Showing papers on "Aluminium published in 1993"

Damage in composite materials

Abstract: Part 1 Analysis: constitutive behaviour of multiphase metal matrix composites with interfacial damage by the generalized cells model, J. Aboudi an energy-based failure criterion for anisotrophic solids subject to damage, M.W. Biegler and M.M. Mehrabadi damage in solids due to periodically distributed cracks of arbitrary geometry, S. Nemat-Nasser et al the behaviour of of cracked cross-ply composite laminates under general in-plane loading, C.-L. Tsai and I.M. Daniel micromechanical characterization of damage-plasticity in metal matrix composites, G.Z. Voyiadjis and P.I. Katan on the micromechanics of defects in fibre-matrix composites, H.M. Zbib and I. Demir. Part 2 Analysis/applications: heterogeneity and its implications - micromechanical, statistical, fractal approach and their similarity, G. Frantziskonis fatigue crack growth characteristics of Ti-beta21S monolithic laminate, H. Ghonem et al progressive brittle damage modelling of fibrous composities by micromechanics based failure surfaces, C.-M. Huang and D.C. Lagoudas damage modelling at the macro- and meso-scales for 3D composites, P. Ladeveze et al. Part 3 Experiments: fracture toughness of discontinuous metal matrix composites, R.J. Arsenault analysis of residual stresses induced by cool down in viscoplastic metal matrix composites, G.S. Jeong et al eddy current characterization of silicon carbide reinforced aluminium metal-matrix composites, P.K. Liaw et al.

The role of organic acids in the soil solution chemistry of a podzolized soil

Abstract: SUMMARY The soil solution chemistry of a podzolized soil in the north of Sweden was monitored for four years using percolation lysimeters. Weak organic acids were a major constituent of the soil solution and are important because of their ability to form complexes with aluminium. Dissolved organics leached from the mor layer enhance the weathering rate in the eluvial horizon by forming complexes with aluminium, especially during the autumn when the leaching of dissolved organics was greatest. The weak organic acids were titrated and their pKa values were evaluated. Aluminium was speciated with an ion-exchange method and by applying equilibrium calculations. Formation constants for the organic aluminium complexes were calculated to be log KAlong=5.42±0.32 m−1 (n=13) in spring and summer and log KAlorg=4.87±0.14 m−1 (n=6) in autumn. Equilibria of Al3+ with solid phases were also examined using solubility constants. Percolation lysimeters below undisturbed and cut-off mor layers were compared.

Diamond/Al metal matrix composites formed by the pressureless metal infiltration process

Abstract: Diamond particles are unique fillers for metal matrix composites because of their extremely high modulus, high thermal conductivity, and low coefficient of thermal expansion. Diamond reinforced aluminum metal matrix composites were prepared using a pressureless metal infiltration process. The diamond particulates are coated with SiC prior to infiltration to prevent the formation of Al4C3, which is a product of the reaction between aluminum and diamond. The measured thermal conductivity of these initial diamond/Al metal matrix composites is as high as 259 W/m-K. The effects of coating thickness on the physical properties of the diamond/Al metal matrix composite, including Young's modulus, 4-point bend strength, coefficient of thermal expansion, and thermal conductivity, are presented.

Effect of aluminium addition on the combustion reaction of titanium and carbon to form TiC

Abstract: Aluminium was incorporated into the reactant mixture with a molar ratio of Ti/C of 1.0 to study the effect of its addition on the combustion reaction between titanium and carbon to form TiC. Thermal analysis of the reactant mixture and component analysis of the reaction product suggest that the combustion reaction of the Ti-C-Al system proceeds in such a way that aluminium initially reacts with titanium to form titanium aluminide compounds of TiAl3, Ti2Al, and TiAl with heat evolution, and then the reaction between titanium and carbon and the decomposition of titanium aluminide to titanium and aluminium is subsequently followed. As the amount of aluminium incorporated was increased over the range of 0 to 40 wt%, the grain size of TiC decreased from approximately 15 μm to 0.4 μm. It was also observed that most of the aluminium in the TiC-Al composite was distributed on the surface of the spherical TiC grain.

Properties of reactively cast aluminium–TiB2 alloys

Abstract: A salt base reactive casting process has been employed to produce A356 aluminium casting alloys containing fine dispersions of TiB2. These have been compared with commercially available Duralcan A356 material with SiC particles which have also been incorporated by a casting technique. Structural, mechanical, and wear properties have been measured. These show that TiB2 is extremely effective in enhancing modulus in addition to significantly reducing the coefficient of friction when used against an alloy steel plate. The wear rate of the alloy is found to be independent of particle type but is governed mainly by volume fraction, as is the load transition from mild to severe wear. However, the wear mechanisms for TiB2 and SiC composites are different when the steel disc is taken into account and the wear debris examined. The plate is effectively machined by SiC, resulting in extensive damage of the mating plate. Alloy A356 with TiB2 additions is made by reactive casting a simple alloy to process and ...

Repair efficiency in fatigue‐cracked aluminium components reinforced with boron/epoxy patches

Abstract: This paper describes studies on fatigue crack propagation in cracked aluminium alloy (2024 T3) panels repaired with boron/epoxy patches, adhesively bonded with either an epoxy-nitrile film adhesive or an acrylic adhesive. Studies were undertaken to assess the effect on patching efficiency of (a) disbonding of the patch system and (b) test temperature. A simple model is proposed for estimating the reduction of patching efficiency due to cyclic disbonding of the reinforcement. In the elevated-temperature tests it was found, unexpectedly, that patching efficiency in panels patched using the film adhesive was unaffected by temperatures up to 100°C.

Mechanical properties of aluminium alloy 6061–Al2O3 composites

Abstract: One of the most beneficial property improvements that can be realised using metal matrix composite technology is the ability to increase the relatively low stiffness and hardness of aluminium alloys by the addition of high modulus particles such as Al2O3 The stiffness and hardness of the resulting composites increase with increasing volume fraction of particles Unfortunately, these increases are accompanied by corresponding reductions in the ductility Because of this compromise in properties with increasing volume fraction, a balanced combination of tensile strength, ductility, creep resistance, toughness, and fatigue resistance must be achieved for successful industrial application In this regard, mechanical testing of a cast and extruded 6061 aluminium alloy containing 0, 10, or 20 vol-%Al2O3 particles has been carried out with emphasis on measuring the properties which would be the most important for an application such as steam turbine blading In addition to an increased room temperature

Effects of electromagnetic vibrations on the microstructure of continuously cast aluminium alloys

Abstract: The influence of electromagnetic vibrations imposed during solidification on grain refinement in the 1085 and 2214 aluminium alloys, characterized by a narrow and a wide freezing range respectively, has been examined. The vibrations were produced by the simultaneous application of a stationary magnetic field B0′ and a variable magnetic field B of frequency 50 Hz in the sump of continuously cast ingots. Extensive grain refinement has been observed in both alloys with increasing magnetizing force. This study shows the mean grain size obtained by this vibrational technique is always smaller than that produced by the recently developed CREM (carting, refining, electromagnetic) process.

Improvement of the temperature resistance of aluminium-matrix composites using an acid phosphate binder

Abstract: Binders are used in preforms from which metal-matrix composites are fabricated by liquid-metal infiltration. This paper (Part I) reports the preparation and characterization of various binders (by themselves). The characterization was in terms of the composition (by atomic absorption spectrometry and X-ray spectrometry), morphology, phases (by X-ray diffraction) and changes upon heating to 1200 °C (by thermogravimetric analysis and mass spectrometry). The binders studied include silica, phosphates (prepared from Al (OH)3 and H3PO4) with the P/Al molar ratio ranging from 1–23, sodium silicate and acrylic emulsion. A phosphate binder was in the form of type B aluminium metaphosphate (Al(PO3)3) at 500 °C when the P/Al atom ratio = 2.2 in the liquid binder, and was in the form of type A aluminium metaphosphate (Al/(PO3)3) when the atom ratio ≥ 5.8 in the liquid binder. Most of the phosphate binders formed type A aluminium metaphosphate (Al(PO3)3) after heat treatment at 800 °C. The phosphate binder with P/Al atom ratio = 2.2 in the liquid binder formed cristobalite aluminium orthophosphate (AlPO4), and the phosphate binder with P/Al atom ratio = 24 in the liquid binder formed a combination of cristobalite aluminium orthophosphate (AlPO4) and metaphosphate glass after heat treatment at 1200 °C in argon.

Angle-dependent X-ray emission and resonance absorption in a laser-produced plasma generated by a high intensity ultrashort pulse.

Abstract: Plasmas were generated by 400 fs KrF laser pulses at intensities of \ensuremath{\sim}${10}^{17}$ W ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ on aluminum targets. Reflectivity and x-ray emission were measured as a function of laser polarization, angle of incidence, and intensity. For the same absorbed intensity, p-polarized laser light is up to a factor of 5 more efficient in generating x rays (g0.5 keV) than s-polarized light. These results show the importance of an additional absorption process, besides collisional absorption, for short scale length plasmas that is effective for p-polarized light only and has the characteristics of resonance absorption.

Interface structure and fractography of a magnesium-alloy, metal-matrix composite reinforced with SiC particles

Abstract: The interfacial structure in SiC-particle-reinforced, as-cast and heat-treated magnesium-alloy-matrix composites was investigated using analytical electron microscopy. No extensive chemical reactions were observed between the magnesium and the SiC particles or the SiC and the eutectic phase. However, most of the eutectic phase appeared to nucleate at the surface of the SiC particles. In addition to the lamellar eutectic, a fine eutectic and Mg2Si particles have been identified at the SiC surface using nanoprobe micro-analysis. As with the aluminium base composite, precipitation was observed to take place on dislocations, and dense precipitation was found to occur in the stress fields around the SiC particles. Examination of the fracture surface indicated that the bonding between the SiC/eutectic is stronger than between the SiC/magnesium matrix. Intergranular cracks have been observed both in the fracture surface and also in a polished and etched section. The fracture surface tends to exhibit a more brittle morphology in the composite than is observed in the alloy.

Piezoelectric paints: preparation and application as built-in vibration sensors of structural materials

Abstract: Piezoelectric paints were prepared using lead zirconate titanate (PZT) ceramic powder as a pigment and epoxy resin as a binder. The obtained paints were spread on the surface of an aluminium beam and cured at room temperature, thus forming the final thin films having thicknesses of 35–81 μm and PZT volume fractions of 25%–53%. The thin films were then poled under electric fields of up to 350 kV cm−1 at room temperature, and the resulting piezoelectric activity was evaluated from vibration measurements on the aluminium beam. Although not strictly quantitative, the piezoelectric activity of the thin film showed a tendency to increase with an increase in the film thickness and the PZT volume fraction. From the standpoint of the thin film application as built-in vibration sensors, the piezoelectric activity was confirmed to be high enough to determine the natural frequencies and mode shapes of the aluminium beam.

Correlation between 27Al and 71Ga NMR chemical shifts

Abstract: A linear relationship has been found to exist between the aluminium-27 and gallium-71 NMR chemical shifts of a series of structurally analogous aluminium and gallium compounds having only oxygen in the first metal coordination spheres; ∂ 71 Ga=2.83 (δ 27 Al)-4.50. This relationship allows the prediction of 71 Ga chemical shifts for such gallium compounds from the 27 Al values already known for their aluminium analogues, and also a greater understanding of observed 71 Ga chemical shifts

Experimental determination of the GaAs and Ga1-xAlxAs band-gap energy dependence on temperature and aluminum mole fraction in the direct band-gap region.

Abstract: The band-gap energy of GaAs and ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As has been measured with the use of photoluminescence from 10 to 300 K, and at various values of the aluminum mole fraction x, in the direct band-gap region. The temperature dependence has been fitted with the Varshni relation, and a discussion of this fitting is given. The results for GaAs are discussed in relation to previous experimental and theoretical data and good agreement is found in some, but not all cases. The observed variation of the band-gap energy of ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As with x is presented and compared to previous results.

Mechanism and kinetics of the chemical interaction between liquid aluminium and silicon-carbide single crystals

Abstract: Previous investigations of phase equilibria in the ternary system Al-C-Si have shown that silicon carbide is attacked by pure aluminium at temperatures higher or equal to 923±3 K and up to about 1600 K, according to the chemical reaction: 4Al+3SiC ↔ Al4C3+3Si In the present work, a study has been carried out to obtain more detailed information on the mechanism and kinetics of this reaction. For that purpose, 6H silicon carbide platelets with broad Si (0 0 0 1) and C (0 0 0 ¯1) faces were isothermally heated at 1000 K in a large excess of liquid aluminium. Characterization of the resulting samples by Auger electron spectroscopy (AES) and scanning electron microscopy (SEM) revealed that the reaction proceeds in both faces via a dissolution-precipitation mechanism. However, the polarity of the substrate surface strikingly influences the rate at which silicon carbide decomposes: dissolution starts much more rapidly on the Si face than on the C face, but, while a barrier layer of aluminium carbide is formed on the Si face protecting it against further attack, the major part of the C face remains directly exposed to liquid aluminium and thus may continue to dissolve at a low but constant rate up to complete decomposition of the α-SiC crystal.

Determination of attenuation lengths of photoelectrons in aluminium and aluminium oxide by angle‐dependent x‐ray photoelectron spectroscopy

Abstract: Angle-dependent x-ray photoelectron spectroscopy (AD-XPS) measurements have been carried out on thin aluminium oxide lagers formed on pure aluminium by oxidation in oxygen at 25 o C and at 250 o C. The amounts of oxygen of the oxide overlagers were measured by nuclear reaction analysis (NRA). The equivalent thickness of the oxide lagers were 14 A and 21.5 A for the oxides formed at 25 o C and at 250 o C, respectively. The AD-XPS measurements were carried out in the range of take-off angles 12-122 o . The signals emitted by Al 3+ in the oxide and by Al m in the metal versus take-off angle can he, within experimental error, HMS by an exponential fraction in the range of take-off angles ∼30-120 o

The wettability of silicon carbide by liquid aluminium : the effect of free silicon in the carbide and of magnesium, silicon and copper alloy additions to the aluminium

Abstract: Results from the sessile-drop method are reported for the effects on wetting angle, θ, of free silicon in the silicon carbide substrate and of alloy additions of silicon, copper or magnesium to the aluminium drop for the temperature range 700–960 or 1040 °C in a titanium-gettered vacuum (10−4/10−5 torr; 1 torr=133.322 Pa). Wetting angle, θ, was reduced by a factor as large as 2.8 for pure aluminium on reaction-bonded, compared with sintered silicon carbide, attributable to partial dissolution by the aluminium of the 18 wt% free silicon present in the reaction-bonded material. For wetting of reaction-bonded silicon carbide, the addition of 5 wt% silicon, copper or magnesium to the aluminium gave contact angles that decreased in the sequence Si→Cu→Mg, with the magnesium addition being the only one to result in wetting (i.e. θ<90 °) for all conditions studied. These results may have implications for design of conditions for joining or promotion of infiltration of silicon carbide parts, preforms or arrays with aluminium alloy melts.

The wettability and the reaction for SiC particle/Al alloy system

Abstract: The incorporation process and the wettability for an SiC particles/aluminium alloy system were measured. The wettability between SiC particle and liquid aluminium was evaluated by the time required for the particulate incorporation. The incorporation time could be measured from a stirring time-melt temperature chart. Magnesium and titanium shortened the incorporation time of α -SiC particles into liquid aluminium and improved the wettability because of their strong affinity for SiC. Copper and zinc prolonged the incorporation time and no reaction products were found in the matrix. Furthermore, surface active elements with weak affinity for SiC (lead and bismuth) extremely prolonged the incorporation time because these elements prevent the reaction at the interface, whereas lithium shortened the incorporation time remarkably.

The Stresses and Strains in a Thick-Walled Tube for Functionally Graded Material under Uniform Thermal Loading

Abstract: The combination of materials consists of aluminium and silicon carbide particles, and the distribution profiles are assumed to be the same as the expression for the plaster/corundum model FGM material