Aluminum alloys are presently used extensively as a conductor material for overhead transmission wires. Their lack of strength must be compensated by using a reinforcing agent, namely steel. The aim of this thesis was to investigate the possibility of deforming Al-Fe and Al-Ni alloys in order to produce high strength, high conductivity wire product. The main goal was to produce a two phase Al alloy wire with adequate strength so that the wire would be self supporting as an overhead electrical power transmission line. The Al-Fe and Al-Ni two phase alloy rods were Ohno cast to provide directional solidification. In both alloys, wire drawing was unsuccessful due to fiber fracture and damage accumulation during drawing. The Al-Fe alloy was subjected to hydrostatic extrusion in an attempt to induce co-deformation of the matrix material and the brittle intermetallic second phase, Al6Fe. Hydrostatic extrusion proved to be successful in inducing some deformation of the Al6Fe and provided valuable initial insight into the investigation of the deformation of Al6Fe. The final stage in the development of an aluminum alloy for use as a self supporting overhead transmission wire was the development of a “macrocomposite”. This macrocomposite was a combination of an Fe rod 4 mm in diameter and a tube of aluminum 8 mm in diameter. This macrocomposite was successfully cold worked to achieve an overall yield strength of 395 MPa. / Thesis / Master of Engineering (MEngr)

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Aluminum and metal-oxide powders were mixed using mechanical alloying. Exothermic displacement reactions could be initiated in the powders either by mechanical alloying alone or by heat treating the mechanically alloyed powders. Exponential relationships developed between the initiation time of the reaction and the mechanical alloying charge ratio. The exponential relationships were the result of changes in the intensity and quantity of collisions occurring during mechanical alloying. Differential thermal analysis of the mechanically alloyed powders indicated that increased milling time inhibited the initiation of the displacement reactions. It is believed that the reactions were inhibited because of heat dissipation from reacting oxide particles in the surrounding metal. Determining the effects of mechanical alloying on displacement reactions will lead to a more thorough understanding of the kinetics of mechanical alloying. Reacted powders were densified by uniaxial compaction and extrusion. Metallographic analysis of the reacted specimens confirmed the findings of the thermal analysis. Increased mechanical alloying inhibited the chemical reactions. Densified specimens from longer-milled mechanically alloyed specimens showed finer, more uniformly dispersed reaction products. These samples also showed increased mechanical properties as a result of their finer microstructure. Current particle strengthening models were used to accurately predict room temperature properties. Because of the fine microstructures produced, it may be possible to use similar techniques to yield new high-temperature aluminum alloys. / Ph. D.

The lack of ductility of the B2 NiAl alloy stands in the way of promising applications. In an effort to understand the dislocation behavior, computer simulation of the planar faults involved in the core spreadings of <100> and <111> dislocations was carried out. Seven γ-surfaces were computed for different crystallographic planes ({110}, {112}, {123}, {210}, {100}, {111} and {122}). Stable APB's are observed in the {110} and {112} planes but they are deviated from the exact 1/2a<111> position. No other stable planar fault was observed. The dislocation core spreadings are explained by the energy balance among the directions of lowest restoring forces observed in the γ-surfaces. The complete <111> screw dislocation was stable in the simulation. According to the stable APB's, two dissociation reactions of the <111> screw dislocation in the {110} and {112} planes are proposed. The simulation of metastable superpartials shows that the dissociation in the {112} planes is very close to a stable dissociation. / Master of Science

The formation of Ti₃Al and its embrittling characteristics have been investigated in Ti-Al binary alloys up to 9.0 weight percent aluminum. The investigating tools were optical metallography, the Brown-type stress corrosion test and the Charpy V-notch Impact test. Segregated microstructures resulting from annealing in the (α+β) region were found to be extremely difficult to homogenize below the α-transus and could possibly explain the two-phase regions reported by many investigators. Sea-water stress corrosion tests reveal that a Widmanstatten structure is susceptible to stress corrosion cracking after aging for two hours at 1100°F. Much longer annealing times are required to produce susceptibility in equiaxed α-grains resulting from annealing in the (α+β) region. Toughness is less affected as a result of aging a Widmanstatten structure than an equiaxed structure, although the reduction is significant in both cases. / M.S.

The last decade has seen many new developments in the foundry industry, among them the CO₂ process for curing molds and cores. The CO₂ process consists essentially of mixing dry, clay-free, silica sand with an organic liquid sodium silicate binder, then ramming this mix into molds or core boxes and injecting CO₂ gas. The CO₂ gas reacts with the sodium silicate binder forming a silica gel which hardens rapidly in atmospheric conditions. The CO₂ molds are more resistant to metallostatic pressure and erosion than either green or dry sand molds but more expensive also. The CO₂ cores are hardened rapidly without the benefit of a baking cycle characteristic of the production of conventional organically-bonded cores. The CO₂ cores are more economically compared with other core-making processes than the CO₂ molds are compared with other sand-molding processes. The casting property, fluidity, is a qualitative measure of the ability of a metal to completely fill a mold cavity and is normally expressed as inches of flow in a small channel. Mold material variables, gating and flow-channel variables, and metallurgical variables, such as metal composition and the number of degrees superheat, all affect the fluidity values. This paper presents a spiral fluidity pattern for determining the fluidity of aluminum-silicon alloys in CO₂ molds made by a standard procedure. A standardized molding, melting, and pouring procedure is suggested to control certain fluidity variables while investigating the influence of other fluidity variables. Finally, a statistical method is presented to ascertain the significance of the effect certain variables may have on fluidity. Preliminary investigations pertinent to the major objective of this paper indicate aluminum-silicon alloys are less fluid in CO₂ molds than in green sand. Investigations also indicate that certain variabilities in testing procedure which an operating foundry might encounter have no statistically significant effect on fluidity. / Master of Science

Three theories - the time-hardening theory, the strain-hardening theory, and the life-traction theory - are investigated in an effort to predict creep strains under conditions of varying loads from data obtained at constant load in the range of interest to the structural designer. A method is presented for computing an equivalent rupture stress for the varied load case using the lite-traction theory and the rupture curve tor constant stress tests. The analytical methods are compared with data obtained from 2024-T3 aluminum-alloy sheet under tensile creep at constant and varying loads. / M.S.

The objective of this work is to study the effects of dissolved hydrogen on the mechanical properties of aluminum-lithium alloys: 2090, 2091, and Weldalite 049, and to compare with the effects on aluminum-copper 2219 alloy. Prior to mechanical testing, aging studies were performed for 2090 and 2219 using microhardness Vickers to determine the peak aged condition required by NASA. The Charpy tests are part of this study designed to investigate the effects of temperature and notch orientation on fracture behavior. Disk rupture tests were used with various gases (hydrogen and nitrogen) and three strain rates (increment of 50 psi every 20, 200 and 300 seconds) and two temperatures (room and liquid nitrogen temperatures) to determine the effects of hydrogen on the sample during the tests. Some independent studies on the corrosion behavior and electrochemical hydrogen charging of 2219 and 2090 were also performed. An effect of double peak aged condition was found for both 2219 and 2090 alloys. Prior to mechanical testing, the 2090 received in the T3 or W51 conditions was chosen to be aged in an air furnace at 170°C for 16 hours. The Charpy studies showed a higher propagation energy needed for the T-S and L-S orientations than for the L-T and T-L orientations, due in large part to the extensive delamination propagation of the fracture. The disk rupture tests showed a important decrease of the fracture to failure on the 2090 and 2091 due to hydrogen while no important variations were seen for the 2219 and the weldalite 049 alloys. No effect of hydrogen were found, with the disk rupture test, at cryogenic temperature and for all alloys. The corrosion behavior of 2219, as well as 2090, showed development of pits under neutral and acidic environments while general corrosion was obtained with basic environment. Two solutions were found to charge the samples in hydrogen: a potentiostatic test for 5 hours at -3V, and a galvanostatic test for 20 hours at -500μA, both performed in a 0.04 N HCl plus As₂O₃ environment. / Master of Science

A study has been carried out to investigate the growth and closure behavior of short cracks in 2024-T351 aluminum alloy and four different conditions of 4340 steel using through thickness cracks of straight fronts. The experiments were carried out to study the influence of stress level, stress ratio, yield strength and prior austenitic grain A sizes in notched and unnotched specimens. The stereoimaging technique was developed and adapted to obtain crack closing and opening points, and also near tip displacement fields. Experimental results are presented with a general discussion. It was found that long cracks showed good correlation when analyzed in terms of effective stress intensity range. However,correlations were poor for short cracks. lt was found that short cracks show less closure behavior than long cracks. The estimates of initial crack lengths based on linear elastic data were made. These estimates differed significantly from the actual initial crack lengths for completely reversed cycling tests. Suggestions have been made to the equivalent initial flaw size approach and conclusions have been drawn. / Ph. D.

The experimental alloy powders of 1% Mg treated Al-8Fe-1.8V-8Si were obtained by air atomization. The screen analysis of powders was made by sieves with meshes ranging from +90&micro / m, +63&micro / m, +53&micro / m, +45&micro / m, +38&micro / m to -38&micro / m. Unreinforced and TiC particulate reinforced specimens were produced by hot dynamic consolidation which is known as hot swaging. Powders were canned into pure aluminium tubes of about 10cm length and 2.2cm diameter. Single action and double action cold pressing were applied to some of the specimens before hot dynamic compaction and some specimens of canned loose powder were also processed. The diameters of the hot compacts were decreased in a two step process by swaging machine (rotary dynamic compaction). During the first step, after canning, compacts had been held at 480&deg / C for 1 hour and swaged, thus the diameter decreased from 2.2 cm to 1.97cm. Secondly, the compacts were reheated to 480&ordm / C and held for 1 hour and further swaged to obtain a diameter decrease from 1.97cm to 1.54cm. Generally, the microstructures of the hot dynamic compacted specimens were homogeneous except the specimens produced by using -63 &micro / m +53 &micro / m powder size fraction. By SEM study, a vanadium free cross like AlFeSi phase was observed near the outer regions of the specimen. No considerable coarsening of the dispersoids was observed after hot dynamic compaction of +63 &micro / m size powder. For -90&micro / m +63&micro / m size powders, maximum flexural strength values obtained by three point bending test increased by addition of 10% TiC to from 152 MPa to 285 MPa at double pressed condition and from 76MPa to 190MPa at loose powder canning condition. By hardness tests, it was observed that hardness values were inversely proportional to powder size and increased from 107 BHN to 147 BHN for corresponding powder size range of +90&micro / m to -38&micro / m. Porosity values obtained by Archimedes principle for single pressing varied between 0.03 % and 1.10% for corresponding size range of +38&micro / m to +90&micro / m. No considerable porosity was detected for double pressing. Porosity values of canned loose powder were between 3% and 10% for the range of +38 &micro / m- +45 &micro / m. By X-Ray analysis, it was revealed that Mg2Si reaction did not form after artificial aging of specimens up to 8 hours at 190&deg / C. Also, x-ray analysis of individual powders and specimens obtained by hot dynamic compaction of the same powder showed that / after hot dynamic compaction, the alloy powders were stable and no new phase formation was detected for +63&micro / m size. DSC examination of the specimens produced from +90&micro / m, +63&micro / m, +53&micro / m, -38&micro / m powder confirmed the microstructure stability up to the melting temperature. Melting temperature was detected to be in the range of 560&deg / C-575&deg / C by DSC.