2xxx Series Aluminium Alloys Research Articles

A generalised framework for modelling anisotropic creep-ageing deformation and strength evolution of 2xxx aluminium alloys

The 2xxx aluminium alloys are extensively applied in the aerospace industry due to their lightweight and balanced performance characteristics. However, a comprehensive method for modelling both the anisotropic creep deformation and strengthening behaviour in creep age forming (CAF) for 2xxx aluminium alloys remains lacking. This paper presents a generalised framework for establishing constitutive models capable of describing the anisotropic creep deformation coupled with the microstructure and material strength evolutions during creep-ageing of both the original and the pre-deformed 2xxx series Al alloys. This framework extends the rolling direction-based material model to anisotropic scenarios at varying angles between the loading and rolling directions, by employing the non-uniform rational B-splines (NURBS). The details about the anisotropic model calibration and numerical simulation implementation are demonstrated. The feasibility of this method was verified by its application to various 2xxx series aluminium alloys with or without pre-deformation, through constitutive modelling and numerical simulation, with satisfactory agreements between prediction and experimental data. For the first time, the proposed framework provides a generalised routine for establishing anisotropic creep-ageing models for various 2xxx aluminium alloys.

Microstructure and Mechanical Properties of Similar/Dissimilar Resistance Spot‐Welded Aluminum Alloys for Aerospace Applications

2195 aluminum–lithium (Al–Li) and 2XXX series aluminum alloys are joined using resistance spot welding for the first time. The macrostructure, microstructure, element distribution, microhardness, and tensile‐shear property of spot‐welded joints are investigated. The microstructure of the fusion zone of 2195/2195, 2195/2219, and 2195/2A14 joints is fine equiaxed spherical grains. It is found that solute segregation of Cu occurs in the grain boundaries in the fusion zone, forming Al2Cu. The microhardness shows that due to the dissolution of strengthening phase T1, the hardness of the fusion zone of the three types of joints is lower than that of the base material. The 2195/2195 joint has the best mechanical performance among the three combinations, with maximum tensile‐shear force and absorbed energy reaching 16893.7 N and 24.9 J, respectively. The fracture surfaces of all three types of joints exhibit mixed ductile‐brittle characteristics.

Effect of Zn/Mg ratio on aging precipitates and mechanical property of high Mg content Al-Mg-Zn alloys with Sc and Zr additions

To enhance the strength of traditional 5xxx series alloys, this work designed Al-Mg-Zn alloys with high Mg content and different Zn/Mg ratios (wt%, Zn/Mg ratio<1.0) drawing inspiration from aging precipitation strengthening of 2xxx or 7xxx series aluminum alloys and thermodynamic calculation. Measurement of density, microhardness and tensile property as well as electron backscatter diffraction (EBSD) and high-resolution transmission electron microscopy (HRTEM) were used to investigate the effects of four different Zn/Mg ratios on the aging precipitation behavior and mechanical property of the studied alloys. As Zn/Mg ratio increases, both N3 (Zn/Mg = 0.37) and N4 (Zn/Mg = 0.71) precipitate fine and dispersed distributed nano T-Mg32(Al,Zn)49 precipitates. After a two-step aging treatment process of 90 °C/24 h + 140 °C/8 h, N4 exhibits tensile strength of 595.5 MPa, yield strength of 484 MPa, and elongation of 10.2% in the peak state. N4 features higher specific strength and lower density compared to the popular 7075-T6. The TEM analysis reveals that the addition of trace Sc and Zr leads to the formation of Al3(Sc,Zr) precipitates, which significantly refines grain size thus enhancing strength. The primary strengthening mechanisms of Al-Mg-Zn-Sc-Zr alloy include grain boundary strengthening, solid solution strengthening, and precipitation strengthening. A yield strength model considering multiple strengthening mechanisms and thermodynamic calculation has been adopted to achieve accurate yield strength predictions. This work provides reference for composition design, microstructure and property regulation of lightweight high-strength aluminum alloys.

New neural network-based algorithm for predicting fatigue life of aluminum alloys in terms of machining parameters

Various classification of aluminum alloys is one of the most common applied materials in transportation industries due to the specific mechanical and material properties. Body of vehicles, including cars, ships, and airplanes, are constantly exposed to different cyclic loads that lead to surface damage and finally, fatigue failure occurs by crack growth. Therefore, the quality of the machined surface has a direct effect on the fatigue life of the products. In this regard, the most important source of surface roughness is the choice of machining parameters. To understand it, turning operations were performed on 2xxx and 7xxx series aluminum alloys considering different values of process parameters. For any series of aluminums, 189 high-cycle fatigue testing specimens were prepared, and experiments were performed by axial tension–compression fatigue test machine in 7 levels of stress (all tests were repeated three times and the mean failure cycles were reported as the fatigue life). Next, an Artificial Neural Network (ANN) based on the Back Propagation (BP) error algorithm was developed to predict fatigue life of Al alloys which are machined with different conditions. To this end, the parameters considered as input variables to the neural network structure include the Yield Strength (YS) and Ultimate Tensile Strength (UTS) to identify the aluminum series, as well as the process parameters such as cutting depth (d), rotational speed (R), and feed speed (V). In addition, the applied cyclic stress (S) to specimen was considered as input. Furthermore, surface roughness (Z) and number of cycles to failure (N) were considered as ANN output. The comparison of the obtained results from ANN predicting with the experimental values indicates that this approach was tuned finely. Eventually, the presented model can be a suitable alternative to perform fatigue tests with high costs and time-consuming.‌‌ Also, the most effective machining parameter on the surface roughness and fatigue limit was reported.

Machine-learning assisted compositional optimization of 2xxx series aluminum alloys towards tensile strength

High-strength 2xxx series aluminum alloys (Al-Cu system) have been favored by the aerospace and railway transportation industries. Traditionally, developing new materials with targeted properties is guided by extensive experiments and expert experience, causing the development process to be dismayingly slow and expensive. Here, a Kriging model-based efficient global optimization(EGO) lgorithm is applied to search for new 2xxx series aluminum alloys with high tensile strength in a huge search space. After four iterations, the alloy’s ultimate tensile strength increased by 60 MPa, which is higher than that of the best alloy in the initial data set. This study demonstrates the feasibility of using machine-learning to search for 2xxx alloys with good mechanical performance.

Characterization of Hot Extruded Hybrid Composites Al 2024 Metal Matrix Reinforced with TiO2 and ZrO2

In this study, the microstructure and mechanical properties of Al 2024 powder, the prominent type of Al 2XXX series aluminum alloys widely used in the aerospace industry, and TiO2 and ZrO2 reinforcement elements used to improve material properties were investigated. Each reinforcement element is included in the material at the rate of 10%. For hybrid composite sample production, 10% hybrid composite material was procured by adding each reinforcing element equally. For each sample, powders were mixed in a 3D mixer to ensure an equal distribution of matrix powder and reinforcement elements in the samples. The samples were churned out by subjecting the two-stage them to a one-way hot press process. The furnace temperature was kept at 600 o C to preserve samples. Density and microstructure analyses were performed on the formed samples, and the results were evaluated. After all, the Archimedean density measurement method was used to obtain final densities, these samples were taken to bakelite for optical images, then scanning electron microscope (SEM) and Brinell hardness of the samples was measured. The cross-fracture strength test was completed to analyze each sample’s microstructural behavior. Finally, the theoretical radiation shielding properties of each sample were investigated. The Phy-X/PSD program was used to examine the radiation permeability properties. According to the test and analysis results, the effect of reinforcement elements on the material was determined. As a result, the highest hardness value measured was 97.5 HB at the 10% ZrO2 -reinforced MMCs. However, the relative density of the hybrid composite is better than ZrO2-reinforced MMCs. Thus, the best cross-fracture strength measured was 635 MPa in 10% hybrid MMCs. The radiation shielding parameters showed that the 10% ZrO2 -reinforced MMCs are best for shielding. Therefore, the second reasonable material for radiation shielding is hybrid reinforced materials. In the final decision, hybrid composite materials became prominent because the distinctive features of each material enhanced the samples.

Investigating the effect of water cooling on hardness of 2xxx series aluminium alloy micro-alloyed with 0.02 and 0.04 wt% of Titanium

In this study, the hardness values were analyzed to compare the micro-alloying (0.02 and 0.04 wt%) effect of Titanium (Ti) in 2xxx series Aluminium (Al) alloys. Al-Cu-Mg (alloy-A), Al-Cu-Mg-0.02Ti (alloy-B) and Al-Cu-Mg-0.04Ti (alloy-C) were the alloys which were prepared using standard casting process. Different conditions of heat treatment were applied on the alloys. Using Rockwell Hardness tester hardness was investigated for the said alloys under as-cast and heat treated conditions. Addition of 0.02 wt% of Ti to the investigated alloy improves the hardness value by about 3.61% when the alloy was naturally aged and water-cooled (NAW). After adding 0.04 wt% of Ti to the investigated alloy improves the hardness value by about 15.66% when the alloy was naturally aged and water-cooled (NAW). In the study the hardness values were recorded for 31 days at different time intervals such as at Day 1, 7, 15, 21 and 31. The hardness of the alloys was maximum when it reaches Day 15 and gradually decreases after that. The hardness of the water-cooled samples (Alloy A, B and C) was seen to be decreasing in a specific order in all the days the hardness test was performed. The order observed is, NAW > AC > AAW > NAWSH > NAWS > AAWH.

Material parametric optimisation of wing leading edge profile against soft body impact

The present study aims to optimise the material parameters of the 2xxx series aluminium alloy used in aircraft wing leading edges to improve its mechanical properties against bird impact. For this study, a bird model is established and validated with an experiment test from literature and with a bird strike test on the wing leading edge. The significant material parameters which affect the energy absorption characteristics of the wing leading edge is selected from the comparison of parametric study results. Then the selected parameters are optimised and validated with bird impact analysis studies based on Taguchi’s L16 factorial design of experiments combined with grey relational analysis. The significant improvement in the mechanical properties, i.e. yield strength, ultimate tensile strength, and tensile toughness of the new optimised aluminium alloy has been proved with a series of uniaxial tension tests. The new alloy shows average property improvement up to 24.44% in tensile toughness and 19.4% in tensile strength than baseline alloy AA 2024-T3.

Effect of dislocations, Al3(Sc,Zr) distribution and ageing temperature on θ′ precipitation in Al-Cu-(Sc)-(Zr) alloys

The 2xxx series aluminium alloys, which contain Cu as the main addition element, are widely used in the aerospace industry for their high specific strength. The main strengthening contribution in these alloys comes from the formation of θ′ precipitates. Recent work, has revealed that minor additions of Sc and Zr result in significant strength increase through the formation of fine Al3(Sc,Zr) dispersoids that help nucleate and refine the θ′ precipitates. The aim of the present work is to understand the impact of dispersoids distribution, ageing temperature and stretching on θ′ precipitation. In order to separate these different contributions, specific thermo-mechanical routes were conducted on an Al-3.5 wt.%Cu and an Al-3.5 wt.%Cu-0.1 wt.Sc-0.14 wt.Zr alloy. Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT) characterisations were conducted to study the nano-precipitation. While stretching has a significant impact on the θ′ distribution in the Al-3.5 wt.%Cu alloy, it has a reduced impact in the Al-3.5 wt.%Cu-0.1 wt.%Sc-0.14 wt.%Zr alloy. In the latter alloy, the θ′ precipitates are already refined, even without stretching, due to preferential heterogeneous nucleation on the finely dispersed Al3(Sc,Zr) phase. This nucleation mechanism was found to dominate when ageing at 160 °C. When increasing the ageing temperature to 190 °C, θ′ increasingly nucleates homogeneously and less on the dispersoids. Ageing at a higher temperature allows for a redistribution of Sc at the θ′ interface hence increasing its thermal stability. This competition in nucleation mechanisms is revealed for the first time and provides different strategies to design high strength 2xxx-series alloys with purpose-specific properties.

Experimental investigation and modelling of yield strength and work hardening behaviour of artificially aged Al-Cu-Li alloy

The yield strength and work hardening properties of an Al-Cu-Li alloy AA2050 after artificial ageing have been experimentally investigated and modelled in this study. Uniaxial tensile stress-strain curves of the alloy artificially aged for up to 500 h have been acquired and evolutions of main precipitates during ageing have been summarised to elucidate the underlying mechanisms of the observed mechanical properties, such as yield strength and work hardening behaviour. Work hardening analysis with Kocks-Mecking plots has been performed to analyse the shearing-to-bypassing transition progress of the aged alloy and it has been found that the transition does not occur at the peak-ageing state. A new mechanism-based unified constitutive model, comprising three sub-models, has been developed to simultaneously predict the evolutions of microstructures, yield strength and work hardening properties of the artificially aged AA2050. It is the first unified model covering a wide range of artificial ageing conditions from under-ageing to over-ageing, providing an effective tool for performance prediction of the aged alloys for industrial applications. The model has the generic feature and could be applied to artificial ageing of other 2xxx series aluminium alloys with dominant T1 precipitates.

Polyoptimisation of the refill friction stir spot welding parameters applied in joining 7075-T6 Alclad aluminium alloy sheets used in aircraft components

In the aerospace industry, the refill friction stir spot welding (RFSSW) method is increasingly used to join thin sheets, especially those made of 2xxx and 7xxx series aluminium alloys. This paper presents the results of spot welding lap joints of 7075-T6 aluminium alloy sheets. The load capacity of joints was determined by tensile/shear tests using a universal testing machine. The effect of tool plunge depth, tool rotational speed and duration of welding on joint load capacity and failure mode was investigated. The polyoptimisation of the values of welding process parameters was carried out to ensure the highest load capacity of the joint at a minimum variance of the results obtained. The selection of the optimal parameters of the RFSSW process was carried out using an adequate mathematical model obtained on the basis of Weierstrass’ theorem. It was found that tool rotational speed had the greatest impact on the load capacity of the joints. It was possible to increase the load capacity of the joint by increasing the duration of welding but only to a limited extent. The selection of optimal welding parameters requires a compromise solution, i.e. the selection of a tool rotational speed that ensured adequate plasticisation of the material with a welding duration that ensured that an appropriate joint microstructure was obtained and assured the required load capacity of the joint. The methodology of mathematical modelling of polyoptimisation presented can be useful in optimising similar joining processes.

Stress Corrosion Cracking Sensitivity of High-Strength 2xxx Series Aluminum Alloys in 3.5 % NaCl Solution

Stress Corrosion Cracking Sensitivity of High-Strength 2xxx Series Aluminum Alloys in 3.5 % NaCl Solution

Measuring fatigue crack deflections via cracking of constituent particles in AA7050 via in situ x-ray synchrotron-based micro-tomography

Brittle constituent particles play a significant role in the fatigue behavior of 2XXX and 7XXX series aluminum alloys. In this work, in situ fatigue crack growth combined with x-ray synchrotron computed micro-tomography (μXSCT) characterization is used to observe and quantify three dimensional propagating fatigue cracks interacting with constituent particles. A relationship is observed with the size of the constituent particle ahead of the crack tip and the maximum distance the crack path deflects to interact with the particle. This crack deflection behavior agrees with the Murakami and Endo model, for the effect of small defects on fatigue performance. A stress field analysis, based on (i) an Eshelby inhomogeneity solution of a perfectly bonded particle, and (ii) a cracked particle, based on the Westergaard solution, indicates the stress concentration developed by the presence of a constituent particle contributes to crack path deflections. This finding has implications for modeling fatigue crack growth in AA7050-T7451, specifically in determining the actual crack length in terms of a tortuous crack topography, as opposed to a flat projected length.

An Examination of the Composition and Microstructure of Coarse Intermetallic Particles in AA2099-T8, Including Li Detection.

Electron and proton microprobes, along with electron backscatter diffraction (EBSD) analysis were used to study the microstructure of the contemporary Al-Cu-Li alloy AA2099-T8. In electron probe microanalysis, wavelength and energy dispersive X-ray spectrometry were used in parallel with soft X-ray emission spectroscopy (SXES) to characterize the microstructure of AA2099-T8. The electron microprobe was able to identify five unique compositions for constituent intermetallic (IM) particles containing combinations of Al, Cu, Fe, Mn, and Zn. A sixth IM type was found to be rich in Ti and B (suggesting TiB2), and a seventh IM type contained Si. EBSD patterns for the five constituent IM particles containing Al, Cu, Fe, Mn, and Zn indicated that they were isomorphous with four phases in the 2xxx series aluminium alloys including Al6(Fe, Mn), Al13(Fe, Mn)4 (two slightly different compositions), Al37Cu2Fe12 and Al7Cu2Fe. SXES revealed that Li was present in some constituent IM particles. Al SXES mapping revealed an Al-enriched (i.e., Cu, Li-depleted) zone in the grain boundary network. From the EBSD analysis, the kernel average misorientation map showed higher levels of localized misorientation in this region, suggesting greater deformation or stored energy. Proton-induced X-ray emission revealed banding of the TiB2 IM particles and Cu inter-band enrichment.

Microstructure Evolution and the Resulted Influence on Localized Corrosion in Al-Zn-Mg-Cu Alloy during Non-Isothermal Ageing.

A non-isothermal ageing process was proposed for an Al-Zn-Mg-Cu alloy aiming to accommodate the slow heating/cooling procedure during the ageing of large components. The evolution of microstructure and microchemistry was analyzed by using transmission electron microscopy, high-angle annular dark field imaging, and energy dispersive spectrometry. The age-hardening of the alloy was examined to evaluate the strengthening behavior during the non-isothermal process. The corrosion behavior was investigated via observing the specimens immersed in EXCO solution (solution for Exfoliation Corrosion Susceptibility test in 2xxx and 7xxx series aluminum alloys, referring ASTM G34-01). Secondary precipitation was observed during the cooling stage, leading to increased precipitate number density. The distribution of grain boundary precipitates transits from discontinuous to continuous at the cooling stage, due to the secondary precipitation’s linking-up effect. The solutes’ enrichment on grain boundary precipitates and the depletion in precipitate-free zones develops during the heating procedure, but remains invariable during the cooling procedure. The corrosion in NIA (Non-isothermal Ageing) treated specimens initiates from pitting and then transits to intergranular corrosion and exfoliation corrosion. The transition from pitting to intergranular corrosion is very slow for specimens heated to 190 °C, but accelerates slightly as the cooling procedure proceeds. The transition to exfoliation corrosion is observed to be quite slow in all specimens in non-isothermal aged to over-aged condition, suggesting a corrosion resistance comparable to that of RRA condition.

Developing a Framework for Improved Accelerated Testing of Aluminum-Lithium Alloys

Third generation Aluminum-lithium (Al-Li) alloys such as AA2060 are attractive for aerospace applications due to their high strength-to-weight ratios and their corrosion resistance during seacoast exposures.1 However characterizing these alloys in laboratory corrosion tests can be difficult as the results from conventional accelerated tests do not always agree with seacoast results. For example, ASTM G34 is a standard test for exfoliation corrosion, which is a form of localized attack that produces blisters when corrosion products due to intergranular attack produce a wedging pressure and lift un-attacked grains upward. This test was developed for alloys 7075 and 7178,2 but is considered applicable to 2xxx and 7xxx series aluminum alloys.3 However when Al-Li alloys 2099 and 2060 are tested in ASTM G34, the trend in exfoliation susceptibility over different aging conditions is opposite to the trend observed after seacoast exposures.4 This kind of disagreement between laboratory testing and seacoast exposure slows down the process of optimizing aging practices for new products. As new generation aluminum alloys become available, improved accelerated corrosion tests must be designed to accurately predict the corrosion response under atmospheric conditions in a short time. Many different approaches can be used to accelerate corrosion (high testing temperature, high chloride content in the testing solution, added oxidizing agents, very acidic or very alkaline testing solution etc.), and each of these parameters alters the corrosion response by changing electrochemical kinetics. Improved accelerated test protocol requires a better understanding of the relationship between testing parameters, electrochemical kinetics, and corrosion morphology. The purpose of the current study is to develop a framework for new accelerated corrosion test design by connecting attack morphology to electrochemical kinetics. Both the exfoliation susceptible under-aged (T36) temper and the exfoliation resistant near peak-aged (T86) temper of Al-Cu-Li alloy 2060 were considered in this work. ASTM G343, ANCIT2, and ASTM G85-A25 were used to study the impact of various testing parameters on the corrosion response of AA2060. Electrochemical measurements were used to determine corrosion potential (Ecorr) and polarization resistance (Rp) during standard and modified versions of each test in-situ. After each exposure, samples were also cross-sectioned and examined with optical microscopy. Results indicate that for immersion tests (ASTM G34 and ANCIT), testing temperature has a significant impact on anodic kinetics, while solution pH affects cathodic kinetics. The higher testing temperature of ANCIT led to faster anodic kinetics and faster formation of exfoliation in the T36 temper compared to ASTM G34. For salt spray testing (ASTM G85-A2), it was found that the lower bound of relative humidity (RH) during RH cycling had an impact on Rp as well as extent of attack. When the test was run with a lower bound of 60% RH, Rp remained relatively constant throughout the salt spray, dry air purge, and dwell portions of the cycle. However when the test was run with a lower bound of 20% RH, Rp increased (corresponds to a decrease in corrosion rate) during the dry air purge and dwell periods. This time at very low RH resulted in much slower development of exfoliation on the T36 temper compared to the test with a lower RH bound of 60%. Acknowledgements This work is supported by the Office of the Undersecretary of Defense Corrosion University Pilot Program under the direction of Dr. D. Dunmire, Rolls-Royce, and the Virginia Space Grant Consortium. References R.J. Rioja, J. Liu, Metal. Mater. Trans. A 43 (2012): p. 3325-3337S. Lee, B.W. Lifka, “Modification of the EXCO Test Method for Exfoliation Corrosion Susceptibility in 7XXX, 2XXX, and Aluminum-Lithium Alloys,” in New Methods for Corrosion Testing of Aluminum Alloys, eds. V.S. Agarwala, G.M. Ugiansky, STP 1134 (West Conshohocken, PA: ASTM International, 1992), p. 1-19.ASTM G34-1, “Standard Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys” (West Conshohocken, PA: ASTM International, 2001), p. 1-7.J.P. Moran, F.S. Bovard, J.D. Chrzan, P. Vandenburgh, “Corrosion Performance of New Generation Aluminum-Lithium Alloys for Aerospace Applications,” 13th Int. Conf. on Aluminum Alloys, held June 3-7, 2012 (Hoboken, NJ: John Wiley & Sons, Inc., 2012).ASTM G85-A2, “Standard Practice for Modified Salt Spray (Fog) Testing” (West Conshohocken, PA: ASTM International, 2002), p. 1-14.

The Effect of Dispersion Phases of SiC and Al2O3 on the Properties of Galvanic Nickel Coatings

In this study, Ni, Ni-SiC and Ni-Al2O3 coatings were electroplated on the 2xxx series aluminium alloy. The following parameters of the electroplating process were applied: current density - 4A/dm2, time - 60 minutes, and temperature - 60°C. Hard particles of submicrometric size were used. The results of the research showing the effect of the addition of hard particles (introduced into the nickel bath as a dispersed phase) on the properties of coatings, including the effect of the type (SiC or Al2O3) and content (0, 25, 50 g / l) of these particles, were discussed. Based on extensive investigations, it was found that the type of ceramic particles significantly affects the structure of produced coatings. The dispersed particles incorporated into the nickel coatings improve their abrasion resistance. Improving of the corrosion properties were observed only in the case of coatings containing silicon carbide particles.

Influence of Li Additions on the Microstructure and Corrosion Response of 2XXX Series Aluminium Alloys

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.

SVET, SKP and EIS study of the corrosion behaviour of high strength Al and Al–Li alloys used in aircraft fabrication

The 2XXX and 7XXX series aluminium alloys are commonly used in aircraft applications where high strength-to-weight ratios are required. The present study aims to compare the corrosion resistance of two novel alloys developed for aircraft industry (AA2198-T851 and 7081-T73511) to that presented by the alternative base alloys (AA2524-T3 and 7050-T7451, respectively). Results indicate that AA2198-T851 may show a superior corrosion performance compared to AA2524-T3, being a potential candidate for its replacement, due to best mechanical properties. In what concerns the 7081-T73511, its resistance to pitting corrosion may be lower than for the base line alloy 7050-T7451.

Effect Of Cathodic Current Density on Microstructure and Properties of Nickel Composite Coatings

Abstract Studies were carried out to characterise the nickel composite coatings deposited on a 2xxx series aluminium alloy. The composite coatings were prepared in a Watts bath with the addition of fine-dispersed particles of Al2O3 powder introduced in an amount of 100 g/l using current densities of 2, 4, 6 and 8 A/dm2. The morphology, structure, thickness and microhardness of the obtained composite coatings were described. The volume fraction of Al2O3 particles in composite coating was determined. The corrosion resistance of thus produced coatings was examined. Based on the results of the conducted studies it was stated that all the produced coatings were characterised by good adhesion to the substrate, but coatings produced at high current densities were characterised by a lower content of the Al2O3 reinforcing phase present in the composite.