Selected Aluminum Alloys Research Articles

Evolution of surface oxide film of typical aluminum alloy during medium-temperature brazing process

The evolution of the surface oxide film along the depth direction of typical aluminum alloy under medium-temperature brazing was investigated by means of X-ray photoelectron spectroscopy (XPS). For the alloy with Mg content below 2.0wt%, whether under cold rolling condition or during medium-temperature brazing process, the enrichment of Mg element on the surface was not detected and the oxide film was pure Al2O3. However, the oxide film grew obviously during medium-temperature brazing process, and the thickness was about 80 nm. For the alloy with Mg content above 2.0wt%, under cold rolling condition, the original surface oxide film was pure Al2O3. However, the Mg element was significantly enriched on the outermost surface during medium-temperature brazing process, and MgO-based oxide film mixed with small amount of MgAl2O4 was formed with a thickness of about 130 nm. The alloying elements of Mn and Si were not enriched on the surface neither under cold rolling condition nor during mediumtemperature brazing process for all the selected aluminum alloy, and the surface oxide film was similar to that of pure aluminum, which was almost entire Al2O3.

Dynamic Fracture Behaviors of Selected Aluminum Alloys Under Three-point Bending

Abstract The dynamic fracture behaviors of the extruded 2024-T4 and 7075-T6 aluminum alloys are investigated by using an instrumented drop tower machine. The specimens are made from a 25 mm diameter extruded circular rod. The dynamic three-point bending tests of each alloy are carried out at different impact velocities. The initiation fracture toughness and average propagation fracture toughness of 2024-T4 and 7075-T6 are determined at different loading rates. The results show that both the initiation toughness and the propagation toughness increase with the loading rate. Further, the difference between the fracture toughness behaviors of 2024-T4 and 7075-T6 is found to be dependent on the variation of fracture mechanism. The comprehensive fractographic investigations of the fracture surfaces clearly demonstrate that the fracture mode of 2024-T4 is predominantly transgranular fracture with high density small-sized dimples, and the fracture mode of 7075-T6 is mainly intergranular fracture with many intermetallic particles in the bottom of voids located in the fracture surface.

The experimental research on the random variability in the local strength of the selected aluminum alloys

This paper presents the results of the experimental research on mechanical properties of selected aluminum alloys, representative of the heat treated alloys (6xxx series) and the strengthened one from cold working only alloys (5xxx series). Results of laboratory tests, which describe the local changes of the strength characteristics of Re, Rm and Young’s modulus E, indicate that variability in the local characteristics of the bars are oscillations around the average values along the axis of the bars. A mathematical model for describing this type of variation is random noise, or random fluctuations around a central value.

Dynamic Tensile Fracture Behaviours of Selected Aluminum Alloys under Various Loading Conditions

ABSTRACTExperiments investigating dynamic tensile fracture were performed on the extruded rods of 2024‐T4 and 7075‐T6 aluminum alloys under varying loading conditions. The initial yield stress and fracture strain of 7075‐T6 alloy obtained in spilt Hopkinson tension bar tests are higher than that of 2024‐T4 alloy. But the initiation fracture toughness and spall strength of 2024‐T4 alloy are higher than those of 7075‐T6 alloy in three‐point bending and plate impact experiments, which indicates that 2024‐T4 alloy has better crack initiation tolerance and stronger spall failure resistance. Based on metallurgical investigations by using optical and scanning electron microscopes, it is revealed that the microstructure has a profound effect on the dynamic tensile fracture mechanism of each aluminum alloy. The 2024‐T4 alloy is relatively brittle due to voids or cracks nucleated at many coherent CuMgAl2 precipitate phases in the grain interiors, and the fracture mode is predominantly transgranular. The 7075‐T6 alloy exhibits relatively ductile fracture because voids or cracks growth is partly intergranular along the grain boundaries and partly transgranular by void formation around coarse intermetallic particles. The obvious differences of damage distribution and void coalescence mechanisms for 2024‐T4 and 7075‐T6 alloys under plate impact are also discussed.

Design, Materials and Processing for the Summer Olympic Torches

Olympic torches are the fantastic combination of successful design, appropriate materials and optimum processing which are the basic concept concepts in the major of Materials science and engineering. London Olympic torch was designed to be a three-sided pyramidal in shape, reflecting the features of the Olympic host country and the implication of designers. The material of Olympic torch selected aluminum alloys with a lightweight, high-strength, low thermal conductivity and environmentally friendly recycle; if low weight and high strength are key criteria for the torch, perhaps we can look forward to the incorporation of grapheme in the 2016 Olympic Games torch. The processing of Olympic torch involved laser cutting for 8000 holes and physical vapor deposition for gold-colored titanium nitride film on the surface of the aluminum plates, which embodied the best manufacturing route and the host country's technological capabilities.

Revealing the three dimensional internal structure of aluminium alloys

ABSTRACTMaterials ultramicrotomy has been progressed at Manchester for many years, enabling generation of suitably thin specimens for transmission electron microscopy. In addition, the remaining block specimen from which thin, electron transparent specimens have been generated also provides the basis for specimen preparation for high resolution backscattered electron imaging in the scanning electron microscope. This knowledge allows generation of serial sections of appropriate specimens that are oxide‐ and contamination‐free for high resolution observation in the backscattered imaging mode. With recent instrumental developments, i.e. the GATAN 3View System, enabling ultramicrotomy to be performed in‐SEM, relatively rapid sectioning and imaging can now be performed with ready reconstruction of electron tomographs. Further, correlative microscopy can be undertaken by utilising the GATAN XuM system in the same scanning electron microscope, enabling non‐destructive X‐ray tomography in addition to destructive electron tomography. The in‐SEM, serial sectioning of selected aluminium alloys is considered here, as well as correlation of the X‐ray and electron tomography approaches on the penetration of localised corrosion into an AA2024 T351 aluminium aerospace alloy. Copyright © 2013 John Wiley & Sons, Ltd.

Material properties of friction stir spot welded joints of dissimilar aluminum alloys

Mechanical properties and material mixing patterns of friction stir spot welded (FSSW) joints of dissimilar aluminum alloys were investigated. Two aluminum alloys typically used in automotive applications, 5052-H32 and 6061-T6, were selected. During the experiment, the process parameters including the z-axis force and torque histories were measured as a function of the tool displacement. The mechanical properties were investigated by microhardness measurements of the joint, and the material mixing in the stir zone was investigated by EPMA. The experimental results illustrate different process parameter histories, material mixing in the stir zone and material properties including microhardness distributions for FSSW joints of dissimilar aluminum alloys, likely due to different mechanical behaviors of the selected aluminum alloys in the FSSW process temperature range.

Mould Filling Ability Characterisation of Cast Aluminium Alloys Using Design of Experiments

Mould filling ability characteristic has been influencing the liquid metal flow, heat transfer, and solidification there by affecting the quality of aerospace castings. Mould filling is a critical parameter in the production of sound and quality castings, especially in the case of complex-shaped castings where section thickness is varying considerably. The mould filling ability of aluminium alloys LM6 and LM25 has been studied in the present investigation. Experimentation has been carried out using orthogonal array experimental layout. The process parameters studied in the present investigation are alloy composition, sand fineness, mould coating, and pouring temperature. The mould filling ability of selected aluminium alloy has been studied using pin test piece with cylindrical cores. The results from experimentation are analyzed to find the influence of the process parameters on mould filling ability. Based on the above, LM6 alloy has been found to have better mould filling ability characteristics and the analysis of variance has also revealed the same optimum factor combination.

Dynamic compressive behavior of selected aluminum alloy at low temperature

This paper deals with the effect of low temperature on the compressive behavior at high strain rate of two aluminum alloys, 2024-T4 and 7075-T6 using a modified split Hopkinson pressure bar (SHPB) with a pulse shaper technique. A cooling device is specially designed to be coupled to the SHPB, which can reach temperatures as low as 123K. Using experimentally determined stress–strain curves, the effect of low temperature on the dynamic compressive behavior is determined and discussed, showing that flow stress increases with the decrease of temperature, and the strain hardening behavior is almost independent of temperature ranging from 123 to 300K. A simplified constitutive model based on the consideration of thermally activated dislocation motion is proposed. The prediction provided by the model gets satisfactory agreement with the experiments.

Research on Structural Strength of Catamaran Superstructure Constructed with Aluminum Alloy

The design of Superstructure constructed with aluminum alloy do not have to follow the traditional standard design method. It can be designed by applying strength theory and ANSYS program or MSC Patran / Nastran program, which can ensure the strength requirements with the selected aluminum alloy components and make the weight of the ship lightest. In this paper, the 42.4m catamaran sightseeing boat is used as an example. The structural strength of the superstructure constructed with aluminum alloy is calculated by MSC Patran / Nastran program. The distribution of the superstructure stress is obtained, which proved the size of the selected components of the superstructure can meet the requirements of the local strength and can be the reference of selecting the structure size. As the other conditions are unchanged, the the local thickness of the junction of the front wall and the side wall of the compass deck is changed. the relationship between plate thickness and stress is obtained. It is found that as The plate thickness is thicker, the stress there decreases; and as the thickness is smaller, it is obvious to reduce stress as the plate thickness Increase. when the thickness increases to a certain extent, the effect of the plate stress decreases is not obvious.

Surface analysis of Al‐Mg alloy series for ship after cavitation test

Aluminum alloys for ships have high mechanical strength and light, and their specific strength is higher than steel ships, enabling high speed and light weight. To lengthen the life of aluminum alloy ships, many studies are being conducted to improve durability through heat treatment and the addition of various elements, but they are still exposed to the harsh ocean environment. As the possibility of cavitation damage is getting higher because of the high speed of aluminum ships, it is critical to select aluminum alloys for ships that have excellent characteristics in ocean environment. For this purpose, cavitation experiments were conducted for the Al‐Mg alloy of the 5000 series as hull materials that directly contact seawater, and their behaviors were examined and compared. The cavitation experiments revealed that the 5083‐O and the 5083‐H116 alloys showed the largest and the smallest weight loss, respectively. Copyright © 2012 John Wiley & Sons, Ltd.

Surface Free Energy and 7075 Aluminium Bonded Joint Strength Following Degreasing Only and Without Any Prior Treatment

Adhesion is a surface phenomenon occurring in many processes, e.g., bonding, painting or varnishing. Knowing the adhesion properties is critical for evaluating the usability or behaviour of materials during these processes. Good adhesion properties favour the processes of bonding, resulting in high strength of adhesive joints. Adhesive bonded joints are used in many industries, and the subject of this study was 7075 aluminium alloy sheet bonded joints as typically used in the aviation or construction industry. Surface free energy (SFE) can be used to determine the adhesion properties of the materials. The SFE of the tested sheets was determined with the Owens–Wendt method, which consists in determining the dispersion and polar components of SFE. The purpose of this work was to correlate the bonded joint strength of selected aluminium alloy sheets to the surface free energy of the sheets that had been subjected to degreasing only and no other prior treatment was used. Single-lap bonded joints of 7075 aluminium alloy sheets were tested. Higher joint strength was measured for the thinner sheets, while the lowest strength was measured for the thickest sheets. This suggests that the thickness of the joined parts is an important factor in the strength of bonded joints. The comparison of adhesion properties to the strength of adhesive joints of tested materials shows that there is no direct relation between good adhesion properties (i.e., high SFE) and joint strength. As for degreasing, the highest joint strength was observed for aluminium alloy sheets with the lowest SFE; the sheets which were not degreased gave the highest SFE and highest joint strength.

Wetting of pure aluminum and selected alloys on polycrystalline alumina and sapphire

Using a modification of the dispensed drop method to measure true contact angles of readily oxidizing metals and alloys, the wettability of polycrystalline alumina and A-plane sapphire by pure aluminum and selected aluminum alloys was investigated. The experiments were performed under high vacuum in a horizontal tube furnace. The experimental setup produces a sessile drop free of its natural surface oxide layer minimizing flight time of the drop, and maintaining a drop impingement on the substrate. The experiments showed that there is no significant difference in the wettability of alumina and sapphire by aluminum as well as Al–11.5Si, Al–1Mg and Al–7Cu. On both substrates, aluminum shows a strong increase in contact angle well into the non-wetting regime just above the melting point. The wetting behavior of Al–7Cu on both substrates is slightly but significantly reduced in comparison to pure aluminum. The contact angles of Al–1Mg and Al–11.5Si remain rather constant between the respective liquidus temperatures of the alloys and 800 °C with θ (Al–1Mg) < θ (Al–11.5Si). Only Al–7Cu above 730 °C achieves the contact angle interval of 70–86° suggested to be most beneficial in terms of aluminum foam stabilization.

Overload Effects in Aluminum Alloys: Influence of Plasticity and Environment

Abstract This paper presents the behavior of selected aluminum alloys when subjected to a single overload, with an aim to highlight the effects of plasticity and environment. The delaying effect of a single overload is given in terms of number of delay cycles. The delay behavior is systematically compared with the constant amplitude crack growth resistance. It is shown that for most of the studied alloys, a strong parallel can be drawn between the constant amplitude crack growth behavior and the overload induced delay. Delay induced by an overload in vacuum is higher than that in air for the 7075 and the 2024 alloys, compatible with stronger constant amplitude crack growth resistance in vacuum. The influence of the elastic-plastic behavior is stronger in vacuum than in air. In the case of the Aluminum Lithium alloy, delay in air is higher than that in vacuum, which is opposite to the behavior under constant amplitude loading. The basic mechanisms governing crack growth in aluminum alloys and their influence on the delay induced by an overload are revealed. The experimental results are compared with a phenomenological model, taking into account the cyclic plastic behavior of materials.

Effect of chemical cleaning on the corrosion behaviour of painted aluminium alloys

Painted aluminium alloys are sometimes affected by filiform corrosion. Such a phenomenon which was intensively studied in the last few years is mainly a cosmetic type of attack. Usually it starts at coating defects or at cut edges following an anodic undermining mechanism. As described in the literature, water permeability and elasticity of the coating, oxygen diffusion paths, and presence of salts are the main controlling parameters. However, the metal coating interface is the critical point; then the substrate chemical composition, as well as the type of chemical cleaning or the type of applied chemical conversion coating proved to be fundamental aspects to improve resistance to filiform corrosion. The aim of this work is to study the filiform corrosion behaviour of aluminium alloys surface cleaned using chemically different products (alkaline, acid, combination of the two) and then treated using environmentally friendly pretreatment baths and chromates baths. The selected aluminium alloy was AA6060 type. After powder painting, aluminium samples were tested following the DIN 65472 standard. At the same time electrochemical tests were carried out following a particular procedure on samples exposed for different times to the environment promoting filiform corrosion. Under the experimental conditions used in our tests, electrochemical impedance spectroscopy was shown to be useful and allowed to obtain more quantitative data in a shorter testing time with respect to traditional testing. It was observed that resistance to filiform corrosion is greatly affected by the chemical composition of the aluminium substrate and that chemical cleaning modifies the surface chemical composition of the alloy so modifying its corrosion behaviour.

Acoustic quality factor of aluminium and selected aluminium alloys from 50 mK to 300 K

The amplitude-independent quality factors ( Qs) of polycrystalline aluminium of 99.999 wt% purity, and the commercial aluminium alloys 2024, 6061 and 7075 have been measured in the temperature range 50 mK–300 K. Data were obtained at about 1 kHz from a torsional mode of machined monolithic mechanical resonators. The as-machined alloys exhibited maximum Qs of 1.5 to 9.5 million. The annealed alloys exhibited maximum Qs from 4.3 to 7.4 million. After several weeks at room temperature, substantially higher Qs were observed in all of the annealed materials, as compared to values obtained within a few days subsequent to the thermal treatment. Nevertheless, the maximum Qs were appreciably lower than those which have been measured in aluminium–magnesium alloys. Three loss peaks were observed in the aluminium, and a single peak in two of the alloys, even after annealing. The temperature dependence of the shear moduli was also obtained. This study is part of the continuing effort in this laboratory to evaluate the acoustic loss of high- Q materials at low temperatures, of particular interest for the construction of sensitive detectors of gravitational radiation.

High strain rate properties of selected aluminium alloys

The strain rate sensitivity of two commercial aluminium alloys AA6082 and AA7108 in peak temper T6 and overaged T79 condition is analysed. These alloys are precipitation hardenable and as such, are expected to have a relatively low strain rate sensitivity. Their response to rapid loading has been tested over a wide range of strain rates, from 0.1 to 3000 s −1 at room temperature, 375 and 515°C for AA6082 and room temperature, 280 and 340°C for AA7108. Specimens were cut from planar extruded sections and tested in uniaxial compression with the deformation axis parallel to the extrusion direction. Intermediate strain rate testing was carried out using a computer controlled servo-hydraulic testing machine and high strain rate testing above 500 s −1 on a Split Hopkinson Pressure Bar (SHPB). Owing to inaccuracies of the conventional Kolsky solution of the SHPB, a numerical simulation was performed. The flow stress at a plastic strain of 5% was plotted as a function of strain rate and temperature. Up to 2000 s −1, there is very little change of the activation volume with increasing temperature for both alloys, indicating that barriers to thermal activation are large and approximately the same. However, at higher strain rates, the rate controlling mechanism appears to change and at lower temperatures, a trend towards negative strain rate sensitivity was observed. Metallographic examination of AA7108 revealed strain localisation, seen as parallel deformation bands. The strain localisation could be the cause of the negative strain rate sensitivity.

Microstructural Evolution and Age Hardening in Aluminium Alloys: Atom Probe Field-Ion Microscopy and Transmission Electron Microscopy Studies

This paper examines the microstructural evolution in selected aluminium alloys based on commercial age hardenable 2000, 6000, and 7000 series alloys. Atom probe field-ion microscopy and transmission electron microscopy have been used to examine the effects of microalloying and the origins of hardening. The combined application of these techniques is particularly important in the study of nanoscale precipitation processes. It is shown that the nature and kinetics of the precipitation process depend on the solute–solute interactions that produce solute clusters. The solute clusters precede the formation of GP zones or precipitation, and have a defining role on the nature and kinetics of the subsequent precipitation processes. Moreover, interactions between solute clustering and dislocations can have a significant hardening effect, the origins of which seem to be distinctly different from the conventional notion of precipitation hardening.

Single Asperity Plowing of Metallic and Polymeric Surfaces in an Atomic Force Microscope: An Overview of Recent Developments

Previous experimental and theoretical work in plowing phenomena have primarily focused on the effects of many asperities and hence wear phenomena due to a single asperity have not been adequately investigated. In response to this apparaent lack of information around single asperity plowing effects, two of the authors [1] developed an experimental technique wherein the plowing motion of a pyramidal diamond indentor affixed to a stainless steel cantilever is controlled by the piezoelectric transducers of an atomic force microscope and appropriate software macros. Using the mathematical model of Azarkhin and Richmond [2], they were able to estimate the friction stress developed between the substrate and the indentor as well as the material flow stress for selected aluminum alloys. In particular, the measured ridge heights gave an estimate of friction factor for a particular plow track, and the measured normal and plowing forces lead to an estimate of flow strength. The plow track morphologies were found to depend upon material hardness and specific alloying agents in the material, with the softer materials exhibiting oscillatory ridges due to the development of a built-up edge of the indentor, and the harder materials exhibiting detached ridges due to their reduced fracture toughness [3]. The purpose of the present article is to present an overview of recent developments in single asperity plowing of selected metal surfaces in an atomic force microscope. We shall discuss results from dry plowing experiments as well as plowing experiments in the presence of selected boundary additives. Corresponding theoretical modeling developments will also be discussed as well as the roll of indentation size effect in single asperity plowing. We shall also present results of plowing experiments on HMWPE which is used in orthopaedic prostheses. Finally, some discussion about ongoing work will be presented.

Sliding behavior of selected aluminum alloys

This project was undertaken to achieve thee principal objectives: to improve understanding of the behavior of selected aluminum-based bearing materials used in sliding applications, to develop improved guidelines for the design of such bearings, and to respond to increasing environmental concerns about the use of lead in bearing materials. Unlubricated sliding tests have been conducted using disks of AlSn and AlPb binary alloys as well as multicomponent alloys produced with the aid of an MHD (magnetohydrodynamic) technique at the Institute for Solid State Physics, Chernogolovka, Russia. For comparison, commercial alloys produced by Glacier Vandervell Inc. have also been tested. The counterface in each case was a hardened 52100 ball. Sliding speeds were kept low (15–30 mm s −1) to limit frictional temperature increases. Normal loads ranged from 0.8 to 1.2 kgf. Earlier results on PbSn and babbitt alloys demonstrated that the environment strongly affects the friction coefficient, the smoothness of sliding and the hardness and hardness gradient at the surface. Therefore we have performed tests in vacuum (as a reference condition) and in air. A range of complementary techniques (optical and electron microscopy, X-ray fluorescence analysis using energy dispersive spectroscopy (EDS), microhardness) was used for structural and chemical characterization of debris and of surface and near-surface material. In all cases, sliding in vacuum was smooth and the wear rates were low. In fact, the rate of production of debris during the vacuum tests was negligible. However, the friction coefficient, the fluctuations in friction and the wear rate were all much higher for tests in air. The reasons for this behavior are associated with dramatic differences in structure and composition which develop near the surface of the bearing material. The effects of environment are larger than those associated with changes in composition for the alloys studied.