Papers by Keyword: Aluminium Alloy

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Authors: Annalisa Pola, Roberto Roberti, Ermanno Bertoli, Disman Furloni
Abstract: Semi-solid processing is nowadays a powerful technology for the realization of structural components; in addition to the increase in their mechanical properties, due to the globular structure instead of the dendritic one, further developments are most likely to be expected from alloy chemical composition adjustments in order to achieve higher performances compared with the industrially used A356 and A357. Aim of this research is to try to set up new aluminium alloys for semisolid foundry applications, starting from the standard Al-Si system, at the base of all known casting processes. Different chemical compositions, based on either foundry or wrought Al alloys, have been investigated by means of computational thermodynamics (Pandat®), producing quantitative data about solidus-liquidus interval, solid fraction as a function of temperature, phase diagrams i.e. potential for age hardening, etc.. Some selected alloys, fitting the needs of good castability, proper concentration of hardening elements in the alpha phase and, obviously, easy production of feedstock material have been mechanically stirred by means of an experimental apparatus designed and self-constructed in the foundry laboratory of the university; the effect of different stirring tool configurations on the semi-solid state obtainment has also been assessed. Subsequently, the manufactured alloys have been reheated and cast into a simple die, properly designed, for the production of small samples. Microstructural investigations have been done on the stirred alloy (before and after re-heating), on the as cast and the heat treated samples to evaluate the efficiency of the designed system and of the defined alloys. Experimental tests on the processed alloys have been carried out by means of an instrumented crucible in order to verify the predicted thermodynamic properties supplied by simulation study (i.e. fs-temperature curve).
Authors: Glenda T. Motsi, Peter A. Olubambi, Tleyane J. Sono, Lerato Shoke
Abstract: In this study tensile deformation mechanisms of aluminium alloy 5083 were investigated under observations made from SEM equipped with a tensile stage. Observations during tensile testing revealed a sequence of surface deformation events. These included micro-cracking of large intermetallic particles, decohesion of small intermetallic particles from the matrix producing microvoids and slip bands distribution. The fracture surface was characterised with closely spaced dimples, typical for aluminium alloys.
Authors: Jean Marie Drezet, Bastien Mireux, Guven Kurtuldu
Abstract: During solidification of metallic alloys, coalescence corresponds to the formation of solid bridges between grains when both solid and liquid phases are percolated. As such, it represents a key transition with respect to the mechanical behaviour of solidifying alloys and to the prediction of solidification cracking. Coalescence starts at the coherency point when the grains begin to touch each other, but are unable to sustain any tensile loads. It ends up at the rigidity temperature when the solid phase is sufficiently coalesced to transmit macroscopic tensile strains and stresses. This temperature, also called mechanical or tensile coherency temperature, is a major input parameter in numerical modelling of solidification processes as it defines the point at which thermally induced deformations start to generate internal stresses in a casting. The rigidity temperature has been determined in Al Zn alloys using in situ X-ray diffraction (XRD) during casting in a dog bone shaped mould. This set-up allows the sample to build up internal stress naturally as its contraction is prevented. The cooling on both extremities of the mould induces a hot spot at the middle of the sample which is irradiated by X-rays. Diffraction patterns were recorded every 0.5 s using a detector covering a 426 x 426 mm2 area. The change of diffraction angles allowed us to observe agglomeration/decohesion of growing grain clusters and to determine a solid volume fraction at rigidity around 98 % depending on solidification time for grain refined Al 6.2 wt% Zn alloys.
Authors: Sofiane Terzi, Luc Salvo, Michel Suéry, Jérôme Adrien, Éric Maire, Elodie Boller
Abstract: This paper is concerned with an investigation of the deformation behaviour of an Al-Cu alloy during tensile testing in the semi-solid state. It was carried out by fast in-situ X-Ray microtomography at ESRF, Grenoble. Deformation was performed at constant velocity, which was chosen to be small enough so as not to affect the acquisition of the images. It is observed that deformation is accompanied, initially, by some liquid flow from the adjacent regions towards the deformed zone. Then pores form in the liquid films and grow until they occupy a significant part of the cross section of the specimen. Quantification of this phenomenon was carried out thus leading to a better understanding of pore formation in semi-solid mixtures.
Authors: Masakazu Kobayashi, Hiroyuki Toda, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki
Abstract: Recently, three-dimensional (3D) observation and analysis have attracted considerable attention in materials science field. By using the synchrotron radiation, the tomography makes possible high-resolution 3D observation dynamically and the recent diffraction analysis is available for 3D orientation mapping. In this study, grain deformation behavior in polycrystalline aluminum alloy has been characterized by 3D observation method applying the synchrotron radiation. The method to measure inner strain distribution by means of microstructural features tracking provides strain distribution within the sample, which we could not access before. The effect of grain orientation and its interaction during tensile deformation was discussed with the obtained strain distribution.
Authors: Xia Jin, Shi Hong Lu
Abstract: Bending of the aluminum alloy is one of the processes frequently applied during manufacture of aircraft sheet metal. The bending operation involves springback, which is defined as elastic recovery of the part during unloading. In manufacturing industry, it is still a practical and difficult problem to predict the final geometry of the part after springback and to design appropriate tools in order to compensate for springback. In this study, 3D commercially available finite element analysis (FEA) software-MARC is used to analyse bending and springback of different aluminium materials (LY12CZ) with different thickness. The amount of springback, total equivalent plastic strains and equivalent von mises stresses are obtained. Moreover, the relation between bent angle and springback angle, R/t ratio and springback angle are presented and discussed in detail.The comparison results of FEA result and experiment data indicate that the FEM (finite element analysis method) simulation is a power tool for the highly accurate prediction of springback behavior in sheet metal bending.
Authors: L. Qian, Hiroyuki Toda, Kentaro Uesugi, Masakazu Kobayashi, Toshiro Kobayashi
Abstract: Traditional computational models always assume idealized crack geometry. However, actual crack geometry is very complex in real materials and thus, those simulations do not realistically represent the actual loading conditions of a real crack. In this paper, three-dimensional (3D) image-based simulation was performed to investigate the fracture behavior of an aluminum alloy, and the model takes into account the real crack geometry based on the 3D images of the crack. Accordingly, many essential features of fracture can be identified and interpreted, and some new insight into fracture behavior in real materials can be offered.
Authors: D. Ruvalcaba, Dmitry G. Eskin, Laurens Katgerman
Abstract: In the present investigation, serial sectioning and 3D reconstructions are made on samples quenched at selected temperatures during unconstrained solidification in order to observe the evolution in morphology of coarse dendrites in 3D. The 3D microstructure reconstruction during the solidification of an Al−7 wt.% Cu alloy allowed the identification of a complex coarse morphology of dendrites. High-ordered branches present different morphologies at different temperatures and locations in the microstructure due to coarsening and coalescence. 3D visualization of complex dendritic structures is discussed in the present investigation.
Authors: D. Ruvalcaba, Dmitry G. Eskin, Laurens Katgerman
Abstract: In the present research the possibility of studying the solidification of aluminum alloys by using the quenching technique is analyzed. Since the quenching technique does not provide reliable information (i.e. due to an overestimation of solid fraction) when measuring the solid fraction over 2D images from samples quenched at high temperature, the overestimation problem is investigated by analyzing 3D reconstructed microstructures from quenched samples. The 3D reconstructed microstructure may provide better understanding about the cause of overestimation of solid fraction when quenching at high temperatures. Consequently, the reconstruction of the microstructure that has existed before quenching may be possible after identifying and removing the solid phase that develops during quenching. In the present research, binary aluminum alloys are solidified and quenched at different temperatures, and then 3D reconstructed images are analyzed. The possibility of reconstructing the microstructure that develops during solidification before quenching is discussed.
Authors: Barnik Saha Roy, Subhash Chandra Saha, John Deb Barma
Abstract: A 3D thermal pseudo mechanical model formulated in an Eulerian frame considering a quassisteady approach to Friction Stir welding modeling of AA6061 Aluminium alloy is proposed and implemented using nonlinear finite element code in Comsol Multiphysics v 4.1. The effect of different operating parameters on the temperature distribution was analyzed. The material flow is found to be enhanced with the increase in traverse speed and angular velocity of the pin with a pronounced swirl on the advancing side. The distribution of equivalent plastic strain and dynamic viscosity was found to correlate with the distribution of the microstructure zones in the weld.
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