Aluminium Alloys 2006 - ICAA10

Volumes 519-521

doi: 10.4028/www.scientific.net/MSF.519-521

Paper Title Page

Authors: Yu.V. Milman, A.V. Byakova, A.I. Sirko, S. Gnyloskurenko, T. Nakamura
Abstract: Metal foams based on high-strength Al-Zn-Mg alloy are promising material for energy absorption application. The performance of coated calcium carbonate (CaCO3) as foaming agent for Alporas like route is studied in the present paper by comparison with the conventional titanium hydride (TiH2). Compressive response of the foams was examined and microstructure of cell wall was investigated. The advantages of CaCO3–foam are shown and discussed.
573
Authors: Vidar Hansen, Aferdita Vevecka-Priftaj, J. Fjerdingen, Y. Langsrud, J. Gjønnes
Abstract: Solid solution treatment at 450°C and 550°C and subsequent two step age hardening at 100°C and 150 °C up to 144 hrs. have been carried out for two conventional and four experimental 7xxx type of alloys with different Mg, Zn, Fe and Si content. The influence of silicon on phase and kinetics of age hardening zones and particles has been followed. Increase in silicon required higher solid solution temperature in order to achieve reasonable age hardening response. High silicon alloys, solid solution treated at high temperature, have tendency to recrystallize during aging. The GP-zone formation is affected by the ratio between Mg, Zn and Si. In alloys with Mg/Zn ratio in the range 1:2 GP(I)-type zones are formed, at higher solid solution temperature also GP(II); low Mg-content favor GP(II)- zones. In high silicon alloys GP-zones of b’’’-type (from the Al-Mg-Si) system contribute to age hardening. The precipitation kinetics of the main hardening phase h’, is influenced by the preceding GP-zone stage.
579
Authors: Brian M. Gable, Barry C. Muddle
Abstract: The ability to improve mechanical properties through trace alloying additions that enhance the precipitation-hardening response has been a cornerstone of aluminium research and alloy development. It is now known that many of these alloying additions are beneficial (or deleterious) because of their influence on the competitive precipitation kinetics, in many cases arising from the formation of chemical and structural heterogeneities in the matrix. In order to better our understanding of this phenomenon, the earliest stages of microstructural evolution of indium precipitates and θ' plates in an Al-Cu-In ternary alloy have been investigated. Quantitative microstructural characterization reveals that there is a correlation between the size of the pre-existing indium particle and the resulting heterogeneous precipitation kinetics, with larger indium particles favouring θ' precipitation.
585
Authors: Kate M. Nairn, Brian M. Gable, Rüdiger Stark, Natalie Ciccosillo, Anita J. Hill, Barry C. Muddle, Timothy J. Bastow
Abstract: Nuclear magnetic resonance (NMR) was used to systematically monitor the amount of copper in the matrix of various age hardenable Al-Cu alloys as a function of ageing treatment. These NMR results were used to compare the measured amount of copper residing in the matrix during microstructural evolution with that suggested from the equilibrium phase diagrams. Our results indicate that the matrix copper composition for under- and peak-aged microstructures is generally far from equilibrium, with much more copper in solution than expected based on equilibrium phase diagrams. NMR is shown to be a sensitive and efficient metallurgical characterization technique to monitor the partitioning of solute in both non-equilibrium and equilibrium phases.
591
Authors: Terence Kratzer, Brian M. Gable, Kate M. Nairn, Timothy J. Bastow, Barry C. Muddle, Anita J. Hill
Abstract: The effect of Si additions on vacancy behavior following solution treatment and quenching was studied for an Al-Cu-Mg-Ag alloy system using positron annihilation lifetime spectroscopy (PALS). Both the initial positron lifetime and steady state positron lifetime increase as the Si concentration increases. This behavior is interpreted in terms of Si interacting with vacancies, leading to their retention in the alloy. The ability of PALS to monitor vacancy behavior after solution treatment should allow the improved prediction of phase transformation kinetics and hence the tailoring of ageing treatments.
597
Authors: Alex Cho, Bernard Bès
Abstract: The effects of dispersoid forming elements on the mechanical properties of Al-Cu- Mg-Ag alloys are examined. It is found that a small amount of Zr addition is detrimental to the damage tolerance of Al-Cu-Mg-Ag alloys in artificially aged temper, while Mn addition is beneficial. The superior damage tolerance capability of Alloy 2139 is demonstrated by comparing it to other high performance alloys used for DT critical applications
603
Authors: R.G.S. Mussi, Tetsuichi Motegi, Fumi Tanabe, H. Kawamura, K. Anzai, D. Shiba, M. Suganuma
Abstract: The influence of an inclined cooling plate utilized as a modification in the compocasting process of aluminum alloy is studied in this paper. Based on the crystal separation theory, molten A356 is poured on the inclined copper plate in order to produce solidification nuclei inside the fluid metal, which is, then, mechanically stirred while reinforcement is added through its surface. Carbon nano fibers (CNF) and particulate SiC were utilized as reinforcement, in quantities varying from 0.5 to 15vol%. Dispersion of the reinforcements was observed by macro and microstructure analysis. For CNF, addition of quantities up to 1vol% resulted in homogeneous dispersion through the matrix, although SEM analysis showed the presence of clusters of up to 50μm in some points of the samples. SiC was properly mixed into matrix until 10vol%. Globular crystals were obtained, but some coarsening occurred, especially for small quantities of reinforcement. Utilization of the inclined cooling plate produced good inclusion and homogenization for two different reinforcements through an A356 matrix. The best results were obtained for a 180mm cooling plate, with inclination of 60o. The pouring temperature utilized was 10oC over the melting point of the alloy, and temperature of the tundish was kept around 598oC during stirring.
609
Authors: George E. Thompson
Abstract: The influence of alloying elements, deliberate or otherwise, and material processing on the performance of aluminium during surface treatment and finishing are considered. Thus, with a significant focus on copper, but with consideration of other elemental additions, the behaviour of aluminium during growth of oxide at ambient temperature, etching or pickling, conversion coating and anodizing, essential processes for generation of fit-for-purpose products, is highlighted. Further, such processes generate, modify or transform the initially present air-formed alumina film. Consequently, with knowledge of the phenomena proceeding at the alloy/film and film/environment interfaces and those within anodic or other films, the possibility of controlling features of nanoscale dimensions for improved performance arises. For example, deliberate selection of alloying elements enables control of nanotextures formed at treated surfaces, and formation of compositionally and morphologically modified films as well as generation of nanoparticles with various functional properties.
615
Authors: S.A. Kulinich, A.S. Akhtar, D. Susac, K.C. Wong, P.C. Wong, K.A.R. Mitchell
Abstract: Surface science methods including scanning Auger microscopy (SAM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy have been used to study the initial growth of chromate conversion coatings on aluminum 2024-T3 alloy, using a coating bath formed by dissolving CrO3, Na2Cr2O7 and NaF in water. The objective is to learn more about growth mechanism on the different microstructural regions of this alloy surface, including the second-phase particles and the alloy matrix.
621
Authors: A.J. Coleman, H.N. McMurray, G. Williams, Andreas Afseth, Geoff M. Scamans
Abstract: High levels of surface shear experienced during rolling, grinding or machining can cause 6000 series aluminium to develop an ultra-fine grained surface layers which dramatically increase susceptibility to filiform corrosion (FFC) under paint films. In-situ Scanning Kelvin Probe (SKP) measurements in humid air are used to compare the kinetics and mechanism of FFC on abraded and lacquer-coated samples of high copper containing AA6111 and low level copper AA6016. FFC is initiated by applying a small volume of aqueous HCl to a penetrative defect on polyvinylbutyral (PVB) coated alloy samples prior to placement in a chamber maintained at constant humidity and temperature. The SKP is then repeatedly scanned over a fixed surface area to produce a time-lapse animation showing the dynamic evolution of localized free corrosion potential patterns. The spatial distribution of potential variation provides insight into the FFC mechanism and the numerical integration of areas of dissimilar potential provides a measure of the time-dependent area of coating delamination. Various possible FFC inhibition strategies are investigated for use under circumstances where removal of the surface layer prior to application of an organic (paint) coating is not feasible. The two strategies shown in this paper are the use of an anti-corrosion pigments based on an intrinsically conducting polymer called polyaniline. An anion-exchange pigment called hydrotalcite is also used.
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