Showing papers on "Aluminium alloy published in 1989"

The microstructure and mechanical properties of unidirectionally solidified Al−Si alloys

Abstract: Hypereutectic Al−Si alloys with minor additions of Sr were directionally solidified with a temperature gradient of 125°C cm−1 in the liquid. Silicon in the range 14–17 wt%, Sr in the range 0.0–0.5 wt% and specimen traction velocities between 1 and 1500 μm sec−1 were used. The relationship between hardness and traction velocity and spacing in eutectic silicon morphologies is defined and shown to be of the same form as that for yield stress. The possibility of using hardness measurements to be of the same form as that for yield stress. The possibility of using hardness measurements to indicate mechanical properties is discussed. The complex regular silicon structure makes a significant contribution to the hardness of hypereutectic alloys. This makes the relationship between hardness and traction velocity more complex adding difficulties to the use of hardness to measure mechanical properties.

Wetting improvement of carbon or silicon carbide by aluminium alloys based on a K2ZrF6 surface treatment: application to composite material casting

Abstract: A surface treatment with aqueous solutions of K2ZrF6 has been carried out to improve, in dramatic manner, the wetting of carbon (or SiC)-base ceramics by liquid light alloys at low temperatures (ie within the 700 to 900°C range) The mechanism which is thought to be responsible for the wetting improvement involves two steps: (i) K2ZrF6 reacts with aluminium with the formation of K3AlF6, other complex fluoride species and intermetallics, (ii) K3AlF6 dissolves the alumina thin layer, coating the liquid light alloy and enables the wetting of the ceramics The mechanism has been worked out from sessile drop experiments, solid state chemistry experiments and composite casting The K2ZrF6 surface treatment appears to be particularly suitable for processing composite materials made of carbon (or SiC) fibrous preforms and aluminium-base matrices according to techniques directly derived from the light alloy foundry

Control of microstructure and earing behaviour in aluminium alloy AA 3004 hot bands

Abstract: Control of earing behaviour at the hot band stage is a critical requirement for successful manufacture of aluminium alloy sheet for beverage cans The present study has combined production scale experiments with laboratory examinations to investigate the effect of various material and process parameters on microstructure, texture, and earing of the resulting products It is shown that optimisation of the product is strongly dependent on (i) iron content of the alloy, (ii) ingot homogenisation temperature, (iii) finish hot rolling temperature, and (iv) heating rate during hot band annealing Earing level after annealing is shown to depend on the balance between cube (+ Goss) texture intensity and the volume of material having almost randomly spread orientations Pronounced 0/90° earing tendency is usually associated with coarse and elongated grain structures A model is shown which represents the microstructure–texture evolution as a competition between cube/Goss grains, which nucleate systematica

Corrosion inhibition in magnesium-aluminium-based alloys induced by rapid solidification processing

Abstract: The effect of rapid solidification on the corrosion behaviour in aerated 0.001 M NaCl solution of Mg-Al alloys containing 9.6 to 23.4wt% AI has been investigated in comparison with chill-cast material. Polarization studies show that rapid solidification decreases corrosion current by up to two orders of magnitude corresponding to a corrosion rate of 6 to 11 mil y−1. Increasing the aluminium content in solid solution by rapid solidification gave rise to a steep increase in pitting potential between 10 and 23 wt% Al and resulted in development of an anodic plateau at ∼ 30μAcm−2 attributable to magnesium depletion for the alloy surface and formation of a protective film. Chemical analysis of the electrolyte as a function of dissolution time for the rapidly solidified material indicated that initially only magnesium dissolved and that this dissolution of magnesium ceased within 2 to 5 min. The results indicate the formation of an aluminium-enriched interdiffusion zone at the surface underlying a more stable surface oxide than for ingot-processed Mg-Al-based alloys.

Mechanical properties of Al–Li alloys Part 1 Fracture toughness and microstructure

Abstract: Mechanisms influencing the ambient temperature mechanical properties of commercial Al–Li alloys 2090, 8090, 8091, and 2091 are examined as a function of plate orientation, with specific emphasis on the role of microstructure. In Part 1, results on the uniaxial tensile and plane strain fracture toughness properties are presented and the behaviour is discussed in terms of the role of the matrix and grain boundary precipitates, associated precipitate free zones (PFZs), and the occurrence of short-transverse delamination. It is seen that in general peak aged microstructures show an excellent combination of strength and toughness (L–T, T–L), equal to or exceeding that shown by traditional 2000 and 7000 series high strength aluminium alloys. The superior toughness of peak aged compared with naturally aged microstructures seems to be associated with widespread matrix precipitation of platelike precipitates (T1 in Al–Li–Cu alloys and S in Al–Li–Cu–Mg alloys), β′-dispersoids and second phase particles whi...

Pitting of Sputtered Aluminum Alloy Thin Films

Abstract: Etude de la corrosion par piqure des alliages Al−Ti et Al−Cr dans une solution saline de NaCl

AA6061 composite reinforced with potassium titanate whisker

Abstract: Recent works reported the reduction in strength of the AA6061 matrix composite fabricated by powder metallurgy by T6 treatment. Thus, reactions between whisker and aluminium matrix seems to restrict the application of the aluminium matrix composites with potassium titanate whisker. The aim of the present work was to examine whether or not any reaction occurs at the whisker/matrix interface caused by high-pressure infiltration or by T6 heat treatment. This was carried out using carried out using transmission electron microscopy (TEM)

Calorimetric evaluation of the effects of SiC concentration on precipitation processes in SiC particulate-reinforced 7091 aluminium

Abstract: A comprehensive differential scanning calorimetric (DSC) investigation has been conducted on the precipitation and dissolution behaviour of SiC particulate-reinforced 7091 aluminium. DSC is shown to be a particularly attractive experimental technique for developing new thermal and thermomechanical processes for aluminium-based metal matrix composites. These new processes are necessitated due to the deleterious effects that the SiC reinforcement causes on the aluminium matrix precipitation behaviour and the resultant ductility and fracture toughness properties. In this study the effects of SiC concentration and ageing temperatures, times, and sequences were evaluated. In addition to the unreinforced 7091 alloy, composites containing 10, 20 and 30 vol% particulate SiC were characterized. Identifications of specific phases involved in reactions detected with DSC were achieved by making direct correlations to previously published transmission electron microscopy studies. It was found that the presence of SiC in the aluminium significantly affects the solid state transformation kinetics of the 7091 aluminium matrix. Specifically, increasing the SiC concentration was found to decrease the temperatures at which GPI and GPII zones precipitate at their maximum rates and to increase the temperature at which GPI zones revert at maximum rate. The transition phase,η, and equilibrium phase,η, formation kinetics were observed to be insensitive to SiC concentration. Also, increasing the SiC concentration was seen to decrease the temperature at which the equilibrium phase dissolution occurred at its maximum rate. Transformation mechanics have been proposed which are consistent with these observations.

Characterisation of different grades of commercially pure aluminium as prospective galvanic anodes in saline and alkaline battery electrolyte

Abstract: The effect of calcium chloride and sodium chloride on the electrochemical properties of various grades of aluminium namely 2s, 3s, 26s and 57s in alkaline citrate solution has been examined by studying the self corrosion, open circuit potential, anodic polarization and anode efficiency. It has been found that among the different grades of aluminium the 57s grade is found to be the most promising galvanic anode material in the 4N NaOH containing 20% wt/vol. of sodium citrate and 2.5% wt/vol. of CaCl2·2H2O. Further, it has been found that the above alkaline citrate electrolyte required for aluminium air batteries can be prepared from tap water, saline water and even sea water. The presence of chloride ions in the electrolyte, even up to a concentration of 2.5% wt/vol. as CaCl2·2H2O, is not found to alter the electrochemical properties of the different grades of aluminium as anode materials, though 57s is found to be the best.

Finite-element modeling of heat flow in deep-penetration laser welds in aluminum alloys

Abstract: A two-dimensional finite-element nonlinear transient heat conduction model was developed and used to simulate deep-penetration keyhole laser welds in aluminum alloys. The weld thermal profiles were calculated in an arbitrary reference plane as the laser beam approached and passed the plane. From the calculated thermal profiles, three-dimensional quasi-steady-state shapes of the weld pools were determined. The predicted weld bead shape and dimensions were in good agreement with the experimental results. The experimental laser welds in aluminum alloys contained large amounts of porosity. The model predicted large mushy zones for aluminum laser welds during solidification, which in turn increase the probability of porosity formation by increased bubble entrapment.

Micromechanisms governing fatigue behaviour of lithium containing aluminium alloys

Abstract: The emergence of lithium containing aluminium alloys as potential light metals for aircraft structures has engendered an unprecedented widespread interest aimed at improving their mechanical properties and studying their cyclic fatigue characteristics. The phenomenon of fatigue is environment sensitive and the alternating moisture conditions experienced by this candidate airframe material can be a handicap when designing for enhanced fatigue resistance. In this paper, the fatigue properties, deformation characteristics, and cyclic stress response of the commercial Al–Li–Cu–Mn and the experimental Al–Li–Mn and Al–Li–Cu–Mg–Zr alloys cycled to failure are compared over a range of plastic strain amplitudes in various environments, spanning the inert to the very aggressive. Abnormal plastic strain–fatigue life behaviour was observed for all the alloy systems and is attributed to differences in the distribution of deformation as a function of plastic strain amplitude and to change in the relative amount...

Application of fracture mechanics techniques to the environmentally assisted cracking of aluminium 2024

Abstract: — Stress corrosion cracking of 2024 T351 aluminium alloy in an aqueous 3.5% sodium chloride solution was investigated using three fracture mechanics based testing techniques: constant load, constant displacement, and constant displacement rate. In spite of their different loading characteristics, all three test methods yielded approximately the same Klscc value. Crack growth rates in the plateau region, as measured from bolt loaded DCB specimens and from CT specimens tested at low constant displacement rates are similar. The tests at constant displacement rate not only provide results in a much shorter time, but produce additional information in terms of crack growth resistance curves as a function of the displacement rate. Linear elastic as well as elastic-plastic fracture mechanics test evaluation procedures are applied and discussed in view of an assessment of criteria for the accelerated evaluation of SCC parameters such as Klscc, Jlscc, and δlscc.

Hardening mechanisms in Al-Sc alloys

Abstract: The hardening mechanism in Al-Sc alloys with scandium content of 0.11 and 0.19 at% is studied. Applying theoretical results due to the yield stress and work hardening of two phase alloys as a function of volume fraction and precipitate particle size, it is shown that after ageing at above 300° C the Orowan mechanism operates in these alloys. Using the experimental results, the volume fraction and average radius of the precipitate particles are determined.

Solid-metal-induced embrittlement of aluminium alloys and other materials

Abstract: The effects of temperature and other variables on the kinetics of solid-metal-induced embrittlement (SMIE) of an aluminium alloy 7075-T651 by indium were studied, and the data obtained compared with published data for other materials and embrittling elements. Analysis of the data indicated that rates of cracking were controlled by transport of embrittling elements to crack tips by a surface diffusion process. The rates of this process were approximately the same for different embrittling elements and different substrates at the same homologous temperatures T/T m , where T is the testing temperature and T m is the melting temperature of the embrittling element in kelvins. Metallographic and fractographic observations for the SMIE of aluminium alloy 7075, high strength steels and titanium alloys are also described, and a mechanism of embrittlement involving an adsorption-induced localized-slip process is outlined. Some observations which suggest that cracking in AlLi-based alloys is associated with SMIE due to embrittling impurities within the alloy are also briefly discussed.

Microstructure, tensile properties and fracture behaviour of an Al-Cu-Li-Mg-Zr alloy 8090

Abstract: The addition of lithium to aluminium alloys has the potential for providing a class of high strength alloys with exceptional properties suitable for aerospace applications. One such candidate is 8090, a precipitation hardenable Al-Li-Cu-Mg alloy. Detailed optical microscopical observations were used to analyse the intrinsic microstructural features of the alloy. It is shown that microstructural characteristics have a pronounced influence on tensile properties and fracture behaviour of the alloy in the peak-aged, maximum strength condition. Tensile test results indicate that the alloy has property combinations comparable with other high strength commercial aluminium alloys. The elongation and reduction in area are higher in the transverse direction of the extruded plate. A change in fracture mode was observed with direction of testing. We rationalize such behaviour based on the grain structure of the material, and the nature, distribution and morphology of the second-phase particles. An attempt is made to discuss the kinetics of the fracture process in terms of several competing mechanistic effects involving intrinsic microstructural features, deformation characteristics of the matrix, brittleness of the grain boundary precipitates and grain boundary failure. The role of stress on particle fracture is highlighted.

Mechanical properties of Al–Li alloys Part 2 Fatigue crack propagation

Abstract: Mechanisms influencing the ambient temperature mechanical properties of commercial Al–Li alloys 2090, 2091, 8090, and 8091 are examined, with specific emphasis on the role of microstructure. In Part 2, results on fatigue crack propagation behaviour are presented for both ‘long’ (≥ 5 mm) and ‘microstructurally small’ (~1–1000 μm) cracks and compared with behaviour in traditional high strength aluminium alloys. In general, it is found that the growth rates of long fatigue cracks in Al–Li alloys are up to two to three orders of magnitude lower than in traditional 7000 and 2000 series alloys, when compared at an equivalent stress intensity range ∆K. By contrast, corresponding growth rates of microstructurally small fatigue cracks were up to two to three orders of magnitude higher than the long crack results. Such observations are attributed to the prominent role of crack tip shielding in Al–Li alloys resulting from the tortuous and deflected nature of the crack paths which results in a reduced crack t...

Investigation of the crystallography and morphology of the s' precipitate in an al(cumg) alloy by hrem

Abstract: The crystal lattice of the S′ phase in a 2024 aluminium alloy with 4·43 wt% Cu and 2·00 wt% Mg, and the precipitate–matrix orientation relationship are directly illustrated by the [100] lattice image of both the S′ and matrix phases. Two types of the precipitation morphology of the S′ phase, which correspond to homogeneous and preferential nucleation respectively, are also shown.

Modification of cast structures in Al–Mg alloys by thermal treatments

Abstract: A study has been carried out on the modification of ingot microstructure of commercial Al–Mg alloys by homogenisation treatments. A marked change in the hardness of the alloy ingots was produced af...

Effect of high rate deformation induced precipitation hardening on the failure of aluminium rivets

Abstract: Aluminium alloy (7050-T73) rivets were fabricated by an electromagnetic riveting process. Each rivet was formed in less than 500μsec. Microcracks and severely deformed regions were observed in the rivet head. Microprobe analysis, optical and scanning electron microscopic examination on the rivets did not yield conclusive evidence that the microcracks were caused by impurities such as iron and silicon. The data obtained in this study support the view that heat generated by material flow at high speed in the rivet head induced precipitation hardening. The precipitation hardening significantly increased the material hardness in the severely deformed shear zone. It Is believed that the increment of hardness in the shear zone of the rivets fabricated from the slugs which were previously age hardened resulted in a further decrease in ductility. Hence the initiation of voids which subsequently coalesced to form microcracks in the shear zone.

Growth kinetics of interface intermetallic compounds in stainless steel fibre reinforced aluminium matrix composites

Abstract: Growth kinetics of binary intermetallic compounds in the fibre/matrix interface has been studied in stainless steel fibre reinforced aluminium matrix composites fabricated by the P/M hot pressing, squeeze casting, and infiltration techniques. As expected in most binary diffusion couples, more than one intermetallic compound of the type FexAly forms at the interface. However, not all the iron-aluminide intermetallic compounds possible as dictated by the binary phase diagram are present. This is primarily the result of the non-equilibrium conditions at the interphase boundaries as the activation-controlled and diffusion-controlled interfacial reactions progress between the fibre and the matrix. Two equations have been established for the growth kinetics of the interface; one relates to hot pressing, the other to squeeze casting and infiltration. Parabolic rate constants have been determined. A rate constant of about 0.7 × 10−16 m2 sec−1 for hot-pressed composites produces an optimum thickness of the interface of about 3 μm and results in the maximum strength of the composites. In addition to the FeAl and Fe2Al5 that form at the interface, the presence of NiAl3 intermetallic compound is also predicted. Further investigation is suggested for the determination of the rate constants in squeeze-cast and infiltrated composites.

On the question of stability and disorder in icosahedral aluminum - transition metal alloys

Abstract: Through an X-ray diffraction and thermal analysis investigation of melt spun Al – transition metal (Al–TM) alloys, we report the formation of a highly stable and well-ordered pure icosahedral (i) phase in Al80TMl20−xTM2x(TM1 = V, Cr; TM2 = Fe, Co). The superior i-phase formation over that in the binary Al–TM alloys is interpreted in terms of the distribution of TM sites known to exist in this phase. A comparison of the i-phase formation ranges indicates the presence of two distinct classes of TM sites and a strong interaction between adjacent TM sites.

Aluminium alloy product having improved combinations of strength, toughness and corrosion resistance

Abstract: An alloy product having improved combinations of strength, density, toughness and corrosion resistance, consists essentially of about 7 to 12% zinc, about 1.5 to 2.7% magnesium, about 1.75 to 3% copper, one or more elements selected from 0.05 to 0.2% zirconium, 0.05 to 0.4% manganese, 0.03 to 0.2% vanadium and 0.03 to 0.5% hafnium, the total of said elements not exceeding about 1%, the balance aluminum and incidental elements and impurities. A preferred product consists essentially of about 7.6 to 8.6% zinc, about 1.6 to 2.2% magnesium, about 2 to 2.8% copper and at least one element selected from zirconium, vanadium and hafnium present in an amount not exceeding about 0.2%, the balance aluminum and incidental elements and impurities. The alloy product is suitable for aerospace applications.

Structural modification of Al-Si eutectic alloy by Sr and its effect on tensile and fracture characteristics

Abstract: Modification of the commercial A-S13 alloy and high purity Al-Si eutectic alloy has been successfully achieved using Al-5 Sr master alloy. The refined structure showed more fine and uniformly distributed eutectic silicon in the high purity alloy. The incidence of Al-dendrites due to modification was related to the movement of the eutectic point to the higher-silicon side. The chill-cast alloys showed better refined structure and higher mechanical properties in comparison with the sand-cast alloys. The modified chill-cast alloy exhibited the best mechanical properties. The ultimate. tensile strength of which reached 280 M Pa and the elongation was 9.2%. The fracture patterns changed from well faceted brittle appearance to smooth silky and dimple-like for the normal and modified alloys respectively. This reflects the change from brittle to ductile behaviour after modification. A model for the fracture mechanism was proposed to explain the observed higher ductility for the modified alloy.

Quasicrystals as part of the precipitation sequence in an industrially cast aluminium alloy

Abstract: Etude experimentale par microscopie electronique en transmission apres traitement de vieillissement.Analyse des relations d'orientation entre les precipites et la matrice,et de la transformation possible quasicristal-phase intermetallique.