Effect of Load on Dry Sliding Wear of Aluminum-Silicon Alloys

Aluminum-silicon alloy pins were slid against steel disks under nominally dry condition at a speed of 0.6 m s-1. Each pin was slid at a constant load for 5 min, the load being increased in suitable steps from 2 to 65 N. The results show the wear to increase almost monotonically with load, to be sensitive to the presence of silicon in the alloy, and to be insensitive to actual silicon content. The monotonic nature of wear rate-load characteristic suggests that one dominant wear mechanism prevails over the load range studied. Morphological studies of the pin surface and the debris support this contention and point to delamination as being the dominant mode of wear.

Wrought aluminum-nickel alloys for high strength-high conductivity applications

Aluminum-Nickel alloys ranging from 0.06 pct to 6.1 pct (by wt) Ni have been developed for high strength-high conductivity applications. These alloys were produced by solidification in a permanent mold followed by homogenization, hot extrusion or hot rolling and cold drawing to wire form. This sequence of fabrication a) led to the production of fine fibrous dispersoids of NiAl3 as part of the Al-NiAl3 eutectic during the initial casting operation, b) permitted the retention of fine fibrous dispersiods of NiAl3 produced during casting without any significant coarsening during processing and c) led to uniform dispersion and general alignment of these fibrous dispersoids along a given direction in the product without any measurable fiber-matrix separation, extensive fiber-fragmentation or crack production in the matrix. These alloys can be processed to wire form as easily as aluminum and when processed by the above sequence, possess very attractive combination of high strength-high electrical conductivity. Tensile strengths range from 173 N/mm2 (at 0.6 pct Ni) to 241 N/mm2 (at 6.1 pct Ni) in combination with corresponding conductivity values between 62 pct IACS and 55.5 pct IACS. The wires also possess attractive yield strength; for instance, the 0.2 pct off-set strength of Al-6.1 pct Ni wire is 213 N/mm2. Using simple composite rules, the estimated strength and the conductivity of NiAl3 fibers were found to be 1380 N/mm2 and 18 pct IACS respectively, in these wires.

Role of aluminum-magnesium alloys in humid aging of composite solid propellants

The humid aging of composite propellants containing a terpolymer of polybutadiene, acrylic acid, and acrylonitrile (PBAN) as a binder has been studied as a function of aging temperature, relative humidity, and aging time. Three composite types - AP-PBAN, AP-Al-PBAN, and AP-(Al-Mg) alloy- PBAN - have been studied. The burning rates of all three propellant types were unaffected by aging. The calorimetric values of composites containing aluminum-magnesium alloy decreased on aging, and the lattice parameter of the alloy decreased to a value close to that of aluminum. Water absorption in all of the samples increased with increases in the temperature, relative humidity, and aging time. The compression strength of the nonmetalized and aluminized samples decreased on aging, whereas that of the composites containing the alloy increased. The latter effect has been traced to reaction of residual carboxyl groups on the polymer chains with magnesium, leading to cross-linking. The reaction between the -COOH groups and magnesium has been proved using infrared spectroscopy. (Author)

Thermodynamics Of Aluminum Strontium Alloys

The activity of strontium in liquid Al-Sr alloys (X(Sr) less-than-or-equal-to 0.17) at 1323 K has been determined using the Knudsen effusion-mass loss technique. At higher concentrations (X(Sr) greater-than-or-equal-to 0.28), the activity of strontium has been determined by the pseudoisopiestic technique. Activity of aluminium has been derived by Gibbs-Duhem integration. The concentration - concentration structure factor of Bhatia and Thornton at zero wave vector has been computed from the thermodynamic data. The behaviour of the mean square thermal fluctuation in composition and the thermodynamic mixing functions suggest association tendencies in the liquid state. The associated solution model with Al2Sr as the predominant complex can account for the properties of the liquid alloy. Thermodynamic data for the intermetallic compunds in the Al-Sr system have been derived using the phase diagram and the Gibbs' energy and enthalpy of mixing of liquid alloys. The data indicate the need for redetermination of the phase diagram near the strontium-rich corner.

Electrochemical studies of copper-aluminum-silver alloys in 0.5 M H2SO4

The electrochemical behavior in 0.5 M H2SO4 at 25 degreesC of a Cu-Al(9.3 wt%)-Ag(4.7 wt%) alloy submitted to different heat treatments and an annealed Cu- Al(9.7 wt%)-Ag(34.2 wt%) were studied by means of open circuit potential (E-mix) measurements, potentiodynamic polarizations and cyclic voltammetry. SEM and EDX microanalysis were used to examine the changes caused by the electrochemical perturbations. The steady state potentials observed for the studied samples were correlated in terms of the phases present in the alloys surface. The resulting E/I potentiodynamic profiles were explained in terms of the potentiodynamic behavior of pure copper and pure silver. The presence of aluminum decreased the extent of copper oxidation. In the apparent Tafel potential region, two anodic Tafel slopes were obtained: 40 mV dec(-1) in the low potential region and 130 mV dec(-1) in the high potential region, which were related with the electrochemical processes involving copper oxidation. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Extrusion of uranium, uranium alloys, and uranium compacts : a literature search /

This literature search consisting of 240 references to unclassified reports and published literature has been taken from Nuclear Science Abstracts, the official abstract journal of the United States Atomic Energy Commission. The period covered is January 1951 through May 31, 1961. Abstracts for the references can be found by use of the NSA abstract numbers provided.

Damage by eutectic particle cracking in aluminum casting alloys A356/357

The strain dependence of particle cracking in aluminum alloys A356/357 in the T6 temper has been studied in a range of microstructures produced by varying solidification rate and Mg content, and by chemical (Sr) modification of the eutectic silicon. The damage accumulates linearly with the applied strain for all microstructures, but the rate depends on the secondary dendrite arm spacing and modification state. Large and elongated eutectic silicon particles in the unmodified alloys and large pi-phase (Al9FeMg3Si5) particles in alloy A357 show the greatest tendency to cracking. In alloy A356, cracking of eutectic silicon particles dominates the accumulation of damage while cracking of Fe-rich particles is relatively unimportant. However, in alloy A357, especially with Sr modification, cracking of the large pi-phase intermetallics accounts for the majority of damage at low and intermediate strains but becomes comparable with silicon particle cracking at large strains. Fracture occurs when the volume fraction of cracked particles (eutectic silicon and Fe-rich intermetallics combined) approximates 45 pct of the total particle volume fraction or when the number fraction of cracked particles is about 20 pct. The results are discussed in terms of Weibull statistics and existing models for dispersion hardening.

Eutectic grains in unmodified and strontium-modified hypoeutectic aluminum-silicon alloys

Additions of strontium to hypoeutectic aluminum-silicon alloys modify the morphology of the eutectic silicon phase from a coarse platelike structure to a fine fibrous structure. Thermal analysis, interrupted solidification, and microstructural examination of sand castings in this work revealed that, in addition to a change in silicon morphology, modification with strontium also causes an increase in the size of eutectic grains. The eutectic grain size increases because fewer grains nucleate, possibly due to poisoning of the phosphorus-based nucleants, that are active in the unmodified alloy. A simple growth model is developed to estimate the interface velocity during solidification of a eutectic grain. The model confirms, independent of microstructural observations, that the addition of 100 ppm strontium increases the eutectic grain size by at least an order of magnitude compared with the equivalent unmodified alloy. The model predicts that the growth velocity varies significantly during eutectic growth. At low strontium levels, these variations may be sufficient to cause transitions between flake and fibrous silicon morphologies depending on the casting conditions. The model can be used to rationally interpret the eutectic grain structure and silicon morphology of fully solidified aluminum-silicon castings and, when coupled with reliable thermal data, can be used to estimate the eutectic grain size.

Progress relating to civilian applications during ...

"Contract No. W-7405-eng-92."

The constitution of delta-phase alloys of the system uranium-zirconium-titanium /

"March 22, 1955."

Reactivity of certain uranium oxides with aluminum : terminal report /

"Contract No. AT-30-1 Gen-366."

Void formation and grain boundary sliding in aluminum-magnesium solid solution alloys

"Materials Central, Contract no. AF 33(616)-5926. Project no. 7351."

Compressive behaviour of nanocrystalline Mg-5Al alloys

Magnesium alloys are attracting increasing research interests due to their low density, high specific strength, good machinability and availability as compared to other structural materials. However, the deformation and failure mechanisms of nanocrystalline (nc) Mg alloys have not been well understood. In this work, the deformation behaviour of nc Mg-5Al alloys was investigated using compression test, with focus on the effects of grain size. The average grain size of the Mg- Al alloy was changed from 13 to 50 nm via mechanical milling. The results showed that grain size had a significant influence on the yield stress and ductility of the Mg alloys, and the materials exhibited increased strain rate sensitivity with a decrease in grain size. The deformation mechanisms were also strongly dependent on the grain sizes.

Eutectic nucleation in Al-Si alloys

In addition to a change in silicon morphology, modification of aluminium-silicon alloys with strontium or sodium increases the size of the eutectic grains. To determine the mechanism responsible, eutectic solidification in commercial purity and ultra-high purity aluminium-si I icon alloys, with and without strontium additions, was examined by a quenching technique. In the commercial unmodified alloy, nucleation was prolific while in the high-purity unmodified alloy few eutectic grains nucleated. The addition of strontium to the commercial alloy reduced the number of eutectic grains that nucleated. Addition of strontium to the high-purity alloy did not significantly alter nucleation. It is concluded that commercial purity alloys contain a large number of potent nuclei that are susceptible to poisoning by impurity modification. The flake-to-fibre transition that occurs with impurity modification is shown to be independent of any change in eutectic nucleation mode and frequency. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.