bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative Study between Natural and Artificial Zeolites as Supports for Biosorption Systems
Authors: Tavares Maria Teresa , Quintelas Cristina , Figueiredo Hugo , Neves Isabel
Published: March 2009

This study aims the definition of a new material that may act as a robust and yet cost
effective biosorbent for treatment of wastewater with low concentration of heavy metals. A
comparative study was made between two biosorption systems composed of an Arthrobacter
viscosus biofilm supported on Cuban natural zeolites and on prepared NaY and NaX, in terms of
their ability to retain ionic chromium. The bacterium is able to reduce Cr(VI) to Cr(III) and, only
then, this smaller and positive ion may be entrapped in the zeolite cages by ion exchange. The first
support was tested in a continuous flow semi-packed bed column. The highest removal ratio, 42%,
was achieved for initial chromium concentration of 10 mg/L, but the best up-take, 5.5 mg/gzeolite,
was obtained for initial concentration of 70 mg/L. Biosorbents prepared with the same biofilm
supported in NaY and NaX zeolites were also considered in batch studies, with a typical kinetics of
biosorption processes, reaching 20% of initial chromium removal within an initial range of Cr(VI)
concentration between 50 and 250 mg/L. These last structures were characterized by spectroscopic
methods (FTIR and ICP-AES), surface analysis (DRX) and thermal analysis (TGA). All these
techniques indicated that the biosorption process does not modify the morphology and structure of
the FAU-zeolites.
Multifunctional Thin Film Zinc Oxide Semiconductors: Application to Electronic Devices
Authors: Fortunato Elvira , Gonçalves Alexandra , Marques António , Pimentel Ana , Barquinha Pedro , Águas Hugo , Pereira Luís , Raniero Leandro , Gonçalves Gonçalo , Ferreira Isabel , Martins Rodrigo
Published: March 2009

In this paper we report some of the recent advances in transparent thin film oxide
semiconductors, specifically zinc oxide (ZnO), produced by rf magnetron sputtering at room temperature with multifunctional properties. By controlling the deposition parameters it is possible to produce undoped material with electronic semiconductor properties or by doping it to get either n-type or p-type semiconductor behavior. In this work we refer our experience in producing n-type
doping ZnO as transparent electrode to be used in optoelectronic applications such as solar cells and position sensitive detectors while the undoped ZnO can be used as UV photodetector or ozone gas sensor or even as active layer of fully transparent thin film transistors.
Phase Transformation and Structural Studies of EUROFER RAFM Alloy
Authors: Paúl A. , Beirante A. , Franco Nuno , Alves Eduardo , Odriozola José Antonio
Published: March 2009

High temperature phase transformations in EUROFER reduced activation ferritic
martensitic (RAFM) steel were studied in-situ by means of X-ray diffraction. Results show that, during slow cooling, the austenite to ferrite transformation takes place around 755 oC. Full transformation of the austenitic phase into pure martensite is observed for cooling above 5 oC/min. This transformation was found in samples annealed at 950 oC for 3 h and quenched in liquid nitrogen. TEM analyses reveal a high concentration of carbides along the grain boundaries of the martensitic structure. The thermal expansion coefficient derived from the measurements was
12.7x10-6 K-1.
Photoluminescence Processes in the Triplet State of Phosphorescent Organic Materials: Ir(ppy)3 Doped in TPD
Authors: Aljaroudi Nadeer , Tsuboi Taiju
Published: March 2009

Photoluminescence (PL) measurements have been made for a spin-coated thin film of phosphorescent tris(2-phenylpyridine) iridium [Ir(ppy)3] doped in N,N’-bis (3-methylphenyl)-N, N’-bis(phenyl)-benzidine (TPD) host material in the temperature range from 10 K to room temperature. When temperature is increased from 10 K to 300 K, the PL intensity of Ir(ppy)3 increases from 10 K and decreases above about 200 K. Theoretical calculations are undertaken for the temperature dependence using (1) a three-level model where three zero-field splitting substates are generated in the triplet state of Ir(ppy)3 and (2) endothermic energy transfer from the TPD host to the Ir(ppy)3 guest, and (3) energy diffusion from the excited TPD to the neighboring unexcited TPD. A good agreement was obtained between the measured and calculated temperature dependences of the PL intensity.
Effect of Ru Substitution on Structural, Electrical Transport and Magnetoresistive of La2/3Ba1/3MnO3
Authors: Huda A. , Halim S.A. , Lim K.P. , Lee O.J. , Elias S. , Sidek A.A. , Hishamuddin Z.
Published: March 2009

Polycrystalline samples of La0.67Ba0.33(Mn1-xRux)O3 with x = 0, 0.05, 0.1, 0.15 and 0.2 have been prepared using solid state reaction. The effects of doping of Ru at Mn site on La-Ba-Mn- O ceramics, the characteristics and magnetotransport properties of CMR materials are investigated. The magnetoresistance (MR) effect is measured using the four point probe technique. The magnetoresistance defined as MR% = (Ro – RH)/RH x 100% was measured at a magnetic field of H ≤ 1T at 90K, 100K, 150K, 200K, 250K, 270K and 300K for the sample of doping x = 0, 0.05, 0.1, 0.15 and 0.2. Overall, MR drops slowly when temperature rises. All doping concentration gives small variation range (~2.7% to ~26.78%). The electrical property has determined by using standard four-point probe resistivity measurement in a temperature range of 30 K to 300 K. Metalinsulator transition temperature (Tp) shifted to lower temperatures as Ru doping is increased. In this paper the structural pattern and microstructure property have investigated via XRD. XRD patterns show that these systems are in orthorhombic distorted perovskite structures.
Electrical Characterization of the Grain-Boundary Region of SnO2 Varistors
Authors: Žunić M. , Branković Z. , Branković G. , Poleti D.
Published: March 2009

The effect of Co, Cr and Nb on the electrical properties of the grain boundaries of
SnO2-based varistors was investigated. The powders were prepared by the method of evaporation
and decomposition of solutions and suspensions. Varistor samples were obtained by uniaxial
pressing followed by sintering at 1300 °C for 1h. The electrical properties of the grain-boundary
region, such as resistance (R) and capacitance (C), were determined using ac impedance
spectroscopy in the 27-330 °C temperature interval. Activation energies for conduction (EA) were
calculated from the Arrhenius equation. The non-linear coefficients (α) and the breakdown electric
fields (Eb) of the samples were determined from the current-voltage characteristics. The potential
barrier height (Φb) was calculated using the Schottky-type conducting model. After a comparison of
the characteristic parameters for different varistor compositions it was found that the Cr/Nb ratio
has a crucial influence on the grain-boundary properties in SnO2 varistors.
Many-Body Calculations of Dynamic Polarizability, Refractive Index and Verdet Coefficient
Authors: Tančić A.R. , Davidović M.
Published: March 2009

Within the framework of the many-body theory by using the Random Phase Approximation with Exchange (RPAE) method we calculated the frequency dependent polarizability, refractive index, and Verdet coefficient of some atoms. Calculated time-dependent peculiarities of a set of atoms are very significant in the nano-region and might be important for designing new materials.
Molecular Modeling of New Dioxomolybdenum(VI) Complexes with Heteroalicyclic Dithiocarbamates. In Silico Models for Metal–Implant Coating within Living Systems
Authors: Sovilj S.P. , Drakulić B.J. , Stojić D.Lj. , Katsaros N.
Published: March 2009

A huge variety of nano-objects, allowing specific reactions at well-defined positions can
be generated using oxo-molybdenum compounds based building blocks and fragments. On the other
side, the use of suphur-based interfaces as metal-based organic materials is a new area with many
potential applications in medicine, particularly as implants. In that respect, as precursors for
building new materials with pronounced characteristics five new dioxomolybdenum(VI) complexes
of the general formula [MoO2(Rdtc)2] have been used in the present work. Their predicted
geometries optimized by the MO calculations are in excellent agreement with the reported crystal
structure data, and therefore can be used as models for docking study between complexes and
biomolecules. In silico screening for complex-protein interaction will be able to predict behavior of
such materials implanted in living systems.
Raman Spectroscopy of Hg1-xMnxSe Alloys: Part II
Authors: Milutinović A. , Romčević M.J. , Romčević N.Ž
Published: March 2009

In Part I of this paper, we used X-ray, far-infrared reflectivity and electron paramagnetic resonance measurements to investigate optical and magnetic properties of Hg1-xMnxSe (x≤0.26) alloys. In Part II, we expand our investigation to Raman spectroscopy and galvanomagnetic measurements. We registered two-mode behaviour of long wavelength optical phonons and described it by modified Genzel’s model. Except modes from the centre of Brillouin zone, there are some of forbidden modes in Raman spectra that originate from the edge of the zone, as well as a mode that corresponds to the maximum of phonon density of states. Modes of unalloyed α–MnSe are registered, too.
Plasma Coating and Surface Modification of Amorphous Carbon for Biomedical Applications
Authors: Maguire P.D. , Okpalugo T.I.T. , Ahmad I.
Published: March 2009

Amorphous carbon coatings for implantable medical devices require high mechanical
strength, adhesion and uniform biocompatibility response across the devices. Investigation of a-C:H
properties and structure variation with thickness and substrate material provides valuable insight
into requirements for device coating. A number of devices are coated and the effect of interfacial
layers, film doping and the spatial variation in quality is investigated.
Assessment of Damage and Fracture Behaviours in a Cast Aluminium Alloy via In Situ Synchrotron Microtomography
Authors: Yamamoto Shin , Toda Hiroyuki , Qian L. , Ohgaki Tomomi , Kobayashi Masakazu , Kobayashi Toshiro , Uesugi Kentaro
Published: March 2009

High resolution phase contrast imaging technique has been applied to obtain clear crack images together with the detailed of microstructural features in a cast aluminum alloy. Crack opening/closure, crack extension and damage evolution in the vicinity of a crack-tip is observed three-dimensionally (3-D). 3-D image analysis is performed to evaluate void initiation and growth near the crack-tip. The information on physical displacement of each microstructural feature is provided for analyzing local crack driving forces at crack front. This technique has been identified to provide a unique possibility to quantitatively interpret the 3-D cracking behavior in bulk materials.
Effect of Periodic Overloads on Fatigue Crack Propagation in Aluminium Alloys
Authors: Heidemann J. , Albrecht J. , Lütjering G.
Published: March 2009

The influence of variable amplitude loading on fatigue crack propagation was
investigated for two high purity versions of the alloy Al 2024 in sheet form, one with fine equiaxed
grains, and the other with coarse elongated grains. Fatigue tests on center cracked specimens were
conducted in vacuum at constant amplitude (R-ratio of 0.1) and with periodically applied single
tensile overloads with an overload ratio of 1.5. The number of intermittent baseline cycles between
consecutive overloads was varied (n=100 and n=10.000). Detailed fractographic investigations
were carried out for the identification of changes in the fracture surfaces due to the overloads.
Crack closure measurements were performed in all cases. The results revealed a strong influence of
the overloads on the crack propagation rate. Whether overloads are retarding or accelerating the
fatigue crack propagation depends on the crack propagation mechanism at constant amplitude
loading and the number of intermittent baseline cycles. For n=100 retardation occurred for the fine
grained alloy exhibiting homogeneous slip at constant amplitude while acceleration was observed
for the alloy with coarse elongated grains showing pronounced slip band fracture at constant
amplitude. For n=10.000, the formation of steps parallel to the direction of crack propagation by
overloads is assumed to be the reason for the observed increase in fatigue crack propagation
resistance resulting in retardation for both alloys compared to constant amplitude and n=100. The
influence of crack closure on the overload effects was minor. This was verified by additional tests
at R=0.5.
Mechanical and Corrosion Behaviour of the 2139 Aluminium-Copper Alloy Welded by the Friction Stir Welding Using the Bobbin Tool Technique
Authors: Alléhaux Delphine , Marie François
Published: March 2009

The present study deals with the properties assessment of a new generation aluminium-copper alloy,
developed by ALCAN and designed 2139, welded by the bobbin tool technique of the FSW
process. Considering the best performances of this age formable alloy after T8 aging, both the T4
and T8 tempers prior to welding are assessed. Therefore, the behaviour under static and fatigue load
conditions and also in damage tolerance including both fracture toughness and fatigue crack
propagation of the FSW bobbin tool weld on 2139 after T8 post aging and on the T8 as welded
condition are discussed. The corrosion resistance of the welds is investigated through an accelerated
corrosion test with intent to evaluate the intergranular corrosion sensitivity of the weld and the
impact of an artificial aging on the properties developed by the T8 as welded condition is also
presented.
Creep and Creep Rupture of FSW Joints of 5052 Aluminium Alloy Plates
Authors: Sugamata Makoto , Genei Masayuki , Kubota Masahiro , Kaneko Junichi
Published: March 2009

Creep and creep rupture tests were carried out for friction-stir-welded (FSW) joints of
5052 aluminum alloy plates at temperatures between 573 and 723 K. The results were compared
with those of the base metal. 5052-O plates of 20 mm in thickness were joined by FSW and round
bar creep specimens were machined out of the welded plates. Tensile tests were also conducted at
RT, 623 and 723K for both FSW joints and base metal. The tensile strength of the joints was almost
the same as that of the base metal at room and elevated temperatures. However, the FSW joints
showed appreciably higher minimum creep rate and shorter rupture time than the base metal at all
the tested temperatures and initial creep stresses. Creep rupture of the joints always occurred within
the plastically stirred zone with lower contraction of cross-sectional area. Thus, FSW joints of 5052
alloy plates showed lower creep strength than the base metal.
AluMATTER, a New Interactive e-Learning Tool
Authors: Hirsch Jürgen , Leroy Christian , Green Andrew
Published: March 2009

The web-based e-learning tool “AluMATTER” is presented which can be accessed under the
address “http://aluminium.matter.org.uk” and offers a new interactive course for students, engineers
or technicians to learn all about Aluminium science and technologies. The e-learning program
fulfils all distant learning requirements and intends to supplement regular teaching courses. It
allows users to access the material in a context relevant to their own requirements and background.
Structure and Properties of Mechanically Alloyed Composite Materials from Scrap of Al Alloys
Authors: Aksenov A.A , Samoshina M.E. , Belov Nikolay A.
Published: March 2009

The structure and phase composition of dispersion-strengthened composite materials based
on multicomponent aluminium alloys of the Al–Cu–Mg and Al–Si–Cu–Fe systems at various stages
of mechanical alloying were studied by the methods of optical, scanning electron and ion
microscopies, electron probe microanalysis and X-ray diffraction analysis. A possibility of the
efficient use of commercial scrap of Al alloy chips and initially large strengthening ceramic
particles as the base of composite materials was shown, as well as a possibility of synthesis of
strengthening particles during the treatment. After mechanical alloying, these materials possessed a
homogeneous and disperse structure, high hardness at room and elevated temperatures and a low
linear thermal expansion coefficient.
Neutron Diffraction Techniques for Alloy Characterization and Development
Authors: Gharghouri Michael A.
Published: March 2009

Important activities in the aluminum industry are the development of new alloys, and the
optimization of thermo-mechanical treatments to obtain desired performance. The strength and
formability of aluminum alloys depend on the distribution and scale of precipitating phases, on the
grain size and grain orientation distribution, on the distribution and scale of flaws, and on the
presence of residual stresses. Thus it is useful to have detailed quantitative data on the crystal
structures and volume fractions of phases that form during thermomechanical treatment, on the
kinetics of solid state reactions, on the distribution of grain orientations, and on the stresses that
develop during mechanical testing and forming. Neutron scattering is a powerful tool that can
provide unique data to guide the development of improved materials and processes. Of particular
interest are in-situ experiments: such experiments are uniquely suited to neutron diffraction because
of the high penetrating power of neutrons, which allows data to be collected from materials
subjected to realistic conditions (load, temperature, atmosphere) in specialized sample
environments. In this presentation, we discuss several examples of neutron scattering studies,
including residual strain mapping, in-situ loading experiments, texture analysis, powder diffraction,
and tomography.
Industrial Application of Through-Process Modelling II: Microstructural Models and Descriptors Required for Thermo-Mechanical Processing
Authors: Crumbach Mischa , Quested Tom , Hamerton Richard
Published: March 2009

Through-Process modelling (TPM) of microstructure evolution during thermomechanical
processing of sheet produced from direct chill (DC) cast non-heat treatable aluminium
alloys is discussed. In a companion paper [1] the upstream processes of casting and homogenisation
were dealt with, whereas the present paper focuses on the downstream deformation and annealing
steps. Some recent advances in relevant model development are reviewed, and the important
microstructural descriptors and their interactions are outlined. Together with two application
examples – coiling of hot strip, and cold rolling of foil – current knowledge gaps in theory and
modelling capability are highlighted.
A Heat Transfer Model for the Production of Semi-Solid Billets with the SEED Process
Authors: Colbert Josée , Bouchard Dominique
Published: March 2009

A heat transfer model was built to predict the temperature evolution of semi-solid aluminum billets produced with the SEED process. An inverse technique was used to characterize the heat transfer coefficient at the interface between the crucible and the semi-solid billet. The effect of several process parameters on the heat transfer coefficient was investigated with a design of experiments and the coefficient was inserted in a computer model. Numerical simulations were carried out and validated with experimental results.
Influence of Concurrent Precipitation on the Nucleation Kinetics during Recrystallisation in AA3003
Authors: Chen Shang Ping , Miroux A. , van der Zwaag Sybrand
Published: March 2009

A simple model for recovery of a subgrain structure is used to distinguish and explain the
respective influence of the deformed microstructure characteristics, annealing temperature and
concurrent precipitation kinetics on the nucleation kinetics of recrystallisation. Simulation results
demonstrate how the balance between recovery and precipitation kinetics controls nucleation.
The Grain Structures in some 5000 Series Aluminium Alloys after Asymmetric Rolling and Annealing
Authors: Jin Hai Ou , Lloyd David J.
Published: March 2009

The development of grain structures after asymmetric rolling (ASR) and annealing was
investigated in Al-Mg alloys AA5754, AA5182 and AA5083. It has been demonstrated that a fine
grain structure could be produced through continuous recrystallization, but it is strongly affected by
the presence of large second phase particles. In AA5754 the volume fraction of large particles is
relatively low and continuous recrystallization is able to occur throughout the sheet thickness,
resulting in a fine grain structure of 2μm mean grain size. In AA5182 the fraction of large particles
increases to a level that the continuous recrystallization occurs only in the sheet surface, whereas
the sheet centre undergoes discontinuous recrystallization. The discontinuous recrystallization due
to particle stimulated nucleation (PSN) is dominant in AA5083 so that no continuous
recrystallization has been observed. The fully recrystallized grain structure is slightly finer in the
ASR processed AA5083 than the conventionally rolled one.
Solidification Behaviour of 357 Al-Alloy under Intensive Forced Convection
Authors: Hitchcock Michael , Fan Zhong Yun
Published: March 2009

Solidification behaviour of 357 Al-alloy under intensive forced convection in the rheo-die-casting (RDC) process, was investigated experimentally to understand the effects of the intensity of forced convection and shearing time on the nucleation and growth behaviour. It was found that under intensive forced convection, heterogeneous nucleation occurred continuously throughout the entire volume of the solidifying melt. All the nuclei could survive due to the uniform temperature and composition fields created by the forced convection. This has been named as ‘effective and continuous nucleation’. It is also found that the nuclei grow spherically with an extremely fast growth rate. This makes the primary solidification essentially a slow coarsening process, in which Ostwald ripening takes place by dissolution of the smaller particles. In addition, it was found that intensive forced convection suppresses partially the formation of the primary phase, promote nucleation of the primary particles, and hinders the particle growth.
A Combined Numerical and Experimental Study of the Effects of Controlled Fluid Flow on Alloy Solidification
Authors: Steinbach Sonja , Dagner Johannes , Hainke Marc , Friedrich Jochen , Ratke Lorenz
Published: March 2009

A quantitative understanding of the effect of fluid flow on the microstructure of cast
alloys is still lacking. The application of time dependent magnetic fields during solidification offers
the possibility to create defined flow conditions in solidification processing. The effect of rotating
magnetic fields (RMF) on the microstructure formation in cast Al-alloys (Al-7wt.%Si, Al-7wt.%Si-
0.6wt.Mg) is studied experimentally and numerically. The forced fluid flow conditions result in
pronounced macrosegregation effects and affect microstructural parameters. With increasing fluid
flow the primary dendrite spacing decreases whereas the secondary dendrite arm spacing increases.
The experimental analysis is supported by a rigorous application of numerical modeling with the
software package CrysVUn.
CDS Method for Casting Aluminium-Based Wrought Alloy Compositions: Theoretical Framework
Authors: Apelian Diran , Makhlouf M.M. , Saha D.
Published: March 2009

A novel process named Controlled Diffusion Solidification (CDS) has been developed to
circumvent problems that are typically associated with casting wrought aluminum alloy
compositions into near net shaped components. The process involves bringing two precursor alloys
of precisely controlled composition, temperature, and quantity into intimate contact, and then
casting the resultant alloy using a conventional casting process to yield a component of predetermined
composition with a microstructure that is similar to that of semi-solid processed alloys.
Describing the many interactions that occur during solidification of aluminum alloys in a consistent
manner is virtually impossible without the use of computational tools that are based on
thermodynamic models. In this paper, we describe how the CALPHAD method, which allows
calculating all the necessary data from thermodynamic model parameters, was used along with
theoretical calculations and empirical rules to allow describing the Gibbs free energy of each phase
in the alloy system and yield quantitative data that guided the development and optimization of the
CDS method.
A Validated Through Process Model to Predict the Fatigue Life of a Cast A356 Automotive Wheel
Authors: Lee Peter D. , Li Pei Feng , Maijer Daan M. , Lindley Trevor C.
Published: March 2009

Models describing the critical steps in the manufacturing process of aluminum alloy
wheels were integrated with a model of in-service loading to predict component fatigue
performance. A multiscale solidification model was coupled with models of the subsequent heat
treatment and machining to predict the residual stress distribution in a finished wheel. A second
multiscale model was incorporated into a service model to relate the pore size and local stress state
to fatigue performance. The predictions resulting from this through process modeling approach
have been validated by comparisons with a series of measurements: 1) thermocouple measurements
during casting; 2) characterization of pore size and distribution using X-ray microtomography and
optical metallography; 3) residual strain measurements on finished wheels; 4) in-service strain
measurements during a rotating bend test; and 5) in-service fatigue performance during rotating
bend tests.
Direct Chill Casting of CLAD Ingot
Authors: Wagstaff Robert B. , Lloyd David J. , Bischoff Todd F.
Published: March 2009

Novelis Inc. recently released its first new innovative technology which
opens new opportunities in the clad aluminum product marketplace, where a combination
of mechanical and physical properties can be obtained which are superior to the
monolithic material alone.
Clad aerospace and brazing products are well known commercial products which
are provided by commercial roll bonding processes, but which can now be produced with
the new Novelis technology. This paper discusses the new technology, e.g., the casting,
fabrication, the properties of clad sheet are reported and it is established that the clad-core
interface is comprised of a high strength, oxide free zone. This technology enables a new
family of clad products with clad/core combinations which cannot be produced by the
conventional roll bonding process.
Role of Grain Refining in Macrosegregation upon Direct Chill Casting of AA 2024 Round Billet
Authors: Nadella Ravi , Eskin Dmitry G. , Katgerman Laurens
Published: March 2009

The addition of grain refiners during industrial direct chill (DC) casting of aluminum
billets promotes formation of smaller equiaxed grains with obvious advantages. However, the role
of grain refining in the extent of macrosegregation in DC cast Al alloys is still unclear. This is
particularly evident in the case of commercial aluminum alloys with various alloying elements. In
this work, the structure and associated macrosegregation patterns in DC cast AA 2024 (Al–Cu–Mg)
aluminum alloy billets were studied at different casting speeds. The concentration profiles of Cu
and Mg, measured along the billet diameter, showed an expected negative segregation in the center
and close to the surface. The severity of segregation increases at a higher casting speed. On the
other hand, grain refining does not seem to have any dramatic effect on the macrosegregation
patterns. The experimental results are correlated with microstructural observations such as grain
size and morphology and the occurrence of “floating” grains across the cross-section of the billet.
Work Hardening Behaviour of Heat-Treatable Al-Mg-Si-Alloys
Authors: Friis Jesper , Holmedal Bjørn , Ryen Øyvind , Nes Erik , Myhr Ole R. , Grong Øystein , Furu Trond , Marthinsen Knut
Published: March 2009

The work hardening of alloys hardened by precipitate heat treatments depends on the distribution of the precipitate sizes and the solute level left in the metal matrix. A mean field theory for precipitation is first applied for the ageing and subsequently it is coupled to a work hardening model to study the stress-strain responses of age hardened conditions of AA6xxx alloys. The predictions are compared to mechanical experiments and to TEM characterisations.
Hot Deformation Behaviour and Microstructure in Al-Cu-Li Alloy Containing Small Amount of Ag and Mg
Authors: Chen Zhi Guo , Zheng Zi Qiao , Han Dong Feng
Published: March 2009

The hot deformation behaviors and microstructure in Al-Cu-Li alloy containing small amount of Ag and Mg were investigated by transmission electron microscopy and isothermal compression tests.When the strain rate is 0.1, 0.01 and 0.001s-1(the deformation temperature within the range of 360-520􀀀 ) and 1 s-1(deformation temperature 520 􀀀 )respectively, the flow stress decreases after a peak value, showing dynamic recrystallization,while the steady-state flow characteristics exist on the other deformation conditions. The flow stress of Al-Cu-Li-Mg-Ag alloy during hot deformation can be expressed by a Zener-Hollomon parameter in the hyperbolic-sine function with the hot deformation activation energyDH of 250.45kJ/mol. The dislocations may climb with support from many vacancies generated during hot deformation, thus forming lots of helical dislocations. The dynamic precipitation and successive dynamic particles coarsening during hot compression have been assumed to be responsible for further flow softening when deformed at low strain rates.
Effect of Trace Addition of Sn in Al-Cu Alloy
Authors: Honma Tomoyuki , Saxey David W. , Ringer Simon P.
Published: March 2009

The trace addition of Sn (0.01 at.%) to an Al-1.7Cu (at.%) alloy has been investigated using atom probe tomography (APT), transmission electron microscopy (TEM) and high resolution transmission electron microscope (HRTEM). We have studied samples in the as-quenched (AQ) condition and following ageing at both 160 and 200 °C for very short ageing times so as to better understand the early stages of the decomposition processes. Our data reveal independent Cu-Cu and Sn-Sn clusters in the AQ condition, though we did not observe Cu-Sn clustering. We observed for the first time that some of these initial Cu-clusters develop into GP zones during subsequent ageing at temperatures as high as 200 °C. The Sn atom clustering results in precipitation of independent 􀀂- Sn particles after aging for 30 sec. The GP zones consequently undergo reversion and this liberates Cu atoms which seem to participate in a cluster-assisted heterogeneous nucleation of the 􀀃􀀂 phase at the interface of the 􀀂-Sn. For ageing at 200 °C, this process is complete within 180 sec.
Evolution of Nanostructure during the Early Stages of Ageing in Al-Zn-Mg-Cu Alloys
Authors: Liddicoat Peter V. , Honma Tomoyuki , Stephenson L.T. , Ringer Simon P.
Published: March 2009

During age-hardening of certain Al-Zn-Mg-Cu alloys, a 90% hardness increase can occur with 75 seconds. The clustering and precipitation of solute element species during this early rapid hardening (RH) period has been investigated through atom probe tomography, transmission electron microscopy, and Vickers hardness measurements. This study has focussed on the effect of copper by analysing three alloys; Al-2.0Zn-1.8Mg-0.7Cu, Al-2.0Zn-1.7Mg-0.2Cu and Al-1.9Zn-1.7Mg (at.%). The early RH reaction in these alloys accounts for up to 70% of the total hardening (peak hardness minus as-quenched hardness) and takes place during the first 60 seconds of ageing. We report preferred solute-solute interactions in the as-quenched materials. This quenched-in nanostructure acts as a template for subsequent solute clustering, the nature of which we have correlated with ageing.
Identification of Quasicrystalline Particles in an Isothermally Aged Al-10Mg-0.5Ag Alloy
Authors: Kubota Masahiro , Nie Jian Feng , Muddle Barry C.
Published: March 2009

The trace additions of Ag to binary Al-Mg alloys promote precipitation of a phase in the under-aged condition. The structure of the phase in an Al-10Mg-0.5Ag (mass%) alloy have been characterised using transmission electron microscopy and electron microdiffraction. An icosahedral quasicrystalline phase, which is identified by the electron microdiffraction patterns, has been found in the Al-10Mg-0.5Ag (mass%) alloy after solution treatment, water quenched and then aged during the time between 20 and 40 min. at 513K. The orientation relationship between the quasicrystalline phase and the a - Al matrix is as follows; i5 // <011>a and i3 // <111>a. A uniform distribution of finer-scale (typically 20 nm), faceted precipitate icosahedral quasicrystalline particles was observed within the core of the grains, but the precipitates became coarser (60-80 nm) approaching the grain boundary precipitate-free zone. The quasicrystalline particles contain elements of Al, Mg and Ag. The quasicrystalline precipitate particles, which are the metastable phase, appear to be the primary strengthening phase in the Al-10Mg-0.5Ag (mass%) alloy aged at 513K.
Monitoring the Evolution of the Matrix Copper Composition in Age Hardenable Al-Cu Alloys
Authors: Nairn Kate M. , Gable Brian M. , Stark Rüdiger , Ciccosillo Natalie , Hill Anita J. , Muddle Barry C. , Bastow Timothy J.
Published: March 2009

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.
The Effect of Alloying Additions on Vacancy Behaviour in Aluminium-Copper Alloys
Authors: Kratzer Terence , Gable Brian M. , Nairn Kate M. , Bastow Timothy J. , Muddle Barry C. , Hill Anita J.
Published: March 2009

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.
Corrosion and Protection of Friction Stir Welds
Authors: Davenport Alison J. , Jariyaboon Manthana , Padovani Cristiano , Tareelap Napachat , Connolly Brian J. , Williams Stewart W. , Siggs Eirian
Published: March 2009

The corrosion susceptibility of friction stir welds in AA2024-T351 was found to vary
with the weld processing parameters. Corrosion attack was investigated with in situ X-ray
tomography, which showed how the penetration of corrosion into the interior of the structure varied
with weld microstructure. The susceptibility to corrosion was related to the degree of overageing
by comparing the corrosion behaviour to samples of the base alloy that had been aged at different
temperatures. A systematic increase first in the anodic reactivity and then the cathodic reactivity of
the overaged structures with temperature can be used to predict the location of the region of the
weld with the highest susceptibility to corrosion. Similar investigations were made for a dissimilar
weld between AA2024 and AA7010. Laser surface melting produces a thin homogeneous melted
and rapidly solidified layer over the weld surface leading to a substantial improvement in corrosion
resistance.
Overview of Forming and Formability Issues for High Volume Aluminium Car Body Panels
Authors: Daniel Dominique , Guiglionda Gilles , Litalien Pierre , Shahani Ravi
Published: March 2009

Cost-efficient designs of aluminum autobody structures consist mainly of stampings
using conventional technology. Progress in metallurgy and forming processes has enabled
aluminum body panels to achieve significant market share, particularly for hoods. Fast bake
hardening alloys with better hemming performance were developed for improved outer panel sheet
products. Specific guidelines for handling and press working were established to form aluminum
panels using similar schedules and production lines as steel parts. Stamping productivity was
improved by optimization of the trimming process to reduce sliver/particle generation and resulting
end-of-line manual rework. Both hemming formability and trimming quality not only depend on
tooling setup but also on microstructural features, which govern intrinsic alloy ductility. Targets for
the next high volume aluminum car body applications, such as roof panels and doors, require higher
strength and/or better formability. The challenges of complex stampings can be met with optimized
alloys and lubricants, with improved numerical simulation to fine-tune stamping process
parameters, and with the introduction of new technologies. Warm forming was examined as a
potential breakthrough technology for high volume stamping of complex geometries.
Effect of Deformation Route and Sc and Zr Addition on Ultra-Fine Grain Formation and Superplasticity in Al-Mg Alloys
Authors: Kang Suk Bong , Kim Jae Woon , Kim Hyoung Wook
Published: March 2009

Recently the method for obtaining ultra-fine grained metallic materials has developed
using severe plastic deformation (SPD), such as equal channel angular pressing (ECAP),
accumulative roll bonding (ARB), torsion straining, and warm multiple deformation (WMD) etc. In
order to enhance thermal stability of ultra-fine grained aluminum alloys manufactured by SPD
process, the addition of Sc and Zr elements has been considered to devise fine Al3Sc, Al3Zr and
Al3(Scx Zr1-x) precipitates for inhibiting the grain growth. In this study, the microstructure evolution
has been investigated in Al-Mg alloys with and without Sc and Zr addition during the warm multiple
deformation process. In addition Al-Mg alloys were compressed at a strain rate of 10-1 sec-1 by two
different routes, that is, route A and route B. Route A is to rotate the specimen throughout 90o around
the vertical axis of loading direction at every pass. Route B is to rotate the specimen throughout 90o
around the parallel axis of loading direction and then rotate it again as route A. The specimen
deformed by route B had finer grain size and more uniform distribution of grains than those deformed
by route A. When the warm multiple deformation process repeated up to 8 passes at 673 K, the
specimen consisted of ultra-fine grained structure with the average grain size less than 3 μm. The
superplastic behavior can also be observed at the high strain rate and low temperature regime.
Numerical Analysis on the Extruded Volume and Length Ratios of Backward Tube to Forward Rod in Combined Extrusion Processes
Authors: Ham B.S. , Ok J.H. , Seo Jung Min , Hwang Beong Bok , Min K.H. , Koo H.S.
Published: March 2009

This paper is concerned with forward rod extrusion combined simultaneously with
backward tube extrusion process in both steady and transient states. The analysis has been conducted
in numerical manner by employing a rigid-plastic finite element method. AA 2024 aluminum alloy
was selected as a model material for analysis. Among many process parameters, major design factors
chosen for analysis include frictional condition, thickness of tube in backward direction, punch
corner radius, and die corner radius. The main goal of this study is to investigate the material flow
characteristics in combined extrusion process, i.e. forward rod extrusion combined simultaneously
with backward tube extrusion process. Simulation results have been summarized in term of
relationships between process parameters and extruded length and volume ratios, and between
process parameters and force requirements, respectively. The extruded length ratio is defined as the
ratio of tube length extruded in backward direction to rod length extruded in forward direction, and
the volume ratio as that of extruded volume in backward direction to that in forward direction,
respectively. It has been revealed from the simulation results that material flow into both backward
and forward directions are mostly influenced by the backward tube thickness, and other process
parameters such as die corner radius etc. have little influence on the volume ratio particularly in
steady state of combined extrusion process. The pressure distributions along the tool-workpiece
interface have been also analyzed such that the pressure exerted on die is not so significant in this
particular process such as combined operation process. Comparisons between multi-stage forming
process in sequence operation and one stage combined operation have been also made in terms of
forming load and pressure exerted on die. The simulation results shows that the combined extrusion
process has the greatest advantage of lower forming load comparing to that in sequence operation.
An Analysis on the Surface Expansion of Aluminium Alloys in Backward Can Extrusion Process
Authors: Ok J.H. , Hwang Beong Bok
Published: March 2009

This paper is concerned with the analysis on the surface expansion of AA 2024 and AA
1100 aluminum alloys in backward extrusion process. Due to heavy surface expansion appeared
usually in the backward can extrusion process, the tribological conditions along the interface between
the material and the punch land are very severe. In the present study, the surface expansion is
analyzed especially under various process conditions. The main goal of this study is to investigate the
influence of degree of reduction in height, geometries of punch nose, friction and hardening
characteristics of different aluminum alloys on the material flow and thus on the surface expansion on
the working material. Two different materials are selected for investigation as model materials and
they are AA 2024 and AA 1100 aluminum alloys. The geometrical parameters employed in analysis
include punch corner radius and punch face angle. The geometry of punch follows basically the
recommendation of ICFG and some variations of punch geometry are adopted to obtain quantitative
information on the effect of geometrical parameters on material flow. Extensive simulation has been
conducted by applying the rigid-plastic finite element method to the backward can extrusion process
under different geometrical, material, and interface conditions. The simulation results are
summarized in terms of surface expansion at different reduction in height, deformation patterns
including pressure distributions along the interface between workpiece and punch, comparison of
surface expansion between two model materials, geometrical and interfacial parametric effects on
surface expansion, and load-stroke relationships. It has been concluded from the present study that
the geometrical condition of punch is the most significant factor among the parameters employed in
this study. It is also known from the simulation results that the difference in surface expansion
according to different material properties is not more or less significant.
The Influence of Die Geometry on the Radial Extrusion Processes with AA 6063 Aluminium Alloy
Authors: Jang Dong Hwan , Ok J.H. , Koo H.S. , Lee G.M. , Hwang Beong Bok
Published: March 2009

The rigid-plastic finite element method has been applied to three variants of radial extrusion processes to investigate the influence of die geometry on the material flow into the flange gap. Case I involves forcing a cylindrical billet against a flat die, which is a single action pressing process. In case II, another single action pressing process, the upper punch forces a billet against a stationary punch recessed in the lower die. Both the upper and lower punches move together in Case III toward the center of billet at the same speed with a double action tool. Major process parameters are identified as the relative gap height and the die corner radius in constant relative deformation. The relative gap height is defined as the ratio of gap height to billet diameter. Extensive simulation work for various combinations of process parameter value has been performed and then the main characteristics of the deformation patterns of each case are observed to define the terms which represent the forming characteristics of the flange in radial extrusion processes in terms of separation height, asymmetric ratio of height, and asymmetric ratio of angle, respectively. The effect of major process parameters on the material flow into the flange gap has been also analyzed in terms of flange radius and flange angle. The effect of frictional condition on the separation height has been also analyzed to investigate the edge separation of flange from the flat die. AA 6063 aluminum alloy is selected as a model material throughout the analysis. Simple comparison between AA 6063 and AISI 1006 steel has been also made to investigate the effect of material selection on the deformation pattern, especially in terms of separation height in Case I and asymmetry in Case II, respectively.
Metal Dusting Reaction Mechanisms
Authors: Young David J.
Published: March 2009

Iron and nickel, model alloys of Ni-Cu and Fe-Cr, and commercial heat resisting alloys were exposed at 650-680oC to flowing CO-H2-H2O gases which were supersaturated with respect to carbon. All ferritic materials, including chromia and alumina formers, developed a coke deposit of carbon nanotubes, the growth of which was catalysed by nanoparticles of Fe3C. Austenitic materials formed graphite filaments and clusters in association with nanoparticles of austenite. Graphite cluster formation was suppressed by alloying copper with nickel. The sensitivity of coking kinetics to alloy copper content was consistent with a mechanism involving graphite nucleation within the subsurface metal. Chromia forming alloys resisted dusting until damage to the scale could no longer be repaired by Cr2O3 regrowth, and carbon gained access to chromium – depleted metal.
Environmental Effect of Hot Corrosion on Creep and Fatigue Failure of Thermal Barrier Coating Systems
Authors: Takahashi Satoru , Yoshiba Masayuki , Kakuta Wataru , Matsuoka Sayuri , Harada Yoshio
Published: March 2009

In order to clarify the failure behavior of plasma sprayed thermal barrier coating (TBC)
systems under the complicated modes of thermal-mechanical-chemical loadings, the stress rupture
property evaluation and failure analysis were conducted for Y2O3-ZrO2 (YSZ) and CaO-SiO2-ZrO2
(C2S-CZ) TBC systems in air and two kinds of high-temperature corrosive environments.
Static creep loading was found to bring about the typical creep failure for TBC systems even in the
aggressive environment so called hot corrosion almost in similar manner to the case in air. On the
contrary, it was revealed that the dynamic fatigue loading tends to cause a significant failure life
reduction of TBC systems both in air and in corrosive environments. For YSZ TBC system, the
penetration crack preexisting through the top-coat layer tends to provide a nucleation site for the
fatigue crack even in air, and more significantly a short circuit path for the corrosive species in hot
corrosive environment. For C2S-CZ system, on the contrary, the top-coat / bond-coat interface tends
to provide easily the nucleation site for a main crack to propagate thereafter toward both the alloy
interior and outer surface. Under lower stress level at 950°C, however, the oxide-induced crack
closure together with crack tip blunting attributed mainly to the high reactivity of Ca compounds as a
major constituent of the TC is effective to suppress substantially the crack propagation, so as to cause
the prolonged failure life as compared to YSZ system even in aggressive gaseous environment.