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Aluminum Alloys (aluminum + alloy)
Selected AbstractsWarm Laser Shock Peening Driven Nanostructures and Their Effects on Fatigue Performance in Aluminum Alloy 6160,ADVANCED ENGINEERING MATERIALS, Issue 4 2010Chang Ye Warm laser shock peening is an innovative manufacturing process that integrates laser shock peening and dynamic aging to improve materials' fatigue performance. Compared to traditional laser shock peening (LSP), warm laser shock peening (WLSP) , i.e., LSP at elevated temperatures , provides better performance in many aspects. WLSP can induce nanoscale precipitation and high density dislocation arrangement, resulting in higher surface strength and lower surface roughness than LSP, which are both beneficial for fatigue life improvement. Due to pinning of the dislocation structure by nanoscale precipitates , so-called dislocation pinning effects , the relaxation of residual stress and surfaces dislocation arrangement is significantly reduced. In this study, AA6061 alloy is used to evaluate the WLSP process. It is found that the fatigue life improvements after WLSP are not only caused by large compressive residual stress and high density dislocations but also by the higher stability of the residual stresses and surface strength during cyclic loading. [source] Environmental Behavior and Stress Corrosion Characteristics of Nano/Sub-Micron E950 Aluminum Alloy,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Eli Aghion The corrosion performance and stress corrosion resistance of E950 Aluminum alloy with nano/sub-micron structure were evaluated in 3.5% NaCl solution. The results obtained indicated that the corrosion and stress corrosion resistance of E950 alloy were relatively reduced compared to that of the conventional coarse-grained alloy (Al,4.65%Mg). In particular, the inherently improved ultimate tensile strength of E950 alloy was significantly decreased under stress corrosion conditions. [source] Negative Strain-rate Sensitivity in a Nanostructured Aluminum Alloy,ADVANCED ENGINEERING MATERIALS, Issue 10 2006Q. Han The influence of strain rate in the range of 10,1 to 10,5 s,1 on the compression behavior of a cryomilled 5083 Al alloy is studied. The compression flow stress remains constant after an initial short strain hardening and a small stress dip, which indicates a dynamic saturation of dislocations. It is found that the compression flow stress increases with decreasing strain rate, which is believed to be attributed to dynamic strain aging. [source] Environmental Behavior and Stress Corrosion Characteristics of Nano/Sub-Micron E950 Aluminum Alloy,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Eli Aghion The corrosion performance and stress corrosion resistance of E950 Aluminum alloy with nano/sub-micron structure were evaluated in 3.5% NaCl solution. The results obtained indicated that the corrosion and stress corrosion resistance of E950 alloy were relatively reduced compared to that of the conventional coarse-grained alloy (Al,4.65%Mg). In particular, the inherently improved ultimate tensile strength of E950 alloy was significantly decreased under stress corrosion conditions. [source] Study of corrosion resistance improvement by metallic coating for overhead transmission line conductorELECTRICAL ENGINEERING IN JAPAN, Issue 1 2008Masanori Isozaki Abstract Applying anticorrosion grease and aluminum-clad steel (AC) wires to ACSR have been adopted as general methods to protect overhead transmission line conductors and/or wires from corrosion. However, in some cases those means have been found to be ineffective on some transmission lines passing through acid atmosphere in the vicinity of a factory exhausting acid smoke. The corrosion caused by acid atmosphere is characterized by a higher speed in its progress as is well known. As means against such acid corrosion, application of high-purity aluminum, selective removal of intermetallic compound in aluminum, and plastic coating wires have been reported before, and each has both advantages and disadvantages. In a former report, we found that a new type of anticorrosion grease shows an excellent property against acid atmosphere as well as in a salty condition. Here we present a new type of anticorrosion technology of applying high-corrosion-resistance aluminum alloy or zinc coatings on each component wire of a conductor that we succeeded in developing through a serial study of anticorrosion methods on overhead transmission lines. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(1): 41,47, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20365 [source] Derivation of Recovery Kinetics From Stress Relaxation Tests,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Sheila Bhaumik The recovery behavior of a commercial aluminum alloy 3103 was investigated by the means of two alternative experimental methods: stress relaxation (SR) and double tension tests (DT). In case of SR, the stress,time evolution after deformation was recorded, and for DT the yield stress after several recovery times were measured. The DT tests were further sub-divided into tests with and without external load during recovery. The results revealed that the recovery kinetics is clearly accelerated by the external stress during the SR. However, the difference between the DT and SR stresses is much larger. It is caused by continued dislocation glide after the deformation, which causes continued plastic elongation of the specimens. This is demonstrated quantitatively by appropriate evaluation models for both experiments. In contrast to DT, the SR evaluation accounts for the elastic SR due to plastic elongation, but the recovery parameters are the same ones as for DT. This makes it possible to replace DT by SR experiments, which are materially less laborious. [source] Microstructural Investigation of Walking Parts of Military Tanks Coated with Arc SprayingADVANCED ENGINEERING MATERIALS, Issue 7 2008U. Ozsarac The walking parts are the most important mechanical components in military tanks and other vehicles having palettes. The matrix phase of carrying wheels is Cu-based aluminum alloy. In this study, the microstructure of walking parts of military tanks was investigated deeply by optically and scanning electron microscopy. [source] Surface-Modified Mesoporous SiO2 Containers for Corrosion ProtectionADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Ekaterina V. Skorb Abstract The development of active corrosion protection systems for metallic substrates is an issue of prime importance for many industrial applications. The present work shows a new contribution to the design of a new protective system based on surface modified mesoporous silica containers. Incorporation of silica-based containers into special sol,gel matrix allows for a self-healing effect to be achieved during the corrosion process. The self-healing ability occurs due to release of entrapped corrosion inhibitors in response to pH changes caused by the corrosion process. A silica,zirconia-based hybrid film is used in this work as a coating matrix deposited on AA2024 aluminum alloy. Mesoporous silica nano-particles are covered layer-by-layer with polyelectrolyte layers and loaded with inhibitor [2-(benzothiazol-2-ylsulfanyl)-succinic acid]. The hybrid film with nanocontainers reveals enhanced long-term corrosion protection in comparison with the individual sol,gel films. The scanning vibrating electrode technique also shows an effective healing ability of containers to cure the corrosion defects. This effect is due to the release of the corrosion inhibitor triggered by the corrosion processes started in the cavities. The approach described herein can be used in many applications where active corrosion protection of materials is required. [source] Infrared stealth and anticorrosion performances of organically modified silicate-NiZn ferrite/polyaniline hybrid coatingsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2008K. H. Wu Abstract Hybrid coatings based on organically modified silicate-Ni0.5Zn0.5Fe2O4/polyaniline were synthesized through a sol,gel technique with different NiZn ferrite/polyaniline weight ratio (1/1, 1/2, 1/5). These hybrid films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection and to act as infrared stealth coatings. The effects induced by the NiZn ferrite/polyaniline hybrids on the chain dynamic, ferromagnetic behavior, infrared stealth, and anticorrosion performances of the coated samples were investigated. The rotating-frame spin-lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly cross-linked and dense. The thermal extinction of the hybrid coatings increased with the increase in the polyaniline content. Potentio-dynamic and salt-spray analysis revealed that the hybrid films provided an exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 926,935, 2008 [source] Degradation processes in Al/SiCp/MgAl2O4 composites prepared from recycled aluminum with fly ash and rice hull ashMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 11 2007M. I. Pech-Canul The degradation characteristics of Al/SiCp/spinel composites prepared with fly ash (FA) and rice hull ash (RHA) under environmental conditions were investigated. Composite specimens were prepared with recycled aluminum via reactive infiltration in the temperature range 1050,1150,°C for 50,70 min and, in argon atmosphere at a pressure slightly above that of the atmospheric pressure. Results reveal that although both FA and RHA help in preventing SiCp dissolution and the subsequent chemical degradation of the composites, due to the interaction of native carbon in FA with liquid aluminum, FA-composites are susceptible to corrosion via Al4C3. Moreover, this phase accelerates the degradation process and increases the damage severity. The primary corrosion mechanism in both types of composites is attributed to microgalvanic coupling between the intermetallic Mg2Si and the matrix. Accordingly, an appropriate control of the Si/(Si,+,Mg) molar ratio in the aluminum alloy hinders the Mg2Si corrosion mechanism in both types of composites and a proper FA calcination prevents chemical degradation in FA composites. [source] The influence of artificial aging on the microstructure, mechanical properties, corrosion, and environmental cracking susceptibility of a 7075 friction-stir-weldMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 10 2007C. S. Paglia The influence of overaging to the T7451 temper on the microstructure, the mechanical properties, and the corrosion susceptibility of friction-stir-welded 7075 aluminum alloy was investigated by means of transmission electron microscope (TEM), SEM investigations, constant extension rate tests (CERT), alternate immersion tests, and potentiodynamic scans. The overaging that occurs during welding within the heat-affected zones of the friction-stir-welded 7075-O tempered plates promotes a slight formation of intragranular and grain boundary precipitates and increases the mechanical as well as the corrosion resistance properties as compared to the T7451 welded plates. The "double" overaging treatment, consisting of the T7451 temper and the thermal transient experienced by the heat-affected zones of the 7075-T7451 welded plates, increases the size of the intragranular and the grain boundary precipitates as well as the precipitate-free zones. These facts decrease the mechanical and corrosion properties of the 7075-T7451 weld. The T7451 thermal treatment applied after the welding of the 7075-O plates promotes the high presence of small precipitates and reduces the size of the precipitate-free zones. This fact increases the general corrosion resistance, but decreases the mechanical properties. Therefore, the corrosion as well as the mechanical properties are greatly correlated with minute changes in the microstructure, which can arise by short-term heat exposure as for instance during welding. It was also found that the environmental susceptibility measured by means of CERTs may be influenced by "solution-strengthening" corrosion mechanisms which increase the strain. This fact is present in weld microzones particularly susceptible to corrosion. [source] Electrochemical impedance spectroscopy analysis on aluminum alloys in EXCO solutionMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 5 2005F.-H. Cao Abstract Electrochemical impedance spectroscopy (EIS) of Al-Zn-Mg-Cu alloy in EXCO solution has been investigated. The results show that the impedance spectroscopy of the investigated electrode consists of two capacitive loops in the high and middle frequency domain respectively and an inductive loop in the low frequency domain at the first 30 h of immersion; the inductive arc disappears between 30 h and 60 h while it takes on at the low frequency domain at the last 36 h of the immersion time. A model based on the corrosion mechanism of the aluminum alloy and corroding morphology was proposed and applied to analyze the EIS results. [source] Exfoliation corrosion of aluminum alloy AA7075 examined by electrochemical impedance spectroscopyMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2004F.-H. Cao Abstract A typical aluminum alloy, AA7075, was immersed in the EXCO solution, and its corrosion properties during different immersion time were measured repetitively using electrochemical impedance spectroscopy technique (EIS). The EIS data a were simulated using equivalent circuit with ZView program. The results show that once the exfoliation occurs, the low frequency inductive loop in the Nyquist plot associated with the relaxation phenomenon of reaction intermediates disappears, and the Nyquist plane is mainly composed of two capacitive arcs in the high frequency range and low frequency range respectively. The former originates from the original corroded surface, while the latter from the newly formed interface by exfoliation corrosion (EXCO). With the increased immersion time, the high frequency capacitance arc decreases gradually, while the low frequency capacitance arc increases gradually. From the beginning of immersion up to 9 hours, charge transfer resistance gradually decreases, illustrating the acceleration of the corrosion rate, whereas the proton concentration decreases steeply, indicating the cathodic process is pre-dominant. Then the corrosion rate decreases gradually corresponding to the exhausting of proton ions. The results also show that the exfoliation corrosion is developed from pitting corrosion through intergranular corrosion to general corrosion at the end. [source] Theoretical and experimental analysis of plastic response of isotropic circular plates subjected to underwater explosion loadingMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 2 2008J. Z. Ashani Abstract Dynamic response analysis of structures subjected to underwater explosion (UndEx) loading has been always an interesting field of study for ship designers and metal forming specialists. Understanding the deformation and rupture mechanism of simple structures plays an important role in successful designing of a reliable structure under this kind of loading. In this paper, first the major parameters of the UndEx phenomenon (peak overpressure, impulse per unit area, dimensionless damage parameter ,, etc.) are discussed and determined by means of available experimental relations mostly offered by R. Cole. After that, the maximum deflection of a fully clamped circular plate has been calculated using a theoretical procedure assuming two different conditions: (1) neglecting the effect of strain rate, (2) considering the strain rate sensitivity of the material. Some experiments have been conducted on 5010 aluminum circular plates, using C4 as explosive. In order to simulate reality, a fixture was designed so that the plates are loaded in air-backed condition. Plates were fixed on top of the fixture, so the fully clamped condition which was assumed as the boundary condition was achieved. The test specimens were measured, not only their maximum deflection but also their thickness at different radii were determined. The results are compared to experimental-based predictions offered by Nurick and Rajendran who has conducted similar experiments. The results show reasonable agreement with theoretical predictions, especially when strain rate effects are considered. In addition, two new material constants (D, q) for this special aluminum alloy are introduced. Theoretische und experimentelle Analyse der plastischen Umformung isotroper kreisförmiger Platten bei Unterwasser-Explosionsbelastung Die Analyse der dynamischen Reaktion einer Struktur bei einer Explosionsbelastung unter dem Wasser ist für die Konstrukteure von Schiffen und Umformspezialisten eine interessante Forschungsaufgabe. Das Verständnis der Umformung und der Bruchmechanismen einfacher Strukturen spielt eine wichtige Rolle im erfolgreichen Konstruieren einer festen Struktur gegen diese Belastungsart. In diesem Beitrag werden erstens die Hauptparameter der Explosionserscheinung unter Wasser (maximaler Druck, Impulse per Flächeneinheit, dimensionsloser zerstörender Parameter usw.) dargestellt und zweitens durch die vorhandenen Methoden, die überwiegend von R. Cole vorliegen, berechnet. Danach ist die maximale Durchbiegung einer ganz gespannten kreisförmigen Platte durch eine analytische Methode in zwei Formen bestimmt worden: (1) Vernachlässigung der Dehnungsgeschwindigkeit, (2) Berücksichtigung der Dehnungsgeschwindigkeitsempfindlichkeit des Werkstoffes. Einige Untersuchungen wurden an kreisförmigen Platten aus Aluminium 5010 mittels Sprengstoff C4 durchgeführt. Zur Praxissimulation wurde die Spannvorrichtung so konstruiert, so dass die Platten Luft-gepuffert belastet wurden. Die Platten wurden oben auf der Spannvorrichtung vollständig eingespannt, um Grenzbedingungen zu erhalten. Bei den Proben wurde nicht nur die maximale Durchbiegung sondern auch die Dicke in verschiedenen Radien ermittelt. Die Ergebnisse wurden mit den experimentellen Abschätzungen von Nurick und Rajendran, die ähnliche Versuche durchgeführt haben, verglichen. Die Ergebnisse zeigen eine gute Übereinstimmung mit den theoretischen Abschätzungen, insbesondere bei Betrachtung der Dehngeschwindigkeit. Zusätzlich wurden für diese spezielle Aluminiumlegierung zwei neue Materialkonstanten (D, q) eingeführt. [source] Laboratory simulation of impacts on aluminum foils of the Stardust spacecraft: Calibration of dust particle size from comet Wild-2METEORITICS & PLANETARY SCIENCE, Issue 2 2006A. T. Kearsley The ability of soft aluminum alloy to record hypervelocity impacts as bowl-shaped craters offers an opportunistic substrate for recognition of impacts by particles of a potentially wide size range. In contrast to impact surveys conducted on samples from low Earth orbit, the simple encounter geometry for Stardust and Wild-2, with a known and constant spacecraft-particle relative velocity and effective surface-perpendicular impact trajectories, permits closely comparable simulation in laboratory experiments. For a detailed calibration program, we have selected a suite of spherical glass projectiles of uniform density and hardness characteristics, with well-documented particle size range from 10 ,m to nearly 100 ,m. Light gas gun buckshot firings of these particles at approximately 6 km s,1 onto samples of the same foil as employed on Stardust have yielded large numbers of craters. Scanning electron microscopy of both projectiles and impact features has allowed construction of a calibration plot, showing a linear relationship between impacting particle size and impact crater diameter. The close match between our experimental conditions and the Stardust mission encounter parameters should provide another opportunity to measure particle size distributions and fluxes close to the nucleus of Wild-2, independent of the active impact detector instruments aboard the Stardust spacecraft. [source] Dry Machining Using CrAlYN Coated CarbidesPLASMA PROCESSES AND POLYMERS, Issue S1 2007Eberhard Abele Abstract The current study discusses the influence of yttrium content of magnetron sputtered chromium-based coatings on the wear behavior in dry machining of steel and aluminum alloy. Both tribological tests and practical wear experiments in dry turning and drilling were performed. The characterization of the coatings includes the measurement of thickness and hardness, as well as a detailed analysis of the coating composition. Dry turning and drilling operations were performed in order to evaluate the wear resistance of CrxAlyN and CrxAlyYzN during practical applications. [source] Cost-Affordable Technique Involving Equal Channel Angular Pressing for the Manufacturing of Ultrafine Grained Sheets of an Al,Li,Mg,Sc Alloy,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Rustam Kaibyshev A two-step process consisting of modified equal channel angular pressing (ECAP) and subsequent isothermal rolling (IR) was developed to produce thin sheets of aluminum alloys with ultra-fine grained (UFG) structure. Significant increase in the efficiency of ECAP was attained by using flat billets and a back pressure system. The incorporation of final IR into technologic route provides a reduced strain which is necessary to impose for the fabrication of thin sheets with UFG structure. In addition, it allows producing relatively "long billets." In order to demonstrate the feasibility of this technique an Al,5.1Mg,2.1Li,0.17Sc,0.08Zr (wt %) alloy was subjected to ECAP at 325,°C to a total strain of ,8 using processing route CX. The operation time of this processing did not exceed 15,min. Subsequent IR at the same temperature with a total reduction of 88% was applied to produce thin sheets with a 1.8,mm thickness and an average size of recrystallized grains of ,1.6,µm. These sheets exhibit extraordinary high superplastic ductilities. In addition, this material demonstrated almost isotropic mechanical behavior at room temperature. The maximum elongation-to-failure of ,2700% was attained at a temperature of 450,°C and an initial strain rate of 1.4,×,10,2 s,1. Thus it was demonstrated that the two-step processing consisting of ECAP with a back pressure followed by IR was a simple technique providing potential capability for the fabrication of superplastic sheets from an Al,Mg,Li,Sc alloy on a commercial scale. [source] Tailoring Materials Properties by Accumulative Roll Bonding,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Tina Hausöl Accumulative roll bonding (ARB) as a method of severe plastic deformation (SPD) is an interesting established process to produce ultrafine-grained (UFG) sheet materials with high potential for light weight constructions. The ARB process offers a high flexibility for tailored material design. Al2O3 particles, carbon fibers and titanium foils are used as reinforcement of aluminum sheets introduced during accumulative roll bonding. Furthermore multicomponent materials are produced by cladding of different aluminum alloys. These sandwich-like structures allow to combine desired properties of the materials involved. Post-ARB heat treatment offers another possibility for tailoring materials properties of graded structures as shown by formation of TiAl3 in Al/Ti laminates. The tailored materials are investigated by means of SEM, EDX, nanoindentation experiments and tensile testing. [source] Global Techniques for Characterizing Phase Transformations , A Tutorial ReviewADVANCED ENGINEERING MATERIALS, Issue 6 2010Michel Perez To characterize phase transformations, it is necessary to get both local and global information. No experimental technique alone is capable of providing these two types of information. Local techniques are very useful to get information on morphology and chemistry but fail to deal with global information like phase fraction and size distribution since the analyzed volume is very limited. This is why, it is important to use, in parallel, global experimental techniques, that investigate the response of the whole sample to a stimulus (electrical, thermal, mechanical,). The aim of this paper is not to give an exhaustive list of all global experimental techniques, but to focus on a few examples of recent studies dealing with the characterization of phase transformations, namely (i) the measurement of the solubility limit of copper in iron, (ii) the tempering of martensite, (iii) the control of the crystallinity degree of a ultra high molecular weight polyethylene and (iii) a precipitation sequence in aluminum alloys. Along these examples, it will be emphasized that any global technique requires a calibration stage and some modeling to connect the measured signal with the investigated information. [source] Specific aspects on crack advance during J -test method for structural materials at cryogenic temperaturesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2006K. WEISS ABSTRACT Cryogenic elastic plastic, J -integral investigations on metallic materials often show negative crack extension values with respect to resistance curve J - R. According to the present ASTM standard, the use of unloading compliance technique relies on the estimation procedure of the crack lengths during the unloading sequences of the test. The current standard, however, does not give any specific procedure for treating such negative data. To date, the applied procedure uses the shifting of the negative crack extension values either to the onset of the blunting line or to the offset of the resistance curve. The present paper represents a solution of the negative crack length problem on the basis of a mechanical evaluation procedure of the unloading slopes. The achieved progress using this evaluation technique is demonstrated on different materials such as cryogenic high toughness stainless steels, low carbon ferritic steel and aluminum alloys from the series of 7000 and 5000. In addition, this work deals with the crack tunnelling phenomenon, observed for high toughness materials, and shows the reduction of this crack extension appearance by using electro discharge machining (EDM) side groove technique. The differences between EDM processed side grooves and standard V-notch machining have been investigated within these test series. [source] Hydrophilic and Antimicrobial Zeolite Coatings for Gravity-Independent Water Separation,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2005Abstract Condensing heat exchangers onboard manned spacecraft require hydrophilic fin surfaces to facilitate wetting and wicking of condensate to achieve gravity-independent water separation in the zero- or micro-gravity environment of space. In order to prevent the proliferation of microbes, the coating must also be biocidal. Here we show for the first time that zeolite,A and ZSM-5 coatings deposited via in-situ crystallization on stainless steel and aluminum alloys have excellent hydrophilicity, biocidal properties, and adhesion. Water contact angles below 5° were obtained on most substrates tested. When silver-ion exchange is carried out on the zeolite,A coating, it becomes highly antibacterial. This biocidal capability of zeolite,A is regenerative by repeated ion exchange. All coatings exhibit the highest rating of 5B as determined by adhesion test ASTM D-3359-02 (American Society for Testing and Materials). These properties, in addition to zeolite coating's low-temperature crystallization process and demonstrated corrosion resistance, make zeolite coatings advantageous over the current sol,gel coatings and well suited for use in condensing heat exchangers onboard manned spacecraft. [source] Electrochemical impedance spectroscopy analysis on aluminum alloys in EXCO solutionMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 5 2005F.-H. Cao Abstract Electrochemical impedance spectroscopy (EIS) of Al-Zn-Mg-Cu alloy in EXCO solution has been investigated. The results show that the impedance spectroscopy of the investigated electrode consists of two capacitive loops in the high and middle frequency domain respectively and an inductive loop in the low frequency domain at the first 30 h of immersion; the inductive arc disappears between 30 h and 60 h while it takes on at the low frequency domain at the last 36 h of the immersion time. A model based on the corrosion mechanism of the aluminum alloy and corroding morphology was proposed and applied to analyze the EIS results. [source] Verarbeitung hochfester Aluminiumlegierungen durch umformende VerfahrenMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 7 2009R. Neugebauer ECAP; rolling; extrusion; incremental forming Abstract Basierend auf experimentell ermittelten Werkstoffkennwerten wird ein Vergleich des Umformverhaltens der beiden Aluminiumlegierungen im Anlieferungszustand (EN AW-7075 T651) sowie im modifizierten Zustand (EN AW-7075 ECAP) bei der Verarbeitung mit herkömmlichen Umformverfahren (Walzen, Fließpressen) angestellt. Zudem werden die Verfahrensgrenzen des Umformgrades durch Variation der Werkzeuggeometrien experimentell lokalisiert. Dabei ist ebenfalls Untersuchungsgegenstand, den Einfluss des Verfahrens auf das Umformvermögen zu ermitteln. Davon ausgehend werden Werkzeugkonzepte entwickelt, die eine Umformung des hochfesten Aluminiums unter Erzeugung von hydrostatischen Druckzuständen in der Umformzone ermöglichen. Sowohl die Simulation als auch die Versuche zeigten Materialversagen der ultrafeinkörnigen Werkstoffe beim Fließpressen. Das Walzen als inkrementelles Umformverfahren ermöglichte hingegen eine schadensfreie Herstellung der Werkstücke. Forming of high-strength aluminium alloys A comparison of the forming behavior of both aluminum alloys in as-received condition (EN AW-7075 T651) as well as modified condition (EN AW-7075 ECAP) when processed with conventional forming processes (rolling, extrusion) is conducted on the base of experimentally determined material characteristics. In the following the process limits of the true strain are located by variegating the tool geometry. The influence of the manufacturing method on the plasticity is also a subject matter to analysis. Based upon the outcome of this analysis special tool conceptions are being developed, which allow the forming of highest-strength aluminum while creating hydrostatical pressure states in the deformed zone. Both simulation and experiments showed material failure of the ultra-fine-grained materials when extruded whereas rolling, being the incremental forming process, allowed damage-free manufacturing of components. [source] Validation of numerical codes for impact and explosion cratering: Impacts on strengthless and metal targetsMETEORITICS & PLANETARY SCIENCE, Issue 12 2008E. PIERAZZO When properly benchmarked and validated against observation, computer models offer a powerful tool for understanding the mechanics of impact crater formation. This work presents results from the first phase of a project to benchmark and validate shock codes. A variety of 2D and 3D codes were used in this study, from commercial products like AUTODYN, to codes developed within the scientific community like SOVA, SPH, ZEUS-MP, iSALE, and codes developed at U.S. National Laboratories like CTH, SAGE/RAGE, and ALE3D. Benchmark calculations of shock wave propagation in aluminum-on-aluminum impacts were performed to examine the agreement between codes for simple idealized problems. The benchmark simulations show that variability in code results is to be expected due to differences in the underlying solution algorithm of each code, artificial stability parameters, spatial and temporal resolution, and material models. Overall, the inter-code variability in peak shock pressure as a function of distance is around 10 to 20%. In general, if the impactor is resolved by at least 20 cells across its radius, the underestimation of peak shock pressure due to spatial resolution is less than 10%. In addition to the benchmark tests, three validation tests were performed to examine the ability of the codes to reproduce the time evolution of crater radius and depth observed in vertical laboratory impacts in water and two well-characterized aluminum alloys. Results from these calculations are in good agreement with experiments. There appears to be a general tendency of shock physics codes to underestimate the radius of the forming crater. Overall, the discrepancy between the model and experiment results is between 10 and 20%, similar to the inter-code variability. [source] Thermal vacancies and self-diffusion energy in 2024 Al-alloy by positron annihilation lifetime techniquePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009Emad A. Badawi Abstract Positron annihilation lifetime technique (PALT) is one of the most important nuclear non-destructive techniques. It was used to study the thermal vacancies in one of the most important engineering aluminum alloys , the 2024 Al-alloy. Quenching experiments were usually performed on thin specimens to ensure a uniform quenching rate throughout the specimen. The specimens were prepared with dimensions of 0.15 × 1.5 × 1.5 cm3. After grinding, polishing and etching, samples of 2024 were homogenized for 12 h at 673 K and annealed for 90-min., before being quenched in water (277 K). Positron lifetime measurements followed. From such measurements, it is possible to deduce the vacancy formation enthalpy, which in combination with the results of self-diffusion measurements, gives a value for migration enthalpy of the vacancy. These are very important quantities in the study of the annealing of irradiation induced defects. The use of the quenching technique in the positron annihilation study has the advantage that it allows a distinction between vacancy and dislocation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Economical Advantages of Low-Pressure Plasma Polymerization CoatingPLASMA PROCESSES AND POLYMERS, Issue 6 2005Hirotsugu Yasuda Abstract Summary: Low-pressure plasma polymerization coating, as described in this paper, is an ultimately green process that uses a minimum amount of substances and produces a minimum amount of effluent and hence does not require an environmental remediation process. The super-green aspect of the processing entirely changes the equation for the viability of the process in industrial applications. The main hampering factors for the low-pressure processes are 1) psychological fear of vacuum processes, 2) relatively high initial equipment costs, and 3) a lack of adequate cost estimate for the entire process. In many cases, the first two factors are enough for planners to shy away from this promising technology. However, when one examines the overall cost of processing as a whole, the cost of initial equipment often is not the decisive factor. Such cases are presented in the nano-film coating applied in corrosion protection of aluminum alloys, steel, and surface-state modification of contact lenses. The benefits of environmental friendliness, non-hazardous processing and superior performance of products that can be achieved only by low-pressure plasma polymerization coatings are more than enough to compensate the initial cost of the equipment. For nanofilm (20 nm) coatings, the most expensive annual operation cost is for wastewater treatment, which is much more than the initial cost of vacuum plasma polymerization reactor. [source] Experimental and theoretical investigation on the microstructure of aluminum alloys during extrusionPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Tobias Kayser The purpose of this work is the investigation of the material behavior of aluminum alloys during extrusion and cooling. In particular, the alloys of the 6000 series (Al,Mg,Si) and 7000 series (Al,Zn,Mg) are relevant here. Under the corresponding conditions, their behavior is controlled mainly by dynamic recovery during the extrusion and static recrystallization during cooling. For the development of a suitable material model EBSD measurements are done on different parts of an extruded Al6060 specimen. For this sample a microstructure picture is generated and a statistical analysis is performed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thermomechanical modeling and simulation of aluminum alloys during extrusion processPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Farhad Parvizian The purpose of this work is to simulate the microstructure development of aluminum alloys during hot metal forming processes such as extrusion with the help of the Finite Element Method (FEM). To model the thermomechanical coupled behavior of the material during the extrusion process an appropriate material model is required. In the current work a Johnson,Cook like thermoelastic viscoplastic material model is used. To overcome the numerical difficulties during simulation of extrusion such as contact problem and element distortion an adaptive meshing system is developed and applied. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||||||||