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A new casting defect healing technology

Description: A new technology is presented for healing of defects in 356 aluminium alloys that provides economic upgrading of these cast alloys. It uses pneumatic isostatic forging (PIF) to produce high quality Al alloys products with enhanced mechanical properties uniform throughout the part, allowing higher design allowables and increased usage of Al alloy castings. The fundamental mechanism underlying PIF is a single mode plastic deformation process that uses isostatic application of pressures for 10-30 seconds at temperature. The process can be integrated in-line with other production operations, i.e., using the latent heat from the previous casting step. Results of applying the PIF process indicate lower cost and significant improvement in mechanical properties that rival and often exceed corresponding properties of other technologies like hot isostatic pressing and related processes. This process offers many advantages that are described in this paper in addition to presenting case histories of property enhancement by PIF and the mechanism responsible for property enhancement.
Date: January 1, 1997
Creator: Hodge, E.S.; Reddoch, T.W. & Viswanathan, S.
Partner: UNT Libraries Government Documents Department

The response of hydrotalcite coated aluminum to sealing with transition metal salt solutions

Description: Objective was to determine if the protective coating could be enhanced by filling intercrystalline spaces or by reinforcing the coating at intermetallic particles by exposure to aqueous transition metal salt solutions. Two oxy-anion analogs to chromate were used: permanganate and molybdate. Ce(III) (as Ce(NO{sub 3}){sub 3}) was also studied. (Al alloys 2024-T3 and 6061-T6 were used as substrates.) Results are summarized. 4 figs, 1 tab, 3 refs.
Date: 1994
Creator: Buchheit, R. G. & Martinez, M. A.
Partner: UNT Libraries Government Documents Department

Processing of aluminum 7075-T73 components after prolonged storage

Description: Three years ago, production requirements for a T73-tempered aluminium 7075 (Al 7075-T73) component were curtailed and the ``in-process`` parts were stored. During recent attempts to complete processing, visible defects were discovered in this component. Defects at such an early stage in the 20+ year lifetime of the component pose reliability concerns. Chemical and microstructural analysis, mechanical testing, and corrosion evaluation were performed to determine the impact of the defects on material properties.
Date: June 1, 1996
Creator: Guilinger, T.R.; Stevenson, J.O.; Yang, R.G.; Buchheit, R.G.; Schmale, D.T.; Shin, K. et al.
Partner: UNT Libraries Government Documents Department

Microstructure Development and Characteristics of Semisolid Aluminum Alloys

Description: A drop forge viscometer was employed to investigate the flow behavior under very rapid compression rates of A357, A356 diluted with pure aluminum and Al-4.5%Cu alloys. The A357 alloys were of commercial origin (MHD and SIMA) and the rheocast, modified A356 and Al-4.5Cu alloys were produced by a process developed at the solidification laboratory of MIT.
Date: May 15, 2001
Creator: Flemings, Merton & Viswanathan, srinath
Partner: UNT Libraries Government Documents Department

Interfacial segregation and deformation of superplastically deformed Al-Mg-Mn alloys

Description: Microstructural and microchemical studies have been carried out on superplastically deformed Al-Mg-Mn (AA5083-type) alloys. Grain boundary composition was measured using a Scanning Auger Microprobe (SAM) and an Analytical Transmission Electron Microscope (ATEM), while conventional TEM was used for microstructural evaluation. Non-equilibrium segregation of Si to grain boundaries following deformation was measured by both techniques. Significant interfacial Si enrichment was only detected in gage sections of tensile specimens after uniaxial strains from 50 to 200%. Grip regions which experience identical thermal histories, but without plastic deformation, did not reveal Si segregation. Selected samples also showed a slight depletion of Mg at grain boundaries after deformation. The only reproducible observation of equilibrium segregation was in Zr-modified alloys, where Sn was detected by SAM in both the deformed and undeformed sections of the sample. Microstructural analysis documented subgrain formation and subgrain-precipitate interactions during superplastic deformation. In addition, many grain boundaries and precipitate interfaces contained small (5 to 20 nm) voids. Compositional analysis of these nano-voids revealed that they were enriched in Mg with the adjacent boundary regions correspondingly depleted.
Date: March 1, 1995
Creator: Vetrano, J.S.; Lavender, C.A. & Bruemmer, S.M.
Partner: UNT Libraries Government Documents Department

On the influence of dispersoids on the particle stimulated nucleation of recrystallization

Description: Recrystallization of Al alloys is controlled by precipitates. Whereas large particles are generally assumed to promote recrystallization by particle stimulated nucleation, finely dispersed precipitates, either already present in the as-deformed state or precipitating during the recrystallization anneal, are known to strongly retard the progress of recrystallization. It was the aim of this study to elucidate these concurring effects of large particles, and small dispersoids as well as of a supersaturation of solutes on recrystallization in a ternary Al-Fe-Si model alloy. Samples were prepared with different pre-annealing treatments to produce different states of precipitation and supersaturation. Evolution of the microstructure and of the crystallographic texture was followed during cold rolling and recrystallization. Conclusions were drawn on the efficiency of recrystallization nucleation at the various nucleation sites and, especially, on the influence of dispersoids on recrystallization.
Date: December 31, 1996
Creator: Engler, O.
Partner: UNT Libraries Government Documents Department

Measurement of the density of liquid aluminum-319 alloy by an x-ray attenuation technique

Description: This study was made for assisting in casting simulations. A relatively simple apparatus was constructed for measuring the density of Al-based alloys in the solid and liquid states up to 900 C. One of the more important physical properties of a casting alloy, solidification shrinkage, was measured for a commercial Al alloy (Al-319). It was found that while the thermal expansion of Al-319 in both solid and liquid phases is similar to that of pure Al, the density of the liquid alloy is lower than estimated by averaging the atomic volumes of the pure liquid components. The densities were measured by x-ray attenuation.
Date: November 1, 1994
Creator: Smith, P.M. & Gallegos, G.F.
Partner: UNT Libraries Government Documents Department

Neural network modeling of pulsed-laser weld pool shapes in aluminum alloy welds

Description: A model was developed to predict the weld pool shape in pulsed Nd:YAG laser welds of aluminum alloy 5754. The model utilized neural network analysis to relate the weld process conditions to four pool shape parameters: (1) penetration width, (2) width at half-penetration, and (3) cross-sectional area. The model development involved the identification of the input (process) variables, the desired output (shape) variables, and the optimal neural network architecture. The latter was influenced by the number of defined inputs and outputs as well as the amount of data that was available for training the network. After appropriate training, die best network was identified and was used to predict the weld shape. A routine to convert the shape parameters into predicted weld profiles was also developed. This routine was based on the actual experimental weld profiles and did not impose an artificial analytical function to describe the weld profile. The neural network model was tested on experimental welds. The model predictions were excellent. It was found that the predicted shapes were within the experimental variations that were found along the length of the welds (due to the pulsed nature of the weld power) and the reproducibility of welds made under nominally identical conditions.
Date: September 1, 1998
Creator: Vitek, J.M.; Iskander, Y.S.; Oblow, E.M.; Babu, S.S.; David, S.A.; Fuerschbach, P.W. et al.
Partner: UNT Libraries Government Documents Department

Growth and Oxidation of Thin Film Al(2)Cu

Description: Al{sub 2}Cu thin films ({approx} 382 nm) are fabricated by melting and resolidifying Al/Cu bilayers in the presence of a {micro} 3 nm Al{sub 2}O{sub 3} passivating layer. X-ray Photoelectron Spectroscopy (XPS) measures a 1.0 eV shift of the Cu2p{sub 3/2} peak and a 1.6 eV shift of the valence band relative to metallic Cu upon Al{sub 2}Cu formation. Scanning Electron microscopy (SEM) and Electron Back-Scattered Diffraction (EBSD) show that the Al{sub 2}Cu film is composed of 30-70 {micro}m wide and 10-25 mm long cellular grains with (110) orientation. The atomic composition of the film as estimated by Energy Dispersive Spectroscopy (EDS) is 67 {+-} 2% Al and 33 {+-} 2% Cu. XPS scans of Al{sub 2}O{sub 3}/Al{sub 2}Cu taken before and after air exposure indicate that the upper Al{sub 2}Cu layers undergo further oxidation to Al{sub 2}O{sub 3} even in the presence of {approx} 5 nm Al{sub 2}O{sub 3}. The majority of Cu produced from oxidation is believed to migrate below the Al{sub 2}O{sub 3} layers, based upon the lack of evidence for metallic Cu in the XPS scans. In contrast to Al/Cu passivated with Al{sub 2}O{sub 3}, melting/resolidifying the Al/Cu bilayer without Al{sub 2}O{sub 3} results in phase-segregated dendritic film growth.
Date: January 18, 2000
Creator: SON,KYUNG-AH; MISSERT,NANCY A.; BARBOUR,J. CHARLES; HREN,J.J.; COPELAND,ROBERT GUILD & MINOR,KENNETH G.
Partner: UNT Libraries Government Documents Department

Concurrent solid state diffusion bonding and superplastic forming of aluminum alloy 7475

Description: Earlier studies on diffusion bonding (DB) of Al alloys have focused mostly in extrinsically changing the bonding conditions through the use of interlayers, surface etching, or environment. The problem with focusing on the extrinsic conditions only is that the benefits of the DB process are not fully utilized and instead, it can create problems for the base alloy. The approach we have taken to study solid state diffusion bondability of Al alloy is to utilize the intrinsic behavior of superplastic material. Beginning with this preprocessed material, we used a unique method, to obtain diffusion bonding concurrently with superplastic forming to achieve ductile, oxide-free bonds at significantly lower pressures and temperature in an argon atmosphere.
Date: January 1, 1995
Creator: Sunwoo, A.; Lum, R. & Vandervoort, R.
Partner: UNT Libraries Government Documents Department

Thermal Stability and Aging Characteristics of Chromate Conversion Coatings on Aluminum Alloy 2024-T3

Description: XANES and electrochemical impedance spectroscopes were used in parallel to correlate the amount of Cr(VI) in chromate conversion coatings (CCC) on Al 2024 and their corrosion resistance in order to understand the degradation mechanisms upon aging or heating. Cr(VI) species appear to be immobilized for temperatures higher than 80 C due to dehydration. CCC are shown to be dynamic in the first month of aging with no significant dehydration. Another degradation mechanism involving chemical changes is to be considered.
Date: October 17, 1999
Creator: Laget, V.; Jeffcoate, C.; Isaacs, H. S. & Buchheit, R. G.
Partner: UNT Libraries Government Documents Department

Melting and casting of FeAl-based cast alloy

Description: The FeAl-based intermetallic alloys are of great interest because of their low density, low raw material cost, and excellent resistance to high-temperature oxidation, sulfidation, carburization, and molten salts. The applications based on these unique properties of FeAl require methods to melt and cast these alloys into complex-shaped castings and centrifugal cast tubes. This paper addresses the melting-related issues and the effect of chemistry on the microstructure and hardness of castings. It is concluded that the use of the Exo-Melt{trademark} process for melting and the proper selection of the aluminum melt stock can result in porosity-free castings. The FeAl alloys can be melted and cast from the virgin and revert stock. A large variation in carbon content of the alloys is possible before the precipitation of graphite flakes occurs. Titanium is a very potent addition to refine the grain size of castings. A range of complex sand castings and two different sizes of centrifugal cast tubes of the alloy have already been cast.
Date: November 1, 1998
Creator: Sikka, V.K.; Wilkening, D.; Liebetrau, J. & Mackey, B.
Partner: UNT Libraries Government Documents Department

Aspects of two corrosion processes relevant to military hardware

Description: Corrosion is a leading material degradation mode observed in many military systems. This report contains a description of a small project that was performed to allow some of the important electrochemical aspects of two distinct and potentially relevant degradation modes to be better understood: environmentally assisted cracking (EAC) of aluminum alloys and corrosion in moist salt. Two specific and respective tasks were completed: (A) the characterization of the effect of aluminum microstructural variability on its susceptibility to EAC, and (B) the development of experimental and analytical techniques that can be used to identify the factors and processes that influence the corrosivity of moist salt mixtures. The resultant information constitutes part of the basis needed to ultimately predict component reliability and/or possibly to identify techniques that could be used to control corrosion in critical components. In Task A, a physical model and related understanding for the relevant degradation processes were formulated. The primary result from Task B included the identification and qualitative validation of a methodology for determining the corrosivity of salt mixtures. A detailed compilation of the results obtained from each of these two diverse tasks is presented separately in the body of this report.
Date: November 1, 1997
Creator: Braithwaite, J.W. & Buchheit, R.G.
Partner: UNT Libraries Government Documents Department

High temperature deformation in 2036 Al and 0.2 wt % Zr-2036 A1

Description: The microstructure and high-temperature deformation of 2036 Al and a 0.2 wt % Zr modified 2036 Al were characterized. A particle-simulated- nucleation process was applied to refine grain structure in both alloys. Thermomechanically processed materials were tested from 450 to 500 C and strain rates from 2{times}10{sup {minus}1} to 2{times}10{sup {minus}4}s{sup {minus}1}. Strain rate sensitivity exponent, activation energy, and total elongation were measured, and the deformation mechanism was proposed. Effect of Zr on microstructure and deformation of 2036 Al at elevated temperatures was discussed.
Date: November 1, 1995
Creator: Huang, J.S.; Schwartz, A.J. & Nieh, T.G.
Partner: UNT Libraries Government Documents Department

Enhanced tensile ductility in Al-Mg alloys by solid-solution interactions

Description: The development of methods for obtaining high tensile elongation in aluminum alloys is of great importance for the practical forming of near-net-shape parts. Current superplastic alloys are limited in use by high material costs. The utilization of solute-drag creep processes, the approach used in this study, to obtain enhanced tensile ductility in aluminum alloys has lead to tensile elongations of up to 325% in simple, binary Al-Mg alloys with coarse grain sizes. This method has the advantage of lowering processing costs in comparison with superplastic alloys because a fine grain size is not necessary. Whereas superplastic alloys typically have a strain-rate sensitivity of m = 0.5, the enhanced ductility Al-Mg alloys typically exhibit m = 0.3 where maximum ductility is observed. Although a strain-rate sensitivity of rn = 0.5 can lead to elongations of over 1000% (superplastic materials) a value of m = 0.3 is shown experimentally to be sufficient for obtaining elongations of 150% to a maximum observed of 325%. Enhanced ductility is also affected strongly by ternary alloying additions, such as Mn, for which a preliminary understanding is pursued.
Date: November 29, 1995
Creator: Taleff, E.M.; Henshall, G.A.; Lesuer, D.R.; Nieh, T.G. & Wadsworth, J.
Partner: UNT Libraries Government Documents Department

A molecular dynamics study of the {Sigma}11 <1{bar 1}0>/(113)(133) grain boundary in Al and Al-Cu

Description: We present results of molecular dynamics simulation studies of Cu segregation to the {Sigma}11{l_angle}1{bar 1}0{r_angle}/(113)(113) grain boundary (GB) in Al. Simulations were performed with EAM potentials for Al and Al-Cu. Results predict that Cu atoms tend to order along either side of the interface even in the pure symmetrical tilt boundary, forming alternating chains along the {l_angle}{bar 3}{bar 3}2{r_angle} direction. Nucleation of the chains is driven by a change in the local atomic level stress induced by the pre-existing Cu atoms at the GB.
Date: May 16, 1996
Creator: Huang, H.; Rubia, D. de la & Fluss, M.J.
Partner: UNT Libraries Government Documents Department

Growth and oxidation of thin film Al{sub 2}Cu

Description: Al{sub 2}Cu thin films ({approximately}382 nm) are fabricated by melting and resolidifying Al/Cu bilayers in the presence of a {approximately}3 nm Al{sub 2}O{sub 3} passivating layer. X-ray Photoelectron Spectroscopy (XPS) measures a 1.0 eV shift of the Cu2p{sub 3/2} peak and a 1.6 eV shift of the valence band relative to metallic Cu upon Al{sub 2}Cu formation. Scanning Electron Microscopy (SEM) and Electron Back-Scattered Diffraction (EBSD) show that the Al{sub 2}Cu film is composed of 30--70 {mu}m wide and 10--25 mm long cellular grains with (110) orientation. The atomic composition of the film as estimated by Energy Dispersive Spectroscopy (EDS) is 67{+-}2% Al and 33{+-}2% Cu. XPS scans of Al{sub 2}O{sub 3}/Al{sub 2}Cu taken before and after air exposure indicate that the upper Al{sub 2}Cu layers undergo further oxidation to Al{sub 2}O{sub 3} even in the presence of {approximately}5 nm Al{sub 2}O{sub 3}. The majority of Cu produced from oxidation is believed to migrate below the Al{sub 2}O{sub 3} layers, based upon the lack of evidence for metallic Cu in the XPS scans. In contrast to Al/Cu passivated with Al{sub 2}O{sub 3}, melting/resolidifying the Al/Cu bilayer without Al{sub 2}O{sub 3} results in phase-segregated dendritic film growth.
Date: November 9, 1999
Creator: Son, K.A.; Missert, N.A.; Barbour, J.C.; Hren, J.J.; Copeland, R.G. & Minor, K.G.
Partner: UNT Libraries Government Documents Department

Launch capabilities to 16 km/s

Description: A systematic study is described that has led to the successful launch of thin flier-plates to velocities of 16 km/s. In this paper, the authors describe a novel technique that has been implemented to enhance the performance of the Sandia Hyper Velocity Launcher (HVL). This technique of creating an impact-generated acceleration reservoir, has allowed the launch of 0.5 mm to 1.0 mm thick titanium (Ti-6Al-4V) and aluminum (6061-T6) alloy plates to record velocities up to 15.8 km/s. These are the highest metallic projectile plate velocities ever achieved for macroscopic masses in the range of 0.1 g to 1 g.
Date: August 1, 1995
Creator: Chhabildas, L.C.; Kmetyk, L.N. & Reinhart, W.D.
Partner: UNT Libraries Government Documents Department

The influence of grain structure on the reliability of narrow Al- based interconnects

Description: The work reported here concerns the effect of grain structure on electromigration failure in pure A1 and A1-2wt.% Cu-1 wt.% Si lines. The grain structure of fine lines were controlled by annealing after pattering to promote the formation of ``bamboo`` structures. Significant improvements in the median time to failure (MTF) and the deviation of the time to failure (DTF) were observed with the development of near-bamboo structures with polygranular-segment lengths shorter than {approximately} 5 {mu}m. The most common failure sites are voids or slits across bamboo grains at the upstream ends of polygranular segments. The time-to-failure decreases with the polygranular segment length, and can be significantly enhanced by controlling the grain structure.
Date: May 1, 1995
Creator: Kang, S.H.; Kim, C.l Morris, J.W. Jr. & Genin, F.Y.
Partner: UNT Libraries Government Documents Department

Mechanism of electromigration failure in Al thin film interconnects containing Sc

Description: In order to understand the role of Sc on electromigration (EM) failure, Al interconnects with 0.1 and 0.3 wt.% Sc sere tested as a function of post-pattern annealing time. In response to the evolution of the line structure, the statistics of lifetime evolved. While the addition of Sc greatly reduces the rate of evolution of the failure statistics because the grain growth rate decreases, the MTF variation was found to be very similar to that of pure Al. These observations seem to show that Sc has little influence on the kinetics of Al EM; however, it has some influence on the EM resistance of the line since it is an efficient grain refiner. Unlike Cu in Al, Sc does not seem to migrate, which may explain its lack of influence on the kinetics of Al EM.
Date: May 1, 1995
Creator: Kim, Choong-un; Kang, S.H.; Morris, J.W. Jr. & Genin, F.Y.
Partner: UNT Libraries Government Documents Department

Incommensurate magnetic order in UNi{sub 2}Al{sub 3}

Description: Elastic neutron scattering measurements performed on single crystal UNi{sub 2}Al{sub 3} show this heavy fermion superconductor to display long-range incommensurate (IC) magnetic order below T{sub N}=5.2K. The ordering wavevector is (1/2 {+-} {tau},0,1/2) with {tau}=0.110{+-}0.003, and the size of the maximum ordered moment is 0.24{+-}0.1{mu}{sub B}/U.
Date: December 31, 1993
Creator: Lussier, J. G.; Schroeder, A.; Gaulin, B. D.; Garrett, J. D.; Buyers, W. J. L.; Rebelsky, L. et al.
Partner: UNT Libraries Government Documents Department

Influence of grain structure and solute composition on the work hardening behavior of aluminium at cryogenic temperatures

Description: An unrecrystallized structure is found to significantly improve the work hardening characteristics by lowering the work hardening rate during early stages of deformation. This is in contrast to a recrystallized structure, which requires a higher work hardening rate to accommodate the greater degree of multiple slip necessary to maintain strain compatibility between the more randomly oriented grains. The stronger texture associated with the unrecrystallized structure allows deformation to occur more efficiently. Addition of magnesium also improves work hardening by increasing overall level of the work hardening rate. The improved characteristics of the work hardening behavior result in a parallel increase in both the strength and ductility at cryogenic temperatures. These findings are positive since they suggest a method by which improvements in the work hardening behavior and subsequent mechanical properties may be obtained through practical modifications of the microstructure and composition.
Date: July 1, 1993
Creator: Chu, D. & Morris, J. W. Jr.
Partner: UNT Libraries Government Documents Department

Failures to model the development of a cube texture during the high temperature compression of Al-Mg alloys

Description: A strong (100) fiber texture has been observed under some circumstances after the compression and tension of Al-Mg alloys. It is not due to static recrystallization after the text, but probably connected with some form of dynamic recrystallization. Possibilities that this unusual texture might rise from some unconventional deformation mechanisms were searched for but not found.
Date: December 31, 1993
Creator: Kocks, U. F.; Chen, Shuh Rong & Dawson, P. R.
Partner: UNT Libraries Government Documents Department

TIG welding of aluminum alloys for the APS storage ring - a UHV application

Description: The Advanced Photon Source (APS) incorporates a 7-GeV positron storage ring 1104 meters in circumference. The storage ring vacuum system is designed to maintain a pressure of 1 nTorr or less with a circulating current of 300 mA to enable beam lifetimes of greater than 10 hours. The vacuum chamber is an aluminum extrusion of 6063T5 alloy. There are 235 separate aluminum vacuum chambers in the storage ring connected by stainless steel bellows assemblies. Aluminum was chosen for the vacuum chamber because it can be economically extruded and machined, has good thermal conductivity, low thermal emissivity, a low outgassing rate, low residual radioactivity, and is non-magnetic. The 6063 aluminum-silicon-magnesium alloy provides high strength combined with good machining and weldability characteristics. The extrusion process provides the interior surface finish needed for the ultrahigh vacuum (UHV) environments There are six different vacuum chambers with the same extrusion cross section. The average vacuum chamber length is 171.6 inches. The extruded vacuum chambers are welded to flange assemblies made up of machined 2219 aluminum alloy pieces and 2219 aluminum vacuum flanges from a commercial source.
Date: May 29, 1996
Creator: Goeppner, G.A.
Partner: UNT Libraries Government Documents Department