Showing papers on "Aluminium alloy published in 2005"

Recent Progress in Corrosion and Protection of Magnesium Alloys

Abstract: Magnesium alloys are advanced light structural and functional materials being increasingly used in the automotive, aerospace, electronic, and energy industries. However, their corrosion performance at the current stage of development is still not good enough for increasingly diverse practical applications. The Cooperative Research Centre for Cast Metals Manufacturing (CAST) in Australia is one of the most active research organizations in the world established to cope with the problems associated with the development and application of advanced light metals. Corrosion and prevention of magnesium and its alloys is an important part of CAST'S research program. This paper presents a brief summary of recent research achievements by CAST and relevant research work in this area in the world. This overview covers "anodic hydrogen evolution", estimation of corrosion rate, corrosion of aluminum- and non-aluminum-containing magnesium alloys, influences of composition and microstructure on corrosion, corrosion of a die-cast magnesium alloy, galvanic corrosion, coolant corrosion, and an aluminum-alloyed coating. The aim of this overview is to deepen the current understanding of corrosion and protection of magnesium and its alloys and to provide a base for future research work in this field.

Dynamic compressive strength properties of aluminium foams. Part I—experimental data and observations

Abstract: This study of the dynamic compressive strength properties of metal foams is in two parts. Part I presents data from an extensive experimental study of closed-cell Hydro/Cymat aluminium foam, which elucidates a number of key issues and phenomena. Part II focuses on modelling issues. The dynamic compressive response of the foam was investigated using a direct-impact technique for a range of velocities from 10 to 210 ms - 1 . Elastic wave dispersion and attenuation in the pressure bar was corrected using a deconvolution technique. A new method of locating the point of densification in the nominal stress–strain curves of the foam is proposed, which provides a consistent framework for the definition of the plateau stress and the densification strain, both essential parameters of the ‘shock’ model in Part II. Data for the uniaxial, plastic collapse and plateau stresses are presented for two different average cell sizes of approximately 4 and 14 mm. They show that the plastic collapse strength of the foam changes significantly with compression rate. This phenomenon is discussed, and the distinctive roles of microinertia and ‘shock’ formation are described. The effects of compression rates on the initiation, development and distribution of cell crushing are also examined. Tests were carried out to examine the effects of density gradient and specimen gauge length at different rates of compression and the results are discussed. The origin of the conflicting conclusions in the literature on the correlation between nominal strain rate ɛ ˙ (ratio of the impact velocity V i to the initial gauge length l o of the specimen) and the dynamic strength of aluminium alloy foams is identified and explained.

Effect of cryo-rolling and annealing on microstructure and properties of commercially pure aluminium

Abstract: Influence of cryo-rolling reduction and annealing of commercially pure (CP) Al is evaluated in four aspects: microstructure, mechanical properties, electrical conductivity and general corrosion. It is shown that by selecting optimal cryo-rolling reduction and subsequent annealing condition result in ultrafine grains in CP Al with good combination of high strength and ductility. Electrical conductivity of the cryo-rolled samples decreased due to increased number of the electron scattering centers (lattice defects and grain boundary area). However, optimization of cryo-rolling and annealing treatment could restore the conductivity coupled with high strength in CP Al. Corrosion behaviour of cryo-rolled CP Al improved after annealing treatment. High dissolution rate and low thermal stability of the ultrafine grain structure could override the anticipated advantage of uniform corrosion in ultrafine grain CP Al.

Thixoforming 7075 aluminium alloys

Abstract: Commercially extruded 7075 alloy (extrusion ratio of 16:1) has been used as a feedstock for thixoforming in order to investigate thixoformability of a high performance aluminium alloy. The microstructure in the semi-solid state consists of fine spheroidal solid grains surrounded by liquid. The results of thixoforming with one step, two-step and three-step induction heating regimes are presented. Typical defects in poorly thixoformed material (e.g. liquid segregation, impedance of flow by unrecrystallised grains and porosity) are shown alongside successfully thixoformed material (thixoforming temperature of between 615 and 618 °C with a three-step induction heating regime). The highest yield strength and elongation obtained for material thixoformed into a simple graphite die and heat treated to the T6 condition is 478 MPa and 6.9% elongation. For thixoforming at 615 °C into a tool steel die heated to 250 °C, the highest yield strength and elongation obtained are 474 MPa and 4.7% (ram velocity 2000 mm/s). These values (particularly for strength) are approaching those of 7075 in the wrought heat treated condition (505 MPa and 11% elongation).

The fracture properties of a fibre–metal laminate based on magnesium alloy

Abstract: A range of fibre–metal laminates (FML) based on a lightweight magnesium alloy have been manufactured and tested. Two types of composite reinforcement have been investigated, a woven carbon fibre reinforced epoxy and a unidirectional glass fibre reinforced polypropylene. Initial tests using the single cantilever beam geometry (SCB) have shown that little or no surface treatment is required to achieve a relatively strong bond between the composite plies and the magnesium alloy. Tests on both types of laminate indicated that increasing the volume fraction of composite, Vc, in the FML resulted in a significant increase in its tensile strength. Similar tests showed that the addition of the woven carbon fibre/epoxy plies did not have any effect on the Young's modulus of the FML whereas increasing the Vc of the glass/polypropylene plies resulted in a continuous decrease in the modulus of these thermoplastic–matrix systems. Fatigue tests on both types of laminate highlighted the positive contribution of the composite plies in the FMLs. Here, the crack growth rates in centre-notched tension specimens were significantly lower in the FMLs than in the plain magnesium alloy system. Low velocity impact tests on the FMLs highlighted their excellent energy-absorbing characteristics relative to two aluminium-based FMLs. The specific perforation energy of the glass fibre/PP laminate was higher than that offered by a similar aluminium alloy FML and significantly higher than that for a glass reinforced epoxy/aluminium FML. Here, extensive delamination and shear fracture in the outer magnesium alloy plies were found to contribute to the energy-absorbing capacity of these laminates.

The dependence of the β-AlFeSi to α-Al(FeMn)Si transformation kinetics in Al–Mg–Si alloys on the alloying elements

Abstract: An homogenisation process is applied to as cast billets Al–Mg–Si alloys in order to improve the extrudability. During this homogenisation, plate-like β-AlFeSi phase transforms to a more rounded α-Al(FeMn)Si phase which are more favourable for the extrusion process. In this paper, the influence of the alloying elements on the rate of the intermetallic β-to-α transformation is studied. A Finite Element Model (FEM) predicts the kinetics of the β-to-α transformation for various Mn and Si concentrations. The software package Thermo-Calc is used to derive the equilibrium solubilities for various alloy compositions. These solubilities are used in the Finite Element Method as boundary conditions for the interfacial concentrations of the intermetallics. Subsequently, the results of the Finite Element Model are validated with experimental data.

Study of the deposition of cerium oxide by conversion on to aluminium alloys

Abstract: This paper reports work aimed at finding an alternative treatment to chromate conversion coatings (CCC) that could meet all the requirements of industrial applications. A first step was made by carrying out the deposition of films of CeO 2 ·2H 2 O on aluminium alloys in a few minutes at room temperature with or without a catalyst. Different types of pretreatment (acidic or alkaline) led to drastically different results. A model for the catalytic deposition mechanism is suggested which is consistent with scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) observations. The anticorrosive properties of these coatings were investigated by potentiokinetic curves measurements and by electrochemical impedance spectroscopy (EIS). Encouraging results were obtained though the performances still do not equal those of CCC. Some of the coating features (adhesion, sealing of the anodic sites, etc.) which should still be improved are highlighted.

Crystallographic texture evolution of three wrought magnesium alloys during equal channel angular extrusion

Abstract: Texture strongly impacts the plasticity of metals and the equal channel angular extrusion (ECAE) process has been demonstrated to induce unusual textures and enhance the room temperature ductility of magnesium alloys. This paper documents a wide range of textures that may be generated by ECAE of magnesium alloys. Considered broadly, the ECAE processing of magnesium alloys tends to produce 〈0 0 0 1〉 fiber textures. Unlike conventional rolling, which tends to produce 〈0 0 0 1〉 || normal direction textures, the orientation of the 〈0 0 0 1〉 fiber texture (as well as its strength) is strongly affected by alloying additions and processing history. For example, route B-processing of Mg–Al–Zn (AZ) alloys tends to produce textures with 〈0 0 0 1〉 highly inclined (∼55°) from the extrusion axis. This texture appears to promote excellent ductilities along the axis of the ECAE billets. End effects, which influence the distribution of strain and texture, are modeled.

Quantification of Aluminum Outward Diffusion During Oxidation of FeCrAl Alloys

Abstract: The outward flux of aluminum during the oxidation of four similar alumina-forming alloys is determined using two types of experiments. One is measurement of the total thickness of the oxide and the ratio of the thickness of the characteristic equiaxed layer to the total oxide thickness. The second is measurement of the new oxide formed along the grain boundaries of the oxide upon re-oxidation. The former provides information about the ratio of outward diffusion of aluminum to inward diffusion of oxygen during oxidation. The latter experiment directly quantifies the outward flux of aluminum as a function of oxide thickness. Both the outward aluminum flux and the ratio of inward to outward diffusional fluxes are found to vary with the minor concentrations of “reactive element” alloying additions. Specifically, Y in solution in the alloy is found to limit outward aluminum diffusion more than Zr in solution, with Y2O3 limiting aluminum diffusion more than Zr, Y, and ZrO2.

Effect of machining parameters and coating on wear mechanisms in dry drilling of aluminium alloys

Abstract: The temperature generated by friction and plastic deformation in the secondary shear zone strongly controls tool wear. At lower cutting speeds tool wear is not severe insofar as the temperature is not significant. When the cutting speed is increased, there is a transition in wear mechanisms from abrasion and/or adhesion to diffusion. In the present paper, the change in wear mechanisms as a function of cutting speed and coating material is discussed. The cutting tests were performed on a rigid instrumented drilling bench without the use of cutting fluids. AA2024 aluminium alloy was used to investigate the wear mechanisms of cemented tungsten carbide and HSS tools. Three cutting speeds (25, 65 and 165 m/min) and a constant feed rate of 0.04 mm/rev were selected for the experiments. The best results in terms of maximum and minimum hole diameter deviations and surface roughness are obtained for the uncoated and coated tungsten carbide drills. The results also show that HSS tool is not suitable for dry machining of AA2024 aluminium alloy.

CDRX modelling in friction stir welding of aluminium alloys

Abstract: In the paper a numerical model aimed to the determination of the average grain size due to continuous dynamic recrystallization phenomena (CDRX) in friction stir welding processes of AA6082 T6 aluminum alloys is presented. In particular, the utilized model takes into account the local effects of strain, strain rate and temperature; an inverse identification approach, based on a linear regression procedure, is utilized in order to develop the proper material characterization.

Structural and mechanical properties of Al-Si alloys obtained by fast cooling of a levitated melt

Abstract: Data on the structure and mechanical properties of cast Al–Si alloys in a wide compositional range from hypo-to high hyper-eutectic composition are scares. These properties depend on many factors during solidification of the alloys. In the present work, samples were obtained by rapid cooling of levitated melts of various compositions from 11.5 to 35 wt.% Si. The measurements revealed linear concentration dependences of density and Young's modulus. The average temperature coefficient of Young's modulus in the range from room temperature to 500 °C and the yield point for bending both had maxima at about 20 wt.% Si. The hysteresis of the temperature dependence of Young's modulus had a minimum at about 20 wt.% Si as well. Changing Young's modulus temperature coefficient and Young's modulus hysteresis as a function of the Si content are connected with the creation of the Guinier–Preston zones. Values of the yield point are explained by the plasticity of components of the eutectic structure, primary crystals and grain boundaries. The extrema of the concentration dependences of the mechanical properties occurred for the fine-grained structure arisen from coupled eutectic-like growth. Solidification at other conditions led to formation of primary crystals of α solid solution or primary Si crystals.

Microstructure and mechanical properties of rheo-diecast (RDC) aluminium alloys

Abstract: A new semisolid metal (SSM) processing technology, the rheo-diecasting (RDC) process, has been developed for manufacturing near-net shape components, of high integrity, directly from liquid Al-alloys. The RDC process innovatively adapts the well-established high shear dispersive mixing action of the twin-screw mechanism to the task of in situ creation of high quality SSM slurry under high shear rate and high intensity of turbulence. This is followed by direct shaping of the semisolid slurry into a near-net shape component using the existing cold chamber diecasting process. The RDC process has been applied to process various Al-alloys, including cast alloys and wrought alloys. In this paper, we present the microstructure and mechanical properties of the RDC Al-alloys under as-cast, and various heat treatment conditions. Although the focus is on A357 alloy, we also present experimental results on other Al-alloys. The results indicate that the RDC samples have close-to-zero porosity, fine and uniform microstructure throughout the entire sample in the as-cast condition. Compared with those produced by conventional high-pressure diecasting (HPDC) and any other SSM processing techniques, RDC samples have much improved tensile strength and ductility. It is also found that heat treatment of the RDC Al-alloys, under both T5 and T6 conditions, can substantially improve strength but with a slight sacrifice of ductility.

Diagnostics of an electrolytic microarc process for aluminium alloy oxidation

Abstract: Optical emission spectroscopy and fast video imaging of the microarc oxidation process of aluminium alloys are carried out. Optical measurements allow the establishment of relationships between the sparks aspect and the aluminium emission line intensity. The transition from spark to microarc is quantified through the decay of the aluminium line intensity. The characteristic time of that decay is shown to be strongly dependent on the current density. Scanning electron microscopy characterization shows that the oxide layer structure and growth rate are strongly dependent on the process duration and on the applied current density. Finally, the correlations that are drawn between the material analyses and the plasma measurements allow proposing some ways to enable the process control through optical measurements.

Mechanical properties of Friction Stir Processed 2618/Al2O3/20p metal matrix composite

Abstract: The effect of Friction Stir Processing (FSP) on the mechanical properties of 2618 aluminium alloy reinforced with 20% of alumina particles aluminium alloy has been studied in the present paper. The material was processed into the form of sheets of 7 mm thickness after T6 treatment and was tested in tension and fatigue at room temperature. Tensile tests were also performed at higher temperatures and different strain rates in the nugget zone, in order to analyse the superplastic properties of the recrystallized material and to observe the differences with the parent materials as a function of the strong grain refinement due to the Friction Stir Process. The high temperature behaviour of the material was studied, in longitudinal direction, by means of tensile tests in the temperature and strain rate ranges of 400–500 °C and 10 −3 –10 −1 s −1 , respectively. Fracture surfaces of the deformed fatigue test specimens were comprehensively examined in a scanning electron microscope equipped with field emission gun to determine the macroscopic fracture mode and characterize the fine-scale topography and microscopic mechanisms governing fatigue fracture. The mechanisms governing fatigue life, cyclic deformation and fracture characteristics are analysed in function of magnitude of applied stress, intrinsic micro structural evolution and material deformation behaviour.

Properties of aluminium oxide coating on aluminium alloy produced by micro-arc oxidation

Abstract: Aluminium oxide coating was directly synthesized on aluminium alloy by micro-arc oxidation (MAO) in NaAlO 2 solution. XRD results show that the coating consists of α-Al 2 O 3 and γ-Al 2 O 3 in its whole thickness; the content of α-Al 2 O 3 in the coating is 64±4%. The coating consists of a relatively compact inner layer and a porous outer layer, and its porosity is 7–10%. The density of the coating is 3.47g/cm 3 , its highest hardness 22 GPa and elastic modulus 279 GPa appear at around 12 μm from interface. The thermal expansion coefficient of the coating is 7.38×10 −6 K −1 . The coating can suffer the thermal impact of 873 K; it indicates that the aluminium oxide coating possesses a good thermal shock-resistant and adhesion strength to the substrate.

Energy absorption of aluminium alloy circular and square tubes under an axial explosive load

Abstract: The energy absorption of circular and square aluminium alloy tubes subjected to an axial explosive load, which is transmitted to a tube by a small attached mass, is discussed. Particular attention is paid to the interaction between the inertia of the attached mass and a tube when the importance of the initial compression phase is revealed. The effect of this phase on the mean load, which is characteristic of the energy absorption capacity of structural elements, is demonstrated. The influence of the material models on the prediction of the response of aluminium alloy circular and square tubes is also discussed in relation with the temperature effects caused by the high strain rates. The analysis shows that the material properties play an important role for the formation of the buckling pattern due to the finite duration of the initial compression phase when plastic stress waves at different speeds propagate along a shell.

Investigation of the clustering behaviour of titanium diboride particles in aluminium

Abstract: The clustering of reinforcement particles in cast metal matrix composite (MMC) material has a number of deleterious effects on its mechanical properties and castability. In order to better understand this phenomenon, the clustering behaviour of TiB2 particles in molten commercial purity aluminium was investigated. A novel method of sampling the melt was developed in order to investigate the clustering behaviour as a function of holding time at 700 °C. The initially clustered distribution of TiB2 became increasingly dispersed with increased holding time. The maximum observed cluster size decreased from 50 to 10 μm after a holding period of 73 h. X-ray microtomography (XMT) and SEM micrograph analyses were carried out to quantify the rate of dispersion of the clusters. XMT was shown to be a powerful tool for visualizing and quantifying 3-dimensional features within the MMC microstructure.