarding the Cu/Li ratio of the alloys was taken into account when the mechanical properties were correlated with the thermally affected microstructure of the weldments.
Article
Aluminium-lithium alloys commonly used in aerospace at home and abroad. In this paper, Al-Li alloys are classified into four categories according to their different elements. It also summarizes its corrosion in common acidic medium, and prospects for the development and research of the next generation of new Al-Li alloys.
Article
A combined experimental and simulation investigation is carried out to characterize the high temperature deformation behavior of a recently developed Al-Li alloy, AA2070, over a temperature range including typical forging temperatures. Focus is placed on providing explanations for the temperature-dependent plastic and fracture behavior observed for this material using macroscale tensile tests, microscale imaging and analysis, and physics-based micromechanical modeling. It is shown that AA2070 experiences non-monotonic elongation to failure with a rise in temperature. Detailed fractography and microstructural analysis, including dynamic recrystallization analysis, provide insight into this interesting and practically useful behavior. In addition, a validated crystal plasticity model is called upon to explain the unique texture observed in the necked region of the ductile tensile specimen. The insights provided by this investigation will allow improved design of high temperature forming operations for AA2070 and similar alloys which can extend the application of third generation Al-Li alloys.
Chapter
In the past two decades, there has been an ever-increasing demand for solid-state welding of dissimilar materials. This type of solid-state welding technique is gaining prominence in various disciplines but more importantly in naval, marine, aerospace and military applications. Most of the leading car manufactures today are exploring the possibilities of joining magnesium with aluminium, via solid-state welding process. In the present scenario these techniques are applicable for automotive applications like transmission cases and oil pans. In this work, the different types of solid-state welding techniques that were used for joining of aluminium alloys with magnesium alloys are reviewed from different perceptions. One of the important issues that is faced during joining of these dissimilar materials, is the formation of intermetallic compounds (IMCs) at the welded interface. The work also highlights the influence of various process parameters, structural morphology, intermetallic compound formation and variations in mechanical properties. Some of the important Solid-state welding processes that are elucidated here includes: friction welding, friction stir welding, friction stir spot welding, diffusion welding and third body welding. The above said techniques are carefully analysed for the formation of a satisfactory and quality sound aluminium-magnesium joints. In the overview, it can be summarized that friction-based joining processes have great potential to obtain sound Al–Mg joints. The amount of frictional heat generated at the surface of the contact helps to decide the type and volume fraction of IMCs that are subsequently affecting the mechanical properties of the joints. The joint properties can be enhanced by optimizing the process parameters.
Article
Full-text available
A retrogression and reaging (RRA) treatment was performed on 2195 Al-Li Alloy. The exposure times were from 5 to 60min, and the temperatures were from 200 to 250°C. Samples that were exposed to a salt spray test had overall similar mechanical properties as compared to those that were not exposed. The percent elongation, however, was significantly deteriorated due to the salt spray exposure. The mechanical properties of the 2195 samples were compared to those of 2099 samples exposed to similar treatments in an earlier study. Keywordsaluminum lithium alloys–retrogression and reaging–2195 and 2099 alloys
Article
Alloy 2090 fabricated as O-Temper sheet exhibited the presence of the T2 phase. The morphology and nucleation characteristics of the T2 phase in alloy 2090 were investigated by transmission electron microscopy. Also, the crystal structure was documented by electron and X-ray diffraction analyses. It was found that T2 precipitates formed preferentially at the interface of heterogeneities in the alloy. Several types of heterogeneities were identified. From these results it was proposed that as the impurities are eliminated, the propensity for nucleation of the T2 phase should be reduced.
Article
After a description of the evolution of Al-Li alloys, this paper first reviews the subject of anisotropy in mechanical properties of Al-Li wrought products. In plane, through thickness and axisymmetric flow anisotropies present in Al-Li wrought products are defined. The root causes for these anisotropies are discussed. Pros and cons arising from anisotropic products are then discussed in the context of designing and manufacturing for space and aerospace structures. Numerous attempts aimed to reduce anisotropy in rolled and extruded products are summarized. It is concluded that ‘isotropic’ Al-Li products can be manufactured via the selection of appropriate process, composition and processing parameters.
  • R J Rioja
  • A Cho
  • E L Colvin
  • A K Vasudevan
  • Al-Li Alloys
R.J.Rioja, A.Cho, E.L.Colvin, A.K.Vasudevan., Al-Li Alloys, U.S. Patent 5,137,686 (1992).
Aluminum-Lithium Alloys and Method of Making the Same
  • R J Rioja
  • J A Bowers
  • R S James
R.J.Rioja, J.A.Bowers and R.S.James, Aluminum-Lithium Alloys and Method of Making the Same, U.S. Patent 5,066,342 (1991).
Al-Li Alloys Having Improved Corrosion Resistance Containing Mg and Zn
  • R J Rioja
  • A Cho
  • P E Bretz
R.J.Rioja, A.Cho, P.E.Bretz, Al-Li Alloys Having Improved Corrosion Resistance Containing Mg and Zn., U.S. Patent 4,961,792 (1990).
Precipitation Reactions Strength and Toughness of Al-Li-Cu Alloys, Aluminum Alloys
  • R J Rioja
  • R R Bretz
  • W H Sawtell
  • E A Hunt
  • Ludwiczak
R.J.Rioja, P E Bretz, R R Sawtell, W H Hunt and E.A.Ludwiczak, Precipitation Reactions Strength and Toughness of Al-Li-Cu Alloys, Aluminum Alloys, Their Physical and Mechanical Properties, EAMS (3) (1986), pp.1781.
Texture and Properties of 2090, 8090 and 7050 Extruded Products, Ibid
  • D K Denzer
  • P A Hollinshead
  • J Liu
  • K P Armanie
  • R J Rioja
D. K. Denzer, P. A. Hollinshead, J. Liu, K. P. Armanie and R. J. Rioja, Texture and Properties of 2090, 8090 and 7050 Extruded Products, Ibid. (II) (1992), pp.903.