2xxx Series Aluminium Alloys Research Articles

FSW of AA 2139 Plates: Influence of the Temper State on the Mechanical Properties

Nowadays the fiber reinforced materials are finding more and more widespread use in aeronautic field due to their features of lightness, high strength and flexibility of manufacturing systems. The only way for metals to remain competitive for the aerospace applications is to improve new technologies and alloys in order to realize lighter and more resistant structures. The development of new alloys (lighter and stronger) and technologies will allow to use metals also in the future for aerospace applications. In this scenario the research activity has a fundamental importance, and the key point is to work simultaneously on both innovative materials and new technologies that allow to obtain the best performances with the innovative alloys. Welding is nowadays playing a fundamental role in transport industry thanks to the important advantages it allows. Friction Stir Welding (FSW) [1] is one of the most promising welding techniques, particularly suitable for applying to light alloys. FSW in butt joint configuration allows to achieve very high mechanical performances, often absolutely superior to those achievable with all other joining techniques, and lots of researches and results are now available [2]. The AA 2139 is an innovative Al-Cu-Ag alloy that has higher mechanical performances than the conventional 2xxx series aluminum alloys. The AA 2139 is designed to work in service in T8 temper condition, but is simplest to work in T3 temper condition. The aim of this work is to compare the performances of AA 2139 butt joints welded in T8 temper conditions, presented in a previous work [3], with the ones of joints welded in T3 condition and heat treated post welding in order to achieve the T8 temper condition.

Robotic welding of thin wall components made of 6xxx and 2xxx series aluminium alloys using low-energy methods

The application of low-energy methods of metal inert gas welding (ColdArc and CMT) for the manufacture of joints in hard-weldable aluminium alloys is presented. The purpose of the technological research was to show the usefulness of the CMT and ColdArc methods for production of butt and T-joints in 2.0 mm thick aluminium alloy plates. Basic difficulties related to welding of 6xxx and 2xxx series aluminium alloys and the specificity of welding by low-energy methods are discussed. Selected results of metallographic macro- and microscopic examination as well as those of tensile and bend tests are given; detailed analysis of the results is also carried out. The article shows also that ColdArc and CMT methods provide high quality and aesthetic welded joints in aluminium alloys that are considered to be non-weldable or of limited weldability.

CMT and MIG-Pulse Robotized Welding of Thin-Walled Elements Made of 6xxx and 2xxx Series Aluminium Alloys

The article presents the course and the results of research on material and technological welding conditions of different aluminium alloys using standard (MIG-Pulse) and low energy welding method (CMT) as well as discusses the properties of welded joints and the application fields of modern low energy welding devices for joining thin aluminium sheets.

Powder metallurgy processing of 2xxx and 7xxx series aluminium alloys

Aluminium powder metallurgy (APM) is an advanced metal forming technology frequently employed to fabricate complex structural components in a near net shape fashion. Exhibiting nearly 100% material utilisation, APM continues to rise in popularity. Recent research initiatives in this field have emphasised the development and processing of advanced 2xxx and 7xxx series alloys. In particular, APM equivalents to wrought 7075 and 2024 have been sought. An overview of work completed in this area is presented. Data on the various production stages (powder compaction, sintering, forging and heat treatment) as well as the microstructure and mechanical properties of the finished products are included. Data confirmed that both alloys were highly responsive to sintering and hot upset forging. The forging behaviour of these alloys was akin to that observed for traditional wrought systems while the yield strengths of the hot worked APM systems were superior to those of wrought materials tested.La métallurgie des poudres d’aluminium (APM) est une technologie avancée de façonnage sans enlèvement de copeaux du métal, employée fréquemment dans la fabrication des composantes structurelles complexes de haute précision. Exhibant une utilisation du matériau de près de 100%, l’APM est de plus en plus populaire. Des initiatives récentes de recherche dans ce domaine ont mis l’accent sur le développement et le traitement des alliages avancés des séries 2XXX et 7XXX. En particulier, on a recherché les équivalents APM du 7075 et du 2024 de corroyage. On présente une revue du travail complété dans ce domaine. On inclut des donnés sur les diverses étapes de production (compaction de la poudre, frittage, forgeage et traitement thermique) ainsi que sur la microstructure et les propriétés mécaniques des produits finis. Les données ont confirmé que les deux alliages étaient hautement sensibles au frittage et au forgeage par refoulement à chaud. Le comportement de forgeage de ces alliages était apparenté au comportement observé pour les systèmes corroyés traditionnels alors que les limites d’élasticité des systèmes APM travaillés à chaud étaient supérieures à celles des matériaux corroyés évalués.

Preferential anodic oxidation of second‐phase constituents during anodising of AA2024‐T3 and AA7075‐T6 alloys

AbstractModel analogues of the metallurgical phases found in 2xxx and 7xxx series aluminium alloys were produced by magnetron sputtering and employed to investigate the local and general anodising behaviour of the alloys. Electrochemical tests, allied with scanning and transmission electron microscopy, enabled insight into the local anodising behaviour of the constituents and related effects on the overall porous oxide morphology. Under potentiodynamic conditions, the observed anodic current peaks of the commercial alloys were related with the anodic oxidation of specific second‐phase particles. At 0 V, magnesium‐containing particles, including S‐phase, were preferentially removed from the alloy surface; at 5–6 VSCE, the copper‐ and/or iron‐containing particles, such as θ phase and Al7Cu2Fe particles were anodically oxidised. The initial voltage transient revealed for the commercial alloys during galvanostatic anodising was related to the previous findings and reproduced by the use of coupled alloy analogues. Transmission electron microscopy revealed that the voltage transient associated with oxidation of second‐phase material influence the morphology of the anodic film formed on the aluminium matrix. Copyright © 2010 John Wiley & Sons, Ltd.

Galvanic coupling between copper and aluminium in a thin-layer cell

The Al/Cu coupling was investigated in a thin-layer cell formed by a large Cu electrode and an Al microelectrode embedded in an insulator placed above the Cu electrode. By using a scanning electrochemical microscope (SECM) the thickness of the thin layer was perfectly controlled with a precision in the micrometer range. A copper deposit on an electrochemical quartz crystal microbalance (EQCM) was also used as SECM substrate to quantify the copper dissolution rate. It was shown that such an experimental set-up allows to mimic the galvanic corrosion of intermetallic particles embedded in the aluminium matrix of the 2XXX series aluminium alloys. The combination of the SECM and the EQCM permitted the evaluation of the corrosion rate of copper at the corrosion potential of the 2024 Al alloy, whereas cyclic voltammetry performed on the SECM tip indicated the enrichment in Cu 2+ ions in the thin electrolyte layer.

Observations of oxide films on fatigue fracture surfaces of a sintered 2xxx series aluminium alloy

An unusual feature observed in some grain boundaries on the fatigue fracture surfaces of a sintered 2xxx series aluminium alloy is a serrated, film-like structure. Chemical analysis indicates a significant level of oxygen on the serrated features, indicating that they may be oxide films. It is suggested that these films are not a key microstructural feature of the material but are the result of fretting between mating surfaces during fatigue testing.

Study of TiCn Additions to an 2xxx Series Aluminium Alloy

The increasing demand of PM parts for automobile and aerospace applications has caused a strong development of the aluminium based metal matrix composites (MMCs).Aluminium alloys are one of most widely used materials as matrix in MMCs, both in research and development as well as in industrial applications. The main reason is the combination of good specific properties, the first requirement in most applications, and the competitive price compared to other low density alloys such as Mg or Ti alloys. In the present work, the influence of the ceramic reinforcement addition to a 2xxx series aluminium alloy is studied. Several percentages of TiCN have been added to the Al-Cu alloy using PM techniques, in order to analyze its influence on the liquid phase sintering process and also on the final properties of the material. The materials have been uniaxially compacted using two different pressures to determine the optimal pressing condition. They have been subsequently sinterized in a N2-H2 atmosphere. Analysing the results obtained, it can be concluded that the addition of TiCN allows a better distribution of the liquid phase up to the 10 %wt, where the optimal results are observed: For higher quantities of reinforcement, elemental copper is observed in the microstructure with the consequent decrease in densification.

Fatigue crack propagation in a sintered 2xxx series aluminium alloy

Many potential applications for sintered aluminium are limited by the poor fatigue properties of the material. In order to increase understanding of the fatigue mechanisms in sintered aluminium, fatigue tests were carried out on a sintered 2xxx series aluminium alloy, AMB-2712. The alloy has a fatigue endurance strength of approximately 145 MPa ( R = 0.1). Three regions were identified on the fatigue fracture surfaces. Region 1 contains the initiation site and transgranular crack propagation. When the size of the cyclic plastic zone ahead of the crack becomes comparable to the grain size, microstructural damage at the crack tip results in a transition to intergranular propagation. Region 2 mainly contains intergranularly fractured material, whilst the final fracture area makes up Region 3, in the form of dimple coalescence and intergranular failure. Transgranular fractographic features observed on fatigued specimens include fissure-type striations, cross-hatched grains, furrowed grains and grains containing step-like features.

Atomistic modelling of diffusional phase transformations with elastic strain

Phase transformations in 2xxx series aluminium alloys (Al–Cu–Mg) are investigated withan off-lattice atomistic kinetic Monte Carlo simulation incorporating the effects of strainaround misfitting atoms and vacancies. Atomic interactions are modelled by Finnis–Sinclairpotentials constructed for these simulations. Vacancy diffusion is modelled bycomparing the energies of trial states, where the system is partially relaxed for eachtrial state. No special requirements are made about the description of atomicinteractions, making our approach suitable for more fundamentally based models such astight binding if sufficient computational resources are available. Only a limitedprecision is required for the energy of each trial state, determined by the value ofkBT. Since the change in the relaxation displacement field caused by a vacancy hop decays as1/r3, it is sufficient to determine the next move by relaxing only those atoms in a sphere offinite radius centred on the moving vacancy. However, once the next move has beenselected, the entire system is relaxed.Simulations of the early stages of phase separation in Al–Cu with elastic relaxation showan enhanced rate of clustering compared to those performed on the same system with arigid lattice.

Characterization of the precipitation in Al–Li–Cu–Mg–(Mn, Zr) alloys

AbstractThe three‐dimensional atom probe has been used to characterize the precipitates in two Li‐containing 2xxx series aluminium alloys: Al–6Li–Cu–Mg–0.2Mn (alloy A) and Al–6Li–Cu–Mg–0.03Zr (alloy B). The alloys have been heat treated at 150°C for times in the range 6–24 h. In alloy A, the particles identified can be classified into two categories: those rich in Cu and Mg (similar to GPB zones and S′ precipitates); and spherical particles rich in Li (δ′ precipitates). Clusters rich in Li are also observed. The same phases are observable in alloy B, although growth of the δ′ phase precipitates is accompanied by the formation of a Zr‐rich phase similar to β′. Copyright © 2004 John Wiley & Sons, Ltd.

WELDURAL

Abstract Weldural is a mold alloy for applications in the low-pressure molding of rubber and other elastomers at temperatures in the 175 to 205 deg C (350 to 400 deg F) range. These applications need a mold alloy with moderate strength and good property retention at moderately elevated temperatures. Alloys for mold applications are based on the 2xxx series aluminum alloys. This alloy is similar to 2219. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on high temperature performance as well as joining. Filing Code: AL-387. Producer or source: Corus Aluminum Rolled Products USA.

Mechanical behaviour of the interphase between matrix and reinforcement of Al 2014 matrix composites reinforced with (Ni3Al)p

The 2XXX series aluminium alloys reinforced with intermetallics present a special behaviour due to the reaction between matrix and reinforcement. This reaction forms an interphase that influences the mechanical and chemical behaviour of the composite, reducing the capability of the material to improve its properties after heat treatment. In this work, an approach is made to the study of this interphase, using particulate intermetallics with the same chemical and stoichiometric composition but obtained in different ways: mechanical alloying and gas atomising. A microstructural study was carried out by SEM, including qualitative analysis, showing the chemical gradient formed at the interphase both as-extruded and after T6 treatment. The mechanical behaviour of the interphase is studied through nanoindentation that allows the determination of hardness and Young modulus. Finally, all these properties are correlated with a fractrographic study of the fracture mechanisms. A harder interphase is formed for the mechanically alloyed system promoting a transgranular cleavage fracture micromechanisms, while intergranular cleavage fracture is found in atomised intermetallic containing composites.

Effect of artificial aging on the fatigue crack propagation resistance of 2000 series aluminum alloys

Artificial aging performed to impart higher strength generally degrades the fatigue crack propagation (FCP) resistance of naturally aged 2xxx-series aluminum alloys. This behavior is examined for commercial AA2024-T351 and a naturally aged Al–Cu–Mg–Li alloy stressed in high-humidity air. Environmental fatigue crack growth rate decreases with initial-artificial aging, then increases monotonically with increasing aging time. Overaging does not improve cracking resistance. This effect of microstructure is pronounced at low stress intensity factor range and persists for high stress ratio conditions that minimize crack closure. For both alloys, the highest resistance to fatigue crack growth correlates with the presence of artificial aging intensified solute clusters, and absence of distinct precipitates, as evidenced by electron microscopy and small-angle neutron scattering (SANS). Increased crack growth rates correlate with the dissolution of clusters and/or the formation of an increasing amount of S′ precipitates for AA2024 and T 1 precipitates for the Li-bearing alloy. The fundamental effects of very fine-scale clusters and precipitates on cyclic-slip mode and environment-sensitive crack tip damage are unresolved.

Processing-Property Correlation in Friction Stir Welds

Friction Stir Welding (FSW) is a relatively new process for joining of metals. The process was invented in 1992 at The Welding Institute, Cambridge, UK. FSW is particularly well suited to use in highly alloyed aluminum because it is a solid state process; therefore, no undesirable, brittle, low-melting eutectic phases are formed during the welding process. The microstructure of a typical friction stir weld is that of a wrought product. The details of the weld formation mechanism have been the subject of some debate. Previous work on elucidation of flow patterns in friction stir welds indicated that the process may be described as an in-situ extrusion. Material flow in two friction stir welds produced using different welding parameters was visualized using embedded marker materials and the fidelity of the visualization technique was demonstrated. Flow of material in the friction stir welds was observed to depend strongly on the temperature of the weld. In this paper, welding temperature measurements are combined with tensile test data to further promote understanding of the process in 2XXX, 5XXX, 6XXX, and 7XXX series aluminum alloys. Weld parameters (spindle rotation rate and welding speed) and time-temperature histories are correlated with the global and local tensile properties, and microstructure of the resulting welds.

Low cycle fatigue resistance of Al–Li alloys

Low cycle fatigue (LCF) resistance data from binary Al–Li, ternary Al–Li–Cu, and quaternary Al–Li–Cu–Mg alloys have been compiled and discussed. The LCF resistance is measured in terms of the variation of the number of reversals to failure 2Nfwith the plastic strain amplitude Δɛp /2 as well as a modified average plastic strain energy per cycle (ΔWp )modified , obtained at different applied total strain amplitudes (Δɛt /2). The data show the effects of microstructural features, namely dominant strengthening precipitates and the degree of recrystallisation as well as crystallographic texture. Lithium content, when in excess of 2·5 wt-%in aluminium decreases the low cycle fatigue resistance the most. The degree of aging, the degree of recrystallisation, and the degree of texture also influence the LCF resistance; among which the effect of the degree of aging is the most pronounced. The effects of lithium content in aluminium solid solution and strengthening precipitates obtainable by the change in the Li/Cu ratio are found to be marginal. Based on a modified total cyclic plastic strain energy till fracture, it is shown that most of the Al–Li alloys exhibit degradation in their LCF resistance in both hypotransition (higher fatigue lives) and hypertransition (lower fatigue lives) regions. Such degradation is attributed to the combined effects of mechanical fatigue, strain localisation through dislocation–precipitate interaction, environmental effects, and finally strain localisation through the high angle grain boundaries. In comparison with the currently used 2XXX and 7XXX series aluminium alloys, Al–Li alloys require substantial improvement before they can be considered for fatigue critical applications.

Intergranular Corrosion Resistance of 2014 Aluminium Alloys Reinforced with Ni<sub>3</sub>Al

Intergranular corrosion is typical from 2xxx series aluminium alloys. In this work, this property has been evaluated in 2014 aluminium matrix composites. The base alloy was manufactured through mechanical alloying, and reinforced with Ni 3 Al particles of two types (manufactured through mechanical alloying and through rapid solidification). Corrosion tests were carried following ASTM G110 standard. Corrosion was evaluated by scanning electron microscopy and energy dispersive X-ray analysis. It has been studied the influence that the different kinds of intermetallic and T6 heat treatment have on the corrosion resistance of 2014 aluminium alloy. Results show that, in all cases, intermetallics highly improve the corrosion resistance of base aluminium alloy, and that T6 heat treatment is also favourable.

The Postulated Mechanisms for Stress Corrosion Cracking of Aluminum Alloys: A Review of the Literature 1980-1989

Abstract The stress corrosion cracking (SCC) of aluminum alloys is a well-documented phenomenon, but there is considerable disagreement in the scientific literature as to what mechanism causes it. This paper reviews the past 10 years of publications and describes the experimental methods and the proposed SCC mechanisms of about 90 selected papers. Different SCC mechanisms have been proposed for the different aluminum alloy systems: for example, anodic dissolution is generally favored in the 2xxx series aluminum alloys, while hydrogen-induced cracking is favored in the 7xxx series. However, considering the conflicting reports in the literature, it is still possible that other mechanisms are operational.

Influence of corrosion deposits on near-threshold fatigue crack growth behavior in 2xxx and 7xxx series aluminum alloys

The role of corrosion deposits in influencing the near-threshold fatigue crack propagation behavior of 2XXX and 7XXX series aluminum alloys is examined in detail. The composition, thickness, and distribution of fracture surface oxide films are characterized with the aid of X-ray photoelectron spectroscopy, scanning Auger spectroscopy, and secondary ion mass spectroscopy analyses. It is found that the extent of crack closure due to corrosion debris in aluminum alloys is strongly dependent on the composition and aging treatment. The results suggest that environmentally-influenced near-threshold crack propagation in some aluminum alloys is controlled by twoconcurrent andmutually-compctitive mechanistic processes: a dominant role of crack closure due to corrosion deposits (which tends toarrest completely the near-threshold crack) and a strong embrittling effect (which considerablyincreases near-threshold crack growth rates) concomitantly with the crack tip oxidation phenomenon in the moist medium. The near-threshold corrosion fatigue characteristics of aluminum alloys are contrasted with those in a wide range of steels in order to gain an insight into the various