Papers by Keyword: Al-Si

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Authors: Sonja Steinbach, Johannes Dagner, Marc Hainke, Jochen Friedrich, Lorenz Ratke
Abstract: A quantitative understanding of the effect of fluid flow on the microstructure of cast alloys is still lacking. The application of time dependent magnetic fields during solidification offers the possibility to create defined flow conditions in solidification processing. The effect of rotating magnetic fields (RMF) on the microstructure formation in cast Al-alloys (Al-7wt.%Si, Al-7wt.%Si- 0.6wt.Mg) is studied experimentally and numerically. The forced fluid flow conditions result in pronounced macrosegregation effects and affect microstructural parameters. With increasing fluid flow the primary dendrite spacing decreases whereas the secondary dendrite arm spacing increases. The experimental analysis is supported by a rigorous application of numerical modeling with the software package CrysVUn.
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Authors: Anne Zulfia
Abstract: Aluminium Silicon reinforced with 50Vf% SiC has been produced by spontaneous infiltration at 900°C for 1 hour. Aluminium infiltrated preforms containing 1%wt Mg mixed with various of Si between 2 and 14wt%, as external dopant. However Al did not infiltrate a preform containing 1wt%Mg but if mixed with Si in the preform generated in more extensive infiltration. Effect of Si on characterisation of pure Al composites by spontaneous infiltration were studied and compared to Al-Si based matrix. Microstructural analysis of MMC as well as mechanical properties were also observed. It was found that increasing of Si content generated lower porosity thus increasing hardness due to aluminium could wet SiC preform well. Although the dopant was uniformly distributed throughout the perform but microstructural analysis and hardness measurements indicate that the resultant composite may not be uniform as infiltration inwards from the top to the bottom of preform. The hardness of Al-Si composites is significantly increased with increasing of Si for both externally and internally doped system. This is associated with decreasing porosity with higher Si in composites.
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Authors: Jenny Venema, Javad Hazrati, David Matthews, Ton van den Boogaard
Abstract: Hot stamping is often used in the automotive industry to combine formability and strength. However, during forming process at high temperatures, friction and tool wear are determining factors that can affect the efficiency of the whole process. The goal of this paper is to investigate the effects of temperature on the local coefficient of friction and tool wear and to provide an insight in the phenomena which take place at the tool-sheet metal interface during hot stamping processes. For this purpose, hot friction draw tests between uncoated tool steel and Al-Si coated press hardening steel were carried out at several temperatures between 500-700°C. Consecutive tests were performed to mimic industrial hot stamping process and to investigate the effect of tool wear on the friction phenomenon. Finally, tool-sheet metal tribological behavior and the interaction between the friction and tool wear mechanisms were analyzed using different imaging and chemical characterization techniques. The results show that several stages can be distinguished at the interface between tool and sheet metal coating during hot stamping: flattening due to initial normal contact, ploughing of tool asperities through coating, secondary ploughing in the coating by adhered material on the tooling, and abrasive wear in the tool by embedded particles in the sheet metal coating. Furthermore, tool wear shows some major differences in the temperature range of 500-700°C. At high temperature a larger abrasive area and more severe compaction galling occurs that can be explained by material properties of Al-Si coating at elevated temperatures. The results of this study can be used for more efficient process design and a more realistic modelling of the hot stamping process.
131
Authors: Chun Y. Chan, Philip B. Prangnell, Simon J. Barnes
Abstract: Friction Stir Processing (FSP) has potential for locally enhancing the properties of Al-Si alloy castings, for demanding applications within the automotive industry, by greatly refining the second phase particle size. In the present study, the homogeneity of particle refinement and second phase spatial distribution within the process zone, as well as the relationship to the processing parameters, were investigated in a gravity die cast Al-Si LM24/A380 alloy, subjected to a range of FSP conditions. Detailed image analysis and the dirichlet tessellation method were used to quantify particle clustering. ‘Stop-action’ experiments were also used to study the process of particle break up, by following the behaviour through the deformation zone surrounding the tool.
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Authors: C.L. Chen, G.D. West, Rachel C. Thomson
Abstract: Multicomponent Al-Si based casting alloys are used for a variety of engineering applications. The presence of additional elements in the Al-Si alloy system allows many complex intermetallic phases to form, which make characterisation non-trivial due to the fact that some of the phases have either similar crystal structures or only subtle changes in their chemistries. A combination of electron backscatter diffraction (EBSD) and energy dispersive X-ray analysis (EDX) have therefore been used for discrimination between the various phases. It is shown that this is a powerful technique for microstructure characterisation and provides detailed information which can be related to microstructure evolution during initial casting and subsequent heat treatment. The mechanical properties of different intermetallic phases have been investigated as a function of temperature using the nanoindentation technique. In particular, the hardness and modulus of a number of phases have been established for a range of alloy compositions. Physical properties of some of the intermetallic phases are also discussed. Phase identity, composition, physical and mechanical properties are set in context to inform alloy design strategies.
359
Authors: José Barros, Tanya Ros-Yáñez, Yvan Houbaert
Abstract: The chemical and physical interaction between Fe-Si alloys in the range 0-3.8 Si wt% and a molten Al-(Si 25wt%) alloy at 800 °C has been studied for different reaction times (from 0.1 to 200s) by hot dipping tests. Several intermetallic phases have been identified, Fe2Al5, τ1-Al3Fe3Si2, τ2-Al12Fe6Si5, τ3- Al2FeSi and τ4- Al3FeSi2, which already were reported in the literature dealing with the interaction between iron and molten Al-Si alloys. In addition an ordered phase Fe3Si (D03) appears in contact with the Fe-Si substrate. Diffusion reaction and solidification phenomena appear to be involved in the developing of the coating. The growth kinetic has been studied and diffusion appears as the step controlling the intermetallic compounds growth. Special attention was paid to the effect of the microstructure of the dipped sheet on the interaction with the molten alloy. The higher deformed structures react faster; this effect can be explained by the faster diffusion through high diffusivity paths like grain boundaries and dislocations.
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Authors: Soon Jik Hong, S. Patil, Chang Kyu Rhee, S. Seal
Abstract: The microstructure and mechanical properties of Al-21 wt% Si components fabricated by plasma spray forming are analyzed. The microstructure of the plasma spry formed component showed a homogeneous distribution of fine Si particles embedded in the Al matrix. The grain size of α-Al varied between 200 to 500 nm and the size of the Si particles was about 50 to 100 nm in the plasma spray formed component. The room temperature tensile strength of the plasma spray formed component was 215 MPa with 0.5 % elongation, while for cast material, it was 130 MPa. Despite the porosities, the ultra-fine microstructure and homogeneous distribution of Si particles embedded in matrix are the foundation of the increased strength of the plasma spry formed component.
183
Authors: Jung Pyung Choi, Ki Bae Kim, Eui Pak Yoon
Abstract: In general, the element (Sr, Na, Sb, etc.) is used as a modifier of eutectic Si phase in the hypoeutectic Al-Si system. When these elements are added into the hypoeutectic Al-Si melt, the flake shaped Si phase transforms to fibrous shape and the size of Si phase is also decreased. In this study, the electromagnetic vibration is adopted for modifying eutectic Si phase and reducing its size. The higher the current density and frequency of electromagnetic vibration(EMV), the finer the size of eutectic Si phase. The tensile strength and elongation of EMVed alloy were highly improved. Measured twin probability of EMVed alloy at a frequency of 1000Hz was approximately six times as high as that of the normal alloy and a half of that of Sr modified alloy. The mechanism for the increase in twin density due to EMV during solidification could be supposed from the fact that the preferential growth along <112> in silicon was suppressed by preventing Si atom from attaching to the growing interface of Si phase and by changing the solid/liquid interfacial energy of silicon.
157
Authors: Supparerk Boontein, Wattanachai Prukkanon, Kongkiat Puparatanapong, Julathep Kajornchaiyakul, Chaowalit Limmaneevichitr
Abstract: A356 is the aluminum casting grade which has compositions that combines outstanding casting characteristics with excellent properties after heat treatment. Mechanical properties of A356 can be improved by reducing of secondary dendrite arm spacing (SDAS), precipitation hardening, and the interaction effect of both. It is generally accepted that dendrite arm spacing and fine distribution microstructure are related to each other and they also affect the precipitation hardening in a way that smaller SDAS results in shorter time required to obtain a satisfactory degree of solution of the undissolved or precipitated soluble phase constituents and to achieve good homogeneity. Minor addition of Sb was successfully used in reducing the SDAS in previous work. However, the effect of Sb addition on age hardening has not been investigated, especially in a high cooling rate condition. In this research, effects of minor addition of Sb on SDAS, age hardening and mechanical properties; i.e. hardness and tensile properties, are reported. It was found that Sb addition did not clearly affect SDAS at the high cooling rate, i.e. as in permanent mold casting process. Moreover, we found that the addition of Sb into A356 also lowered mechanical properties.
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Authors: Ahmed Hakem, Youcef Bouafia, Ali Bilek
Abstract: The addition of a high percentage of silicon and a small percentage of magnesium to aluminum are the main enhancers largely used to improve the mechanical characteristics. Our goal, here, is to make a direct contribution to the mechanical properties in traction, the hardness, the resilience and the structural properties of the AlSi13 alloy used in sand molding and shell metal molding, mechanical as well as manual. The reference state is designated by crude casting, noted: F. To increase the characteristics and obtain substantially large yield stresses and higher stiffnesses, the material of numerical designation 44100 is subjected to the specific heat treatments, quenching and annealing. This study aims to determine the influence of the chemical composition, the structural hardening of sand casting and metal shell casting by gravity on the evolution of the tensile behavior, hardness, resilience and microstructure of the binary alloy 44100.
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