Aluminum Alloy Research Papers - Academia.edu (original) (raw)

An Al-6.3Li-0.07Sc-0.02Yb (at.%) alloy is subjected to a double-aging treatment to create nanoscale precipitates, which are studied by atom-probe tomography and transmission electron microscopy. After homogenization and quenching, Yb atoms form clusters exhibiting L1 2-like order. A first aging step at 325°C leads to a doubling of microhardness as a result of the formation of coherent precipitates with an Al 3 Yb-rich core and an Al 3 Sc-rich shell. The core and shell both exhibit the L1 2 structure and both contain a large concentration of Li, which substitutes for up to 50% of the Sc or Yb atoms at their sublattice positions. These core/single-shell precipitates provide excellent resistance to overaging at 325°C. Subsequent aging at 170°C increases the microhardness by an additional 30%, through precipitation of a metastable d 0-Al 3 Li second shell on the core/single-shell precipitates, thereby forming a chemically and structurally complex core/double-shell structure. The metastable d 0-Al 3 Li phase is observed to form exclusively on pre-existing core/shell precipitates.

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- Materials Engineering, Mechanical Engineering, Materials Science, Microstructure

International Journal of Offshore and Polar Engineering Vol. 14, No. 4, December 2004 (ISSN 1053-5381) Copyright © by The International Society of Offshore and Polar Engineers ... A Microstructural Study of Friction Stir Welded Joints of... more

- by HyunWoo Jin
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- Friction Stir Welding, Phase Transformation, Emerging Technology, Microstructures

Ceramic coatings are produced on aluminum alloy by autocontrol AC pulse Plasma Electrolytic Oxidation (PEO) with stabilized average current. Transient signal gathering system is used to study the current, voltage, and the transient wave during the PEO process. SEM, OM, XRD and EDS are used to study the coatings evolution of morphologies, composition and structure. TEM is used to study the micro profile of the outer looser layer and inner compact layer. Polarization test is used to study the corrosion property of PEO coatings in NaCl solution. According to the test results, AC pulse PEO process can be divided into four stages with different aspects of discharge phenomena, voltage and current. The growth mechanism of AC PEO coating is characterized as anodic reaction and discharge sintering effect. PEO coating can increase the corrosion resistance of aluminum alloy by one order or two; however, too long process time is not necessarily needed to increase the corrosion resistance. In condition of this paper, PEO coating at 60 min is the most protective coating for aluminum alloy substrate.

Aluminum based alloys are widely used as journal bearing materials in tribological applications. Duralumines, AlMgSi are widely used as journal bearing materials for aluminum based alloys. These alloys provide properties expected from journal bearings. In this study, tribological and mechanical properties of these journal bearings manufactured from aluminum alloys were investigated. SAE 1050 steel shaft was used as counter abrader. Experiments were carried out in every 30 min for the total of 150 min by using radial journal bearing wear test rig. Wear resistance of Al alloyed bearings increased about 2-3 times and journal wear resistance increased about 2-8 times. The highest bearing wear rate occurred in pure Al bearings while the lowest bearing wear rate occurred in AlMgSi bearing.

- by hülya durmuş
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- Materials Engineering, Condensed Matter Physics, Wear resistance, Aluminum Alloy

Friction stir welding is becoming increasingly desirable in many applications, including tailor-welded blanks in which two sheets of different thicknesses are joined together to form blanks that can be subsequently stamped into a final product shape. In this article, we have studied the static tensile and tensiontension fatigue behavior of friction stir welded joint in a tailor-welded blank of aluminum alloy 5754. It was observed that the yield and tensile strengths of friction stir welded specimens with weld located 90°to the tensile direction are close to the base material values, but its elongation is nearly half the elongation for the base material. The friction stir welded joints had relatively high-fatigue strength, and was even superior to that of the base aluminum alloy in the high-cycle region. Pre-straining caused by press forming lowered the elongation to failure, but improved the fatigue performance.

- by Ghassan Kridli
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- Materials Engineering, Materials Science, Friction Stir Welding, Tensile Strength

Past efforts to predict hardness-strength relationships in aluminum alloys have been reviewed. Hardness data for Al-7wt.%Si-Mg alloys with three different Mg levels and artificially aged for different durations have been analyzed for possible hardness-yield strength relationships. All models reported in the literature, except for the one developed by Shabel and Young, have been found to be affected by alloy temper. A new model that is unaffected by alloy temper has been developed that can be used to predict yield stress of these alloys from multiple hardness readings. These effects, as well as that of microstructure are discussed in the paper.

- by Murat Tiryakioglu
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- Materials Engineering, Mechanical Engineering, Microstructures, Yield stress

Effect of Mold Coating Materials and Thickness on Heat Transfer in Permanent Mold Casting of Aluminum Alloys A. HAMASAIID, MS DARGUSCH, CJ DAVIDSON, S. TOVAR, T. LOULOU, F. REZAI¨-ARIA, and G. DOUR ... These coatings maintain mechanical... more

A study has been made of the mechanics and mechanisms of fatigue crack propagation in a commercial plate of aluminum-lithium alloy 2090-T8E41. In Part II, the crack growth behavior of naturallyoccurring, microstructurally-smaU (2 to 1000/xm) surface cracks is examined as a function of plate orientation, and results compared with those determined in Part I on conventional long (~>5 mm) crack samples. It is found that the near-threshold growth rates of small cracks are between 1 to 3 orders of magnitude faster than those for long cracks, subjected to the same nominal stress intensity ranges (at a load ratio of 0.1). Moreover, the small cracks show no evidence of an intrinsic threshold and propagate at AK levels as low as 0.7 MPa~mm, far below the long crack threshold AKrH. Their behavior is also relatively independent of orientation. Such accelerated small crack behavior is attributed primarily to restrictions in the development of crack tip shielding (principally from roughness-induced crack closure) with cracks of limited wake. This notion is supported by the close correspondence of small crack results with long crack growth rates plotted in terms of AKcff (i.e., after allowing for closure above the effective long crack threshold). Additional factors, including the different statistical sampling effect of large and small cracks with microstructural features, are briefly discussed.

- by Robert Ritchie
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- Materials Engineering, Mechanical Engineering, Fatigue crack growth, Growth rate

The fatigue damage analysis is examined from a historical perspective. The analysis indicates that some of the issues concerning the basic disparities between the experiment and model/interpretations. To help understand these issues, we have developed an approach with two driving force parameters to analyze the fatigue behavior. Such an approach helps in viewing the damage in terms of an intrinsic problem rather than an extrinsic one. In the final analysis one needs to unify the overall damage processes such that the description is complete from the crack initiation stage to short crack to long crack to final failure. In order to unify the damage process, three basic parameters are introduced for describing the overall fatigue process. These are ⌬K, K max and internal stress contribution to K max. In addition, there are other effects from environment and temperature that can contribute to these parameters. In particular K max seems to play an important role in the overall damage process. We find that the internal stress is the missing link that can bridge the gap between the four main stages of damage that lies between the crack nucleation stage to final failure. Examples are sited in support of this view of explanation. Finally, it is suggested that systematic experimental data and analytical modeling to describe the internal stress gradients is required to help in forming a reliable life prediction methodology. Published by Elsevier Science Ltd.

- by A.K., Vasudevan and +1
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- Mechanical Engineering, Civil Engineering, Titanium, Fatigue

Rotary degassing is one of the most frequently used melt treatment technologies used for processing liquid aluminum alloys. Despite this, the information available about the possible effects of this method on the double oxide-and nitride film (bifilm) content, especially when using different purging gases, is quite limited. For this reason, in this study, the effects of multiple rotary degassing treatments conducted with N 2 and Ar purging gases on the bifilm quantity of a casting aluminum alloy were compared. The characterization of the melt quality was realized by the computed tomographic (CT) analysis of reduced pressure test (RPT) specimens, image analysis, and scanning electron microscopy (SEM) of the fracture surfaces of K-mold samples. Based on the results, by the application of Ar as a purging gas, relatively low bifilm content can be achieved. On the other hand, while the use of N 2 leads to the formation of numerous small-sized nitride bifilms, which significantly increased the pore number density inside the RPT specimens. This can be associated with the nitride formation by the chemical reaction between the liquid aluminum alloy and the N 2 purging gas bubbles during the degassing treatments.

In friction stir welding (FSW), the welding tool geometry plays a fundamental role in obtaining desirable microstructures in the weld and the heat-affected zones, and consequently improving strength and fatigue resistance of the joint. In this paper, a FSW process with varying pin geometries (cylindrical and conical) and advancing speeds is numerically modeled, and a thermo-mechanically coupled, rigid-viscoplastic, fully 3D FEM analysis able to predict the process variables as well as the material flow pattern and the grain size in the welded joints is performed. The obtained results allow finding optimal tool geometry and advancing speed for improving nugget integrity of aluminum alloys.

- by Rajiv Shivpuri
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- Materials Engineering, Mechanical Engineering, FEM, Friction Stir Welding

This paper deals with the definition of a new finishing process named fluidized bed machining (FBM). Material is removed from the workpiece by an abrasive solid emulsion and air flowing through all the equipment, scratching the surface to be finished. This process is able to produce an accurate surface finishing both on areas inaccessible to traditional methods and complex passages. 9 10 11

The viscoelastic response of commercial Al–Zn–Mg and Al–Cu–Mg alloys was measured with a dynamic-mechanical analyzer (DMA) as a function of the temperature (from 30 to 425°C) and the loading frequency (from 0.01 to 150 Hz). The time-temperature superposition (TTS) principle has proven to be useful in studying mechanical relaxations and obtaining master curves for amorphous materials. In this work, the TTS principle is applied to the measured viscoelastic data (i.e., the storage and loss moduli) to obtain the corresponding master curves and to analyze the mechanical relaxations responsible for the viscoelastic behavior of the studied alloys. For the storage modulus it was possible to identify a master curve for a low-temperature region (from room temperature to 150°C) and, for the storage and loss moduli, another master curve for a high-temperature region (from 320 to 375°C). These temperature regions are coincidental with the stable intervals where no phase transformations occur. Th...

- by Daniel Crespo
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- Engineering, Materials Science, Microstructure, Viscoelasticity

The paper provides an overview of tribological properties of nanocomposites with aluminium matrix. Nanocomposites represent a new generation of composite materials with better properties than conventional composite materials. The paper presents and explains the most common methods of nanocomposites production. In addition, the overview of tribological properties is presented through the equipment used for testing; amount, size and type of reinforcement; matrix material and manufacturing process; and test conditions. ARTICLE HISTORY Received 15 August 2016 Accepted 3 September 2016 Available online 30 September 2016

The effects of extrusion parameters on the resulting profile exit temperature of industrially extruded 6063 aluminum alloy have been studied using statistical design of experiments (DOE). Two operating parameters (initial billet... more

- by ABDUL KAREEM ABDUL JAWWAD
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- Materials Engineering, Modeling, Manufacturing Engineering, Temperature

The dislocation density and subgrain size were detennined in the base material and friction-stir welding (FSW) of 6061-T6 aluminum alloy. First, the high-resolution x-ray diffraction measurement was perfonned in the base material. The result of the line profile analysis of the x ray diffraction peak shows that the dislocation density is about 4.5 x 10 14 m-2 and the subgrain size is about 200 nm. Secondly, the deep penetration capability of the neutrons enables us to measure the diffraction peaks from the mid-plane of the Al plate underneath the tool shoulder at 8 mm from the tool center during FSW. The broadening peak profiles were analyzed usin¥ the Williamson-Hall method. The result shows the dislocation density of about 3.2 x 10 15 m-and subgrain size of about 160 nm during FSW. The significant increase of the dislocation density is likely due to the severe plastic defonnation during FSW. This study provides an insight to understand the transient behavior of the microstructure.

- by Edward Kenik
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- Materials Engineering, Mechanical Engineering, Neutron Diffraction, Friction Welding

The purpose of this research is to determine the effect of heat treatment hardening of AlMgSi-Fe12% casting aluminium alloys on wear. The tests were carried out on specimens of raw materials and heat-treated specimens with variations of temperature used were 550 C, 575 C, 600 C and 625 C, and used 15 minutes of holding time in each heat treatment, then quenching in SAE 20 oil. The method used for wear tested was high speed ogoshi universal testing machine wear. The result had shown on raw material a specific wear rate was 2.256102E-07 mm2/kg. Test results on the specimens that has received heat treatment hardening temperature 550 C increased the wear value decreased to 1.7471E-07 mm2/kg. In materials with temperature heat treatment 575 C causes wear values were increased when compared with raw material, respectively, 2,83739E-07 mm2/kg. In materials with temperature heat treatment 600 C also causes wear values were increased when compared with raw material, respectively, 2,65105E-07 mm2/kg. Test results on the test material that has received heat treatment temperature 625 C increased the wear value decreased to 2.16777E-07 mm2/kg.

- by Wardoyo Wardoyo
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- Casting, Metal Casting, Quenching, Temperature

The fatigue crack growth of commercial AA2219 has been examined under different aging treatments, namely, naturally aged (NA), under aged (UA), peak aged (PA) and over aged (OA) conditions. From the near threshold stress intensity range (K NTH), the alloy in the NA condition is found to have the highest resistance to fatigue crack initiation. The crack growth rate increases and the near threshold stress intensity range decreases with advancing aging. This observation is found to be consistent with lower levels of crack closure and decreasing levels of tortuosity in crack path for PA and OA tempers. The inhomogeneous transcrystalline slip in the UA condition results in the slower crack growth at low stress intensity range (K). The fracture morphology changes from crystallographic facets near the threshold region to clearly developed ductile striations in the Paris power-law regime to microvoid coalescence in the high K regions.

An international consortium is studying the feasibility of performing in situ geochemical analysis of Mars soils and rocks at stand-off distances up to several meters using the laser-induced breakdown spectroscopy (LIBS) technique. Stand-off analysis for Martian exploration imposes particular requirements on instrumentation, and it is necessary to first test the performance of such a system in the laboratory. In this paper, we test the capabilities of two different experimental setups. The first one is dedicated to the qualitative analysis of metals and rocks at distances between 3 and 12 m. With the second one, we have obtained quantitative results for aluminum alloys and developed a spectral database under Martian conditions for sulfur and chlorine, two elements that are geologically interesting but generally difficult to detect by LIBS under standard conditions (atmospheric pressure, close distance). These studies were carried out to determine an optimal instrumental design for in situ Mars analysis. The quality of analytical results affected by the optical elements and spectrometer has been particularly highlighted. D

- by Pascal Fichet
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- Physical sciences, Atmospheric Pressure, Qualitative Analysis, CHEMICAL SCIENCES

The thermal contact conductance of coated, contacting aluminum 6061-T651 surfaces was studied experimentally. Four different coating materials, copper, silver, a phase mixture of copper-carbon, and a phase mixture of silver-carbon were evaluated using four different surface roughnesses for each coating material. All of the samples were tested at contact pressures of 125, 250, 375, and 500 kPa. The test results of thermal contact conductance are presented in terms of coating thickness, surface texture, and properties of the coating materials. Using the experimental data, dimensionless expressions were developed that relate the contact conductance of the phase mixture and pure coatings to the coating thickness, the surface roughness, the contact pressure, and the properties of the aluminum substrate. The effects of the surface roughness and of the phase mixture of the coatings on the thermal contact conductance were investigated. In addition, the load cycling effect on the thermal contact conductance was examined for bare aluminum 6061-T651 specimens.

- by John W Sheffield
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- Mechanical Engineering, Aerospace Engineering, Heat Transfer, Surface Roughness

The objective of the research described in this article was to characterize and numerically describe the ductility of weld material in aluminum tailor welded blanks under uniaxial tension conditions. Aluminum tailor welded blanks consist of multiple thickness and alloy sheet materials welded together into a single, variable thickness blank. To evaluate the mechanical properties of the weld material in these tailor welded blanks, a series of tensile specimens containing varying ratios of weld and monolithic material in the gage area of the specimen were tested. These experimental results show that increasing the amount of weld in the cross-sectional area of the specimen decreases the ductility of the specimen and that the weld characteristics have a pronounced impact on ductility. Using the experimental results and classical tensile instability and necking models, a numerical model was developed to describe the ductility of the weld metal. The model involves basic material properties and an initial imperfection level in both the weld and monolithic materials. The specimens studied were produced from 1- to 2-mm AA5182-O aluminum alloy sheet material welded into blanks using an autogenous gas tungsten arc welding process.

- by Mohammad Khaleel
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- Materials Engineering, Mechanical Engineering, Metallurgical, Numerical Model

In this work optimization of turning parameters for turning Ti-6Al-7Nb Titanium alloy has been investigated by orthogonal array along with Grey relational analysis coupled with principle component. Parameters such as surface roughness, tool wear, roundness, material removal rate, temperature and power consumption are considered as performance characteristics of the turning process. By orthogonal array eighteen experiments are carried out in the CNC machine by considering cutting environment, cutting speed, feed rate, depth of cut, nose radius, tool coating type and insert shape angle as turning parameters. From the grey relational grade the optimum turning parameters were predicted. Also the influence of individual turning parameters is carried out by Analysis of Variance. From the largest value of grey relational grade parameters , cutting environment: wet, feed rate : 0.08 mm /rev, cutting speed: 100 m/min ,insert angle: 80 0 , nose radius: 0.4 mm, tool coating type : TiAlN and depth of cut:0.4 mm are found to be better turning parameters levels. About 11.3 % enhancement of grey relation grade value is achieved when compared to initial parameter grey relational grade value.

- by Santanu Duari
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- Mathematics Education, Production, Engineering Product Design, Metal Cutting

A simple method for estimating the oxide thickness on aluminum alloys using ESCA was investigated. The method is based on a uniform overlayer model and requires only a single ESCA measurement per sample. Expressions are shown which relate the experimental intensity ration of the oxidic and metallic Al 2p ESCA peaks to the oxide thickness, for both MG and Al x-ray sources. The method does not require ion etching or separate calibration procedures. Several practical examples that illustrate the usefulness of this method are presented. The method can also be applied to other thin film (i.e. <∼ 100 Å) metal oxide/metal systems. The maximum oxide thickness that can be measured using the method is limited to approximately three times the inelastic mean free path of the appropriate photoelectrons within the material of interest.

- by Brian Strohmeier
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- Condensed Matter Physics, Oxidation, Aluminum Alloy

The use of aluminum in fabricated cage windings of large induction motors has been explored, and it was found that aluminum and its alloys present a viable alternative to copper and its alloys. This paper enumerates the advantages and limitations of aluminum as a cage material, outlines the considerations necessary in the utilization of the material for this application, and summarizes the results of a testing program which demonstrated the adequacy of aluminum alloy cages in full scale machines.

- by Jack Cage
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- Engineering, Manufacturing, Copper, Welding

The corrosion process of the alloy AA5083 in an aerated solution of NaCl at 3.5% has been studied. The results obtained indicate that the main process that this alloy undergoes, under the conditions of exposure studied, is related to localized corrosion that takes place as a consequence of the process of alkalinization around the cathodic precipitates existing in the alloy. The pitting formed presents a hemispherical morphology that is clearly dierent from crystallographic pitting. The formation of crystallographic pitting has not been observed, even in samples submitted to tests of very long duration. In order to obtain the formation of crystallographic pitting, it is necessary to polarize the alloy at the nucleation potential of pitting and, in addition, the density of the current must be above a critical value. Only when the layer of oxide is eliminated does the formation of crystallographic pitting take place by simple exposure in an aerated solution of NaCl at 3.5%. Ó

A technique for measuring the linear contraction during and after solidification of aluminum alloys was improved and used for examination of binary and commercial alloys. The effect of experimental parameters, e.g., the length of the mold and the melt level, on the contraction was studied. The correlation between the compositional dependences of the linear contraction in the solidification range and the hot tearing susceptibility was shown for binary Al-Cu and Al-Mg alloys and used for the estimation of hot tearing susceptibility of 6XXX series alloys with copper. The linear thermal contraction coefficients for binary and commercial alloys showed complex behavior at subsolidus temperatures. The technique allows estimation of the contraction coefficient of commercial alloys in a wide range of temperatures and could be helpful for computer simulations of geometrical distortions during directchill (DC) casting.

- by Lauren Mooney
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- Materials Engineering, Mechanical Engineering, Computer Simulation, Copper

In this study, 6060 aluminum alloy was coated by plasma electrolytic oxidation (PEO) process. The effect of sodium silicate concentration (A solution-7.5 g/L-B solution-15 g/L) on various morphological properties and corrosion resistance of the surface was investigated. The correlation between the microwave sintering of 6060 aluminum alloy coated by PEO and non-microwave sintering of 6060 aluminum alloy properties are discussed. Detailed estimation of the quality of the coated metal surface was performed by additional testing of chemical compositions by EDS, crystalline structure of the films was examined using x-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed that the oxidation layer was of typical morphology for the PEO process. The porosity amount of 6060 aluminum sample coated with 15 g/L was obtained higher than that of 7.5 g/L. In addition to, the porosity of all coated samples was decreased with increasing microwave sintering time. The corrosion resistance of coated samples with microwave sintering process was better than non-microwave sintering of 6060 aluminum alloy.

Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure-property relationships. #

- by John Carsley and +1
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- Engineering, Mechanical Engineering, Materials Science, Friction Stir Welding

The present investigation has been conducted in order to develop a rational approach able to describe the changes in flow stress of AA7075-T6 aluminum alloy with deformation temperature and strain rate, when this material is deformed at temperatures in the range of 123-298 K at strain rates in the range of 4 × 10 −4 to 5 × 10 −2 s −1 . The constitutive formulation that has been advanced to accomplish these objectives represents a simplified form of the mechanical threshold stress (flow stress at 0 K) model developed at Los Alamos National Laboratory (Los Alamos, New Mexico, USA). Thus, it is assumed that the current flow stress of the material arises from both athermal and thermal barriers to dislocation motion. In the present case, the effect of three thermal barriers has been considered: solid solution, precipitation hardening and work-hardening. The first two effects do not evolve during plastic deformation, whereas the last one is considered as an evolutionary component of the flow stress. Such an evolution is described by means of the hardening law earlier advanced by [20]. The law is implemented in differential form and is integrated numerically in order to update the changes in strain rate that occur during tensile tests carried out both at constant and variable crosshead speed. The extrapolation of the hardening components from 0 K to finite temperatures is accomplished by means of the model earlier advanced by Kocks (1976) [19]. The results illustrate that the constitutive formulation developed in this way is able to describe quite accurately both the flow stress and work-hardening rate of the material, as well as temperature and strain rate history effects that are present when deformation conditions change in the course of plastic deformation. The evaluation of the ductility of the alloy indicates that the changes in this property are mainly determined by deformation temperature rather by strain rate. When deformation temperature decreases from 298 to 123 K, ductility also decreases from ∼35 to 24%. However, despite these relatively small variations, significant changes in the fracture morphology could be observed on the fracture surfaces of the examined specimens, with the predominance of a mixed ductile-brittle mechanism at lower temperatures.

- by Mariana H Staia
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- Materials Engineering, Mechanical Engineering, Materials Science, Strain Rate

- by Swathi Byreddy
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- Engineering, Materials Engineering, Mechanical Engineering, Materials Science

Nanostructured diamond films were grown to a thickness of approximately 35 µm by a 30 kW, 915 MHz, microwave plasma-assisted chemical vapor deposition (MPCVD) on chemically treated WC-6 wt.% Co tool inserts. Rockwell indentation tests were performed to evaluate the adhesion of the films and compared to that of traditional microcrystalline diamond. A series of high speed dry turning tests on high-silicon (18 wt.% Si) aluminum alloy A390 under continuous and interrupted modes were performed and comparisons were carried out to investigate the wear behavior on tool inserts that were uncoated, coated with nanostructured diamond, and commercial PCD (polycrystalline diamond cutter) ones. The tests showed that nanostructured diamond coatings demonstrated excellent durability against the highly abrasive A390 aluminum-silicon alloys in high speed dry turning. Ultra fine grain structure of this coating produces workpiece surface finish comparable or even better than PCD tools in the range we studied. Excellent coating adhesion of nanostructured diamond on WC-6% Co substrates leads to reliable wear behavior. For the first time, we evaluated the performance of nanostructured diamond film coated insert under high speed interrupted turning mode. A "self-cleaning" mechanism was observed which can significantly improve the performance of nanostructured diamond films. Micro-Raman spectra were taken on tested tools to study the wear mechanism of the coating.

of the materials to be joined is not reached during FSW operation, reducing the probability of distortions, porosities and loss of mechanical properties. Moreover, the technology can join heat treatable aluminum alloys, for example 2XXX Schematic description of the friction stir welding process. The weld is realized by a combined advance and rotation of the tool without any addition of material, enabled by the control of the depth force, tool spindle speed and advance and transversal position & orientation of the tool.

- by Laurent Dubourg and +3
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- Mechanical Engineering, Dynamic Simulation, Friction Stir Welding, Real Time Control

The present work deals with studies on the manufacturing and investigation of mechanical and wear behavior of aluminum alloy matrix composites (AAMCs), produced using powder metallurgy technique of ball milled mixing in a high energy attritor and using a blend-press-sinter methodology. Matrix of pre-mechanical alloyed Al-4.5 wt.% Cu was used to which different fractions of nano and micron size TiC reinforcing particles (ranging from 0 to 10 wt.%) were added. The powders were mixed using a planetary ball mill. Consolidation was conducted by uniaxial pressing at 650 MPa. Sintering procedure was done at 400°C for 90 min. The results indicated that as TiC particle size is reduced to nanometre scale and the TiC content is increased up to optimum levels, the hardness and wear resistance of the composite increase significantly, whereas relative density, grain size and distribution homogeneity decrease. Using micron size reinforcing particulates from 5% to 10 wt.%, results in a significant hardness reduction of the composite from 174 to 98 HVN. Microstructural characterization of the as-pressed samples revealed reasonably uniform distribution of TiC reinforcing particulates and presence of minimal porosity. The wear test disclosed that the wear resistance of all specimens increases with the addition of nano and micron size TiC particles (up to 5 wt.%). Scanning electron microscopic observation of the worn surfaces was conducted and the dominant wear mechanism was recognized as abrasive wear accompanied by some delamination wear mechanism.

- by Narguess Nemati
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- Powder Metallurgy, Metal matrix composite, Mechanical Alloying, Materials Design

An extensive investigation of the correlation between die design and the extrusion process of AA6082 aluminum alloy is presented. A profile with a central seam weld line suitable for mechanical testing is extruded under different processing conditions, by varying the dimensions of the die feeder, the length of the welding chamber, the billet preheating temperature and the process speed. For each condition the workability area was defined by detecting tearing defects in the production stage. Tension tests were then carried out on the extruded profiles, to evaluate the effect of the geometrical features of the die, so that an interpretation could be made of the influence of each parameter in a wide spectrum of operating conditions. In particular, tensile strength and equivalent fracture strain were evaluated on the final product to assess the effectiveness of welding.

Joining steel plates and aluminum plates by means of using Fe/Al structural (Triclad) transition joints has been well-received in the shipbuilding industry, but is rarely applied in other industries. In this work, 12.7 mm thick plates of advanced high-strength steel and AA 6061 alloy were successfully joined by using hybrid laser-arc welding with the help of Triclad transition joints. The parameters were optimized for welding dissimilar steels (A516 to advanced high-strength steel) and welding dissimilar aluminum alloys (AA 5456 to AA 6061). The optimization controlled the total heat input and kept the Al/Fe interface
of the Triclad transition joint below the maximum allowable temperature of 315.56 C in order to minimize the growth of brittle intermetallic phases and retain the mechanical properties of the Triclad transition joint. A finite element model was developed to study the temperature evolution at the Triclad interface and the heat distribution along with the welded structure. A ‘‘4:1’’ ratio was used between the width
of the Triclad transition joint and the thickness of the webs. This ratio improved the load-bearing property of the Triclad transition joint and compensated for the microcracks and brittle Al-rich intermetallic
phases observed at the Triclad interface. Tensile strength of 220 MPa was achieved at the welded structure. The fracture occurred at the heat-affected zone of the AA 5456-to-AA 6061 weld.

The quantitative prediction of the consequences of a heat treatment, in terms of microstructure and hardness, residual stresses and distortions, implies a thorough knowledge of the coupled thermal, metallurgical, and mechanical phenomena that occur during the treatment and their modeling. Recent progress made in that field for metallic alloys (steels, aluminum alloys, and titanium alloys) is reviewed through different examples.

- by Elisabeth Aeby-gautier
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- Materials Engineering, Materials, Heat Treatment, Phase Transformation

In the last decades, the improvement in the coatings of carbide tools and in the chemical and mechanical properties of tool materials, has caused the increase of tool working life in machining processes. This fact has allowed the use of the so-called dry machining technology and also machining with minimal quantity of lubricant. There are many important factors that justify the development of such technologies, including the high costs of refrigeration, the ecological damages caused by the use of lubricants, the increasing law demands, related to the preservation of the environment, workers' health, etc. The main objective of this work is to compare the performance of the uncoated and diamond coated carbide drills, using minimal lubrication (10 ml/h of oil in a flow of compressed air) and abundant soluble oil as a refrigerant/ lubricant in the drilling of aluminum-silicon alloys (A356). The results showed an irregular wear in the surface of the diamond coated drill and a decrease in the quality of the hole made by it, compared to the uncoated drill. Taking into consideration all the conclusions reached in this work, the most important one is that the performance of the process (in terms of forces, tool wear and quality of holes), when using minimal lubrication, was very similar to that obtained when using a high amount of soluble oil, with both, coated and uncoated drills. This conclusion proves the potential of using this technique in the drilling process of aluminum-silicon alloys. # 2002 Published by Elsevier Science B.V.

For almost half a century the catastrophic failure of direct chill (DC) cast high strength aluminum alloys has been challenging the production of sound ingots. To overcome this problem, a criterion is required that can assist the researchers in predicting the critical conditions which facilitate the catastrophic failure of the ingots. This could be achieved at first glance by application of computer simulations to assess the level and distribution of residual thermal stresses. However, the simulation results are only able to show the critical locations and conditions where and when high stresses may appear in the ingots. The prediction of critical void/crack size requires simultaneous application of fracture mechanics. In this paper, we present the thermo-mechanical simulation results that indicate the critical crack size distribution in several DCcast billets cast at various casting conditions. The simulation results were validated upon experimental DC-casting trials and revealed that the existence of voids/cracks with a considerable size is required for cold cracking to occur.

- by L. Katgerman
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- Materials Engineering, Mechanical Engineering, Computer Simulation, Thermal Stress

Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field which increases fatigue crack initiation life and reduces fatigue crack growth rate. Specimens of 6061-T6 aluminum alloy are used in this investigation. A convergent lens is used to deliver 1.2 J, 8 ns laser pulses by a Q-switch Nd:YAG laser, operating at 10 Hz. The pulses are focused to a diameter of 1.5 mm onto a water-immersed type aluminum samples. Effect of pulse density in the residual stress field is evaluated. Residual stress distribution as a function of depth is assessed by the hole drilling method. It is observed that the higher the pulse density the larger the zone size with compressive residual stress. Densities of 900, 1350 and 2500 pulses/cm2 with infrared (1064 nm) radiation are used. Pre-cracked compact tension specimens were subjected to LSP process and then tested under cyclic loading with R = 0.1. Fatigue crack growth rate is determined and the effect of LSP process parameters is evaluated. Fatigue crack growth rate is compared in specimens with and without LSP process. In addition fracture toughness is determined in specimens with and without LSP treatment. It is observed that LSP reduces fatigue crack growth and increases fracture toughness in the 6061-T6 aluminum alloy.

Microstructure and material flow of aluminum alloys have a significant influence on the mechanical properties and surface quality. In extrusion of aluminum billets at high temperatures the microstructure is dependent on the alloy and the forming and temperature history. A prediction of grain size and precipitation is of increasing importance in order to design the process by adjustment of parameters such as punch speed, temperatures, and quenching. To give references for microstructure prediction based on material flow, and with it strain and strain rate history, this paper deals with the microstructure during the extrusion process of AA6060, AA6082, and AA7075 alloys. Billets have been partly extruded to axisymmetric round profiles and the microstructure of the press rests consisting of the billet rests in container and die has been considered. Furthermore, these rests have been analyzed to show the material flow, dynamic and static recrystallization based on macro etchings and visible microstructure under different conditions, e.g. as in the area of high strain rate near the container wall, or in dead zones [I]. To allow an accurate simulation of the extrusion process, punch force and temperature conditions during the tests have been measured and are presented in this paper, too.

- by Erman Tekkaya
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- Materials Engineering, Mechanical Engineering, Applied Mathematics, Microstructure

A recently proposed plane stress yield function [Yld2000-2d; Int. J. Plasticity 19 (2003) 1297-part I of this work] that well describes the anisotropic behavior of aluminum alloy sheets was implemented in a finite element code. A short review of the Yld2000-2d relevant features was provided and the complete formulation for the yield function implementation was proposed for its convenient use. Yield surface shapes, yield stress and r-value directionalities predicted with Yld2000-2d for Al-5 wt.% Mg and 6016-T4 alloy sheet samples were compared with those of previously suggested yield functions. Simulations of the cup drawing process for the Al-Mg binary sheet were performed to compute the cup height profiles (earing profiles) with different yield functions. The predicted profiles were compared to experimental data and it was shown that the simulation using Yld2000-2d led to the best agreement between theoretical and experimental results. The drawing and redrawing processes of a circular cup using the NUMISHEET'99 (J.W. Yoon). simulated. The predicted load-punch displacement curves and sheet thickness profiles along different radial directions of the cup were shown to be in excellent agreement with experimental data. #

- by Farhang Pourboghrat
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- Materials Engineering, Mechanical Engineering, Civil Engineering, Plasticity

This work provides empirical evidence needed for an in depth phenomenological study of dendrite growth phenomena during brazing of aluminum alloys in form of composite brazing sheets. The main objective of this study was (1) a collection of experimental evidence associated with heat and mass transfer modeling of the Al + Si solid solution dendrite macro morphology evolution inherent to joint formation during brazing, and (2) the dendrite growth kinetics analysis. The isothermal dwell and the quench that follow the clad molten aluminum binary alloy surface-tension-driven flow into the joint at the peak brazing temperature upon melting lead to the solidification of the metal micro layer and joint formation. Before, during and after the isothermal dwell a significant reduction of Si content in the melt is found. So, a subsequent dissolution may affect the interface zone between the molten clad and substrate. a-phase dendrite assemblies imbedded in an irregular eutectic in the joint zone are the main morphological features of the solidification microstructures. The major characteristic of the phenomenon is a sensitivity of the dendrite pattern selection and dendrite population on brazing process parameters, in particular on the temperature during the dwell.

- by M. Krivilyov
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- Engineering, Kinetics, Pattern Formation, Heat and Mass Transfer

Alloy wheels are automobile wheels which are made from an alloy of aluminum or magnesium Metals or sometimes a mixture of both. Alloy wheels differ from steel wheels because Of their lighter weight, which improves the driving and handling of the motorcycle. Alloy wheels made up of composite materials will reduce the unstrung weight of a vehicle compared to one fitted with standard aluminum alloy wheels. The benefit of reduced unstrung weight is more precise handling and reduction in fuel consumption. Alloy is an excellent conductor of heat, improving heat dissipation from the Brakes, reducing the risk of brake failure. At present Motor cycle wheels are made of Aluminum Alloys. In this project, Aluminum alloy are comparing with other Alloy and composite materials. In this project a parametric model is designed for Alloy wheel used in two wheelers from existing model. Wheel rim is that part of an automotive where it undergoes static and fatigue loads because it traverses on a lot of r...

- by saurabh paropate
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- Materials Science, Composite Materials, Model Analysis, Aluminum Alloy

- by rajesh mishra
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- Engineering, Materials Engineering, Mechanical Engineering, Materials Science

Aluminum alloy 7050 was friction-stir welded (FSW) in a T7451 temper to investigate the effects on the microstructure and mechanical properties. Results are discussed for the as-welded condition (as-FSW) and for a postweld heat-treated condition consisting of 121 ЊC for 24 hours (as-FSW ϩ T6). Optical microscopy and transmission electron microscopy (TEM) examination of the weld-nugget region show that the FS welding process transforms the initial millimeter-sized pancake-shaped grains in the parent material to fine 1 to 5 m dynamically recrystallized grains; also, the FS welding process redissolves the strengthening precipitates in the weld-nugget region. In the heat-affected zone (HAZ), the initial grain size is retained, while the size of the strengthening precipitates and of the precipitatefree zone (PFZ) is coarsened by a factor of 5. Tensile specimens tested transverse to the weld show that there is a 25 to 30 pct reduction in the strength level, a 60 pct reduction in the elongation in the as-FSW condition, and that the fracture path is in the HAZ. The postweld heat treatment of 121 ЊC for 24 hours did not result in an improvement either in the strength or the ductility of the welded material. Comparison of fatigue-crack growth rates (FCGRs) between the parent T7451 material and the as-FSW ϩ T6 condition, at a stress ratio of R ϭ 0.33, shows that the FCG resistance of the weldnugget region is decreased, while the FCG resistance of the HAZ is increased. Differences in FCGRs, however, are substantially reduced at a stress ratio of R ϭ 0.70. Analysis of residual stresses, fatiguecrack closure, and fatigue fracture surfaces suggests that decrease in fatigue crack growth resistance in the weld-nugget region is due to an intergranular failure mechanism; in the HAZ region, residual stresses are more dominant than the microstructure improving the fatigue crack growth resistance.

Most of the existing methods for estimating eN parameters are based on a relatively limited amount of experimental data. In addition, sound statistical evaluation of the popular rules of thumb used in practice to estimate fatigue properties is scarce, if available. In this work, an extensive statistical evaluation of the existing Coffin-Manson parameter estimates is presented based on monotonic tensile and uniaxial fatigue properties of 845 different metals, including 724 steels, 81 aluminum alloys, and 15 titanium alloys. The studied Coffin-Manson estimates include the methods proposed by Muralidharan and Manson, Bäumel and Seeger, Roessle and Fatemi, Mitchell, Ong, Morrow, Raske, as well as Manson's universal slope and four-point correlation methods. From the collected data, it is shown that all correlations between the fatigue ductility coefficient e 0 f and the monotonic tensile properties are very poor, and that it is statistically sounder to estimate e 0 f based on constant values for each alloy family. Based on this result, a new estimation method which uses the medians of the individual parameters of the 845 materials is proposed. #

- by Jaime T P Castro
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- Mechanical Engineering, Civil Engineering, Fatigue, Parameter estimation

Silicon carbide reinforced aluminum alloy composite materials produced by casting methods are increasingly used in many engineering fields. However, these materials suffer from poor distribution of the reinforcement particles in the matrix and high content of porosity. The effect of subsequent cold rolling process with different reductions on the porosity, microstructure and mechanical properties of cast Al6061/10 vol.% SiCp composite was investigated in this study. Composites fabricated by compocasting method were rolled at five different reductions of 30, 60, 75, 85 and 95%. The rolled specimens exhibited reduced porosity as well as a more uniform particle distribution when compared with the as-cast samples. Microscopic investigations of the composites after 95% reduction showed an excellent uniform distribution of silicon carbide particles in the matrix. During cold rolling process it was observed that the tensile strength and ductility of the samples increased by increasing the reduction content. After 95% reduction, the tensile strength and elongation values reached 306.7 MPa and 7.9%, which were 4.6 and 3.3 times greater than those of the as-cast composite, respectively.► When the reduction increased during rolling process, the porosity of the composites decreased. ► Increasing the reduction ratio greatly improved the uniformity of SiC particles. ► The tensile strength of the composites increased by increasing the reduction ratio. ► By increasing the reduction ratio, the elongation of the composites improved.

- by behzad niroumand
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- Metal matrix composite, Silicon Carbide, Composite Material, Materials Design

A series of Al-Cu-Mg-(Ag)-Si alloys were prepared to investigate the role of Si additions on formation. Trace amounts of Si were found to quell precipitation, indicating that it is necessary to overcome a critical Mg/Si ratio for... more