bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of Deformable-Adhesive Application on the Chip-Apply Process
Authors: Macedo Isabel , Oliveira Marta C. , Cardoso André
Published: March 2009

A study on the impact of batch-to-batch variability of a commercial wet adhesive on its plastic deformation behaviour is here presented. In the chip-apply process, a controlled and stable plastic deformation under thermal-mechanical compression is expected after the first of a two-step curing, named pre-cure. Wet adhesive batches rheological, mechanical and chemical characteristics are available but no information on deformation behaviour is provided. Different pre-curing recipes and oven atmospheres were tested and the plastic deformation was induced by applying pre-defined thermo-compression parameters. Results indicate that shorter pre-cure cycles at higher temperature, under air atmosphere, reduce batch-to-batch deformation variability. DSC curves support these findings. A correlation between deformation level and rheological properties could also be observed, which can be very useful in the triage of adhesive batches for specific process parameters
window.
Electrical and Microstructural Changes of β-PVDF under Uniaxial Stress Studied by Scanning Force Microscopy
Authors: Serrado-Nunes Jivago , Sencadas Vitor , Wu Ai Ying , Vilarinho Paula M. , Lanceros-Méndez Senentxu
Published: March 2009

Chain reorientation may be induced in polyvinylidene fluoride (PVDF) in its β-phase by applying a deformation perpendicular to the pre-oriented polymeric chains. This reorientation begins right after the yielding point and seems to be completed when the stress-strain curve stabilizes. As the deformation process plays an important role in the processing and optimisation properties of the material for practical applications, different deformation stress was applied to the
PVDF lamellas and their topographic change and piezoelectric response were studied by means of scanning force microscopy in a piezo-response mode.
The experimental results confirm the previously observed chain reorientation that occurs right after the yielding point and that is completed when the yielding region is passed. This reorientation is accompanied by a stretching of the granular structures observed in the topographical images and variations in the domain response. The observed results help to explain the variations in the macroscopic response of the material.
Space Charge Studies in XLPE from Power Cables Using Combined Isothermal and Thermostimulated Current Measurements
Authors: Carmo Lança M. , Neagu Eugen R. , Dissado Len A. , Marat-Mendes José N.
Published: March 2009

Cross-linked polyethylene (XLPE) peelings from aged power cables from three different sources were studied using a combined procedure of isothermal and thermo-stimulated current measurements. Different parameters, such as electric field, temperature, charging/discharging times, can be selected in order to make an analysis of the space charge characteristics (such as, relaxation times and activation energies). Three different cables peelings were analyzed: A – electrically aged in the laboratory at high temperature, B – service aged for 18 years and C – thermally aged in the laboratory at high temperature. The results were compared for the different types of samples and also with previous results on laboratory aged and produced films of low-density polyethylene (LDPE) and XLPE.
Effect of Poling on the Mechanical Properties of β-Poly(Vinylidene Fluoride)
Authors: Costa Carlos M. , Sencadas Vitor , Mano João F. , Lanceros-Méndez Senentxu
Published: March 2009

In this work, mechanical and thermal experimental techniques have been applied in order to relate the mechanical response with the microscopic variations of the material. Stress-strain results along the main directions of β-poly(vinylidene fluoride), β-PVDF, in poled and non-poled samples enables to investigate the influence of the poling process on the mechanical response of the
material. Further, differential scanning calorimetry experiments allow the investigation of the effect of poling in the degree of crystallinity of the material as well as on the stability of the crystalline phase. Thermogravimetric analysis was used to investigate the kinetics of the thermal degradation of poled and non-poled β-PVDF samples. The differences observed between the two materials suggest that the poling affects the mechanical properties of the material especially in the direction parallel to the polymeric chains and originates changes at a molecular level that remain beyond the
melting of the material.
Effects of Annealing on Phase Formation and Critical Current Density of Dip-Coated Tl0.5Pb0.5 Sr1.8Yb0.2CaCu2O7 Superconducting Tapes
Authors: Salleh Faizah Md. , Yahya Ahmad K. , Ismail M.H. , Jumali M.H.
Published: March 2009

In this study, single-core and multi-core Tl1212 tapes were fabricated from Tl-1212
superconducting powder of Tl0.5Pb0.5Sr1.8Yb0.2CaCu2O7 starting composition derived by
conventional solid state synthesis. Single core tapes showed maximum Jc and enhanced 1212 phase
formation were achieved for tapes annealed at a higher temperature for a longer duration. Multi
core tapes showed a general increase in Ic and Jc with the number of tapes core. The highest Jc of
521 A/cm2 was observed for the 4-core tapes annealed at 870 °C for 90 minutes. The initial drastic
drop of the tapes Jc in low magnetic fields (≤1T) indicates limitation on tapes performance by weak
links. The low Jc of the tapes may be due to the lack of texture in the tapes core as revealed by
SEM.
Structure and Surface Properties of Anatase TiO2 Thin Film by Sol-Gel Technique
Authors: Al-Jufairi N.
Published: March 2009

TiO2 coating films of 50-200nm thickness were prepared by the sol-gel technique using hydrolysis of titanium isopropoxide (TIP) in an attempt to study structure and surface properties of anatase at ambient temperature. The anatase phase is exhibited by the XRD peak at 2θ'=25o with orientation in (101), the crystal parameters of XRD for TiO2 thin films (50-200 nm), were varied depending on the thickness of film and substrate type. An annealing temperature and annealing time had an effect on the film surface quality and exhibit porosity and aggregates in the films. The surface of TiO2 thin film showed cluster particles through SEM and the shrinkage rate on the film increased as a result of heat treatment during annealing process. The film was uniform and homogeneous under AFM investigate. EDS have determined the stochiometric ratio of TiO2 film.
Magnetic Nanoparticles as Pinning Center in Bi-Sr-Ca-Cu-O/Ag Superconductor Tapes
Authors: Abd-Shukor R. , Yahya S.Y.
Published: March 2009

This paper reports on the effectiveness of magnetic nanoparticles as pinning center in
the Bi-based superconductor tapes. Nanosize γ-Fe2O3 and ultrafine Fe3O4 have been employed to
enhance the transport current density of Ag-sheathed-(Bi1.6Pb0.4)Sr2Ca2Cu3O10 superconductor
tapes prepared by the powder-in-tube technique. The transport critical current density, Jc of
(Bi1.6Pb0.4)Sr2Ca2Cu3O10-(γ-Fe2O3)0.01, sintered at the optimum temperature of 845 oC is 6490
A/cm2 when measured at 77 K. A further single intermediate rolling step increases Jc to 9560
A/cm2. Samples without γ-Fe2O3 prepared under the same condition showed a lower Jc with a
maximum of 1560 A/cm2. Similar results are also obtained for ultrafine Fe3O4. Magnetic
impurities generally suppress superconductivity. However, our study shows great promise of
magnetic nanorod γ-Fe2O3 and ultrafine Fe3O4 as novel pinning centers in enhancing the transport
critical density of Ag sheathed Bi-Sr-Ca-Cu-O superconductor tapes. This is in line with previous
calculations on frozen flux superconductor with magnetic nanoparticle as pinning centers.
Structural Studies of Potassium Hexatitanates Prepared under Hydrothermal and Solid State Conditions
Authors: Yahya Rosiyah , Hassan A. , Aiyub Z.
Published: March 2009

The structural studies of potassium hexatitanates prepared under both hydrothermal and solid state conditions were carried out. Fourier Transform Infra-red spectroscopy (FTIR) results revealed that potassium hexatitanate structure consisted of TiO6 octahedral units irrespective of the preparative conditions and particle size. X-ray diffraction (XRD) results showed that the only potassium hexatitanate phase was detectable and the structure is of the Wadsley-type consisting of chains of Ti-O octahedral sharing edges with tunnels in which the potassium ions are located. From scanning electron microscopy (SEM) results, the different preparative conditions resulted in different particle sizes and morphologies of the potassium hexatitanate formed.
Pinning Fermi Level of p-GaN due to Three Different (Zr, Ti, and Cr) Metal Contact
Authors: Tan C.K. , Aziz Azlan Abdul , Zainuriah Hassan , Yam F.K. , Lim C.W. , Hudeish A.Y.
Published: March 2009

The Current-Voltage-Temperature (I-V-T) characteristics of single layer deposition, consisting of Zr, Ti, or Cr/p-GaN Schottky diodes were determined in the temperature range 27- 100oC. Sputtering method was used for deposition of these metals on p-GaN. Analysis of the measured characteristics at room temperature allows the determination of the electrical parameters, the saturation current Io and the ideality factorη. The barrier heights and effective Richardson coefficients were determined through activation energy plot. It was found that pinning of Fermi level occurred for these metal contacts on p-GaN with the carrier concentration of 5.6x 1017 cm-3, where the Schottky barrier heights of Zr, Ti, or Cr/p-GaN are determined to be in the same range (~0.87eV).
Studies on the Corrosion Protection Property of Acrylic Resin Mixed with Curcumin and Dammar
Authors: Abidin Z.H.Z , Ramesh K. , Taha R.M. , Puteh R. , Arof A.K.
Published: March 2009

The corrosion protection property of the coating consisting of acrylic resin mixed with
curcumin and dammar was investigated by immersing in 3% NaCl solution using potential - time
measurement. The investigation was performed until corrosion occurred at the coating and substrate
interface. As the coating degraded the penetration of electrolyte, the potential value of the coated
sample decreases to a value of – 0.65 V. In this study the coating with pigment volume
concentration of KC30% can withstand against corrosion by 3% NaCl solution.
Investigation on Ag/Ti Ohmic Contacts to Si-Doped n-Type Al0.27Ga0.73N and the Effect of Post Annealing Treatments
Authors: Othman Surina , Yam F.K. , Haslan Abu Hassan , Zainuriah Hassan
Published: March 2009

In this study, we investigated the contact characteristics of bi-layer thin films, Ag
(200nm)/Ti (100nm) on Si-doped n-type Al0.27Ga0.73N film grown on sapphire substrate. The
contacts were annealed at different temperatures (400°C-800°C) for 10 min in N2 ambient. The
effects of cryogenic cooling immediately after heat treatment for improving ohmic behavior (I-V
linearity) of the samples were reported. Specific contact resistivity, ρc, was determined using
transmission line method (TLM) via current-voltage (I-V) measurements. Scanning electron
microscopy (SEM) measurements were carried out on the as-deposited, annealed (N), and
annealed-and-cryogenically (N+C) treated contacts where the surface morphology of each of these
conditions were compared. In addition, measurement of the samples by atomic force microscopy
(AFM) was taken in order to characterize the surface morphology.
Effects of Layer Thickness and Incident Angle Variations on DBR Reflectivity
Authors: Mahmoud Ahmed Naser , Hashim M. Roslan , Zainuriah Hassan
Published: March 2009

In this paper we discussed the relation between depth errors that happened in films growth and incidence angle variation on DBR reflectivity. We assume that there is 10% depth error in high and low index materials, and there are four plus one situations to be considered. Four are combinations of Hi +/- 10% error and Lo +/- 10% error, and no error. Our simulation results show that the depth error makes the reflective band shift and it almost doesn’t reduce reflectivity. The thickness error of +/- 10% in (Al0.4Ga0.6N/GaN) DBR structure (15 pairs) at 420nm was 42nm. A theoretical analysis using Transfer Matrix Mode with MATLAB software on the influence of layer thickness and incidence angle variation in vertical-cavity surface-emitting lasers with distributed Bragg reflectors (DBRs) on lasing wavelength is presented. It is shown that changing the thickness of the layers in the DBR mirror by only 10% is sufficient to produce shifts in the peak reflectance wavelength up to ± 20 nm (for a blue laser at 420nm). This could limit the precision of a desired wavelength, which is its reproducibility.
Characteristics of Paints Prepared from Lawsonia Pigment and Dammar from Dipterocarpus Grandifoleus
Authors: Abidin Z.H.Z , Taha R.M. , Puteh R. , Arof A.K.
Published: March 2009

In this work, lawsonia pigment obtained from Henna leaves was mixed with acrylic
resin and a mixture of acrylic and dammar resins (RD50%) to form two paint systems BC30% and
BDP30%. The two paint systems were characterized by potential-time measurements, impact
resistance, glass transition temperature (Tg) and cross hatch tests.
Silica -Titania Glass Fibers from Polytitanosiloxanes: Effect of Polymerization Mechanism on Mechanical Properties
Authors: Sopyan Iis
Published: March 2009

SiO2 -TiO2 glass fibers have been prepared via dry spinning of the viscous solutions of
polytitanosiloxanes followed by steam treatment and pyrolysis at 500, 700, and 900 °C for 1 h
under ambient condition. The polymer was prepared via polycondensation of partially hydrolyzed
tetraethoxysilane (TEOS) and an acetylacetone-chelated titan compound at various H2O/TEOS and
Si/Ti ratios. Gel fibers formed shown tensile strength as low as 200 MPa and increased around 3
times after pyrolysis. The higher degree of TEOS hydrolysis the higher tensile strength of the
fibers. The polymer with higher Si/Ti ratio also provided stronger fibers due to more extensive
siloxane network. Fibers with the highest tensile strength, 610 MPa, was obtained from the
polymer synthesized with SiO2/TiO2 mol ratio 20 and pyrolysis temperature 700 °C.
Epitaxial GaN Film Grown at Low Temperature by Hydrogen-Plasma Assisted MOCVD
Authors: Yam F.K. , Zainuriah Hassan , Ibrahim Kamarulazizi , Barmawi M. , Sugianto  , Budiman M. , Arifin P.
Published: March 2009

A comparative study of the structural and electrical properties of GaN films grown by
plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) at 700°C, with and
without AlN buffer layer is presented . Hydrogen plasma was used in addition to nitrogen plasma to
produce GaN. The introduction of H-plasma is found to influence the properties of the films.
Scanning electron microscopy (SEM), atomic force microscopy (AFM) and Hall Effect
measurements show that the sample with AlN buffer layer possesses a smoother and more
homogenous morphological characteristics as well as a lower background electron and higher Hall
mobility as compared to the sample without buffer layer. X-ray diffraction (XRD) reveals that
hydrogenation is capable of producing the epitaxial GaN films at reduced temperatures with the full
width at half maximum (FWHM) of the x-ray rocking (XRC) of GaN (0002) reflection was found
to be 54.8 and 256 arcmin for samples with buffer layer and without buffer layer, respectively.
Composition Dependent Resonant Raman Scattering in Al0.33Ga0.67As/InxGa1-xAs1-yNy Multiquantum Wells
Authors: Lazić S. , Calleja J.M. , Hey R. , Ploog K.
Published: March 2009

InxGa1-xAs1-yNy/Al0.33Ga0.67As multiquantum wells grown by plasma-assisted molecular beam epitaxy are studied by resonant inelastic light scattering. Sharp vibration modes have been observed at 323, 402, 454 and 501 cm-1. Their intensities resonate at the barrier bandgap reduced by the presence of N. Their resonance energies reveal the influence of the N concentration on the barrier gap at the multiquantum well interfaces. These peaks are interpreted in terms of local vibrations involving the pairing of N atoms, which seems to occur mostly at the quantum well interfaces due to preferential bonding of N to Al.
Magnetism of the Compounds in the Hf-Co Phase System
Authors: Belošević-Čavor J. , Congiu F. , Koteski V. , Cekić Bozidar , Concas Giorgio
Published: March 2009

Magnetization M as a function of applied magnetic field H up to 50 kOe was measured at low temperature T = 5K, using an SQUID magnetometer, for HfCo2 and Hf2Co intermetallic compounds. Both samples showed paramagnetic behaviour with a weak ferromagnetic contribution due to impurities (0.01-0.001 wt%). The values of the mass susceptibilities χ were deduced from the measurements. In addition, calculations using full-potential linearized augmented plane wave (FP-LAPW) WIEN 97 programme package were done, in order to check their agreement with the experimental results.
Structural, Electronic and Optical Properties of Some Oligo-Phenylenes
Authors: Radisavljević I. , Marjanović D. , Novaković N. , Ivanović N.
Published: March 2009

Using semi-empirical quantum mechanic (AM1, ZINDO/S) and ab-initio Hartree-Fock
(HF) calculations we investigated selected structural, electronic and vibrational properties of
phenylene-based oligomers from biphenyl P2P to para-sexiphenil P6P. Special attention is paid to
the interplay of electrostatic and conjugation effects on torsion barrier, energy gap, charge
distribution and selected vibrational modes, and their dependence on torsion angle and oligomer
size.
Optical Properties of PTCDA Bulk Crystals and Ultrathin Films
Authors: Vragović Igor , Scholz R. , Šetrajčić J.P.
Published: March 2009

Thin films and interfaces of crystalline organic dyes with semiconducting properties attracted a lot of attention in the last decade due to their numerous applications in electronics and optoelectronics. One of the most studied molecules is 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA); an archetypal organic material that can grow into multilayer films. Despite the great interest and intensive investigations, its optical properties are still not completely understood. The interpretations range from the Wannier-Mott exciton model to models of excitons of small radii. In the present work, we apply the Frenkel exciton model in order to describe the optical behavior of the solid phase of PTCDA, influenced by the transfer of excitations between different molecules. We are able to model the anisotropy of dielectric tensor, lineshape of the complex index of refraction, exciton dispersion and the large Stokes shift between absorption and photoluminescence, results of electron-energy loss spectroscopy, and photoluminescence transition energies and decay times. In addition, we made an extension of the model towards ultrathin PTCDA films.
Broadband Dielectric Spectroscopy of Inorganic Solids
Authors: Badot J.C.
Published: March 2009

This paper deals with the fundamental aspect of dielectric relaxations in conducting inorganic solids. It has been shown that it is possible to evidence dielectric relaxations due to charge carriers such as electrons (small-polarons) and ions, dipole reorientations (e.g. water molecules in hydrates) and to interfacial polarization phenomena (e.g. grain boundaries) in polycrystalline compounds. The importance of all these phenomena is discussed in relation to their possible interventions in dielectric spectra.
Low Temperature Synthesis of Nanocrystalline ZnFe2O4 Powders
Authors: Maletin Marija , Cvejić Željka , Rakić S. , Nikolić L.M. , Srdić Vladimir V.
Published: March 2009

Advances in nanoscale electronics require superior ceramic powders, preferable prepared
with techniques for the direct synthesis of crystalline nanoparticles. Zinc ferrite (ZnFe2O4)
nanopowders were prepared by co-precipitation method, from nitrate precursors. Crystalline
powders having the single-phase cubic spinel structure were directly synthesized at temperature
≥80°C in the presence of NaOH. The obtained powders are agglomerated with ultra-fine crystallites
having the average crystallite size about 3-4 nm.
Liquid Film Migration in Aluminium Brazing Sheet?
Authors: Wittebrood A. , Desikan S. , Boom R. , Katgerman Laurens
Published: March 2009

From literature and own observations it is known that the clad and core alloys that make up aluminium brazing sheet can show severe interaction during the brazing cycle. This interaction leads to a complete re-distribution of elements, changing essential properties like strength and corrosion resistance. This interaction has been reported many times but up to present time no clear explanation is given why this interaction is actually occurring. There are a number of publications addressing the circumstances under which the interaction is more severe. Chemistry and low levels of strain applied before brazing have a significant influence on the severity of the interaction. As a yet possible mechanism behind the interaction Liquid Film Migration is mentioned. The observations done so far are in line with this described mechanism but no ultimate proof has been given so far. The question why the interaction takes place cannot be answered yet, clearly a change of free energy of the system is involved but the mechanism or mechanisms behind the change is unclear.
Microstructure and Mechanical Properties of Fe-Containing Al-Alloys Processed by a Rheo-Diecasting Process
Authors: Fang X. , Shao G. , Fan Z.
Published: March 2009

Al-Fe compounds are usually present in the as-cast microstructure of Al-alloys as large needles or plates. As such, they have a detrimental effect on the mechanical properties of Al-alloys containing Fe, either as an impurity element or as an alloying addition. However, Fe-containing Al-alloys also offer attractive physical properties, such as improved stiffness, wear resistance and thermal resistance. If the needle and plate morphology of the Al-Fe compounds can be modified to a more compact morphology, with refined particle size and uniform distribution, the mechanical properties of Al-Fe based Al-alloys can be substantially improved, and therefore, they will find wider applications in many engineering sectors. A new semisolid metal processing technology, rheodiecasting (RDC), has been developed for production of Al-alloy components with high integrity. The RDC process innovatively combines the dispersive mixing power of the twin-screw mechanism, for the creation of high quality semisolid slurry, with the high efficiency, low cost nature of the high-pressure diecasting (HPDC) process for component shaping. In this paper, we present our experimental results on the effects of intensive melt shearing on the size and morphology of Al-Fe compounds in A380 alloys, with different levels of Fe additions. The experimental results have shown that intensive melt shearing during solidification can effectively change the particle shape from the usual needles and plates, to an equiaxed morphology. Samples which have undergone with melt shearing, exhibit much improved strength and ductility compared to those with the same level of Fe addition, but without exposure to melt shearing.
Influence of Surface Defect Geometry on the Localization and Failure of AA6111 Sheet: Necking versus Shear
Authors: Pilkey A.K. , Bayley C.J. , Györffy M.
Published: March 2009

The influence of surface defect geometry on the localization and failure behaviour of AA6111 sheet has been investigated through experimentation and numerical modelling. A series of uniaxial tensile samples were produced with idealized top and bottom surface defects (i.e. grooves), located either symmetrically or asymmetrically on the opposing surfaces. The symmetric arrangement corresponds to the “groove-like” initial imperfection of the classical Marciniak- Kuczyński (M-K) model. Experimental results indicate that both the symmetry of the defects and their wavelength have a profound effect on the resulting mode of localization and failure as well as on the limit strains. Specifically, symmetric surface defects are seen to induce localization and failure through simple necking, whereas asymmetric defects tend to promote macroscopic, throughthickness shearing. Furthermore, asymmetric surface defect geometries are found to produce lower limit strains in the AA6111 sheet under study for defect wavelengths below about 1.5 mm, while the reverse is true when defect wavelengths are above 1.5 mm. Finite element method (FEM) modelling simulations are also presented, demonstrating that the experimentally-observed trends in localization and failure behaviour can be replicated using a mixed isotropic-kinematic hardening implementation of the Gurson-Tvergaard-Needleman (GTN) material model.
Development of Oxide Film in Aluminium Melt
Authors: Huang Li Wu , Chen Yeong Jern , Shih Teng Shih , Hwang Lih Ren
Published: March 2009

Pure aluminum ingot (99.8 wt%) was melted to prepared chilled samples in this study. These samples were then removed to polish their surfaces and put in an ultrasonic cleaner filled with tap water. The polished surface would gradually show foggy marks after being subjected to a period of treating time. Oxide films, if entrapped, would crack, erode and detach from the chilled sample forming foggy marks on the polished surface. The sample then removed to measure oxygen and aluminum concentrations varied along the transition layer between the oxide film and aluminum matrix. Part of chilled samples was melted in a muffle furnace and subjected to different holding time. As the holding time increased, the transition layer between the oxide film and the matrix was increased and composed of different constituents varying from the Al matrix to the oxide film (mainly γ-Al2O3). This transition layer also showed different hardness measured by a nano-hardness tester. The morphologies of cracked oxide film and the eroded oxide particles were affected by the holding time after melted, and small amounts of silicon in the pure aluminum.
Microstructural Characterization of the Crystallization Sequence of a Severe Plastically Deformed Al-Ce-Ni-Co Amorphous Alloy
Authors: Kovács Zsolt , Henits P. , Zhilyaev Alexandre P. , Chinh Nguyen Q. , Révész Ádám
Published: March 2009

Discs of Al85Ce8Ni5Co2 amorphous alloy were severely deformed by high pressure torsion. Severe plastic deformation exceeding equivalent strain of 8.2 induces the formation of nanocrystalline fcc-Al in a more stable residual amorphous matrix. Calorimetric and X-ray diffraction measurements revealed that the deformed outer part of the disc crystallizes into a mixture of equilibrium phases during the first thermal event. However, in the amorphous ribbon the same crystalline mixture develops only after the second stage.
Modelling Heterogeneous Precipitation in 7xxx Aluminium Alloys during Complex Processing
Authors: Kamp Nicolas , Sullivan A. , Tomasi R. , Robson Joseph D.
Published: March 2009

A numerical model based on the Kampmann and Wagner method was
developed to predict the evolution of precipitate distribution in 7xxx aluminium alloy
during non-isothermal heat treatments. The model considers the nucleation, growth
and coarsening/dissolution of the metastable and equilibrium precipitate phases, η'
and η with their stochiometric composition, MgZn2. Constitutive model equations for
nucleation were based on the classical theory of nucleation whilst growth and
coarsening were treated using classical phase transformation theory. The transition
between η' and η, where η' acts as a precursor for η was also accounted for in the
model. Differential scanning calorimetry was used to calibrate the homogeneous
precipitation kinetics. The model also predicts the evolution of grain boundary
precipitates and their effect on precipitate free zone size. Jominy end quench tests
were performed to calibrate grain boundary precipitation kinetics. Precipitation on
dislocations and dispersoids was considered. The dislocation and dispersoid densities
were varied to represent different regions of a grain and therefore account for the
spatial distribution of preferential heterogeneous precipitation sites. Comparison
between the model prediction and experimental characterisation of the microstructure
evolution of a friction stir welded 7449 aluminium alloy was found to be reasonably
consistent.
Continuous Cooling Transformation (CCT) Diagram of Aluminium Alloy Al-4.5Zn-1Mg
Authors: Kessler O. , von Bargen R. , Hoffmann Fabian , Zoch H.W.
Published: March 2009

Age hardening is one of the most important processes to strengthen aluminium alloys. It usually consists of the steps solution annealing, quenching and aging. For heat treatment simulations as well as for the appropriate choice of quenching processes in heat treatment shops, knowledge of the temperature- and time-dependent precipitation behaviour during continuous cooling is required. Quenching should happen as fast as necessary to reach high strengths, but also as slow as possible, to reduce residual stresses and distortion. This optimal quenching rate of an aluminium component depends on its chemical composition, initial microstructure and solution annealing parameters as well as on its dimensions. Unfortunately continuous cooling transformation (CCT) diagrams of aluminium alloys do almost not exist. Instead isothermal transformation (IT) diagrams or given average quenching rates are used to estimate quenching processes, but they are not satisfying neither for heat treatment simulations nor for heat treatment shops. Thermal analysis, especially Differential Scanning Calorimetry (DSC) provides an approach for CCT-diagrams of aluminium alloys, if the relevant quenching rates can be realized in the DSCequipment. The aluminium alloy Al-4.5Zn-1Mg (7020) is known for its relatively low quenching sensitivity as well as for its technical importance. The complete CCT-diagram of 7020 with cooling rates from a few K/min to some 100 K/min has been recorded. Samples have been solution annealed and quenched with different cooling rates in a high speed DSC. The resulting precipitation heat peaks during cooling have been evaluated for temperature and time of precipitation start, as well as their areas as a measure for the precipitate amount. Quenched samples have been further investigated regarding their microstructure by light and electron microscopy, hardness after aging and precipitation behaviour during re-heating in DSC. The CCT-diagram correlated very well with the microstructure, hardness and re-heating results. A critical cooling rate with no detectable precipitation during continuous cooling 155 K/min could be determined for 7020. A model to integrate the CCT-diagram in heat treatment simulation of aluminium alloys is under development.
Historical Evolution of Thermomechanical Processes Applied to Aluminium Alloys
Authors: McQueen H.J.
Published: March 2009

Thermo-mechanical processing (TMP), coined 50 years ago for steels to describe combined thermal and mechanical treatments that define both product shape and microstructure/properties, has been practiced since the early industrial revolution. The improved function and control in mechanical shaping equipment were easily adapted to newly discovered aluminum, integrating hot forming, cold deformation and annealing. The TMP goals for Al alloys were grain refinement, substructure preservation, texture control and enhanced precipitation. Hot extrusion became widely employed with exploitation of elongated grains with substructure and strong texture and of press heat treatment (solution during deformation, quenching upon exit). Rolling schedules were tuned to generate desired grain size/shape, substructure and texture. This historical account aims to enhance application of metallography to process optimization and innovation that makes metals more competitive with other materials.
Recrystallization of AA1050 Studied by 3DXRD
Authors: Juul Jensen Dorte
Published: March 2009

By 3 dimensional X-ray diffraction (3DXRD) using high energy X-rays from synchrotron sources it is possible to study in-situ the nucleation and growth during recrystallization. In this paper it is described and discussed how 3DXRD can supplement EBSP measurements of nucleation and growth. Three types of studies are considered: i) orientation relationships between nuclei and parent deformed matrix, ii) recrystallization kinetics of individual bulk grains and iii) filming of growing grains in deformed single crystals.
Deformation and Recrystallization Behaviour of a Homogenised and a Heterogenised Al-Mg-Si Alloy
Authors: Morgenstern R. , Videm M. , Marthinsen Knut , Nes Erik , Furu Trond
Published: March 2009

The starting material, the deformed state, as well as the recrystallised microstructure and texture have been analysed as a function of Zener-Hollomon parameter and strain for two differently heat-treated AlMgSi alloys, deformed in torsion. An interesting and somewhat surprising observation is that the grain size was always higher in the material heat treated to form large Mg2Si particles. Moreover, no indications of PSN effects were observed in any of the materials, even at the highest Zener-Hollomon parameters. This observation was quite unexpected as the highest Zener-Hollomon parameters were well above the typical critical level for which significant PSN effects have been observed in similar alloys. The results have been carefully analysed and possible explanations are discussed.
An Investigation of Novel Spraycast Al-Mg-Li-Zr-(Sc) Alloys
Authors: Hogg S.C. , Palmer I.G. , Grant Patrick S.
Published: March 2009

This work describes the microstructure and properties of a range of Al-(4-6)Mg-
(1.2-1.6)Li-(0.3-0.4)Zr-(0-0.2)Sc alloys produced at Oxford University by spraycasting. Follow-
ing hot isostatic pressing of the as-spraycast billets to close any porosity and to precipitate a
¯ne, coherent dispersoid population, forging to a true strain of 1 at 250 and 400±C led to a
substantial re¯nement of the microstructure with grain sizes in the range 0.8 to 5¹m. A large
intra-granular orientation gradient with distance measured using EBSD showed that at 250±C,
partial dynamic recrystallisation by progressive lattice rotation led to a `necklace' structure of
very ¯ne grains surrounding larger deformed grains. At 400±C, dynamic recrystallisation oc-
curred by nucleation of new grains at prior grain boundaries and triple points. The strength
of as-forged alloys was 200-350MPa and the high ductilities of up to 30% rendered the alloys
amenable to post-forging cold work. A proof strength of 460MPa with 9.5% elongation was
achieved in a non-heat-treatable spraycast Al-6Mg-1.3Li-0.4Zr alloy, matching the best prop-
erties of similar mechanically alloyed AA5091, and exceeding the properties of AA7010-T74.
The as-forged alloys showed excellent thermal stability up to » 0.9Tm, with no abnormal grain
growth and grain size stagnation due to Zener pinning. Finally, strain rate sensitivity testing
revealed the potential for superplasticity at 400 and 500±C and strain rates of 0.001-0.05s¡1.
Recovery of Tensile Properties of AA5182 after Cold Rolling
Authors: Diak B.J. , Verlinden Bert
Published: March 2009

An experimental AA5182 sheet was cold rolled 80%, and tensile specimens removed with orientations 0, 45 and 90 degrees to the rolling direction. Room temperature monotonic tensile tests were performed on the specimens in different recovered states obtained by isothermal annealing at 230°C from 0.1 to 10h. The tests were instrumented to measure instantaneous plastic strain ratio, and unloaded just after incipient necking, but before failure if possible. With annealing the flow curves are characterized by lower strains to the onset of jerky flow, the reappearance of yield point elongation, decrease in work hardening, and increasing ductility. The recovery in substructure was described using a constitutive parameter proportional to the mean slip distance.
The Effect of Casting Variables on the Structure of Hypereutectic Al-Si Alloys
Authors: Faraji M. , Todd Iain , Jones H.
Published: March 2009

The effect of size refinement of primary silicon and modification of eutectic silicon,
separately and simultaneously, on microstructure of hypereutectic Al-20wt%Si has been
investigated under different casting conditions. Results showed that number per unit volume of
primary silicon particles was doubled by inoculation with 0.02% phosphorus in the alloy with
0.0015% phosphorus already in it, whereas 70% of a small ingot (40×35 mm) became modified
eutectic, and the formation of primary silicon was suppressed, on adding 0.1% strontium.
Simultaneous addition of phosphorus and strontium still refined the primary silicon but did not
modify the eutectic. Addition of strontium alone caused roughening of the primary silicon,
exemplified by increased undercooling registered on the cooling curve. Also crystallographic
relationships between polyhedral primary silicon particles have been investigated by Electron Back
Scattered Diffraction (EBSD).
Production of AA6082 Feedstock for Forming in the Semi-Solid State
Authors: Birol Yücel
Published: March 2009

Thixoforming offers the possibility of forming complex aluminum parts with a superior quality and a reduction of processing steps. The production of a fine, equiaxed, globular microstructure is essential for thixoforming. Strain Induced Melt Activation (SIMA) and the Cooling Slope (CS) casting processes were employed to produce AA6082 thixotropic feedstock in the present work.. SIMA process produces such a microstructure through recrystallization of heavily deformed billets and a subsequent heat treatment in the mushy zone. Molten metal with a suitable superheat is cast over a water-cooled, inclined metal plate into a permanent mould to produce the thixotropic billet in the CS casting route. The effect of cold work and heating temperature and time were investigated for the SIMA process where as the effect of CS length, casting temperature on the final microstructures were investigated for a fixed set of heating conditions in the CS casting route.
Through Process Modelling of Microchemistry in AA3103
Authors: Liu Cheng , Norman Andrew , van der Winden Menno
Published: March 2009

One of the challenges for the Aluminium industry is to reduce the costs and lead times of the development of novel alloys. This can be achieved by applying increasingly sophisticated models to predict the microstructures and properties of novel chemistries and processing routes. At Corus RD&T, several physically based microstructure models and one process model have been developed and integrated into a Through Process Model (TPM). The TPM presented here is constructed from microstructural sub-models that predict precipitation, work-hardening, recovery and recrystallisation. Furthermore, there is a finite difference based process model that predicts the local process variables like strain, strain rate and temperature. The final sub-model translates the predicted microstructures into product properties. In this paper the integrated model has been applied to the production chain of brazing sheet (AA3103) covering all steps from homogenisation to the braze cycle as applied by the manufacturers of for instance heat exchangers. The model predictions have been verified by comparing them to the results of full-scale a plant trial. Microstructure and mechanical properties were experimentally characterized and predicted at various production steps. Due to the limited space, here, only the results of the through process modelling on microchemistry are presented. Nevertheless it can be concluded that the (fully predictive) results of the models compare well with those found experimentally which opens up the option to use such models for alloy development.
Characterisation of Intermetallic Phases in Multicomponent Al-Si Casting Alloys for Engineering Applications
Authors: Chen C.L. , West G.D. , Thomson Rachel C.
Published: March 2009

Multicomponent Al-Si based casting alloys are used for a variety of engineering applications. The presence of additional elements in the Al-Si alloy system allows many complex intermetallic phases to form, which make characterisation non-trivial due to the fact that some of the phases have either similar crystal structures or only subtle changes in their chemistries. A combination of electron backscatter diffraction (EBSD) and energy dispersive X-ray analysis (EDX) have therefore been used for discrimination between the various phases. It is shown that this is a powerful technique for microstructure characterisation and provides detailed information which can be related to microstructure evolution during initial casting and subsequent heat treatment. The mechanical properties of different intermetallic phases have been investigated as a function of temperature using the nanoindentation technique. In particular, the hardness and modulus of a number of phases have been established for a range of alloy compositions. Physical properties of some of the intermetallic phases are also discussed. Phase identity, composition, physical and mechanical properties are set in context to inform alloy design strategies.
Mechanical Properties of Dispersion-Hardened P/M Al-Mn-Cu-Mg-Zn Alloys at Elevated Temperature
Authors: Adachi Hiroki , Osamura Kozo , Kusui Jun
Published: March 2009

In order to improve the high-temperature strength of an Al-Cu-Mg alloy, Mn was added at
supersaturation to form a high-density dispersion of an intermetallic phase. In the P/M Al-3.6Mn-
6.4Cu-3.6Zn-1.7Mg alloy (mass%), rod-like Al-Mn-Cu-Zn quaternary intermetallic phases (Q phase)
several hundred nanometers in length were dispersed in the matrix. The chemical composition of the
Q phase was determined by TEM/EDX to be 78.8Al-12Mn-8Cu-1.2Zn (at%). The crystal system,
space group, and lattice parameters of the unit cell were identified to be orthorhombic, Cmcm and a =
0.76, b = 2.11, c = 1.25 nm, respectively, by Rietveld analysis. Since the matrix of the alloy obtained
was of the Al-Cu-Mg-(Zn) system, age-hardening occurred by formation of a GPB zone at room
temperature and 448 K. At the peak level of age-hardening at room temperature, the tensile strength
at room temperature was 704 MPa, and the elongations were 8.0%. The high temperature strengths at
523 and 573 K were 319 and 141 MPa, respectively, and the elongations were 17 and 34%,
respectively.
Understanding the Compromise between Strength and Exfoliation Corrosion in High Strength 7000 Alloys
Authors: Marlaud T. , Baroux B. , Deschamps Alexis , Chemin J.L. , Hénon C.
Published: March 2009

The microstructural evolution has been investigated in three alloys of the 7000 series possessing increasing zinc contents by combining small-angle X-ray scattering, differential scanning calorimetry and transmission electron microscopy, in order to gain understanding on the evolution of the compromise between yield strength and corrosion resistance. We show that the three materials show qualitatively identical precipitation sequences; however the precipitated volume fraction is shown to increase in parallel to the Zn content. Moreover, the precipitate size evolution is faster in the high Zn alloy. The precipitate composition is inferred to vary in the three materials, and this difference is shown to explain the differences in calorimetric behavior, precipitation kinetics and corrosion resistance.
Precipitation Behaviour of Zirconium Compounds in Zr-Bearing Al-Mg-Si Alloy
Authors: Himuro Yoshiyuki , Koyama Katsumi , Bekki Yoichiro
Published: March 2009

In commercial aluminum alloys, Zr is recognized as an important additional element
improving their properties such as strength, corrosion resistivily, and so on. It forms very fine
particles of the metastable Al3Zr phase with L12 ordered configuration, in the case of alloys without
Si. On the other hand, the DO22-type (Al, Si)3Zr phase besides the L12-type Al3Zr phase is
precipitated in alloys including large amounts of Si, such as 6000 series. In this study the main
stress falls on precipitation behavior of these Zr compounds in a Zr bearing Al-Mg-Si alloy. The
Al-0.67Mg-0.97Si-0.37Zr alloy was cast into a metal mold and hot-rolled to a 5 mm thick plate. A
lot of fine L12-type Al3Zr particles were coherently precipitated in the matrix by aging the plate at
673K. The aged plate was cold-rolled to a 1 mm thick sheet and annealed at 553-813K, and then
microstructure was investigated by using a transmission electron microscope. It was realized that
fine coherent L12-type Al3Zr particles are transformed to incoherent and coarse DO22-type (Al,
Si)3Zr particles through recrystallization. The DO22-type (Al, Si)3Zr particles reduced recrystallized
grain size owing to their pinning effect.
Influence of Microstructure on Electrochemical Properties of Severely Deformed Al-5 wt% Cu Alloy by ECAP
Authors: Zhang Zuo Gui , Akiyama Eiji , Watanabe Yoshimi , Katada Yasuyuki , Tsuzaki Kaneaki
Published: March 2009

The influence of microstructure on the electrochemical properties of an Al-5 wt% Cu binary alloy which was severely deformed by equal-channel angular pressing (ECAP) has been investigated in a borate-boric acid buffer solution containing Cl¯ ions at pH 8.3 and 25°C by potentiodynamic polarization test. The anodic polarization results showed that pitting potentials of ECAPed Al-Cu alloy samples were higher than that of the sample without ECAP and increased with repetitive ECAP passes. The pitting corrosion attack of Al-Cu alloy samples took place in the surroundings of Al2Cu (θ) phase. It is considered that the grain refinement of θ phase and the solid solution generated in Al matrix during ECAP process are responsible for the improvement of the corrosion resistance of ECAPed Al-Cu alloy.
Mapping the Crystal Orientation Distribution Function to Discrete Orientations in Crystal Plasticity Finite Element Forming Simulations of Bulk Materials
Authors: Roters Franz
Published: March 2009

The crystal plasticity finite element method (CPFEM) is probably the method with the best potential to directly incorporate crystal anisotropy and its evolution into forming simulations. However, when it comes to the simulation of bulk materials, the representation of the crystal orientation distribution function (ODF), i.e. of the statistical texture, within the CPFEM framework becomes a key issue for the efficiency of the approach. In this work two different approaches for sampling the ODF are compared. The first is the so called Texture-Component-CPFEM, where the discretisation is based on the representation of the ODF by texture components. The second approach is based on the representation of the ODF by series expansion and uses a direct mapping of the ODF represented in the form of C-coefficients to individual orientations as needed by the CPFEM. Both methods are compared using the textures of Aluminum hot band as well as cold rolled material.
Modelling of Ductile Fracture in the Presence of Two Populations of Voids - Applications to Aluminium Alloys
Authors: Fabrègue Damien , Lassance D. , Pardoen Thomas
Published: March 2009

A micromechanical model has been developed in order to capture the influence of a
second population of voids on the coalescence of large primary voids. FE unit cell simulations have
been performed by introducing the primary voids explicitly in a finite element mesh and by using a
Gurson type model for the surrounding matrix in order to reproduce the influence of the second
population. These simulations have guided the development of a closed-form void coalescence
model. The new coalescence condition accounts for the softening introduced by the second
population by integrating the Gurson model based on an approximate solution for the stress and
strain field near the surface of the primary voids. The evolution of the primary voids is modelled
using an advanced Gurson model involving an evolution law for the void shape. The model is
applied to the prediction of the fracture strain of 6xxx aluminium alloys measured on smooth and
notched round bars. The model successfully captures, without any parameter adjustment, the
variation of the ductility as a function of the stress triaxiality for various shapes of the primary
particles and various volume fraction of second population.