bluuebunny/crossref_metadata_2025 huggingface dataset:
High Temperature Tensile Behaviour of the A354 Aluminum Alloy
Authors: Ceschini Lorella , Jarfors Anders E.W. , Morri Alessandro , Morri Andrea , Rotundo Fabio , Seifeddine Salem , Toschi Stefania
Published: June 2014

The high temperature tensile behaviour of the A354 casting aluminum alloy was investigated also evaluating the influence of secondary dendrite arm spacing (SDAS). Cast specimens were produced through a gradient solidification equipment, obtaining two different classes of SDAS, namely 20-25 µm (fine microstructure) and 40-50 µm (coarse microstructure). After hot isostatic pressing and T6 heat treatment, the samples underwent mechanical characterization both at room and high temperature (200 °C). Results of tensile tests and hardness measurements were related to the microstructural features and fractographic characterization, in order to investigate the effect of microstructure and high temperature exposure on the mechanical behaviour of the alloy.
Solution Strengthening of Various Elements in Aluminium Alloys
Authors: Liu Zhen Shan , Mohles Volker
Published: June 2014

In the aluminium wrought alloys, the solid solution strengthening is one of the dominant hardening mechanism. Every solute element shows different strengthening effect. In present work the strengthening effect of different elements in a large temperature range was studied with the microstructure and flow stress model 3IVM+. This model was developed for cell forming metals, in which the work hardening and softening effects due to interaction of dislocation densities are taken into account. Compression tests for various binary aluminium alloys (Al-Mg, Al-Mn, Al-Si) were carried out under various deformation temperatures and strain rates. The contribution of each element to solution strengthening was investigated with 3IVM+. It was found that the dislocation interaction, especially cross slip and climb, is sensitive to the solute type and concentration.
Effects of Zn Addition and Aging Condition on Serrated Flow in Al-Mg Alloys
Authors: Matsumoto Katsushi , Aruga Yasuhiro , Tsuneishi Hidemasa , Iwai Hikaru , Mizuno Masataka , Araki Hideki
Published: June 2014

The serrated flow phenomena in Al-Mg alloys with and without Zn were investigated after aging on several conditions, focusing on the role of precipitates. Al-6mass%Mg-0~3mass%Zn alloys were solution treated at 753~803K, quenched, and then aged at room temperature. Further artificial aging at 323~573K for 86.4ks was performed for some of them after natural aging for 2.6Ms. The serrated flow behavior was evaluated by tensile test. Microstructure was characterized by differential scanning calorimetry, transmission electron microscopy, atom probe tomography, and positron annihilation lifetime spectroscopy. The increase in the amount of Zn addition and the natural aging time lead to a delayed onset of serrated flow. The artificial aging at higher temperatures after natural aging, on the other hand, decreases the onset strain. A large number of small coherent Zn-Mg clusters are formed during natural aging in the Al-Mg-Zn alloys, which are transformed to the larger incoherent meta-stable precipitates during subsequent artificial aging. These results suggest that the mechanism of interfering with serrated flow is related to the vacancy trapping effect, which is enhanced by the coherent clusters.
Mechanical Performance of a Cast A354 Aluminium Alloy
Authors: Sandoval J.H. , Mohamed Adel M.A. , Valtierra S. , Samuel F.H.
Published: June 2014

Cast aluminum alloys are an important group of materials which find wide application in the automotive industry. Insufficient studies have been carried out to date with regard to the mechanical performance of the aged A354 alloy. Therefore, the present work investigates the Quality index charts with the purpose of setting the limits of the tensile properties, as well as for comparing the mechanical behavior of cast alloy A354, to delineate the effect of the solution treatment applied. Tensile properties upon artificial aging in the temperature range of 155–350oC for times ranging from 2 to 100 hours are also investigated. The results showed that the use of quality index charts is a satisfactory method for presenting tensile test results and, for assessing the effect of solution and aging treatment conditions subjected to the modified and grain-refined A354 alloys. It is also observed that the quality index, Q, is more sensitive to variations in the tensile ductility than to tensile strength.
Correlation between Supersaturation of Solid Solution and Mechanical Behaviour of Two Binary Al-Si-Alloys
Authors: Schumacher Philipp , Reich Michael , Mohles Volker , Pogatscher Stefan , Uggowitzer Peter J. , Milkereit Benjamin
Published: June 2014

Cooling of age-hardening Al-alloys after solution annealing is a critical step with respect to distortion and residual stresses. In order to predict their extent by simulation models, the mechanical behaviour must be known in a wide range of conditions and compositions. Therefore, experimental data is needed both for calibration and validation of the mechanical model. It is known for Al-Mg-Si alloys that supersaturation of the solid solution leads to a significant increase of strength during cooling. In order to understand the influence of single alloying elements on the strengthening effect, the mechanical properties of different binary alloys are investigated experimentally. The precipitation behaviour during cooling was investigated by Differential Scanning Calorimetry in a wide cooling rate range. A methodology to determine the degree of supersaturation of the solid solution based on the calorimetric results is presented. This approach is compared to atom probe tomography data. The mechanical behaviour of the alloys after various heat treatments was analysed by mechanical tests performed in a quenching and deformation dilatometer. Flow curves with high resolution at small strains (< 3 %) were measured at different temperatures. The results of the different experimental techniques are discussed in comparison and with respect to their testing limitations.
A New Wheel Design for Reducing Weight
Authors: Perrier Frédéric , Bouvier Véronique , Duperray Lionel
Published: June 2014

Reducing weight is one of the most important challenges in the automotive industry. A wheel design which enables to reduce weight from 13.5 kg to 10 kg is presented. This achievement is possible thanks to the use of a wide variety of technical processes. The disc is manufactured by CobapressTM, a casting/forging process which combines the advantages of a high design freedom, good mechanical properties and the absence of porosities. The alloy used is an A356 aluminum alloy modified with strontium. The rim is made of an AA6082 aluminum alloy which is extruded and flow-formed with a thickness from 3.3 down to 2.2 mm. Finally, the FSW (Friction Stir Welding) allows us to weld the two parts with a cavity to minimize the weight. With this technique the welding of the two different alloys is possible with good mechanical properties, the fracture happens outside of the weld during tensile tests. The final wheels passed bending and radial fatigue tests as well as radial impact tests with success.
Numerical Study on the Influence of Crystallographic Texture and Grain Shape on the Yield Surface of Textured Aluminum Sheet Material
Authors: Saai Afaf , Hopperstad Odd Sture , Dumoulin Stéphane , Tabourot Laurent
Published: June 2014

The paper investigates by numerical modeling the effects of crystallographic texture and grain shape on the shape of the yield surface of aluminum sheet material at small strains. Different representative volume elements (RVEs) of the material are considered. Plane stress state is assumed in the sheet. A rate-dependent model of crystal plasticity (CP) is used in combination with either the full-constraint (FC) Taylor model or the finite element method (FEM) to compute the volume averaged stress of the material. The effect of different crystallographic textures observed in aluminum alloys on the shape of the yield surface is firstly investigated. An analytical yield function is used to generate yield surfaces for the different crystallographic textures. The deviation between the stress states at yielding computed by FC-Taylor model and the analytical yield surface is used to evaluate the capability of the yield function to fit the anisotropic yield surfaces representing different strong crystallographic textures. Two different shapes of the grains are introduced in the RVEs of CP-FEM in order to study the effect of the grain morphology. Small effects of grain shape are found at small strain compared with the marked influence of crystallographic texture.
Experimental Detection of the Onset of Local Necking in an Aluminium Sheet
Authors: Vysochinskiy Dmitry , Coudert Terence , Hopperstad Odd Sture , Lademo Odd Geir , Reyes Aase
Published: June 2014

Forming limit diagrams (FLDs) are widely used to assess metal sheet formability. Experimental FLDs are obtained by performing formability tests and determining failure strains. The standard method for detection of forming limits is based on the spatial distribution of the strains and requires formation of a single local neck. Some aluminium alloys, such as AA6016, have a tendency to form multiple strain localizations in formability tests, which can be interpreted as multiple local necks. Thus, use of the standard method is questionable for these aluminium alloys. The present paper presents an alternative, digital-image-correlation-based method for experimental detection of the onset of local necking in an aluminium sheet. The method is based on monitoring the sheet-thickness evolution, and is developed to be user independent and resistant to noise in the measurements. The method can be used in combination with different types of formability tests. The main requirement is that digital image correlation is used for strain measurements. Here, the method is initially tested on uniaxial tension tests of AA6016 aluminium alloy sheets and then extended to formability tests.
A New Diffusivity Database for Multi-Component Al Alloys: Focusing on Ternary Systems and its Effect on Microstructure Evolution during Solidification
Authors: Zhang Li Jun , Liu Dan Dan , Zhang Wei Bin , Wang Shao Qing , Tang Ying , Ta Na , Wei Ming , Du Yong
Published: June 2014

A new atomic mobility database for Fcc_A1, L12, Bcc_A2, Bcc_B2, and liquid phases in the Al-Cu-Fe-Mg-Mn-Ni-Si-Zn system has been established via a hybrid approach of experiment, first-principles calculations and DICTRA (DIffusion Controlled TRAnsformation) software, focusing on the atomic mobility parameters in ternary systems. Various diffusivities can be computed as a function of temperature and composition. The reliability of this diffusivity database is further validated by comparing the calculated and measured diffusion properties in a series of ternary and quaternary diffusion couples, including concentration profiles, diffusion paths, interdiffusion fluxes, and so on. The effect of the diffusivity database on microstructure evolution during solidification is demonstrated by the phase field simulation of primary (Al) grains in Al356.1 alloy. The simulation results indicate that such accurate diffusivity database is highly needed for the quantitative simulation of microstructural evolution during solidification.
Determination of a Simple Geometry for the Characterisation of the Energy Absorption Behaviour of Cast Aluminium
Authors: Hartmann Matthias , Anders Kevin
Published: June 2014

Aluminium cast products are becoming more and more interesting for energy absorbing applications, as a higher functional integration can be achieved with casting processes. Therefore, it is required to find a way to characterise different aluminium alloys regarding their energy absorption behaviour.
Energy absorption phenomena in materials depend on the combination of material and geometry on a macro scale level. One of the main contributions of the current research work is to show that the full realization of material absorbing capacity may not be achieved by more complex geometries. Consequently, for the characterisation of cast material under crash load, it is very important to keep the geometry influence on the energy absorption behaviour as low as possible. The ultimate aim herein is to determine an optimised geometry setup to characterise different aluminium casting materials.
Three different test geometries were chosen for numerical investigations. All specimens possess the same cross-sectional area and also the same second moment of inertia. The specimens have been tested under an axial crash load at constant speed. Failure has been simulated using a Johnson-Cook damage and failure model.
Their absorbing behaviours will be compared and based on the existing literature a theoretical discussion about the geometrical influence will also be given.
Interfacial and Strain Energy Analysis from Ab Initio Based Hierarchical Multi-Scale Modelling: The Al-Mg-Si Alloy β'' Phase
Authors: Ehlers Flemming J.H. , Dumoulin Stéphane , Marthinsen Knut , Holmestad Randi
Published: June 2014

Precipitate-host lattice interface studies have not traditionally been viewed as requiring hybrid model schemes for accurate determination of the interfacial and strain energies. On the other hand, the interfaces of main hardening precipitates of age hardenable alloys are often characterized by both high levels of coherency and considerable subsystem misfits. Near the interface, linear elasticity theory evidently fails in such cases to fully correctly predict the subsystem strains. Further, density functional theory based studies on isolated supercells may prove inadequate in capturing strain influences on the chemical interactions underlying the interfacial energy. Recent work within the group has focussed on the implementation of a first principles based hierarchical multi-scale model scheme, capable of determining the interfacial and strain energies for the same model system. Choosing the fully coherent Al-Mg-Si alloy main hardening phase β'' as our test system and limiting our studies to 2D, we discuss the variation in these energies with changing precipitate cross-section morphology and size.
Material Flow and Grain Deformation during Extrusion
Authors: Mahmoodkhani Y. , Wells Mary A. , Grajales Lina , Poole Warren J. , Parson Nick C.
Published: June 2014

A combination of numerical simulation using the finite element method (FEM) and experimental characterization was used to study material flow and grain deformation during the hot extrusion process for an AA3003 aluminum alloy. The grain structure of the extrudate was experimentally studied using optical microscopy and Electron Back-Scattered Diffraction (EBSD) methods. Using the FEM model predictions of material flow, a simple procedure was used to predict the spatial variation of grain thickness both through the extrusion and along its length. Experimental measurements using EBSD of the grain thickness at the center of the extrudate show that the model predictions are in good agreement with the measurements. The model was then used to calculate the grain thickness changes along the extrudate.
Modelling the Combined Effect of Room Temperature Storage and Cold Deformation on the Age-Hardening Behaviour of Al-Mg-Si Alloys-Part 1
Authors: Myhr Ole Runar , Schafer Carmen , Grong Øystein , Engler Olaf , Brinkman Henk Jan , Hirsch Jürgen
Published: June 2014

In the present paper, an extended age hardening model for Al-Mg-Si alloys is presented. In this new approach the combined precipitation, yield strength and work hardening model, known as NaMo Version 1, has been further developed to account for the effects of room temperature storage and cold deformation on the resulting age hardening behaviour. Incorporation of these two new stages in NaMo largely increases the versatility of the model by allowing simulations of complex multi-stage industrial processing involving thermomechanical treatment as well. Part 1 of this work deals with the theoretical background and experimental validation of the extended version of NaMo, while Part 2 focuses on the new applications of the model by showing some numerical examples related to production of automotive body panels.
Through Process Modelling of Extrusion for AA3xxx Alloys
Authors: Poole Warren J. , Wells Mary A. , Azizi-Alizamini Hamid , Parson Nick C.
Published: June 2014

A through process model for high temperature extrusion of AA3xxx aluminum alloys is presented. An overview of the various chemistry dependent sub-models, e.g. homogenization, extrusion, cold deformation and annealing, are described with an emphasis on the linkages between the models. Examples are presented to illustrate the importance of including the linkages between the sub-models. For example, there is a strong linkage between dispersoids which form during homogenization on subsequent recrystallization behavior after high temperature extrusion or ambient temperature deformation. Finally, a number of observations are presented on the prognosis (opportunities and challenges) for the future of through process modelling.
Reference Dies for the Evaluation of Tensile Properties of Gravity Cast Al-Si Alloys: An Overview
Authors: Adamane Anilchandra R. , Fiorese Elena , Timelli Giulio , Bonollo Franco , Arnberg Lars
Published: June 2014

Aluminium-Silicon (Al-Si) alloys are the most extensively used Al foundry alloys and are widely used in gravity die-casting (GDC) of automotive components. Reference dies are used to characterize the tensile properties of the castings. Among the various die configurations, the ASTM B-108 (also called the Stahl Mold), and the AA Step Mold are most popular in the foundries. Several modifications to the standard dies have been suggested in the scientific literature to obtain better mechanical properties in minimizing casting defects. This work reviews the scientific literature on the effect of different reference dies on the porosity and tensile properties of the Al alloy castings.
Modelling the Combined Effect of Room Temperature Storage and Cold Deformation on the Age-Hardening Behaviour of Al-Mg-Si Alloys-Part 2
Authors: Schäfer Carmen , Myhr Ole Runar , Brinkman Henk Jan , Engler Olaf , Hirsch Jürgen
Published: June 2014

The present investigation deals with modelling of the age-hardening behaviour of 6xxx series automotive sheet alloys. The basis for this work is the established precipitation model NaMo developed for coupled nucleation, growth, dissolution and coarsening in Al-Mg-Si extrusion alloys. It has recently been extended for applicability for Al-Mg-Si automotive sheet alloys by incorporating the important effects of room temperature (RT) storage and deformation prior to the final artificial ageing of Al-Mg-Si sheet alloys. The 6xxx automotive sheet alloys change due to natural ageing during the time elapsing between their processing and their paint baking in the customers process. This RT storage time has an impact on the artificial ageing response during the OEMs paint baking cycle. A second effect originates from the deformation introduced in the material during the part forming process prior to the artificial ageing in the paint bake cycle. This deformation leads to the introduction of dislocations which further modify the artificial ageing response by providing heterogeneous nucleation sites for nucleation of additional strengthening phases. Part 1 of this work deals with the theoretical background and experimental validation of the extended version of NaMo, while Part 2 focuses on the new applications of the extended model by simulation of ageing during paint baking according to typical customer requirements. The model validation is based on a comprehensive set of tensile tests. A comparison between model predictions and measurements shows reasonable agreement, and it is concluded that, after some further development, the model can be used to model the yield strength response of 6xxx automotive sheet alloys incorporating the (combined) effects of natural ageing, deformation and the accurate heat treatments in the paint bake cycle.
Phase Field Modeling of Solute Trapping in a Al-Sn Alloy during Rapid Solidification
Authors: Yang Xiong , Zhang Li Jun , Du Yong
Published: June 2014

During rapid solidification, interfaces are often driven far from equilibrium and the "solute trapping" phenomenon is usually observed. Very recently, a phase field model with finite interface dissipation, in which separate kinetic equations are assigned to each phase concentration instead of an equilibrium partitioning condition, has been newly developed. By introducing the so-called interface permeability, the phase field model with finite interface dissipation can nicely describe solute trapping during solidification in the length scale of micrometer. This model was then applied to perform a phase field simulation in a Al-Sn alloy (Al-0.2 at.% Sn) during rapid solidification. A simplified linear phase diagram was constructed for providing the reliable driving force and potential information. The other thermophysical parameters, such as interface energy and diffusivities, were directly taken from the literature. As for the interface mobility, it was estimated via a kinetic relationship in the present work. According to the present phase field simulation, the interface velocity increases as temperature decreases, resulting in the enhancement of solute trapping. Moreover, the simulated solute segregation coefficients in Al-0.2 at.% Sn can nicely reproduce the experimental data.
Effect of Reloading on Dynamic Recrystallization in Shock Deformed Aluminum Alloy
Authors: Atroshenko Svetlana , Divakov Aleksandr , Meshcheryakov Yuri , Naumova Natalia
Published: June 2014

In order to verify influence of particle velocity non-uniformity on dynamic recrystallization (DRX), shock tests of D16 Al alloy were conducted under uniaxial strain conditions within strain-rate range of 105 ÷ 107 s-1. The particle velocity non-uniformity arises due to both initial heterogeneity and non-linearity of shock-wave process. Apart from the nature of DRX mechanism, migrational or rotational, the particle velocity non-uniformity facilitates growth of local strain, strain rate and temperature. To adjust a duration of the particle velocity non-uniformity degree, two limiting situations is provided by means of single and double shock loading (reloading). The experimental technique used allows to register both mean particle velocity profile and particle velocity variation which is the quantitative characteristic of velocity non-uniformity. Shock tests of D16 Al alloy in single and reloading regimes [ show that dynamic recrystallization takes place only in the second case. The reloading regime initiates a ten-fold increase in duration of the particle velocity non-uniformity stage, which is sufficient for fulfillment of the well-known DRX conditions: γ 3, dγ/dt 104 s1, T 0.4Tm. The regions of DRX with equal-axis grains of ~1 μm in diameter are revealed with the metallography and X-ray analysis.
Aging and Precipitation Behavior in Supersaturated Al-2%Fe Alloy Produced by High-Pressure Torsion
Authors: Cubero-Sesin Jorge M. , Watanabe Masashi , Arita Makoto , Horita Zen Ji
Published: June 2014

The aging behavior of a cast Al-2 wt.% Fe alloy processed by High-Pressure Torsion (HPT) at room temperature was studied by subsequent aging treatments at 200 °C. Observations by Transmission Electron Microscopy (TEM) revealed that the microstructure after HPT processing reached an ultrafine-grained level with an average grain size in the Al matrix of ~120 nm. The initial eutectic structures were fragmented into particles with sizes of less than 400 nm and partially dissolved in the matrix up to a supersaturated Fe content of ~1% as confirmed by X-Ray Diffraction (XRD) analysis. The peak-age condition was achieved within 0.25 h of aging, which provides the maximum hardness of ~200 HV. Analyses by high-resolution S/TEM show that round particles of Al6Fe with sizes of ~5-10 nm and semi-coherent with the matrix are the dominant precipitates in the peak-aged condition. The hardness increases by aging for 12 h above the as-HPT-processed level of 185 HV. The dominant precipitate phase transforms to Al3Fe in the over-aged condition with a loss of coherency during growth. Enhanced precipitation kinetics was observed because of high density of lattice defects induced by the HPT processing, which were also confirmed by significant recovery in the electrical conductivity of the samples after aging.
Effect of Casting Temperature on Grain Size of Al-Si Alloys Refined by a Novel Grain Refiner
Authors: Bolzoni Leandro , Nowak Magdalena , Hari Babu N.
Published: June 2014

The automotive industry is willing of employing a greater amount of light metals like aluminium, magnesium and titanium, in order to reduce the total weight of the cars and, consequently, fuel consumption. Even though some casting aluminium alloys are commonly employed for automotive structural applications, their mechanical performances can be improved by means of appropriate grain refining by heterogeneous nucleation. This practise is well established for wrought aluminium alloys by using Al-Ti-B master alloys but they are not effective in casting alloys due to the much higher silicon percentage (poisoning). A novel chemical composition which, actually, refines appropriately Al-Si alloys was developed at Brunel University. In this study the combined effect of casting temperature and addition of this novel grain refiner (NGR) on the microstructure of binary Al-Si alloys was considered. The addition of this NGR leads to the formation of finer primary α-Al grains, finer eutectic Al-Si intermetallics and less and smaller primary Si particles.
Casting of Clad Strip by a Twin Roll Caster
Authors: Haga Toshio
Published: June 2014

Clad strip consisting of 5182 aluminum alloy and other aluminum alloys could be cast using a twin roll caster equipped with a scraper. This twin roll caster could carry out the strip casting and the bonding of the strips. The equipment, that was developed to prevent the contact between the bonding surface of the strip and oxidizing environment, was adopted. The developed equipment was a scraper. The 5182 strip could be bonded to other aluminum alloy strips by the effect of the scraper. Aluminum alloys for casting has poor formability, especially, bending ability is poor. The clad strip consisting of A356 casting aluminum alloy and 3003 wrought aluminum alloy was cast. 180 degree bending test was carried out on this clad strip. In the condition that the 3003 strip was outer side and A356 strip was inner side, the crack did not occur at the outer 3003 strip. In the deep drawing test or the clad strip, LDR (Limiting Drawing Ratio) was 1.8. These results mean that the casting aluminum alloy has ability to be used for the sheet forming, if the casting aluminum alloy is cladded with the wrought aluminum alloy.
Mechanisms of Dynamic Recrystallization in Aluminum Alloys
Authors: Kaibyshev Rustam , Malopheyev Sergey
Published: June 2014

Mechanisms of dynamic recrystallization operating at severe plastic deformation in a wide temperature range are reviewed for aluminum alloys. The main mechanism of grain refinement in all aluminum alloys is continuous dynamic recrystallization (CDRX). Temperature, deformation process and distribution of secondary phases strongly affect the CDRX mechanism. Initial formation of geometrically necessary boundaries (GNBs) and a dispersion of nanoscale particles accelerate CDRX facilitating the formation of a 3D network of low-angle boundaries (LAB) followed by their gradual transformation to high-angle boundaries (HAB). At high and intermediate temperatures, 3D networks of LABs may evolve due to rearrangement of lattice dislocations by climb, and mutual intersection of GNB, respectively. At high temperatures, in aluminum alloys containing no nanoscale dispersoids the CDRX occurs through the impingement of initial boundaries forced by deformation-induced LABs. This recrystallization process is termed as geometric dynamic recrystallization (GDRX). At low temperatures, the extensive grain refinement occurs through a continuous reaction which is distinguished from CDRX by restricted rearrangement of lattice dislocation. Introduction of large misorientation may occur through the formation of 3D networks of GNBs, only.
Morphological Control of Porous Structure in Al-Ti Intermetallics Foam Manufactured by Reactive Precursor Process
Authors: Kobashi Makoto , Kanetake Naoyuki
Published: June 2014

In this paper, a novel processing method (reactive precursor method) to manufacture high-melting point porous Al-Ti intermetallics is investigated. Especially, morphological control of porous structure is focused. In the reactive precursor process, precursors are made by blending aluminum and titanium powders. The precursor is heated to ignite an exothermic reaction (so called “combustion reaction”) between the elemental powders. Pore formation is a well-known intrinsic feature of the combustion reaction, and we tried to control the pore morphology. Fundamentally, the closed-cell structure can be obtained when the maximum temperature during the reaction exceeds the melting point of the reaction product. By blending the exothermic agent powder in the precursor, the maximum temperature is increased and the reaction products are melted. The porosity is controlled by the maximum temperature. In contrast, an open-cell porous structure can be obtained when the maximum temperature is below the melting point of the reaction product. Microwave heating turned out to be an effective method to create an open cell structure. A powdery substance that does not react with other elemental powders (heat-absorbing agent powder) decreases the temperature during the reaction. Closed, open and bimodal-sized open pores have been achieved by the reactive precursor process so far.
Characterization of High Strength Al-Zn-Mg Alloy Sheet for Hot Stamping
Authors: Kumar Manoj , Sotirov Nikolay , Chimani Christian
Published: June 2014

High formability is required to stamp aluminium into complex structural automotive components such as the A-pillar and B-pillar. Formability of an Al-Zn-Mg (AA7xxx) alloy sheet is characterised through hot stamping a prototype part and simulating paint baking procedures. The precipitation behaviour is assessed by differential scanning calorimetry and the tensile properties measured between 350°C and 475°C over a range of strain rates from 0.01s-1 to 1s-1. Natural ageing was found to increase the hardness of the hot stamped parts due to the formation of GP zone precipitates. A simulated three step paint baking procedure produced η precipitates and resulted in a yield strength and ultimate tensile strength of 480MPa and 512MPa, respectively.
Superplasticity of Ultra-Fine Grained 7075 Alloy Processed by High-Pressure Torsion
Authors: Lee Seungwon , Horita Zen Ji
Published: June 2014

An Al 7075 alloy (5.63mass%Zn-2.56mass%Mg-1.68mass%Cu-0.21mass%Fe-0.19mass%Cr-0.14mass%Si-0.02mass%Ti with balance of Al) was processed by high-pressure torsion (HPT) under an applied pressure of 6 GPa for 1, 3 and 5 revolutions with a rotation speed of 1 rpm at room temperature. Vickers microhardness saturated to a level of 220 Hv after the HPT processing and the grain size was refined to 120 nm at the state of the hardness saturation. Tensile tests were conducted with initial strain rates from 2.0 × 10-4 to 2.0 × 10-2 s-1 at temperatures as 200 °C and 250 °C (equivalent to 0.52Tm and 0.57Tm, respectively, where Tm is the melting point of the alloy). The HPT-processed samples for 3 revolutions exhibited superplastic elongations of 640% and 510% at 250 °C with initial strain rates of 2.0 × 10-3 s-1 and 2.0 × 10-2 s-1, respectively.
Multiscale Deformation and Dynamic Recrystallization in Shock Deformed Aluminum Alloy
Authors: Meshcheryakov Yuri , Divakov Alexandre , Zhigacheva Natali , Barakhtin Boris
Published: June 2014

Two regimes, equilibrium and non-equilibrium interaction of shock wave and inner structure of solid are studied. The theoretical analysis of the regimes is carried out by using the concept of the meso-macro momentum exchange. As a test material for the experiments, D16 Al alloy is taken, firstly because of its initial heterogeneity in equilibrium regime of dynamic straining and, secondly, due to increasing heterogeneity in non-equilibrium regime. Shock tests of D16 Al alloy within impact velocity range of 85÷450 m/s evidence that maximum dynamic strength is realized under conditions: (i) equilibrium regime of meso-macro momentum exchange, (ii) velocity defect equals to mean velocity variation. In non-equilibrium regime, the shock-induced dynamic recrystallization occurs, which is investigated with the metallography and X-ray analysis.
Effect of Hot Deformation on Microstructure and Mechanical Properties of Al-B4C Composite Containing Sc
Authors: Qin Jian , Zhang Zhan , Chen X.-G.
Published: June 2014

Scandium has been introduced into the Al-B4C composite to form Al3Sc precipitates which offer a significant strengthening effect and a good thermal stability of the mechanical properties at elevated temperatures. In the present study, the grain structure and Al3Sc precipitation of the hot-rolled Al-15vol.% B4C composite containing Sc were examined by optical and electron microscopes. The mechanical properties of the hot deformed composite were evaluated by means of Vickers microhardness measurements. The post heat treatment after hot rolling was conducted to obtain desirable mechanical properties. The hot-rolled Al-B4C composite containing Sc can yield a considerable precipitation hardening under an appropriate post heat treatment. Results show that some Sc could be consumed during high temperature solution treatments, which remarkably reduced the precipitation hardening of Al3Sc precipitates. The amount of Sc loss is associated with the deformation ratio and solution time.
Strength and Electrical Conductivity Relationships in Al-Mg-Si and Al-Sc Alloys
Authors: Rometsch Paul A. , Xu Zhou , Zhong Hao , Yang Huai , Ju Lin , Wu Xin Hua
Published: June 2014

Aluminium alloys play an important role in overhead power transmission applications. All-aluminium alloy conductor cables require increasingly hard-to-achieve combinations of high tensile strength and high electrical conductivity. The problem is that a high strength is normally associated with a reduced electrical conductivity. Both heat-treatable 6xxx series aluminium alloys and work-hardening 1xxx series aluminium alloys are important contenders for these applications. By contrast, the addition of rare earths and/or transition metals to aluminium may provide further opportunities to achieve improved combinations of precipitation hardening, substructural hardening and elevated temperature stability. In this work, strength and electrical conductivity relationships are investigated for a range of 6xxx series aluminium alloys and an Al-Sc alloy. The Al-Sc alloy was produced by means of a direct laser metal deposition process that allowed more Sc to be placed into solid solution than by conventional casting or solution treatment. The paper explores the relative effects of composition, cold working and age hardening on the balance of strength and electrical conductivity, including examples of how improved combinations of both strength and conductivity can be achieved.
Segregation during Metal Sampling
Authors: Razaz Ghadir , Carlberg Torbjörn
Published: June 2014

In order to obtain accurate chemical compositions in as-cast billets and ingots the sampling methods for the analysis have to give reproducible results with high precision. OES analysis made on samples at certain milling depths does not always show the desired nominal composition, and especially the segregation profiles within the samples can show significant variations. The present work examine the influence of main sampling parameters, such as the volume of the melt, the melt temperature, the mould design and the method of filling the mould, on the segregation. The results point out the importance of the convection in the mould during solidification, and thus the technique of pouring the melt into the sampling mould.
Effect of Heat Treatment on Phase Composition and Microstructure of Al-Cu-Fe Alloys with Quasicrystalline Phases
Authors: Samoshina Marina , Bryantsev Pavel
Published: June 2014

The microstructure and phase composition of alloys Al-Cu-Fe in as-cast state and after heat treatment at different temperatures were investigated. The presence of a quasicrystalline phase Al65Cu20Fe15 which coexists with crystalline phases in as-cast condition is found. The formation of single quasicrystalline phase composition in Al - 40 wt.% Cu - 17 wt.% Fe alloy after annealing at 800 °C for 100 hours is established. After heat treatment, i.e. closer to equilibrium conditions, the quasicrystalline phase Al65Cu20Fe15 is transformed into quasicrystalline phase Al13Cu4Fe3 with more complicated lattice.
Mechanical Properties and Aging Behavior of Ultrafine Grained Al-Ag Alloy Fabricated by Accumulative Roll-Bonding
Authors: Nagae Tadashiege , Tsuji Nobuhiro , Terada Daisuke
Published: June 2014

Accumulative roll-bonding (ARB) process is one of the severe plastic deformation processes for fabricating ultrafine grained materials that exhibit high strength. In aluminum alloys, aging heat treatment has been an important process for hardening materials. In order to achieve good mechanical properties through the combination of grain refinement hardening and precipitation hardening, an Al-4.2wt%Ag binary alloy was used in the present study. After a solution treatment at 550°C for 1.5hr, the alloy was severely deformed by the ARB process at room temperature (RT) up to 6 cycles (equivalent strain of 4.8). The specimens ARB-processed by various cycles (various strains) were subsequently aged at 100, 150, 200, 250°C, and RT. The hardness of the solution treated (ST) specimen increased by aging. On the other hand, hardness of the ARB processed specimen decreased after aging at high temperatures such as 250°C. This was probably due to coarsening of precipitates or/and matrix grains. The specimen aged at lower temperature showed higher hardness. The maximum harnesses achieved by aging for the ST specimen, the specimens ARB processed by 2 cycles, 4 cycles and 6 cycles were 55HV, 71HV, 69HV and 65HV, respectively. By tensile tests it was shown that the strength increased by the ARB process though the elongation decreased significantly. However, it was found that the tensile elongation of the ARB processed specimens was improved by aging without sacrificing the strength. The results suggest that the Al-Ag alloy having large elongation as well as high strength can be realized by the combination of the ARB process for grain refinement and the subsequent aging for precipitation hardening.
Influence of Mg Content, Grain Size and Strain Rate on Mechanical Properties and DSA Behavior of Al-Mg Alloys Processed by ECAP and Annealing
Authors: Zha Min , Li Yan Jun , Mathiesen Ragnvald H. , Baumgart Christine , Roven Hans J.
Published: June 2014

Ultrafine-grained (UFG) binary Al-xMg (x=1, 5 and 7 wt %) alloys were processed by equal channel angular pressing (ECAP) at room temperature via route Bc combined with inter-pass annealing. The effects of Mg content, grain size and strain rate on mechanical properties and dynamic strain aging (DSA) behaviour of the Al-Mg alloys upon tensile testing at room temperature were studied. An increase in Mg content from 5 to 7 wt % leads to a pronounced increase in strength and uniform elongation in both the as-homogenized and as-ECAP Al-Mg alloys. Thereby, the Al-7Mg alloy, either prior to or after ECAP processing, possess significantly higher strength and comparable or even higher uniform elongation than the more dilute Al-Mg alloys. However, the as-ECAP Al-Mg alloys exhibit significantly higher strength but little work hardening and hence rather limited uniform elongation. In general, decreasing grain size leads to significant increase in strength while dramatic decrease in ductility. Moreover, DSA serration amplitudes increase with reducing grain size in the micrometer range. However, the UFG Al-Mg alloys exhibit much less DSA effect than the micrometer scaled grain size counterparts, i.e. probably due to the high dislocation densities and special grain boundary features in the UFG materials. Also, the Al-Mg alloys, especially those with a UFG structure, exhibit higher strength and ductility at lower strain rate than at higher strain rate, due mainly to enhanced DSA effect and hence work hardening at a lower strain rate.
The Structure Evolution of a 99.995 Percent High Purity Aluminum during Multi-Forging Process in Room Temperature
Authors: Zhu Qing Feng , Zhao Zhi Hao , Zuo Yu Bo , Li Lei , Cui Jian Zhong
Published: June 2014

In this study, a purity of 99.995percent high purity aluminum was multi-directionally forged up to a maximum cumulative strain of 4.5 at room temperature. The macro and micro structure evolution in the multi-directionally forge process was investigated by structure observations and hardness measurements. The results show that the inhomogeneous deformation of multi-directional forging results in that the structure and hardness is quite different between the easy deformation zone and stagnant zone. Dynamic recrystallization occurs in easy deformation zone of high purity aluminum sample at room temperature as the cumulative true strain is 1.5 (3 forging passes), while the structure in the stagnant zone is still not recrystallizated even at a cumulative true strain of 4.5 (9 forging passes). The recrystallized grain size in the easy deformation zone is reduced with the number of forging passes, and the area of recrystallize grains increase with the number of forging passes.
Structure Development and Deformation Behaviour of Pure Aluminium Processed by Constrained Groove Pressing
Authors: Zrník Jozef , Cieslar Miroslav , Slama Peter
Published: June 2014

In this study, the relationship between the structure and properties of commercial purity aluminium alloy A1199 was investigated by applying constrained groove pressing (CGP) deformation method. The refinement of the coarse grain aluminium (Al) microstructure to sub microcrystalline size by large plastic strain at room temperature defined. The impact of various strains upon microstructure changes is investigated using transmission electron microscopy (TEM of thin foils) and electron back scatter diffraction (EBSD). A mixture of subgrains produced by grains subdivision and polygonized subgrains formed locally due to dynamic recovery was found in the deformed aluminium structure. The tensile properties and resulting hardness are related to microstructural evolution induced by constrained groove pressing deformation. A substantial impact of straining upon the increasing in tensile strength was observed after the first deformation step (first pass) Further strain increase had an insignificant effect on tensile strength but was accompanied by ductility loss. The post deformation annealing effect was then explored with aim to increase the ductility. The results indicate that changes in strength and ductility may be related to formation of a bimodal structure in deformed plates.
Influence of Ultrasonic Treatment on the Microstructure of Hypereutectic Al-17 Wt%Si Alloys
Authors: Cho Young Hee , Lee Jung Moo , Yoon Woon Ha , Jung Jae Gil
Published: June 2014

The effect of ultrasonic melt treatment (UST) on the microstructure of hypereutectic Al-17 wt.% Si alloys was investigated. UST applied to a melt at a temperature range of 750 - 800 °C refines the primary Si dramatically but has little influence on the grain size of primary Al. The solidification behaviour was characterised by thermal analysis and a mechanism responsible for the primary Si refinement was suggested. Whilst UST has no effect on the grain refinement, a significant increase in the matrix hardness as well as the tensile strength in the as cast condition is possibly associated with solid solution hardening. Detailed microstructure analysis was carried out and characteristics of the intermetallic formation in the Al-17 wt.% Si alloys were further discussed in the view point of Cu solubility in the Al matrix, which is considered to increase with UST.
Effects of Isothermal Aging on Clustering and Paint-Bake Hardening Behavior in an Al-Mg-Si Alloy
Authors: Aruga Yasuhiro , Kozuka Masaya , Takaki Yasuo , Sato Tatsuo
Published: June 2014

The relationship between the cluster morphology formed during natural or artificial aging and the paint-bake hardening response in an Al-0.62Mg-0.93Si (mass%) alloy have been investigated using atom probe tomography (APT). Increasing the subsequent aging time at 170 °C causes a gradual increase in hardness in the artificially aged materials, while the retardation period of the hardness increase appears in the naturally aged materials at the early stage of aging. The statistically-proved records in the APT analysis have shown that the artificially aged materials have some large clusters. It is revealed that the hardening at the early stage of the subsequent aging at 170 °C is not promoted in the long-time naturally aged material although the number density of small clusters increases approximately 1.3 times by prolonged natural aging.Hence, we believe that the small clusters are hard to transform continuously into the β'' phase during aging at 170 °C. As for the naturally aged materials, the long-time aging leads to a significant drop in hardness at the early stage of aging at 170 °C. It is speculated that the Mg-Si mixed clusters formed after long-time natural aging can be reversed during the subsequent heat treatment.
Influence of Pre-Straining and Pre-Ageing on the Age-Hardening Response of Al-Mg-Si Alloys
Authors: Yan Yong , Liang Ze Qin , Banhart John
Published: June 2014

The effect of pre-straining and pre-ageing on the age hardening response of Al-0.6%Mg-0.8%Si alloy is studied by Vickers hardness and differential scanning calorimetry (DSC). It is found that pre-ageing can suppress the formation of unwanted clusters and keeps the structure stable for a certain time. A pre-ageing treatment can effectively reduce or avoid the negative effect of natural ageing on artificial ageing and even produce a positive effect. Cluster formation can also be reduced by pre-straining, but the kinetics of clustering is still similar to that of the as-quenched condition. In contrast, after pre-straining, the peak positions of β and β move to lower temperatures and peak hardness is achieved in a shorter time, indicating that the formation of β and β is accelerated by pre-straining. However, the negative effect of natural ageing still persists after pre-straining. Pre-straining before pre-aging can take advantage of both techniques and produce a positive strength response. For pre-straining after pre-aging, pre-straining tends to destabilize the structure created by pre-ageing and can reactivate the clustering process, which has negative effect on subsequent artificial ageing.
Monitoring Precipitation Kinetics in Heat Treatable Aluminium Alloys Using In Situ Resistivity in Gleeble Thermomechanical Simulator
Authors: Chobaut Nicolas , Carron Denis , Drezet Jean Marie
Published: June 2014

A conventional way to determine precipitation kinetics in heat treatable aluminium alloys is to monitor the associated solute loss by in-situ resistivity. A Gleeble machine is used to perform so called isothermal quenching (IQ) resistivity measurements. IQ consists in quenching the alloy down to a given temperature and holding it at this temperature. The results are validated against measurements performed with a classical four-points method using continuous current on the same alloy.